The effect of constant and fluctuating incubation temperatures on the phenotype of black ratsnakes (Elaphe obsoleta)

Patterson, L. D.; Blouin-Demers, G.
August 2008
Canadian Journal of Zoology;Aug2008, Vol. 86 Issue 8, p882
Academic Journal
According to the maternal manipulation hypothesis, females manipulate the phenotypes of their offspring by selecting favourable incubation conditions. In oviparous black ratsnakes (Elaphe obsoleta Say in James, 1823), females manipulate offspring phenotype through nest-site selection. This study aimed to determine whether the thermal mean and variance of the incubation regime affect fitness-related traits in hatchlings. We incubated 136 eggs in a split-clutch design at two thermal means (26 and 29 °C) and variances (constant and ±3 °C). Hatchlings incubated at higher temperatures hatched earlier, were longer, faster, and less defensive. Hatchlings incubated at constant temperatures hatched earlier and were longer. For athletic performance, there was a significant interaction between temperature mean and variance: hatchlings incubated at 29 °C swam faster, had a lower muscular strength, and righted themselves equally fast when incubated at constant temperatures, whereas hatchlings incubated at 26 °C were stronger, swam faster, and righted themselves more slowly. Overall, constant incubation temperatures produced hatchlings with phenotypes favouring higher survival than fluctuating temperatures, but the effect of thermal variance was not as pronounced as the effect of thermal mean. Therefore, we found some support for the hypothesis that black ratsnakes prefer communal over single-female nests because communal nests have higher, more constant temperatures. L’hypothèse de la manipulation maternelle veut que les femelles manipulent les phénotypes de leurs rejetons en choisissant des conditions favorables d’incubation. Chez la couleuvre obscure (Elaphe obsoleta Say in James, 1823) qui est ovipare, les femelles manipulent le phénotype de leurs rejetons par leur choix du site de nidification. Notre étude cherche à déterminer si la moyenne et la variance de la température du régime d’incubation affectent les traits reliés à l’aptitude chez les nouveau-nés. Nous avons incubé 136 œufs, d’après un plan expérimental de couvées divisées, à deux moyennes (26 et 29 ºC) et deux variances (température constante et ±3 ºC) de température. Les nouveau-nés incubés aux températures plus élevées éclosent plus tôt, ils sont plus longs, plus rapides et moins défensifs. Les nouveau-nés incubés à des températures constantes éclosent plus tôt et sont plus longs. Il y a une interaction significative entre la moyenne et la variance de température en ce qui a trait à la performance athlétique : les nouveau-nés incubés à 29 ºC nagent plus vite, possèdent une force musculaire plus faible et se redressent à la même vitesse lorsqu’ils sont incubés à température constante; en contraste, les nouveau-nés incubés à 26 ºC sont plus forts, nagent plus rapidement et se redressent moins vite. Globalement, l’incubation à température constante produit des nouveau-nés qui possèdent des phénotypes qui favorisent une meilleure survie que l’incubation à température fluctuante; cependant, les effets de la variance de température ne sont pas aussi prononcés que ceux de la moyenne. Nous trouvons donc un certain appui pour l’hypothèse qui veut que les couleuvres obscures préfèrent les nids communautaires aux nids de femelles solitaires, parce que les nids communautaires ont des températures plus élevées et plus constantes.


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