Population structure of long-finned pilot whales in the North Atlantic: a correlation with sea surface temperature?

POPs in long-finned pilot whales mass stranded in Iceland as a proxy for their physiological condition

Long-finned pilot whales (Globicephala melas) are the most frequently stranded cetaceans in the world; however, the predominant drivers of these events are poorly understood. In this study the levels of persistent organic pollutants from pilot whales stranded in North-east Iceland were quantified and compared to historical data and physical parameters to investigate whether contaminant load may have influenced the physiological state of stranded individuals, how these loads fluctuate with sex and age group, and if this is consistent with the literature. Historical comparison was also carried out to discern how pollutant contamination has changed throughout the past few decades. DDE, transnonachlor and PCB-153 were the top three pollutants respectively. The accumulation of POPs was greater on average in immature individuals than adults, whilst among adults, males had higher concentration than females. Moreover, despite an indication of decreasing POP loads throughout the years, knowledge of harmful thresholds remains exceedingly limited.

Lack of intergenerational reproductive conflict, rather than lack of inclusive fitness benefits, explains absence of post-reproductive lifespan in long-finned pilot whales

Life-history theory suggests that individuals should reproduce until death, yet females of a small number of mammals live for a significant period after ceasing reproduction, a phenomenon known as post-reproductive lifespan. It is thought that the evolution of this trait is facilitated by increasing local relatedness throughout a female's lifetime. This allows older females to gain inclusive fitness through helping their offspring (known as a mother effect) and/or grandoffspring (known as a grandmother effect), rather than gaining direct fitness through reproducing. However, older females may only benefit from stopping reproducing when their direct offspring compete with those of their daughters. Here, we investigate whether a lack of post-reproductive lifespan in long-finned pilot whales (Globicephala melas) results from minimal benefits incurred from the presence of older females, or from a lack of costs resulting from mother-daughter co-reproduction. Using microsatellite data, we conducted parentage analysis on individuals from 25 pods and find that younger females were more likely to have offspring if their mother was present in their pod, indicating that mothers may assist inexperienced daughters to reproduce. However, we found no evidence of reproductive conflict between co-reproducing mothers and daughters, indicating that females may be able to reproduce into old age while simultaneously aiding their daughters in reproduction. This highlights the importance of reproductive conflict in the evolution of a post-reproductive lifespan and demonstrates that mother and grandmother effects alone do not result in the evolution of a post-reproductive lifespan.

A novel expert-driven methodology to develop thermal response curves and project habitat thermal suitability for cetaceans under a changing climate

Over the last decades, global warming has contributed to changes in marine species composition, abundance and distribution, in response to changes in oceanographic conditions such as temperature, acidification, and deoxygenation. Experimentally derived thermal limits, which are known to be related to observed latitudinal ranges, have been used to assess variations in species distribution patterns. However, such experiments cannot be undertaken on free-swimming large marine predators with wide-range distribution, like cetaceans. An alternative approach is to elicit expert's knowledge to derive species' thermal suitability and assess their thermal responses, something that has never been tested in these taxa. We developed and applied a methodology based on expert-derived thermal suitability curves and projected future responses for several species under different climate scenarios. We tested this approach with ten cetacean species currently present in the biogeographic area of Macaronesia (North Atlantic) under Representative Concentration Pathways 2.6, 4.5 and 8.5, until 2050. Overall, increases in annual thermal suitability were found for Balaenoptera edeni, Globicephala macrorhynchus, Mesoplodon densirostris, Physeter macrocephalus, Stenella frontalis, Tursiops truncatus and Ziphius cavirostris. Conversely, our results indicated a decline in thermal suitability for B. physalus, Delphinus delphis, and Grampus griseus. Our study reveals potential responses in cetaceans' thermal suitability, and potentially in other highly mobile and large predators, and it tests this method's applicability, which is a novel application for this purpose and group of species. It aims to be a cost-efficient tool to support conservation managers and practitioners.

Persistence, bioaccumulation and vertical transfer of pollutants in long-finned pilot whales stranded in Chilean Patagonia

Long-finned pilot whales (LFPW) are cetaceans with strong social groups often involved in mass strandings worldwide. However, these beachings occur for reasons that are not fully understood. In 2016, 124 LFPW were stranded on the Chilean Patagonian islands, offering a unique opportunity to obtain crucial information on the ecology, biology, and genetics of this population. In addition, we examined whether persistent organic pollutants (POPs) and trace elements (TEs) were responsible for this mass mortality. Stable isotopes (δ¹³C & δ¹⁵N) and genetic analyses were used to reconstruct the trophic ecology, social structure, and kinship of LFPW and compared to POPs and TEs levels found in LFPW. Mitochondrial DNA analyses on 71 individuals identified four maternal lineages within the stranded LFPW. Of these animals, 32 individuals were analyzed for a suite of POPs, TEs, and lipid content in blubber. The highest levels were found for ΣDDXs (6 isomers) (542.46 ± 433.46 ng/g, lw) and for total Hg (2.79 ± 1.91 mg/kg, dw). However, concentrations found in these LFPW were lower than toxicity thresholds and those reported for LFPW stranded in other regions. Evidence was found of ΣDDX, Σ7PCBs, and Cd bioaccumulation and maternal transfer of POPs in mother/offspring groups. Nevertheless, no clear relationship between contaminant concentrations and LFPW mortality was established. Further research is still needed to assess LFPW populations including conservations status and exposure to chemicals in remote areas such as Patagonia.

Why don’t long-finned pilot whales have a widespread postreproductive lifespan? Insights from genetic data

In a handful of mammals, females show an extended postreproductive lifespan (PRLS), leading to questions over why they spend a substantial portion of their lifespan nonreproductive. Theoretical and empirical studies suggest that PRLS may evolve when 1) demographic patterns lead to increasing local relatedness as females age, and 2) females come into reproductive competition with their daughters, as these conditions lead to high relative benefits of helping kin versus reproducing in later life. However, evolutionary pathways to PRLS are poorly understood and empirical studies are scarce. Here, we use a dataset of 1522 individuals comprising 22 pods to investigate patterns of reproduction and relatedness in long-finned pilot whales Globicephala melas; a toothed whale without species-wide PRLS. We find a similar relatedness structure to whales with PRLS: pods appear composed of related matrilines, and relatedness of females to their pod increases with age, suggesting that this species could benefit from late-life help. Furthermore, females with a large number of philopatric adult daughters are less likely to reproduce, implying intergenerational reproductive competition between females. This suggests that individuals may display a plastic cessation of reproduction, switching to investing in existing offspring when they come into competition with their daughters. To the best of our knowledge, this is the first time such a relationship has been described in relation to PRLS, and it raises questions about whether this represents a step towards evolving PRLS or is a stable alternative strategy to widespread postreproductive periods.

Identifying mechanisms of genetic differentiation among populations in vagile species: historical factors dominate genetic differentiation in seabirds

Elucidating the factors underlying the origin and maintenance of genetic variation among populations is crucial for our understanding of their ecology and evolution, and also to help identify conservation priorities. While intrinsic movement has been hypothesized as the major determinant of population genetic structuring in abundant vagile species, growing evidence indicates that vagility does not always predict genetic differentiation. However, identifying the determinants of genetic structuring can be challenging, and these are largely unknown for most vagile species. Although, in principle, levels of gene flow can be inferred from neutral allele frequency divergence among populations, underlying assumptions may be unrealistic. Moreover, molecular studies have suggested that contemporary gene flow has often not overridden historical influences on population genetic structure, which indicates potential inadequacies of any interpretations that fail to consider the influence of history in shaping that structure. This exhaustive review of the theoretical and empirical literature investigates the determinants of population genetic differentiation using seabirds as a model system for vagile taxa. Seabirds provide a tractable group within which to identify the determinants of genetic differentiation, given their widespread distribution in marine habitats and an abundance of ecological and genetic studies conducted on this group. Herein we evaluate mitochondrial DNA (mtDNA) variation in 73 seabird species. Lack of mutation-drift equilibrium observed in 19% of species coincided with lower estimates of genetic differentiation, suggesting that dynamic demographic histories can often lead to erroneous interpretations of contemporary gene flow, even in vagile species. Presence of land across the species sampling range, or sampling of breeding colonies representing ice-free Pleistocene refuge zones, appear to be associated with genetic differentiation in Tropical and Southern Temperate species, respectively, indicating that long-term barriers and persistence of populations are important for their genetic structuring. Conversely, biotic factors commonly considered to influence population genetic structure, such as spatial segregation during foraging, were inconsistently associated with population genetic differentiation. In light of these results, we recommend that genetic studies should consider potential historical events when identifying determinants of genetic differentiation among populations to avoid overestimating the role of contemporary factors, even for highly vagile taxa.

Global phylogeography and genetic diversity of the long-finned pilot whale Globicephala melas, with new data from the southeastern Pacific

The matrilineal long-finned pilot whale presents an antitropical distribution and is divided into two subspecies, one in the temperate seas of the Southern Hemisphere and the other restricted to the North Atlantic and Mediterranean. Until now, population genetic and phylogeographic studies have included localities of most of its Northern Hemisphere distribution, while only the southwestern Pacific has been sampled in the Southern Hemisphere. We add new genetic data from the southeastern Pacific to the published sequences. Low mitochondrial and nuclear diversity was encountered in this new area, as previously reported for other localities. Four haplotypes were found with only one new for the species. Fifteen haplotypes were detected in the global dataset, underlining the species’ low diversity. As previously reported, the subspecies shared two haplotypes and presented a strong phylogeographic structure. The extant distribution of this species has been related to dispersal events during the Last Glacial Maximum. Using the genetic data and Approximate Bayesian Calculations, this study supports this historical biogeographic scenario. From a taxonomic perspective, even if genetic analyses do not support the subspecies category, this study endorses the incipient divergence process between hemispheres, thus maintaining their status and addressing them as Demographically Independent Populations is recommended.

Global vulnerability of marine mammals to global warming

Although extinctions due to climate change are still uncommon, they might surpass those caused by habitat loss or overexploitation over the next few decades. Among marine megafauna, mammals fulfill key and irreplaceable ecological roles in the ocean, and the collapse of their populations may therefore have irreversible consequences for ecosystem functioning and services. Using a trait-based approach, we assessed the vulnerability of all marine mammals to global warming under high and low greenhouse gas emission scenarios for the middle and the end of the 21^st century. We showed that the North Pacific Ocean, the Greenland Sea and the Barents Sea host the species that are most vulnerable to global warming. Future conservation plans should therefore focus on these regions, where there are long histories of overexploitation and there are high levels of current threats to marine mammals. Among the most vulnerable marine mammals were several threatened species, such as the North Pacific right whale (Eubalaena japonica) and the dugong (Dugong dugon), that displayed unique combinations of functional traits. Beyond species loss, we showed that the potential extinctions of the marine mammals that were most vulnerable to global warming might induce a disproportionate loss of functional diversity, which may have profound impacts on the future functioning of marine ecosystems worldwide.

Sea surface temperature predicts the movements of an Arctic cetacean: the bowhead whale

The effects of climate change constitute a major concern in Arctic waters due to the rapid decline of sea ice, which may strongly alter the movements and habitat availability of Arctic marine mammals. We tracked 98 bowhead whales by satellite over an 11-year period (2001-2011) in Baffin Bay - West Greenland to investigate the environmental drivers (specifically sea surface temperature and sea ice) involved in bowhead whale's movements. Movement patterns differed according to season, with aggregations of whales found at higher latitudes during spring and summer likely in response to sea-ice retreat and increasing sea temperature (SST) facilitated by the warm West Greenland Current. In contrast, the whales moved further south in response to sea temperature decrease during autumn and winter. Statistical models indicated that the whales targeted a narrow range of SSTs from -0.5 to 2 °C. Sea surface temperatures are predicted to undergo a marked increase in the Arctic, which could expose bowhead whales to both thermal stress and altered stratification and vertical transport of water masses. With such profound changes, bowhead whales may face extensive habitat loss. Our results highlight the need for closer investigation and monitoring in order to predict the extent of future distribution changes.

Patterns of population structure at microsatellite and mitochondrial DNA markers in the franciscana dolphin (Pontoporia blainvillei)

The franciscana dolphin, Pontorporia blainvillei, is an endemic cetacean of the Atlantic coast of South America. Its coastal distribution and restricted movement patterns make this species vulnerable to anthropogenic factors, particularly to incidental bycatch. We used mitochondrial DNA control region sequences, 10 microsatellites, and sex data to investigate the population structure of the franciscana dolphin from a previously established management area, which includes the southern edge of its geographic range. F‐statistics and Bayesian cluster analyses revealed the existence of three genetically distinct populations. Based on the microsatellite loci, similar levels of genetic variability were found in the area; 13 private alleles were found in Monte Hermoso, but none in Claromecó. When considering the mitochondrial DNA control region sequences, lower levels of genetic diversity were found in Monte Hermoso, when compared to the other localities. Low levels of gene flow were found between most localities. Additionally, no evidence of isolation by distance nor sex‐biased dispersal was detected in the study area. In view of these results showing that populations from Necochea/Claromecó, Monte Hermoso, and Río Negro were found to be genetically distinct and the available genetic information for the species previously published, Argentina would comprise five distinct populations: Samborombón West/Samborombón South, Cabo San Antonio/Buenos Aires East, Necochea/Claromecó/Buenos Aires Southwest, Monte Hermoso, and Río Negro. In order to ensure the long‐term survival of the franciscana dolphin, management and conservation strategies should be developed considering each of these populations as different management units.

Conservation Status of Long-Finned Pilot Whales, Globicephala melas, in the Mediterranean Sea

Mediterranean Sea long-finned pilot whales (Globicephala melas) are currently classified as Data Deficient on the International Union for the Conservation of Nature (IUCN) Red List. Multiple lines of evidence, including molecular genetic and photo-identification mark-recapture analyses, indicate that the Strait of Gibraltar population (distributed from 5.8°W longitude to west of Djibouti Bank and Alborán Dorsal in the Alborán Sea) is differentiated from the Mediterranean Sea population (east of Djibouti Bank and the Alborán Dorsal up to the Ligurian Sea). There is low genetic diversity within the Mediterranean population, and recent gene flow with the Strait of Gibraltar population is restricted. Current total abundance estimates are lacking for the species in the Mediterranean. Pilot whales in the Alborán Sea region were negatively affected by a morbillivirus epizootic from 2006 to 2007, and recovery may be difficult. The Strait of Gibraltar population, currently estimated to be fewer than 250 individuals, decreased by 26.2% over 5 years after the morbillivirus epizootic. Population viability analyses predicted an 85% probability of extinction for this population over the next 100 years. Increasing maritime traffic, increased contaminant burdens, and occasional fisheries interactions may severely impair the capacity of the Strait of Gibraltar population to recover after the decline due to the pathogen.

Parentage-Based Group Composition and Dispersal Pattern Studies of the Yangtze Finless Porpoise Population in Poyang Lake

Social behaviors are poorly known for the critically endangered Yangtze finless porpoise (YFP, Neophocaena asiaeorientalis asiaeorientalis). Here, group composition and dispersal patterns of the YFP population living in the Poyang Lake were studied by parentage-based pedigree analyses using 21 microsatellite loci and a 597 bp segment of the mitochondrial DNA control region. In this study, 21 potential mother-offspring pairs and six potential father-offspring pairs (including two potential parents-offspring pairs) were determined, among which 12 natural mother-offspring groups and a maternal group of three generations were found. No genetically-determined fathers were found associated with their offspring. This study also found that maternally related porpoises at the reproductive state tend to group together. This suggest maternal relationship and reproductive state may be factors for grouping in the YFP population. In natural mother-offspring groups, male offspring were all younger than two years old, which suggest male offspring may leave their mothers at approximately two years of age, or at least they were not in tight association with their mothers as they may have been under two years old. However, female offspring can stay longer with their mothers and can reproduce in the natal group.

Interspecific Hybridization in Pilot Whales and Asymmetric Genetic Introgression in Northern Globicephala melas under the Scenario of Global Warming

Pilot whales are two cetacean species (Globicephala melas and G. macrorhynchus) whose distributions are correlated with water temperature and partially overlap in some areas like the North Atlantic Ocean. In the context of global warming, distribution range shifts are expected to occur in species affected by temperature. Consequently, a northward displacement of the tropical pilot whale G. macrorynchus is expected, eventually leading to increased secondary contact areas and opportunities for interspecific hybridization. Here, we describe genetic evidences of recurrent hybridization between pilot whales in northeast Atlantic Ocean. Based on mitochondrial DNA sequences and microsatellite loci, asymmetric introgression of G. macrorhynchus genes into G. melas was observed. For the latter species, a significant correlation was found between historical population growth rate estimates and paleotemperature oscillations. Introgressive hybridization, current temperature increases and lower genetic variation in G. melas suggest that this species could be at risk in its northern range. Under increasing environmental and human-mediated stressors in the North Atlantic Ocean, it seems recommendable to develop a conservation program for G. melas.

Fatal Asphyxiation in Two Long-Finned Pilot Whales (Globicephala melas) Caused by Common Soles (Solea solea)

Long-finned pilot whales (Globicephala melas) are rare visitors to the southern North Sea, but recently two individual strandings occurred on the Dutch coast. Both animals shared the same, unusual cause of death: asphyxiation from a common sole (Solea solea) stuck in their nasal cavity. This is a rare cause of death in cetaceans. Whilst asphyxiation has been reported in smaller odontocetes, there are no recent records of this occurring in Globicephala species. Here we report the stranding, necropsy and diet study results as well as discuss the unusual nature of this phenomenon. Flatfish are not a primary prey species for pilot whales and are rarely eaten by other cetaceans, such as harbour porpoises (Phocoena phocoena), in which there are several reports of asphyxiation due to airway obstruction by soles. This risk may be due to the fish’s flexible bodies which can enter small cavities either actively in an attempt to escape or passively due to the whale ‘coughing’ or ‘sneezing’ to rid itself of the blockage of the trachea. It is also possible that the fish enter the airways whilst the whale is re-articulating the larynx after trying to ingest large, oddly shaped prey. It is unlikely that the soles entered the airways after the death of the whales and we believe therefore that they are responsible for the death of these animals.

Population Genetics of Franciscana Dolphins (Pontoporia blainvillei): Introducing a New Population from the Southern Edge of Their Distribution

Due to anthropogenic factors, the franciscana dolphin, Pontoporia blainvillei, is the most threatened small cetacean on the Atlantic coast of South America. Four Franciscana Management Areas have been proposed: Espiritu Santo to Rio de Janeiro (FMA I), São Paulo to Santa Catarina (FMA II), Rio Grande do Sul to Uruguay (FMA III), and Argentina (FMA IV). Further genetic studies distinguished additional populations within these FMAs. We analyzed the population structure, phylogeography, and demographic history in the southernmost portion of the species range. From the analysis of mitochondrial DNA control region sequences, 5 novel haplotypes were found, totalizing 60 haplotypes for the entire distribution range. The haplotype network did not show an apparent phylogeographical signal for the southern FMAs. Two populations were identified: Monte Hermoso (MH) and Necochea (NC)+Claromecó (CL)+Río Negro (RN). The low levels of genetic variability, the relative constant size over time, and the low levels of gene flow may indicate that MH has been colonized by a few maternal lineages and became isolated from geographically close populations. The apparent increase in NC+CL+RN size would be consistent with the higher genetic variability found, since genetic diversity is generally higher in older and expanding populations. Additionally, RN may have experienced a recent split from CL and NC; current high levels of gene flow may be occurring between the latter ones. FMA IV would comprise four franciscana dolphin populations: Samborombón West+Samborombón South, Cabo San Antonio+Buenos Aires East, NC+CL+Buenos Aires Southwest+RN and MH. Results achieved in this study need to be taken into account in order to ensure the long-term survival of the species.

Microsatellite markers reveal strong genetic structure in the endemic Chilean dolphin

Understanding genetic differentiation and speciation processes in marine species with high dispersal capabilities is challenging. The Chilean dolphin, Cephalorhynchus eutropia, is the only endemic cetacean of Chile and is found in two different coastal habitats: a northern habitat with exposed coastlines, bays and estuaries from Valparaíso (33°02′S) to Chiloé (42°00′S), and a southern habitat with highly fragmented inshore coastline, channels and fjords between Chiloé and Navarino Island (55°14′S). With the aim of evaluating the potential existence of conservation units for this species, we analyzed the genetic diversity and population structure of the Chilean dolphin along its entire range. We genotyped 21 dinucleotide microsatellites for 53 skin samples collected between 1998 and 2012 (swab: n = 8, biopsy: n = 38, entanglement n = 7). Bayesian clustering and spatial model analyses identified two genetically distinct populations corresponding to the northern and southern habitats. Genetic diversity levels were similar in the two populations (He: 0.42 v/s 0.45 for southern and northern populations, respectively), while effective size population was higher in the southern area (Ne: 101 v/s 39). Genetic differentiation between these two populations was high and significant (F_ST = 0.15 and R_ST = 0.19), indicating little or no current gene flow. Because of the absence of evident geographical barriers between the northern and southern populations, we propose that genetic differentiation may reflect ecological adaptation to the different habitat conditions and resource uses. Therefore, the two genetic populations of this endemic and Near Threatened species should be considered as different conservation units with independent management strategies.

Interspecific introgression in cetaceans: DNA markers reveal post-F1 status of a pilot whale

Visual species identification of cetacean strandings is difficult, especially when dead specimens are degraded and/or species are morphologically similar. The two recognised pilot whale species (Globicephala melas and Globicephala macrorhynchus) are sympatric in the North Atlantic Ocean. These species are very similar in external appearance and their morphometric characteristics partially overlap; thus visual identification is not always reliable. Genetic species identification ensures correct identification of specimens. Here we have employed one mitochondrial (D-Loop region) and eight nuclear loci (microsatellites) as genetic markers to identify six stranded pilot whales found in Galicia (Northwest Spain), one of them of ambiguous phenotype. DNA analyses yielded positive amplification of all loci and enabled species identification. Nuclear microsatellite DNA genotypes revealed mixed ancestry for one individual, identified as a post-F1 interspecific hybrid employing two different Bayesian methods. From the mitochondrial sequence the maternal species was Globicephala melas. This is the first hybrid documented between Globicephala melas and G. macrorhynchus, and the first post-F1 hybrid genetically identified between cetaceans, revealing interspecific genetic introgression in marine mammals. We propose to add nuclear loci to genetic databases for cetacean species identification in order to detect hybrid individuals.

Seascape genetics of a globally distributed, highly mobile marine mammal: the short-beaked common dolphin (genus Delphinus)

Identifying which factors shape the distribution of intraspecific genetic diversity is central in evolutionary and conservation biology. In the marine realm, the absence of obvious barriers to dispersal can make this task more difficult. Nevertheless, recent studies have provided valuable insights into which factors may be shaping genetic structure in the world's oceans. These studies were, however, generally conducted on marine organisms with larval dispersal. Here, using a seascape genetics approach, we show that marine productivity and sea surface temperature are correlated with genetic structure in a highly mobile, widely distributed marine mammal species, the short-beaked common dolphin. Isolation by distance also appears to influence population divergence over larger geographical scales (i.e. across different ocean basins). We suggest that the relationship between environmental variables and population structure may be caused by prey behaviour, which is believed to determine common dolphins' movement patterns and preferred associations with certain oceanographic conditions. Our study highlights the role of oceanography in shaping genetic structure of a highly mobile and widely distributed top marine predator. Thus, seascape genetic studies can potentially track the biological effects of ongoing climate-change at oceanographic interfaces and also inform marine reserve design in relation to the distribution and genetic connectivity of charismatic and ecologically important megafauna.

Population genetic structure and social kin associations of franciscana dolphin, Pontoporia blainvillei

We investigated population and social structure of the franciscana dolphin, Pontoporia blainvillei, an endemic and the most endangered cetacean of the southwestern Atlantic Ocean. We analyzed samples from the Rio de la Plata estuary obtained in Uruguayan waters and from the Atlantic Ocean obtained in both Uruguayan and Brazilian waters. Mitochondrial and microsatellite DNA markers were used to study differentiation between the estuary and the ocean and the association between kinship and social group structure. Although multilocus analyses suggested that franciscanas are structured into 2 subpopulations (K = 2, divergence among clusters: F(ST) = 0.06, P = 0.002; R(ST) = 0.3, P = 0.001), mitochondrial markers did not support such divergence (F(ST) = 0.02, P = 0.12; Ф(ST) = 0.06, P =0.06). However, these units are not entirely segregated geographically. Regarding social structure, some groups are composed by first-order related individuals (R ≥ 0.5, P < 0.5). Overall, the data suggest that matrilines could be the social unit in this species. We argue that the divergence found could be associated to local adaptation and social structure, resulting from either feature leading to a recent divergence or reflecting equilibrium between local differentiation and gene flow. This evidence supports considering franciscanas from the Rio de la Plata estuary a discrete management unit.

Molecular ecology meets remote sensing: environmental drivers to population structure of humpback dolphins in the Western Indian Ocean

Genetic analyses of population structure can be placed in explicit environmental contexts if appropriate environmental data are available. Here, we use high-coverage and high-resolution oceanographic and genetic sequence data to assess population structure patterns and their potential environmental influences for humpback dolphins in the Western Indian Ocean. We analyzed mitochondrial DNA data from 94 dolphins from the coasts of South Africa, Mozambique, Tanzania and Oman, employing frequency-based and maximum-likelihood algorithms to assess population structure and migration patterns. The genetic data were combined with 13 years of remote sensing oceanographic data of variables known to influence cetacean dispersal and population structure. Our analyses show strong and highly significant genetic structure between all putative populations, except for those in South Africa and Mozambique. Interestingly, the oceanographic data display marked environmental heterogeneity between all sampling areas and a degree of overlap between South Africa and Mozambique. Our combined analyses therefore suggest the occurrence of genetically isolated populations of humpback dolphins in areas that are environmentally distinct. This study highlights the utility of molecular tools in combination with high-resolution and high-coverage environmental data to address questions not only pertaining to genetic population structure, but also to relevant ecological processes in marine species.

Genetic differentiation among North Atlantic killer whale populations

Population genetic structure of North Atlantic killer whale samples was resolved from differences in allele frequencies of 17 microsatellite loci, mtDNA control region haplotype frequencies and for a subset of samples, using complete mitogenome sequences. Three significantly differentiated populations were identified. Differentiation based on microsatellite allele frequencies was greater between the two allopatric populations than between the two pairs of partially sympatric populations. Spatial clustering of individuals within each of these populations overlaps with the distribution of particular prey resources: herring, mackerel and tuna, which each population has been seen predating. Phylogenetic analyses using complete mitogenomes suggested two populations could have resulted from single founding events and subsequent matrilineal expansion. The third population, which was sampled at lower latitudes and lower density, consisted of maternal lineages from three highly divergent clades. Pairwise population differentiation was greater for estimates based on mtDNA control region haplotype frequencies than for estimates based on microsatellite allele frequencies, and there were no mitogenome haplotypes shared among populations. This suggests low or no female migration and that gene flow was primarily male mediated when populations spatially and temporally overlap. These results demonstrate that genetic differentiation can arise through resource specialization in the absence of physical barriers to gene flow.

Isolation by environmental distance in mobile marine species: molecular ecology of franciscana dolphins at their southern range

The assessment of population structure is a valuable tool for studying the ecology of endangered species and drafting conservation strategies. As we enhance our understanding about the structuring of natural populations, it becomes important that we also understand the processes behind these patterns. However, there are few rigorous assessments of the influence of environmental factors on genetic patterns in mobile marine species. Given their dispersal capabilities and localized habitat preferences, coastal cetaceans are adequate study species for evaluating environmental effects on marine population structure. The franciscana dolphin, a rare coastal cetacean endemic to the Western South Atlantic, was studied to examine these issues. We analysed genetic data from the mitochondrial DNA and 12 microsatellite markers for 275 franciscana samples utilizing frequency-based, maximum-likelihood and Bayesian algorithms to assess population structure and migration patterns. This information was combined with 10 years of remote sensing environmental data (chlorophyll concentration, water turbidity and surface temperature). Our analyses show the occurrence of genetically isolated populations within Argentina, in areas that are environmentally distinct. Combined evidence of genetic and environmental structure suggests that isolation by distance and a process here termed isolation by environmental distance can explain the observed correlations. Our approach elucidated important ecological and conservation aspects of franciscana dolphins, and has the potential to increase our understanding of ecological processes influencing genetic patterns in other marine species.

Population Differentiation in the Pacific White-sided Dolphin Lagenorhynchus obliquidens Inferred from Mitochondrial DNA and Microsatellite Analyses

We investigated genetic diversity and differentiation of the Pacific white-sided dolphin (Lagenorhynchus obliquidens) in Japanese coastal waters and offshore North Pacific by analyzing mitochondrial DNA and nuclear microsatellite variation. A total of 519 bp of the mitochondrial control region was sequenced and five microsatellite locus were genotyped for 59 individuals. A high level of haplotypic diversity (h=96.1%), moderate level of nucleotide diversity (pi=1.65%) and average expected heterozygosity (HE=0.66-0.76) were within an extent of those reported for other odontocetes. Consistent genetic difference between the samples from Japanese coastal Pacific-Sea of Japan and offshore North Pacific was indicated by analyses of molecular variance (AMOVAs) based on mtDNA and microsatellite variations, comparison of genetic variabilities, and geographical distributions of mtDNA haplotypes and microsatellite alleles. This result suggests that Pacific white-sided dolphins in each of the above two areas belong to different populations between which gene flow has been severely restricted. The low genetic diversity and mtDNA genealogy of the population in Japanese coastal waters suggest that it originated from a small population that colonized the Sea of Japan or that experienced population reduction when this Sea was isolated from the North Pacific during a glacial period in the Late Pleistocene.

Disparate patterns of population genetic structure and population history in two sympatric penaeid shrimp species (Farfantepenaeus aztecus and Litopenaeus setiferus) in the eastern United States

Analysing the population genetic structures of sympatric species provides opportunities to compare patterns of population genetic structure and phylogeography in order to gain insight into the factors that influence the development of the observed patterns. In this study, we compared the population genetic structures and phylogeographies of brown shrimp (Farfantepenaeus aztecus) and white shrimp (Litopenaeus setiferus), two sympatric penaeid shrimp species that inhabit the waters of the eastern USA, using sequence analysis of the mitochondrial DNA control region. Brown shrimp showed no significant phylogenetic structure or population subdivision, and closely related haplotypes were geographically dispersed. Mismatch analysis indicated that brown shrimp experienced a late-Pleistocene era sudden population expansion. In contrast, white shrimp had a complex haplotype phylogeny consisting of two distinct lineages and two less well-defined sublineages, and the haplotypes and lineages were geographically structured. Mismatch analysis for white shrimp also showed evidence of sudden population expansion, albeit for each lineage separately and more recently than in the brown shrimp. These disparate patterns may have developed as a result of species-specific differences in physiological tolerances and habitat preferences that caused greater fluctuations in white shrimp population sizes and reductions in long-term effective population size relative to that of the brown shrimp, and thereby increased the susceptibility of the white shrimp populations to stochastic genetic change.

Behavioural evidence for social units in long-finned pilot whales

In general, mammal species show geographic or social dispersal by one or both sexes. Long-term behavioural observations and genetic evidence have confirmed that fish-eating resident killer whales, Orcinus orca, are a rare exception. Female and male offspring travel with their mothers for their whole lives: this is natal group philopatry. It is suspected that pilot whales, Globicephala spp., also follow this social pattern, but longitudinal data on the social structure of live long-finned pilot whales, Globicephala melas, are rare. We observed G. melas through July and August of 1998–2000 off northern Nova Scotia, Canada. Estimated group sizes ranged from 2 to 135 (mean = 20, SD = 17, median = 15, n = 249). We distinguished 322 individuals on the basis of distinctive marks on the dorsal fin, with estimated mark rates of 0.336 (proportion) (SE = 0.041) and 0.352 (mean of estimates) (SE = 0.036). Permutation testing rejected the null hypothesis of random association between individuals (p < 0.0005). The best fit model of the standardized lagged association rate suggests short-term associations of individuals over hours to days and long-term associations with a subset of those individuals over years. When scaled according to mark rate, sets of long-term associates average approximately 11–12 individuals, a much lower estimate than that presented previously from drive-fishery data from the Faroe Islands. Genetic sampling of behaviourally studied individuals is recommended.