Microsatellite-associated heterosis in hatchery-propagated stocks of the shrimp Penaeus stylirostris Auteur(s) : Bierne, Nicolas Bezuart, Ivan Vonau, Vincent Bonhomme, François Bedier, Edouard Éditeur(s) : Elsevier Résumé : Correlation between DNA microsatellite heterozygosity and growth rate was investigated in two hatchery-propagated stocks of the shrimp Penaeus stylirostris, which had been genetically isolated from wild founders for 17 generations, and from each other for five more generations. presumed demographic history of these populations suggested that they were maintained at small effective population sizes. and this was confirmed by significant changes in allelic frequencies between the two stocks. Despite a small sample size (n = 60) and a small number of loci screened, a significant positive correlation was detected between microsatellite tri-locus heterozygosity and growth rate in one of the two stocks (r = 0.3, P = 0.02). In the other stock (n = 48), the positive correlation was not significant, but the combined test of single locus heterozygote advantage over the three loci was significant (P = 0.005).Use of DNA microsatellite markers, whose selectively neutral status is generally accepted, allowed us to reject the hypothesis of direct overdominance at marker loci as an explanation for an association of growth rate with heterozygosity. The average depression associated with one locus in our case is above or equivalent to the amount observed for a 10% increase of inbreeding in other species. These results suggest that heterozygosity at neutral marker loci is sufficiently well correlated with individual inbreeding coefficients to reveal a significant residual inbreeding load for growth rate in Tahitian P. stylirostris stocks. Inbreeding during hatchery propagation was, thus, insufficient to purge the ancestral load. Aquaculture (0044-8486) (Elsevier), 2000-04 , Vol. 184 , N. 3-4 , P. 203-219 Droits : 2000 Elsevier Science B.V. All rights reserved http://archimer.ifremer.fr/doc/2000/publication-753.pdf DOI:10.1016/S0044-8486(99)00331-2 http://archimer.ifremer.fr/doc/00000/753/ | Partager Voir aussi Penaeus stylirostris Heterozygosity Marker associated heterosis Inbreeding depression Microsatellites Télécharger |
Conséquences génétiques de la production de larves d'huîtres en écloserie : étude des processus de dérive et de sélection Auteur(s) : Taris, Nicolas Sauvage, Christopher Batista, Frederico Baron, Sophie Ernande, Bruno Haffray, Pierrick Boudry, Pierre Éditeur(s) : Actes du 6e colloque national BRG, La Rochelle, 2-3-4 octobre 2006 Résumé : Previous studies have shown heritable variation in larval developmental traits in the Pacific oyster Crassostrea gigas. In order to study the genetic consequences of production of oyster larvae in hatcheries, two factors, specific to hatcheries, were examined: the effect of discarding the smallest larvae (i.e. culling) and the effect of temperature (20°C versus 26°C). A mixed-family approach was used in order to infer the genetic composition of larval populations and family assignment, limiting possible environmental bias and allowing the study of a relatively large number of families using a limited number of larval tanks. Our results show that three multiplexed highly polymorphic microsatellite markers are a powerful tool for family assignment and, consequently, for the study of bivalve larvae genetics. Culling, by selective sieving of the smallest larvae is an advantageous practice at a phenotypic scale as it reduced variance in larval size, variance of developmental rate and time to settlement. Culling of 50% of the larval population only led to 15% less spat, showing a positive phenotypic correlation between larval growth and settlement success. However, culling represents a substantial risk for diversity loss, because it increases the variance of reproductive success among parental oysters. The effective population sizes of early settling cohorts of settlement were lower than those of later ones. Our results show that the settlement of slow growing larvae significantly contributes to minimizing the variability of reproductive success and therefore to maximizing genetic diversity. These results corroborate the low estimations of variability of broodstocks sampled in several French commercial hatcheries, relative to natural populations. The genetic composition of the larval population and the resulting spat was significantly different between the two tested temperatures, revealing genotype x environment interaction for survival. Similarly, genotype x environment interaction was also observed for larval growth as a higher temperature exerted a positive influence on the expression of genetic variability for this trait. Consequently, we can conclude that a temperature of 26°C coupled with culling, to common practice in oyster hatcheries, is likely to amplify the selection pressure for fast growing larvae. To test for this hypothesis, we compared larval developmental traits in the progeny of a hatchery broodstock closed for 7 generations, with the progeny of wild oysters and the two possible hybrids. Our results show that selection of fast growing larvae can counteract presumed inbreeding depression, due to higher mean relatedness among hatchery broodstock than in the wild. Genetic effects of intensive rearing conditions at larval stage are significant and should be taken into account in hatchery practices, especially in terms of genetic diversity management. Afin d'étudier les conséquences génétiques des pratiques de production en écloserie d'huître creuse, deux facteurs ont été examinés : l'élimination des petites larves et la température. Nos résultats montrent que l'assignation de parenté par marqueurs microsatellites est un outil performant pour les études génétiques en phase larvaire de familles élevées en mélange. Bien qu'avantageux d'un point de vue phénotypique, le tamisage sélectif représente un risque de perte de diversité. La fixation des larves à croissance lente permet en effet de minimiser la variabilité du succès reproducteur et de fait, de maximiser la variabilité génétique. Ces résultats corroborent les estimations de variabilité sur les stocks d'écloseries françaises où l'on constate une diversité allélique inférieure à celle de populations issues du milieu naturel. La température exerce également une influence sur la précocité de l'expression de la variabilité génétique pour la croissance larvaire. Ainsi une température élevée associée à une procédure de tamisage peut amplifier l'effet sélectif. Enfin, la sélection de larves à croissance rapide semble démontrée, s'opposant à la dépression de consanguinité présumée. Les conditions d'élevage peuvent donc avoir un effet génétique significatif qui devrait être pris en considération dans les pratiques d'écloserie, notamment dans la gestion de la diversité génétique. Droits : info:eu-repo/semantics/openAccess http://archimer.ifremer.fr/doc/2006/acte-1505.pdf http://archimer.ifremer.fr/doc/00000/1505/ | Partager |
Etude des processus de dérive et de sélection liés aux pratiques d'élevage en écloserie d'huître creuse Auteur(s) : Boudry, Pierre Résumé : Genetic consequences of production of Pacific oyster larval in hatchery: drift and selective pressures related to rearing practices. In order to study the genetic consequences of production of oyster larvae in hatcheries, two factors were examined: the effects of discarding the smallest larvae (i.e. culling) and temperature effects. A mixed-family approach was used in order to infer the genetic composition of the larval population. The results show that high polymorphic microsatellite-based family assignment is a powerful tool for the study of bivalve larvae genetics. Culling by selective sieving is an advantageous practice at a phenotypic scale, but also represents a substantial risk for diversity loss if parentage assignment is not introduced as a breeding practice. Settlement of slow growing larvae contributes to minimizing the variability of reproductive success and therefore to maximizing genetic diversity. These results corroborate the lower estimations of variability made on broodstocks from French commercial hatcheries relative to natural populations. Temperature exerts an influence on the expression of genetic variability for larval growth. A temperature of 26°C, coupled with culling could amplify the selective effect. Furthermore, selection of fast growing larvae has proven to counteract inbreeding depression at this stage. Genetic effects of intensive rearing conditions are significant and should be taken into account in hatchery practices, especially in terms of genetic diversity management. Afin d'étudier les conséquences génétiques des pratiques de production de larves en écloserie d'huître creuse, deux facteurs ont été examinés : l'effet de l'élimination des plus petites larves et l'effet de la température. Une approche de familles élevées en mélange a été utilisée afin d'avoir accès à l'information génétique au stade larvaire. Les résultats obtenus montrent que l'assignation de parenté basée sur des marqueurs microsatellites hautement discriminants est un outil performant pour les études génétiques en phase larvaire. Bien qu'avantageuse d'un point de vue phénotypique, la pratique de tamisage sélectif représente un risque substantiel de perte de diversité si cette pratique n'est pas associée à une assignation de parentée par empreintes génétiques. La fixation des larves à croissance lente permet de minimiser la variabilité du succès reproducteur et de fait, de maximiser la variabilité génétique. Ces résultats corroborent les estimations de variabilité sur les stocks d'écloseries commerciales françaises où l'on constate une diversité allélique inférieure à celle de populations issues du milieu naturel. La température exerce également une influence sur la précocité de l'expression de la variabilité génétique pour la croissance larvaire. Ainsi une température élevée (26°C) associée à une procédure de tamisage peut amplifier l'effet sélectif. Enfin, la sélection de larves à croissance rapide semble démontrée, s'opposant à la dépression de consanguinité présumée en phase larvaire. Les conditions d'élevage peuvent donc avoir un effet génétique significatif qui devrait être pris en considération dans les pratiques d'écloserie, notamment dans la gestion de la diversité génétique. Droits : info:eu-repo/semantics/openAccess http://archimer.ifremer.fr/doc/2006/rapport-1459.pdf http://archimer.ifremer.fr/doc/00000/1459/ | Partager |
Life after disturbance (II): the intermediate disturbance hypothesis explains genetic variation in forest gaps dominated by Virola michelii Heckel (Myristicaceae) Auteur(s) : Scotti, Ivan Montaigne, William Cseke, Klára Traissac, Stéphane Auteurs secondaires : INRA, UR629 Université des Antilles et de la Guyane (UAG) Dept Forest Tree Breeding Expt Stn & Arboretum ; Forest Research Institute Ecologie des forêts de Guyane (ECOFOG) ; Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD) - Institut National de la Recherche Agronomique (INRA) - Université des Antilles et de la Guyane (UAG) - AgroParisTech - Université de Guyane (UG) - Centre National de la Recherche Scientifique (CNRS) The research was funded by the "ECOFOR-Biodiversite et gestion forestiere" program. IS is currently supported by an "Investissement d'Avenir" grant managed by Agence Nationale de la Recherche (CEBA, ref. ANR-10-LABX-0025) Éditeur(s) : HAL CCSD Springer Verlag/EDP Sciences Résumé : International audience Key message: Genetic diversity appears to be unaffected by disturbance in a stand of the light-demanding Neotropical treeV. michelii. Although spatial genetic structure is modified in post-disturbance cohorts, mixing of seeds from different mother trees in canopy gaps appears to efficiently maintain genetic admixture. Context: The interplay between genetic and demographic processes has major consequences on population viability. Population size affects demographic trends, while genetic diversity insures viability by reducing risks of inbreeding depression and by maintaining adaptive potential. Yet, the consequences of increases in census size (as opposed to effective size) on genetic diversity of forest populations are poorly known. Aims: We have studied the structure of genetic diversity in populations of saplings of the light-responsive tree, Virola michelii (Myristicaceae, the nutmeg family), in two plots having undergone different levels of canopy-gap opening disturbance. This allowed us to test the “intermediate disturbance” hypothesis, which generally applies to species diversity, at the intra-specific scale. Methods: Levels and distribution of genetic diversity were compared between plots and between life stages. Sapling parentage was analysed to infer each adult tree’s contribution to regeneration. Results: Genetic diversity was higher, and spatial genetic structure was stronger in the post-disturbance than in the control seedling population. Parentage analysis suggested that a limited number of parents contributed to most of the regeneration, but that efficient mixing of their progeny may have enhanced the diversity of saplings occupying canopy gaps. Conclusion: A mixture of demo-genetic processes may contribute to maintain genetic diversity in spite of, or possibly due to, ecosystem disturbance in V. michelii. ISSN: 1286-4560 hal-01502942 https://hal-agroparistech.archives-ouvertes.fr/hal-01502942 https://hal-agroparistech.archives-ouvertes.fr/hal-01502942/document https://hal-agroparistech.archives-ouvertes.fr/hal-01502942/file/art_10.1007_s13595-015-0508-3-1_%7B869D58F4-272C-491F-A903-DAD6CDBDC042%7D.pdf DOI : 10.1007/s13595-015-0508-3 | Partager |