Costs and benefits of brooding in glossiphoniid leeches with special reference to hypoxia as a selection pressure

Comparative survey of published data on reproductive output for glossiphoniid leeches that brood eggs and young, and for erpobdellid leeches that desert eggs but leave them in an encapsulated cocoon, did not support the hypothesis that brooding is metabolically more expensive than encapsulation and trades off with direct investment of resources in eggs. The metabolic cost of brooding for Glossiphonia complanata, as measued by weight loss, oxygen consumption and ventilation rate in brooding parents and parents from which the brood had been removed, revealed no extra energy cost for parents in terms of the carrying or ventilation of broods. Weight loss through lost feeding opportunity was a cost of brooding; this may be energetically similar to the cost of encapsulation for erpobdellids. Hatching of eggs was unaffected by oxygen saturation (down to 25% saturation at 15°C) but developmental rate of eggs and the survival and weight of hatchlings were all reduced at low oxygen saturation for non-brooded offspring. -from Authors