Do males with higher mating success invest more in armaments? An across‐populations study in damselflies

1. Males with higher mating success would be expected to invest more in traits that facilitate mating, leading to steeper allometry of those traits with respect to body size. Across‐population studies following latitudinal variation in male mating success are an excellent study system to address this question. 2. Males of the damselfly L estes sponsa were used to investigate whether the allometric patterns of the length and width of the anal appendages, used for grasping the female prior to mating, corresponded to male mating success. Across a large latitudinal gradient, it was hypothesised that there is a larger investment in the grasping apparatus, i.e. a steeper allometric slope, following higher mating success. 3. Behavioural observations in field enclosures showed the highest mating success at high latitude, while there were no significant differences in mating success between the central and low latitudes. Positive allometry was found for the length of the anal appendages in high‐latitude males, while central‐ and low‐latitude males showed no significant regressions of the traits on body size. 4. These results partially support the hypothesis, as high‐latitude, more successful males invested more in the length (but not the width) of the grasping apparatus than did central‐ and low‐latitude males. Therefore, higher mating success might be facilitated by larger investment in armaments. Intraspecific studies on allometric patterns of traits that participate in mating success might offer new insights into the role of those traits in the reproductive behaviour of a species.