Variation in life history traits in the little brown bat, Myotis lucifugus (chiroptera: vespertilionidae)
Reynolds, D. Scott
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This thesis examines the intrinsic and extrinsic factors that influence the reproductive strategy of a temperate insectivorous bat, Myotis lucifugus. Body composition was measured using both direct analysis (dehydration and fat extraction) and total body electrical conductivity (TOBEC) analysis. Changes in body composition during the reproductive season show that both fat and mineral stores are mobilized during lactation. However, the changes were small relative to the level of reproductive effort supporting the hypothesis that small insectivorous bats use direct-costing to meet the costs of reproduction. An increase in size of the digestive tract suggests that increased foraging capacity is an important component of this strategy. Changes in body composition in young bats show a two-week period of linear postnatal growth followed by a rapid transition to adult body composition. By the end of August, young bats had achieved a mass-specific body composition similar to post-lactating adult females, although they had a smaller body mass. Body composition did not influence any of the reproductive traits investigated in the present study. Young bats born early in the parturition period had a higher postnatal growth rate, suggesting that time-dependent effects influence reproductive strategy in Myotis lucifugus. Sex-dependent influences suggest that maternal costs are higher when producing female young: female offspring 1) had a higher postnatal growth rate, 2) had more body fat at weaning, 3) were born earlier and remained with the mother longer than male offspring. High levels of precipitation during early pregnancy resulted in a delayed parturition period and a male-biased sex-ratio at birth. High levels of precipitation in late summer increased overwinter recapture rate in adult females. Low ambient temperature in early summer reduced the reproductive rate and level of reproductive synchrony. Low temperatures in late summer reduced overwinter recapture rate in yearling bats. These extrinsiv factors may influence the energy budget of M. lucifugus by increasing thermoregulatory costs and reducing foraging opportunity or prey availability. Thus intrinsic factors influenced some of the within-season variation in reproductive traits, whereas extrinsic factors primarily affected between-year variation.
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