Water deprivation tolerance and humidity response in a larval dragonfly: a possible adaptation for survival in drying ponds

Abstract.  Water deprivation tolerance is investigated in the last larval stadium of Libellula depressa under various conditions of relative humidity (60–100% relative humidity; RH). Most of the larvae maintained at 100% RH emerge and, at lower RH levels show some resistance to dehydration because they die after a mean period ranging from 1.4 days at 60% RH up to 6.7 days at 90% RH. In dual-choice chambers with humidity gradients from 63–74% RH and from 68–84% RH, larvae spend most of the time in the moist side of the chamber. In a Y-tube olfactometer, the larvae reveal a positive hygrotaxis to two airstreams carrying different amounts of water vapour (98% vs. 50%) and spend most of their time in the 'humid' arm. The ecological significance of desiccation tolerance and hygropositive response in the last larval stadium of L. depressa is discussed in relation to the presence of hygroreceptors in dragonfly larvae.     

Female gametes of the black coral Cirrhipathes cfr. anguina (Anthozoa,Antipatharia) from the Indonesian Marine Park of Bunaken

Summary

Female polyps of Cirrhipathes cfr. anguina were collected in August 2007 from the coral reef of Siladen Island in the Bunaken Marine Park (North Sulawesi, Indonesia). The primary transverse mesenteries, which separate the adjacent lateral tentacles from one another, were filled with oocytes developing within the mesoglea. Cross-sections of the oral region revealed that young gametes were located both at the emergence of the primary transverse mesenteries from the gastroderm lining the coelenterons, and at the point where the mesenteries were linked to the pharynx. By contrast, at a lower level, where the mesenteries gave rise to mesenterial filaments, young gametes were limited to the initial part of the mesenteries. Oocytes were lodged in individual chambers, and were separated from one another by mesogleal elements. On occasion, oocytes were found in proximity to cells with short microvillous-like processes that interdigitated with those emerging from the oocyte surface. Oocytes varied in size according to the stage of the vitellogenetic process, the largest measuring 125 μm in diameter. Their cytoplasm was enriched with inclusions of three main kinds: lipids, yolk and both rod- and ovoid-shaped bodies. These bodies were characterized by an electron-dense core with a dotted appearance, surrounded by a sequence of tightly-packed fibrils arranged in parallel fashion. These bodies pushed the oocyte membrane slightly outwards, giving rise to irregular “spiny” protrusions. In addition to the microvillous-like extensions, oocytes also showed short lobose pseudopodia; both are probably involved in nutrient uptake. No other membrane specializations were observed in the oocytes, the general morphology of which seemed to be coherent with the assumption that they had reached their final stage of growth. Investigations on the reproduction of the black coral may provide insights into the feasibility of transplanting fertile colonies into areas where they have been decimated by anthropogenic pressure.