Genetic Monogamy and Low Reproductive Skew in a Disease-Impacted, Communal-Breeding Frog

Genetic mating systems shape reproductive skew, mate choice, and effective population size, yet remain poorly understood in many communally breeding amphibians. We used genetic parentage analysis to examine mating structure in the alpine tree frog (Litoria verreauxii alpina), a Batrachochytrium dendrobatidis (Bd) impacted amphibian that breeds in communal aggregations. Over a 6-week breeding season, we recorded 477 capture events involving 197 unique adults and observed 55 egg masses. Using DArTseq-derived SNP markers and COLONY, we reconstructed mating pairs, assessed male breeding success, and estimated effective population size (N _e ). Of the 45 egg masses with at least one successfully genotyped embryo, 97.7% had a definitive sire assigned, and every egg mass with more than one genotyped embryo was assigned to a single sire. Only one sampled male and one inferred female showed evidence of multiple mates, indicating a predominantly genetically monogamous mating structure despite communal breeding. Male reproductive success was not predicted by body size, recapture frequency, or breeding-season timing. Effective population size was low, suggesting ongoing genetic vulnerability, but relatively even reproductive contribution among breeders may help limit reproductive skew. These findings contrast with expectations for communal-breeding frogs, where high breeding-site encounter rates and male-biased attendance can create opportunities for multiple mating and unequal reproductive success. More broadly, these results show how genetic parentage data can reveal unexpected mating-system structure in disease-impacted amphibian populations.