Islands in the sea: extreme female natal site fidelity in the Australian sea lion,Neophoca cinerea

Abstract

Pinnipeds (seals, fur seals, sea lions and walrus) form large breeding aggregations with females often remaining faithful to a natal site or area. In these cases, females are philopatric to regional areas on broad geographical scales of hundreds to thousands of kilometres. An investigation of variation in a control region sequence of mtDNA in the Australian sea lion (Neophoca cinerea) has shown a case of extreme female natal site fidelity that has resulted in almost fixed population differentiation across its range (F ST Z0.93). This high level of population subdivision over short geographical distances (approx. 60 km) is unparalleled in any social marine mammal and reflects the unique lifehistory traits of this rare species. The high level of population subdivision and exclusive female natal site fidelity has important ramifications for conservation management, and poses many interesting questions of both academic and applied interest.

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

“…Previously reported mtDNA structure (Campbell et al, 2008;Lowther et al, 2012) was greater than genetic partitioning detected in this study with nuclear markers (consistently higher ST -values than F ST and Jost's D-values reported here). While this might be indicative of male-biased dispersal, cautiousness should be applied in direct comparison of two classes of markers (Prugnolle and de Meeus, 2002).…”

“…However in comparison to other pinniped studies conducted at similar or larger spatial scales the F ST values reported here between these two regions were higher (Hoelzel et al, 2001;Palo et al, 2001;Coltman et al, 2007;Graves et al, 2009;Andersen et al, 2011;Feijoo et al, 2011). Strong genetic partitioning between South Australian and West Australian colonies is also evident with mtDNA data (significant pairwise ST values ranged from 0.83 to 0.94, Campbell et al, 2008). Although, isolation by distance explains the large-scale divergence observed between South Australian and Western Australian colonies, other factors must play a role in driving differentiation at geographical scales that are within the movement capabilities of adult individuals, a conclusion supported by other similar scale studies conducted on this species (Campbell et al, 2008;Lowther et al, 2012).…”

“…Strong genetic partitioning between South Australian and West Australian colonies is also evident with mtDNA data (significant pairwise ST values ranged from 0.83 to 0.94, Campbell et al, 2008). Although, isolation by distance explains the large-scale divergence observed between South Australian and Western Australian colonies, other factors must play a role in driving differentiation at geographical scales that are within the movement capabilities of adult individuals, a conclusion supported by other similar scale studies conducted on this species (Campbell et al, 2008;Lowther et al, 2012). Distances among the six South Australian colonies included in this study varied from only a few kilometers to almost 400 km.…”

“…Two recent mitochondrial DNA studies have shown that females exhibit strong natal site philopatry (Campbell et al, 2008;Lowther et al, 2012). Campbell et al (2008) suggested almost no effective migration of adult females by reporting incredibly high population differentiation across colonies ( ST = 0.93).…”

“…Campbell et al (2008) suggested almost no effective migration of adult females by reporting incredibly high population differentiation across colonies ( ST = 0.93). However, this study concentrated mainly on Western Australian colonies and covered only a small part of the Australian sea lion range in South Australia.…”