Low genetic diversity and lack of population structure in the endangered Galápagos penguin (Spheniscus mendiculus)

Long-term monitoring of the endangered Galápagos penguin (Spheniscus mendiculus) has indicated poor reproductive periods and severe population fluctuations in association with El Niño – Southern Oscillation events. An earlier mark and recapture study indicated that adults exhibit some degree of breeding-site and mate fidelity, and that juveniles potentially move more frequently than adults; however, the extent to which migrants and gene flow occur between islands within the Galápagos archipelago is largely unknown. This study tested the hypothesis that geographic isolation and adult breeding philopatry has led to a degree of genetic differentiation between island subpopulations within the archipelago. We examined the genetic diversity within and among different subpopulations and the extent to which gene flow occurs between island subpopulations. Estimates of allelic richness and gene diversity were not significantly different between subpopulations. Tests to detect genetic heterogeneity failed to reject the H0 of no difference in allele frequencies for chi-square (P = 0.28) and Fisher’s exact test (P = 0.19). All pairwise values of the FST variant θ were not significant, while a power analysis revealed a >99% probability of detecting a biologically true FST of 0.05. Migration estimates in BAYESASS+ suggest symmetrical gene flow throughout the species’ distribution. Our results indicate a low level of genetic diversity throughout the population and a seemingly high level of gene flow between subpopulations. We argue that the Galápagos penguin should be managed as one panmictic population and we discuss the risk of disease threats in the archipelago.