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, 5 (7), e1000554

Rapid Response of a Marine Mammal Species to Holocene Climate and Habitat Change


Rapid Response of a Marine Mammal Species to Holocene Climate and Habitat Change

Mark de Bruyn et al. PLoS Genet.


Environmental change drives demographic and evolutionary processes that determine diversity within and among species. Tracking these processes during periods of change reveals mechanisms for the establishment of populations and provides predictive data on response to potential future impacts, including those caused by anthropogenic climate change. Here we show how a highly mobile marine species responded to the gain and loss of new breeding habitat. Southern elephant seal, Mirounga leonina, remains were found along the Victoria Land Coast (VLC) in the Ross Sea, Antarctica, 2,500 km from the nearest extant breeding site on Macquarie Island (MQ). This habitat was released after retreat of the grounded ice sheet in the Ross Sea Embayment 7,500-8,000 cal YBP, and is within the range of modern foraging excursions from the MQ colony. Using ancient mtDNA and coalescent models, we tracked the population dynamics of the now extinct VLC colony and the connectivity between this and extant breeding sites. We found a clear expansion signal in the VLC population approximately 8,000 YBP, followed by directional migration away from VLC and the loss of diversity at approximately 1,000 YBP, when sea ice is thought to have expanded. Our data suggest that VLC seals came initially from MQ and that some returned there once the VLC habitat was lost, approximately 7,000 years later. We track the founder-extinction dynamics of a population from inception to extinction in the context of Holocene climate change and present evidence that an unexpectedly diverse, differentiated breeding population was founded from a distant source population soon after habitat became available.

Conflict of interest statement

The authors have declared that no competing interests exist.


Figure 1
Figure 1. Map of study region showing major and minor southern elephant seal (Mirounga leonina) breeding colonies.
With the exception of VLC (shown in gray), size of the circles indicates relative colony size.
Figure 2
Figure 2. Networks of phylogenetic relationships among ancient and extant mitochondrial DNA haplotypes.
(A) Median-joining network where the size of the circle indicates relative frequency of the haplotype. Yellow – Victoria Land Coast (VLC); dark blue – Macquarie Island (MQ); brown – Falklands; orange – Elephant Island; green – Marion Island; light blue – Peninsula Valdés; red – South Georgia; black – Heard Island. South Georgia and Heard Island relationships are based on 240 bp of mtDNA (see Materials and Methods). Networks were post-processed to reduce complexity using the Maximum Parsimony option in Network 4.5 . (B) Network showing torso only, illustrating major connections among basal haplotypes. Image has been rotated to fit the page. Samples coloured as in part ‘A’. Likely VLC founder haplotypes, based on rho (ρ) estimates, indicated by ‘*’. (C) MQ and VLC clade only, illustrating relationship between MQ haplotypes and the age of the VLC samples. Blue: MQ; light gray: VLC<1500 YBP; dark gray: VLC 1501–3000; black: VLC 3000+. Likely VLC founder haplotypes, based on rho (ρ) estimates, indicated by ‘*’. Nearest VLC neighbours of the proposed VLC-founder haplotype (sampled from MQ) indicated by ‘#’.
Figure 3
Figure 3. Mismatch distributions for mitochondrial DNA haplotypes sampled from the VLC and MQ populations.
Figure 4
Figure 4. Bayesian skyline plots of effective population size change through time.
The black line indicates the median posterior effective population size through time. The gray lines illustrate the 95% HPDI, taking into account coalescent model and phylogenetic uncertainty, for: (A) VLC alone; (B) MQ alone; (C) VLC and Marion Island combined; (D) VLC and MQ combined.

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