Ontogeny of heterothermy

Interest is rising on how physiological flexibility can buffer organisms from environmental hazards, such as periods of food shortage. Heterothermy (i.e. daily torpor and hibernation) allows animals to save energy in response to reduced food availability. Although heterothermy in adult mammals has been studied in detail, there is very little knowledge on juvenile heterotherms, which are under strong selective pressure to grow and fatten prior to winter. This study first aims at investigating how the expression of heterothermy, in response to varying food availability during development, shapes torpor proneness at adulthood. We specifically hypothesize that individuals born under harsh conditions, hence using torpor extensively, are better prepared to use this strategy later in life. We hence chose to study the use of torpor during different developmental stages in a heterothermic species, the garden dormouse (Eliomys quercinus). This model species, which can use both daily torpor and hibernation, will allow us to investigate the flexibility of torpor use at different developmental stages. Complementary to torpor, another widespread energy-saving strategy is huddling (social thermoregulation). Only a few species use both strategies, among them is the garden dormouse. A major advantage of huddling is that it allows the maintenance of a high body temperature necessary for growth. Little is known about the synergetic physiological mechanisms linked to the use of both torpor and huddling. The second aim of this study is then to determine how the use of both strategies allows individuals to maximise energy savings in response to environmental constraints. Hence, we expect to reveal different phenotypic strategies, i.e. difference in the separate or combined use of torpor and huddling in response to varying food availability at differing developmental stages. Moreover, these strategies could be spread in a population through epigenetic transmission. As a third aim, we will hence determine the inter-generational epigenetic transmission of factors involved in the regulation of torpor and huddling. Such a mechanism is thought to explain how these energy-saving phenotypic traits can be transferred across generations during episodes of energetic shortage.