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Patterns of genetic structure among marine populations involve a variety of dispersal mechanisms and spatial scales. Pelagic species, such as the dolphinfish Coryphaena hippurus, epitomize the open and continuous nature of the marine environment due to their extensive migrations. Many studies have revealed that oceanic pelagic species tend to be genetically homogeneous over local and often extended geographic scales and only show levels of differentiation among extreme localities or ocean basins. Here we present genetic data suggesting genetic heterogeneity in the dolphinfish at geographic scales much smaller than those predicted by those generalizations. Mitochondrial NADH1 gene RFLPs revealed a highly significant (ΦST = 0.029, P = 0.004, AMOVA) molecular genetic structure among fish from Baja California Sur (BCS), Sinaloa and Hawaii, consistent with heterogeneous haplotype frequencies (P = 0.014, exact test of genetic differentiation) and a depressed molecular diversity in fish sampled off BCS.

We analyzed the genetic diversity and structure of three allopatric populations of the Pacific red snapper Lutjanus peru (Nichols and Murphy, 1922) by means of restriction fragment length polymorphisms of the entire mitochondrial control region (1350 bp). We found high levels of haplotype (h = 0.966) and nucleotide (π = 3.23%) diversities among the 100 organisms analyzed from Baja California Sur, Sinaloa and Jalisco (Mexico). Most of the molecular variability was detected with only one of the five restriction enzymes used (MseI). Heterogeneity analysis of haplotype frequencies was not significant (χ2 = 125.1, P > 0.25); neither were Wright's fixation index (FST = 0.0062, P = 0.140) nor its molecular analogue (ΦST = 0.0194, P = 0.056). An analysis of molecular variance (AMOVA) confirmed the absence of differentiation between peninsular and continental populations, even though it produced a marginally significant ΦST (ΦST = 0.0116, P = 0.048). No phylogeographic pattern was detected in a Neighbor-Joining gene tree. We argue that high molecular diversity levels are consistent with a large population size and that the absence of an apparent genetic structure, in the extreme north of the species distribution, suggests the action of mechanisms favoring passive larval transport among allopatric populations; although active adult migration cannot be ruled out.

Defining species boundaries is important not only for the appropriate attribution of life history and ecological traits but also for sustainable fishery management and for the conservation of biodiversity. Problems arise from taxonomic uncertainty and incorrect species delineation leading to historical misidentification. This is the case of Pacific guitarfishes in the genus Zapteryx. We use a molecular phylogenetic approach combining mitochondrial and nuclear loci to investigate genetic variation in fish along the Mexican Pacific coast. Our analyses reveal a lack of nuclear and mitochondrial distinction between rays identified morphologically as banded guitarfish Z. exasperata and as southern banded guitarfish Z. xyster, casting doubts on the validity of their current systematics. However, we detected two mitochondrial lineages in accordance with the number of species described for the Pacific: a "northern" lineage corresponding to Z. exasperata and a "southern" lineage possibly attributable to Z. xyster. The poorly understood phenotypic plasticity in coloration and size of the evolutionary lineage of Z. exasperata and its apparently wider than currently thought geographic distribution (at least to Oaxaca) are the major sources of confusion regarding the taxonomic and geographic delineation of these nominal species. In light of our findings, eastern Pacific guitarfishes in the genus Zapteryx require a thorough taxonomic revision using morphological and genetic data to unveil what appears to be a complex pattern of diversification. [ABSTRACT FROM AUTHOR]

White sharks (Carcharodon carcharias, WS henceforth) are globally and regionally threatened. Understanding their patterns of abundance and connectivity, as they relate to habitat use, is central for delineating conservation units and identifying priority areas for conservation. We analyzed mitochondrial data to test the congruence between patterns of genetic connectivity and of individual movements in the Northeastern Pacific (NEP) and to trace the matrilineal origin of immature WS from coastal California and Baja California to adult aggregation areas. We analyzed 186 mitochondrial control region sequences from sharks sampled in Central California (CC; n = 61), Southern California Bight (SCB; n = 25), Baja California Pacific coast (BCPC; n = 9), Bahía Vizcaíno (BV; n = 39), Guadalupe Island (GI; n = 45), and the Gulf of California (GC; n = 7). Significant mitochondrial differentiation between adult aggregation areas (CC, GI) revealed two reproductive populations in the NEP. We found general concordance between movement patterns of young and adult WS with genetic results. Young sharks from coastal California and Baja California were more likely born from females from GI. Mitochondrial differentiation of young-of-the-year from SCB and BV suggests philopatry to nursery areas in females from GI. These results provide a genetic basis of female reproductive behavior at a regional scale and point to a preponderance of sharks from GI in the use of the sampled coastal region as pupping habitat. These findings should be considered in Mexican and US management and conservation strategies of the WS NEP population. [ABSTRACT FROM AUTHOR]

The northern Mexican Pacific (NMP), the Gulf of California (GC), and Baja California have been recognized as an ecological and evolutionarily dynamic region having experienced significant tectonic and climatic changes leading to the diversification of terrestrial and marine biotas. Zapteryx exasperata is a predominant ray caught in the artisanal fisheries of the NMP. Morphometric and reproductive differences between rays from the GC and the Pacific coast of Baja California (PCBC) regions suggest the presence of distinct populations. We investigate whether this distinction correlates with differences in genetic diversity and differentiation using sequences of the mitochondrial nicotinamide adenine dinucleotide dehydrogenase subunit 2 (ND2) gene and the noncoding control region (CR) in 63 specimens. Contrary to our expectations, ND2 bore significantly more diversity (h = 0.76) than CR (h = 0.39). Geographic patterns of diversity of CR were opposite to those of ND2, with GC being significantly less (ND2) and more (CR) diverse than PCBC. The diversity of concatenated haplotypes was high (h = 0.84). Low nucleotide diversity suggests the recent coancestry of haplotypes. Marked genetic structure (Φst = 0.23, P < 0.0001) revealed the existence of reproductive isolation and limited matrilineal gene flow between GC and PCBC, which correlates with their phenotypic distinction. These results suggest the influence of factors such as female reproductive philopatry, and ecological or historical vicariant barriers to gene flow. Our results point to the existence of a distinct management unit of banded guitarfish in each region, and add to the increasing evidence attesting to the diversifying nature of this evolutionarily dynamic region. [ABSTRACT FROM PUBLISHER]

Abstract: The sometimes-distant association between dispersal movements and mating strategies may govern seabird ecology. Despite their large dispersal capability, pelagic seabirds are subject to the influence of physical and non-physical barriers that may limit the magnitude of realized effective dispersal and gene flow. The Magnificent Frigatebird (Fregata magnificens) is a widespread, tropical, pelagic, sequentially monogamous seabird capable to breach physical barriers, such as land masses. Nevertheless, Mexican frigatebirds have shown movement preferences by sex (female migration and high male site fidelity), which, along with the complex female mate choice behavior, may promote breeding isolation. In order to ascertain if levels of population structure are influenced by physical or non-physical barriers, we analyzed mitochondrial DNA variation of adult Magnificent Frigatebirds breeding in the main nesting colonies in Mexico, three in the eastern Pacific Ocean and one in the Caribbean Sea. Control region sequences revealed significant genetic structure between Pacific and Caribbean frigatebirds (AMOVA, ΦSC = 0.105, P < 0.0001), but none among Pacific breeding colonies (non-significant pairwise ΦST). Whereas the C-haplotype was shared by Pacific and Caribbean frigatebirds, the T-haplotype was absent in the Caribbean. Genetic differentiation between ocean basins and available evidence of Mexican frigatebird movements suggest that in spite of the capability of frigatebirds to breach physical barriers, movement preferences by sex and mate selection acting in a large inter-oceanic scale are the prime behaviors promoting population structure, which is highly consequential for their conservation. [Copyright &y& Elsevier]

The mitogenome of the beaubrummel damselfish,Stegastes flavilatusGill, 1862 (Genebank accession number KP136922), has a total length of 16,816 bp. It encodes 13 protein-coding, two ribosomal RNAs (rRNAs), and 22 transfer RNA (tRNA) genes. Base composition is 28.6% A, 26.0% T, 29.8% C, and 15.7% G and 45.5% GC content. The gene arrangement was found to be the same of other pomacentrid mitogenomes. [ABSTRACT FROM AUTHOR]

The complete mitochondrial genome of the giant electric ray is 17,081 bp long (GenBank accession KM386678) and includes 2 ribosomal RNA, 22 transfer RNA, 13 protein-coding genes, an origin of replication, 2 non-coding regions. The mitochondrial gene arrangement is similar to that found in other batoids. The control region possessed a set of tandem repeats. Start codon ATG and stop codon TAA/T were found in most protein-coding genes. The base composition of the genome is 36.2% A, 29.9% T, 21.9% C, and 11.9% G. [ABSTRACT FROM PUBLISHER]

The complete mitochondrial genome of the banded guitarfish is 17,310 bp long and includes 2 ribosomal RNA, 22 transfer RNA, and 13 protein-coding genes, a replication origin and a control region (GenBank accession number KM370325). Gene arrangement is similar to that found in other batoids. An extra non-coding region was found between the genes coding for transfer RNA proline and threonine possessing a set of tandem repeat motifs pointing to its origin as a duplication remnant. Start codon ATG and stop codon TAA/T were found in most protein-coding genes. The base composition of the genome is 32.3% A, 30.2% T, 24.3% C and 13.1% G. [ABSTRACT FROM PUBLISHER]

Patterns of genetic structure among marine populations involve a variety of dispersal mechanisms and spatial scales. Pelagic species, such as the dolphinfish Coryphaena hippurus, epitomize the open and continuous nature of the marine environment due to their extensive migrations. Many studies have revealed that oceanic pelagic species tend to be genetically homogeneous over local and often extended geographic scales and only show levels of differentiation among extreme localities or ocean basins. Here we present genetic data suggesting genetic heterogeneity in the dolphinfish at geographic scales much smaller than those predicted by those generalizations. Mitochondrial NADH1 gene RFLPs revealed a highly significant (ΦST = 0.029, P = 0.004, AMOVA) molecular genetic structure among fish from Baja California Sur (BCS), Sinaloa and Hawaii, consistent with heterogeneous haplotype frequencies (P = 0.014, exact test of genetic differentiation) and a depressed molecular diversity in fish sampled off BCS. [ABSTRACT FROM AUTHOR]

Previous studies of the olive ridley Lepidochelys olivacea population structure in the tropical eastern Pacific have indicated the existence of a single panmictic population ranging from Costa Rica to Mexico. This information has been used to design specific management measures to conserve primary nesting beaches in Mexico. However, little is known about olive ridleys in the Baja California Peninsula, their northernmost reproductive limit, where recent observations have shown differences in nesting female behaviour and size of hatchlings relative to other continental rookeries. We used mtDNA control region sequences from 137 turtles from five continental and four peninsular nesting sites to determine whether such differences correspond to a genetic distinction of Baja California olive ridleys or to phenotypic plasticity associated with the extreme environmental nesting conditions of this region. We found that genetic diversity in peninsular turtles was significantly lower than in continental nesting colonies. Analysis of molecular variance revealed a significant population structure (ΦST = 0.048, P = 0.006) with the inclusion of peninsular samples. Our results: (i) suggest that the observed phenotypic variation may be associated with genetic differentiation and reproductive isolation; (ii) support the recent colonization of the eastern Pacific by Lepidochelys; (iii) reveal genetic signatures of historical expansion and colonization events; and (iv) significantly challenge the notion of a single genetic and conservation unit of olive ridleys in the eastern Pacific. We conclude that conservation measures for olive ridleys in Mexico should be revised to grant peninsular beaches special attention. [ABSTRACT FROM AUTHOR]

The shovelnose guitarfishRhinobatos productusis an evolutionarily, ecologically, and economically important ray, with a continuous distribution from San Francisco, California (USA), to Mazatlan, Sinaloa, and in the Gulf of California (Mexico). Regional studies have revealed morphometric differences between shovelnose from the Gulf of California and the Pacific coast of Baja California, which may result from phenotypic plasticity in the presence of high levels of gene flow or from a degree of genetic differentiation in the presence of cryptic isolation within a continuous distribution. We used PCR-RFLP of the mitochondrial control region to assess the degree of genetic differentiation between Gulf of California and Pacific shovelnose guitarfish. We found very high levels of molecular diversity (averages:h=0.77,p=1.19%), which may be associated with historically large and stable populations, as well as very significant levels of genetic differentiation between gulf and Pacific samples (?2=64,P<0.0001;FST=0.63,P<0.0001, mean nucleotide divergenced=2.47%). We found a deep phylogeographic break between haplotypes from the gulf and the Pacific, which may suggest the existence of cryptic species but clearly indicates more than one evolutionarily significant unit ofR.productus. Our results show a pattern of genetic structure and levels of differentiation consistent with the geological history of the region. Furthermore, these findings have wide-ranging implications for the management and conservation of cartilaginous fish in Mexico, as they reveal the existence of biological diversity that will go unnoticed without the genetic scrutiny of intraspecific variation and that is highly relevant for much needed management and conservation efforts. [ABSTRACT FROM AUTHOR]

Presents a study which analyzed base pairs of mitochondrial DNA for molecular lineages in a species-rich subgenus of Leptasterias. Materials and methods; Results and discussion.

Presents information on a study which used mitochondrial DNA sequence variation of Sebastes to address issues regarding the number of species in the Southern Hemisphere. Materials and methods; Results and discussion.

The mitogenome of the Cortés geoduck clamPanopea globosa(Genbank accession KM580068) has a length of 15,469 bp and contains 13 protein-coding genes, 2 ribosomal RNA and 22 transfer RNA genes, as conventional metazoan mitochondrial genomes. Structural genes start with ATG, ATA and GTG codons; whereas TAG and TAA are used as stop codons. Base composition is: 23.3% A, 40.4% T, 10.1% C and 26.1% G. As is typical of marine bivalves, all genes are coded on the same strand. On the other hand, the gene arrangement is considerably different from those found in other heterodont bivalve mitogenomes. [ABSTRACT FROM PUBLISHER]

The complete mitochondrial genome of the Pacific GeoduckPanopea generosa(Genbank accession KM580067) is 15,585 bp in size and contains the typical 37 genes (13 protein-coding, 2 ribosomal RNA and 22 transfer RNA) found in metazoan mitogenomes, including the rare ATPase subunit 8 gene (ATP8). All genes are coded in the same strand but the gene arrangement is novel among heterodont bivalves. The base composition was: A 25.0%, T 38.7%, C 11.2% and G 25.0%. The genome is structurally similar to that of its congener the Cortes GeoduckPanopea globosa. [ABSTRACT FROM PUBLISHER]

Abstract: Pelagic fish that are distributed circumtropically are characterised by a low population structure level as a result of a high capacity for dispersion and large population sizes. Nevertheless, historical and contemporary processes, including past demographic and/or range expansions, secondary contact, dispersal, gene flow, and the achievement of large effective population sizes, may play a part in the detection of divergence signals, especially in the case of tropical pelagic species, whose distribution range depends strongly on the sea surface temperature. The connectivity and historical demography of Atlantic, Indian, Pacific and Mediterranean populations of dolphinfish (Coryphaena hippurus) was studied using partial sequences of the mitochondrial DNA NADH dehydrogenase subunit 1 (ND1). AMOVA analyses revealed significant inter-oceanic divergence with three phylogroups located in the Indo-Pacific, Eastern Atlantic, and Mediterranean Sea, the last one being the most divergent. However, it was not possible to clearly observe any genetic differentiation between the Indo-Pacific and Atlantic populations, as has been reported for most tropical pelagic species of tuna and billfishes. This supports the assumption of recent dispersal among basins facilitated by the actual continuous distribution of dolphinfish populations. Moreover, the lack of a divergence signal for populations separated by the Panamanian Isthmus reveals that genetic drift does not exert a strong influence on tropical pelagic species with large effective population sizes. [ABSTRACT FROM AUTHOR]