This is what it looks like when two genera are the same genus. Wakabayashi et al. published a paper in the Journal of the Marine Biological Association of the U.K. this month providing molecular evidence, as well developmental evidence, for the synonymy of two genera, Moroteuthis and Onykia. Apparently someone had the observation that Onykia might an immature stage of Moroteuthis (which is large, see picture below). The authors tested this by collecting paralarvae, a small planktonic phase of cephalopods, north of Hawai'i and corroborating morphological analysis with sequence data from the COI gene. The tree above is a good representation of what it should look like when two genera are one and the same. You see them intermingling in the branches. Onykia has nomenclatural precedence so all species under Moroteuthis are now Onykia. Priority is another way of saying first published first served. The oldest date always has priority when synonymzing taxa.
This is an example of a good straight-forward synonymy using data from morphology and genes. Corroboration is the wave of the future man. You can't get rid of morphology, its too damn cool, and you can't ignore genetics, it makes too much damn sense. So what do you do? Use total evidence in understanding phylogeny. Morphological characters have a genetic basis. We don't have the genomes sequenced of every living thing on earth. So can we use morphology as a proxy for genetic divergence? To do so we have to convince ourselves that a morphological trait is shared with other species that are closely related to it. This makes more sense on a lower taxonomic scale such as species, genus or sometimes even family level. For instance, anatomical structures like isopod mouth parts or shrimp legs are easier to group on shared ancestry than say numbers of ass hairs. Variation in the latter is much greater between individuals that between species, while variation in the former may be less between individuals than between species or genera. Modifications in the phenotype are based on changes in the genotype. Since we don't know a priori what gene to sequence to understand the evolution of shrimp legs (called pereopods by the way), we can use the morphological character as a proxy for the genetic evolution. Corroborating these results against gene trees provides powerful evidence.
It's 1 am so I might have to reread what i just wrote in the morning to make sense of it all...
In other squid news, the mighty Humboldt Squid, Dosidicus gigas, is invading California! Taco del Mar will be offering squid tacos en masse. Craig at Deep Sea News recently posted on a study tracking the range expansion of the Humboldt into California's water. Today, the study came out in PNAS, authored by Zeidberg & Robison. This is a 16-year video time-series of beautiful, scenic and constantly overcast Monterey Bay.
"Climate-related changes in fish distribution have been typically characterized as range shifts or displacement away from the center of the home range, as temperatures grew warmer. In contrast, Dosidicus has enlarged its distribution without abandoning its historical center."-Zeidberg & Robison 2007The authors correlated squid appearance with loss of Hake. Hake rebounded in years where the Humboldt was absent from surveys. Additionally squid abundance in Monterey Bay is positively correlated with increase in the sea surface temperature of the tropical Pacific (used as a measure of the El Nino effect). But the authors warn,
"The expansion of Dosidicus’ range does not appear to be directly linked to a regional increase in sea-surface temperatures. Although its tropical center of distribution and the El Nino-linked episodic range expansions suggest a warm-water affinity, its vertical distribution in the water column demonstrates a physiological tolerance for temperatures far lower than it encounters near the surface."-Zeidberg & Robison 2007
The authors also made an interesting point that the expansion may in part be due to loss of the Humboldts predators, namely tuna and billfish. Being freed from the constraints of predation, the Humboldt physiological plasticity and rapid growth rate enable it to expand into new habitats quickly. So the negative effect of tuna loss has the positive effect of more calimari rings and squid tacos!