Project Title: Microsatellites, mating systems and males influence on management units in the Australian sea lion
Chief Investigators: Associate Professor Robert Harcourt & Dr Adam Stow
The Australian sea lion (ASL) is Australia’s only endemic and rarest seal species and was listed as Threatened under the EPBC Act in February 2005. A risk-assessment by Goldsworthy & Page (2007) determined that within South Australia subpopulations are at risk from even low-levels of fisheries bycatch and a similar situation exists in Western Australia (Campbell 2003). They have an unusual life history, unique among pinnipeds with a non-annual breeding cycle that is also temporally asynchronous across its range and within any one colony the breeding period is prolonged (Gales et al. 1994, Gales & Costa 1997).The evolutionary determinants of this atypical life-history are unknown but the implications are profound. Recent population genetic studies have shown that the Australian sea lion has a level of female population structure unparalleled in marine vertebrates with little or no interchange of females among breeding colonies, even those separated by short (20 km) distances (Campbell et al. 2007).
The important management implication of extreme philopatry is that each colony could represent a closed population. But male mediated gene flow between colonies remains likely, and maybe critical to the identification of management units. Preliminary studies by Campbell (2003) suggested male dispersal of the order of 250-300 km, but were based on limited samples and few microsatellite loci. Moreover, the non-annual, asynchronous breeding system provides for the possibility that, in contrast to all other pinnipeds, males may not be restricted to breeding at single colony during any one breeding cycle.
High quality DNA was extracted from 50 male skin samples collected from five different islands and used to develop a microsatellite library. Microsatellite development was enhanced by the use of pyrosequencing technologies with a 454 sequencer. From these sequence data 200+ potential microsatellite markers were isolated and characterised. From this pool of candidate markers 20 loci were selected on the basis of microsatellite length and the characteristics of the nucleotide motif. Primers were developed and conditions to optimise Polymerase Chain Reaction identified. A library of 17 microsatellite markers has been developed (Table 1) and the library will be published shortly. A further eight loci are in the process of being optimised. This should provide us with a library of 20-25 markers.
Analysis of male mtDNA haplotypes shows unequivocally that they are shared over a significantly larger range than are females, with males on Olive Island showing overlap with those breeding in Lilliput and Blefuscu in the Nuyts archipelago, despite being 6 months out of synchrony with that island group. This has implications for paternity across regions with the sharing of haplotypes opening the possibility of males being successful sires at multiple colonies across different temporal scales. At the same time a degree of differentiation from the Liguanea Island males suggests that regional differentiation is likely even if male dispersal exceeds female dispersal by some orders of magnitude.
