HERPETOLOGICAL JOURNAL, Vol. 16, pp. 177-182 (2006) REPRODUCTIVE ECOLOGY OF A MEDITERRANEAN RATSNAKE, THE LADDER SNAKE RHINECHIS SCALARIS (SCHINZ, 1822) JUAN M. PLEGUEZUELOS AND MÓNICA FERICHE Departamento de Biologia Animal, Facultad de Ciencias, Universidad de Granada, E-18071 Granada, Spain Organisms that produce more than one newborn at every reproductive event must choose between two options with respect to their reproductive output: to produce a few large or many small young. The decision will be influenced by the spectrum of prey sizes available to young. The ladder snake (Rhinechis scalaris), a heavy-bodied Mediterranean colubrid, is well suited for the study of its reproductive ecology under this cue: the species consumes only endothermic prey and, thereafter, hatchlings of this gape-size-limited predator must be large enough to prey on small mammals. We analysed the reproductive ecology of this species, a quasi-endemic to the Iberian Peninsula, by studying a large sample of specimens collected in the south-eastern Iberian Peninsula. Most adult females (83.3%) reproduced in sequential years, with vitellogenesis beginning in early spring, and oviposition occurring in the first half of July. In contrast to the general rule for most temperate snakes, no depletion in fat bodies was observed during the period of vitellogenesis, females exhibiting a very high level of fat-body reserves throughout all months of the activity period. When compared with other Mediterranean species, hatching occurred very late in the activity season (October), newborns were rather heavy bodied, with very high fat-body levels, and apparently did not feed until the following spring. From our dataset, we suggest that female R. scalaris produce hatchlings large enough to enter hibernation without feeding, perhaps increasing in this way the survival rate of juveniles in their first calendar year. They probably need to devote their reserves at hatching to growth and to better face their first, bulky prey. Key words: colubrid, fat bodies, hatching time, hatchling size Correspondence: J. M. Pleguezuelos, Departamento de Biologia Animal, Facultad de Ciencias, Universidad de Granada, E-18071 Granada, Spain. E-mail: juanple@ugr.es INTRODUCTION Snakes have begun to attract increasing attention from many researchers as model organisms in ecological stud- ies (Shine & Bonnet, 2000). Reproductive ecology is among the topics most addressed by researchers, as snakes exhibit wide diversity in reproductive strategies, in terms of frequency of reproduction, strategies to fuel reproductive energy cost (“capital” versus “income” breeders, as proposed by Drent & Daans, 1980), and clutch size or hatchling size (Ford & Seigel, 1989). Moreover, noteworthy links can be found between the re- productive ecology of a snake and other traits of its natural history, such as feeding ecology (Shine, 2003). Certainly, food intake determines the reproductive out- put of snakes (Ford & Seigel, 1989). The reproductive output of organisms, in the simplest analysis, can be split into two possibilities: to produce a few large young, or to produce many small young (Roff, 1992; Gregory & Larsen, 1993). The choice would be mediated by the spectrum of prey sizes available to the hatchlings (Nussbaum, 1981). With a given amount of energy supplied for reproductive output, a species that preys on a wide range of prey types and size would choose between the two possibilities. However, species with a narrower spectrum in prey type and/or size, par- ticularly if available prey for neonates are large, would find the choice of producing a few large hatchlings to be more adaptive (Sun et al., 2002). The ladder snake, Rhinechis scalaris, is a rather large, heavy-bodied and oviparous colubrid, that inhabits the Iberian Peninsula, south-eastern France, and the westernmost part of Italy (Pleguezuelos & Cheylan, 1997), and is a suitable or- ganism for analysing links between reproductive and feeding ecology. This colubrid has the peculiarity of feeding only on endotherms, mostly small mammals (Cheylan & Guillaume, 1993). As opposed to other medium-sized Mediterranean predators, whether snakes (Díaz-Paniagua, 1976; Saint Girons, 1980) or other animals (Jacksic et al., 1982), R. scalaris does not undergo a typical ontogenetic shift in dietary hab- its. While young individuals of many snake species prey on small-sized, slender-bodied ectotherms, and large individuals prey on bulky prey such as small mammals, both young and adult R. scalaris prey al- most exclusively on small mammals (Pleguezuelos, 1998). Thus, we would expect R. scalaris, a gape-lim- ited predator, to produce few large hatchlings to minimize predator/prey size constraints in the first pe- riod of individual development (King, 1993). Here we study a large sample of free-ranging ani- mals and museum specimens from the south-eastern Iberian Peninsula to determine the reproductive ecol- ogy of this snake; individuals were also checked for stomach contents to obtain an index of the feeding rate of the species. We address the following main ques- tions: (1) Do male and female reproduce in sequential years? (2) Is there fat-body cycling in sexually mature individuals, and if so, is cycling tied to vitellogenesis in females? (3) Is clutch size related to maternal size? Does the female produce large clutches of small