Male pheromone composition depends on larval but not adult diet in Heliconius melpomene

Abstract

1. Condition-dependent traits can act as honest signals of mate quality, with fitter individuals being able to display preferred phenotypes. Nutrition is known to be an important determinant of individual condition, with diet known to affect many secondary sexual traits. 2. In Heliconius butterflies, male chemical signalling plays an important role in female mate choice. Potential male sex pheromone components have been identified previously, although it is unclear what information they convey to the female. 3. In the present study, the effect of diet on androconial and genital compound production is tested in male Heliconius melpomene rosina. To manipulate larval diet, larvae are reared on three different Passiflora host plants: Passiflora menispermifolia, the preferred host plant, Passiflora vitifolia and Passiflora platyloba. To manipulate adult diet, adult butterflies are reared with and without access to pollen, a key component of their diet. 4. No evidence is found to suggest that adult pollen consumption affects compound production in the first 10 days after eclosion. There is also a strong overlap in the chemical profiles of individuals reared on different larval host plants. The most abundant compounds produced by the butterflies do not differ between host plant groups. However, some compounds found in small amounts differ both qualitatively and quantitatively. Some of these compounds are predicted to be of plant origin and the others synthesised by the butterfly. Further electrophysiological and behavioural experiments will be needed to determine the biological significance of these differences.

Keywords: Chemical signalling; Lepidoptera; effect of diet; host plant; mate choice; pollen feeding; sexual selection.

Figure 1

Larval host plant affects forewing length of Heliconius melpomene male adults (anova, d.f. = 2, F = 3.755, P = 0.032). Post hoc testing using Tukey's honestly significant difference found no significant pairwise differences between groups.

Figure 2

Non‐metric multidimensional scaling (NMDS) plot illustrating in three dimensions the overlapping variation in chemical compounds of male Heliconius melpomene raised on three different Passiflora species. Passiflora menispermifolia is the preferred host plant of this species. (a) Androconial compound bouquets do not differ significantly after 10 days. Stress = 0.140. (b) Genital compound bouquets do not differ significantly after 10 days. Stress = 0.098. [Colour figure can be viewed at wileyonlinelibrary.com].

Figure 3

Non‐metric multidimensional scaling (NMDS) plot illustrating in three dimensions the overlapping variation in chemical compounds of male Heliconius melpomene raised with or without pollen. (a) Androconial compound bouquets do not differ significantly after 10 days. Stress = 0.131. (b) Genital compound bouquets do not differ significantly after 10 days. Stress = 0.108. [Colour figure can be viewed at wileyonlinelibrary.com].