Delimiting species without nuclear monophyly in Madagascar's mouse lemurs.

BACKGROUND: Speciation begins when populations become genetically separated through a substantial reduction in gene flow, and it is at this point that a genetically cohesive set of populations attain the sole property of species: the independent evolution of a population-level lineage. The comprehensive delimitation of species within biodiversity hotspots, regardless of their level of divergence, is important for understanding the factors that drive the diversification of biota and for identifying them as targets for conservation. However, delimiting recently diverged species is challenging due to insufficient time for the differential evolution of characters--including morphological differences, reproductive isolation, and gene tree monophyly--that are typically used as evidence for separately evolving lineages. METHODOLOGY: In this study, we assembled multiple lines of evidence from the analysis of mtDNA and nDNA sequence data for the delimitation of a high diversity of cryptically diverged population-level mouse lemur lineages across the island of Madagascar. Our study uses a multi-faceted approach that applies phylogenetic, population genetic, and genealogical analysis for recognizing lineage diversity and presents the most thoroughly sampled species delimitation of mouse lemur ever performed. CONCLUSIONS: The resolution of a large number of geographically defined clades in the mtDNA gene tree provides strong initial evidence for recognizing a high diversity of population-level lineages in mouse lemurs. We find additional support for lineage recognition in the striking concordance between mtDNA clades and patterns of nuclear population structure. Lineages identified using these two sources of evidence also exhibit patterns of population divergence according to genealogical exclusivity estimates. Mouse lemur lineage diversity is reflected in both a geographically fine-scaled pattern of population divergence within established and geographically widespread taxa, as well as newly resolved patterns of micro-endemism revealed through expanded field sampling into previously poorly and well-sampled regions.

Investigating the Intrinsic and Extrinsic Drivers of Primate Heterothermy

Seasonal heterothermy—an orchestrated set of extreme physiological responses—is directly responsible for the over-winter survival of many mammalian groups living in seasonal environments. Historically, it was thought that the use of seasonal heterothermy (i.e. daily torpor and hibernation) was restricted to cold-adapted species; it is now known that such thermoregulatory strategies are used by more species than previously appreciated, including many tropical species. The dwarf and mouse lemurs (family Cheirogaleidae) are among the few primates known to use seasonal heterothermy to avoid Madagascar’s harsh and unpredictable environments. These primates provide an ideal study system for investigating a common mechanism of mammalian seasonal heterothermy. The overarching theme of this dissertation is to understand both the intrinsic and extrinsic drivers of heterothermy in three species of the family Cheirogaleidae. By using transcriptome sequencing to characterize gene expression in both captive and natural settings, we identify unique patterns of differential gene expression that are correlated with extreme changes in physiology in two species of dwarf lemurs: C. medius under captive conditions at the Duke Lemur Center and C. crossleyi studied under field conditions in Madagascar. Genes that are differentially expressed appear to be critical for maintaining the health of these animals when they undergo prolonged periods of metabolic depression concurrent with the hibernation phenotype. Further, a comparative analysis of previously studied mammalian heterotherms identifies shared genetic mechanisms underlying the hibernation phenotype across the phylogeny of mammals. Lastly, conducting a diet manipulation study with a captive colony of mouse lemurs (Microcebus murinus) at the Duke Lemur Center, we investigated the degree to which dietary effects influence torpor patterns. We find that tropical primate heterotherms may be exempt from the traditional paradigms governing cold-adapted heterothermy, having evolved different dietary strategies to tolerate circadian changes in body temperature.