title: Using GAMM to examine inter-individual heterogeneity in thermal performance curves for Natrix natrix indicates bet hedging strategy by mothers.
abstract: The thermal performance curve (TPC) illustrates the dependence on body- and therefore environmental- temperature of many fitness-related aspects of ectotherm ecology and biology including foraging, growth, predator avoidance, and reproduction. The typical thermal performance curve model is linear in its parameters despite the well-known, strong, non-linearity of the response of performance to temperature. In addition, it is usual to consider a single model based on few individuals as descriptive of a species-level response to temperature. To overcome these issues, we used generalized additive mixed modeling (GAMM) to estimate thermal performance curves for 73 individual hatchling Natrix natrix grass snakes from seven clutches, taking advantage of the structure of GAMM to demonstrate that almost 16% of the deviance in thermal performance curves is attributed to inter-individual variation, while only 1.3% is attributable to variation amongst clutches. GAMM allows precise estimation of curve characteristics, which we used to test hypotheses on tradeoffs thought to constrain the thermal performance curve: hotter is better, the specialist-generalist trade off, and resource allocation/acquisition. We observed a negative relationship between maximum performance and performance breadth, indicating a specialist-generalist tradeoff, and a positive relationship between thermal optimum and maximum performance, suggesting "hotter is better". There was a significant difference among matrilines in the relationship between Area Under the Curve and maximum performance - relationship that is an indicator of evenness in acquisition or allocation of resources. As we used unfed hatchlings, the observed matriline effect indicates divergent breeding strategies among mothers, with some mothers provisioning eggs unequally resulting in some offspring being better than others, while other mothers provisioned the eggs more evenly, resulting in even performance throughout the clutch. This observation is reminiscent of bet-hedging strategies, and implies the possibility for intra-clutch variability in the TPCs to buffer N. natrix against unpredictable environmental variability.
authors.affiliation: Station d'Ecologie Théorique et Expérimentale, UMR 5321, CNRS 2 route du CNRS, 09200 Moulis, France.
authors.forename: Mathew J
authors.initials: MJ
authors.lastname: Vickers
authors.affiliation: Station d'Ecologie Théorique et Expérimentale, UMR 5321, CNRS 2 route du CNRS, 09200 Moulis, France.
authors.forename: Fabien
authors.initials: F
authors.lastname: Aubret
authors.affiliation: CESCO UMR 7204, Bases écologiques de la Conservation, Muséum national d'Histoire naturelle, 4 Avenue du Petit Château, 91800 Brunoy, France; CEFE UMR 5175, CNRS - Université de Montpellier - Université Paul-Valéry Montpellier - EPHE, Laboratoire Biogéographie et Ecologie des Vertébrés, 1919 route de Mende, 34293 Montpellier, France. Electronic address: acoulon@mnhn.fr.
authors.forename: Aurélie
authors.initials: A
authors.lastname: Coulon
mesh_terms: D000064:Acclimatization; D000818:Animals; D017812:Colubridae / Q000502:physiology*; D005260:Female; D006358:Hot Temperature; D008962:Models, Theoretical; D012098:Reproduction
keywords: Ectotherm; Evolutionary; Inter-individual variation; Reptile; Snake; Specialist-generalist tradeoff