Restricted gene flow in the endangered Capricorn Yellow ChatEpthianura crocea macgregori: consequences for conservation management

Abstract

SummaryThe 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.

Towards inclusion of genetic diversity measures into IUCN assessments: a case study on birds

“…Variability estimated using molecular markers not only helps to distinguish genetically distinct populations that may be vulnerable to environmental changes (e.g., Lee and Mitchell-Olds, 2011;Hansen et al, 2012;Limborg et al, 2012;Munday et al, 2013;Razgour et al, 2018) but also infers phylogenetic relationships between individuals both within and between species, reconstructing genealogies and gathering information on inbreeding rates (e.g., Zollinger et al, 2012;McCormack et al, 2013;Lyu et al, 2018). The current use of microsatellite markers in biodiversity conservation studies is particularly useful to address issues related to the conservation genetics of various bird species (e.g., Moura et al, 2017;Houston et al, 2018;Moussy et al, 2018;Stojanovic et al, 2018). Conservation Genetics has been defined as the discipline that applies genetic concepts and tools, including molecular markers, to small populations to reduce their risk of extinction (Frankham et al, 2002;Allendorf et al, 2012).…”

Mitochondrial phylogeny within the Yellow Chat (Epthianura crocea) does not support subspecific designation of endangered Alligator Rivers population

“…Only small‐scale movements of approximately 10 km have been documented in E. c. macgregori (Houston, Elder, et al, 2018 ). Further, in a study of the genetic structuring of E. c. macgregori using microsatellites, there was no evidence of recent dispersal between two subpopulations of E. c. macgregori that were 140 km apart (Houston, Aspden, et al, 2018 ).…”

“…Keast ( 1958 ) stated that “taxonomic findings conclusively support distributional evidence that birds breed in the general area of their birth and that there is no interchange of individuals between the four isolated populations” but Higgins et al ( 2001 ) described it as nomadic and dispersive, with the ability to fly long distances to colonize newly suitable habitat. A study of E. c. macgregori dispersal found a pattern of small‐scale (<10 km) seasonal movement between breeding habitat and interconnected dry season habitat (Houston, Aspden, et al, 2018 ). It is therefore possible that E. c. crocea and E. c. tunneyi are encountering one another, and possibly inter‐breeding.…”