Acute and chronic effects of temperature on membrane adjustments in the gills of a neotropical catfish.

Structural modifications in the gill membranes maintain homeostasis under the influence of temperature changes. We hypothesized that thermal acclimation would result in significant modification of phospholipid fatty acids, with modulation of sodium pump activity during acute (24 and 48 h) and chronic (15 days) thermal shifts in the neotropical reophilic catfish Steindachneridion parahybae. Indeed, the time-course experiment showed acute and chronic changes in gill membrane at the lowest temperatures, notably linked to maintenance of membrane fluidity: significant preferential changes in phosphatidylethanolamine, with decrease of saturated fatty acids and increase of C18:1 in all groups kept below 30 °C in chronic trial, increase in polyunsaturated fatty acids n6 and C18:1 at 17 and 12 °C compared to 24 °C, as soon as the temperature was changed (initial time). Additionally, the activity of the sodium pump increased at 12 °C, but without apparent connection with the altered lipid environment. The animals maintained at the lowest temperature showed a higher mortality, possibly because of the approach to the minimum critical temperature for this species, and unexpected results of changes in the fatty acid profile, such as decreased docosahexaenoic acid in phosphatidylethanolamine and increased saturated fatty acids in phosphatidylcholine. This set of mechanisms highlights rheostatic adjustments in this species in the face of temperature changes.

Two castes sizes of leafcutter ants in task partitioning in foraging activity / Participação de dois tamanhos de castas de operárias de formigas cortadeiras no particionamento de tarefas da atividade de forrageamento

ABSTRACT: Task partitioning in eusocial animals is most likely an evolutionary adaptation that optimizes the efficiency of the colony to grow and reproduce. It was investigated indirect task partitioning in two castes sizes; this involves task partitioning in which the material transported is not transferred directly from one individual to another, but where it is dropped by one ant to be picked up by another. In two separate approaches, it was confirmed previous results pertaining to leaf caching activities among Atta colombica with task partitioning activities involving leaf dropping among Atta sexdens rubropilosa , in which there is a correlation between the size of an individual ant and the leaf fragment it transports. It was also suggested that this correlation exists only in individual ants that cut and transport (CaT) the same fragment to the nest. When task partitioning occurs and individual ants transporting (T) leaf fragments cut by other ants, the correlation becomes looser or disappears. We also observed that CaT ants are smaller than T ants.

RESUMO: Particionamento de tarefas em animais eusociais é provavelmente uma adaptação evolutiva, que otimiza a eficiência de forrageio da colônia, gerando maior capacidade de crescimento e reprodução. Nós investigamos o particionamento indireto de tarefas, com o envolvimento de castas de dois tamanhos distintos. Assim, o material coletado por uma formiga não era transportado diretamente ao ninho, nem transferido diretamente de um indivíduo para outro, mas sim descartado por uma formiga e coletado por outra. Em duas abordagens distintas, nós confirmamos em Atta sexdens rubropilosa resultados anteriores relativos à ocorrência deste particionamento indireto de tarefas, observado em Atta colombica . Mostramos também que, assim como em Atta colombica , há uma correlação entre os tamanhos da formiga e do fragmento de folha transportado quando esta corta e transporta este fragmento ao ninho (CaT). Mais ainda, confirmamos em Atta sexdens que, quando o particionamento de tarefas ocorre e as formigas apenas transportam o fragmento de folhas (T) cortadas por outras formigas, a correlação desaparece. Nós também descrevemos que as formigas CaT são menores do que as T.