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Abstract A longstanding goal of evolutionary biology is to understand among-individual variation in resource allocation decisions and the timing of these decisions. Recent studies have shown that investment in elaborate and costly weapons can result in trade-offs with investment in testes. In this study, we ask the following questions: At what point plasticity in resource allocation to these different structures ceases during development, if at all? Furthermore, can individuals tailor their reproductive behavior to accompany structural changes? We experimentally addressed these questions in the insect Narnia femorata, quantifying resource reallocation across development for the first time, using a phenotypic engineering approach. To investigate whether allocation plasticity diminishes throughout ontogeny, we induced weapon loss at a range of different developmental stages and examined subsequent testes mass and reproductive behavior. We found that relative testes mass increased as weapon investment decreased, implying a direct trade-off between testes and weapon investment. However, autotomy postadulthood ceased to induce larger testes mass. Intriguingly, losing a weapon while young was associated with extended adult mating duration, potentially enabling compensation for reduced fighting ability. Our results highlight the importance of examining the ontogeny of trade-offs between reproductive traits and the flexibility of the relationship between reproductive morphology and behavior.
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This content will become publicly available on July 1, 2026
Loss of Paired Weapons Leads to Larger Testes and a Lighter Load for Dispersal
ABSTRACT Reproduction is often costly for males, as it may require the growth of structural traits that aid in dispersal to find females, competition over mating opportunities, and ejaculate production. The growth of such traits can be energetically demanding, and these demands often arise concurrently during development. As such, these traits may be especially prone to resource allocation trade‐offs. Yet, such traits are rarely studied in tandem. We designed a study to improve understanding of investment dynamics in flight muscle, a dispersal trait; a sexually selected weapon used in mate competition; and testes used for sperm production. We used the leaf‐footed cactus bug,Narnia femorata(Hemiptera: Coreidae), a species where males use their hindleg as weapons to compete for matings. Males can naturally drop their limbs, and when hindlegs are lost during development, adult males do not grow a weapon. Existing studies have revealed that testes growth increases when investment in weapons ceases. Yet, this work only examined responses to the loss of a single hindleg and limited the scope of traits to testes. Here, we examined weapon loss at two levels and investigated a third trait: dispersal. We found that testes size increased stepwise with limb loss; the loss of one hindleg weapon increased testes mass by around 9%, and two legs increased it by 20%. This intriguing pattern suggests a direct, quantity‐specific trade‐off in tissue development across traits. We also detected only a limited increase in dispersal investment when males did not grow weapons. Yet, dispersal may still be enhanced for those that drop hind legs; those without the substantial weight of hind limbs may have the potential to disperse farther.
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- Award ID(s):
- 2226881
- PAR ID:
- 10629653
- Publisher / Repository:
- John Wiley & Sons
- Date Published:
- Journal Name:
- Ecology and Evolution
- Volume:
- 15
- Issue:
- 7
- ISSN:
- 2045-7758
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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