Do female newts modify thermoregulatory behavior to manipulate egg size?

• Female ectotherms affect offspring phenotypes by their thermoregulatory behavior.
• We examined the influence of maternal thermoregulation on egg size in newts.
• Reproductive females maintained less variable body temperatures than nonreproductive.
• Maternal thermal requirements had no effect on egg size and early cleavage rate.
• Newts do not manipulate egg traits by maternal thermoregulation.

Reproductive females manipulate offspring phenotypes by modifying conditions during embryogenesis. In ectotherms, the environmental control over embryogenesis is often realized by changes in maternal thermoregulation during gravidity. To determine if reproduction influences thermoregulatory behavior in species where females lay eggs shortly after fertilization (strict oviparity), we compared preferred body temperatures (Tp) between reproductive (egg-laying) and non-reproductive female newts, Ichthyosaura alpestris. Next, we exposed reproductive females to temperatures mimicking Tp ranges of reproductive and non-reproductive individuals to find out whether the maternally modified thermal regime influences ovum and jelly coat volume, and early cleavage rates at the time of oviposition. In the thermal gradient, reproductive females maintained their body temperatures within a narrower range than non-reproductive individuals. The exposure of ovipositing females to temperatures preferred during their reproductive and non-reproductive period had a negligible influence on egg size and early cleavage rates. We conclude that the modification of maternal thermoregulatory behavior provides a limited opportunity to manipulate egg traits in newts.