Abstract
Phenotypic plasticity can allow animals to adapt their behavior, such as their mating effort, to their social and sexual environment. However, this relies on the individual receiving accurate and reliable cues of the environmental conditions. This can be achieved via the receipt of multimodal cues, which may provide redundancy and robustness. Male Drosophila melanogaster detect presence of rivals via combinations of any two or more redundant cue components (sound, smell, and touch) and respond by extending their subsequent mating duration, which is associated with higher reproductive success. Although alternative combinations of cues of rival presence have previously been found to elicit equivalent increases in mating duration and offspring production, their redundancy in securing success under sperm competition has not previously been tested. Here, we explicitly test this by exposing male D. melanogaster to alternative combinations of rival cues, and examine reproductive success in both the presence and absence of sperm competition. The results supported previous findings of redundancy of cues in terms of behavioral responses. However, there was no evidence of reproductive benefits accrued by extending mating duration in response to rivals. The lack of identifiable fitness benefits of longer mating under these conditions, both in the presence and absence of sperm competition, contrasted with some previous results, but could be explained by (a) damage sustained from aggressive interactions with rivals leading to reduced ability to increase ejaculate investment, (b) presence of features of the social environment, such as male and female mating status, that obscured the fitness benefits of longer mating, and (c) decoupling of behavioral investment with fitness benefits.
Highlights
Many animals exhibit plasticity in their reproductive behavior and/or reproductive investment in response to the other organisms around them, allowing them to allocate resources across mating opportunities in order to maximize lifetime reproductive success (Dewsbury, 1982; Gage, 1995; Kokko & Rankin, 2006; Parker, 1982; Rodriguez, Rebar, & Fowler-Finn, 2013; Wedell, Gage, & Parker, 2002)
The results supported the previous finding that removing one cue of rival presence does not affect the ability of male D. melanogaster to detect rivals and respond to them by extending their subsequent mating duration (Bretman, Westmancoat, et al, 2011)
Together with our results that extended mating duration did not have any observed fitness benefits, these findings suggest that the relationship between cues of competition, behavior, and reproductive success may not be as simple or direct as previously thought
Summary
Many animals exhibit plasticity in their reproductive behavior and/or reproductive investment in response to the other organisms around them, allowing them to allocate resources across mating opportunities in order to maximize lifetime reproductive success (Dewsbury, 1982; Gage, 1995; Kokko & Rankin, 2006; Parker, 1982; Rodriguez, Rebar, & Fowler-Finn, 2013; Wedell, Gage, & Parker, 2002). Redundancy may be incomplete, whereby separate components relay partially overlapping, but not identical, information about the environment (Bretman, Westmancoat, Gage, & Chapman, 2011b; Dore et al, 2018) In this scenario, altering the combination of cue components to which an individual is exposed may result in subtle effects on subsequent phenotypes, with associated fitness consequences. In addition to eliciting equivalent behavioral responses, perceiving any two of the three rival cues appears to result in comparable increases in the number of offspring fathered (Bretman, Westmancoat, et al, 2011) Far this has only been tested in the absence of realized sperm competition; an important facet of the fitness consequences of responding to rival males is not yet known. This would support the idea that the cues of rival presence perceived by male D. melanogaster are redundant
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