Anthonysamy, W. J. B. | Search bioRxiv

bioRxiv2020

Metapopulation Connectivity in Voles (Microtus sp.) as a Gauge for Tallgrass Prairie Restoration in Midwestern North America

Applying quantifiable metrics to validate the success of restoration efforts is crucial for ongoing management programs in anthropogenically fragmented habitats. Estimates of dispersal can provide such baseline data because they measure not only the extent to which restored patches are colonized and interconnected, but also their metapopulation source/sink dynamics. In this context, we estimated dispersal and population connectivity among prairie (Microtus ochrogaster; N=231) and meadow vole (M. pennsylvanicus; N=83), sampled from eight restored plots at five tallgrass prairie sites embedded within the agricultural matrix of midwestern North America. Our expectation was that extensive distances separating these restored habitats (i.e., 48-246 km) would spatially isolate vole metapopulations, resulting in significant genetic differentiation. We first used molecular taxonomy to validate the field-identifications of all sampled individuals, then used pairwise FST derived from 15 microsatellite DNA loci to estimate genetic connectivity among the species-delimited study populations. Metapopulation stability was gauged by assessing migration rates and deriving effective population sizes (Ne). We also calculated relatedness values (r) as a potential surrogate for contact in prairie vole, a primary vector for Lyme disease. Molecular species-assignments contravened field-identifications in 25% of samples (11 prairie/67 meadow) and identified two instances of species-hybridization (0.6%). Local effects (i.e., population crash/drought) were manifested at two sites, as documented by significant temporal declines in Ne and r. Overall, high migration rates and non-significant (10/15) pairwise FST values underscored elevated metapopulation connectivity. A single site that recorded five significant FST values also displayed significant r-values indicating the inadvertent sampling of closely related individuals. This highlights the close social groupings among cooperatively-breeding prairie vole that can exacerbate Lyme disease transmission. Thus, while elevated population connectivity aligns with prairie restoration goals, it also reinforces a need in adaptive management to evaluate environmental matrices for their permeability to vector-borne diseases.

ecology↗

bioRxiv2020

Taxonomic hypotheses and the biogeography of speciation in the Tiger Whiptail complex (Aspidoscelis tigris: Squamata, Teiidae)

(225)Biodiversity in southwestern North America has a complex biogeographic history involving tectonism interspersed with climatic fluctuations. This yields a contemporary pattern replete with historic idiosyncrasies often difficult to interpret when viewed from through the lens of modern ecology. The Aspidoscelis tigris (Tiger Whiptail) complex (Squamata: Teiidae) is one such group in which potential taxonomic boundaries have been confounded by a series of complex biogeographic processes that have defined the evolution of the clade. To clarify this situation, we first generated multiple taxonomic hypotheses, which were subsequently tested using mitochondrial DNA sequences (ATPase 8 and 6) evaluated across 239 individuals representing five continental members of this complex. To do so, we evaluated the manner by which our models parsed phylogenetic and biogeographic patterns. We found considerable variation among species hypotheses, which we suggest in part reflects inflated levels of inter-population genetic divergence caused by historical demographic expansion and contraction cycles. Inter-specific boundaries with A. marmoratus juxtaposed topographically with the Cochise Filter Barrier that separates Sonoran and Chihuahuan deserts (interpreted herein as case of soft allopatry). Patterns of genetic divergence were consistent across the Cochise Filter Barrier, regardless of sample proximity. Surprisingly, this also held true for intraspecific comparisons that spanned the Colorado River. These in turn suggest geomorphic processes as a driver of speciation in the tigris complex, with intraspecific units governed locally by demographic processes. HIGHLIGHTSO_LIPhylogeographies of vertebrates within the southwestern deserts of North America have been shaped by climatic fluctuations imbedded within broad geomorphic processes. C_LIO_LIThe resulting synergism drives evolutionary processes, such as an expansion of within-species genetic divergence over time. Taxonomic inflation often results (i.e., an increase in recognized taxa due to arbitrary delineations), such as when morphological divergences fail to juxtapose with biogeographic hypotheses. C_LIO_LIHowever, isolated groups can be discriminated within-species by mapping genetic variability onto geographic distances. This approach can often diagnose hard barriers to dispersal, or alternatively, strong selection acting against hybridization. On the other hand, elevated genetic divergences among groups less-isolated would underscore isolation-by-distance (i.e., an increase in genetic differentiation concomitant with geographic distance). C_LIO_LIThe biogeographic patterns we identified in Tiger Whiptail are largely synonymous with those found in other regional species, particularly given the geomorphic separation of Mohave and Sonoran deserts by the Colorado River, and Sonoran/ Chihuahuan deserts by the Cochise Filter Barrier. C_LIO_LIOur results for the Tiger Whiptail complex broaden and extend the context within which polytypic species are conserved and managed, particularly those that reflect an incongruence among molecular and morphological standards. C_LI

evolutionary biology↗