Rm. Neems et al., LIFETIME REPRODUCTIVE SUCCESS IN A SWARMING MIDGE - TRADE-OFFS AND STABILIZING SELECTION FOR MALE BODY-SIZE, Behavioral ecology, 9(3), 1998, pp. 279-286
Body size in male animals has profound effects on fitness; large males
are commonly favored by sexual selection. However, if body size is a
stable trait, then advantages of large size must be balanced by disadv
antages. In males of the midge Chironomus plumosus we identified the t
rade-offs that result in stabilizing selection on body size. The small
est individuals have the greatest mating advantage in swarms, perhaps
due to their greater agility in capturing females. This measure of mat
ing success in the individual's own swarm was corrected to a populatio
n-level measure to take account of the positive correlation between bo
dy size and swarm size, the relationship between swarm size and mating
success, and the distribution of swarm sizes on an evening. The small
male advantage is maintained in the population-level measure. In cont
rast, large males have greater fecundity and, when unfed, live longer
and can remain longer in the swarm each evening (due to their greater
stamina). Consequently, lifetime reproductive success is greatest for
males of intermediate size, and the most successful body-size class cl
osely matches the most frequent class in the wild. This represents, to
our knowledge, the first evidence of stabilizing selection on body si
ze in males of an insect species, as measured by trade-offs in lifetim
e reproductive success.