Cryptic Patterns of Speciation in Cryptic Primates: Microendemic Mouse Lemurs and the Multispecies Coalescent (original) (raw)
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Hybridization between mouse lemurs in an ecological transition zone in southern Madagascar
Hybrid zones in ecotones can be useful model systems for the study of evolutionary processes that shape the distribution and discreteness of species. Such studies could be important for an improved understanding of the complex biogeography of Madagascar, which is renowned for its outstanding degree of small-scale endemism. Certain forest remnants in central Madagascar indicate that transitional corridors across the island could have connected microendemics in different forest types in the past. Evolutionary processes in such corridors are difficult to study because most of these corridors have disappeared due to deforestation in central Madagascar. We studied a hybrid zone in one of the few remaining ecotonal corridors between dry and humid forests in Madagascar, which connects two species of mouse lemurs, Microcebus griseorufus in dry spiny forest and Microcebus murinus in humid littoral forest. We sampled 162 mouse lemurs at nine sites across this boundary. Morphometric analyses revealed intermediate morphotypes of many individuals in transitional habitat. Bayesian clustering of microsatellite genotypes and assignment tests yielded evidence for a mixed ancestry of mouse lemurs in the ecotone, where we also observed significant linkage disequilibria and heterozygote deficiency. In contrast to these observations, mitochondrial haplotypes displayed a sharply delimited boundary at the eastern edge of spiny forest, which was noncoincident with the signals from microsatellite data. Among several alternative scenarios, we propose asymmetric nuclear introgression due to male-biased dispersal, divergent environmental selection, and an expansion of dry spiny forest in the course of aridification as a probable explanation of our observations.
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The Central Highland Plateau of Madagascar is largely composed of savannah, interspersed with patches of closed-canopy forests. The origins of this landscape are now accepted as long preceding the arrival of humans in Madagascar, but whether savannah vegetation has remained static or expanded over time remains a topic of debate. By analyzing multiple populations of Goodman’s mouse lemur (Microcebus lehilahytsara), a small-bodied nocturnal primate, we reconstruct its phylogeographic and demographic history to serve as a proximal estimate of the time at which the Central Highland and eastern forests became discontinuous. We applied coalescent methods to RADseq data to infer phylogeographic relationships, population structure, and migration corridors among sampling sites. Analyses revealed that forest fragmentation occurred rapidly and affected both the Central Highlands and eastern forests during a period of decreased precipitation near the last glacial maximum. There was clear struct...