A solution to a sex ratio puzzle in Melittobia wasps

Abstract

The puzzling sex ratio behavior of Melittobia wasps has long posed one of the greatest questions in the field of sex allocation. Laboratory experiments have found that, in contrast to the predictions of theory and the behavior of numerous other organisms, Melittobia females do not produce fewer female-biased offspring sex ratios when more females lay eggs on a patch. We solve this puzzle by showing that, in nature, females of Melittobia australica have a sophisticated sex ratio behavior, in which their strategy also depends on whether they have dispersed from the patch where they emerged. When females have not dispersed, they lay eggs with close relatives, which keeps local mate competition high even with multiple females, and therefore, they are selected to produce consistently female-biased sex ratios. Laboratory experiments mimic these conditions. In contrast, when females disperse, they interact with nonrelatives, and thus adjust their sex ratio depending on the number of females laying eggs. Consequently, females appear to use dispersal status as an indirect cue of relatedness and whether they should adjust their sex ratio in response to the number of females laying eggs on the patch.

How many cooperators are too many? Foundress number, reproduction and sex ratio in a quasi‐social parasitoid

“…We would also expect that, due to limited mating capacity of adult males, the numbers of males in broods would increase gradually as brood sizes increase (as observed in this study and previously by Kapranas et al, 2016;Abdi et al, 2021). Until these possibilities are further evaluated, the extremely biased sex ratios exhibited by Sclerodermus constitute one of the remaining sex allocation puzzles among parasitoid hymenopterans (Abe et al, 2021). future studies will investigate foundress behaviour when provided with such options.…”

“…While formal modelling has recently supported this suggestion qualitatively (Iritani et al, 2021), the predicted reduction in brood sex ratios (an increase in female bias) is insufficient to provide a close match to observations, although it remains possible that refinement of the modelling assumptions employed may provide a better match. Other studies have tested for possible relationships between the kinship of Sclerodermus foundresses (either directly experimentally controlled or inferred from wing dimorphism) and sex ratio, since reproducing with close relative co-foundresses is predicted to select for female bias (Abe et al, 2021;Gardner & Hardy, 2020; see also Abdi et al, 2020c) but have found no effect (Abdi et al, 2020a(Abdi et al, , 2020b.…”

“…The laboratory study of Tang et al (2014) found that on the largest class of hosts presented, per capita reproduction was greatest among groups of 8 foundresses, but larger group sizes are possible. For instance, in the most comparable parasitoid genus, Melittobia Westwood, Abe et al (2021) found groups of up to 36 foundresses in the field. In this study, we extend the evidence for Sclerodermus to groups of between 10 and 55 foundress and explore whether cooperative reproductive system remains functional when there are large numbers of foundresses present and no alternative reproductive resources are available.…”

Density-dependent dispersal promotes female-biased sex allocation in viscous populations

“…Density-dependent dispersal has been observed across diverse taxa, from microbes to mammals [12,[33][34][35][36]. Empirical studies suggest that sex allocation can be shaped by population density and dispersal status [37][38][39], yet the possible role for density-dependent dispersal to modulate the evolution of sex allocation remains to be investigated empirically. Species with readily measurable dispersal and sex phenotypes, such as thrips [12,40], may provide opportunities for empirical testing.…”

Acute and Prolonged Effects of Dermal Suction on Joint Range of Motion and Passive Muscle Stiffness: A Preliminary Study

“…Thereafter, we simplified the models by removing non-significant factors ( α > 0.05) from the least-significant ones with a backward stepwise deletion procedure to arrive at a minimum adequate model [ 19 ]. We evaluated the statistical significance of the fixed effect using a likelihood ratio test to compare the change in deviance between the models [ 20 , 21 ]. To verify whether dermal suction changes joint ROM and SWV, we tested the difference between PRE and the other conditions.…”