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Evolution of winged parasites revealed in queenless ants

The clonal raider ant, Ooceraea biroi, is known to lack a queen caste, but researchers have now reared winged individuals.

Figures depicting Ooceraea biroi and the related Ooceraea octoantenna.
Figures depicting Ooceraea biroi and the related Ooceraea octoantenna. Trible et al., 2023.

Most ants are known to have a queen caste separate from the worker caste, but some genera have noticeable exceptions. Genera such as Diacamma and Dinoponera possess gamergates, which are workers that mate and function as fertilized reproductives. However, some, such as Ooceraea biroi go a step further, and clone themselves to reproduce. Because of this, they too have lost the need for a queen caste.

In a March study by Waring Trible and 7 other researchers, genetically distinct winged individuals were discovered within a colony of clonal raider ants, and their brood was successfully reared into more winged individuals. Besides having wings, these individuals were very similar to workers, with some consistent differences. Independent ants tend to have queens that develop from genotypes that promote larger growth, but many parasites have smaller queens that express other morphological differences to differentiate themselves. The winged individuals in the study were found to overlap in body size with standard workers, but they consistently had longer mesosomas, more ovarioles (used in egg production), and longer eyes.

Two close relatives of O. biroi—Ooceraea octoantenna and Ooceraea siamensis were then analyzed due to their existing presence of a defined queen caste. The results showed that the winged individuals were aligned with the other species' queens, and the same for each's corresponding workers, but that the winged individuals of O. biroi were consistently smaller, indicating a modern mutation rather than expression of an ancestral queen genotype. The smaller size of the winged individuals is a trait consistent with workerless inquiline parasites, especially considering the loss of a worker caste developing from their eggs.

Behavioral analyses showed that the winged individuals were also less productive than standard workers, being less coordinated and conducting smaller raids. This could represent the start of facultative parasitism where the parasites leech off of their hosts, but can still function—this may then evolve into a more obligate form of parasitism in which productive behaviors are completely lost, replaced by those of the workforce of hosts.


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