Ana Veríssimo

Global population structure of the spiny dogfish Squalus acanthias, a temperate shark with an antitropical distribution

The spiny dogfish (Squalus acanthias) is a temperate, coastal squaloid shark with an antitropical distribution in the Atlantic and Pacific oceans. The global population structure of this species is poorly understood, although individuals are known to undergo extensive migrations within coastal waters and across ocean basins. In this study, an analysis of the global population structure of the spiny dogfish was conducted using eight polymorphic nuclear microsatellite markers and a 566‐bp fragment of the mitochondrial ND2 gene region. A low level of genetic divergence was found among collections from the Atlantic and South Pacific basins, whereas a high level of genetic divergence was found among Pacific Ocean collections. Two genetically distinct groups were recovered by both marker classes: one exclusive to North Pacific collections, and one including collections from the South Pacific and Atlantic locations. The strong genetic break across the equatorial Pacific coincides with major regional differences in the life‐history characters of spiny dogfish, suggesting that spiny dogfish in areas on either side of the Pacific equator have been evolving independently for a considerable time. Phylogeographic analyses indicate that spiny dogfish populations had a Pacific origin, and that the North Atlantic was colonized as a result of a recent range expansion from the South American coast. Finally, the available data strongly argue for the taxonomic separation of the North Pacific spiny dogfish from S. acanthias and a re‐evaluation of the specific status of S. acanthias is warranted.

Reproductive biology and embryonic development of Centroscymnus coelolepis in Portuguese mainland waters

A total of 871 females (76-122 cm) and 86 males (68-100 cm) of Centroscymnus coelolepis caught in Portuguese mainland waters were examined for reproductive characteristics. One hermaphroditic individual of 95 cm was found. Males were few in numbers and dominated by immature specimens. Female length at first sexual maturity was 98.5 cm. Mean ovarian and uterine fecundity were 13.2 oocytes per female and 9.9 embryos per pregnant female, respectively. Total length of embryos with completely absorbed external yolk sacs ranged between 233 and 300 mm. Sex ratio (F/M) of embryos with completely absorbed external yolk sac was 0.9. All stages of reproduction were found during the 12-month sampling period. Results were compared with those from other regions. A hypothesis is formulated on the existence of several regional populations based on morphometric and reproductive parameters observed in different areas.

Genetic population structure and connectivity in a commercially exploited and wide-ranging deepwater shark, the leafscale gulper (Centrophorus squamosus)

The leafscale gulper (Centrophorus squamosus) is a wide-ranging deepwater benthopelagic shark threatened by commercial fisheries in parts of its range. Despite concerns about resource sustainability, little is known about the population structure and connectivity between critical habitats of the leafscale gulper. This study investigates the genetic population structure and the migration patterns of C. squamosus using nuclear microsatellites and mitochondrial NADH dehydrogenase subunit 2 (ND2) gene sequences. Genetic diversity was estimated and compared among sample collections from off Ireland, Portugal, the Azores, South Africa and New Zealand. The null hypothesis of genetic homogeneity among all collections was not rejected by the nuclear loci (FST (the overall genetic differentiation among sample collections) = –0.002, P = 0.88), but we found long-term genetic divergence between New Zealand and the remaining collections at the mtDNA ND2 (FCT (genetic differentation among groups of sample collections) = 0.366, P = 0.000). Migration rate estimates indicated limited female dispersal across the Indian Ocean whereas males showed less restricted dispersal. Our results are consistent with a single genetic stock of C. squamosus and the existence of sex-biased dispersal across the Indian Ocean. Widespread genetic homogeneity at nuclear loci minimizes the loss of unique adaptive genetic diversity in the event of localised depletion. However, high local fishing mortality may have far reaching impacts given the marked sex- and maturity-stage-based habitat partitioning previously reported for C. squamosus.

The Pillars of Hercules as a bathymetric barrier to gene flow promoting isolation in a global deep‐sea shark (Centroscymnus coelolepis)

Knowledge of the mechanisms limiting connectivity and gene flow in deep‐sea ecosystems is scarce, especially for deep‐sea sharks. The Portuguese dogfish (Centroscymnus coelolepis) is a globally distributed and near threatened deep‐sea shark. C. coelolepis population structure was studied using 11 nuclear microsatellite markers and a 497‐bp fragment from the mtDNA control region. High levels of genetic homogeneity across the Atlantic (ΦST = −0.0091, FST = 0.0024, P > 0.05) were found suggesting one large population unit at this basin. The low levels of genetic divergence between Atlantic and Australia (ΦST = 0.0744, P < 0.01; FST = 0.0015, P > 0.05) further suggested that this species may be able to maintain some degree of genetic connectivity even across ocean basins. In contrast, sharks from the Mediterranean Sea exhibited marked genetic differentiation from all other localities studied (ΦST = 0.3808, FST = 0.1149, P < 0.001). This finding suggests that the shallow depth of the Strait of Gibraltar acts as a barrier to dispersal and that isolation and genetic drift may have had an important role shaping the Mediterranean shark population over time. Analyses of life history traits allowed the direct comparison among regions providing a complete characterization of this sharks populations. Sharks from the Mediterranean had markedly smaller adult body size and size at maturity compared to Atlantic and Pacific individuals. Together, these results suggest the existence of an isolated and unique population of C. coelolepis inhabiting the Mediterranean that most likely became separated from the Atlantic in the late Pleistocene.

A new record of Callinectes sapidus in a western European estuary (Portuguese coast)

This paper confirms the occurrence of the blue crab, Callinectes sapidus , in a Portuguese estuary (Sado estuary), demonstrating a full south-western extension of the species distribution along the Atlantic and Mediterranean coasts bordering the European continent. The present record associated with current and previous anecdotal occurrence reports suggests that the blue crab has established a population in the Sado estuary but with low census size.

Isolation and characterization of ten nuclear microsatellite loci for the Portuguese dogfish Centroscymnus coelolepis

The Portuguese dogfish Centroscymnus coelolepis is a deepwater squaloid shark with a wide distribution and is also an important fishing resource in parts of its range. Despite concerns about the species’ sustainability, current fisheries management measures have been implemented without a good understanding of the stock structure. The assessment of the population structure of C. coelolepis using molecular markers will provide important information for future management efforts. Here we describe the first attempt at isolating nuclear microsatellite markers for C. coelolepis. Ten polymorphic microsatellite loci were developed and screened in 43–45 individuals collected off western Portugal, showing 3–29 alleles per loci (average: 12.5 alleles/locus) and observed heterozygosities ranging from 0.60 to 0.98. None of the markers exhibited genotypic distributions that deviated from HWE expectations, or showed evidence of linkage disequilibrium or the presence of null alleles.

A tale of two seas: contrasting patterns of population structure in the small-spotted catshark across Europe

Elasmobranchs represent important components of marine ecosystems, but they can be vulnerable to overexploitation. This has driven investigations into the population genetic structure of large-bodied pelagic sharks, but relatively little is known of population structure in smaller demersal taxa, which are perhaps more representative of the biodiversity of the group. This study explores spatial population genetic structure of the small-spotted catshark (Scyliorhinus canicula), across European seas. The results show significant genetic differences among most of the Mediterranean sample collections, but no significant structure among Atlantic shelf areas. The data suggest the Mediterranean populations are likely to have persisted in a stable and structured environment during Pleistocene sea-level changes. Conversely, the Northeast Atlantic populations would have experienced major changes in habitat availability during glacial cycles, driving patterns of population reduction and expansion. The data also provide evidence of male-biased dispersal and female philopatry over large spatial scales, implying complex sex-determined differences in the behaviour of elasmobranchs. On the basis of this evidence, we suggest that patterns of connectivity are determined by trends of past habitat stability that provides opportunity for local adaptation in species exhibiting philopatric behaviour, implying that resilience of populations to fisheries and other stressors may differ across the range of species.

A global perspective on the trophic geography of sharks

Sharks are a diverse group of mobile predators that forage across varied spatial scales and have the potential to influence food web dynamics. The ecological consequences of recent declines in shark biomass may extend across broader geographic ranges if shark taxa display common behavioural traits. By tracking the original site of photosynthetic fixation of carbon atoms that were ultimately assimilated into muscle tissues of 5,394 sharks from 114 species, we identify globally consistent biogeographic traits in trophic interactions between sharks found in different habitats. We show that populations of shelf-dwelling sharks derive a substantial proportion of their carbon from regional pelagic sources, but contain individuals that forage within additional isotopically diverse local food webs, such as those supported by terrestrial plant sources, benthic production and macrophytes. In contrast, oceanic sharks seem to use carbon derived from between 30° and 50° of latitude. Global-scale compilations of stable isotope data combined with biogeochemical modelling generate hypotheses regarding animal behaviours that can be tested with other methodological approaches.Carbon isotopic analysis reveals global biogeographic traits in shark trophic interactions, and sheds light on the diverse foraging behaviour of sharks.

Molecular diversity and distribution of eastern Atlantic and Mediterranean dogfishes Squalus highlight taxonomic issues in the genus

The alpha taxonomy of the globally distributed shark genus Squalus has been under intense investigation recently, and many new species have been described over the last decade. However, taxonomic uncertainty remains about several taxa. Without consistent nomenclature and the ability to reliably distinguish between the different Squalus species, basic data collection, downstream conservation and management efforts are seriously compromised. To aid in clarifying the taxonomic status of Squalus species in the eastern Atlantic and Mediterranean, we assessed species diversity at the molecular level and evaluated the consistency in species identification in the region. Samples from all nominal Squalus species recognized in the above regions were collected in an international effort and sequenced for regions of the mitochondrial COI and ND2 genes. These data were further analysed alongside publicly available sequences, including 19 of the 26 Squalus species globally recognized, to compare the regional genus‐level diversity with that found elsewhere. Our results confirm inconsistent species identification in the eastern Atlantic and Mediterranean Squalus, particularly concerning S. blainville and S. megalops, and reinforce the need to revise the status of S. megalops and S. mitsukurii as they may include several distinct species distributed around the world. The status of S. blainville is also discussed in the light of the current findings and its problematic taxonomic history.

Phylogenetic analysis of apicomplexan parasites infecting commercially valuable species from the North-East Atlantic reveals high levels of diversity and insights into the evolution of the group

BackgroundThe Apicomplexa from aquatic environments are understudied relative to their terrestrial counterparts, and the seminal work assessing the phylogenetic relations of fish-infecting lineages is mostly based on freshwater hosts. The taxonomic uncertainty of some apicomplexan groups, such as the coccidia, is high and many genera were recently shown to be paraphyletic, questioning the value of strict morphological and ecological traits for parasite classification. Here, we surveyed the genetic diversity of the Apicomplexa in several commercially valuable vertebrates from the North-East Atlantic, including farmed fish.ResultsMost of the sequences retrieved were closely related to common fish coccidia of Eimeria, Goussia and Calyptospora. However, some lineages from the shark Scyliorhinus canicula were placed as sister taxa to the Isospora, Caryospora and Schellakia group. Additionally, others from Pagrus caeruleostictus and Solea senegalensis belonged to an unknown apicomplexan group previously found in the Caribbean Sea, where it was sequenced from the water column, corals, and fish. Four distinct parasite lineages were found infecting farmed Dicentrarchus labrax or Sparus aurata. One of the lineages from farmed D. labrax was also found infecting wild counterparts, and another was also recovered from farmed S. aurata and farm-associated Diplodus sargus.ConclusionsOur results show that marine fish apicomplexans are diverse, and we highlight the need for a more extensive assessment of parasite diversity in this phylum. Additionally, parasites recovered from S. canicula were recovered as basal to their piscine counterparts reflecting hosts phylogeny.