Me against who? Male guppies adjust mating behaviour according to their rival’s presence and attractiveness

Abstract

Sexual selection theory suggests that males need to constantly reappraise their mating decisions to take account of the presence and the phenotypes of their rivals. Here we examine this expectation by asking: (i) If the presence of a rival influences male mating behaviour; (ii) How important is the attractiveness of the rival (absolute attractiveness) in shaping male behaviour; and (iii) How does a male's attractiveness in comparison to his rival (relative attractiveness) influence a male's mating decisions. Using the Trinidadian guppy, a species in which female mate choice (based on males’ attractive traits) plays an important role in male mating outcomes, we recorded the frequency of courtship displays and unsolicited attempts by focal males. First, we quantified focal male mating behaviour with and without a rival. Since the probability of a successful mating is, on average, halved by the presence of a rival, we predicted that under competition the focal male would invest more in less costly mating tactic—unsolicited attempts. Second, we examined how the rival's standard length and area of orange coloration mediated focal male mating behaviour. We found that rival presence influenced how focal males responded to females in terms of both mating tactics. However, the rival attractiveness elicited changes only in male courtship display. Focal males increased courtship display rate if his rival was small or if possessed large amounts of orange, regardless of considering rival absolute or relative attractiveness. Our results show that males invest in the costlier mating tactic when there is no rival or in the presence of a smaller rival. Interestingly, they make a similar investment in the presence of an attractive orange rival. Overall, this study highlights the importance of fine‐grained male decisions in mating encounters and shows that mating tactics are differentially shaped by multiple competition risk cues.

The effect of phenotypic heterogeneity on behaviours linked to invasive success

“…Through the same mechanism, heterogeneity in sexual traits influences mating success, reproductive output, population growth, and a population's long‐term fitness (Evans et al, 2004; Fox et al, 2019; Kelly & Adam‐Granger, 2020). These traits are of particular relevance to invasion biology as reproductive traits play a key role in the establishment of introduced species (Allen et al, 2017; Órfão et al, 2019).…”

“…Firstly, it is itself an invasive species that poses a threat to native fish communities (Global Invasive Species Database, 2006). Secondly, male guppies display a diverse range of heritable colour patterns which are linked to reproductive success and offspring viability (Evans et al, 2004; Hughes et al, 2013; Órfão et al, 2019). Female guppies often choose mates based upon the varied expression of male secondary sexual traits, with males possessing novel or rare colour patterns acquiring more mates and siring proportionally more offspring (Hughes et al, 2013).…”