The elaborate plumage in peacocks is not such a drag

Abstract

One of the classic examples of an exaggerated sexually selected trait is the elaborate plumage that forms the train in male peafowl Pavo cristatus (peacock). Such ornaments are thought to reduce locomotor performance as a result of their weight and aerodynamic drag, but this cost is unknown. Here, the effect that the train has on take-off flight in peacocks was quantified as the sum of the rates of change of the potential and kinetic energies of the body (P CoM ) in birds with trains and following the train's removal. There was no significant difference between P CoM in birds with and without a train. The train incurs drag during take-off; however, while this produces a twofold increase in parasite drag, parasite power only accounts for 0.1% of the total aerodynamic power. The train represented 6.9% of body weight and is expected to increase induced power. The absence of a detectable effect on take-off performance does not necessarily mean that there is no cost associated with possessing such ornate plumage; rather, it suggests that given the variation in take-off performance per se, the magnitude of any effect of the train has little meaningful functional relevance. KEY WORDS: Sexual selection, Pavo cristatus, Flight, Peafowl, Take-off, Performance INTRODUCTIONSexual selection may favour the evolution of extravagant secondary sexual characteristics that are important in mate choice and confer reproductive benefits (Darwin, 1871). There are several theories about the origin and maintenance of such sexual traits, but central to 'handicap' and 'good genes' models of sexual selection is the assumption that such ornaments incur a cost (Zahavi, 1975;Andersson, 1994). It is hypothesised that exaggerated sexually selected traits negatively affect organismal performance (e.g. endurance or escape response) by directly (e.g. through increased predation risk) or indirectly (e.g. through increased metabolic energy expenditure) incurring costs (Kotiaho, 2001). However, while the sexual trait has a negative affect on organismal performance, it is an indicator of overall superior genetic quality and therefore has a net positive effect on fitness [e.g. fecundity or offspring success (Petrie, 1994;Rowe and Houle, 1996;Möller and Alatalo, 1999;Hale et al., 2009;Husak and Swallow, 2011)]. Examples of such traits are found throughout nature, and include the ornate plumage exhibited in the males of some bird species [e.g. long-tailed widowbirds, Euplectes sp. (Andersson, 1982); peafowl, Pavo sp. (Petrie, 1994); and paradise whydas, Vidua sp. (Alatalo et al., 1988)]. It has been suggested that these structures may impair flight performance (Balmford et al., 1993). However, empirical evidence quantifying the costs associated with sexually selected traits is generally lacking (Kotiaho, 2001). Demonstrating whether sexually selected traits do RESEARCH ARTICLEFaculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, UK. incur a cost is necessary to test current theories in evolutionary biology.Arguably one of the most i...

The peacock train does not handicap cursorial locomotor performance

“…Recently, Askew19 found that the train did not reduce take off flight performance, which combined with our results, indicates that neither terrestrial or volant locomotion are negatively impacted by the exaggerated sexually selected train of peacocks. The maintenance of economical locomotion during periods when locomotor behaviour is focused on procuring a mate is likely to be particularly important for reducing the overall costs13.…”

“…Several studies have made inferences about the costs of carrying exaggerated traits by either removing or artificially exaggerating them further51516171819. However, while manipulating sexually selected traits by artificially removing them will produce clearly defined experimental testing of the role of the train it does mean any changes in general body condition, hormone levels, plumage quality or the influence of diurnal rhythms is not taken into account in the animals being investigated.…”

“…However, there is a surprising lack of evidence to support the idea that locomotion in peacocks is in some way affected by sexually selected traits19. Accordingly, here we test the hypothesis that locomotor performance is hindered and the metabolic cost of locomotion is increased by the presence of the peacock train.…”

“…Understanding how animals move is important as all animals must expend energy to locomote in order to ensure predator avoidance, prey capture and reproduction, and they may only have limited reserves to do so14. Previous studies in birds have tended to focus on the influence of sexually selected traits during flight rather than terrestrial locomotion51516171819. Yet, at the very least, exaggerated traits will add extra mass to a terrestrially locomoting animal which should require extra energy expenditure, as energy is needed to produce forces proportional to body mass ( M b )20.…”

Experimental trait mismatches uncover specificity of evolutionary links between multiple signaling traits and their interactions in hummingbirds*

“…However, recent work on peacocks, hummingbirds, and rhinoceros beetles ( Trypoxylus dichotomus ) found that longer, and theoretically more unwieldy, tails/horns do not negatively impact various aspects of flight (Clark and Dudley ; McCullough et al. ; Askew ), potentially dismissing this idea. Instead, the evolved pairing between display flashiness and plumage patch size among species may have arisen because a bigger area of feathers may be more difficult to coordinate and orient to produce uniform/specific flash patterns.…”