Phylogeography, Dispersal and Movement of Fleay's Barred Frog, Mixophyes fleayi

Abstract

This thesis investigates historical and current dispersal in Mixophyes fleayi, an endangered, wet forest-restricted frog species, found exclusively on the Great Dividing Range of mid-eastern Australia. The phylogeographic structuring and genetic divergence among isolated forest fragments and the presence of multiple populations within continuous forest is used to investigate historical connectivity of populations and current dispersal. Indirect genetic methods as well as field based direct methods are also used to investigate dispersal and movement. These results are used to explore the consequences of dispersal in terms of conservation and management of the species. Few studies have investigated genetic differentiation between upland mesic rainforest areas in southern parts of Queensland, which potentially acted as historical refugia for rainforest dependant species. The broad scale investigation of genetic diversity and structure in M. fleayi, using sequence variation within the mitochondrial ND2 gene, revealed two scales of genetic structure. Two deeply divergent and geographically isolated lineages were found to group populations across the Brisbane River Valley, with isolation of the Conondale Range in the north from all other populations to the south. This can be attributed to regional isolation of rainforest fragments during the Pliocene. Lower levels of genetic variation and sequence divergence were found across forest fragments within the southern distribution of the species (Springbrook, Mount Barney, McPherson, Main, Upper Richmond and Nightcap Ranges), resulting from more recent fragmentation and restricted dispersal related to expansion and contraction of rainforest habitat during the Pleistocene. Genetic structure among populations indicates that comparatively high levels of genetic differentiation exist on very small geographic scales relative to other amphibian species. These data suggest isolation by distance within forest fragments and significant genetic structuring between populations separated by more than two kilometres. Despite the relatively low vagility of individuals, terrestrial dispersal occurs among nearby streams, both within as well as across major catchments. The extent of shared subcatchment boundary between nearby streams provided some indication of the probability and magnitude of gene flow, with sites that share more subcatchment boundaries showing lower levels of genetic differentiation. The indirect genetic evidence of restricted dispersal within the species is supported by mark-recapture, spooling and radio-tracking investigations of movements made by individual M. fleayi in the field. The activity of both sexes is characterized by intervals of small, localized movements. In adult females this behaviour is punctuated by large movements that generally displace individuals away from breeding habitat after relatively short amounts of time spent at the stream. While migration of females between breeding sites was not detected, the movements made by adult females are large enough to enable dispersal between breeding sites, although such dispersal events are probably infrequent. Adult males are extremely philopatric and remain within the breeding area, rarely moving away from the stream, making exchange of adult males between populations extremely unlikely. The management of M. fleayi is particularly important given the potential impact recent declines in both population size and number may have had on genetic variation. Intraspecific genetic divergence, across the Brisbane River Valley, highlights the need to conserve populations in isolated forest fragments both north and south of this putative barrier. Within fragments of continuous forest habitat, evidence of restricted, infrequent terrestrial dispersal of individuals suggests colonization of vacant habitat is unlikely, particularly among streams that do not share subcatchment boundaries. To maintain important, albeit low levels of gene flow and movement between nearby streams, it is critical that habitat connectivity between populations is maintained