(SSD), male contest competition favours smaller male
size because smaller males are more aggressive (Schulte-
Hostedde & Millar 2002). In these systems, selection for
larger or smaller male size through male contest competition
is offset by opposing natural or sexual selection on
male body size (Schulte-Hostedde & Millar 2002; Schulte-
Hostedde et al. 2002). For instance, in the case of the
web-building spider Stegodyphus lineatus, smaller, early
maturing males have an advantage obtaining matings
with virgin females early in the breeding season even
though larger males win physical contests over access to
mates (Maklakov et al. 2004). Male size is consequently
under balancing selection, while selection for fecundity
favours larger female size, thereby maintaining femalebiased
SSD (Schulte-Hostedde et al. 2002; Maklakov et al.
2004). As these contrasting examples show, the role of
body size in male contest competition in species with
female-biased SSD remains controversial, but has so far
been examined in very few species, and especially few
vertebrates.