Restricted gene flow in the endangered Capricorn Yellow Chat Epthianura crocea macgregori: Consequences for conservation management

Abstract

Summary The Yellow Chat Epthianura crocea is comprised of three disjunct subspecies. Subspecies E. c. macgregori (Capricorn Yellow Chat) is listed as Critically Endangered under the EPBC Act and has a distribution that also appears to be disjunct, with a limited geographic area of less than 7,000 ha. Some populations are threatened by rapid industrial development, and it is important for conservation of the subspecies to determine the extent to which the putative populations are connected. We used 14 microsatellite markers to measure genetic diversity and to determine the extent of gene flow between two disjunct populations at the northern and southern extremes of the subspecies' range. No significant differences in genetic diversity (number of alleles and heterozygosity) were observed, but clear population structuring was apparent, with obvious differentiation between the northern and southern populations. The most likely explanation for reduced gene flow between the two populations is either the development of a geographic barrier as a consequence of shrinkage of the marine plains associated with the rise in sea levels following the last glacial maxima, or reduced connectivity across the largely unsuitable pasture and forest habitat that now separates the two populations, exacerbated by declining population size and fewer potential emigrants. Regardless of the mechanism, restricted gene flow between these two populations has important consequences for their ongoing conservation. The relative isolation of the smaller southern groups (the Fitzroy River delta and Curtis Island) from the much larger northern group (both sides of the Broad Sound) makes the southern population more vulnerable to local extinction. Conservation efforts should focus on nature refuge agreements with land owners agreeing to maintain favourable grazing management practices in perpetuity, particularly in the northern area where most chats occur. Supplemental exchanges of individuals from northern and southern populations should be explored as a way of increasing genetic diversity and reducing inbreeding.