Evolution of Moth Dancing
Rota and Wagner (R&W) provide good experimental data supporting the hypothesis that the movements and wing pattern display performed, while perching on leaves, by moths of the genus Brenthia helps them mimic jumping spiders, thus increasing their chances of escaping predation. However, this study leaves open one intriguing evolutionary question about this behaviour (called “peacock display” by Aiello and Becker [1]).
It is possible that jumping spider predation is responsible of both the evolutionary origin and the elaboration and selective maintenance of the “peacock display”. An environment with a high risk of predation by jumping spiders could favour the evolution of the “peacock display” in both sexes to decrease their chances of being captured. A high risk of spider predation is important to explain why the “peacock display” is performed upon alighting and in the absence of spiders [1]; it also explains why moths performing the “peacock display” are favoured by selection despite the probably high energy costs they pay. However, this explanation leaves open the question why moths of both sexes spend so much time perching (and, therefore, “displaying”) on vegetation (“Displays may be repeated for hours at a time…”; [1: p. 57]). The facts suggest that resting, basking or host searching are not the functions of this behaviour for the following reasons. Contrary to what happens during the “peacock display”, during resting and basking lepidopterans stay almost motionless most of the time. On the other hand, with exception of the, probably few, species in which males defend territories at host plants [2], only female Lepidoptera search for host plants. Furthermore, it is unlikely that females (and males) need to “taste” the plant surface for hours to assess their quality. Additionally, although not explicitly stated, it seems that, at least in some cases, the plants on which Brenthia perch are not their host plants.
The absence of food resources at the perching sites, the location of these sites in conspicuous places (“…males and females perch on upper surfaces of vegetation…”; [R&W: p. 2]), and the considerable amount of time spent in these sites, are consistent with the hypothesis that perching sites are display sites. Therefore, according to this hypothesis, the “peacock display” has a double function: jumping spider mimicry and display behaviour. Display behaviour could have at least two, non-mutually exclusive, social functions: territory defense, and attraction/courtship of mates. A problem with this hypothesis is that non-resource based territoriality in Lepidoptera is considered a mating strategy employed by males to increase their mating rates, and males are usually considered the active sex in mate attraction and courting [3], whereas the “peacock display” is performed by both sexes. However, the high investment made by male Lepidoptera in ejaculate production [3] suggests that the potential reproductive rates of males and females could be similar in some species, which, therefore, should be good candidates for the evolution of mutual mate attraction, courtship and choice. Therefore, this hypothesis predicts that Brenthia males invest particularly high amounts of resources during copulation.
It is interesting to consider how the “peacock display” could have evolved in the light of the previous hypothesis. On the one hand, it could have been originally a type of social display that later was modified to also accomplish a predation avoidance function by the selection exerted by jumping spiders. On the other hand, the “peacock display” could have been originally a predator avoidance strategy that was later incorporated or turned into a social display. Finally, it could be useful to assess if the above hypotheses help us understand the different types of dancing behaviour exhibited by moths [1, 4, R&W].

References
1. Aiello A, Becker VO (2004) Display of the “Peacock Moth”: Brenthia spp. (Choreutidae: Brenthiinae). J Lep Soc 58: 55-58.
2. Lederhouse RC, Codella SG, Grossmuller DW, Maccarone AD (1992) Host plant-based territoriality in the white peacock butterfly, Anartia jatrophae (Lepidoptera: Nymphalidae). J Insect Behav 5: 721-728.
3. Thornhill R, Alcock J (1983) The Evolution of Insect Mating Systems (Harvard University Press, Cambridge, Mass).
4. Kawahara AY, Adamski D (2006) Taxonomic and behavioral studies of a new dancing Beltheca Busck (Lepidoptera: Gelechiidae) from Costa Rica. Proc Entomol Soc Wash 108: 253-260.