No evidence for loss of genetic variation following sequential translocations in extant populations of a genetically depauperate species

Abstract

Repeated population bottlenecks can lead to loss of genetic variation and normally should be avoided in threatened species to preserve evolutionary potential. We examined the effect of repeated bottlenecks, in the form of sequential translocations, on loss of genetic variation in a threatened passerine, the saddleback (Philesturnus carunculatus carunculatus), a species that has recovered from a remnant population with historically low levels of genetic variation. Although a slight but nonsignificant loss of alleles may have occurred between the first-order translocation and the extirpated source population, first-, second-, and third-order translocated populations had very similar levels of genetic variation to each other. The most obvious difference among the seven island populations appeared to lie in allele frequencies with little or no loss of alleles among extant populations. Although sequential translocations are known to cause loss of variation in genetically diverse species, our study indicates that genetically depauperate species may be less sensitive to loss of genetic variation through founder events presumably because the few remaining alleles are well represented in founding individuals. These results show that ancient bottlenecks may have a long-term effect on genetic variation, to the extent that contemporary population bottlenecks may leave no appreciable genetic signature. Our results suggest that subjecting genetically depauperate endangered species to sequential translocations could be used to rapidly establish new populations without further eroding genetic variation.

Colonization of Brazil by the cattle egret (Bubulcus ibis) revealed by mitochondrial DNA

“…The present results can be explained by multiple introductions or compared to reported cases in which no evident loss of variability was detected. For example, the saddleback (Philesturnus carunculatus carunculatus) has not exhibited a significant loss of variability after repeated population bottlenecks (Taylor and Jamieson 2008). According to Kekkonen et al (2011), the house sparrow (Passer domesticus) has suffered a severe population decline in Finland over the last four decades, with no significant loss of genetic diversity.…”

Differential patterns of diversity at microsatellite, MHC, and TLR loci in bottlenecked South Island saddleback populations

“…Previous studies indicate that South Island saddleback diversity at microsatellite loci was historically degraded and that no further losses of genetic diversity occurred through sequential contemporary translocations (Taylor & Jamieson 2008). Despite contemporary populations of South Island saddlebacks also having reduced MHC diversity compared to historical populations (Sutton et al 2015), it is currently unclear whether diversity at functional genes has been sufficiently depleted to make the genetic effects of contemporary bottlenecks negligible.…”

“…at variable microsatellite loci differed considerably on Big Island compared to Kaimohu Island, likely due to anthropogenic sampling effects (note that one portion of known remaining South Island saddlebacks was transferred to Big Island and the other portion was translocated to Kaimohu Island; Taylor & Jamieson 2008). In contrast, microsatellite allelic frequencies on Motuara Island in 2002 mirrored that of Big Island, likely because only one individual was transferred from Kaimohu to North Island (the source population for Motuara Island) while 18 were transferred from Big to North Island (Fig.…”

“…It has been shown that factors such as location of the population (insular or mainlandoriginating), bottleneck severity (duration and intensity) and prior history of bottlenecks, are all strong determinants of remaining genetic diversity in threatened species (e.g. Taylor & Jamieson 2008;Sutton et al 2015). However, it is currently unknown whether population bottleneck circumstance (e.g.…”

“…Although translocations are a classic solution given the urgency of action required when an organism is declining in number (Griffith et al 1989), there may be detrimental effects of inducing contemporary bottlenecks in already vulnerable species. It is commonly reported that translocation events contribute to the degradation of remaining genetic diversity in historically bottlenecked populations (Stockwell et al 1996;Miller & Lambert 2004;Lambert et al 2005;Olson et al 2013), although this depends on the extent to which genetic diversity has already been depleted (Taylor & Jamieson 2008) (i.e. the variation at some genetic markers may be sufficiently depleted that there is none left to lose).…”