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doi: 10.1046/j.1420-9101.1992.5010013.xpmid: N/A
This paper comments on recently revived discussion about the most adequate definition of homology. Homologues are considered as similarities of complex structures or patterns which are based on a continuity of biological information or instruction. Dependent on the level of comparison four types of homology are defined: (1) Iterative ( = serial = homonomy), (2) ontogenetic, (3) di- or polymorphic, and (4) supraspecific homology. The significance of all four types for evolutionary biology and phylogenetic analysis is outlined.
Boileau, Marc G.; Hebert, Paul D. N.; Schwartz, Steven S.
doi: 10.1046/j.1420-9101.1992.5010025.xpmid: N/A
The estimation of gene flow using gene frequency divergence information has become increasingly popular because of the difficulty involved in the direct determination of gene flow among populations. The present study examined allozyme gene frequencies in populations of eighteen aquatic invertebrate taxa at two sites in northern Canada. Gene frequencies at polymorpic loci were significantly different among 8–31 localized populations of all species at Igloolik and among 10–36 populations at Churchill confirming the generality of gene pool fragmentation in pond-dwelling organisms. Measures of gene flow estimated from gene frequency divergence, which assume that gene frequency distributions are at equilibrium, were inconsistent with the probable dispersal capacities of taxa. This provoked an examination of historical events as alternative explanations. Both theory and computer simulations demonstrated that when populations grow rapidly in size after founding from few individuals, the gene frequency divergence established during colonization is resistant to decay by gene exchange. Our work suggests that gene frequency distributions are often not in equilibrium and that caution should be employed in attempts to infer gene flow from them in natural populations.
Gabriel, Wilfried; Lynch, Michael
doi: 10.1046/j.1420-9101.1992.5010041.xpmid: N/A
A tolerance curve defines the dependence of a genotype's fitness on the state of an environmental gradient. It can be characterized by a mode (the genotype's optimal environment) and a width (the breadth of adaptation). It seems possible that one or both of these characters can be modified in an adaptive manner, at least partially, during development. Thus, we extend the theory of environmental tolerance to include reaction norms for the mode and the width of the tolerance curve. We demonstrate that the selective value of such reaction norms increases with increasing spatial heterogeneity and between-generation temporal variation in the environment and with decreasing within-generation temporal variation. Assuming that the maintenance of a high breadth of adaptation is costly, reaction, norms are shown to induce correlated selection for a reduction in this character. Nevertheless, regardless of the magnitude of the reaction norm, there is a nearly one to one relationship between the optimal breadth of adaptation and the within-generation temporal variation perceived by the organism. This suggests that empirical estimates of the breadth of adaptation may provide a useful index of this type of environmental variation from the organism's point of view.
Rodriguez, Lucy; Sokolowski, Marla B.; Shore, Joel S.
doi: 10.1046/j.1420-9101.1992.5010061.xpmid: N/A
Drosophila melanogaster larvae are used to examine habitat choice behavior and its effect on a component of preadult fitness (pupal survivorship). We established strains of flies by collecting pupae from two microhabitats from an orchard. Strain differences in pupation site choice (on versus off fruit) persisted in a field-like laboratory assay without artificial selection. To produce heterogeneous environments, air temperature and soil water content were varied in these assays. A habitat suitability difference measure was used to determine for each environment, which microhabitat (on or off fruit) resulted in greater pupal survivorship. We found 1) that habitat choice behavior had both plastic and heritable components, 2) that strain-by-environment interactions influenced habitat choice behavior and pupal survivorship and, 3) a significant positive correlation between habitat suitability and larval habitat choice behavior.
Moritz, Robin F. A.; Meusel, Michael S.
doi: 10.1046/j.1420-9101.1992.5010071.xpmid: N/A
A population genetical model is used to investigate the effects of queen and drone fitness and swarming ability on nuclear and mitochondrial (mt) DNA variation in honeybees. The analysis of both types of DNA is particularly useful for a genetic study of the Africanized bee problem in the Americas. Both an analytical model and a Monte Carlo simulation show that even if mtDNA proves to be selectively neutral, Africanized mitotypes are expected at high frequencies because of the more frequent swarming of Africanized honeybees. Since the fitness of Africanized drones is higher than that of European drones, European and African mitotypes are expected to be polymorphic and consequently unreliable as diagnostic tools to discriminate between the two types. Samples of Africanized honeybees in Brazil reveal high mtDNA polymorphisms as predicted by the theoretical models.
Barrett, Spencer C. H.; Harder, Lawrence D.
doi: 10.1046/j.1420-9101.1992.5010083.xpmid: N/A
Genotypes of the mid-styled morph of tristylous Eichhornia paniculata (Spreng.) Solms (Pontederiaceae) exhibit developmental instability in the position of short-level stamens under both field and glasshouse conditions. Elongation of one of the stamens to a position adjacent to the stigma results in automatic self-pollination of flowers. This modification initiates subsequent changes to floral morphology leading to the evolution of predominant self-fertilization in E. paniculata. The influence of genetic, developmental and environmental factors on the expression of stamen instability was investigated in experiments with genotypes from two populations from northeast Brazil and interpopulation hybrids. Genotypes from the three sources differed significantly in the degree and pattern of stamen instability expressed under uniform growing conditions. Significant position effects in the production of modified flowers were detected among genotypes using logistic regression techniques. Modified flowers were most frequently produced on later inflorescence branches in the flowering sequence and at proximal flower positions within an inflorescence branch. However, these patterns were complex, varying among genotypes and experimental conditions. Stamen modification increased in clones grown under water stress or at high temperature, demonstrating a significant environmental component to floral instability.
Weber, Stephanie L.; Scheiner, Samuel M.
doi: 10.1046/j.1420-9101.1992.5010109.xpmid: N/A
The contributions of each chromosome to the traits thorax size and plasticity of thorax size as affected by temperature in Drosophila melanogaster were measured. A composite stock was created from lines previously subjected to selection on thorax size or plasticity of thorax size. A chromosome extraction was performed against a uniform background lacking genetic variation, provided by a stock of marked balancer flies. With regard to amount of plasticity, chromosome I and the balancer stock showed no plasticity, the composite stock showed the greatest plasticity, and chromosomes II and III were intermediate. Chromosome I showed significant genetic variation for thorax size at both 19° C and 25° C, but not for plasticity, while chromosome II showed significant genetic variation for plasticity, but not for thorax size. Chromosome III showed significant genetic variation for both thorax size and plasticity. We tested the predictions of three models of the genetic basis of phenotypic plasticity: overdominance, pleiotropy, and epistasis. The results support the epistasis model, in agreement with earlier work. The amount of developmental noise was correlated with phenotypic plasticity at 25° C, in agreement with earlier work. A negative correlation was found at 19° C for chromosome II, contrary to earlier work.
Allegrucci, Giuliana; Caccone, Adalgisa; Cesaroni, Donatella; Sbordoni, Valerio
doi: 10.1046/j.1420-9101.1992.5010121.xpmid: N/A
In this paper we attempt to investigate relationships between the amount of genetic divergence in nuclear genes and the degree of morphological differentiation for different sets of characters in Dolichopoda cave crickets.Six populations representing five Dolichopoda species from Central and Southern Italy have been studied. The overall genetic divergence at nuclear genes was estimated both by single copy DNA-DNA hybridization and allozyme frequencies at 26 loci. Euclidean distances for two multivariate sets of morphometric variables: one describing body and appendage morphology, the other male epiphallus shape. Results showed a close agreement between the branching patterns of ΔTm values from DNA hybridization and Nei's allozyme distance values. On the other hand, patterns of morphological divergence revealed independent trends, although the branching pattern based on epiphallus morphology matched to some extent the phylogenies inferred from molecular data. The relative value of molecular and morphological characters as reliable phylogenetic tracers was evaluated in relation to their dependence on evolutionary factors.Implications of these findings on the calibration of molecular clocks are also discussed. The absolute rate of molecular change based on scDNA was estimated to be at least 0.98% divergence/my/lineage. This result is in agreement with calibrations attempted on other insects. Estimates of time of divergence based on allozymes (Nei's D) were highly consistent with the estimate from geological data.
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