Microsatellites for the Neotropical Ant, Odontomachus chelifer (Hymenoptera: Formicidae)

Odontomachus chelifer (Latreille) (Ponerinae) is a ground-dwelling, predominantly carnivorous ant whose colonies may contain multiple egg-laying queens and are potentially susceptible to border effects in the Brazilian savanna known as Cerrado. The ecology and natural history of O. chelifer is well studied, but very little is known about the genetic diversity of O. chelifer colonies. In this study, we developed microsatellite markers for the study of genetic variation in O. chelifer. We created a microsatellite-enriched library that resulted in the development and characterization of 22 markers, of which 18 were found to be polymorphic in the population studied. The mean expected heterozygosity was 0.59, whereas the mean rarified allelic richness was determined as 4.27 alleles per locus. The polymorphism level detected was similar to genetic diversity estimates found in other poneromorph ant species. The microsatellites developed here are likely to be useful for the investigation of colony structure, functional polygyny, breeding system, and population genetics in O. chelifer. Moreover, the description of O. chelifer’s genetic diversity is crucial for its conservation and maintenance of its ecological role in the Cerrado savanna.

Worker-behavior and behavior-behavior interaction networks in the trap-jaw ant Odontomachus chelifer (Latreille, 1802)

Division of labor is among the main factors to explain the evolutionary success of social systems, from the origins of multicellularity to complex animal societies. The remarkable ecological success of social insects seems to have been largely driven by ergonomic advantages stemming from the behavioral specialization of workers. However, little is known about how individuals and their correspondent behavioral repertoire are related to each other within a division of labor context, as this relationship can be viewed as a complex network. Applications of network theory in the study of social insects are almost exclusively used to analyze behavioral interactions between individuals, rather than to the study of relations among individuals and behaviors. Here, we use a new approach to the study of the organization of the behavioral repertoire of ant colonies, which consider both individual-task interactions and task-task interactions, besides colony time budgets. Our study investigates for the first time the organization of division of labor in colonies of the trap-jaw ant Odontomachus chelifer (Latreille 1802). Data from all the behavioral acts (including inactivity) performed within three queenright colonies of different sizes (n = 7, 30, and 60 workers) were studied under controlled laboratory conditions. Each ant within the colonies was individually marked and observed by scan sampling in 10 min intervals for 10 h each (n = 5820 behavioral acts). We describe the network topologies in terms of centrality, specialization, modularity, and nestedness. This study shows that workers of O. chelifer interact in structured networks composed of specialists and generalists with consistent organization, even across colonies of different sizes. Our results underscore the potential of the use of complex networks in order to discover and study novel organizational patterns of social groups in animal behavior.

Consumption of lipid-rich seed arils improves larval development in a Neotropical primarily carnivorous ant, Odontomachus chelifer (Ponerinae)

Odontomachus chelifer ants collect fallen arillate seeds of Cabralea canjerana (Meliaceae), a bird-dispersed tree of the Atlantic rain forest. In the nest the larvae are fed with the lipid-rich aril, and the viable seed is discarded. Benefits from secondary seed dispersal by ants are well documented for tropical plants, but benefits to ants from consuming vertebrate-dispersed diaspores are uncertain. Twelve captive colonies of O. chelifer were used to investigate the effect of aril consumption on larval development. Treatment colonies were supplemented with 1 g of C. canjerana arils, whereas control colonies were supplemented with 1 g of synthetic diet. Egg and larval production did not differ between experimental colonies after 5 mo. Aril-fed larvae, however, grew 3.5 times larger than those in control colonies. Essential fatty acids in the arils possibly account for improved larval development. Consumption of lipid-rich arils may be critical under scarcity of arthropod prey. Improved larval development through aril consumption confirms that this ant-seed interaction is facultatively mutualistic. This result is meaningful given the predominantly carnivorous diet of O. chelifer, and the generalized nature of ant-seed/fruit interactions in tropical forests. Whether or not benefits to larvae translate into significant gains for ant colonies is uncertain.

Diversidade e distribuição espacial de artrópodes associados ao solo em agroecossistemas

O conhecimento da diversidade e distribuição de artrópodes associados ao solo contribui para o desenvolvimento de sistemas agrícolas sustentáveis. O presente estudo foi realizado em Jaboticabal (SP), durante o período de fevereiro a abril de 2004. O objetivo foi analisar a comunidade de Carabidae, Staphylinidae, Formicidae e Araneae através de índices faunísticos e determinar a distribuição espacial e a interação interespecífica de espécies predominantes em soja (Glycine max (L.) Merr.), milho (Zea mays L.) e seringueira (Hevea brasiliensis Muell. Arg.). Os artrópodes foram amostrados com armadilhas de solo distribuídas a cada 10 m em dois transectos de 210 m de comprimento, que atravessaram o seringal e avançaram 60 m no interior das culturas. A fauna foi caracterizada pelos índices de diversidade de Shannon-Wiener, de equitabilidade e de similaridade de Morisita. As diferenças entre a ocorrência das espécies predominantes nos hábitats foram determinadas por análise de variância e a interação interespecífica por correlação de Pearson. A soja e o milho cultivados em sistema de plantio direto propiciaram comunidades de carabídeos, formigas e aranhas mais bem estruturadas que o seringal. Entre as 88 espécies capturadas, 20 espécies foram predominantes cuja distribuição espacial mostrou que Odontocheila nodicornis (Dejean), Glenus chrysis Gravenhorst, Castianeira sp. e oito espécies de formigas foram mais abundantes no seringal em comparação às culturas de soja e do milho. A abundância dos carabídeos Calosoma granulatum Perty e O. nodicornis diminuiu conforme aumentou a densidade dos formicídeos Pheidole sp.1 e Odontomachus chelifer Latreille respectivamente.