Male song as a predictor of the nuptial gift in bushcrickets: on the confounding influence of male choice

In species in which males provide females with nuptial gifts, females can benefit from choosing mates offering the larger or higher quality donation. The existence of such preferences assumes that females can reliably assess a male's gift before mating. However, in certain species, for example most bushcrickets, prior, direct assessment of the nuptial gift is impossible because females choose males before the gift's transfer. Any female assessment of a male's expected donation could therefore only be made via reliable premating cues or signals. In the bushcricket Ephippiger diurnus, males provide females with a large spermatophore at mating, which consists of an ampulla, housing sperm, surrounded by a nutrient-containing spermatophylax that females consume. As female mate choice occurs before transfer of the spermatophore, females may rely on the premating acoustic signals that males emit to attract females. We investigated whether certain parameters of E. diurnus male song could reliably inform females about the material benefits to come. We found no evidence that any male song traits studied (call rate, syllable number, peak frequency) could predict spermatophylax nutritional content. However, our results provide good evidence that male mate choice is likely to occur concomitantly with female choice as the size and quality of the nuptial gift appeared to vary with female traits (age and size). This added presence of male choice would render premating assessment of direct benefits transferred by males effectively impossible for E. diurnus females.