Effect of the presence of brood and fungus on the nest architecture and digging activity of Acromyrmex subterraneus Forel (Hymenoptera, Formicidae)

ABSTRACT This study investigated the stimuli that trigger digging behavior in Acromyrmex subterraneus during nest building. The hypothesis was that the presence of the fungus garden and/or brood triggers the excavation of tunnels and chambers. For the experiment, the excavation rate of individually marked workers kept in plastic cylinders filled with soil was recorded. Four treatments were applied: (1) 30 medium-sized workers, 5 g fungus garden and 30 brood items (larvae and pupae); (2) 30 medium-sized workers and 5 g fungus garden; (3) 30 medium-sized workers and 30 brood items; (4) 30 medium-sized workers without fungus and brood. After 24 h, morphological parameters of nest structure (length and width of the chambers and tunnels in cm) and the volume of excavated soil were recorded. In contrast to the expected findings, no change in morphological structure, rate of excavation by workers, or volume of excavated soil was observed between treatments, except for tunnel width, which was greater, when no brood or fungus garden was present. Thus, the results do not support the hypothesis that the fungus garden and/or brood are local stimuli for nest excavation or that they mold the internal architecture of the nest. Although this hypothesis was confirmed for Acromyrmex lundii and Atta sexdens rubropilosa, the same does not apply to A. subterraneus. The digging behavior of workers is probably the result of adaptation during nest building in different habitats.

Reproductive behavior and parental roles of the cichlid fish Laetacara araguaiae

We described the reproductive behavior of the small South American cichlid Laetacara araguaiae in streams from Brazil. We predicted that this species will show reproductive cooperation and division of labor between males and females in a similar way presented by other substrate-spawner cichlids. Thus, we studied 34 pairs in the pre-spawning (n = 11), egg/wriggler (n = 11) and fry (n = 12) phases. In the pre-spawning phase both sexes become involved in nest building and territorial defense, but females emphasizes building nest (p = 0.03), while males invest more time in territorial defense (p = 0.04). After spawning, male and female alternate between rearing eggs and defending nest in the territory. In the egg/wriggler phase females devotes more time rearing the brood while males remain defending territory (p = 0.02). These differences disappear when young are in the fry stage, and parents jointly stay closer to fry (p = 0.98). However, at this phase, there is a reduction in the frequency of threats shown by males (p<0.01) and an increase in the frequency of attacks shown by female (p<0.01) that could be a response to an increased demand for parental defense. Our results indicate that the reproductive cooperation between males and females of L. araguaiae is marked by division of labor in the early reproductive phases and by sharing of parental duties as brood develops.

Descrevemos o comportamento reprodutivo do pequeno ciclídeo sul-americano Laetacara araguaiae em riachos do Brasil. Predizemos que essa espécie apresenta cooperação reprodutiva e divisão de trabalho entre machos e fêmeas, como ocorre em outras espécies de ciclídeos substrate-spawners. Assim, estudamos 34 casais nas fases pré-acasalamento (n = 11), ovo/larva (n = 11) e prole natante (n = 12). Na fase pré-acasalamento ambos os sexos envolvem-se na construção de ninhos e na defesa territorial, mas as fêmeas enfatizam a construção de ninho (p = 0,03), enquanto os machos investem mais na defesa do território (p = 0,04). Após a desova, machos e fêmeas alternam entre a manutenção dos ovos e a defesa do ninho. Na fase ovo/larva as fêmeas despendem mais tempo em atividades de manutenção da prole, enquanto os machos investem mais na defesa do território (p = 0,02). Essas diferenças desaparecem quando a prole atinge o estágio natante com ambos os pais permanecendo próximos aos filhotes (p = 0,98). Entretanto, há uma redução na frequência de ameaças emitidas pelos machos (p<0,01) e um aumento na frequência de ataques emitidos pelas fêmeas nessa fase (p<0,01), o que poderia ser uma resposta ao aumento da demanda por defesa da prole. Nossos resultados indicam que a cooperação reprodutiva entre machos e fêmeas de L. araguaiae é representada pela divisão de funções nas primeiras fases reprodutivas, seguida pelo compartilhamento de tarefas parentais à medida que a prole se desenvolve.