Habitat fragmentation and infectious disease threaten amphibians
globally, but little is known about how these two threats interact. In
this study, we examined the effects of Brazilian Atlantic Forest habitat
fragmentation on frog genetic diversity at an immune locus known to
affect disease susceptibility in amphibians, the MHC IIB locus. We used
a custom high-throughput assay to sequence the MHC IIB locus across six
focal frog species in two regions of the Atlantic Forest. We also used a
molecular assay to quantify infections by the fungal pathogen
Batrachochytrium dendrobatidis (Bd). We found that habitat fragmentation
is associated with genetic erosion at the MHC IIB locus, and that this
erosion is most severe in frog species restricted to intact forests.
Significant Bd infections were recovered only in one Atlantic Forest
region, potentially due to the relatively higher elevation. In this
region, forest specialists showed an increase in both Bd prevalence and
loads in fragmented habitats. We also found that reduced
population-level MHC IIB diversity was associated with increased Bd
infection risk. On the individual-level, MHC IIB heterozygotes (by
allelic genotype as well as supertype) exhibited a reduced risk of Bd
infection. Our results suggest that habitat fragmentation increases
infection susceptibility in amphibians, mediated at least in part
through loss of immunogenetic diversity. Our findings have implications
for the conservation of fragmented populations in the face of emerging
infectious diseases.
Long-Term Habitat Fragmentation Is Associated With Reduced MHC IIB Diversity and Increased Infections in Amphibian Hosts
