The evolution of thermal performance curves in semi-aquatic newts: Thermal specialists on land and thermal generalists in water?

a b s t r a c t The position and shape of thermal performance curves (TPCs, the functions relating temperature to physiological performance) for ecologically relevant functions will directly affect the fitness of ectotherms and therefore should be under strong selection. However, thermodynamic considerations predict that relationships between the different components of the TPC will confound its evolutionary optimization. For instance, the ''jack-of-all-temperatures'' hypothesis predicts a trade-off between the breadth of the TPC and the maximal performance capacity; the ''warmer is better'' hypothesis suggests that low thermal optima will come with low absolute performances. Semi-aquatic organisms face the additional challenge of having to adjust their TPCs to two environments that are likely to differ in mean temperature and thermal variability. In this paper, we examine how parameters of the TPCs for maximal running and swimming speed have co-evolved in the semi-aquatic newt genus Triturus. We consider evolutionary relationships between the width and the height of the TPCs, the optimal temperatures and maximal performance. Phylogenetic comparative analyses reveal that in Triturus, swimming and running differ substantially in the (co-)variation of TPC parameters. Whereas evolutionary changes in the TPC for swimming primarily concern the shape of the curve (generalist versus specialist), most interspecific variation in running speed TPCs involves shifts in overall performance across temperatures

Underwater sound production varies within not between species in sympatric newts

Sound production is a widespread phenomenon among animals. Effective sound use for mate or species recognition requires some acoustic differentiation at an individual or species level. Several species of caudate amphibians produce underwater sounds, but information about intra- and interspecific variation in their acoustic production is missing. We examined individual, sex, and species variation in underwater sound production in adults of two sympatric newt taxa, Ichthyosaura alpestris and Lissotriton vulgaris. Individual newts produced simple low- (peak frequency = 7–8 kHz) and mid-high frequency (14–17 kHz) clicks, which greatly overlap between sexes and species. Individual differences explained about 40–50% of total variation in sound parameters. These results provide foundations for further studies on the mechanisms and eco-evolutionary consequences of underwater acoustics in newts

Mothers Matter Too: Benefits of Temperature Oviposition Preferences in Newts

The maternal manipulation hypothesis states that ectothermic females modify thermal conditions during embryonic development to benefit their offspring (anticipatory maternal effect). However, the recent theory suggests that the ultimate currency of an adaptive maternal effect is female fitness that can be maximized also by decreasing mean fitness of individual offspring. We evaluated benefits of temperature oviposition preferences in Alpine newts (Ichthyosaura [formerly Triturus] alpestris) by comparing the thermal sensitivity of maternal and offspring traits across a range of preferred oviposition temperatures (12, 17, and 22°C) and by manipulating the egg-predation risk during oviposition in a laboratory thermal gradient (12–22°C). All traits showed varying responses to oviposition temperatures. Embryonic developmental rates increased with oviposition temperature, whereas hatchling size and swimming capacity showed the opposite pattern. Maternal oviposition and egg-predation rates were highest at the intermediate temperature. In the thermal gradient, females oviposited at the same temperature despite the presence of caged egg-predators, water beetles (Agabus bipustulatus). We conclude that female newts prefer a particular temperature for egg-deposition to maximize their oviposition performance rather than offspring fitness. The evolution of advanced reproductive modes, such as prolonged egg-retention and viviparity, may require, among others, the transition from selfish temperature preferences for ovipositon to the anticipatory maternal effect

Raw data_control group

Maximum swimming velocities of newt larvae in the control group (without predator)

Growth rates in newt larvae

Growth rates of larvae in two newt species exposed to three thermally fluctuating regimes

Thermoregulatory indices in larvae of two newt species

Thermoregulatory indices of larvae exposed to intra- or interspecific social interactions

Data from: Can newts cope with the heat? Disparate thermoregulatory strategies of two sympatric species in water

Many ectotherms effectively reduce their exposure to low or high environmental temperatures using behavioral thermoregulation. In terrestrial ectotherms, thermoregulatory strategies range from accurate thermoregulation to thermoconformity according to the costs and limits of thermoregulation, while in aquatic taxa the quantification of behavioral thermoregulation have received limited attention. We examined thermoregulation in two sympatric newt species, Ichthyosaura alpestris and Lissotriton vulgaris, exposed to elevated water temperatures under semi-natural conditions. According to a recent theory, we predicted that species for which elevated water temperatures pose a lower thermal quality habitat, would thermoregulate more effectively than species in thermally benign conditions. In the laboratory thermal gradient, L. vulgaris maintained higher body temperatures than I. alpestris. Semi-natural thermal conditions provided better thermal quality of habitat for L. vulgaris than for I. alpestris. Thermoregulatory indices indicated that I. alpestris actively thermoregulated its body temperature, whereas L. vulgaris remained passive to the thermal heterogeneity of aquatic environment. In the face of elevated water temperatures, sympatric newt species employed disparate thermoregulatory strategies according to the species-specific quality of the thermal habitat. Both strategies reduced newt exposure to suboptimal water temperatures with the same accuracy but with or without the costs of thermoregulation. The quantification of behavioral thermoregulation proves to be an important conceptual and methodological tool for thermal ecology studies not only in terrestrial but also in aquatic ectotherms

Preferred body temperatures of newt larvae

Parameters of preferred body temperatures in larvae of two newt species reared under the presence or absence of heterospecifics