Larval feeding choices in heliconians: induced preferences are not constrained by performance and host plant phylogeny

Induction of feeding preference, a special type of learning found in the larval stage of herbivorous insects, may be a link between evolutionary changes in host selection behaviour, variation in diet breadth and evolution of host races. However, it has been argued that the phenomenon may be phylogenetically constrained in oligophagous species, which in general use closely related host plants. Also, induction might be tied to performance, being more likely to occur in host plants that are more suitable for larval feeding. If so, induction would be less likely to promote increase in diet breadth. By conducting reciprocal rearing and using leaf disks and double-choice feeding tests, we explored the influence of these factors on the induction of larval feeding preference in the first and last instars of two oligophagous heliconian butterflies (Heliconius erato (Linnaeus) and Heliconius ethilla Godart) in relation to the main (five) passion vine species used as host plants by heliconians in southern Brazil. We also determined the effects of host plants on survivorship, growth rates and size attained in the adult stage for both butterfly species. For comparison, we also carried out a phylogenetic analysis of these plants, based on DNA sequencing. For both heliconian species, we found that feeding preference could be induced for most host plant species tested, in the fifth instar in particular, suggesting that habituation is involved in such cases. There was no indication of the existence of host plant phylogenetic constraints. We also found positive responses for induction on plants that supported poor larval performance. We conclude that induction of larval feeding preference in these cases was not limited by phylogenetic relatedness among the hosts or by their ability to support larval performance, which varies in spatial distribution and abundance in the area. We discuss the possible evolutionary consequences of this behavioural phenomenon in these heliconian butterflies.