Abstract
The size of sexually selected weapons and their performance in battle are both critical to reproductive success, yet these traits are often in opposition. Bigger weapons make better signals. However, due to the mechanical properties of weapons as lever systems, increases in size may inhibit other metrics of performance as different components of the weapon grow out of proportion with one another. Here, using direct force measurements, we investigated the relationship between weapon size and weapon force production in two hindleg weapon systems, frog-legged beetles (Sagra femorata) and leaf-footed cactus bugs (Narnia femorata), to test for performance tradeoffs associated with increased weapon size. In male frog-legged beetles, relative force production decreased as weapon size increased. Yet, absolute force production was maintained across weapon sizes. Surprisingly, mechanical advantage was constant across weapon sizes and large weaponed males had disproportionately large leg muscles. In male leaf-footed cactus bugs, on the other hand, there was no relationship between weapon size and force production, likely reflecting the importance of their hindlegs as signals rather than force-producing structures of male-male competition. Overall, our results suggest that when weapon force production is important for reproductive success, large weaponed animals may overcome mechanical challenges by maintaining proportional lever components and investing in (potentially costly) compensatory mechanisms.
Highlights
Animal weapons have a history of strong selection for large size [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]
We analyzed the relationship between weapon size and weapon force production in two systems, froglegged beetles (S. femorata) and leaf-footed cactus bugs (N. femorata)
In male frog-legged beetles, weapon force output scaled hypoallometrically with weapon size. This is partially consistent with lever theory, where both absolute and relative force output are predicted to decrease as weapons become large [29,38]
Summary
Animal weapons have a history of strong selection for large size [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]. As selection pushes weapons toward larger sizes, they face intrinsic, mechanical challenges that impede their performance as fighting tools [19,29,30,31]. This is because animal weapons, like many other mechanical traits (e.g., jaws of fishes [32,33,34] or jumping legs in insects [35,36,37], are lever systems, the components of which must appropriately interact to achieve high performance (e.g., Fig 1C–1E).
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
