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Goodisman,
Michael
Goodisman,
Michael
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ItemGenetic structure and breeding system in a social wasp and its social parasite(Georgia Institute of Technology, 2008-08-20) Hoffman, Eric A. ; Kovacs, Jennifer L. ; Goodisman, MichaelBackground: Social insects dominate ecological communities because of their sophisticated group behaviors. However, the intricate behaviors of social insects may be exploited by social parasites, which manipulate insect societies for their own benefit. Interactions between social parasites and their hosts lead to unusual coevolutionary dynamics that ultimately affect the breeding systems and population structures of both species. This study represents one of the first attempts to understand the population and colony genetic structure of a parasite and its host in a social wasp system. Results: We used DNA microsatellite markers to investigate gene flow, genetic variation, and mating behavior of the facultative social parasite Vespula squamosa and its primary host, V. maculifrons. Our analyses of genetic variability uncovered that both species possessed similar amounts of genetic variation and failed to show genetic structure over the sampling area. Our analysis of mating system of V. maculifrons and V. squamosa revealed high levels of polyandry and no evidence for inbreeding in the two species. Moreover, we found no significant differences between estimates of worker relatedness in this study and a previous investigation conducted over two decades ago, suggesting that the selective pressures operating on queen mate number have remained constant. Finally, the distribution of queen mate number in both species deviated from simple expectations suggesting that mate number may be under stabilizing selection. Conclusion: The general biology of V. squamosa has not changed substantially from that of a typical, nonparasitic Vespula wasp. For example, population sizes of the host and its parasite appear to be similar, in contrast to other social parasites, which often display lower population sizes than their hosts. In addition, parasitism has not caused the mating behavior of V. squamosa queens to deviate from the high levels of multiple mating that typify Vespula wasps. This stands in contrast to some socially parasitic ants, which revert to mating with few males. Overall, the general similarity of the genetic structure of V. maculifrons and V. squamosa presumably reflects the fact that V. squamosa is still capable of independent colony founding and thus reflects an intermediate stage in the evolution of social parasitism.
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ItemGene expression and the evolution of phenotypic diversity in social wasps(Georgia Institute of Technology, 2007-05-15) Hoffman, Eric A. ; Goodisman, MichaelBackground: Organisms are capable of developing different phenotypes by altering the genes they express. This phenotypic plasticity provides a means for species to respond effectively to environmental conditions. One of the most dramatic examples of phenotypic plasticity occurs in the highly social hymenopteran insects (ants, social bees, and social wasps), where distinct castes and sexes all arise from the same genes. To elucidate how variation in patterns of gene expression affects phenotypic variation, we conducted a study to simultaneously address the influence of developmental stage, sex, and caste on patterns of gene expression in Vespula wasps. Furthermore, we compared the patterns found in this species to those found in other taxa in order to investigate how variation in gene expression leads to phenotypic evolution. Results: We constructed 11 different cDNA libraries derived from various developmental stages and castes of Vespula squamosa. Comparisons of overall expression patterns indicated that geneexpression differences distinguishing developmental stages were greater than expression differences differentiating sex or caste. Furthermore, we determined that certain sets of genes showed similar patterns of expression in the same phenotypic forms of different species. Specifically, larvae upregulated genes related to metabolism and genes possessing structural activity. Surprisingly, our data indicated that at least a few specific gene functions and at least one specific gene family are important components of caste differentiation across social insect taxa. Conclusion: Despite research on various aspects of development originating from model systems, growth in understanding how development is related to phenotypic diversity relies on a growing literature of contrasting studies in non-model systems. In this study, we found that comparisons of patterns of gene expression with model systems highlighted areas of conserved and convergent developmental evolution across diverse taxa. Indeed, conserved biological functions across species implicated key functions related to how phenotypes are built. Finally, overall differences between social insect taxa suggest that the independent evolution of caste arose via distinct developmental trajectories.
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ItemClines maintained by overdominant selection in hybrid zones(Georgia Institute of Technology, 2001) Goodisman, Michael ; Crozier, Ross H.Hybrid zone models often consider environment-independent selection to operate against all hybrids. However, empirical studies suggest that hybrids may be as fit or fitter than the hybridizing parental taxa in some environments. In this study we develop a novel mathematical model to explore the effects of one form of hybrid superiority on the genetic structure of hybrid zones. Our primary goals were to investigate the allele frequency· clines at a locus experiencing overdominant selection and at a linked neutral or underdominant locus. Our results indicate that overdominant selection results in flat equilibrium allele frequency clines throughout the hybrid zone and an excess of heterozygosity relative to Hardy-Weinberg equilibrium. However, the genetic clines at linked neutral or underdominant loci tend no( to reflect this overdominance even when the loci are tightly linked. Overall, we conclude that overdominance is unlikely to be detected in genetic surveys unless many loci are assayed.
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ItemQueen Dispersal Strategies in the Multiple-Queen Form of the Fire Ant Solenopsis invicta(Georgia Institute of Technology, 1999-06) DeHeer, Christopher J. ; Goodisman, Michael ; Ross, Kenneth G.Newly produced queens in the multiple-queen (polygyne) form of the fire ant Solenopsis invicta show dramatic variation in dispersal patterns, and this variation is influenced by genotypic variation at a single locus associated with the genetic marker Gp-9. Heavy, homozygous Gp-9BB queens exhibit the highest vagility among polygyne queens and are strongly attracted to the open, disturbed-habitat patches that characteristically attract queens of the single-queen (monogyne) form (all of which possess genotype Gp- 9BB). Intermediate weight, heterozygous Gp-9Bb queens exhibit a mixed dispersal strategy: some remain in the area near their natal nest, while others disperse to land in the same disturbed-habitat patches as Gp-9BB queens. Light, homozygous Gp-9bb queens appear to lack the energy reserves needed to take part in mating flights in substantial numbers. Most queens that disperse from their natal nest site apparently fail to infiltrate mature nests to reproduce. However, consistent with the expectations of game-theoretical models for the evolution of dispersal, the low realized success of dispersing queens does not prevent relatively large numbers of them from dispersing. Furthermore, the results presented here are consistent with the hypothesis that the reproductive syndrome that characterizes polygyny in S. invicta is largely controlled by a single locus.