Sex-ratio selection in a bivoltine thrips. I. Conditional sex-ratio manipulation and fitness variation

Abstract

Females of Elaphrothrips tuberculatus (Thysanoptera) produce broods of either all males (by viviparity) or all females (by oviparity). Female parents tend to be viviparous (produce males) if their offspring will become relatively large adults, and males gain more in fitness from large size than do females, but in spring, when breeding is synchronous, 1) oviparous and viviparous females do not differ in body size, 2) females tend to viviparous where the fungus upon which they feed is relatively dense and where their offspring will become relatively large adults, and 3) fungus density is highly correlated with male and female offspring size. In summer, when breeding is relatively asynchronous, 1) viviparous females are much larger than oviparous females early (but not late) in the season, 2) large viviparous females begin breeding earlier than smaller ones, 3) offspring developing earlier in the season become larger adults, and 4) a higher proportion of females are viviparous earlier than later. Data suggest that females avoid production of males (the sex with higher variance in expected fitness) when the size of their offspring is relatively uncertain. -from Author