Spatial and temporal patterns of genetic diversity in an endangered Hawaiian honeycreeper, the Hawaii Akepa (Loxops coccineus coccineus)

As a result of disease, habitat destruction, and other anthropogenic factors, the Hawaii Akepa (Loxops coccineus coccineus) currently occupies <10% of its original range and exists in five disjunct populations, raising concerns about what effect such reduction and fragmentation has had on the connectivity and diversity of Akepa populations. In this study, we used both historical and contemporary samples to assess genetic diversity and structure in this endangered Hawaiian honeycreeper. We generated sequence data from two mtDNA regions (ND2, control region) and two nuclear introns for contemporary samples representing three of the five current populations. We also generated control region sequence data for museum specimens collected over 100 years ago from throughout the historical range of the bird. Results indicate that despite recent declines and fragmentation, genetic diversity has not been lost. We detected a modest level of genetic differentiation, which followed a combined pattern of isolation-by-barriers and isolation-by-distance, across the historical range of Akepa. The similarly low level of differentiation observed between the contemporary populations indicates that not much divergence, if any, has occurred post-fragmentation. Rather, the present structure seen likely reflects the historical pattern of distribution. Ironically, this declining species exhibits the genetic signal of an expanding population, demonstrating that earlier demographic events are outweighing the effects of recent changes in population size, and genetic estimates of Ne, though crude, suggest Hawaii Akepa were at least an order of magnitude more abundant prior to the decline.