Discriminative host sanctions in a fig-wasp mutualism.

Area of Science:

• Ecology
• Evolutionary Biology
• Mutualism

Background:

• Mutualisms can be unstable due to symbiotic partners cheating (obtaining benefits without reciprocating).
• Hosts often sanction cheats to maintain cooperation, but mechanisms vary.
• Fig-wasp mutualism involves wasps pollinating figs in exchange for reproduction, with potential for wasp exploitation.

Purpose of the Study:

• To investigate fig sanctions (abortion and larval mortality) against cheating wasps in Ficus racemosa.
• To determine how fig abortion and offspring mortality are influenced by pollinator numbers and pollination status.
• To assess the impact of sanctions on wasp fitness and sex ratio manipulation.

Main Methods:

• Experimentally introduced varying numbers of pollen-laden (P+) or pollen-free (P-) female wasps (foundresses) into Ficus racemosa figs.
• Recorded fig abortion rates and offspring production (fitness) per foundress.
• Conducted a second experiment decoupling pollination and oviposition to isolate sanction mechanisms.

Main Results:

• Fig abortion rates were highest with single, pollen-free foundresses and decreased with more foundresses.
• Wasp fitness declined with increased foundress number, particularly in pollen-free figs, due to increased larval mortality.
• Sanctions disproportionately increased mortality of female wasp offspring, leading to male-biased sex ratios in cheated broods.

Conclusions:

• Fig abortion is influenced by both pollinator abundance and pollen presence.
• Sanctions within figs target cheating wasps post-oviposition, reducing their benefits and ability to manipulate sex ratios.
• Discriminative sanctions against cheats likely enhance the stability of the fig-wasp mutualism.