Sex-specific shifts in morphology and diet in a frog after 50 years of anthropogenic habitat fragmentation

Aim: Phenotypic shifts are commonly observed when animals face insular
habitat change and may reflect ongoing stresses on individuals. However,
the generality and the driving processes of this ‘island rule’ remain
equivocal, notably in amphibians. Here, we investigate both morphological
and dietary shifts in a frog using a mosaic of human-created islands to
assess the potential operating mechanisms underlying these phenotypic
responses. Location: Thousand Island Lake, China. Taxon: The Chinese
piebald odorous frog, Odorrana schmackeri. Results: We found insular
dwarfism in female but not male frogs. Meanwhile, insular females also had
smaller gape widths after accounting for snout-vent lengths (SVLs) than
mainland females. According to SEMs, resource availability had a direct
positive effect on body size. Finally, diet composition differed between
island and mainland populations, but only in females. Males and females on
islands exhibited greater overlaps in diet. Main conclusions: In contrast
with most studies in amphibians, we found insular dwarfism rather than
gigantism in females. The smaller gape width after accounting for SVL in
insular females suggests potential changes in prey utilization or food
availability on these human-created islands. This notion is further
supported by the differentiation of diet composition between island and
mainland females. The higher diet overlap between sexes implies stronger
intersexual competition for food resources after habitat fragmentation.
Overall, we found shifts in morphology and diet in frogs which may
implicate the influence of habitat fragmentation and underscores the need
to consider intersexual differences when assessing responses of species to
anthropogenic disturbances.