European colonization, not polynesian arrival, impacted population size and genetic diversity in the critically endangered New Zealand Kakapo

Abstract

Island endemic species are often vulnerable to decline and extinction following human settlement, and the genetic study of historical museum specimens can be useful in understanding these processes. The kakapo (Strigops habroptilus) is a critically endangered New Zealand parrot that was formerly widespread and abundant. It is well established that both Polynesian and European colonization of New Zealand impacted the native avifauna, but the timeframe and severity of impacts have differed depending on species. Here, we investigated the relative importance of the 2 waves of human settlement on kakapo decline, using microsatellites and mitochondrial DNA (mtDNA) to characterize recent kakapo genetic and demographic history. We analyzed samples from 49 contemporary individuals and 54 museum specimens dating from 1884 to 1985. Genetic diversity decreased significantly between historical and contemporary kakapo, with a decline in mean number of microsatellite alleles from 6.15 to 3.08 and in number of mtDNA haplotypes from 17 to 3. Modeling of demographic history indicated a recent population bottleneck linked to the period of European colonization (approximately 5 generations ago) but did not support a major decline linked to Polynesian settlement. Effective population size estimates were also larger for historical than contemporary kakapo. Our findings inform contemporary kakapo management by indicating the timeframe and possible cause of the bottleneck, which has implications for the management of extant genetic diversity. We demonstrate the broader utility of a historical perspective in understanding causes of decline and managing extinction risk in contemporary endangered species.