Sexual patterns of prebreeding energy reserves in the common frog Rana temporaria along a latitudinal gradient

Abstract

The ability to store energy is an important life history trait for organisms facing long periods without energy income, and in particular for capital breeders such as temperate zone amphibians, which rely on stored energy during reproduction. However, large scale comparative studies of energy stores in populations with different environmental constraints on energy allocation are scarce. We investigated energy storage patterns in spring (after hibernation and before reproduction) in eight common frog Rana temporaria populations exposed to different environmental conditions along a 1600 km latitudinal gradient across Scandinavia (range of annual activity period is 3Á7 months). Analyses of lean body weight (eviscerated body mass), weight of fat bodies, liver weight, and liver fat content, showed that 1) post-hibernation/prebreeding energy stores increased with increasing latitude in both sexes, 2) males generally had larger energy reserves than females and 3) the difference in energy stores between sexes decreased towards the north. Larger energy reserves towards the north can serve as a buffer against less predictable and/or less benign weather conditions during the short activity period, and may also represent a risk-averse tactic connected with a more pronounced iteroparous life history. In females, the continuous and overlapping vitellogenic activity in the north may also demand more reserves in early spring. The general sexual difference could be a consequence of the fact that, at the time of our sampling, females had already invested their energy into reproduction in the given year (i.e. their eggs were already ovulated), while the males' main reproductive activities (e.g. calling, mate searching, sexual competition) occurred later in the season.Acquisition and expenditure of energy are important factors affecting life history variation. In fact, different life history strategies largely arise by the different ways organisms allocate the available energy among maintenance, growth, defence and reproduction. An important aspect of energy acquisition and expenditure is how these are temporally related. For example, energetic expenditures of reproduction can be supported by simultaneous energy uptake (income breeders) or by using stored energy that was gathered in advance (capital breeders sensu Stearns 1992 and Jönsson 1997; see also Drent and Daan 1980 for the original formulation of the capital and income breeding concepts). Long-term energy storage and continuous energy intake without storage are not mutually exclusive, and a range of different strategies, from pure capital breeding at one end, through mixed strategies, to pure income breeding at the other end is possible. Energy storage might also be energetically costly (Jönsson 1997), although for ectothermic animals the effect could be minimal (Bonnet et al. 1998). The function of energy stores is often to allow organisms to reproduce, or to survive over periods when feeding is constrained for one reason or another (e.g. absence of food, harsh environmenta...

Hibernation physiology, freezing adaptation and extreme freeze tolerance in a northern population of the wood frog

“…Anuran species, and populations within species, inhabiting especially cold climates tend to stockpile more glycogen, and thus have heavier livers, than counterparts from milder locales (Chen et al, 2011;Jönsson et al, 2009;Pasanen and Koskela, 1974). Accordingly, our Alaskan frogs had extremely rich glycogen deposits and an extraordinary HSI; indeed, the percentage of body mass represented by the liver was 22%, as compared with 8% in our Ohioan frogs.…”

Batrachochytrium dendrobatidis infection dynamics in the Columbia spotted frog Rana luteiventris in north Idaho, USA

“…It is possible that behavior in the breeding season, when females may come in direct skin contact with multiple competing males (Davis & Verrell 2005), can help explain the observed pattern. An alternative explanation for the increased prevalence in females is a differential host immune response, particularly if females devote energy to reproduction at the expense of immune function (Jönsson et al 2009). However, both sexes contributed substantially to the Bd zoospore pool in these north Idaho ponds.…”

Capital and income breeding: the role of food supply

“…These analytical models have tended to emphasize the importance of maternal mass (e.g., Costa 1993, Boyd 1998, Trillmich and Weissing 2006. By contrast, comparative approaches have emphasized the importance of aspects of food supply, such as seasonality and predictability (Thomas 1988, Schulz and Bowen 2005, Jo¨nsson et al 2009). Schulz and Bowen (2005), in particular, found that when phylogeny was controlled for, correlates of different breeding strategies were not well explained by maternal body mass.…”