Ambush predators have vertical pupils for rangefinding; prey horizontal pupils for panorama.
"scientists found that short ambush predators such as alligators and foxes are more likely to have vertical pupils, whereas prey species—like gazelles or sheep—are more likely to have horizontal pupils."
"Circular pupils are generally found on animals that chase down their prey, such as cheetahs, or on taller ambush predators like lions and tigers. This suggests that above a certain shoulder height—about 42 cm—the functional advantages of vertical pupils are lost."
back from The Creek and some real-time camp-fire talk... after climbing...
eeyonkee and Moosedrool were discussing the book 40 Years of Evolution: Darwin's Finches on Daphne Major Island (at least I think they were, I was helping with dinner prep). This discussion spilled over and the speculation of what DNA analysis might be useful in understanding the apparently rapid adaptations was floated, I think this was a breakfast/coffee conversation.
Anyway, my paper copy of Science arrives about a week after the issues release, but having the entire issue at hand means I read most of the articles... and interestingly, this article appeared:
A beak size locus in Darwin’s finches facilitated character displacement during a drought
Sangeet Lamichhaney, Fan Han, Jonas Berglund, Chao Wang, Markus Sällman Almén, Matthew T. Webster, B. Rosemary Grant, Peter R. Grant, Leif Andersson
Ecological character displacement is a process of morphological divergence that reduces competition for limited resources. We used genomic analysis to investigate the genetic basis of a documented character displacement event in Darwin’s finches on Daphne Major in the Galápagos Islands: The medium ground finch diverged from its competitor, the large ground finch, during a severe drought. We discovered a genomic region containing the HMGA2 gene that varies systematically among Darwin’s finch species with different beak sizes. Two haplotypes that diverged early in the radiation were involved in the character displacement event: Genotypes associated with large beak size were at a strong selective disadvantage in medium ground finches (selection coefficient s = 0.59). Thus, a major locus has apparently facilitated a rapid ecological diversification in the adaptive radiation of Darwin’s finches.
Similar species potentially compete for limited resources when they encounter each other through a change in geographical ranges. As a result of resource competition, they may diverge in traits associated with exploiting these resources (1, 2). Darwin proposed this as the principle of character divergence [now known as ecological character displacement (3, 4)], a process invoked as an important mechanism in the assembly of complex ecological communities (5, 6). It is also an important component of models of speciation (6, 7). However, it has been difficult to obtain unequivocal evidence for ecological character displacement in nature (8, 9). The medium ground finch (Geospiza fortis) and large ground finch (G. magnirostris) on the small island of Daphne Major provide one example where rigorous criteria have been met (10). Beak sizes diverged as a result of a selective disadvantage to medium ground finches with large beaks when food availability declined through competition with large ground finches during a severe drought in 2004–2005 (11).
Our results provide evidence of two loci with major effects on beak morphology across Darwin’s finches. ALX1, a transcription factor gene, has been associated with beak shape (15), and here we find that HMGA2 is associated with beak size. ALX1 and HMGA2 are 7.5 Mb apart on chromosome 1 in chicken and zebra finch, and probably also in Darwin’s finches, as expected on the basis of the very high degree of conserved synteny among birds (24). Beak size and beak shape are involved in all the major evolutionary shifts in the adaptive radiation of Darwin’s finches (1). They are also subject to strong selection in contemporary time. In the character displacement episode discussed above, beak size was subject to strong directional selection: The standardized selection differential of –0.66 for sexes combined is an exceptionally high value. We have shown that the HMGA2 locus played a critical role in this character shift. The selection coefficient at the HMGA2 locus (s = 0.59 ± 0.14) is comparable in magnitude to the selection differential on the phenotype and is higher than other examples of strong selection, such as loci associated with coat color in mice (s < 0.42) (25). The main implication of our findings is that a single locus facilitates rapid diversification. The lack of recombination between the two HMGA2 haplotypes, together with abundant polygenic variation and ecological opportunity (2, 5), may help to explain rapid speciation in this young adaptive radiation (1).
Anyway, look at today, then stop and consider how quickly things have happened. Homo Sapiens has totally altered nearly every inch of the Earth, and if he were so inclined, could.
This is new.
I always enjoy his geological perspectives and informative posts, but I have to disagree on that one point. When land plants expanded hugely in biomass, they photosynthesized like crazy and completely poisoned the entire atmosphere of the planet with oxygen, which is incredibly toxic to many species. He'll know exactly, but it went from some fraction of a percent or a few percent right up to 10 and then 20 percent really quickly (geologically speaking). So while it may be new for just one single species to have effected such a big change, the phenomenon is not unprecedented. Changes in physical environment are frequent causes of species evolution, but it can happen the other way around too.
Luckily enough for some clades of organisms, they could use the stuff and quickly diversified and expanded into every niche.... and some of them ultimate became humans and set about trashing the land and ocean environments.