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1989 Britannica Book of the Year
Life Sciences
ZOOLOGY
Detailed observations and experimental studies of animals during 1988 revealed unusual and unanticipated phenomena, serving as a continuing reminder of the complexity of natural systems. In addition, fossil finds and interpretations advanced scientists' understanding of evolutionary possibilities and phylogenetic relationships.
[Excerpt]
A study of marbled salamanders (Ambystoma opacum) by David E. Scott of the
University of Georgia's Savannah River Ecology Laboratory uncovered important connections
between the conditions a larval salamander experiences in the aquatic habitat and the
acquisition of adult traits related to reproductive output. Manipulation of larval
densities in large field enclosures at several breeding sites over a three-year period
demonstrated that larvae reared at low density under natural conditions grow faster than
larvae reared at high density. They also attain larger body size, have a shorter larval
period and higher probability of survival, and emerge from the pond with more
body fat.
The effects were due, in part, to differences experienced by the two groups in competing
for limited food resources. In laboratory studies salamanders from low-density enclosures
survived longer than those from high-density enclosures. In field populations adults from
low-density larval environments returned to breeding sites at a larger size and earlier
age, two traits associated with increased reproductive output. Variation in the number of
days a breeding site holds water also exerts effects on larval traits that carry over to
adults. The effects are most pronounced in drought years, when body size at metamorphosis
is small and survivorship is low.