Free amino acids as phagostimulants in cricket nuptial gifts: support for the ‘Candymaker’ hypothesis

Abstract

Nuptial gifts that are manufactured by the male are found in numerous insect species and some spiders, but there have been very few studies of the composition of such gifts. If, as has been proposed recently, nuptial gifts represent sensory traps, males will be selected to produce gifts that are attractive to females but such gifts will not necessarily provide the female with nutritional benefits (the ‘Candymaker’ hypothesis). We examined the free amino acid content of the spermatophylax of the cricket Gryllodes sigillatus (Orthoptera: Gryllidae) using high performance liquid chromatography (HPLC). The spermatophylax (dry weight) consisted of approximately 7 per cent free amino acids. The free amino acid composition was highly imbalanced, with a low proportion of essential amino acids (18.7%) and a high proportion of proline and glycine. The main free amino acids found in the spermatophylax appeared to act as phagostimulants: the duration of feeding on artificial gels by females was positively related to the free amino acid content of the gels. The results therefore suggest that males use free amino acids to ‘sweeten’ a relatively low-value food item. A possible function of glycine in inhibiting female movement is also proposed.

Biting off more than you can chew: sexual selection on the free amino acid composition of the spermatophylax in decorated crickets

“…PC1 had strong positive loadings on all free amino acids in the spermatophylax, and thus represents the total concentration of free amino acids in the spermatophylax. In an earlier study in which artificial gels containing the four most common amino acids in the spermatophylax (PRO, GLY, ARG and ALA) were fed to female G. sigillatus, feeding duration increased with increasing amino acid concentration up to intermediate values, and then decreased slightly thereafter [14]. In contrast to this result, we found that females were less likely to discard the spermatophylax at the lowest and highest total concentrations of free amino acids, and more likely to discard it at intermediate values, indicative of disruptive selection acting on this PC (table 2 and figure 1).…”

“…If, as has been hypothesized, free amino acids in the spermatophylax influence its gustatory appeal to females [13,14], then we would predict a difference in the amino acid profile between those gifts that are discarded by females after mating and those that are fully consumed. To test this prediction, we compared the amino acid profiles of two classes of spermatophylaxes: (i) spermatophylaxes that were discarded by females after mating and (ii) spermatophylaxes that were destined to be fully consumed.…”

“…Warwick et al [13,14] were the first to propose that free amino acids in the spermatophylax influence its gustatory appeal to females. Although the spermatophylax consists largely of water (approx.…”

“…Although the spermatophylax consists largely of water (approx. 83%) [14,15], chemical analysis of the spermatophylax has revealed that approximately 7 per cent of the solid fraction consists of various free amino acids [13,14]. The free amino acids occurring in the greatest concentration were glycine and proline, whereas those amino acids deemed essential [16] were found only at low concentrations.…”

“…Free amino acids are known phagostimulants in insects [17][18][19][20][21], and are used by some species to assess nutritional quality of plant tissue [22]. Artificial 'gels' containing the four most abundant free amino acids found in the spermatophylax and fed to female Gryllodes resulted in increased feeding time relative to females fed control gels [14].…”