Across free-living organisms, the ecology and evolution of offspring morphology is shaped by interactions with biotic and abiotic environments during dispersal and early establishment in new habitats. However, the ecology and evolution of offspring morphology for symbiotic species has been largely ignored despite host-symbiont interactions being ubiquitous in all ecosystems and across all branches of the tree of life. The kingdom Fungi provides an excellent opportunity to address this fundamental knowledge gap since symbiosis has been a major driver in trait evolution of this group. We assembled a database of fungal offspring morphology covering over 26,000 species of free-living to symbiotic fungi, including symbiotic relationships with plants, insects and humans and found more than eight orders of variation in offspring size. Evolutionary shifts in symbiotic status correlated with shifts in spore size, but the strength of this effect varied widely among phyla. Among plant associated fungi, symbiotic status explained more variation than environmental gradients in the current distribution of offspring sizes at a global scale; while being plant-associated limited the dispersal potential of fungal spores: in free-living saprotrophic fungi shifts to smaller spore size correlated with larger species’ extent of occurrence while in plant associated fungi this relationship does not hold. Our work advances life-history theory by highlighting how the interaction between symbiosis and offspring morphology shapes the reproductive and dispersal strategies among living forms.
