Water balance and apparent oocyte resorption in desert millipedes

Abstract

AbstractOosorption in response to desiccation stress was tested in spirostreptid millipedes from arid environments. Seasonally collected and experimentally stressed adult females were examined for penetration of oocytes by trypan blue, for compartment levels of water in cuticle + tissue and gut + gut contents, and for hemolymph osmolalities.Archispirostreptus syriacus from the winter‐rainfall Judaean and Negev deserts decreased in total body water during the hot dry summer. Simultaneously, water in cuticle + tissue and in gut + gut contents increased and decreased respectively in proportion to total water. Water in both compartments decreased in starved specimens exposed for 19 days to 76% relative humidity; these millipedes resorbed a higher percentage of oocytes than did field controls but not more than specimens in saturated air.Groups of starved premolt (spring) and postmolt (summer) Orthoporus ornatus from New Mexico (summer rainfall) each responded differently when exposed to humidities found in their respective habitats. Compartment water levels in the former remained constant for 19 days under moderate conditions; they declined in the latter after 36–42 days of relative moisture stress. Neither stage showed increased oosorption over field controls when exposed to seasonal humidity ranges.Archispirostreptus syriacus resorbed a higher proportion of oocytes than did O. ornatus, which matured oocytes only in summer rather than most of the year. Patterns of oosorption and oocyte development probably reflect species‐specific life histories and relative states of starvation rather than seasonal water balance and desiccation stress.