Abstract
Taxonomically exhaustive and continent wide patterns of genetic divergence within and between species have rarely been described and the underlying evolutionary causes shaping biodiversity distribution remain contentious. Here, we show that geographic patterns of intraspecific and interspecific genetic divergence among nearly all of the North American freshwater fish species (>750 species) support a dual role involving both the late Pliocene-Pleistocene climatic fluctuations and metabolic rate in determining latitudinal gradients of genetic divergence and very likely influencing speciation rates. Results indicate that the recurrent glacial cycles caused global reduction in intraspecific diversity, interspecific genetic divergence, and species richness at higher latitudes. At the opposite, longer geographic isolation, higher metabolic rate increasing substitution rate and possibly the rapid accumulation of genetic incompatibilities, led to an increasing biodiversity towards lower latitudes. This indicates that both intrinsic and extrinsic factors similarly affect micro and macro evolutionary processes shaping global patterns of biodiversity distribution. These results also indicate that factors favouring allopatric speciation are the main drivers underlying the diversification of North American freshwater fishes.
Highlights
Levels of genetic divergence and mutation rates vary between and among species as well as between geographic regions [1,2,3,4]
Even using a wide range of possible mitochondrial DNA mutation rate
The observed reduction of intraspecific and interspecific genetic divergence with latitudes had been previously reported based on a meta-analysis comprising heterogeneous data sets from 42 fish species [15]
Summary
Levels of genetic divergence and mutation rates vary between and among species as well as between geographic regions [1,2,3,4]. Identifying factors responsible for such variation is of fundamental interest because it might allow understanding general patterns of biodiversity distribution such as the latitudinal gradient of diversity, which ranks among the most striking and oldest recognized pattern in ecology [5,6,7]. It may even allow calibrating the molecular clock to better account for mutation rates variation [8]. Levels of genetic divergence and eventually allopatric speciation near the tropics could be enhanced by the longer persistence of isolated populations
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