Hilltopping, leks and female choice in the Carpenter bee Xylocopa (Neoxylocopa) varipuncta

The mating system of the Carpenter bee, Xylocopa (Neoxylocopa) varipuncta Patton, closely resembles the leks of certain vertebrates. Males defend hovering stations at small creosote bushes on ridgetops in the Sonoran Desert, as well as at large ironwood trees in dry washes. Ridgetops, like washes, may provide orientation guides for dispersing females, channelling potential mates to waiting males. During the height of the two month flight season, both males and females were more concentrated on the ridge than in the wash. Males were particularly densely aggregated at or near two prominent peaks on the study ridge. At times, two or more males occupied the same creosote bush. Females visited hovering males infrequently, and exhibited a high degree of freedom in mate choice, usually rejecting males after a close inspection. The reduction in territorial intolerance exhibited by some males at ridgetop sites may occur: (1) because of the costs of repelling many intruders and (2) because females may choose among males through direct analysis of male phenotype, rather than by selecting a male on the basis of territory position.