Sex‐Specific Consequences of Recent Inbreeding in an Ancestrally Inbred Population of New Zealand Takahe

Abstract

Abstract: Although the negative effects of close inbreeding in captive populations are well known, inbreeding in small, free‐ranging populations is less well understood. During the mid‐1980s, small numbers of the flightless Takahe ( Porphyrio hochstetteri ) were successfully translocated from the last remaining population in mountainous Fiordland to four island refuges. Previous research has shown that introduced island Takahe and their descendents lay significantly more infertile eggs and raise fewer juveniles per egg than Takahe in their native habitat in Fiordland. Here we first show that the remnant population of Takahe in Fiordland was likely to have been severely inbred. From this we hypothesize that further, recent inbreeding ( based on four generations of pedigree data ) by Takahe on islands should have negligible fitness consequences. This hypothesis is only partially supported. Mean hatching and fledging success has remained consistently low ( <40% and 77%, respectively ) and was not correlated with the rapid increase in the average inbreeding coefficient of island Takahe since 1991. Neither the inbreeding coefficient of a pair's offspring nor the inbreeding status of the breeding male had a significant effect on hatching or fledging success. Similarly, the inbreeding status of the breeding female had no significant effect on hatching success. However, the inbreeding status of the female did negatively affect fledging success. Why poor reproductive success was further exacerbated by inbreeding in females but not in males or pairs is unknown, although a similar pattern has been reported in an island population of Song Sparrows ( Melospiza melodia ). We speculate that the generally lower reproductive success that most island Takahe exhibit is a result of environment‐dependent inbreeding depression. We conclude from our pedigree analysis that island Takahe are undergoing further inbreeding depression, but the reduction in fitness appears to be expressed in inbred females only.