Male nutritional history affects female fecundity in a male-dimorphic mite: Evidence for a nuptial gift?

In male-dimorphic species, males are often either armoured 'majors' that can monopolise access to females, or unarmoured and defenceless 'minors' that cannot. However, majors, unlike minors, have to spend energy to maintain their weaponry. Like-for-like, this could mean that minors have relatively more energy available to increase their reproductive output through e.g. sperm competition, or the transference of nutrients by means of a nuptial gift. Such a fitness advantage to minors could therefore contribute to explaining the coexistence of both morphs in single populations. We tested if food-deprived females of the male-dimorphic bulb mite Rhizoglyphus robini produced more eggs when mated to a minor or to a major male, and whether egg production depended on whether their mates were starved or fed prior to mating. We found no effect of male morph on female fecundity, but females did produce more eggs when mated to previously fed males. We also found that females increased in mass, but males decreased in mass over the course of the experiment. From these observations we infer that fed males are able to transfer nutrients, a nuptial gift, to their mate. This is the first observation to suggest nuptial gift transfer in mites. Though males of both morphs appeared able to produce nuptial gifts; other factors, like habitat complexity, should be considered to identify fitness benefits of minor over major males to understand why the two morphs coexist.