Carotenoid‐based colour polyphenism in a moth species: search for fitness correlates

Abstract

Carotenoid‐based integumental coloration is often associated with individual performance in various animals. This is because the limited amount of the pigment has to be allocated to different vital functions. However, most of the evidence for the carotenoid‐based trade‐off comes from vertebrate studies, and it is unclear if this principle can be applied to insects. This possibility was investigated in Orgyia antiqua L. (Lepidoptera: Lymantriidae). The larvae of this species are polyphenic in their coloration, varying from a highly conspicuous combination of yellow hair tufts on black background to cryptic appearance with brown hair tufts. The conspicuous larvae are aposematic, advertising their aversive hairiness. The maintenance of different colour morphs in O. antiqua requires explanation, as an aposematic signal is expected to evolve towards monomorphism. Chromatographic analysis showed that the yellow coloration of the hair is based on the carotenoid pigment lutein (α‐carotene‐3,3’‐diol). The colour of hair tufts was dependent on their carotenoid content. This justifies an expectation of carotenoid‐based physiological trade‐offs between aposematic coloration and individual performance. To test this hypothesis, we monitored life histories of differently coloured larvae reared on various host plants, recording their body sizes, growth rates, and mortalities in each instar. There was a significant but relatively low heritability of tuft coloration, which allowed us to expect environmental effects. We found no phenotypic associations between hair tuft colour and performance indices in O. antiqua larvae, neither did the quality of host plant affect the frequency of colour morphs. However, the frequency of colour morphs differed between larval instars. Our results suggest that carotenoid‐mediated physiological trade‐offs are not involved in the maintenance of colour morphs in O. antiqua larvae, and factors other than individual condition should be responsible for the observed variability.

Complex effects of parasitoids on pharmacophagy and diet choice of a polyphagous caterpillar

“…Pigments such as carotenoids act to add coloration to the insect integument (Sandre et al 2007), and a general association between dark integument and a reduced likelihood of mortality from parasitoids has been observed in a natural assemblage of tree-feeding caterpillars (Barbosa and Caldas 2007). In addition, Ojala et al (2005) found that arctiid larvae consuming plant diets with high carotenoid concentrations had increased melanization responses.…”

Size-dependent colouration in larvae of Orgyia antiqua (Lepidoptera: Lymantriidae): A trade-off between warning effect and detectability?

“…However, we were unable to demonstrate an effect of host plant on larval colour pattern (Sandre et al, 2007), nor was the colour pattern dependent on rearing temperature (Sandre et al, in press). Notably, however, the frequency of colour morphs was found to differ between larval instars: most typically (but not invariably) a larva is pied in its 4th instar, bright in the 5th, and dull in the 6th instar (Sandre et al, 2007) with the larvae switching from one morph to another in connection to moulting. From the data analysed at the level of particular instars, it remained unclear if such a pattern is primarily attributable to larval instar, body size, or sex.…”

“…In holometabolous insects at least, it is common that younger, smaller-bodied developmental stages are cryptic, and the aposematic species acquire their typical warning colouration in their later larval instars, or in the adult stage (Bernays & Montllor, 1989;Ulmer et al, 2003;Sandre et al, 2007). However, following the rationale of the trade-off hypothesis, one should expect also an ontogenetic change in the opposite direction, i.e.…”

“…In a previous study (Sandre et al, 2007), we showed that the colour polyphenism in O. antiqua is proximately based on individually variable concentrations of a carotenoid pigment (lutein). The variation in the colouration has both a genetic and an environmental component.…”

“…These were carried out in summers of 2002 and 2003, in Tartu, Estonia. The larvae of O. antiqua of Estonian and Finnish origin (599 in total, offspring of 20 females) were reared singly in 50 ml plastic vials, they were fed ad libitum with the leaves of their host plants (most on Betula pendula, others on Salix caprea, S. myrsinifolia, S. viminalis, Quercus robur, Cotoneaster lucidus) which were renewed regularly (see Sandre et al, 2007, for further technical details). The insects were monitored throughout their larval lives, and weighed during the inactivity periods preceding each larval moult, to obtain individual-specific initial weights of each instar.…”