Abstract
BackgroundClimatic oscillations throughout the Quaternary had profound effects on temperate biodiversity, but the extent of Quaternary climate change was more severe in temperate regions of the northern hemisphere than in the southern hemisphere. We sought to determine whether this geographic disparity differentially influenced the timing of intraspecific diversification events within ectothermic and endothermic vertebrate species. Using published phylogenetic hypotheses, we gathered data on the oldest intraspecific diversification event within mammal, bird, freshwater fish, amphibian, and reptile species from temperate-zone areas. We then tested whether the timing of diversification events differed between hemispheres.ResultsOur analyses provide strong evidence that vertebrates from temperate regions of the northern hemisphere are younger than those from the southern hemisphere. However, we find little evidence to suggest that this relationship differs between endotherms versus ectotherms, or that it varies widely across the five classes of vertebrates that we considered. In addition, we find that on average, endothermic species are much younger than ectothermic species.ConclusionOur findings suggest that geographic variation in the magnitude of climatic oscillations during the Quaternary led to substantial disparity in the timing of intraspecific diversification events between northern and southern hemisphere vertebrates, and that the magnitude of this divergence is largely congruent across vertebrate taxa.
Highlights
Climatic oscillations throughout the Quaternary had profound effects on temperate biodiversity, but the extent of Quaternary climate change was more severe in temperate regions of the northern hemisphere than in the southern hemisphere
Quaternary (~1.8 million years ago to present), and these changes had profound effects on temperate biodiversity [3,4,5]. The magnitude of these fluctuations is manifested in the genetic structure of extant populations [6], but the severity of Quaternary climate change was not the same in temperate regions of the northern and southern hemispheres
Our analyses provide strong evidence that vertebrates from temperate regions of the northern hemisphere are younger than those from the southern hemisphere (Figure 2; Table 1a)
Summary
Climatic oscillations throughout the Quaternary had profound effects on temperate biodiversity, but the extent of Quaternary climate change was more severe in temperate regions of the northern hemisphere than in the southern hemisphere. The onset of significant climatic oscillations began in the Quaternary (~1.8 million years ago to present), and these changes had profound effects on temperate biodiversity [3,4,5]. The contemporary distributions of many northern hemisphere vertebrates reflect relatively recent recolonisations of previously unsuitable areas from climatic refugia [6,8]. This pattern of extinction and recolonisation should have, in turn, constrained intraspecific divergences between genetic lineages to more recent timescales in the northern hemisphere. The contraction of species to refugia led to a loss of genetic diversity and intraspecific genetic lineages [9], which could have eliminated ancient lineages and resulted in more recent diversification events in the northern hemisphere
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