Changes in milk composition during lactation in three species of insectivorous bats.

Changes in milk composition are described for three species of free-ranging insectivorous bats (Myotis lucifugus, M. velifer, and Tadarida brasiliensis) from early to mid (peak) lactation. Dry matter and energy concentrations in milk increased from early to mid-lactation. In M. lucifugus and T. brasiliensis, but not M. velifer, these increases were due largely to a rise in fat concentration, since protein and carbohydrate remained relatively constant. Energy content of milk (kJ.g-1) for each species from early through mid-lactation was related to dry matter (DM) as follows: M. lucifugus (y = 0.31 DM-0.32, r2 = 0.68), M. velifer (y = 0.48 DM-5.08, r2 = 0.99), and T. brasiliensis (y = 0.37 DM-1.51, r2 = 0.61). Comparison of the effect of sampling method on milk composition of T. brasiliensis indicated that fat, dry matter, and energy concentrations increased significantly from pre-dawn to pre-noon samples. Relatively high fat and low water levels in T. brasiliensis milk may reflect the limited access that lactating females have to free water, as well as need to minimize mass of stored milk during long foraging trips. Conversely, lower fat concentrations and higher water levels in milk in M. lucifugus and M. velifer may relate to the propensity for colonies of these two species to roost and forage near bodies of water. In addition, differences in milk fat concentrations observed among the three species may correlate to daily suckling schedules.(ABSTRACT TRUNCATED AT 250 WORDS)

Maternal energy investment in elephant seal pups: evidence for sexual equality?

Labeled water methodology was used to quantify maternal energy investment in northern elephant seal (Mirounga angustirostris) pups. Pup milk intake, field metabolic rate, mass change, and body composition were monitored during the nursing period and throughout the postweaning fast. Maternal investment did not vary significantly as a function of pup sex. There was no evidence for sex differences in growth rate or milk intake rate, and mean metabolic rate of suckling pups did not differ significantly between the sexes. Males and females appeared to be in similar condition at the end of the postweaning fast, just prior to their first trip to sea. Some male pups may attain greater size relative to females without additional cost to their mothers. These data do not provide evidence to reject R. A. Fisher's theory of equal investment in the sexes.

Circulatory water concentration in suckling and fasting northern elephant seal pups.

This study examined circulatory water concentrations in the neonatal northern elephant seal (Mirounga angustirostris) in order to determine how suckling and fasting would alter the percentage of water in the whole blood, plasma, and red blood cells (RBC). Plasma water concentration dropped by about 3% during suckling and recovered about 1% during the fast (92.38 +/- 0.48% less than 1 week old, 90.15 +/- 0.36% weaning, 91.02 +/- 0.68% end of fast). RBC water values during this time were more variable than plasma values: RBC water increased about 1% during the first 2 weeks of suckling (from 67.80 +/- 0.28% to 68.68 +/- 0.51%) but dropped to slightly below original neonatal values by weaning (67.15 +/- 0.63%). The first several weeks of fasting were marked by wide variability in RBC water, but by the end of the fast RBC water was comparable to that at weaning. These results indicate: 1) Northern elephant seal pups do not exhibit circulatory dehydration during 10 weeks of fasting; 2) Measurements of plasma or RBC metabolites (such as plasma glucose or RBC hemoglobin) may show variations or trends due not to metabolic regulation but rather to changes in circulatory water concentration.

Chemical cues from families delay puberty in male California voles.

The role of chemical cues in the delay of puberty in male California voles (Microtus californicus) was investigated. Males that were raised from weaning in bedding from their families were delayed in attainment of adult androgen levels and seminal vesicle weights compared to males raised in clean bedding. In a second experiment, the source of the suppressive cues was examined by rearing males in bedding from unrelated adult males, their fathers, or their mothers. Males reared with bedding from their mothers showed delayed maturation of both androgen levels and seminal vesicle weights, whereas males exposed to bedding from unrelated males were not delayed. Males exposed to bedding from their fathers showed intermediate androgen levels but large seminal vesicles. Thus, chemical cues from the family, particularly the mother, suppress reproductive development in male California voles. These results are discussed in the context of the puberty delay which occurs in natural populations of this species; it is suggested that puberty delay is an adaptive strategy that may be employed by young voles in times of high density and limited resources.