Genomics reveals the role of admixture in the evolution of structure among sperm whale populations within the Mediterranean Sea.

In oceanic ecosystems, the nature of barriers to gene flow and the processes by which populations may become isolated are different from the terrestrial environment, and less well understood. In this study we investigate a highly mobile species (the sperm whale, Physeter macrocephalus) that is genetically differentiated between an open North Atlantic population and the populations in the Mediterranean Sea. We apply high-resolution single nucleotide polymorphism (SNP) analysis to study the nature of barriers to gene flow in this system, assessing the putative boundary into the Mediterranean (Strait of Gibraltar and Alboran Sea region), and including novel analyses on structuring among sperm whale populations within the Mediterranean basin. Our data support a recent founding of the Mediterranean population, around the time of the last glacial maximum, and show concerted historical demographic profiles in both the Atlantic and the Mediterranean. In each region there is evidence for a population decline around the time of the founder event. The largest decline was seen within the Mediterranean Sea where effective population size is substantially lower (especially in the eastern basin). While differentiation is strongest at the Atlantic/Mediterranean boundary, there is also weaker but significant differentiation between the eastern and western basins of the Mediterranean Sea. We propose, however, that the mechanisms are different. While post-founding gene flow was reduced between the Mediterranean and Atlantic populations, within the Mediterranean an important factor differentiating the basins is probably a greater degree of admixture between the western basin and the North Atlantic and some level of isolation between the western and eastern Mediterranean basins. Subdivision within the Mediterranean Sea exacerbates conservation concerns and will require consideration of what distinct impacts may affect populations in the two basins.

Characterization of 25 new microsatellite markers for the fin whale (Balaenoptera physalus) and cross-species amplification in other cetaceans.

Cetaceans are large mammals widely distributed on Earth. The fin whale, Balaenoptera physalus, is the second largest living animal. In the 20th century, commercial whaling reduced its global population by 70%, and in the Mediterranean Sea not only was their overall population depleted but the migration between the Mediterranean Sea and the Atlantic Ocean was reduced. Previous genetic studies identified isolation between these two regions, with a limited gene-flow between these adjacent populations based on nuclear and mitochondrial markers. However, only limited information exists for the Mediterranean population as genetic diversity and abundance trends are still unknown. In this study, 39 highly polymorphic microsatellite markers were tested, including 25 markers developed de novo together with 14 markers previously published. An average allelic diversity of 8.3 alleles per locus was reported, ranging from 3 to 15 alleles per locus, for B. physalus. Expected heterozygosity was variable among loci and ranged from 0.34 to 0.91. Only two markers in the new set were significantly deviant from the Hardy Weinberg equilibrium. Cross-species amplification was tested in four other cetacean species. A total of 27 markers were successfully amplified in the four species (Balaenoptera acutorostrata, Megaptera novaeangliae, Physeter macrocephalus and Globicephala melas). A multivariate analysis on the multilocus genotypes successfully discriminated the five species. This new set of microsatellite markers will not only provide a useful tool to identify and understand the genetic diversity and the evolution of the B. physalus population, but it will also be relevant for other cetacean species, and will allow further parentage analyses. Eventually, this new set of microsatellite markers will provide critical data that will shed light on important biological data within a conservation perspective.

POPs in free-ranging pilot whales, sperm whales and fin whales from the Mediterranean Sea: Influence of biological and ecological factors.

The pilot whale Globicephala melas, the sperm whale Physeter macrocephalus, and the fin whale Balaenoptera physalus are large cetaceans permanently inhabiting the Mediterranean Sea. These species are subjected to numerous anthropogenic threats such as exposure to high levels of contaminants. Therefore, selected persistent organic pollutants POPs (29 PCBs, 15 organochlorine compounds, 9 PBDEs and 17 PCDD/Fs) were analysed in blubber biopsies of 49 long-finned pilot whales, 61 sperm whales and 70 fin whales sampled in the North Western Mediterranean Sea (NWMS) from 2006 to 2013. Contamination profile and species feeding ecology were then combined through the use of stable isotopes. δ(13)C, δ(15)N values and POPs levels were assessed through IR-MS and GC-MS respectively. To assess the toxic potency of the dioxin-like compounds, the TEQ approach was applied. δ(15)N values were 12.2±1.3‰ for sperm whales, 10.5±0.7‰ for pilot whales and 7.7±0.8‰ in fin whales, positioning sperm whales at higher trophic levels. δ(13)C of the two odontocetes was similar and amounted to -17.3±0.4‰ for sperm whales and -17.8±0.3‰ for pilot whales; whilst fin whales were more depleted (-18.7±0.4‰). This indicates a partial overlap in toothed-whales feeding habitats, while confirms the differences in feeding behaviour of the mysticete. Pilot whales presented higher concentrations than sperm whales for ΣPCBs (38,666±25,731 ng g(-1)lw and 22,849±15,566 ng g(-1) lw respectively), ΣPBDEs (712±412 ng g(-1) lw and 347±173 ng g(-1) lw respectively) and ΣDDTs (46,081±37,506 ng g(-1) lw and 37,647±38,518 ng g(-1) lw respectively). Fin whales presented the lowest values, in accordance with its trophic position (ΣPCBs: 5721±5180 ng g(-1) lw, ΣPBDEs: 177±208 ng g(-1) lw and ΣDDTs: 6643±5549 ng g(-1) lw). Each species was characterized by large inter-individual variations that are more related to sex than trophic level, with males presenting higher contaminant burden than females. The discriminant analysis (DA) confirmed how DDTs and highly chlorinated PCBs were influential in differentiating the three species. Pollutant concentrations of our species were significantly higher than both their Southern Hemisphere and North Atlantic counterparts, possibly due to the particular Mediterranean geomorphology, which influences pollutants distribution and recycle. Dioxin-like PCBs accounted for over 80% of the total TEQ. This study demonstrated (1) an important exposure to pollutants of Mediterranean cetaceans, often surpassing the estimated threshold toxicity value of 17,000 ng g(-1) lw for blubber in marine mammals; and (2) how the final pollutant burden in these animals is strongly influenced not only by the trophic position but also by numerous other factors such as sex, age, body size and geographical distribution.

Isotopic niches of fin whales from the Mediterranean Sea and the Celtic Sea (North Atlantic).

The fin whale (Balaenoptera physalus) is the most abundant and widespread mysticete species in the Mediterranean Sea, found mostly in deep, offshore waters of the western and central portion of the region. In the Mediterranean, this species is known to feed mainly on krill, in contrast to its Atlantic counterpart, which displays a more diversified diet. The International Whaling Commission recognizes several managements units in the Atlantic and the Mediterranean Sea and the connectivity between these populations is still being debated. Questions remain about inter-individual feeding strategies and trophic ecology. The goal of this study was to compare isotopic niches of fin whales from the Mediterranean Sea and the Celtic Sea (North Atlantic). δ13C and δ15N values were analysed in 136 skin biopsies from free-ranging Mediterranean fin whales sampled in 2010 and 2011 during campaigns at sea. δ13C and δ15N values ranged from -20.4 to -17.1‰ and from 5.9 to 8.9‰, respectively. These values are in good agreement with those estimated previously from baleen plates from Mediterranean and North Atlantic fin whales. The narrow isotopic niche width of the Mediterranean fin whale (Standard Ellipses area SEAc) compared to the North Atlantic fin whale raises many concerns in the context of global changes and long-term consequences. One could indeed expect that species displaying narrow niches would be more susceptible to ecosystem fragmentation and other anthropogenic impacts.

Response of rocky reef top predators (Serranidae: Epinephelinae) in and around marine protected areas in the Western Mediterranean Sea.

Groupers species are extremely vulnerable to overfishing and many species are threatened worldwide. In recent decades, Mediterranean groupers experienced dramatic population declines. Marine protected areas (MPAs) can protect populations inside their boundaries and provide individuals to adjacent fishing areas through the process of spillover and larval export. This study aims to evaluate the effectiveness of six marine reserves in the Western Mediterranean Sea to protect the populations of three species of grouper, Epinephelus marginatus, Epinephelus costae and Mycteroperca rubra, and to understand in which circumstances MPAs are able to export biomass to neighbouring areas. All the studied MPAs, except one where no grouper was observed, were able to maintain high abundance, biomass and mean weight of groupers. Size classes were more evenly distributed inside than outside MPAs. In two reserves, biomass gradients could be detected through the boundaries of the reserve as an indication of spillover. In some cases, habitat structure appeared to exert a great influence on grouper abundance, biomass and mean individual weight, influencing the gradient shape. Because groupers are generally sedentary animals with a small home range, we suggest that biomass gradients could only occur where groupers attain sufficient abundance inside MPA limits, indicating a strongly density-dependent process.

Toothed whales in the northwestern Mediterranean: insight into their feeding ecology using chemical tracers.

Risso's dolphins, pilot whales and sperm whales rarely strand in the northwestern Mediterranean. Thus, their feeding ecology, through the analysis of stomach contents, is poorly known. The aim of this study was to gain further insight into the segregation/superposition of the diet and habitat of Risso's dolphins, pilot whales and sperm whales using chemical tracers, namely, stable isotopes (δ(13)C, δ(15)N) and organochlorines. Significantly different δ(15)N values were obtained in Risso's dolphins (11.7±0.7‰), sperm whales (10.8±0.3‰) and pilot whales (9.8±0.3‰), revealing different trophic levels. These differences are presumably due to various proportions of Histioteuthidae cephalopods in each toothed whale's diet. Similar δ(13)C contents between species indicated long-term habitat superposition or corroborated important seasonal migrations. Lower congener 180 concentrations (8.20 vs. 21.73 µg.g(-1) lw) and higher tDDT/tPCB ratios (0.93 vs. 0.42) were observed in sperm whales compared with Risso's dolphins and may indicate wider migrations for the former. Therefore, competition between these species seems to depend on different trophic levels and migration patterns.