Circumpolar Diversity and Geographic Differentiation of mtDNA in the Critically Endangered Antarctic Blue Whale (Balaenoptera musculus intermedia)

To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work.\ud This is the publisher’s final pdf. The published article is copyrighted by the Public Library of Science and can be found at: http://www.plosone.org/home.action.The Antarctic blue whale (Balaenoptera musculus intermedia) was hunted to near extinction between 1904 and 1972, declining from an estimated initial abundance of more than 250,000 to fewer than 400. Here, we describe mtDNA control region diversity and geographic differentiation in the surviving population of the Antarctic blue whale, using 218 biopsy samples collected under the auspices of the International Whaling Commission (IWC) during research cruises from 1990-2009. Microsatellite genotypes and mtDNA sequences identified 166 individuals among the 218 samples and documented movement of a small number of individuals, including a female that traveled at least 6,650 km or 131 degrees longitude over four years. mtDNA sequences from the 166 individuals were aligned with published sequences from 17 additional individuals, resolving 52 unique haplotypes from a consensus length of 410 bp. From this minimum census, a rarefaction analysis predicted that only 72 haplotypes (95% CL, 64, 86) have survived in the contemporary population of Antarctic blue whales. However, haplotype diversity was relatively high (0.968 +/- 0.004), perhaps as a result of the longevity of blue whales and the relatively recent timing of the bottleneck. Despite the potential for circumpolar dispersal, we found significant differentiation in mtDNA diversity (F-ST = 0.032, p<0.005) and microsatellite alleles (F-ST = 0.005, p<0.05) among the six Antarctic Areas historically used by the IWC for management of blue whales

Circumpolar Diversity and Geographic Differentiation of mtDNA in the Critically Endangered Antarctic Blue Whale (Balaenoptera musculus intermedia)

The Antarctic blue whale (Balaenoptera musculus intermedia) was hunted to near extinction between 1904 and 1972, declining from an estimated initial abundance of more than 250,000 to fewer than 400. Here, we describe mtDNA control region diversity and geographic differentiation in the surviving population of the Antarctic blue whale, using 218 biopsy samples collected under the auspices of the International Whaling Commission (IWC) during research cruises from 1990-2009. Microsatellite genotypes and mtDNA sequences identified 166 individuals among the 218 samples and documented movement of a small number of individuals, including a female that traveled at least 6,650 km or 131 degrees longitude over four years. mtDNA sequences from the 166 individuals were aligned with published sequences from 17 additional individuals, resolving 52 unique haplotypes from a consensus length of 410 bp. From this minimum census, a rarefaction analysis predicted that only 72 haplotypes (95% CL, 64, 86) have survived in the contemporary population of Antarctic blue whales. However, haplotype diversity was relatively high (0.968 +/- 0.004), perhaps as a result of the longevity of blue whales and the relatively recent timing of the bottleneck. Despite the potential for circumpolar dispersal, we found significant differentiation in mtDNA diversity (F-ST = 0.032, p<0.005) and microsatellite alleles (F-ST = 0.005, p<0.05) among the six Antarctic Areas historically used by the IWC for management of blue whales

Unexpected patterns of global population structure in melon-headed whales Peponocephala electra

Foraging specialization, environmental barriers, and social structure have driven the development of strong genetic differentiation within many marine species, including most of the large dolphin species commonly referred to as ‘blackfish’ (subfamily Globicephalinae). We used mitochondrial sequence data (mtDNA) and genotypes from 14 nuclear microsatellite loci (nDNA) to examine patterns of genetic population structure in melon-headed whales Peponocephala electra (MHWs), poorly known members of the blackfish family for which genetic structuring is unknown. MHWs are globally distributed in tropical and subtropical waters, and have formed resident populations around oceanic islands. They frequently mass strand, suggesting strong social cohesion within groups. Based on these characteristics, we hypothesized that MHWs would exhibit strong regional genetic differentiation, similar to that observed in other members of the Globicephalinae subfamily. Instead we found only moderate differentiation (median mtDNA ΦST = 0.204, median nDNA FST = 0.012) among populations both within and between ocean basins. Our results suggest that populations of MHWs that are resident to oceanic islands maintain a higher level of genetic connectivity than is seen in most other blackfish. MHWs may be more behaviorally similar to delphinids from the Delphininae subfamily (particularly the spinner dolphin Stenella longirostris), which are known to form coastal and island-associated resident populations that maintain genetic connectivity either through occasional long-distance dispersal or gene flow with larger pelagic populations. Our results suggest that differences in social organization may drive different patterns of population structure in social odontocete

Data from: Targeted multiplex next-generation sequencing: Advances in techniques of mitochondrial and nuclear DNA sequencing for population genomics

Next-generation sequencing (NGS) is emerging as an efficient and cost-effective tool in population genomic analyses of nonmodel organisms, allowing simultaneous resequencing of many regions of multi-genomic DNA from multiplexed samples. Here, we detail our synthesis of protocols for targeted resequencing of mitochondrial and nuclear loci by generating indexed genomic libraries for multiplexing up to 100 individuals in a single sequencing pool, and then enriching the pooled library using custom DNA capture arrays. Our use of DNA sequence from one species to capture and enrich the sequencing libraries of another species (i.e. cross-species DNA capture) indicates that efficient enrichment occurs when sequences are up to about 12% divergent, allowing us to take advantage of genomic information in one species to sequence orthologous regions in related species. In addition to a complete mitochondrial genome on each array, we have included between 43 and 118 nuclear loci for low-coverage sequencing of between 18 kb and 87 kb of DNA sequence per individual for single nucleotide polymorphisms discovery from 50 to 100 individuals in a single sequencing lane. Using this method, we have generated a total of over 500 whole mitochondrial genomes from seven cetacean species and green sea turtles. The greater variation detected in mitogenomes relative to short mtDNA sequences is helping to resolve genetic structure ranging from geographic to species-level differences. These NGS and analysis techniques have allowed for simultaneous population genomic studies of mtDNA and nDNA with greater genomic coverage and phylogeographic resolution than has previously been possible in marine mammals and turtles

Sremba_AntBmu_410_52

Alignment of 52 Antarctic blue whale mtDNA control region haplotypes described from 410 bp in Sremba et al. 2012. File contains key for lab ID codes and GenBank codes for each haplotype not described in LeDuc et al. 2007

Pairwise differentiation (F_ST italicized below and φ_ST above) of mtDNA control region sequences among three populations of blue whales in the Southern Hemisphere: the Antarctic blue whale of the Southern Ocean, as presented in this study, and the pygmy blue whales of the Indian Ocean and South-east Pacific, as reported by LeDuc et al. [15].

<p>Sample sizes are listed for each region. Significance values were based on a permutation test in Arlequin.</p

Number of biopsy samples of Antarctic blue whales collected between 1990 and 2009 (n = 218) on IDCR/SOWER cruises.

<p>Frequency of samples collected in each Area and year are listed as well as within Area (I–VI) and yearly totals. ‘Year’ is referenced to the end-date of the annual surveys, e.g., 1990 refers to the 1989/1990 austral summer. Zeros indicate Areas that were surveyed but in which no biopsy samples were collected that year.</p

Summary of microsatellite loci used to identify likely replicate samples in Antarctic blue whale samples, with test for Hardy Weinberg equilibrium (HWE) and test of differentiation.

<p>Locus name, number of samples genotyped, number of identified alleles (k), probability of identity (p(ID)), number of individuals genotyped, probability of Hardy Weinberg equilibrium (** notes loci out of HWE after a sequential Bonferonni correction), F_ST and significance (p-value) and original reference (Ref.) are listed for each loci. Overall F_ST and p values for 7 and 16 loci are listed. Asterisks (*) denote microsatellite loci included in LeDuc et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032579#pone.0032579-LeDuc1" target="_blank">[15]</a>.</p

Locations of biopsy samples collected from Antarctic blue whales during IDCR/SOWER cruises from 1990 and 2009.

<p>Solid lines demarcate IWC management Areas (I–VI). Dashed line depicts inferred movement of an Antarctic blue whale between Areas over an elapsed time of 4 years based on genotyped recapture locations (Z-51452).</p