Adaptive significance of food income in European snakes: body size is related to prey energetics MARCO A. L. ZUFFI 1 *, SARA FORNASIERO 1 , RICCARDO PICCHIOTTI 1 , PIERA POLI 2 and MARCELLO MELE 2 1 Museo di Storia Naturale e del Territorio, Università di Pisa, via Roma 79, I-56011, Calci (Pisa), Italy 2 Dipartimento di Agronomia e gestione dell’Agroecosistema, Università di Pisa, via San Michele degli Scalzi 5, I-56121 Pisa, Italy Received 7 September 2009; revised 1 December 2009; accepted for publication 1 December 2009 Feeding strategies and diet patterns have been extensively investigated in vertebrates and, more specifically, in snakes. Although it has been hypothesized that prey species may differ in terms of energy content, almost no theoretical or practical study has been carried out to determine actual nutritional values of the common prey types of wild snakes. Our model taxa were a selection of widely distributed and well known European snake species, which have all been studied in depth: approximately 76% of their diet is composed of mammals, reptiles, and insects. We therefore selected a single model species for each of these categories and proceeded with the analyses. Nutritional values were determined using a standard procedure: lizards and mice were richer in proteins than insects (crickets); insects and mice were richer in lipids than lizards, and mice and crickets have a higher energy content than lizards; lizards were rich in ashes. We then applied our experimental results to a selected sample of European terrestrial snakes (11 populations, ten species, seven genera, two families) characterized by different body size (50–160 cm total length) and reproductive strategies (oviparous versus viviparous), aiming to correlate these parameters with patterns of energy income. A direct relationship was found between body mass/body length ratio (BCI, body condition index) and meal energetics: the higher the BCI, the higher was the metabolic requirement, whereas BCI was independent of species or of reproductive system effect. Large-sized snakes thus need a highly diversified and more energy-rich diet than smaller snakes, supporting previous hypotheses. The simple applicability of this method could be of valuable support in further comparative research work, reducing experimental costs and stimulating further ecological, behavioural, and, possibly, phylogenetic comparisons. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 307–317. ADDITIONAL KEYWORDS: Colubridae – comparative analysis – diet – energy balance – Serpentes – Viperidae. INTRODUCTION The energetics of food income, patterns of energy consumption and field metabolic rates among verte- brates have been reported at great length (Nagy, 2005; Codron et al., 2007), and food quality (Lanszki, Molnár & Molnár, 2006), food abundance, and choice of selected prey items (Estades, Vukasovic & Tomasevic, 2008) have been studied in depth. Energy requirements and subsequent dietary patterns have often been related to sex, behavioural patterns, sea- sonal variation, or to body size (Kohler et al., 2008; Jiang et al., 2009). The consequences of different experimental food intake treatments, as well as their resulting effects on growth patterns, physiology of development, and reproduction, have recently received specific attention in amphibians and in reptiles (Cox & Secor, 2007; Secor, Wooten & Cox, 2007). Indeed, analyses on daily energetic metabolism have greatly enhanced our overall knowledge on the metabolic turnover in a number of reptiles (Avery, 1971, 1978; Gallagher *Corresponding author. E-mail: marcoz@museo.unipi.it Biological Journal of the Linnean Society, 2010, 100, 307–317. With 1 figure © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 307–317 307