|SREL Reprint #0565|
The Evolutionary Significance of Delayed Emergence from the Nest by Hatchling Turtles
W. Gibbons and D. H. Nelson
Temperate zone turtles are generally believed to lay
eggs in the spring or summer and emerge as hatchlings in the fall.
The phenomenon of overwintering in the nest as hatchlings or advanced
embryos has been reported anecdotally and has often been considered as unusual
or characteristic only of northern U.S. populations.
However, field data on almost 400 hatchlings of five species from a
climatically mild environment in the southeastern U.S. reveal that overwintering
typifies most species of aquatic turtles indigenous to the region.
A thorough review and consolidation of published literature indicates
that delayed emergence from the nest by turtles is more geographically and
phylogenetically wide-spread than commonly believed.
In the habitats studies, late fall temperatures were
actually higher than those at times of emergence in early spring.
Also, emergence times were not correlated with rainfall.
Therefore, we reject conventional explanations of the “cold
temperature” and “dry weather trap” hypotheses proposed by others to
account for the emergence of hatchlings in the spring.
We submit that delayed emergence is a strategy of those species in which
high environmental variability and uncertainty exist for hatchlings that emerge
immediately upon hatching. Thus,
natural selection favors individuals awaiting an environmental cue (such as
wintering in temperature regions or heavy rainfall in the tropics) which
indicates a high probability of ensuring favorable conditions.
Individuals opting for immediate emergence are more likely to enter a
high risk environment and are therefore usually selected against.
Multiple clutches are implicated as a major cause of hatchling
uncertainty about environmental timing of emergence.
SREL Reprint #0565
Gibbons, J.W. and D.H. Nelson. 1978. The evolutionary significance of delayed emergence from the nest by hatchling turtles. Evolution 32:297-303.