Sexual reproduction and diapause of Hexarthra sp (Rotifera) in short-lived ponds in the Chihuahuan Desert

1. In the life cycle of monogonont rotifers it is generally assumed that diapausing eggs invariably hatch into amictic stem females which produce female offspring parthenogenetically. Diapausing eggs are only produced by later generations after sexual reproduction has been induced by environmental cues. 2. We show that populations of an undescribed Hexarthra species inhabiting small temporary ponds in the Chihuahuan Desert deviate from this life cycle pattern. These ponds may dry within days and up to 85% of females were mictic. Females producing male offspring and diapausing eggs were observed 1 or 2 days, respectively, after ponds had filled with water. 3. Under laboratory conditions, 7-46% of females hatching from re-hydrated sediments were sexual. Male offspring of these females can fertilise other mictic stem females leading to diapausing egg formation. In laboratory experiments, females produced fully developed diapausing eggs within 1.9 days at 20 degrees C and 1.2 days at 30 degrees C. 4. In addition, embryonic development time (1.1-0.3 days at temperatures between 12 and 30 degrees C) and juvenile period (2.1-0.5 days for the same temperature range) are shorter than those of other rotifer species. In short-lived habitats, the potential for rapid population development and production of new diapausing eggs may be crucial in the long-term survival of populations.