Do males bite females' antennae to coerce copulation or to continue mate guarding in Oiceoptoma subrufum (Coleoptera: Silphinae)?

In several species, males frequently immobilize females during copulation. In some species, female immobilization enables males to copulate with unwilling females, while in others, female immobilization prolongs postcopulatory guarding. Male carrion beetles often bite and pull hard on one of the female's antennae during copulatory mounting. Previous descriptive studies have hypothesized that antenna biting is important for postcopulatory guarding in Silphinae. Here, we observed the mating behavior of Oiceoptoma subrufum, to understand the roles of antenna-biting in the initiation and termination of copulation. We compared the success and duration of intromission and pre- and postcopulatory mounting duration between males that did and did not bite female antennae during copulatory mounting. The success and duration of intromission and precopulatory mounting duration were unaffected by antenna biting. However, antenna-biting males mounted females for longer after intromission compared to non-biting males. These results indicate that antenna biting contributes to postcopulatory guarding behavior, not coercive copulation, in O. subrufum.

Japanese queenless ants, Pristomyrmex punctatus, prefer the traces of both nestmates and strangers in nest selection.

Conspecific avoidance may influence the spatial distribution of colonies in some ants. House-hunting ants (Temnothorax albipennis) avoid nesting in areas where non-nestmates have nested previously. However, no reports are available on conspecific avoidance during nest selection in other ants. In the present study, we investigated nest selection in another nomadic species, the Japanese queenless ant, Pristomyrmex punctatus. Two-choice tests revealed that, similar to house-hunting ants, P. punctatus preferred nests soiled by nestmates to clean nests. However, unlike house-hunting ants, P. punctatus also preferred nests soiled by non-nestmates to a clean nest. Given the choice between a nest soiled by nestmates and one soiled by strangers, P. punctatus, unlike house-haunting ants, showed no significant preference. Thus, conspecific avoidance in nest selection was not observed in P. punctatus. Interspecific differences in ecological factors may drive the evolution of different nest selection strategies.

Colony fusion in a parthenogenetic ant, Pristomyrmex punctatus.

In the ant Pristomyrmex punctatus Smith (Hymenoptera: Formicidae), all young workers lay a small number of eggs parthenogenetically. Some colonies consist of monoclonal individuals that provide high inclusive fitness, according to the kin selection theory. However, in some populations, a majority of the colonies contain multiple lineages. Intracolonial genetic variation of parthenogenetic ants cannot be explained by the multiple mating of single founderesses or by the foundation of a colony by multiple foundresses, which are the usual causes of genetically diverse colonies in social insects. Here, we hypothesized that the fusion of established colonies might facilitate the formation of multiclonal colonies. Colony fusion decreases indirect benefits because of the reduction in intracolonial relatedness. However, when suitable nesting places for overwintering are scarce, colony fusion provides a strategy for the survival of colonies. Here, ants derived from different colonies were allowed to encounter one another in a container with just one nesting place. Initially, high aggression was observed; however, after several days, no aggression was observed and the ants shared the nest. When the fused colonies were allowed to transfer to two alternative nests, ants from different colonies occupied the same nest. This study highlights the importance of limiting the number of nesting places in order to understand the genetic diversity of parthenogenetic ant colonies.

The importance of workers for queen hibernation survival in Camponotus ants.

The higher proportion of polygynous ant species in northern areas indicates that cold climates influence queen number per colony. It is unclear, however, what ecological and physiological factors facilitate the dominance of polygynous species in cold climates. This is the case in two common arboreal ants in Japan-Camponotus yamaokai and C. nawai-which are quite similar in morphology, but different in social structure and geographical distribution. Polygynous C. yamaokai inhabits colder areas, whereas monogynyous C. nawai inhabits warmer climates. We compared queen survival in both ants at low temperature to evaluate whether interspecific difference in cold tolerance can explain the geographical distribution. We examined the influence of cohabitation with other individuals, as well as individual cold tolerance. Experimental groups with different caste compositions were prepared and maintained under conditions simulating in the laboratory climates of the northern limit of C. nawai. Wintering experiments revealed that C. yamaokai queens survived longer than C. nawai queens under solitary conditions, although half of the queens died in less than a month, even in C. yamaokai. Queens hibernating with workers survived longer than solitary queens, but queen number did not affect queen survival. Cohabitation with workers allowed 80% of C. yamaokai queens to survive more than two months. Under field conditions, monogynous C. nawai foundresses overwinter without workers, whereas new queens of polygynous C. yamaokai always overwinter with many workers. Thus, the geographical distribution of these ants appears to depend on the overwintering behavior of new queens.

Population structure of the large Japanese field mouse, Apodemus speciosus (Rodentia: Muridae), in suburban landscape, based on mitochondrial D-loop sequences.

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.