Attine Ants–Usurping the Throne

IN THE PAST week or so I’ve been writing about the attine ants, which have a complicated mutualistic network combining cultivated fungi and actinomycete bacteria, and are parasitized by Escovopsis fungi and perhaps black yeasts as well! Today I’m writing about the attine ants again, but along a very different angle. In this case this paper examines the influence of evolution upon reproductive behavior. I actually ran across the paper by accident, having previously planned to write about a paper on evolution and reproductive behavior in humans. This paper nicely transitions between these two themes.

Among organisms in general it is a bad idea evolutionarily to abandon breeding in favor of helping another individual raise its offspring. There are examples of social cheaters among groups as different as myxobacteria, slime molds, vertebrates, and insects. The myxobacteria and slime molds are bacteria and eukaryotes respectively that have converged upon a similar lifecycle. These are organisms capable of lone existence, but which mass together during unfavorable conditions to produce a stalk that launches spores. Ideally every strain in the group will be represented equally in the spores produced, but some cheater strains are able to produce more than their share of spores. Among vertebrates, there are examples in many groups of species that parasitize the nests of others, foisting off their young upon an unsuspecting individual. Cowbirds and cuckoos are well known among the birds, and cuckoos gave their name to the cuckoo catfish, which parasitizes cichlids. A similar parasitism is seen among insects where some wasp species will infiltrate another species nest and lay their eggs. The ants take this type of parasitism even further, with some species going to war against others to capture their larvae, which are raised in their captor’s colony and tend their brood. But the type of reproductive cheating occurring in attine ants is different from all of these!

Attine Ants–Yet Another Symbiont?

ATTINE ANTS have been a theme at my blog recently. They first showed up in a discussion of their evolutionary tree, then in a post examining their relationship with the actinomycete bacteria that help protect their fungal gardens from parasites. In my reading I stumbled across the article that I will write about today, which seems to have discovered another part to the attine ant symbiosis. As of now this is the sole report on the occurrence of black yeasts living apparently parasitically on the attine ants, reliant upon the cuticular crypts that normally house helpful actinomycetes.

Leaf-Cutter Ants Ally Opportunistically with Actinomycetes

WHILE THE ATTINE ants are not well-studied, I posted this week about a study into their evolution that revealed the history of innovations in their cultivation of fungus. The attine ants are part of a symbiotic network between the ants, their fungal cultivars, the parasitic fungus Escovopus, and actinomycete bacteria that serve to suppress this parasite. These bacteria are members of Pseudonocardia and grow in filamentous mycelia on the insects’ integument, where the ants have evolved cuticular crypts to house the bacteria and glandular secretions that support their growth.

The actinomycetes are an order of bacteria that are know to produce a wide range of biologically active molecules, many of which are active against other bacteria and against fungi. Some of these natural products are now used clinically, such as the antibacterial antibiotics streptomycin, erythromycin, and tetracycline, anticancer drugs daunorubicin and doxorubicin, and antifungal drugs amphotericin B and natamycin. Actinomycetes inhabit a variety of environments, but many are ubiquitous soil bacteria.