Epitypification and re-description of the zombie-ant fungus, Ophiocordyceps  unilateralis  (Ophiocordycipitaceae)

Tropical leaf-cutter ants cultivate the fungus Attamyces bromatificus in a many-to-one, diffuse coevolutionary relationship where ant and fungal partners re-associate frequently over time. To evaluate whether ant– Attamyces coevolution is more specific (tighter) in peripheral populations, we characterized the host-specificities of Attamyces genotypes at their northern, subtropical range limits (southern USA, Mexico and Cuba). Population-genetic patterns of northern Attamyces reveal features that have so far not been observed in the diffusely coevolving, tropical ant– Attamyces associations. These unique features include (i) cases of one-to-one ant– Attamyces specialization that tighten coevolution at the northern frontier; (ii) distributions of genetically identical Attamyces clones over large areas (up to 81 000 km 2 , approx. the area of Ireland, Austria or Panama); (iii) admixture rates between Attamyces lineages that appear lower in northern than in tropical populations; and (iv) long-distance gene flow of Attamyces across a dispersal barrier for leaf-cutter ants (ocean between mainland North America and Cuba). The latter suggests that Attamyces fungi may occasionally disperse independently of the ants, contrary to the traditional assumption that Attamyces fungi depend entirely on leaf-cutter queens for dispersal. Peripheral populations in Argentina or at mid-elevation sites in the Andes may reveal additional regional variants in ant– Attamyces coevolution. Studies of such populations are most likely to inform models of coextinctions of obligate mutualistic partners that are doubly stressed by habitat marginality and by environmental change.

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3D mapping of disease in ant societies reveals a strategy of a specialized parasite

10.1101/003574 ◽

2014 ◽

Author(s):

Raquel G Loreto ◽

Simon L Elliot ◽

Mayara LR Freitas ◽

Thairine M Pereira ◽

David P Hughes

Keyword(s):

Disease Spread ◽

Social Immunity ◽

Ant Colonies ◽

Effective Strategies ◽

Insect Societies ◽

The Social ◽

Disease Free ◽

Ophiocordyceps Unilateralis ◽

Disease Present

Despite the widely held position that the social insects have evolved effective ways to limit infectious disease spread, many pathogens and parasites do attack insect societies. Maintaining a disease-free nest environment is an important evolutionary feature, but since workers have to leave the nest to forage they are routinely exposed to disease. Here we show that despite effective social immunity, in which workers act collectively to reduce disease inside the nest, 100% of studied ant colonies of Camponotus rufipes in a Brazilian Rainforest were infected by the specialized fungal parasite Ophiocordyceps unilateralis s.l. Not only is disease present for all colonies but long-term dynamics over 20 months revealed disease is a permanent feature. Using 3D maps, we showed the parasite optimizes its transmission by controlling workers behavior to die on the doorstep of the colony, where susceptible foragers are predictable in time and space. Therefore, despite social immunity, specialized diseases of ants have evolved effective strategies to exploit insect societies.

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