Genetic analysis of a population crash in brush-tailed rock-wallabies (Petrogale penicillata) from Jenolan Caves, south-eastern Australia

Abstract

Although the theoretical effects of a severe reduction in effective population size (i.e. a bottleneck) are well known, relatively few empirical studies of bottlenecks have been based on extensive temporally spaced samples of a population both before and after a bottleneck. Here we describe the results of one such study, utilising the Jenolan Caves (JC) population of the brush-tailed rock-wallaby (Petrogale penicillata). When first sampled in 1985 (n = 20) the JC population comprised ~90 individuals. Subsequently the population crashed, and by 1992 only seven individuals remained. In 1996 the entire population (n = 10) was again sampled. Genetic diversity in the pre- and post-crash JC population was compared using 11 polymorphic microsatellite loci and PCR–SSCP analysis of the mitochondrial DNA control region. Only a single unique control region haplotype was detected in the pre- and post-crash JC population, although variant haplotypes were present in other P. penicillata populations. Of the 35 microsatellite alleles present in the pre-crash population, nine (26%) were lost during the bottleneck. The average number of rare alleles declined by 72%, allelic diversity was reduced by 30% and average heterozygosity declined by 10%. These observations are consistent with theoretical predictions. Additional analyses revealed that a P.�penicillata female at Wombeyan Caves was the only survivor of a 1990/91 reintroduction attempt using animals from JC. Of the microsatellite alleles detected in this female, 21% (4/19) were no longer present in the post-crash JC population. Furthermore, the genetic profiles of animals from the recently discovered Taralga population indicate that they are not derived from JC stock, but represent a threatened remnant of a hitherto undetected natural P. penicillata population.

Significant patterns of population genetic structure and limited gene flow in a threatened macropodid marsupial despite continuous habitat in southeast Queensland, Australia

“…Brushtailed rock-wallaby colonies within the Condamine Valley region, surrounded by large areas of suitable habitat, including Main Range National Park (18,400 ha), exhibited genetic diversity values similar to other relatively undisturbed wild rockwallaby colonies (Browning et al 2001;Eldridge et al 2004) and generally comparable to other out bred vertebrate populations (Paetkau et al 1995;Frankham et al 2002). However, allelic richness, the most reliable measure of a species' ability to respond to selection (Nei et al 1975;Lowe et al 2004), was significantly reduced and levels of heterozygosity were lower in colonies within the more isolated Perseverance Valley than in colonies within the Condamine Valley region.…”

“…Very small, isolated rock-wallaby colonies, or completely isolated island populations, showed severely reduced genetic diversity compared to larger, healthier colonies, resulting in inbreeding depression within some populations (Eldridge et al 1999;Browning et al 2001;Eldridge et al 2004). Significant levels of genetic differentiation have been documented between rock-wallaby colonies only 3 km apart, indicating very low levels of between-colony gene flow or the rarity of successful dispersal events when colonies are separated by unsuitable or modified habitat (Pope et al 1996;Eldridge et al 2001).…”

Genetic diversity and differentiation of the endangered Japanese endemic tree Magnolia stellata using nuclear and chloroplast microsatellite markers

“…A decline in population size can cause random genetic drift, leading to allele loss (Hartl and Clark 1997;Eldridge et al 2004). Moreover, a reduced population size increases the chance of biparental inbreeding.…”

Estimating population size of endangered brush‐tailed rock‐wallaby (Petrogale penicillata) colonies using faecal DNA

“…However, the distribution of P. penicillata is likely to have always been patchy as a result of their strong association with steep and rocky habitat (Jarman & Bayne 1997). In addition, rock‐wallabies may be predisposed to natural fluctuations with cycles of extinction and recolonization (Delaney 1997; Jarman & Bayne 1997; Eldridge et al . 2004).…”