For animals which migrate to breeding areas, the energy expended on locomotion to the breeding area is, in effect, part of the cost of reproduction. Because in many organisms the mass of mature gametes carried by a gravid female may lead to considerable weight loading, the cost of transport to the breeding areas may be substantially higher for females than for males. Thus, the locomotor patterns in females migrating to the breeding ponds may be different than those employed by males in order to minimize the energetic cost incurred. This may lead to differences between the sexes in the time of arrival at the breeding pond and possibly the susceptibility to predation by terrestrial predators during overland migration. We are currently examining metabolism during locomotion, thermal effects on metabolism and locomotion, and energy reserves of males and females of several Ambystoma species to evaluate differences in the overall cost of reproduction between the sexes.
Many species appear to be active and forage during the winter.
While foraging may help supplement fat reserves and enhance the chances that the animal will survive the winter and, in the case of females, increase gamete production in the spring, being active during the winter requires increased energetic expenditure. Thus, active foraging may enhance energy stores only if prey availability is also relatively high. If prey availability is low, foraging may be restricted in order to conserve energy. We are currently conducting a study that investigates the availability of prey on metabolism and energy reserves in the red-backed salamander, Plethodon cinereus . Effects of hydric conditions during incubation on metabolism and long-term energy budgets of neonatal snapping turtles.