田中 嘉成

A simple quantitative genetic model is proposed to explain the observed genetic correlation structure of a bruchid beetle Callosobruchus chinensis in terms of two underlying variables: the resource acquisition and the resource allocation. Heritabilities and genetic correlations among age-specific fecundities are regarded as consequences of genetic variations of the two variables. Genetic correlations are predominantly positive in both predictions and observations. Nonetheless, comparison between observed and predicted values in heritabilities, genetic correlations, and genetic principal components suggested significant genetic variances both of the resource allocation and the resource acquisition. The prediction of the model is discussed in relation to experimental tests of trade-off in life history evolution.

Animal communication systems (sexual and social communications) may cause an extra selection load on populations because of the cost of the signals. Under environmental deterioration, the cost of signaling must increase, resulting in an evolutionary reduction in the signal if it is maintained by natural selection vs. sexual selection balance. And in turn, the degeneration of the signal tends to reduce the selection load imposed by the cost. But if female preference resides in a population, sexual selection may prevent rapid degeneration of the signal, which is increasingly costly. Hence sexual selection may enhance populational extinction by increasing selection load under environmental changes. This paper evaluates the extra selection load that a communication system suffers when an environment deteriorates or the ecological optimum for a signal changes in the opposite direction to the sexual selection optimum. (C) 1966 Academic Press Limited

Social selection is presented here as a parallel theory to sexual selection and is defined as a selective force that occurs when individuals change their own social behaviors, responding to signals sent by conspecifics in a way to influence the other individuals' fitness. I analyze the joint evolution of a social signal and behavioral responsiveness to the signal by a quantitative-genetic model. The equilibria of average phenotypes maintained by a balance of social selection and natural selection and their stability are examined for two alternative assumptions on behavioral responsiveness, neutral and adaptive. When behavioral responsiveness is neutral on fitness, a rapid evolution by runaway selection occurs only with enough generic covariance between the signal and responsiveness. The condition for rapid evolution also depends on natural selection and the number of interacting individuals. When signals convey some information on signalers (e.g., fighting ability), behavioral responsiveness is adaptive such that a receiver's fitness is also influenced by the signal. Here there is a single point of equilibrium. The equilibrium point and its stability do not depend on the genetic correlation. The condition needed for evolution is that the signal is beneficial for receivers, which results from reliability of the signal. Frequency-dependent selection on responsiveness has almost no influence on the equilibrium and the rate of evolution.

The equilibrium genetic variance of a quantitative trail under mutation-selection balance is analysed using a population genetic model. I assume that mutations have both phenotypic effects on a quantitative trait and deleterious effects on fitness itself. Hence, genetic variance is generated by pleiotropic effects of such deleterious mutations. If the deleterious effect is large, the predicted genetic variance is notably smaller than the equilibrium genetic variance predicted by the mutation-selection balance model with the rare-alleles approximation. The model further suggests that the ratio of the equilibrium genetic variance to the variance of allelic effects of new mutations is proportional to the ratio of total mutation load to the net selection coefficient on new mutations. It is also suggested that the net selection coefficient is equal to the per-generation proportional increment of genetic variance by new mutations. (C) 1996 Academic Press, Inc.

Heritabilities and genetic correlations of life-history characters (age-specific fecundities and longevity) in azuki bean weevils were estimated. Heritability estimates were moderate or high for longevity and several age-specific fecundities including early fecundity. A genetic correlation was highly negative between longevity and early fecundity. The negative genetic correlation supports the antagonistic pleiotropy theory for the evolution of senescence. Inbreeding depression for age-specific fecundities was assayed by comparing full-sib mated inbred lines and crosses. There was no tendency for inbreeding depression of fecundities to increase with age. The stability of inbreeding depression at different ages argues against the hypothesis that deleterious mutations accumulated in later ages are one of the causal factors for the evolution of senescence in this insect.

Heritabilities and genetic correlations of life history characters (pupal weight, age-specific fecundities, and egg weight) of small white butterfly Pieris rapae crucivora are estimated by a quantitative genetic method (sib analysis). The results indicate moderate or high heritabilities and a largely negative genetic correlation in age-specific fecundities.

Age-specific effects of inbreeding on fecundity were assayed for adzuki bean weevil Callosobruchus chinensis by comparing inbred lines and their cross. Four consecutive full-sib matings reduced only 10.3 percent in total fecundity, and did not decrease early fecundity at all until third day from the onset of reproduction. It is suggested that recessive detrimental genes have been eliminated from the early period of adult life span when reproductive value is high. There was a slight tendency that inbreeding depression increased as age proceeded through not statistically significant.