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

Abstract

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 ∼8,000 YBP, followed by directional migration away from VLC and the loss of diversity at ∼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, ∼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.

Post-glacial habitat release and incipient speciation in the genus Delphinus

“…Mutation rates vary among species (see, for example, Lambert et al, 2002;de Bruyn et al, 2009;Phillips et al, 2009), and there is no precise estimate for this species. However, we used a rate that falls within the intervals of those derived from time series data and a coalescent approach for other vertebrate species (see Phillips et al, 2009).…”

“…However, we used a rate that falls within the intervals of those derived from time series data and a coalescent approach for other vertebrate species (see Phillips et al, 2009). For example, in the Adélie penguin, Pysocelis adeliae, 9.6 × 10 − 7 s s y − 1 (Lambert et al, 2002), southern elephant seal, Mirounga leonina, 9.8 × 10 − 7 s s y − 1 (de Bruyn et al, 2009) and Steller sea lion, Eumetopias jubatus, 2.7 × 10 − 7 s s y − 1 (Phillips et al, 2009). These estimates are based on HVR1 and our control region sequence is somewhat longer, but we get similar estimates when just the HVR1 region is used (data not shown).…”

Extinction and recolonization of coastal megafauna following human arrival in New Zealand

“…Numerous drivers have been proposed to explain megafaunal extinctions in different parts of the world [8]. For instance, Holocene shifts inferred for Antarctic vertebrate populations have been linked to climatic fluctuations [39]. In mainland New Zealand, however, the distribution of Phocarctos at the time of human arrival spanned a latitudinal range of some 138 (1500 km; electronic supplementary material, figure S1) [19], encompassing a broad thermal envelope, such that minor climatic fluctuations [49] occurring around the time of human arrival are unlikely to explain the near-simultaneous figure S4) imply that Phocarctos persisted in mainland New Zealand throughout the Late Glacial (ca 14-11.6 kya) and Holocene (11.6 kya-present).…”

“…Local DR values [37] were applied to the calibrations of radiocarbon dates (electronic supplementary material, table S3). The large geographical ranges of many pinnipeds in their adult stage can make it difficult to select appropriate DR values for such taxa [38,39]. To account for this issue, we also applied minimum and maximum New Zealand DR values [37] to the adult bones radiocarbon-dated.…”

Looking backwards to look forwards: conservation genetics in a changing world

“…In an application of these methods to track more recent trends in population size, de Bruyn et al (2009) report on a population of elephant seals at a breeding colony in the Antarctic. The sequencing of ancient mtDNA from more than 200 seals permitted the tracking of this population from its founding about 8000 years ago through to its extinction, 7000 years later (Fig.…”