Genetic diversity, population structure, and demographic history of the Hawaiʻi akepa

Abstract

As a result of disease, habitat destruction, and other anthropogenic factors, the Hawaii Akepa (Loxops coccineus coccineus) currently occupies less than 10% of its original range and exists in five widely separated populations, raising concerns about what effect such reduction and fragmentation has had on the connectivity and diversity of Akepa populations. In this study, both historical and contemporary samples were utilized to assess genetic diversity and structure in this endangered Hawaiian honeycreeper. Sequence data from ND2, control region, and two nuclear introns were obtained from three of the five current populations, and control region sequence data were obtained from museum specimens collected over 100 years ago throughout the historical range of the bird. Results indicate that despite recent declines and fragmentation, genetic diversity has not yet been lost. No clear phylogeographic breaks were observed across the historical range of Akepa, but rather genetic differentiation was modest and seemed to follow a pattern of isolation-by-distance. Low levels of differentiation between the contemporary populations observed with mtDNA but not nuclear sequences indicate that not much divergence, if any. has occurred post-fragmentation. Rather, the present structure seen likely reflects historical isolation-by-distance. 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 N., though crude, suggest Hawaii Akepa were at least an order of magnitude more abundant prior to the decline.