Allochronic Divergence Driven by Spatial Asynchrony in Precipitation in Neotropical Frogs?

The role of geographic barriers in promoting reproductive isolation across space is well understood. Isolation by the time of breeding, however, may also promote population divergence when populations reproduce asynchronically in space, even in the absence of geographic barriers. Few examples exist of divergence due to breeding allochrony, particularly in vertebrates. We tested whether in Neotropical frogs asynchrony in precipitation patterns promotes intraspecific genetic divergence, speciation, and regional accumulation of diversity. We assessed the relationship between spatial asynchrony in precipitation and genetic divergence controlling for ecological connectivity across 48 Neotropical frog species. In addition, we examined whether regions within which precipitation regimes are more asynchronous across space have higher species richness and have experienced greater speciation rates. Beyond a generalized expected effect of ecological connectivity on intraspecific genetic divergence, we found that asynchrony in precipitation is positively associated with genetic differentiation in 31% of the species tested, resulting in a significantly positive cross-species effect of asynchrony in precipitation on genetic divergence in a meta-analysis. However, the effect of asynchrony in precipitation on population divergence seems not to scale to macroevolutionary patterns because spatial asynchrony in precipitation was not associated with geographical patterns of species richness or speciation rates. Our results indicate that genetic divergence can be promoted by asynchronous breeding lag in the absence of geographic barriers in species where breeding is associated with water availability, but such effects may not be stable enough through time to influence macroevolutionary patterns.