Biology of Myotis thysanodes and M. lucifugus (Chiroptera: Vespertilionidae). II. Bioenergetics of pregnancy and lactation.

Through bomb calorimetry of known-age young bats, we have determined the energy cost of pregnancy and lactation in Myotis thysanodes and M. lucifugus finding that: 1. Energy demand during pregnancy is hyperbolic. 2. A very rapid increase in energy involved in embryo growth occurs during late pregnancy when the mothers are no longer homeothermic. 3. This increased energy demand occurs earlier pre-partum in M. thysanodes than in M. luci&gus. 4. Energy utilized during late embryo growth in M. lucifugus (130 Cal/day) is significantly greater than in M. thysanodes (78 Cal/day). 5. Lactation in M. thysanodes requires at least 346 Cal/day and is much more energy demanding than is pregnancy. INTRODUCTION ALTHOUGH energy requirements of pregnancy and lactation have been studied in humans, domestic cattle and several common laboratory rodents (see, for example Brody, 1945 ; Nelson & Evans, 1961), only recently have data on energetic demands of reproduction been reported for any feral species (Kaczmarski, 1966; Migula, 1969). Our recent studies have shown that thermoregulatory performances of Mjlotis lucifugus and M. thysanodes are significantly affected by reproductive stages (Studier & O’Farrell, 1972). Like other chiropterans, these bats exhibit extremely rapid preand postnatal growth (O'Farrell & Studier, 1972). This study presents data on the energy demands of pregnancy and lactation in the two species and includes a further analysis of previous work. MATERIALS AND METHODS Known-age embryos with attached placentae from bats used in previous studies (O’Farrell & Studier, 1972; Studier & O’Farrell, 1972) were dried to constant weight, * Present address: Department of Biology, University of Michigan, Flint, Michigan 48503. t Present address : Department of Biology, University of Nevada, Reno, Nevada 89507.