Question

Male and female Hoary Bats have different thermoregulatory and metabolic strategies when exposed to cold stress during spring migration. Discuss how these strategies differ and the potential advantages of each strategy for each sex.

Answer 1

The points to be kept in mind are that females are pregnant during spring migration whereas males are not sexually active therefore energetic demands on males during spring are presumably low(as maximum energy is required for spermatogenesis which occur during summer, followed by mating in late summer or winter).

MALE HOARY BAT- Males showed much wider variation in body temperature and metabolic rate than females. Males enter into torpor(a state of not being active and having very low energy).

The higher frequency of torpor use and more labile body temperatures observed in males reflect the relative lack of selective pressure imposed on them by energetic demands associated with reproduction.

Males, in contrast to females are not constrained physiologically or behaviorally by the needs of the young. As a consequence, males can use torpor to accrue energy or limit foraging.

Mass-metabolic rate(MMR) is dependent upon the size of the body, greater the size lower is the MMR. Therefore due to males having smaller size than females, they have higher MMR.

FEMALE HOARY BAT- Thermoregulation in pregnant female differ from males during spring migration. Females rarely use torpor and maintain a high stable body temperature over a broad range of air temperatures as low body temperatures would
lengthen developmental periods and potentially lead to increased maternal and juvenile mortality, whereas maintenance of normal body temperature in females is likely to minimize the period of embryonic development and thus maximize the time available to both mother and young when favorable foraging conditions exist after weaning.

Unlike males, the mass-specific metabolic rates(MMR) measured in females during this study were lower. Lower metabolic rates in pregnant bats can be due to lower metabolic needs of foetal tissue. Increase in the mass of ametabolic materials during pregnancy may contribute to the low metabolic rates.