Postnatal growth and development in the little brown bat, Myotis
lucifugus, was characterized for two latitudinally separated populations
to examine effects of the length of the growing season . Bats from New
Hampshire (43°N) and bats experiencing a shorter and colder growing
season in Alberta (54°N), were compared with respect to birth size and
growth rate (as measured by forearm length and body mass), flight
development, ontogeny of thermoregulation, body composition, and the
allometric growth of body parts. Alberta bats were shown to grow more
slowly, and flight development was somewhat delayed. However, Alberta
bats were born larger, suggesting that when growth is slowed by colder
growing conditions, selection favors greater prenatal investment
allowing Alberta juveniles to reach the size required to survive the
first hibernal period. Thermoregulatory development is delayed in
Alberta juveniles, indicating that these bats defer investment in
thermogenesis until a critical point in postnatal growth . A model 1s
presented defining this critical point by relating thermogenic ability
and conductance to the timing of onset of homeothermy. Analysis of body
composition revealed that differences between the two populations were
primarily manifested in the proportions of lean dry mass and water. Fat
contributed more to energy density among New Hampshire bats, suggesting
that Alberta bats allocate more energy to structural development than
energy storage during early growth. These results, coupled with evidence
of delayed reproduction in Alberta bats, indicate that growth 1s
constrained by the shorter, colder Alberta growing season.
Geographic variation 1n adult size and sexual dimorphism was
investigated in light of the differences in offspring development. Adult
skull and wing variables indicate that this species conforms to
Bergmann's rule in that Alberta bats are larger. While sexual
dimorphism is not pronounced in New Hampshire, it is evident in Alberta
bats. The most striking result 1s the larger wing size of Alberta
females. Much of the variation in M. lucifugus adults can be explained
by selection for larger offspring which affects female morphology. A new
hypothesis incorporating the effects of selection during offspring
development is advanced to explain patterns of geographic variation 1n
size and sexual dimorphism among birds and mammals with broad
latitudinal distributions.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/46796 |
| Date | January 1986 |
| Creators | Fujita, Martha Sayuri |
| Publisher | Boston University |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
| Rights | This work is being made available in OpenBU by permission of its author, and is available for research purposes only. All rights are reserved to the author. |
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