International Union for the Study of Social Insects (IUSSI2018), August 5-10, 2018 in Guarujá, Brazil.

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Collective behavior during colony emigrations of leaf cutter ants

Author(s):
Lohan Claudio Abreu Valadares, Lohan Valadares , Isabella Padovani Frattini , Laura Ribeiro Soares , Diego Santana Assis , Fabio Santos do Nascimento
Institution(s):
Laboratório de Comportamento e Ecologia de Insetos Sociais, Departamento de Biologia, Universidade de São Paulo, Ribeirão Preto-SP, Brazil. ; Laboratório de Comportamento e Ecologia de Insetos Sociais, Departamento de Biologia, Universidade de São Paulo, Ribeirão Preto-SP, Brazil. ; Universidade Paulista, Ribeirão Preto-SP, Brazil ; Universidade Paulista, Ribeirão Preto-SP, Brazil ; Laboratório de Comportamento e Ecologia de Insetos Sociais, Departamento de Biologia, Universidade de São Paulo, Ribeirão Preto-SP, Brazil. ; Laboratório de Comportamento e Ecologia de Insetos Sociais, Departamento de Biologia, Universidade de São Paulo, Ribeirão Preto-SP, Brazil.
In leafcutter ants (genera Atta and Acromyrmex), interspecific competition leads to frequently emigrations of Acromyrmex colonies, which are considered ‘emigration specialists”. Here, we experimentally investigate the collective behavior and the dynamics of colony emigration in two species of leafcutter ants (A. sexdens and Ac. subterraneus) that are commonly found co-habiting and foraging at the same habitats. We compared across species the strong of association between body size and load mass, as well as estimated colony emigration efficiency by calculating rates of load mass transportation and number of workers engaged in load transporting. Furthermore, we investigated the dynamics of collective behavior by calculating a net entry of workers with different body sizes when arriving at the new nesting sites, and compared how such dynamics are associated with the relocation of load categories (queen, fungus, and brood items). We found a similar correlation between body size and load mass in both species (17% in Ac. subterraneus, and 20% in A. sexdens). However, the lapse of time until emigrations have started indicated that Ac. subterraneus are significantly faster at discovering a new nesting site, and employed a significant larger number of workers to relocate their resources. Net entry rates of different size workers build multiple Gaussian curves over time, where the first load category to be relocated fitted no specific area of a given curve but a trend to relocate items on media workers (head width around 1.4 mm) curves were found and suggest they are the main workforce during colony emigration in both species. Interestingly, A. sexdens sequentially relocated queens, brood items and pieces of fungus garden, while Ac. subterraneus showed no trend at relocation order of load categories. These results indicate that A. sexdens workers are less flexible when deciding to migrate but instead adopt a safer strategy to relocate their resources. 
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