Cross-Temporal Analysis of Genetic Diversity in the Endangered Medium Tree Finch (Camarhynchus pauper) and Closely Related Darwin's Finches

Natural history collections can provide a direct view of past genotypes, which allows greater insight into evolutionary processes that are relevant for conservation and management. However, few studies have used broad surveys of multilocus genotypes from the past to address the wide range of processes that can affect conservation planning of a species today. Therefore, we assessed the history and status of the critically endangered medium tree finch, Camarhynchus pauper, an endemic finch of the Galapagos Islands. Using ancient DNA techniques, we quantified cross-temporal genetic change for 16 microsatellite loci in this species and its relatives. We tested the hypothesis that C. pauper has undergone a recent reduction in population size and loss of genetic diversity, and evaluated the hypothesis that C. pauper is genetically distinct from its two closest relatives, C. parvulus and C. psittacula. We assessed whether decline in C. pauper has led to increased hybridization with other species and evaluated a long-standing hypothesis of its origin from C. psittacula on another island using genetic distances, assignment tests, and migration analyses. Genetic diversity declined significantly in C. pauper over time, and several other tree finch populations showed similar losses of genetic diversity. Genetic distances and assignment tests supported the notion that C. pauper has remained genetically distinct from other species over time, and is actually becoming more distinct, and has experienced substantial genetic change, over the past century. Hybridization between C. pauper and other tree finch species was detected, but has declined to low levels over the last century. However, we could not detect a single origin of this species as hypothesized by Lack (1947). We conclude that C. pauper should be treated as a genetically distinct conservation unit. Management actions to restore habitat quality and mitigate the negative effects of introduced parasites and predators should be continued, to ensure the persistence of this unique and iconic, endangered species.