Cyamus ovalis Photo: Vicky Rowntree, University of Utah
In an earlier post, I joked (well half joked) about the need to save the whale lice, even if you don't care about the right whales. I thought today I would expand on the brief comment about the lice and their special relationship with whale and how they can actually tell us about the populations of right whales and their evolution.
Image courtesy of Mariano Sironi, Institute of Whale Conservation, Buenos Aires
In the image above you can see the characteristic white and black rough patches known as callosities on the face of a right wale. The raised dark grey bits are indeed part of the whale. Those are rough ridges that become sharper and harder. They are not really lice, but a caprellid amphipod, in other words a crustacean. Whale lice specifically are in the family Cyamidae consists of 35+ species in seven genera and are collectively known as cyamids.
On each right whale around 5000 Cyamus ovalis coat the callosities and gives them their white color is Cyamus ovalis. In the spaces between the raised callosities live around 500 C. gracilis. On adult whales approximately 2000 C. erraticus live in the genital and mammary slits. C. erraticus is highly mobile though often occupying wounds, and living in large concentrations on the heads of young calves. Of these C. gracilis is the smallest with ~6mm long adults and with the other two species measuring ~12-15mm long as adults.
Closeup of Right Whale callosity with C. ovalis. From Iain Kerr, Ocean Alliance/Whale Conservation Institute
The cyamids were named "whale lice" by early whalers in reference to their own head and body lice. Mmmmm fun! While not actual lice, they behave similarly in a few key ways. Cyamids have no free swimming stage and spend their entire life on one species of whales, transferring from whale to whale through intimate contact, primarily between a mother and it's calf. They were recently used, similarly to their lice namesakes, to track the population structure and evolution of their hosts.
In 2005 a team of scientists published the results of their study of the population structure and evolution of right whales based on DNA studies of the whales' cyamids. The cyamid DNA is in some ways more informative than the whales' own DNA as the cyamids complete many generation per whale generation and the population of the cyamids, especially C. ovalis, is far greater than that of the whales, offering the researchers more mutations to track.
The team collected cyamids from globally distributed right whale strandings and used variation in the mitochondrial COI gene to analyze the population structures of both the cyamids and by inference the right whales they inhabit. The first finding was that there was no obvious population structure within ocean basins. They also found high levels of haplotype diversity but low gene differentiation suggesting a large population with high transfer rate between individual whales.
The North Atlantic and Southern Ocean populations however have apparently been fully isolated for several million years. This supports the view that the North Atlantic, Southern Ocean and North Pacific right whales have been isolated for millions of years and shouldbe considered separate species. In a gene tree for the right whale cyamids the three different nominal species clustered out as seven distinct species. C. avalis, C. gracilis and C. erraticus fall out with separate North Atlantic and Southern Ocean species which diverged approximately 6.3mya. Interestingly the Northern Pacific C. ovalis form a tight clade nested within the tree of the Southern Ocean C. ovalis suggesting that there was more recent contact those two populations than between the Northern Atlantic and Southern Ocean populations.
By studying the cyamid crustaceans Jon Seger and his team were able to provide another line of evidence that each oceanic basin population of right whales is in fact a distinct species. They also found four new species of right whale cyamids and that the number of right whales in each basin was higher than originally estimated for pre-commercial whaling populations.
Classification of the nominal species Cyamus ovalis:
Kingdom
Animalia
Phylum
Arthropoda
Subphylum
Crustacea
Class
Malacostraca
Order
Amphipoda
Infaorder
Caprellida
Family
Cyamidae
Genus
Cyamus
Species
Cyamus ovalis
References: Kaliszewska et al. (2005). Population histories of right whales (Cetacea: Eubalaena) inferred from mitochondrial sequence diversities and divergences of their whale lice (Amphipoda: Cyamus) Molecular Ecology, 14 (11), 3439-3456 DOI: 10.1111/j.1365-294X.2005.02664.x
In my post about harvestmen, I mentioned the ancient fossilized penis found in 2003, that dated back 400 - 412 million years ago. Unfortunately, I forgot the Dec, 2003 publishing of an even older specimen of male genitals. In Herefordshire England, 425 mya, an ostracod was buried in volcanic ash during the Silurian Period and quickly mineralized, preserving even the soft tissues.
Colymbosathon eclecticos, Greek for "Amazing swimmer with a large penis", could easily be mistaken for a modern ostracod, so similar is the morphology. Like the harvestman example before, this indicates a group with a basic body plan (and even much of the detail) that has shown very little change over a 400+ million year period. Ostracods are well known in the fossil record back to about 500 mya. From this find they have been relatively stable for almost the entire time.
It also shows two examples (one terrestrial, one marine) of male copulatory organs from the late Silurian–early Devonian periods. In the ostracod this is especially interesting as it extends the identification of specific gender in a group that is very common in the fossil record, but for which previous gender identification was only to the Cretaceous Period (65–145 mya).
Not to leave the lady inverts out, where there is a male copulatory organ there hopefully can be found a receptive female. It took the same team a few years to process and publish the finding of a female ostracod from the same area, known as the Herefordshire Lagerstätte. The unique thing about this new fossil ostracod ? Hint the new species name is Nymphatelina gravida.
Like C. eclecticos, this ostracod was found in the Herefordshire Lagerstätte and her soft organs were remarkably well preserved, including her eggs. When the team used their grinding and 3D reconstruction technique, they discovered what appears to be a brood of some 20 eggs preserved in her shell. The same brooding is observed in modern ostracods, such as the modern Gigantocypris dracontovalis pictured below the 3D reconstruction of N. gravida. Another remarkably conserved body plan and biological behavior (parental brooding).
Top is digital reconstruction of N. gravida brooding it's eggs (yellow), bottom is the modern ostracod G. dracontovalis also brooding. Original image from University of Leicester
Update: Todd has reason to ask "Who has the oldest" of C. eclecticos as well, the oldest ostracod eyes in Ostra-blog 4.
References:
D. J. Siveter (2003). An Ostracode Crustacean with Soft Parts from the Lower Silurian Science, 302 (5651), 1749-1751 DOI: 10.1126/science.1091376
David J. Siveter, Derek J. Siveter, Mark D. Sutton, Derek E.G. Briggs (2007). Brood care in a Silurian ostracod Proceedings of the Royal Society B: Biological Sciences, 274 (1609), 465-469 DOI: 10.1098/rspb.2006.3756
Mark D. Sutton, Derek E. G. Briggs, David J. Siveter, and Derek J. Siveter (2001). Methodologies for the Visualization and Reconstruction of Three-Dimensional Fossils from the Silurian Herefordshire Lagerstätte. Palaeontologia Electronica, 4 (1)
Number reefs with (filled) and without (open) A. planci outbreaks in Open fishing and No-take zones.
I'm sure most people here are familiar with the crown-of-thorns starfish (Acanthaster planci) which have been devastating reefs in the Indo-Pacific region, most infamously, the Great Barrier Reef. Some recent research out of AIMS points to no-take fishing zones as a control against the crown of thorns with no-take zones having only 26% of the number of outbreaks of similar areas outside the no-take zones. Strong argument for strong MPA's in a critical area of coral diversity!
The researcher, Hugh Sweatman, notes that the ecolological link between targeted fish and the crown-of-thorns starfish are unknown. Commercial and recreationally targeted fish are not known to prey on A. planci, but are mostly piscavores. The no-take zones thus likely have fewer smaller fish which prey on the worms and crustaceans which prey on juvenile starfish. Hugh is hoping to discover the exact linkage responsible for the results.
Fortunately, in related news, AIMS also reported that the most recent wave of the crown-of-thorns starfish appeared to be waning with fewer starfish surveyed last year and no new outbreaks last year in Swains Reefs, which has has outbreaks each year since 1985.
Sweatman, H. (2008). No-take reserves protect coral reefs from predatory starfish. Current Biology, 18(14), R598-R599.
ScienceNow has a preview (arggh!) of a research article from Journal of Coastal Research comparing coral abundance and diversity from areas in the former Vieques Island military range in Puerto Rico, to areas outside the range and areas in nearby marine parks.
Bottom line ?
Though there are areas of extreme impact (bomb craters anyone?) the researchers found the area as a whole was in better shape than the nearby marine park areas. The chief difference appears to be island development - Vieques Island has almost none.
"The take-home message seems to be that the most glaring problems--like bombing--might not be as serious in the long term as the quiet or silent problems, like runoff and development,"
If anyone can find the article online please let me know...
Bee dancing has long been an interesting, if a bit controversial, subject for science with research articles focused on deciphering the meaning of dances, led by the pioneering work of Nobel Laureate Karl von Frisch. The essence of the dance is that successful foragers return to the hive and dance a figure 8. In the crossing section of the figure 8, the bee waggles its abdomen. The duration of the waggle section indicates the distance to the food source. The angle of the cross part (the tilt of the 8 if you will) indicates direction of the food source. Now new Open Access research published in PLoS One looks at “international” communication capabilities between two species of honeybee: the eastern or asian honeybee, Apis cerana and the Western or European honeybee, Apis melifera. There are several species of honey bees that have been studied and each was observed as having a different dance style. To eliminate as many uncontrolled variables (primarily season, time, spatial scales, wind and geography of separate experiments) as possible, and be able to directly compare two species, a team of scientists from Australia, China and Germany creative a single hybrid hive with an A. cerana queen and a mixed worker population. They tried colonies with an A. melifera queen but in those colonies the A. cerana workers were killed and removed from the hive within 3 days. Even in the A. Cerana queened hybrid hives the team sometimes had to use active measures to keep the hive harmonious including spraying agitated bees with sugar syrup and honey water and removing troublemakers. Without active controls the hybrid hives lasted 20 days before the introduced workers were all killed or driven out, with active control the hives lasted in excess of 50 days. The harmonious hybrid hive also showed food transfer (trophollaxis) between species and mixed species workers tending the queen when she was laying eggs.
The researchers found that each species did have a distinct “dialect” primarily expressed in the duration of waggle to distance relationship. A. cerana bees waggled their butts significantly longer than A. melifera for all distances of food from the hive in both single species and hybrid hives. The team continued to evaluate understanding between the two species and found that the workers from either species were able to understand the dance of foragers regardless of the “dialect” of the dance and that the A. cerana were more likely to follow any successful forager than A. melifera. Both the direction and distance to the food source were accurately communicated between species.
Whats cool is that, as the researchers point out, this might be a social learning situation. Interspecific communication and potentially interspecific learning. It may be that if a longer term experiment can be successfully conducted, the two species of bees waggle durations may converge over a longer period.
Su, S., Cai, F., Si, A., Zhang, S., Tautz, J., Chen, S., Giurfa, M. (2008). East Learns from West: Asiatic Honeybees Can Understand Dance Language of European Honeybees. PLoS ONE, 3(6), e2365. DOI: 10.1371/journal.pone.0002365
While the deep-sea may be the final frontier for marine biologists, caves are one of the least studied environments on land. Some caves can extend dozens of miles below the ground in sinuous networks, all but cut off from the grassy hills and tree-lined horizons above. Its not an easy environment to access and many explorers have perished attempting to map these subterranean labyrinths. Yet, recent investigations have found an astonishing community of invertebrates associated with caves, existing nowhere else. Many of these species are insects and spiders, adapted to the dark conditions, muggy conditions. Nearly every new cave expedition turns up species never before seen.
How do these animals exist down there? What is their source of food? It turns out that nestled in the Blue Mountains of Australia at the 350 million year old Jenolan Caves Karst Conservation Reserve, the base of the invertebrate community consists of decaying leaf litter. Eucalyptus trees, native to the area, historically contributed the most to the leaf litter pool. Over the years, introduced trees have naturalized around the cave opening. Sycamore from Europe was brought in to stabilize steep, rocky slopes and Radiata Pine from North America was provided for the timber industry. Hills and colleagues from the University of Technology Sydney compared leaf litter decomposition rates and invertebrate diversity between the 3 leaf litter pools in "twilight" areas (i.e. near cave openings) and "dark" areas deeper in the cave.
The introduced Sycamore leaves decomposed much faster than the radiata pine needles and native eucalyptus leaves. This suggests that Sycamore leaves release more carbon and nutrients into the cave ecosystem, potentially supporting a more abundant and diverse invertebrate community. Interestingly, there was no difference in leaf mass loss between twilight and dark leaf litter. Proximity to above-ground features like light, rain and wind appear not to affect leaf litter decomposition.
Before I discuss the trends for invertebrates there, I want you to sit back in your chair, take a deep breathe and relax. Close your eyes and envision a cave. Its dark, moist, there is only one opening. All that remains of it is a singularity of daylight. For hundreds or thousands of years this cave has been fed organic matter from the surrounding vegetation. Trees such as Eucalyptus abound in the limestone hills, shedding off their leaves which make their way by the cave opening eventually being blown in by a gust of wind. This occurs daily for millennia. Insects and arachnids feast on the leaves as well as the fungi and bacteria associated with the leaf matter. Over time one might suspect that the animals become adapted to the leaf litter type in some way.
Fast forward to the last 100 years and globalism has introduced new organisms to every corner of the planet at an unprecedented pace, including Sycamore and Radiata Pine to eastern Australia. Are the invertebrate communities more diverse and abundant on the native vegetation that is may have adapted to?
As you can see from the above figures, abundance and species richness are much greater for the introduced european Sycamore than either the pine or Eucalyptus, especially nearer the cave opening. The authors don't really nail the answer with their experiment, but narrow it down to attributes of Sycamore that favor colonization by invertebrates over Pine and Eucalyptus. For instance, Sycamore has a higher specific leaf area (SLA) than both Pine and Eucalyptus. A low SLA is associated with long-lived leaves containing many structural and defensive compounds. These trees invest heavily to guard against plant-eaters whereas the broad-leafed Sycamore does not invest against herbivory, so leaves break down quickly. This faster nutrient release may be part of the reason sycamore leaves have a more abundant and diverse community.
So what would happen if Sycamore were to completely supplant Eucalyptus? It is a higher nutrient leaf and releases carbon faster (i.e. breaks down faster), so it should be better for the spineless society down under, right? One problem is that Sycamore is a deciduous tree. This means nutrient pulses to the caves would occur on a seasonal basis. Since its leaves break down so quickly, this pulse would be short lived compared to the structurally-strengthened Pine and Eucalyptus, both of which keeps their leaves year-round. Being below-ground, caves are protected from the variability of the seasons and are relatively stable environments in terms of climate. The invertebrate community there needs a more constant or stable supply of leaf litter to be sustained. The authors propose
"The short-term influx of energy provided by sycamore litter could be detrimental to subterranean invertebrate diversity in the long term. We would expect to see invertebrate species predisposed to utilizing sycamore derived energy dominating subterranean invertebrate communities and perhaps out-competing other invertebrate species, thereby reducing invertebrate diversity."
Interesting food for thought: nutrient pulses reduce diversity over time. On the other hand, if the authors are talking about partial species replacement, I would also expect to see increase in diversity pooled over the whole year. If this is only a seasonal phenomenon, complete species replacement would be unlikely given that established invertebrates that can utilize multiple plant sources over the year will persist over the long-term. It would certainly be an idea worth funding, especially from the angle that caves may be sheltered from the immediate effects of climate change. A nice replicated mesocosm study within the caves and near the entrances. 'X' amount of replicates sampled throughout the year at various time points to gauge the effect of seasonal nutrient pulses. How about adding various mixtures of different quality leaves to test the hypothesis that maximum food quality results in highest species richness. ------------------------------------------------------------------------------------------------ HILLS, N., HOSE, G.C., CANTLAY, A.J., MURRAY, B.R. (2008). Cave invertebrate assemblages differ between native and exotic leaf litter. Austral Ecology, 33(3), 271-277. DOI: 10.1111/j.1442-9993.2007.01814.x
While there is somedebateoverwhichcreature is the coolest, it is generally understood* that marine molluscs and echinoderms both will face severe stresses coping with increased ocean acidification due to increased CO2 concentrations. The shelled molluscs use calcium carbonate to build their shells and echinoderms use it in creating their exoskeleton. Calcification is strongly related to ocean pH levels and there have been numerous studies looking at the impacts of pH on calcification rates and metabolism in marine inverts.
Much of the published research has been focused on the molluscs and hermatypic (reef building) corals, which has shown that acidification (with levels predicted for the year 2100) will have detrimental effects on calcification and on the metabolic rates of the animals under study.
New research was published yesterday in the Proceedings of the Royal Society B on the effects of ocean acidification on the brittle star Amphiura filiformis and its arm regeneration. The researchers from Plymouth Marine Lab exposed A. filiformis to pH levels of 8.0 (control), 7.7 (IPCC predicted average ocean pH by 2100), 7.3 and 6.8 for a 40 day period. Regeneration effects were tested by detaching one leg from half the subjects and two legs from the rest in each pH group. The team found significant results for the length of regenerated arms, the calcium content and the metabolic rate caused by decreased pH levels.
Some of the results were surprising. Specifically, they found that the amount of calcium - which dissolves in acidic conditions - in regenerated arms was higher in acidified tests than in controls. They also found that non-regenerated arms maintained calcium levels in lower pH and even increased calcium content at a pH of 6.8. The researchers included a test of the calcium content of the separated arms as well. In acidified conditions the dead arms lost calcium as expected.
Brittle stars must increase calcification in the arms just to keep pace with the calcium disolution occuring due to pH. With regenerated arms having an even higher calcium content, this means A. filiformis must significantly increase the calcification under these conditions. The research found that the length of the regenerated arms was longer in acidified test conditions. All of this points to increased energy expenditure under acidified consitions in order to maintain calcium in extant arms and regenerate lost ones. This was confirmed by the oxygen uptake study, which found a significant increase in metabolic activity linked to incresed acidification.
Sounds pretty good then. A. filiformis can increase their metabolism and fuel an increaced calcification to cope with acidification. Except... the researchers also found that muscle wastage occurred and increased with greater acidification. It appears that the muscles are the fuel for the metabolism increase. The muscle wastage happened in regenerated and extant arms subjected to acidification at a rate of up to 20% muscle loss over 40 days. So they can regenerate faster and the calcium levels are higher, but the muscles are weaker and the net effect is a less capable arm. The trade offs to cope with acidification are killing them.
And why do we care?
These brittle stars are an echinoderm model for what may happen as the ocean becomes more acidic. The fact that they will be increasing their metabolism just to maintain calcium levels in their skeleton means greater stress and muscle loss, which in turn may mean less effective use of the arms which they use to burrow and feed. Keep in mind this was a short term experiment. The wastage seen in 40 days, while not fatal, could explain the mortality seen in experiments involving smaller pH changes over longer periods of time.
Burrowing brittle stars, such as A. filiformis, can be siginifcant ecosystem engineers in soft bottom areas through bioturbation and are a major food source (through nipped off arms) for a number of commercially important fish and crustaceans. Other echinoderms responsd in a similar way to acidification. This is a phylum that is, in many ecosystems, a key linkage in ecosystem dynamics and trophic webs so understanding how they react to environmental changes will be important to predict ecosystem changes.
The study also highlights the fact that acidfication affects different organisms in vastly different ways. The effects need to be examined on an organism level instead of only looking at processes. There is still a lot of research needed here, but right now it doesn't look good for the brittle stars, at least A. filiformis.
Wood, H.L., Spicer, J.I., Widdicombe, S. (2008). Ocean acidification may increase calcification rates, but at a cost. Proceedings of the Royal Society B: Biological Sciences, -1(-1), -1--1. DOI: 10.1098/rspb.2008.0343
I guess its to be expected, Intelligent Design proponents just can't seem to tell the truth. Case in point: Casey Luskin, a Discovery Institute lackey attempts his first take at participating in the Bloggers for Peer-Reviewed Research Reporting (BPR3) with a post demonstrating how a recently published article in PLoS ONE using the icon copyrighted by BPR3. Anyone is free to use this icon, you've seen it many times on this blog, so long as they register their blog and abide by the guidelines of this organization. The icon is important not only because it signifies that a post is a thoughtful commentary on a peer-reviewed research article that goes beyond the press releases, but because it contains code that aggregates your post onto an RSS feed with all the posts using the icon and centralizes commentary on peer-reviewed research reporting. I include the icon in post as I will discuss the article simultaneously with a discussion of this issue of fraud.
Luskin failed to register his blog and merely copied and pasted the icon image without any code. Though this is a copyright violation, it also violates a couple of the guidelines.
4. The post author should have read and understood the entire work cited.
This is of course arguable but reading the conclusions Luskin draws from his perverted view of the article in question (open access download here), it may be indeed be argued he didn't understand the "entire work cited". But thats not enough. Anyone is allowed to use the icon and aggregation service in so far as the user abides by the rules and the work is peer-reviewed. What two scientists really have the same interpretation of an experiment?
5. The blog post should report accurately and thoughtfully on the research it presents.
"The hard part is ensuring that the posts more or less fulfill the "accurate and thoughtful" part of that equation. That's handled as a community effort."
Luskin's commentary is not accurate. I'll leave the "thoughtful" open to your interpretation. ------------------------------------------------------------------------------------- Editor's Note: Here is where I'll discuss a few items of the paper in reference to Luskin's post and what Orgel's article stated. I believe this follows the guidelines of BPR3 while counteracting erroneous claims of another blogger.
The article in question is an essay by the late Leslie Orgel of the Salk Institute that discusses the challenges facing the formation of metabolic cycles on prebiotic earth. It is a well-written and thoughtful essay that explains the difficulties with the evolution of the reverse citric acid cycle, hypothesized to operate under a prebiotic chemical environment. Luskin attempts to frame Orgel's essay under an irreducible complexity filter. He claims that Orgel
"... essentially assumes that cyclic metabolic pathways are irreducibly complex systems that require a large number of parts in order to function—including many side pathways that can remove products that will disrupt the cycle. In Orgel's view, it is not plausible to contend that such complex systems, with all of their numerous required components, would simultaneously come into existence."
Orgel in fact didn't make any assumptions about irreducible complexity. Luskin is putting words into his mouth. Orgel lays out a road map for making progress with the origins of life question:
"What is essential, therefore, is a reasonably detailed description, hopefully supported by experimental evidence, of how an evolvable family of cycles might operate. The scheme should not make unreasonable demands on the efficiency and specificity of the various external and internally generated catalysts that are supposed to be involved. Without such a description, acceptance of the possibility of complex nonenzymatic cyclic organizations that are capable of evolution can only be based on faith, a notoriously dangerous route to scientific progress." (emphasis added)
Orgel's problem is with the lack of experimental evidence to support some of the theory. He does not hint at the possibility of giving up on the questions, throwing his arms up and shouting "It was an intelligent designer!" Quite the contrary, he wants more work to be done and encourages further investigation into the evolvability of cyclic metabolic pathways. In the section of the essay called "Peptide Cycles" he states:
"More complex proposals along these lines need to be supported by experimental evidence or compelling theoretical arguments based on the known properties of amino acids and peptides. Claims that they exist cannot be taken seriously without support from experimental or theoretical chemistry."
To me, this statement sounds very anti-ID, since ID and the concept of irreducible complexity asserts that in the end all we have are claims and faith and no hard statistical evidence. One of his concluding sentences really hits home the authors dedication to promoting hard, evidential science:
"Theories of the origin of life based on metabolic cycles cannot be justified by the inadequacy of competing theories: they must stand on their own."
Its a brand new year! Thats means I get to have 2008 in my Endnote catalogue! So what was the first paper of the year that I downloaded?
Perez-Losada, M., M. Harp, J. T. Hoeg, Y. Achituv, D. Jones, H. Watanabe, and K. A. Crandall. 2008. The tempo and mode of barnacle evolution. Molecular Phylogenetics and Evolution 46:328-346.
This was tempered by the news of the passing of one the world's great barnacle biologists, Alan J. Southward. I never got a chance to meet him, though I heard from several people he was great guy. The Liverpool Daily Post's obituary gives a brief example:
"At a more homely level, he was a kind and humorous man, white-haired and bushy-browed, who devoted his immense intellect to discovering more about simple creatures, which, though unseen and unsung, experience the precious gift of life on Earth."
But I have gotten known his research since 2003 when I became interested in stalked barnacles from hydrothermal vents at the East Pacific Rise. Relishing an opportunity to go on board a research expedition with a boat full of taxonomists (though I came with a small geology contingent), I saw for the first time in my life the stalked barnacle, Neolepas zevinae. Barnacles on stalks were a new concept for me. N. zevinae was described in 1979 by Bill Newman from Scripp's Institute for Oceanography. He is still alive and was a colleague of Dr. Southward. The poster below describes them well (from a newspaper by Sam Hinton in 1981).
Alan Southward was more than just a barnacle biologist. Like Charles Darwin, the foremostauthority on barnacles, Dr. Southward studied biogeographic patterns and isolating barriers using barnacle distributions. He studied the damage to the marine ecosystem by pollutants in the 1950s, showing how long it took for ecosystems to recover. Additionally, he was one of the first to study the effects of environmentaltemperature increases on marine invertebrate fauna, way before global warming was a hotbed issue. Alan Southward worked with other marine organisms, most notably Pogonophorans, but limpets and fish as well as being an accomplished marine biologist. He worked 19 beyond his retirement, focusing heavily on hydrothermal vent organisms.
For further information about this naturalist who exemplified a lifetime of learning, I encourage you to look up his publications. I'm happy to provide some from my personal library too! Paul Dando, a researcher at the Marine Biological Station who worked with Dr. Southward, wrote an excellent obituary article in this week's Nature. It is well worth the read. With that being said, this post on barnacle evolution is dedicated to the memory of Alan J. Southward. Cheers! ___________________________________________________________________
Lepas anatifera from Washington state, USA. Photo credit: David Cowles 1997.
Perez-Losada et al. (2008) published a MEGA barnacle data set using 3 nuclear genes and 44 morphological characters for 91 taxa in the superorders Thoracica and Rhizocephala. They rewrote barnacle evolution by rejecting some of the hypotheses that were the foundation for barnacle biology and systematic, while giving statistical and phylogenetic support for others and creating new hypotheses. This study forms the new basis for understanding barnacle evolution and basic biology. This has many implications for other fields. In particular, barnacles are the marine industry's most wanted. They foul docks, boats, and anything else with a part in the seawater, including other animals! Whales, sea turtles, other crustaceans and just about anything else can become a barnacle colonization substrate.
Though Linnaeus, and/or his students, certainly described barnacles, the real authority was Charles Darwin. He spent over 8 years cataloging, describing and monographing every barnacle he could get his hands on from every part of the world. This resulted in 4 comprehensive tomes that are still referenced and cited today. Darwin Online has the complete works freely available over the internet: Living Cirripedia Volumes 1 & 2 and Fossil Cirripedia of Great Britain Volumes 1 & 2. Darwin based much of his taxonomy on shell characteristics, though he certainly studied the internal "soft" parts.
The cirripede shell is formed by plates secreted by the cuticle. They are not molted, or shed, like in other arthropods but increase in size circumferentially and in height. The number of shell plates were traditionally hypothesized to increase from a thoracican ancestor with 4 or 5 plates during the course of evolution. Other groups in the Thoracica with more plates are thus more derived. It is uncertain to what the selective pressure was to develop different numbers of plates. Perhaps more smaller plates offer greater protection than fewer larger plates. What Perez-Losada et al. found out though was there were no clear patterns with plate enumeration. Clades with no plates are mixed in with clades with 5 plates, while a clade with more than 12 plates is sister to a clade with a last common ancestor that had no more than 7 plates. The theory of shell plate evolution is clearly debunked in this analysis, though they can say with some degree of certainty that the last common ancestor to the Thoracica had no more than 4 plates. Another interesting point is that asymmetry (Verrucomorpha) has evolved independently at least twice in the thoracican lineage. I believe this highlights the plasticity in biomineral characters, such as shell characteristics. This is seen in many molluscan clades where general shell characteristics are misleading, sometimes due to external parameters (erosion) and sometimes due to phenotypic plasticity in the mechanisms that construct biomineral structures. Thus, the soft parts and larval characteristics are more important (though often more difficult to study and they leave no fossil trace).
Figure 3 from Perez-Losada et al. (2008): "Thoracican divergence time chronogram estimated using the 50% majority-rule consensus BMCMC tree of morphological and molecular data under mix-models..." See paper for more details.
On a sytematic level they uncovered several polyphyletic clades, such as the Heterlepadomorpha (those that have no shell plates). This clade appears to have evolved at least twice, independently, and in both cases are more derived (within clades that have more than 5 plates) and a more recent radiation. The previously well established clades of the Verrucomorpha, Scalpellomorpha and Sessilia are no more, while the Iblomorpha and Balanomorpha have gained unequivocal support. One grouping that caught my attention is the clade below (magnified from above).
Especially everything under and including the clade marked 'Verrucomorpha (7s)'. All those barnacles - Neoverruca, Ashinkailepas, Vulcanolepas, Leucolepas and the aforementioned Neolepas are - are hydrothermal vent barnacles from the Pacific Ocean. I am very surprised to see this neat and well supported grouping. In particular, the stalked barnacle Vulcanolepas osheai is known the farm chemoautotrophic bacteria on its cirri. The more vent scientists look, the more it seems that vent organisms tend to form clades despite geographic distance, barriers or classical taxonomic ranks. We are seeing similar grouping in anemones, caridean shrimp, bythograeid crabs, and of course all the chemoautotrophic taxa: siboglinid annelids, bathymodiolin mussels, and vesicomyid clams. The habitat appears to be a unifying factor. I wonder what else in this phylogeny groups together by habitat? I know I've found Arcoscapellum sp. hanging off the antenna of an anomuran crab (Eumunida picta), perhaps it is related to other crab hitchhiking barnacles.
This study is a great study for many reasons, partly because it answers some questions, but mostly because it rearranges our thinking about the taxa in question and gives us more avenues to explore. I didn't highlight all the major discoveries from this article, such as the fine-tuning of the tempo of evolution, but I hope to see future papers addressing the evolutionary ecology of barnacles in light of the new systematic rearrangement. Taxonomy is at the point now where they needs to be substantial revolutions to be made in order to progress from stagnancy. This study and others like it using 'total evidence' (i.e. combining morphological characters, life history traits and genetics) will pave the way to understanding animal evolution and give systematics the credit it deserves, both financially and publicly. So cheers Dr. Southward, I'm sure you are resting well in the cirri of your loved organisms.
Author's note: Fireflies will always hold a special place in my heart. Every summer when I was kid I would sit outside in Iowa and watch them, collecting them in my hands so I could peek inside with one eye to see if the lightning bug (as we called them in Midwest) was flashing. I look forward even more now to the day when my children can stay up late enough to watch and collect fireflies themselves. This post is dedicated to my beautiful swedish wife, who discovered fireflies for the first time when we moved east out of California 3 years ago. It is so great to see how excited she gets when they come out each summer!
Fireflies are considered all part of the family of beetles called Lampyridae. Appropriately, this means light. The luminescence is the result of a chemical reaction with the substrate Luciferin and the enzyme Luciferase. The happens in two steps and is energetically expensive (i.e. requires ATP and oxygen). This is a slow reaction, which is why we can see it decay after the initial flash, that is controlled in specialized organ in its abdomen, called the lantern naturally. It sometimes is mistakingly thought of as a bacterial symbiosis like in many marine organisms, but for fireflies (along with many other bioluminescent critters) this is purely a chemical phenomenon.
There are about 2000 species of Lampyrids globally, with about 120 of those in North America. Stanger-Hall et al. recently reported the first phylogeny of North American fireflies in the journal Molecular Evolution and Phylogenetics. Their study also has interesting results for the evolution of light signals in this family. First the basics though, which also have importnat implications. They used nuclear (18S) and mitochondrial genes (16S and COI) to form consensus trees of 27 species of North American fireflies from 17 genera, including one species and genus that was recently placed outside of the family Lampyridae (Pterotus). They found that, in fact, North American fireflies do not form a monophyletic group. This lends support to the hypothesis that firefly diversity has been helped by multiple invasions. Furthermore, they determined that the present taxonomic classification into subfamilies and tribes is not supported by the molecular data, while Pterotus and another genus placed outside of the family are actually nested within the Lampyridae.
Figure 1 from Stanger-Hall et al. 2007. Carbon dust drawings done by Laura Line.
The real interesting result of this study has to do with evolution of the signaling. Branham & Wenzel (2003) report that lampyrid larvae possess of constant, but faint glow in larval light organs on the abdomen. These authors suggest, based morphological character analysis, that light production evolved early, predating the Lampyridae, and was retained from the larval form. This is supported by observational evidence that adults vary widely in light production and light organ placement and use. Typically, lampyrids use their light displays as sexual signals to attract a mate. But more basal family members use pheromones. Citing a chapter by Lloyd (1997), Stanger-Hall et al. describe 3 mating signal systems in the 120 North American species of firefly:
(1) Chemical signals (pheromones): ‘‘dark fireflies’’ (e.g. Ellychnia, Pyropyga, Lucidota) produce no light as adults and are active during the day; they release chemical signals to attract mates. (2) Glows (continuous light signals): ‘‘glowworm fireflies’’ (e.g. Microphotus, Phausis, Pleotomodes) tend to have larvae-like females who spend the day in underground burrows and emerge at night, emitting a continuous glow. This glow (short distance) in combination with pheromones (long distance) attracts males who will fly towards the glow, but usually do not signal themselves. (3) Flashes (short intermittent light signals): ‘‘lightningbug fireflies’’ (e.g. Photinus, Photuris, Pyractomena) are the most commonly observed. They are active at dusk or in the dark and both males and females use species-specific light signals to communicate with each other in an interactive visual morse-code that identifies the species and the sex of the signaler. Some genera (e.g. Pleotomus) and individual species within genera (e.g. Phausis reticulata) may represent intermediate stages in signal evolution (e.g. Pleotomus males glow when disturbed).
In terms of the evolution of signaling, they found no clear patterns. Whether they used flashes, glows or pheromones all the species in the phylogenetic tree were intermingled.
If you click on the above figures from Stanger-Hall et al., you can view them larger but at this size the take-home message is clear. The tree on the top is color-coded by sexual signal modes. Green signifies flashes, orange is glow, grey means using pheromones and weak glows, while black is only pheromones. It is obvious that glows and flashes have multiple origins in the North American firefly fauna.
The tree on the bottom is the same tree, but this time orange branches are for both flashes and glows and black branches are for pheromones only. The asterisks denoted light signal origins (orange) or losses (black) while the letters A & B represent two possible evolutionary scenarios.
"Scenario A, light signals originated once in ancestral adult lampyrids, and were subsequently lost nine times. Scenario B, ancestral lampyrids used pheromones as sexual signal, and the transition to sexual light signals evolved four times independently, followed by four losses. There are at least two other possible 10-step scenarios (multiple gains and losses), but neither is favored by any weighting where losses are considered as likely or more likely than gains. The color-coding of the branches reflects scenario B."
Video firefly larva from Thailand. Note the constant glowing in the posterior segment.
This all provides evidence that supports the hypothesis that the lampyid fauna of North America has invaded the continent multiple times with multiple origins (i.e. Europe or Asia). While scenario A allows for only a single origin of light production followed by 9 losses, scenario B is more parsimonious - requiring fewer steps. It seems to me, and I think there are papers out there that might back it up, that new gains or more rarer than losses. It would be interesting to see a meta-analysis of studies that combined morphology and molecular character data to study if indeed parsimony won out over intuition. If anyone knows of such studies, drop me a line.
Another study published in American Naturalist last month by Woods et al. 2007 studied the energetic costs and the risk of predation associated light production. This video that I couldn't figure out how to embed (might need subscriber access) describes their research (contributed by the authors as additional material with their paper). They measured energetic costs using open flow respirometry, which measures carbon dioxide production, during flashes and when at rest. They found that individual fireflies did have a significant increase in metabolic rate during light production compared to being at rest, but it was less than the rate when they were walking and not flashing. To test the hypothesis that maintaining just the bioluminescent capability has energetic costs, they also tested two other lampyrid species that are diurnal and do not produce light. Standardizing for body, they found no significant differences in the metabolic rate of lampyrids that are capable of producing light and those that have no such capability.
The next step was to see if light production incurred any costs in terms of increased predation. Woods et al. 2007 set up a experiment with arrays of sticky-trap cups with flashing LEDs that simulated the mating signals of Photinus greeni and sticky-trap cups without any light (Figure 1b from Woods et al. 2007, left). P. greeni is chemically defended against would-be predators by synthesizing steroidal pyrones. But there is one predator that is unbothered by this defense and in fact sequesters the compound for use in its own defense. This is another species of firefly called Photuris versicolor that hunts Photinus species by tracking their mating signals and captuing grounded males in the midst of getting it in on. In fact out 218 individuals of Photuris trapped, only 4 were caught on non-flashing traps! Interestingly, 96% of all trapped Photuris were females.
The take home message? Its not energetically expensive to make flash your stuff but you'll attract the wrong company at times!
"Every single night, male fireflies are out there flying a fine line between sex and death. For us, it definitely rivals the most exciting television thriller! So, next time you're outside on a summer night take a moment to admire the firefly romance and risk that’s playing out all around you."-Sara Lewis, Professor of Biology at Tufts University (quoted from press release on physorg.com)
------------------------------------------------------------------------------------ Branham, M.A., J.W. Wenzel (2003). The origin of photic behavior and the evolution of sexual communication in fireflies (Coleoptera: Lampyridae). Cladistics 19(1), 1–22. doi:10.1111/j.1096-0031.2003.tb00404.x
Lloyd, J.E. (1997). Firefly mating ecology, selection and evolution. In: Choe, J.C., Crespi, B.J. (Eds.), Evolution of Mating Systems in Insects and Arachnids. Cambridge University Press, London, pp. 184–192.
Stanger-Hall, K.F., J.E. Lloyd, D.M. Hillis. (2007) Phylogeny of North American fireflies (Coleoptera: Lampyridae): Implications for the evolution of light signals. Molecular Phylogenetics and Evolution, 45, 33-49. doi:10.1016/j.ympev.2007.05.013
Woods Jr., W. A., H. Hendrickson, J. Mason, S.M. Lewis. (2007) Energy and predation costs of firefly courtship signals. American Naturalist, 170, 702-708.
Finding any new fossil is rare. Finding invertebrate fossils is even rarer due to the squishy nature of most invertebrates. They just do not preserve well over time. Sometimes the wandering paleontologist, who must look very carefully under a field scope through dust and debris, can find parts of squishy invertebrates like scolodonts (polychaete jaws), coral rubble, carbonate shell cement, or maybe sea star or sponge spicules. On even rarer conditions, this careful wandering paleontologist may find imprints of the outlines of squishy invertebrates that have no hard parts, none whatsoever.
China has been an amazing hot spot for fossils in recent years. Entire ecosystems have been preserved. Careful, wandering paleontologists are able to move beyond describing the random individual to describing how some dinosaurs formed nests, embryonic fossils still in the egg, biometric trends in populations of fossil fish or molluscs, interspecific interactions and just about anything else. The Chinese paleontologists have been prolific, publishing widely on their discoveries, inviting western paleontologists on digs and getting the Chinese people and government serious about their fossil wealth. They do have a problem with fossil poachers, but the rate of discovery remains high and stiffer penalties are becoming more commonplace.
"Reconstruction of Y. dianensis on the basis of a larval stage with eight thoracomeres (developmental stage 4). The head limbs are drawn in median view and the trunk limbs in lateral view."-Zhang et al. 2007
Zhang et al. 2007 present a new find of a crustacean with some interesting morphology and even more interesting implications. Yicaris dianensis (above drawing) new species, is named for both the people, the Yi, and the place the fossils originated from, Dian. The suffix 'caris' refers to something that is a crustacean and the suffix 'ensis' refers to being from a place. What is remarkable to me is that 6 successional developmental stages are represented in pre-Cambrian strata. This is close to the hypothesized origin of the Arthropoda, specifically the Crustacea. So this form should theoretically be the closest ontologically to the earliest Crustacea.
"With such ontogeny data and having the age of the fossil as a time marker, it is possible to more precisely include ontogenetic evolutionary pathways in the reconstruction of relationships and ground patterns of stem species and monophyla. According to our analysis, Y. dianensis represents the first undoubted eucrustacean known from the Lower Cambrian (the single previously described Lower Cambrian putative eucrustacean species lacks eucrustacean characters) and can serve as a substantial tool for testing relevant character acquisition and phylogenetic hypotheses. This is of particular importance because crustacean phylogeny has gained new interest by recent studies using neurobiological, developmental, biological and molecular investigations."
Y. dianensis shares many features in common with modern day branchiopods and cephalocarids of which I won't go into detail. Some of the similarities are in the mouthparts and other structures involved in food uptake or feeding. The interesting character for this crustacean is called the epipod, or "above-foot", which are lobe-shaped osmoregulatory or respiratory outgrowths on the external limb bases of various Eucrustaceans (SEM below). This structure is derived from setae and many of the Eucrustacea ("true" Crustacea) still bear at least one epipod on some of its appendages. Some authors even believe insect wings are derived from epipods (here and here).
"Fragment of trunk (holotype; developmental stage 6); lateral view"-Zhang et al. 2007; ep=epipod
This all comes home to pushing back the time of arthropod origins as stated by Zhang et al.
Its stratigraphical position provides substantial support to the proposition that the main cladogenic event that gave rise to the Arthropoda was before the Cambrian
It was found in the Orsten layer, which is rich in Phosphatocopina, the sister group to Eucrustacea characterized by a phosphotatized cuticle. By using Lyell's principle of Uniformitarianism, we can assume that since the characters represented in Y. dianensis are present in the Lower Cambrian, Its ancestors possessed some or all of its characters. Hence arthropod origins are likely pre-Cambrian.
Baker 2007 conducted experiments with jumping spiders, Phidippus princeps (Salticidae), in which he manipulated corridors connecting patches of an old growth field (clover and alfalfa). Patches were either all not connected, all connected, or partly connected by vegetated corridors (as opposed to bare corridors) (see schema below, Fig. 1 from Baker 2007).
Baker found that P. princeps always preferred vegetated corridors and was never found on bare strips.
"The results of this experiment show that corridors are important for the interpatch movement of female P. princeps: spiders moved almost exclusively to patches connected by vegetated strips. In the absence of vegetated strips, spiders rarely moved cross bare substrate to a new habitat even in overcrowded conditions."
This has pretty fundamental consequences for movement and dispersal ecology. The fact that these spiders will not move across a non-vegetated corridor, despite reaching carrying capacity (Baker reports using densities 2-3 times that in nature), underlies the importance of connectivity between habitat patches. This is a ripe area of conservation research, which has mostly been done on large mammals like mountain lions, bears and other endangered verts (can we say LAME!). Invertebrates, typically being much smaller, are more subject to small changes and micro-habitat conditions. This study shows how important it is to maintain habitat corridors for the little guys.
"If an animal, as in the case of P. princeps, does not respond to density pressures when habitat patches are surrounded by unfavorable habitat, the persistence of fragmented populations may be severely compromised."
The fact of the matter is that critters won't risk it out in the open. They need cover to help ensure their survival when moving around. This is a nice arguement for conserving or creating corridors between habitat patches. The next step I think is to link similar principles to biodiversity and ecosystem functioning. Given the same initial starting compositions, do communities differ when habitat patches are linked versus unlinked, or various degrees between?
Wrinn & Uetz 2007 studied how leg loss and regeneration affected the condition, growth and development time in the wolf spider, Schizocosa ocreata (Lycosidae). Spiders are able automatize legs as a defense strategy, but it isn't clear what the trade-off is. For instance, if a spider amputates its leg and undergoes regeneration, does that impact future reproduction, make it more susceptible to predation later on, make it less mobile, less of a competitor, or make it harder to find food? Wrinn & Uetz examined the frequency of autonomy in the field and its relationship to size, mass and condition (residuals of the mass to cephalothorax regression, I'll post later about the efficacy of condition indices-something I use in my own research). They also did a laboratory study to test the hypothesis that leg regeneration impairs foraging, decreases growth and/or affects development time.
The field data they collected indicate that reduced foraging ability is associated with leg loss, evidenced by decreases in mass, size and condition. The laboratory experiments also suggest additional trade-offs. Though not significant, spiders regenerating legs took an average of 3.7 days longer to molt. One interesting observation was that
"Although spiders appear to show costs of regeneration, the differences in molt interval, size, and mass between intact and regenerating spiders were only true for the first molt after autonomy. During the second molt after autonomy, regenerating spiders were able to compensate for previous costs by either shortening their molt interval or increasing their growth."
It appears that these spiders are pretty flexible and bounce back to minimize costs of loss and regeneration to only one molt. Another trade-off was between development time and mass. Regeneration resulted in either longer time to molt or lower mass, but not both.
Most snails walk the line and stick with doing the dirty deed missionary-style. No one even thinks about any of that kinky, low-down, unholy ways of propagating the world. But Schilthuizen et al. 2007 report in the latest Journal of Evolutionary Biology (open access!) that one disgusting species of snail actually selects for anti-chiral mates (Fig. 3b, d to the right reproduced under the Creative Commons Deed, Attribution 2.5). This scandalous sixty-nine of satan is even sexually selected for by spermatophore morphology! Just when I thought I heard it all.
Chirality in snails refers to what directions the coils run, clockwise or anti-clockwise (known as counter-clockwise in some localities).
"The cause of directional asymmetry is clear in only a few groups (Vermeij, 1975), such as in gastropods (snails). Their coiling direction (not only of the shell but also of the entire body organization), determined by a single locus of maternal effect, is usually fixed within a species because mating among D and S individuals (so-called ‘inter-chiral mating’) is either impossible or very difficult. Consequently, a rare reverse-coiled morph will normally not persist because of frequency-dependent selection."-Schilthuizen et al. 2007 (references removed)
So typically is a pretty rare thing and it usually dies out of the population fairly quickly. But not satisfied with being a typical gastropod, members of the southeast asian tree snail genus Amphidromus do NOT, yes I repeat do NOT, deviate from a 1:1 ratio of dextral (right-opening) to sinistral (evilleft-opening) individuals. They keep their damned "whole-body chiral dimorphism", but why would a snail do such a thing? Schilthuizen et al. 2007 proposed a series of hypotheses that they tested: 1) Frequency-dependent selection countered by extrinsic balancing selection. Basically, one morph is present in higher number and is predated upon unto rare than other morph which is then, in turn predated on, etc. 2) Occupy separate niches 3) Dimorphism is maintained by intrinsic factors such as coiling genetics or reproduction.
They observed 2 separate populations of Amphidromus inversus, with the same predation frequency. Though the dextral morph was slightly less than 50% (~35%) of the population, predation was the same hence hypothesis 1 can be ruled out (i.e. no increase in predation frequency with the more frequent evilsinistral morph). Additionally, a PCA analysis using 10 biometric features shows there is no difference between D and S morphs. They are in fact mirror images of each other, which suggests to the authors that they are ecologically equivalent. They provide other evidence from previous work led by the first author that both morphs have identical dispersal patterns, habitat preference, and molecular data shows they are panmictic to argue against hypothesis 2.
Which brings us to hypothesis 3. To study inheritance of chirality, they grabbed all the egg bunches they could and waited till the juveniles hatched out (Fig 3f to the left, reproduced under the Creative Commons Deed, Attribution 2.5). Except for one clutch, all other clutches were invariant for coiling direction. In other snails, coiling direction has been found to be maternally transmitted from a single locus, which the data fro this study onA. inversus is consistent with. Still waiting for the cool part?? See below.
Fig. 5 reproduced in its beautiful entirety under the... you get the drift. These pictures are of the spermatophore. Important to note the spiral tip.
Oh yeah, thats one mighty spermatophore, 60mm schlong that curves either to the right or the left. This curvature reflects the chirality of the shell.
"The oviduct is connected with the SRO [spermatophore receiving organ] at an angle to the left or to the right in a sinistral or a dextral recipient, respectively, whereas the spermatophore tail tip points to the left or right in a dextral or a sinistral donor respectively (viewed from the front of the recipient animal). Consequently, it can enter the oviduct more easily in inter- than in intra-chiral copulation (Fig. 5e–h)."-Schilthuizen et al. 2007, italics my own.
Its all about the fit not the size... So what's the conclusion? Why do I think this is a cool study?
"we have shown that mutual mate choice for a partner with mirror-image asymmetry stabilizes antisymmetry in these snails. As far as we are aware, this is the first confirmed case of heritable antisymmetry in the Metazoa."-Schilthuizen et al. 2007
Kevin works at the Duke Marine Lab as a researcher at the Marine Conservation Molecular Facility studying the population genetics of vent fauna. He has an M.Sc. in Biology from Penn State where his research focused on marine invertebrate systematics and the community structure of chemoautotrophic foundation fauna at hydrothermal vents. Visit Kevin's personal website, where his CV lives, and follow him on Twitter, Flickr, Friendfeed, YouTube, Nature Network, Amazon, Research Blogging and Facebook.
Blogger With No Backbone
Eric worked in Satellite communications, computers and design for many years, but returned to school to pursue his early love of marine sciences. He is curently working on his Masters in Biological Oceanography at the University of Connecticut's Avery Point Campus. Eric also photo-blogs at Larval Images, has a personal site at Eclectic Echoes and his images are available on Flickr.
Cyamus ovalis Photo: Vicky Rowntree, University of Utah
Image courtesy of Mariano Sironi, Institute of Whale Conservation, Buenos Aires
Closeup of Right Whale callosity with C. ovalis. From Iain Kerr, Ocean Alliance/Whale Conservation Institute
