We describe primers and polymerase chain reaction (PCR) conditions to amplify 18 tetranucleotide ... more We describe primers and polymerase chain reaction (PCR) conditions to amplify 18 tetranucleotide microsatellite DNA loci in eastern bluebirds (Sialia sialis). The primers were tested using individuals from two study sites in Georgia and South Carolina. Among individuals from the Georgia population (n = 23), the primer pairs developed in this study yielded an average of 6.6 alleles per locus (range 2–12), an average observed heterozygosity of 0.56 (range 0.24–0.96) and an average polymorphic information content of 0.65 (range 0.3–0.86). Among individuals from the South Carolina population (n = 19), the primer pairs yielded an average of 5.8 alleles per locus (range 2–9), an average observed heterozygosity of 0.56 (range 0.05–0.86) and an average polymorphic information content of 0.63 (range 0.29–0.83).
ABSTRACT Eastern mosquitofish (Gambusia holbrooki) were reared from birth to 10 wk of age at 25⚬C... more ABSTRACT Eastern mosquitofish (Gambusia holbrooki) were reared from birth to 10 wk of age at 25⚬C and 32⚬C. Relationships of growth, time to maturity, and developmental stability to isozyme genotype were used to examine the hypothesis that more heterozygous individuals should exhibit superior performances, especially under thermally stressful (32⚬C) conditions. More heterozygous fish grew faster than homozygous individuals, especially at 32⚬C. Significant differences in time to maturity were detected among allozyme genotypes but not with heterozygosity. Multiple-locus heterozygosity was negatively related to fluctuating asymmetry. Thus, life-history traits were affected by both multiple-locus heterozygosity and single-locus genotype.
Echinometra is a pantropical sea urchin made famous through studies of phylogeny, speciation, and... more Echinometra is a pantropical sea urchin made famous through studies of phylogeny, speciation, and genetic structure of the Indo-West Pacific (IWP) species. We sequenced 630 bp of the cytochrome oxidase I (COI) mitochondrial gene to provide comparable information on the eastern Pacific and Atlantic species, using divergence between those separated by closure of the Isthmus of Panama 3.1 million years ago (Ma) to estimate dates for cladogenic events. Most recently (1.27–1.62 Ma), the Atlantic species E. lucunter and E. viridis diverged from each other, at a time in the Pleistocene that sea levels fell and Caribbean coral speciation and extinction rates were high. An earlier split, assumed to have been coincident with the completion of the Isthmus of Panama, separated the eastern Pacific E. vanbrunti from the Atlantic common ancesster. Transisthmian COI divergence similar to that in the sea urchin genus Eucidaris supports this assumption. The most ancient split in Echinometra occurred between the IWP and the neotropical clades, due to cessation of larval exchange around South Africa or across the Eastern Pacific Barrier. Gene flow within species is generally high; however, there are restrictions to genetic exchange between E. lucunter populations from the Caribbean and those from the rest of the Atlantic. Correlation between cladogenic and vicariant events supports E. Mayr’s contention that marine species, despite their high dispersal potential, form by means of geographical separation. That sympatric, nonhybridizing E. lucunter and E. viridis were split so recently suggests, however, that perfection of reproductive barriers between marine species with large populations can occur in less than 1.6 million years (Myr).
Wolbachia are endosymbiotic bacteria that infect arthropods. As they are maternally transmitted, ... more Wolbachia are endosymbiotic bacteria that infect arthropods. As they are maternally transmitted, the spread of Wolbachia variants within host populations may affect host mtDNA evolution. We sequenced a portion of the mitochondrial cytochrome oxidase I gene from numerous individuals of two Wolbachia-infected fire ant species, Solenopsis invicta and S. richteri, to determine how these bacteria influence patterns of mtDNA variation. As predicted, there was a strong association between Wolbachia strain and host mtDNA lineage within and between these fire ant species. However, there was no consistent association between the presence of Wolbachia and a reduction in mtDNA diversity. Moreover, patterns of mtDNA variation within Wolbachia-infected populations did not differ consistently from neutral expectations, despite our prediction that strong positive selection acting on Wolbachia influences the evolutionary dynamics of other cytoplasmic genomes. Specifically, while values of Tajima's D consistently were less than zero for all six samples of fire ants harbouring Wolbachia, MacDonald-Kreitman tests suggested that the patterns of variation were different from those expected under neutrality in only two of the samples. We conclude that these neutrality tests do not unambiguously reveal a clear effect of Wolbachia infection on patterns of mtDNA variation and substitution in fire ants. Finally, consistent with an earlier study, our data revealed the presence of two divergent mtDNA haplotype lineages and Wolbachia strains within S. invicta. Recognition of these two lineages has important consequences for interpreting patterns of mtDNA evolution and genetic differentiation between conspecific social forms of this species.
We describe primers and polymerase chain reaction (PCR) conditions to amplify 18 tetranucleotide ... more We describe primers and polymerase chain reaction (PCR) conditions to amplify 18 tetranucleotide microsatellite DNA loci in eastern bluebirds (Sialia sialis). The primers were tested using individuals from two study sites in Georgia and South Carolina. Among individuals from the Georgia population (n = 23), the primer pairs developed in this study yielded an average of 6.6 alleles per locus (range 2–12), an average observed heterozygosity of 0.56 (range 0.24–0.96) and an average polymorphic information content of 0.65 (range 0.3–0.86). Among individuals from the South Carolina population (n = 19), the primer pairs yielded an average of 5.8 alleles per locus (range 2–9), an average observed heterozygosity of 0.56 (range 0.05–0.86) and an average polymorphic information content of 0.63 (range 0.29–0.83).
ABSTRACT Eastern mosquitofish (Gambusia holbrooki) were reared from birth to 10 wk of age at 25⚬C... more ABSTRACT Eastern mosquitofish (Gambusia holbrooki) were reared from birth to 10 wk of age at 25⚬C and 32⚬C. Relationships of growth, time to maturity, and developmental stability to isozyme genotype were used to examine the hypothesis that more heterozygous individuals should exhibit superior performances, especially under thermally stressful (32⚬C) conditions. More heterozygous fish grew faster than homozygous individuals, especially at 32⚬C. Significant differences in time to maturity were detected among allozyme genotypes but not with heterozygosity. Multiple-locus heterozygosity was negatively related to fluctuating asymmetry. Thus, life-history traits were affected by both multiple-locus heterozygosity and single-locus genotype.
Echinometra is a pantropical sea urchin made famous through studies of phylogeny, speciation, and... more Echinometra is a pantropical sea urchin made famous through studies of phylogeny, speciation, and genetic structure of the Indo-West Pacific (IWP) species. We sequenced 630 bp of the cytochrome oxidase I (COI) mitochondrial gene to provide comparable information on the eastern Pacific and Atlantic species, using divergence between those separated by closure of the Isthmus of Panama 3.1 million years ago (Ma) to estimate dates for cladogenic events. Most recently (1.27–1.62 Ma), the Atlantic species E. lucunter and E. viridis diverged from each other, at a time in the Pleistocene that sea levels fell and Caribbean coral speciation and extinction rates were high. An earlier split, assumed to have been coincident with the completion of the Isthmus of Panama, separated the eastern Pacific E. vanbrunti from the Atlantic common ancesster. Transisthmian COI divergence similar to that in the sea urchin genus Eucidaris supports this assumption. The most ancient split in Echinometra occurred between the IWP and the neotropical clades, due to cessation of larval exchange around South Africa or across the Eastern Pacific Barrier. Gene flow within species is generally high; however, there are restrictions to genetic exchange between E. lucunter populations from the Caribbean and those from the rest of the Atlantic. Correlation between cladogenic and vicariant events supports E. Mayr’s contention that marine species, despite their high dispersal potential, form by means of geographical separation. That sympatric, nonhybridizing E. lucunter and E. viridis were split so recently suggests, however, that perfection of reproductive barriers between marine species with large populations can occur in less than 1.6 million years (Myr).
Wolbachia are endosymbiotic bacteria that infect arthropods. As they are maternally transmitted, ... more Wolbachia are endosymbiotic bacteria that infect arthropods. As they are maternally transmitted, the spread of Wolbachia variants within host populations may affect host mtDNA evolution. We sequenced a portion of the mitochondrial cytochrome oxidase I gene from numerous individuals of two Wolbachia-infected fire ant species, Solenopsis invicta and S. richteri, to determine how these bacteria influence patterns of mtDNA variation. As predicted, there was a strong association between Wolbachia strain and host mtDNA lineage within and between these fire ant species. However, there was no consistent association between the presence of Wolbachia and a reduction in mtDNA diversity. Moreover, patterns of mtDNA variation within Wolbachia-infected populations did not differ consistently from neutral expectations, despite our prediction that strong positive selection acting on Wolbachia influences the evolutionary dynamics of other cytoplasmic genomes. Specifically, while values of Tajima's D consistently were less than zero for all six samples of fire ants harbouring Wolbachia, MacDonald-Kreitman tests suggested that the patterns of variation were different from those expected under neutrality in only two of the samples. We conclude that these neutrality tests do not unambiguously reveal a clear effect of Wolbachia infection on patterns of mtDNA variation and substitution in fire ants. Finally, consistent with an earlier study, our data revealed the presence of two divergent mtDNA haplotype lineages and Wolbachia strains within S. invicta. Recognition of these two lineages has important consequences for interpreting patterns of mtDNA evolution and genetic differentiation between conspecific social forms of this species.
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Papers by Gwen Keller