The Limits of Dispersal: Fine Scale Spatial Genetic Structure in Australian Sea Lions

Abstract

Describing patterns of connectivity throughout a species range is critical to conservation management. In common with other mammals, pinnipeds typically display male-biased dispersal. Earlier studies using mitochondrial DNA showed that the endangered Australian sea lion (Neophoca cinerea) exhibits extreme matrilineal structure throughout its range. If male dispersal were similarly restricted, most breeding colonies may not receive sufficient levels of new genetic variation to buffer against risks associated with inbreeding and environmental change. To address these concerns we used 16 microsatellite loci to obtain a more highly resolving measure of genetic structure among colonies and determine whether dispersal is male-biased. We found that both male and female Australian sea lions are highly philopatric with limited dispersal. Within those constraints, when animals disperse between close colonies (<110 km) there is a tendency for males to move further than females. Our findings are intriguing considering the dispersal potential of Australian sea lions and the unique asynchronous breeding opportunities that might be expected to provide an incentive for male reproductive movements between geographically close colonies.

Genetic structure and signatures of selection in grey reef sharks (Carcharhinus amblyrhynchos)

“…Nevertheless, this pattern of sex-biased dispersal and local adaptation is consistent with the hypothesis advanced by Portnoy et al (2015) that dispersing males and philopatric females may favor local adaptation by simultaneously facilitating the dispersal and local sorting of adaptive alleles. As male-biased dispersal is a common strategy in both elasmobranchs (Pardini et al, 2001;Daly-Engel et al, 2012) and marine mammals (Escorza-Treviño and Dizon, 2000;Möller and Beheregaray, 2004;Ahonen et al, 2016), future comparative studies testing this hypothesis could shed new light on the evolution of local adaptation in marine predators.…”

Intrinsic and extrinsic influences on standard metabolic rates of three species of Australian otariid

“…As male Australian sea lions are not able to use seasonal cues in their environment to predict the onset of the breeding cycle, we contend that they maintain a constant sSMR and a static foraging strategy, remaining close to the breeding colonies, in order to be prepared for breeding with females at any time of year ( Lowther et al ., 2013 ; Ahonen et al ., 2016 ). This is likely to be an adaption to a low-productivity environment that is fairly constant ( McKenzie et al ., 2005 ; Villegas-Amtmann et al ., 2009 ).…”

“…This is likely to be an adaption to a low-productivity environment that is fairly constant ( McKenzie et al ., 2005 ; Villegas-Amtmann et al ., 2009 ). The breeding period of Australian sea lions lasts for 120 days, suggesting that males must have an extended period of spermatogenesis ( Ahonen et al ., 2016 ). Males conserve energy by ‘mate guarding’, i.e.…”

“…choosing a single female to mate with from when they haul out until they go into oestrus ( Higgins, 1990 ). After mating, they leave to forage or to mate at another nearby colony, and therefore may not have the option of layering additional blubber before the next period when spermatogenesis and mate guarding occur ( Ahonen et al ., 2016 ).…”

“…Fur seal numbers in Australia are increasing, whereas sea lions are in decline and classified as endangered. Sea lions may compensate for living in a low-productivity environment by using an 18 month breeding cycle and a static foraging strategy and energy usage ( Lowther and Goldsworthy, 2011 ; Ahonen et al ., 2016 ). It is unclear at this stage whether the sea lion strategy means that they are ready to withstand further change, or they may not persist under more extreme pressures.…”