The Broadbill Swordfish is harvested by fisheries throughout the world. In order to devise more e... more The Broadbill Swordfish is harvested by fisheries throughout the world. In order to devise more effective management strategies, we need a clear understanding of the population structure of the species. From a library of 29 tetranucleotide repeats, 22 microsatellite markers were characterised for 94 swordfish samples captured from eastern and western Australia. The number of alleles ranged from 2 to 26 and observed heterozygosity from 0.066 to 0.923. We have identified 18 microsatellites that will be valuable in the examination of swordfish population structure.
Epinephelus merra (Serranidae) is the most common and widespread species of this genus, mostly fo... more Epinephelus merra (Serranidae) is the most common and widespread species of this genus, mostly found in reef habitats from South Africa to Central Pacific. Thirteen polymorphic microsatellite loci were isolated and characterized from this species. Polymorphism was studied in two localities from the Comoros archipelago—Mohéli and Moroni. Allelic diversity was 7.5, polymorphism ranging from 3 to 13 alleles. Overall heterozygosity was high with an average observed heterozygosity of 0.587. Three of these loci were characterised by heterozygote deficiencies for both populations. Finally, ten of the 13 developed primers could be used in future population genetics study of E.merra that might be useful in a context of marine biodiversity conservation.
The brittle-star Acrocnida brachiata (Montagu) lives in sandy-bottom habitat of both intertidal a... more The brittle-star Acrocnida brachiata (Montagu) lives in sandy-bottom habitat of both intertidal and subtidal zones along the coasts of the northwestern Europe. An allozyme frequency-based survey (five enzyme loci) was combined with a mitochondrial (mt) COI haplotype analysis (598-bp sequences) on 17 populations to trace back past colonization pathways from the actual population structure of the species. Both genetic markers display a sharp genetic break between intertidal (clade I) and subtidal populations (clade S). This break corresponds to an allele frequency inversion at three enzyme loci (Hk, Pgm and Pgi) and a deep divergence of about 20% in mtCOI sequences between most of the intertidal populations and other samples. The geographic distribution of clade I seems to be more restricted than clade S as it is absent from the intertidal of the eastern English Channel and North Sea and may be replaced by clade S in south Brittany. Applying previously published rates of mutation, divergence between the two clades is estimated to pre-date 5 million years ago and may be due to allopatric speciation processes at the Mio–Pliocene transition. The occurrence of putative hybrids in a few localities, however, suggests incomplete cryptic speciation with secondary contact zones. The relative importance of colonization history vs. habitat specialization are discussed in the light of neutral evolution as tested from mtCOI gene sequences. While differential selection seems to have contributed little to the separation of the lineages, it may have played a role in the emergence of adaptive polymorphisms in the hybrid zone. Furthermore, congruent spatial patterns of differentiation were observed in both clades suggesting a recent increase in population size. These findings are in agreement with a recent expansion of the populations during or after the formation of the English Channel, from a southern refuge for the subtidal clade whereas the intertidal clade may have persisted further north. As previously suspected for a species with a very short pelagic larval phase, contemporary gene flow between distant or adjacent populations appears to be extremely reduced or even absent.
The two brittle-stars Acrocnida brachiata (Montagu 1804) and A. spatulispina (Stöhr and Muths in ... more The two brittle-stars Acrocnida brachiata (Montagu 1804) and A. spatulispina (Stöhr and Muths in J Mar Biol Assoc, 2009) exhibit strong spatial segregation along the coast of Brittany (France), the first being subtidally distributed relative to the other intertidal species. Despite a very high degree of mitochondrial DNA divergence, previous preliminary results hinted at the potential for hybridization to occur. Therefore, we specifically aim to determine local levels of hybridization between these two species and to investigate the relative roles of pre- and post- zygotic isolation processes acting to decrease local hybridization patterns. Mitochondrial DNA, allozymes and the Internal Transcribed Spacer 2 region of the ribosomal DNA were all used on 529 brittle-stars sampled locally in June and September 2005, among six stations in Douarnenez Bay, a site situated at the tip of Brittany. Only 2.6% of all samples analyzed were identified as potential hybrids. However, these were twice more frequent in June, just after the reproductive period, than in September after selective mortality acted to reduce the proportions of hybrids. In addition to the abrupt bathymetric segregation between the two species, spawning asynchrony also clearly restricts hybridization to low levels, which shows the importance of pre-zygotic mechanisms in maintaining reproductive isolation. Moreover, both limited hybridization events and adult mortalities following reproduction tend to generate local genetic differentiation at the intra-species level. On the contrary, the genetic structure is homogenized by migration of juveniles or adults and hybrids mortalities over the summer period.
The Broadbill Swordfish is harvested by fisheries throughout the world. In order to devise more e... more The Broadbill Swordfish is harvested by fisheries throughout the world. In order to devise more effective management strategies, we need a clear understanding of the population structure of the species. From a library of 29 tetranucleotide repeats, 22 microsatellite markers were characterised for 94 swordfish samples captured from eastern and western Australia. The number of alleles ranged from 2 to 26 and observed heterozygosity from 0.066 to 0.923. We have identified 18 microsatellites that will be valuable in the examination of swordfish population structure.
Epinephelus merra (Serranidae) is the most common and widespread species of this genus, mostly fo... more Epinephelus merra (Serranidae) is the most common and widespread species of this genus, mostly found in reef habitats from South Africa to Central Pacific. Thirteen polymorphic microsatellite loci were isolated and characterized from this species. Polymorphism was studied in two localities from the Comoros archipelago—Mohéli and Moroni. Allelic diversity was 7.5, polymorphism ranging from 3 to 13 alleles. Overall heterozygosity was high with an average observed heterozygosity of 0.587. Three of these loci were characterised by heterozygote deficiencies for both populations. Finally, ten of the 13 developed primers could be used in future population genetics study of E.merra that might be useful in a context of marine biodiversity conservation.
The brittle-star Acrocnida brachiata (Montagu) lives in sandy-bottom habitat of both intertidal a... more The brittle-star Acrocnida brachiata (Montagu) lives in sandy-bottom habitat of both intertidal and subtidal zones along the coasts of the northwestern Europe. An allozyme frequency-based survey (five enzyme loci) was combined with a mitochondrial (mt) COI haplotype analysis (598-bp sequences) on 17 populations to trace back past colonization pathways from the actual population structure of the species. Both genetic markers display a sharp genetic break between intertidal (clade I) and subtidal populations (clade S). This break corresponds to an allele frequency inversion at three enzyme loci (Hk, Pgm and Pgi) and a deep divergence of about 20% in mtCOI sequences between most of the intertidal populations and other samples. The geographic distribution of clade I seems to be more restricted than clade S as it is absent from the intertidal of the eastern English Channel and North Sea and may be replaced by clade S in south Brittany. Applying previously published rates of mutation, divergence between the two clades is estimated to pre-date 5 million years ago and may be due to allopatric speciation processes at the Mio–Pliocene transition. The occurrence of putative hybrids in a few localities, however, suggests incomplete cryptic speciation with secondary contact zones. The relative importance of colonization history vs. habitat specialization are discussed in the light of neutral evolution as tested from mtCOI gene sequences. While differential selection seems to have contributed little to the separation of the lineages, it may have played a role in the emergence of adaptive polymorphisms in the hybrid zone. Furthermore, congruent spatial patterns of differentiation were observed in both clades suggesting a recent increase in population size. These findings are in agreement with a recent expansion of the populations during or after the formation of the English Channel, from a southern refuge for the subtidal clade whereas the intertidal clade may have persisted further north. As previously suspected for a species with a very short pelagic larval phase, contemporary gene flow between distant or adjacent populations appears to be extremely reduced or even absent.
The two brittle-stars Acrocnida brachiata (Montagu 1804) and A. spatulispina (Stöhr and Muths in ... more The two brittle-stars Acrocnida brachiata (Montagu 1804) and A. spatulispina (Stöhr and Muths in J Mar Biol Assoc, 2009) exhibit strong spatial segregation along the coast of Brittany (France), the first being subtidally distributed relative to the other intertidal species. Despite a very high degree of mitochondrial DNA divergence, previous preliminary results hinted at the potential for hybridization to occur. Therefore, we specifically aim to determine local levels of hybridization between these two species and to investigate the relative roles of pre- and post- zygotic isolation processes acting to decrease local hybridization patterns. Mitochondrial DNA, allozymes and the Internal Transcribed Spacer 2 region of the ribosomal DNA were all used on 529 brittle-stars sampled locally in June and September 2005, among six stations in Douarnenez Bay, a site situated at the tip of Brittany. Only 2.6% of all samples analyzed were identified as potential hybrids. However, these were twice more frequent in June, just after the reproductive period, than in September after selective mortality acted to reduce the proportions of hybrids. In addition to the abrupt bathymetric segregation between the two species, spawning asynchrony also clearly restricts hybridization to low levels, which shows the importance of pre-zygotic mechanisms in maintaining reproductive isolation. Moreover, both limited hybridization events and adult mortalities following reproduction tend to generate local genetic differentiation at the intra-species level. On the contrary, the genetic structure is homogenized by migration of juveniles or adults and hybrids mortalities over the summer period.
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