Variable Selection and Size-related Mating Patterns in Natural Populations of Elaphrothrips tuberculatus: A Path Analysis

Abstract

-In Elaphrothrips tuberculatus, a thrips with male post-copulatory mate guarding, 6 years of study revealed substantial yearly variation in the intensity of sexual selection for large male body size, the standardized size difference between nonguarding males and other nonguarding males, and the magnitude of size-assortative mating. Among years, the intensity of sexual selection for large male body size was positively correlated with the sex ratio (percent males) and the operational sex ratio (ratio of males to females on eggs), and the size difference between sneak and other nonguarding males was positively correlated with the sex ratio. Path analysis of the relationships among variables indicated that: (1) male size-related mating patterns were influenced primarily by the sex ratio; (2) a high magnitude of size-assortative mating was associated with a high sexual selection intensity, a strong tendency for large oviparous females to initiate breeding earlier than smaller ones, a high correlation between the average sizes of males and females among subpopulations (clusters of hanging dead oak leaves), and a low average number of malefemale pairs in subpopulations; and (3) yearly variation in mating patterns may be ultimately caused by yearly variation during the previous summer in amount of breeding, yearly variation during winter in mortality patterns and yearly variation during spring in dispersal rates and the timing of female breeding.