Maternal body size affects sex allocation in a gregarious parasitoid

Area of Science:

• * Evolutionary Biology
• * Insect Reproduction
• * Behavioral Ecology

Background:

• * In Hymenoptera (wasps, ants, bees), haplodiploid sex determination means females control offspring sex by fertilizing eggs with stored sperm.
• * Body size is linked to reproductive success, influencing gamete production and potentially sperm management.
• * Understanding how body size affects female reproductive strategies, particularly sex allocation, is crucial in these organisms.

Purpose of the Study:

• * To investigate the influence of male and female body size on offspring production and sex allocation in the parasitoid wasp Nasonia vitripennis.
• * To test the hypothesis that larger females face sperm limitation, impacting their sex allocation decisions, especially when mated with smaller males.

Main Methods:

• * Categorized 80 male and 80 female Nasonia vitripennis into large and small size groups.
• * Created four mating groups: large females with large/small males, and small females with large/small males.
• * Analyzed brood size and offspring sex ratios after females oviposited on 12 host pupae (Sarcophaga bullata).

Main Results:

• * Larger females produced significantly more offspring and a higher proportion of males compared to smaller females.
• * Sex ratios became increasingly male-biased with greater offspring production, suggesting sperm depletion in larger females.
• * Male body size did not influence offspring sex allocation but had a minor positive effect on female offspring production.

Conclusions:

• * Female body size is a critical factor in Nasonia vitripennis reproduction, affecting both fecundity and sex allocation.
• * Sperm depletion significantly constrains sex allocation in larger, more fecund females, leading to male-biased sex ratios as the sperm supply diminishes.
• * The study reveals a complex interplay between body size, fecundity, and sex allocation strategies in haplodiploid insects.