RESUMEN
Increased potential for disease transmission among nest-mates means living in groups has inherent costs. This increased potential is predicted to select for disease resistance mechanisms that are enhanced by cooperative exchanges among group members, a phenomenon known as social immunity. One potential mediator of social immunity is diet nutritional balance because traits underlying immunity can require different nutritional mixtures. Here, we show how dietary protein-carbohydrate balance affects social immunity in ants. When challenged with a parasitic fungus Metarhizium anisopliae, workers reared on a high-carbohydrate diet survived approximately 2.8× longer in worker groups than in solitary conditions, whereas workers reared on an isocaloric, high-protein diet survived only approximately 1.3× longer in worker groups versus solitary conditions. Nutrition had little effect on social grooming, a potential mechanism for social immunity. However, experimentally blocking metapleural glands, which secrete antibiotics, completely eliminated effects of social grouping and nutrition on immunity, suggesting a causal role for secretion exchange. A carbohydrate-rich diet also reduced worker mortality rates when whole colonies were challenged with Metarhizium. These results provide a novel mechanism by which carbohydrate exploitation could contribute to the ecological dominance of ants and other social groups.
Asunto(s)
Fenómenos Fisiológicos Nutricionales de los Animales/inmunología , Hormigas/inmunología , Metabolismo de los Hidratos de Carbono/inmunología , Animales , Hormigas/fisiología , Resistencia a la Enfermedad/inmunología , Conducta Alimentaria , Aseo Animal , Conducta SocialRESUMEN
Body size and morphology are key fitness-determining traits that can vary genotypically. They are likely to be important in social insect queens, which mate in swarms and found colonies independently, but genetic influences on queen morphology have been little investigated. Here, we show that the body size and morphology of queens are influenced by their genotype in the leaf-cutting ant Acromyrmex echinatior, a species in which certain lineages (patrilines) bias their development towards reproductive queens rather than sterile workers. We found no relationship between the queen-worker skew of patrilines and the size or morphology of queens, but there was a significant relationship with fluctuating asymmetry, which was greater in more queen-biased patrilines. Our results suggest that queen-biased patrilines do not incur a fitness cost in terms of body size, but may face more subtle costs in developmental stability. Such costs may constrain the evolution of royal cheating in social insects.
Asunto(s)
Hormigas/genética , Hormigas/fisiología , Evolución Biológica , Tamaño Corporal/fisiología , Aptitud Genética/fisiología , Jerarquia Social , Análisis de Varianza , Animales , Pesos y Medidas Corporales , Femenino , Aptitud Genética/genética , Genotipo , Repeticiones de Microsatélite/genética , Panamá , Reacción en Cadena de la Polimerasa , Análisis de Componente Principal , Estadísticas no Paramétricas , Alas de Animales/anatomía & histologíaRESUMEN
Social insect castes represent some of the most spectacular examples of phenotypic plasticity, with each caste being associated with different environmental conditions during their life. Here we examine the level of genetic variation in different castes of two polyandrous species of Acromyrmex leaf-cutting ant for the antibiotic-producing metapleural gland, which has a major role in defence against parasites. Gland size increases allometrically. The small workers that play the main role in disease defence have relatively large glands compared with larger workers, while the glands of gynes are substantially larger than those of any workers, for their body size. The gland size of large workers varies significantly between patrilines in both Acromyrmex echinatior and Acromyrmex octospinosus. We also examined small workers and gynes in A. echinatior, again finding genetic variation in gland size in these castes. There were significant positive relationships between the gland sizes of patrilines in the different castes, indicating that the genetic mechanism underpinning the patriline variation has remained similar across phenotypes. The level of expressed genetic variation decreased from small workers to large workers to gynes. This is consistent with the hypothesis that there is individual selection on disease defence in founding queens and colony-level selection on disease defence in the worker castes.
Asunto(s)
Hormigas/genética , Glándulas Exocrinas/anatomía & histología , Variación Genética , Jerarquia Social , Fenotipo , Animales , Hormigas/anatomía & histología , Tamaño Corporal , Glándulas Exocrinas/inmunología , Glándulas Exocrinas/metabolismo , Genotipo , Inmunidad Innata/inmunología , Panamá , Reacción en Cadena de la Polimerasa , Especificidad de la EspecieRESUMEN
Within-host competition is an important factor in host-parasite relationships, yet most studies consider interactions involving only single parasite species. We investigated the interaction between a virulent obligate entomopathogenic fungus, Metarhizium anisopliae var. anisopliae, and a normally avirulent, opportunistic fungal pathogen, Aspergillus flavus, in their leaf-cutting ant host, Acromyrmex echinatior. Surprisingly, the latter normally out-competed the former in mixed infections and had enhanced fitness relative to when infecting in isolation. The result is most probably due to Metarhizium inhibiting the host's immune defences, which would otherwise normally prevent infections by Aspergillus. With the host defences negated by the virulent parasite, the avirulent parasite was then able to out-compete its competitor. This result is strikingly similar to that seen in immunocompromised vertebrate hosts and indicates that avirulent parasites may play a more important role in host life histories than is generally realized.
Asunto(s)
Hormigas/microbiología , Ascomicetos/fisiología , Ascomicetos/patogenicidad , Aspergillus flavus/fisiología , Animales , Hormigas/inmunología , Aspergillus flavus/patogenicidad , Panamá , Factores de Tiempo , VirulenciaRESUMEN
We investigated the prevalence of entomopathogenic fungi associated with leaf-cutting ant colonies in a small area of tropical forest in Panama. There was a high abundance of Metarhizium anisopliae var. anisopliae near the colonies. Beauveria bassiana was also detected in the soil, Aspergillus flavus in dump material, and six Camponotus atriceps ants were found infected with Cordyceps sp. Based on a partial sequence of the IGS region, almost all of the M. anisopliae var. anisopliae isolates fell within one of the three main clades of M. anisopliae var. anisopliae, but with there still being considerable diversity within this clade. The vast majority of leaf-cutting ants collected were not infected by any entomopathogenic fungi. While leaf-cutting ants at this site must, therefore, regularly come into contact with a diversity of entomopathogenic fungi, they do not appear to be normally infected by them.