Summary 1.Additional factors relevant to dispersal are necessary to establish a general theory that can explain the sex-biased dispersal pattern of most taxa. The present study evaluated the influence of pre-dispersal copulation on the evolution of sex-biased dispersal. The influence of fluctuating environment, population size and dispersal cost were also analysed. 2. The simulation models were designed on the basis of the life history of Pieris rapae crucivora , in which female butterflies disperse among local habitats after copulation although male butterflies remain in the natal habitat. In the first model, where females always copulate before dispersal, the evolution of female-biased dispersal was facilitated by the fluctuating environment, but was suppressed by the stable environment. However, the fluctuating environment also suppressed the sex-biased dispersal in the second model where female dispersers always copulate after dispersal. Thus, the interaction between the pre-dispersal copulation and the fluctuating environment is a sufficient condition for the evolution of sex-biased dispersal. 3. The present study is the first report to reveal the important influence of pre-dispersal copulation on the evolution of sex-biased dispersal. In addition, the sexual difference in dispersal pattern increased with the increase of local population size and the decrease of dispersal cost.

Genetic structure of the large Japanese field mouse populations in suburban landscape of West Tokyo, Japan was determined using mitochondrial DNA control region sequence. Samples were collected from six habitats linked by forests and green tract along the Tama River, and from two forests segregated by urban areas from those continuous habitats. Thirty-five haplotypes were detected in 221 animals. Four to eight haplotypes were found within each local population belonging to the continuous landscape. Some haplotypes were shared by two or three adjacent local populations. On the other hand, two isolated habitats were occupied by one or two indigenous haplotypes. Significant genetic differentiation between all pairs of local populations, except for one pair in the continuous habitats, was found by analysis of molecular variance (amova). The geographical distance between habitats did not explain the large variance of pairwise F(ST)-values among local populations. F(ST)-values between local populations segregated by urban areas were higher than those between local populations in the continuous habitat, regardless of geographical distance. The results of this study demonstrated quantitatively that urban areas inhibit the migration of Apodemus speciosus, whereas a linear green tract along a river functions as a corridor. Moreover, it preserves the metapopulation structure of A. speciosus as well as the corridors in suburban landscape.

ABSTRACT-Previous theoretical studies and some empirical studies suggested that the factors which affect female availability should influence male reproductive behavior. We noticed the female post-emergence behavior as one such factor, and investigated how it might influence male reproductive strategy in the butterfly, Pieris rapae crucivora. In the field and the laboratory newly-emerged females stayed on the underside of leaves 2.5 hr after emergence before they flew voluntarily into the open where they are more visible to males. Time spent before initial flight correlated negatively with ambient temperature, and initial flights increased significantly the possibility that the female would be detected by males. To evaluate whether these results could explain the time schedule of males' search for females in the field, female availability was estimated by shifting the observed schedule of female emergence according to the relationship between initial flight and effective cumulative temperature. The resultant female availability correlated well with temporal changes observed in the number of mate-seeking males. Thermal conditions may influence male reproductive behavior via female post-emergence behavior, as well as via male body temperature.

ABSTRACT-It is considered that the mate-locating behaviors of ectothermic insects are constrained by the ambient thermal conditions, since the flight ability depends on the body temperature. However, since ecological factors also influence the mating behaviors, the flight ability would not necessarily determine the time schedule of male mate-locating flight. To reveal how the ambient thermal conditions influence the mating behaviors, we investigated the association of air temperature and sunlight intensity with the diurnal schedule of female-searching behavior in male P. rapae crucivora. In the early morning, the proportion of femalesearching males to basking males increased as the air temperature and sunlight intensity increased. The air temperature was also associated significantly with the diurnal schedule of male female-search on 7 of 8 observation days. The number of female-searching males reached the peak when the air temperature was between 24 and 29°C. On the other hand, the sunlight intensity did not account for the diurnal schedule of male female-search. The associations between the sunlight intensity and male female-search were not consistent among different days. When the air temperature was roughly constant, however, the sunlight intensity was correlated significantly with male activity of female-search. The regression of male activity of femalesearch as a function of sunlight intensity was improved, when it was assumed that the sunlight intensity influenced male behaviors with a delay of 1 to 4 minutes, and when it was assumed that the mean intensity of sunlight for 1 to 9 minutes influenced male behaviors.