Resource quality affects weapon and testis size and the ability of these traits to respond to selection in the leaf‐footed cactus bug,Narnia femorata

Abstract

The size of weapons and testes can be central to male reproductive success. Yet, the expression of these traits is often extremely variable. Studies are needed that take a more complete organism perspective, investigating the sources of variation in both traits simultaneously and using developmental conditions that mimic those in nature. In this study, we investigated the components of variation in weapon and testis sizes using the leaf‐footed cactus bug, Narnia femorata (Hemiptera: Coreidae) on three natural developmental diets. We show that the developmental diet has profound effects on both weapon and testis expression and scaling. Intriguingly, males in the medium‐quality diet express large weapons but have relatively tiny testes, suggesting complex allocation decisions. We also find that heritability, evolvability, and additive genetic variation are highest in the high‐quality diet for testis and body mass. This result suggests that these traits may have an enhanced ability to respond to selection during a small window of time each year when this diet is available. Taken together, these results illustrate that normal, seasonal fluctuations in the nutritional environment may play a large role in the expression of sexually selected traits and the ability of these traits to respond to selection.

Seasonal Effects on the Population, Morphology and Reproductive Behavior of Narnia femorata (Hemiptera: Coreidae)

“…The extent to which these changes are directly related to host plant phenology, temperature, social environment, or other factors cannot be concluded from this single study. However, many results mirror findings from the laboratory [4,8,33,34,35,36,43,45,57]. Together, the existing work makes a powerful case that host plant phenology can alter growth and development in these insects, and that these phenomena extend to real-world settings.…”

“…Temperature, density, or other environmental factors may add to or interact with effects of nutrition on these populations of insects and warrant further study. Finally, thepresence of some red ripe fruit, particularly at the Agricultural Site, should be a boon for insects fortunate enough to develop on this high-quality resource [8,35,36,45,57]. It may be that these well-nourished individuals existed, but that they were outnumbered by those stranded for part of development without cactus fruit at all.…”

“…As plant quality declines, herbivore mortality can increase [5] and traits vital for reproduction can also be affected [6,7,8]. Many insects temper such fluctuations in diet quality through migration [5,9], while others transition to another type of food plant [10].…”

“…Developmental diet is now known to have a large effect on the phenotypes of adults in many Coreidae, including effects on size, shape, internal anatomy, attractiveness to conspecifics, and mating behaviors [8,35,41,42,43,44]. A developmental diet with cactus fruit is very important for juvenile N. femorata [34].…”

“…A developmental diet with cactus fruit is very important for juvenile N. femorata [34]. Juveniles can feed on the cladodes (pads) of Opuntia spp., but without any fruit during the final stages of development they mature into tiny adults, males have greatly reduced weapon size, and sexual dimorphism is diminished [8,32,45]. Pilot data has suggested that beak (mouthpart) length appears to be phenotypically plastic, changing with the presence and phenology of cactus fruit [46].…”