WALSH, E.J.*; HOWARD, S.; BONILLA, L.; SCHROEDER, T.; Univ. of Texas at El Paso; Univ. of Texas at El Paso; Univ. of Texas at El Paso; Academy of Natural Sciences, Philadelphia: Patterns of diapause and sexual reproduction of Hexarthra (Rotifera) in temporary aquatic habitats of the Chihuahuan desert (HuecoTanks State Historic Site)

Aquatic species inhabiting temporary habitats must complete their life cycle before environmental conditions preclude reproduction and survival. In the case of monogonont rotifers, it is generally held that at least one generation of asexual (amictic) reproduction is necessary before diapausing eggs can be produced through sexual (mictic) reproduction. Here we present life history data for an undescribed Hexarthra species inhabiting shallow ponds in the Chihuahuan Desert which may dry up within days. This species deviates from the general life cycle pattern. From diapausing eggs in the sediments, up to 45.5% of females hatching are mictic and produce male offspring. This first generation of males can fertilize other first generation mictic females, thus diapausing eggs production can occur in a matter of days. In the lab, these females can produce fully developed diapausing eggs within 1.9d at 20°C and 1.2d at 30°C. In the ponds, females producing male offspring and diapausing eggs can be observed on the second and the third day, respectively, after ponds have filled with water. In very short-lived habitats, rapid production of new diapausing eggs may be crucial for the long-term survival of populations. In addition, embryonic development time (1.1d at 12°C, 0.5d at 20°C, and 0.3d at 30°C) and juvenile period (2.1d at 12°C, 1.1d at 20°C, 0.5d at 30°C) are shorter than those of other rotifer species and may contribute to rapid population development and production of diapausing eggs.