Phenotypic plasticity in a generalist insect herbivore with the combined use of direct and indirect cues

Abstract

Ultimate causes of phenotypic plasticity in visual appearance are frequently related to increasing the degree of crypsis in a way specific to the environment. The cues used to elicit such plastic responses may be both direct (i.e. straightforward background matching) as well as indirect. In the latter case, cues other than the visual signals from of the environment are used to predict the phenotype best corresponding to the particular situation. On the basis of a series of laboratory experiments we show that the remarkable variability in the visual appearance of the larvae of the geometrid moth Ematurga atomaria, though genetically based in part, involves a substantial environmental component. Using multiple correspondence analysis, we transformed the multidimensional variation in colour and pattern into two dimensions interpretable as patterning and darkness. Plastic changes in the darkness of the larvae were elicited by direct cues: the larvae were darker when reared on dark host‐plants. Host‐specific degree of patterning was also induced in absolute darkness which indicates the use of an indirect cue. This was unexpected because the study species is broadly polyphagous, and thus not likely to have evolved adaptations specific to particular host‐plant species. Indeed, the larvae of E. atomaria originating from geographic populations using different host‐plants showed analogous plastic responses which indicates that the link between the indirect cue and visual appearance of the host needs not to be specific to plant species. In an additional experiment, we showed that surface roughness is a likely candidate to serve as the proximate cue for determination of some pattern elements, a case not reported for insect larvae earlier.

Weak and inconsistent associations between melanic darkness and fitness‐related traits in an insect

“…There is a considerable variation in patterning and darkness of the larvae: they range from light green to dark brown in their overall appearance. The variation is continuous, but with some combinations of traits being more common than others (Sandre et al ., ). Part of this variation has been found to be based on plastic responses to host plant‐related environmental factors (Sandre et al ., ).…”

“…In the present paper, we report results of a quantitative‐genetic study designed to investigate correlations between coloration and growth performance in Ematurga atomaria , a geometrid moth with remarkable within‐species variation in larval appearance (Porter, ; Sandre et al ., ). Three generations of the moths were reared in the laboratory, with a half‐sib design being used in the F2 generation.…”

How to become larger: ontogenetic basis of among‐population size differences in a moth

“…Ematurga atomaria (Lepidoptera, Geometridae, Ennominae) is a medium‐sized (wing span 2–3 cm) day‐flying moth frequently abundant in various habitats of temperate Eurasia. The larvae are cryptic (Sandre et al., ), highly polyphagous (Porter, ), and solitary external feeders. The species is univoltine at northern latitudes, with the pupa as the overwintering stage, whereas two generations annually occur in more southern areas (Leraut, ), lowland Georgia included (T. Tammaru, pers.…”

Effect of host species on larval growth differs between instars: The case of a geometrid moth (Lepidoptera: Geometridae)

“…Once again, the offspring of the resulting half-sib and full-sib families were divided between the two host plants: 12 larvae from each brood were reared on bilberry and three on heather. These experiments were part of a quantitative genetics study of body size and larval colouration the results of which have been published or will be published separately (Sandre et al, 2013;and in prep. ).…”

“…This widespread and common species is found in various habitats across Europe, but is particularly abundant on moors and heaths. The highly polyphagous and colour-polymorphic larvae (Leraut, 2009;Sandre et al, 2013) are solitary and invariably go through five instars (Vellau & Tammaru, 2012). In northern Europe, this species is univoltine and larvae are present in July and August.…”