Males missing their sexually selected weapon have decreased fighting ability and mating success in a competitive environment
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Intraspecific competition over access to females has led to a large diversity of animal weapons. Generally, the relative size (and presence) of these weapons is positively correlated with mating success, as individuals with the largest weapons often obtain most of the mates. Despite their importance, individuals in some species can lose their weapons. For example, a crab’s claw can be dropped to escape life-threatening situations and a beetle’s horn can break if it exceeds its mechanical limit. Previous research has shown that individuals missing their weapons are less successful at male-male competition, but few studies have investigated how weapon loss translates to changes in mating behavior and mating success. Here, we investigated how weapon loss affected fighting ability and mating success in the leaf-footed cactus bug Narnia femorata Stål (Hemiptera: Coreidae). In this study, males who lost their sexually selected weapons fought in the same manner as intact males, but were five times less likely to establish dominance. Despite this decrease in dominance, 34% of the weaponless males were still able to access females, and the lack of weaponry did not affect a female’s willingness to mate. Still, weapon loss ultimately decreased mating success by 37% in a competitive environment.
Sexually selected weapons are important for securing access to mates. Thus, it is often assumed that the permanent loss of a sexually selected weapon dramatically reduces, or even eliminates, an individual’s ability to secure matings. In our study, we tested this commonly held assumption. We found that weapon loss decreased both fighting ability and mating success. The observed difference in mating success was not due to female rejection, but instead was likely due to competitive male interactions. These results provide us with a better understanding of the costs associated with permanently losing a sexually selected weapon.
KeywordsAutotomy Fighting behavior Male-male competition Mating behavior Sexual selection
The authors would like to thank the anonymous reviewers, A. Mortensen, C. Howard, L. Cirino, L. Taylor, P. Allen, and R. Kimball for their insightful discussions and/or feedback that led this manuscript to take its current form. We would also like to thank undergraduate researchers I. Meirom and P. Skelly for their help in collecting data. This research was supported by the National Science Foundation grants IOS-1553100 and IOS-0926855 to CWM.
Compliance with ethical standards
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.
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