No sex in fungus-farming ants or their crops

Abstract

Asexual reproduction imposes evolutionary handicaps on asexual species, rendering them prone to extinction, because asexual reproduction generates novel genotypes and purges deleterious mutations at lower rates than sexual reproduction. Here, we report the first case of complete asexuality in ants, the fungusgrowing ant Mycocepurus smithii, where queens reproduce asexually but workers are sterile, which is doubly enigmatic because the clonal colonies of M. smithii also depend on clonal fungi for food. Degenerate female mating anatomy, extensive field and laboratory surveys, and DNA fingerprinting implicate complete asexuality in this widespread ant species. Maternally inherited bacteria (e.g. Wolbachia, Cardinium) and the fungal cultivars can be ruled out as agents inducing asexuality. M. smithii societies of clonal females provide a unique system to test theories of parent-offspring conflict and reproductive policing in social insects. Asexuality of both ant farmer and fungal crop challenges traditional views proposing that sexual farmer ants outpace coevolving sexual crop pathogens, and thus compensate for vulnerabilities of their asexual crops. Either the double asexuality of both farmer and crop may permit the host to fully exploit advantages of asexuality for unknown reasons or frequent switching between crops (symbiont reassociation) generates novel ant-fungus combinations, which may compensate for any evolutionary handicaps of asexuality in M. smithii.

Thelytokous parthenogenesis, male clonality and genetic caste determination in the little fire ant: new evidence and insights from the lab

“…Thelytokous parthenogenesis is relatively common in insects (Normark, 2003), and has already been observed in seven ant species (see references in the study by Himler et al, 2009). On the contrary, the male clonality system demonstrated here is extremely rare (McKone and Halpern, 2003).…”

Mating system and population structure in the desert ant Cataglyphis livida

“…Such an aptitude does occur neither in C. sabulosa, nor in C. livida. To date, queen reproduction by thelytokous parthenogenesis has been documented in three polygynous ants, Wasmannia auropunctata (Fournier et al, 2005) Vollenhovia emeryi (Ohkawara et al, 2006) and Mycocepurus smithii (Himler et al, 2009), and in the monogynous species C. cursor (Pearcy et al, 2004a). The reason for such a difference in reproductive strategies among species remains unknown.…”

Cryptic sexual populations account for genetic diversity and ecological success in a widely distributed, asexual fungus-growing ant

“…The widespread geographic distribution of asexuality and the complete absence of males from field collections and laboratory colonies suggested that M. smithii might be obligately asexual (16,17), and one study proposed that asexuality in this species might be ancient (16). Among bees, wasps, and ants, thelytokous parthenogenesis has so far been observed in the Cape honey bee (18,19) and in 12 distantly related species of ants (17,(20)(21)(22)(23).…”

“…Asexual reproduction by females, or thelytokous parthenogenesis, has recently been reported in queens of the fungusgrowing ant Mycocepurus smithii in three geographically distant populations in Latin America: Puerto Rico (15), Panama (16), and Brazil (17). The widespread geographic distribution of asexuality and the complete absence of males from field collections and laboratory colonies suggested that M. smithii might be obligately asexual (16,17), and one study proposed that asexuality in this species might be ancient (16).…”