Determining the relative influence of biotic and abiotic factors on genetic connectivity among populations remains a major challenge in evolutionary biology and in the management and conservation of species. North Pacific hake (Merluccius productus) inhabits upwelling regions in the California Current ecosystem from the Gulf of California to the Gulf of Alaska. In this study, we examined mitochondrial DNA (mtDNA) and microsatellite variation to estimate levels of genetic differentiation of M. productus in relation to the role of oceanographic features as potential barriers to gene flow. Samples were obtained from nine sites spanning a large part of the geographic range of the species, from Puget Sound, Washington to Costa Rica. The microsatellite results revealed three genetically discrete populations: one spanning the eastern Pacific coast, and two apparently resident populations circumscribed to the Puget Sound and the northern Gulf of California (FST = 0.032, p = 0.036). Cytochrome b sequence data indicated that isolation between the Puget Sound and northern Gulf of California populations from the coastal Pacific were recent phenomena (18.5 kyr for Puget Sound and 40 kyr for the northern Gulf of California). Oceanographic data obtained from the Gulf of California support the hypothesis that permanent fronts within the region, and strong gradients at the entrance to the Gulf of California act as barriers to gene flow. A seascape genetics approach found significant genetic–environment associations, where the daytime sea surface temperature and chlorophyll concentrations were the best predictive variables for the observed genetic differentiation. Considering the potential causes of genetic isolation among the three populations, e.g. spawning areas in different latitudes associated with upwelling processes, oceanographic barriers, asymmetric migration and specialized diet, oceanographic barriers appear to be a likely mechanism restricting gene flow.
The silky shark mitogenome (GeneBank accession number KF801102) has a total length of 17,774 bp, the base composition of the genomes was as follows: A (31.36%), T (30.18%), C (25.27%) and G (13.17%), which demonstrated an A + T-rich feature (61.64%), similar to other elasmobranch mitogenomes. The mitochondrial genome contained 13 protein-coding genes and 23 tRNA genes. The tRNA genes ranged from 70 to 72 bp. The gene order was the same as in other vertebrates and teleosts.
Despite being one of the most abundant and highly exploited species in the Mexican Pacific Ocean, information on the biology of the silky shark, Carcharhinus falciformis is limited. The objective of the present study was to describe the reproductive biology of this species, based on 262 sharks (117 females and 145 males) caught from September 2004 to May 2006 in the Gulf of Tehuantepec, Mexico. The size of females ranged from 70 to 229 cm total length (TL); males measured from 69 to 220 cm TL. Female reproductive organ measurements showed that between 175 and 190 cm TL there was an increase in oviducal gland width (19–45 mm), as well as in uterus size (20–220 mm width). Mature males over 180 cm had calcified claspers, well-developed testes (184–282 mm) and presence of sperm in the seminal vesicles. The estimated length of males at first maturity was 180 cm, and that of females was 190 cm. Ovarian fecundity varied from 4 to 11 oocytes, and uterine fecundity varied from 2 to 14 embryos. We infer that mating occurs between May and June. We did not find sperm storage in the oviducal glands. Birth size was observed to be between 60 and 69 cm TL. No defined gestation period was observed.
The almaco jack, Seriola rivoliana, is a circumtropical pelagic fish of importance both in commercial fisheries and in aquaculture. To understand levels of genetic diversity within and among populations in the wild, population genetic structure and the relative magnitude of migration were assessed using mtDNA sequence data and single nucleotide polymorphisms (SNPs) from individuals sampled from locations in the Pacific and Atlantic Oceans. A total of 25 variable sites of cytochrome c oxidase subunit 1 and 3678 neutral SNPs were recovered. Three genetic groups were identified, with both marker types distributed in different oceanic regions: Pacific‐1 in central Pacific, Pacific‐2 in eastern Pacific and Atlantic in western Atlantic. Nonetheless, the analysis of SNP identified a fourth population in the Pacific coast of Baja California Sur, Mexico (Pacific‐3), whereas that of mtDNA did not. This mito‐nuclear discordance is likely explained by a recently diverged Pacific‐3 population. In addition, two mtDNA haplogroups were found within the western Atlantic, likely indicating that the species came into the Atlantic from the Indian Ocean with historical gene flow from the eastern Pacific. Relative gene flow among ocean basins was low with rm < 0.2, whereas in the eastern Pacific it was asymmetric and higher from south to north (rm > 0.79). The results reflect the importance of assessing genetic structure and gene flow of natural populations for the purposes of sustainable management.
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