Margaret Mulvey

Allozyme genotype and time to death of mosquitofish, Gambusia affinis (Baird and Girard) during acute toxicant exposure: a comparison of arsenate and inorganic mercury

Abstract Genotypic frequencies at 8 enzyme loci were examined in a population of mosquitofish, Gambusia affinis (Baird and Girard) during acute arsenate exposure. Genotypes at 2 loci (fumarate hydratase and glucose-phosphate isomerase-2) and multiple locus heterozygosity (male fish) were significantly correlated with time to death (TTD). The results from arsenate exposures were contrasted with those reported earlier for acute inorganic mercury exposure. Earlier TTD were associated with a rare homozygous genotype for the Gpi -2 locus in both arsenate and inorganic mercury exposures; however, no other single locus effect-on TTD was common to both toxicants. The results of acute exposures of mosquitofish to mercury and arsenate suggest that most of the effects of multiple locus heterozygosity can be attributed to the summation of single locus effects.

Allozyme genotype and time-to-death of mosquitofish, Gambusia holbrooki, during acute inorganic mercury exposure: a comparison of populations

Abstract Relationships between enzyme genotype and time-to-death (TTD) during acute mercury exposure were examined in mosquitofish taken from two isolated field populations. Results were compared with those from an exposure conducted two years previously, with fish from one of these populations, in which genotypes at three enzyme loci, Icd-1. Gpi-2. and Mdh-1. were significantly related to TTD, as was overall heterozygosity. Neither genotype nor heterozygosity were related to TTD in the present exposure of fish from this population. In the exposure of fish from the population not sampled previously, two loci. Icd-2 and Mpi. were significantly related to TTD. Multiple locus heterozygosity was not related to mortality in this exposure. These two populations exhibited different genotype-TTD relationships during laboratory exposures, suggesting that the response of one population exposed in the laboratory may not accurately represent the responses of other populations, either in the laboratory or during exposures in nature.

Snail (Helix aspersa) exposure history and possible adaptation to lead as reflected in shell composition

Lead sequestration in shell was examined for English and Welsh populations of the common garden snail (Helix aspersa) with different Pb exposure histories. Isotopic Pb ratios provided signatures for Pb source and a means of implying duration of population exposure from decades to millennia. Total Pb concentrations were used to quantify the intensity of exposure experienced by the populations. Snails from populations with long histories of exposure (millennia) to high Pb levels had proportionately more Pb in their shell than soft tissue compared with snails from other surveyed populations. These observations suggest that Pb sequestration in shell has been enhanced in H. aspersa populations with long and intense exposure to Pb.

Phylogenetic analysis of eleven species of Biomphalaria Preston, 1910 (Gastropoda: Planorbidae) based on comparisons of allozymes

Freshwater snails in the genus Biomphalaria transmit Schislosoma mansoni in Africa, South America and the Caribbean region. Although considerable attention has been given to the identification of species, little is known of evolutionary relationships among the species. A phylogenetic analysis of 25 populations representing I I species was performed on 25 enzyme loci examined using starch gel electrophoresis. A phylogenetic analysis of the individual populations produced 60 trees of equal length. The 60 trees have a consistency index value of 75.9% and a retention index value of 76.5%. The phylogenetic analysis provided strong support for the monophyly of Biomphalaria with either 14 or 15 synapomorphies uniting all of the species included and separating them from the outgroup, two species of Helisoma. Four nominal species represented by multiple populations formed monophyletic groups. Populations of B. sudanica, B. choanomphala, and B. alexandrina were interspersed. Ten arrangements were obtained for the populations of these three species. A variety of ingroup taxa were used to root the trees, and all provided support for the use of Helisoma species as an outgroup. In all of the trees obtained, the African species together formed a monophyletic group. In none of the trees obtained did the neotropical species form a monophyletic group. A constrained analysis requiring the monophyly of the neotropical species as well as the African species resulted in 90 trees just two steps longer than the shortest trees. Analysis of the species from either hemisphere alone resulted in decreased resolution, as measured by an increase in the number of trees obtained. This finding suggests that further comparisons of species from the two hemispheres will be of considerable value. Finally, two species which are resistant to infection with S. mansoni were included among the eleven studied. Neither of these species formed the sister group to all of the other species included, indicating that susceptibility is the plesiomorphic state, and that resistance is derived. Similarly, in none of the trees obtained did the two resistant species fall out as sister taxa, indicating that resistance arose independently twice.

Enhanced uranium tolerance of an exposed population of the eastern mosquitofish (Gambusia holbrooki Girard 1859)

Genetic differences between populations of mosquitofish from a uranium(U)-contaminated stream were identified by starch gel electrophoresis. Fish collected from the uncontaminated mainstream of Upper Three Runs Creek (South Carolina, USA) exhibited greater genetic variability than those collected from the contaminated Tims Branch. Lower genetic variation displayed in Tims Branch fish could reflect selection associated with toxicant stress, a genetic bottleneck due to low population numbers at the contaminated site, or random genetic drift. A toxicity assay was performed to determine if these genetically distinct mosquitofish also displayed enhanced U tolerance. Times to death were compared for fish from an uncontaminated site and offspring of fish taken from the U-contaminated Tims Branch. After 7 days of exposure to 2.57 mg/L of U as uranyl nitrate, 98% and 96% of the naive population had died in the replicate tanks. In contrast, the final mortality for the offspring from the population previously exposed to U were 25% and 57% in the replicate tanks. Fish derived from the U-contaminated site were more tolerant than those from the uncontaminated site. Because these were second generation fish, this tolerance likely has a genetic basis.

Time to death of mosquitofish (Gambusia holbrooki) during acute inorganic mercury exposure: Population structure effects

Times-to-death (TTD) of mother and offspring mosquitofish (Gambusia holbrooki) were examined during acute exposure to mercury concentrations of approximately 1.0 mg/L. Median TTD were more similar for fish sharing a common mother (defined herein as a sibship) and microhabitat during maturation than between sibships. Field populations may exhibit structure similar to that of these sibships. Correlations between broods (or other population subunits) and allozyme genotype could be responsible for transient, genotype effects noted during electrophoretic surveys attempting to measure population level response to toxicants.