Cryptic sex and many-to-one coevolution in the fungus-growing ant symbiosis.

The fungus-growing ants have long provided a spectacular example of coevolutionary integration. Their ecological success is thought to depend largely on the evolutionary alignment of reproductive interests between ants and fungi after vertical transmission and the ancient suppression of fungal sexuality. In the present study we test these assumptions and provide the first evidence of recombination in attine cultivars, contradicting widely held perceptions of obligate clonality. In addition, we document long-distance horizontal transmission of symbionts between leaf-cutter ant species on mainland Central America and South America and those endemic to Cuba, suggesting both lack of pairwise coevolutionary specificity in ant/cultivar interactions and dispersal of symbionts independent of their ant hosts. The coevolution between leaf-cutters and their fungal symbionts is thus not reciprocally pairwise. Rather, a single widespread and sexual fungal symbiont species is engaged in multiple interactions with divergent ant lineages. Strict fungal clonality and vertical transmission evidently have not played a critical role in the long-term evolutionary or ecological success of this well known mutualism.