Author: Julie Schofield
Schofield, Julie, 2015 Implications of movement and population structure in the endangered pygmy bluetongue lizard (Tiliqua adelaidensis): Lessons for conservation, Flinders University, School of Biological Sciences
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As habitats becomes more fragmented, changes in normal population processes can become disrupted leading to populations in fragmented habitats having reduced effective population size, with loss of genetic diversity resulting from increased genetic drift and inbreeding. Dispersal is an important function in any population to counter those processes, contribute to gene flow among populations, and allow the spread of a species into available population sites. Dispersal is one of the key factors in preventing inbreeding within populations and can contribute to maintaining stable social structures and viable populations.
The endangered pygmy bluetongue lizard, Tiliqua adelaidensis is known only from small populations in 31 isolated fragments of once more continuous native grassland habitat in the mid north of South Australia. It is a largely solitary scincid lizard and spends the majority of its time in narrow, vertical, single entrance burrows constructed by lycosid and mygalomorph spiders, waiting to ambush passing invertebrate prey. Individual pygmy bluetongue lizards normally remain closely associated with a single burrow.
I used pitfall trapping to monitor out-of-burrow movements by pygmy bluetongue lizards, with a total of 49,440 trap-nights from three sites over 2 years. I found that male pygmy bluetongue lizards were more likely to move than were females, with neonates the second-most captured group. Most movement by males was in the breeding season, representing partner searching moves, rather than dispersal movements away from the local area. This suggests that even when they leave their burrows, most lizards do not move far, and probably remain in or return to the local area of the burrow they originally moved from.
I used genotypes at polymorphic microsatellite DNA loci to investigate the mating system and social structure within populations, and found that 75% of litters had multiple paternity. There was no evidence of active kin avoidance, with mating partners apparently chosen randomly with respect to the level of relatedness among neighbouring lizards. However, mating partners were located closer to each other than expected by chance, and most commonly within 30 m of each other. Drivers for the polygamous mating system may be the single occupancy burrow and the central place territorial defence of those burrows.
Adult lizards within a demographic population belonged to several divergent genetic clusters at both the whole population scale (11-13ha) and within 1.2 ha sampling sites within demographic populations. Significant spatial autocorrelation suggested low natal dispersal distances for both sexes, and that resident adults had settled close to related individuals. The different genetic clusters were not spatially sorted at the local scale, implying different genetic lineages were maintained in the demographic populations possibly due to strong isolation by distance. At this stage, despite the habitat fragmentation and lack of gene flow among adjacent populations, genetic diversity within isolated populations is probably maintained by this genetic structure coupled with localised promiscuous mating.
I investigated phylogenetic relationships among 10 demographic populations across the range of the species using both mitochondrial and microsatellite DNA. These data confirmed that individual populations, separated by inhospitable farmlands, are genetically isolated. There were at least two geographically separated clusters of populations, emphasising the importance of conserving populations in multiple areas to maintain as many genotypes as possible.
This thesis provides important information to guide management strategies for maintaining genetic diversity within species and particularly the pygmy bluetongue lizard. Given the mounting pressures of climate change and of interrupted landscapes limiting dispersal, the findings of this thesis should be used to promote in situ adaptive management processes including informed translocations for maintaining viable populations of this endangered species.
Keywords: Pygmy Bluetongue Lizard, Dispersal, genetics, movement. threatened speceis
Subject: Biological Sciences thesis
Thesis type: Doctor of Philosophy
Completed: 2015
School: School of Biological Sciences
Supervisor: Michael Bull