Wednesday, January 10, 2007
From New Scientist: Amphibians bounced back spectacularly from a series of mass extinctions during their evolution, according to a new genetic analysis.
In the present day, biologists see amphibians as sentinels of environmental change. The extreme sensitivity of their skin makes them more prone than other organisms to soaking up toxins and suffering from fungal infection, and provides little protection from ultraviolet radiation, which causes genetic mutation.
Many amphibian populations have declined in recent years. At least 43% of populations of amphibian species are declining, some research suggests (see, for example, Global frog crisis defies explanation).
That said, a look at their latest evolutionary tree reveals that amphibians have a remarkable capacity to bounce back from environmental changes, says Kim Roelants of Vrije University in Brussels, and colleagues.
Continued at "Amphibians - the comeback kings of evolution"
Based on the Proceedings of the National Academy of Sciences (PNAS) paper:
Global patterns of diversification in the history of modern amphibians
The fossil record of modern amphibians (frogs, salamanders, and caecilians) provides no evidence for major extinction or radiation episodes throughout most of the Mesozoic and early Tertiary. However, long-term gradual diversification is difficult to reconcile with the sensitivity of present-day amphibian faunas to rapid ecological changes and the incidence of similar environmental perturbations in the past that have been associated with high turnover rates in other land vertebrates. To provide a comprehensive overview of the history of amphibian diversification, we constructed a phylogenetic timetree based on a multigene data set of 3.75 kb for 171 species. Our analyses reveal several episodes of accelerated amphibian diversification, which do not fit models of gradual lineage accumulation. Global turning points in the phylogenetic and ecological diversification occurred after the end-Permian mass extinction and in the late Cretaceous. Fluctuations in amphibian diversification show strong temporal correlation with turnover rates in amniotes and the rise of angiosperm-dominated forests. Approximately 86% of modern frog species and >81% of salamander species descended from only five ancestral lineages that produced major radiations in the late Cretaceous and early Tertiary. This proportionally late accumulation of extant lineage diversity contrasts with the long evolutionary history of amphibians but is in line with the Tertiary increase in fossil abundance toward the present. (Abstract)
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