Responses of eastern mosquitofish (Gambusia holbrooki) to acute salinity stress: do family effects obscure inbreeding and genotype effects?

Abstract

Eastern mosquitofish (Gambusia holbrooki) having inbreeding coefficients of 0, 0.125, and 0.25 were exposed to a salinity stress of 14.34 parts per thousand (ppt) for 96 h, and their survival times were determined. Statistical models were fitted to the failure-time data to assess differences between the survival functions based on inbreeding coefficient, family, and genotype of the fish. Predicted median survival times were determined for inbreeding classes, families within inbreeding classes, classes based on number of heterozygous loci, and genotypes at single loci. Family significantly affected survival of individuals in all analyses, regardless of the inbreeding coefficient of the individual. The inbreeding coefficient of an individual did not statistically affect survival. The number of heterozygous loci per individual significantly affected survival time but only when family as well as number of heterozygous loci per individual were included as independent variables in the analysis. Genotypes of two loci, m-isocitrate dehydrogenase A and glucose phosphate isomerase B, also significantly affected survival. Our study demonstrates that family can account for a greater proportion of the variance in survival under environmental stress than either inbreeding coefficient or number of heterozygous loci. Family effects, in addition to inbreeding, should be considered in conservation management plans.Résumé : On a exposé la gambusie (Gambusia holbrooki) possédant des coefficients de consanguinité de 0, 0,125 et 0,25 pendant 96 h à un milieu dont la salinité était de 14,34 ppt, puis on a déterminé son temps de survie. On a appliqué des modèles statistiques aux données échec-temps en vue d'évaluer les différences entre les fonctions de survie basées sur le coefficient de consanguinité, la famille et le génotype du poisson. On a déterminé la valeur médiane des temps de survie prévus pour les classes de consanguinité, les familles à l'intérieur de ces classes, les classes basées sur le nombre de locus hétérozygotes et les génotypes à des locus seuls. Dans toutes les analyses, la famille influait de façon significative sur la survie des individus, indépendamment du coefficient de consanguinité de l'individu. Le coefficient de consanguinité d'un individu n'influait pas statistiquement sur la survie. Le nombre de locus hétérozygotes par individu influait beaucoup sur le temps de survie, mais seulement lorsque la famille ainsi que le nombre de locus hétérozygotes par individu était inclus comme variables indépendantes dans l'analyse. Les génotypes de deux locus, la m-isocitrate-déshydrogénase A et la glucose-phosphate-isomérase B, influaient aussi considérablement sur la survie. Notre étude montre que la famille permet d'expliquer une plus grande proportion de la variance dans la survie en présence d'un stress environnemental, que le coefficient de consanguinité ou le nombre de locus hétérozygotes. En plus des effets de la consanguinité, il y aurait lieu de tenir compte des effets de la famille lors de l'élaboration de plans...

Life-history traits of the invasive fish Gambusia ­holbrooki in saline streams (SE Iberian Peninsula): Does salinity limit its invasive success?

“…population that has long been exposed to harsh environmental conditions would be able to adapt to a gradual increase in hostile environmental conditions (e.g. salinity) (Hubbs 2000 (Congdon 1994, Kandl & Thompson 1996. The clear viability of the G. holbrooki population inhabiting Rambla Salada supports these hypotheses.…”

Genetic and Demographic Responses of Mosquitofish (Gambusia Holbrooki) Populations Exposed to Mercury for Multiple Generations

“…Mulvey et al [21] found that time to reach maturity differed for fish of different Gpi-2 allozyme genotypes in environments with elevated temperature. Differential survivorship of Gpi-2 allozyme genotypes in response to acute salinity stress was found in both Australian [10] and U.S. [13] G. holbrooki populations. Susceptibility to the organophosphate insecticide, chlorpyrifos, also differed among allozyme genotypes at the Gpi-2 locus [11].…”

“…Allozyme analysis has also been used to study the effect of toxicants on populations reared in mesocosms [6]. Of the many isozymes examined in these studies, glucosephosphate isomerase has most consistently been identified as a correlate with differential responses of individuals and populations [1,[4][5][6][7][8][9][10][11][12][13]. Riddoch [14] reported that Gpi allozymes have been correlated with temperature (along altitude and latitude clines), pollutants, salinity, and dissolved oxygen.…”

Genetic and demographic responses of mosquitofish (Gambusia holbrooki) populations exposed to mercury for multiple generations

“…Mulvey et al [21] found that time to reach maturity differed for fish of different Gpi‐2 allozyme genotypes in environments with elevated temperature. Differential survivorship of Gpi‐2 allozyme genotypes in response to acute salinity stress was found in both Australian [10] and U.S. [13] G. holbrooki populations. Susceptibility to the organophos‐phate insecticide, chlorpyrifos, also differed among allozyme genotypes at the Gpi‐2 locus [11].…”