A costly chemical trait: phenotypic condition dependence of cuticular hydrocarbons in a dung beetle

Abstract

Chemical traits are increasingly recognized as important cues used in mate choice. For example, the cuticular hydrocarbons (CHCs) of insects have been shown to influence mating success in a range of taxa. Less is known, however, about how CHCs are expressed in proportion to an individual's condition, and consequently whether CHCs can function as condition-dependent signals of quality. We investigated this question using the dung beetle, Onthophagus taurus. CHCs are subject to sexual selection in this species through mate choice. A dietary manipulation revealed condition dependence of CHC expression for both sexes: dietary restriction decreased overall CHC production and altered the composition of CHCs. Furthermore, CHC production was associated with a measure of condition in beetles fed a limited diet but not those fed ad libitum. These results implicate a resource cost to CHC production that is likely to result in trade-offs with other fitness components in this species, as these respond similarly to a dietary restriction. The CHC profiles showed sexual dimorphism: males produced more CHCs and the sexes differed in the blend of compounds they produced. There was evidence for a male dimorphism in the CHC profile, in line with the presence of the alternative reproductive tactics (minor sneaks and major fighters) in this species. However, rather than mimicking a female CHC profile, minor males differed more from females than major males. Our results suggest that CHCs are a costly trait in O. taurus that has the potential to act as a condition-dependent signal of quality.

Rhinoceros beetle (Trypoxylus dichotomus) cuticular hydrocarbons contain information about body size and sex

“…In dung beetles CHCs are also different across male size and morphotype. This variation could be a signal to other conspecifics or could be due to different desiccation risks for the different morphs [ 22 ]. In flour beetles, the amount of CHCs produced (which was not measured in our study) is correlated with both body size and fighting ability and seems to be under directional selection.…”

“…In contrast to sex and size, we find no evidence that CHCs reflect short term condition ( Fig 4 ). In some other systems CHCs can change quickly to reflect changes in condition, diet, or social hierarchy [ 22 , 24 , 25 ]. It is possible that the condition variation in our beetles was not large enough to affect CHCs.…”

Female mate choice is affected by male condition but not female condition in an assassin bug

“…A. venator , however, has no remarkable sexually exaggerated morphology (Katti et al, 2015b). In several insects, behavioural and chemical traits are influenced by adult nutritional conditions (Berson & Simmons, 2018; Holzer et al, 2003; Kotiaho et al, 2001). These traits, such as calling song, courtship display, cuticular hydrocarbons, or pheromones, act as sexual signals and exhibit heightened condition dependence (Holzer et al, 2003; Kotiaho, 2002; Rantala et al, 2003; Steiger & Stökl, 2014).…”

The role of diversity, body size and climate in dung removal: A correlative and experimental approach

“…We used pronotum width as a proxy for the body size of dung beetles (Berson & Simmons, 2018; Tocco et al, 2019), which we measured using a measuring ocular in a Nikon SMZ 745 stereomicroscope. On each study plot, we took measurements of 10 individuals per species; if there were fewer than 10 individuals, all individuals were measured.…”