Habitat fragmentation differentially shapes neutral and immune gene variation in a tropical bird species.

Habitat fragmentation is a major cause of biodiversity loss, responsible for an alteration of intraspecific patterns of neutral genetic diversity and structure. Although neutral genetic variation can be informative for demographic inferences, it may be a poor predictor of adaptive genetic diversity and thus of the consequences of habitat fragmentation on selective evolutionary processes. In this context, we contrasted patterns of genetic diversity and structure of neutral loci (microsatellites) and immune genes (i.e., toll-like receptors) in an understorey bird species, the wedge-billed woodcreeper Glyphorynchus spirurus. The objectives were (1) to investigate forest fragmentation effects on population genetic diversity, (2) to disentangle the relative role of demography (genetic drift and migration) and selection, and (3) to assess whether immunogenetic patterns could be associated with variation of ectoparasite (i.e., ticks) pressures. Our results revealed an erosion of neutral genetic diversity and a substantial genetic differentiation among fragmented populations, resulting from a decrease in landscape connectivity and leading to the divergence of distinct genetic pools at a small spatial scale. Patterns of genetic diversity observed for TLR4 and TLR5 were concordant with neutral genetic patterns, whereas those observed for TLR3 and TLR21 were discordant. This result underlines that the dominant evolutionary force shaping immunogenetic diversity (genetic drift vs. selection) may be different depending on loci considered. Finally, tick prevalence was higher in fragmented environments. We discussed the hypothesis that pathogen selective pressures may contribute to maintain adaptive genetic diversity despite the negative demographic effect of habitat fragmentation on neutral genetic diversity.

Contrasted patterns of genetic differentiation across eight bird species in the Lesser Antilles.

Archipelagoes are considered as "natural laboratories" for studying processes that shape the distribution of diversity. The Lesser Antilles provide a favorable geographical context for divergence to occur. However, although morphological subspecies have been described across this archipelago in numerous avian species, the potential for the Lesser Antilles in driving intra-specific genetic divergence in highly mobile organisms such as birds remains understudied. Here, we assessed level of intra-specific genetic diversity and differentiation between three islands of the Lesser Antilles (Guadeloupe, Dominica and Martinique) using a multi-species approach on eight bird species. For each species, we built a set of microsatellite markers from cross-species amplifications. Significant patterns of inter-island and/or within-island genetic differentiation were detected in all species. However, levels of intra-specific genetic differentiation among the eight bird species were not always consistent with the boundaries of subspecies previously described in the sampled islands. These results suggest different histories of colonization/expansion and/or different species-specific ecological traits affecting gene flow, advocating for multi-species studies of historical and contemporary factors shaping the distribution of diversity on islands.