Showing papers by "Roger K. Butlin published in 1998"
TL;DR: Both COI and ITS1 evolve half as fast, at most, in darwinulids as in other invertebrates, and molecular evolution has significantly slowed down in ITS1 of D. stevensoni relative to other darwynulids.
Abstract: Genetic variability of the nonmarine ostracod speciesDarwinula stevensoni was estimated by sequencing part of the nuclear and the mitochondrial genome. As Darwinulidae are believed to be ancient as...
132 citations
TL;DR: Overall, the ostracods provide an excellent system in which to study the evolution of reproductive modes and molecular data suggest that some clonal lineages are surprisingly old.
Abstract: Asexual reproduction has evolved repeatedly in nonmarine ostracods and takes a variety of forms from ancient asexuals to species in which sexual and asexual lineages coexist. Clonal diversity is highly variable. There is evidence that some of this diversity is maintained by ecological differentiation. Hybridization between asexual females and males, of the same or related species, contributes to clonal diversity. Molecular data suggest that some clonal lineages are surprisingly old (more than 5 Myr). In the ancient asexual Darwinula stevensoni, from a lineage that has apparently been without sex for more than 100 Myr, a remarkable lack of sequence variation in ITS1 may be explained by occasional automixis, gene conversion or somatic recombination, or by efficient DNA repair. Overall, the ostracods provide an excellent system in which to study the evolution of reproductive modes.
103 citations
TL;DR: It is suggested that allozyme variability is a poor predictor of genetic variation in quantitative traits within populations, but is a better predictor of general phenotypic divergence and of postzygotic isolation between populations or species.
Abstract: Species are the units used to measure ecological diversity and alleles are the units of genetic diversity. Genetic variation within and among species has been documented most extensively using allozyme electrophoresis. This reveals wide differences in genetic variability within, and genetic distances among, species, demonstrating that species are not equivalent units of diversity. The extent to which the pattern observed for allozymes can be used to infer patterns of genetic variation in quantitative traits depends on the forces generating and maintaining variability. Allozyme variation is probably not strictly neutral but, nevertheless, heterozygosity is expected to be influenced by population size and genetic distance will be affected by time since divergence. The same is true for quantitative traits influenced by many genes and under weak stabilizing selection. However, the limited data available suggest that allozyme variability is a poor predictor of genetic variation in quantitative traits within populations. It is a better predictor of general phenotypic divergence and of postzygotic isolation between populations or species, but is only weakly correlated with prezygotic isolation. Studies of grasshopper and planthopper mating signal variation and assortative mating illustrate how these characters evolve independently of general genetic and morphological variation. The role of such traits in prezygotic isolation, and hence speciation, means that they will contribute significantly to the diversity of levels of genetic variation within and among species.
61 citations
TL;DR: Nymph-to-adult survival of the cross classes was found to be highly correlated with mean weight change of the adults, and results are discussed in relation to a presumed host shift from Leersia to rice.
Abstract: We studied the genetic architecture of host plant adaptation in two populations of brown planthopper Nilaparvata lugens (Homoptera: Delphacidae): one feeding on cultivated rice Oryza sativa and the other feeding on a weed grass Leersia hexandra. Proportional weight change, survival and development time of inbred Leersia- and rice-feeding lines, F1, F2, and backcross classes have been examined. Most of the performance differences among populations seem to be controlled by a few genes. Dominance of rice population alleles over Leersia population alleles was quite strong, and there was evidence for epistatic interaction. Nymph-to-adult survival of the cross classes was found to be highly correlated with mean weight change of the adults. These results are discussed in relation to a presumed host shift from Leersia to rice.
57 citations
TL;DR: The results reported here show that, like performance, oviposition preference has a simple genetic basis, but in this case there is no evidence of directional dominance, sex linkage, non–allelic interaction or genotype–environment interaction.
Abstract: We have previously analysed the genetic architecture of host-associated performance differences between stocks of the brown planthopper, Nilaparvata lugens (Homoptera: Delphacidae), derived from two host plants: cultivated rice variety TN1 and the semi-aquatic weed Leersia hexandra. It has been established that performance is influenced by a small effective number of loci (1 to 3), with dominance in the direction of the rice population. The results reported here show that, like performance, oviposition preference has a simple genetic basis, but in this case there is no evidence of directional dominance, sex linkage, non-allelic interaction or genotype–environment interaction. The simple genetic architecture of host-associated performance and oviposition preference are as expected if there was a sympatric host shift, most probably from Leersia to rice. However, contrary to the theoretical expectation from models of sympatric host-race formation, there was no detectable genetic association between the traits. The fact that individual females tend to distribute their eggs between plants may have helped to promote a host shift despite this lack of association.
56 citations
Journal Article•
TL;DR: Substantial genetic divergence was found not only between these species but also between the Mopti and Forest chromosomal forms of An.
Abstract: The potential of microsatellites as population genetic markers in the malarial vectors Anopheles gambiae and Anopheles arabiensis was assessed using 4 loci. Substantial genetic divergence was found not only between these species but also between the Mopti and Forest chromosomal forms of An. gambiae, demonstrating that microsatellites do have the power to detect barriers to gene flow in these mosquitoes. However, application and interpretation of microsatellites was not necessarily straightforward. Despite the use of semiautomated fluorescent technology that enabled fragment sizes to be determined precisely, some difficulty was encountered in allele classification. Sequence analysis revealed insertions/deletions and base changes in the flanking regions of the microsatellite as the probable cause of this problem. The implications of this and other potential pitfalls in the use of microsatellites to study vector populations are discussed.
22 citations
01 Jan 1998
22 citations