MALE MATING SUCCESS AND SURVIVAL IN THE FIELD WITH RESPECT TO SIZE AND COURTSHIP SONG CHARACTERS IN DROSOPHILA-LITTORALIS AND D-MONTANA (DIPTERA, DROSOPHILIDAE)

We investigated the importance of male song and morphological characte rs to the male mating success in a two-year field study in natural pop ulations of D. littoralis and D. montana. We compared the properties o f mating flies with those of a random male sample taken at the same ti me and place. In D. littoralis the male's size had no effect on his ma ting success, while in D. montana small males had a mating advantage i n the field during the first study year. Females preferred males with short sound pulses in both species. We also examined the relationship between male morphological and song characters and viability by collec ting male flies in late summer and comparing the means of male charact ers to those of overwintered flies the next spring. In D. littoralis m ale size had no effect on overwinter survival. In D. montana large fli es survived better than small flies. In both species the shifts in son g characters during the winter dormancy were opposite to those caused by sexual selection. Our results, accordingly, imply a possible balanc e between the forces of sexual and natural selection, which act in opp osing directions on attractive male traits.