Oviposition-site selection by the toad Melanophryniscus rubriventris in an unpredictable environment in Argentina F.J. Goldberg, S. Quinzio, and M. Vaira Abstract: Oviposition-site selection plays an important role in the reproductive success of amphibians. In unpredictable environments where resources vary within a season, amphibians should select oviposition sites using parameters that can be easily evaluated, or spawn in several ponds to increase offspring survival. Melanophryniscus rubriventris (Vellard, 1947) uses shallow ephemeral ponds in an unpredictable montane-forest environment. During 40 consecutive days, we sur- veyed potential spawning sites and measured several biotic and abiotic factors to determine if any of these factors influ- enced breeding-site selection. We also described the spawning behavior of this species. Water temperature and pond level (flooded or not) were significant predictors of whether a pond was used or not. Warmer ponds would permit accelerated development of larvae in habitats where ponds are ephemeral and their presence unpredictable. Because of the short and unpredictable hydroperiods, it will be better to select a pond full of water instead of evaluating other pond characteristics that can be very variable. Mating pairs spread several egg masses to different sites but in the same pond. This behavior is likely a consequence of pairs avoiding interactions with intruding males and not as a strategy to enhance offspring sur- vival. Re ´sume ´: La se ´lection des sites de ponte joue un ro ˆle important dans le succe `s reproductif des amphibiens. Dans les mi- lieux impre ´visibles ou ` les ressources varient en fonction des saisons, les amphibiens devraient choisir leurs sites de ponte d’apre `s des variables qui peuvent e ˆtre facilement e ´value ´es ou alors pondre dans plusieurs e ´tangs afin d’ame ´liorer la survie de leurs rejetons. Melanophryniscus rubriventris (Vellard, 1947) utilise des e ´tangs temporaires peu profonds dans un envi- ronnement forestier de montagne peu pre ´visible. Nous avons inventorie ´ pendant 40 jours successifs les sites potentiels de reproduction et mesure ´ plusieurs facteurs biotiques et abiotiques afin de de ´terminer si certains de ces facteurs influencent le choix du site de reproduction. Nous de ´crivons aussi le comportement reproducteur de l’espe `ce. La tempe ´rature et le ni- veau de l’eau de l’e ´tang (qu’il soit inonde ´ ou non) sont des variables pre ´dictives significatives de l’utilisation ou non d’un e ´tang. Les e ´tangs plus chauds devraient permettre un de ´veloppement acce ´le ´re ´ des larves dans les habitats ou ` les e ´tangs sont temporaires et leur pre ´sence impossible a ` pre ´dire. E ´ tant donne ´ les hydrope ´riodes courtes et impre ´visibles, il vaut mieux choisir un e ´tang rempli d’eau que d’e ´valuer d’autres caracte ´ristiques des e ´tangs qui peuvent e ˆtre tre `s variables. Les couples reproducteurs de ´posent plusieurs masses d’oeufs dans des sites diffe ´rents, mais au sein du me ˆme e ´tang. Ce com- portement s’explique vraisemblablement par le fait que les couples e ´vitent les interactions avec les ma ˆles intrus pluto ˆt que par une strate ´gie pour ame ´liorer la survie des rejetons. [Traduit par la Re ´daction] Introduction Habitat characteristics rarely are constant, and changes may have considerable effects on population dynamics (Southwood 1977; Orians and Wittenberger 1991; Jonze ´n et al. 2004). Some habitat features may change in a negligible way, but some may change dramatically over relatively short periods of time. In habitats where the availability of resources varies with seasons, variability is predictable and reproduction occurs in favourable periods. In contrast, in ha- bitats where changes are unpredictable and the availability of resources varies within a season, the detection of and ra- pid response to favourable conditions may be essential for the achievement of reproductive success (Stearns 1992). Oviposition-site selection plays an important role in the reproductive success of amphibians (Marsh and Borrell 2001). Advantages associated with the selection of oviposi- tion sites include the reduction of risks of mortality as a consequence of cannibalism, predation, competition, or pond duration (Semlitsch and Wilbur 1988; Hopey and Pet- ranka 1994; Denver et al. 1998; Binckley and Resetarits 2002, 2003). Adults of several species can detect the most suitable oviposition sites based on different characteristics such as vegetation (Ambystoma jeffersonianum (Green, 1827); Thompson et al. 1980), temperature (Rana sylvatica LeConte, 1825; Seale 1982), depth, water-holding capacity, and both presence and previous density of eggs, tadpoles, and predators (Edalorhina perezi Jime ´nez de la Espada, 1871 (Murphy 2003); Hoplobatrachus occipitalis (Gu ¨nther, Received 26 September 2005. Accepted 23 February 2006. Published on the NRC Research Press Web site at http://cjz.nrc.ca on 31 May 2006. F.J. Goldberg 1 and S. Quinzio. Instituto de Bio y Geociencias y Museo de Ciencias Naturales, Universidad Nacional de Salta, Mendoza 2, Salta 4400, Argentina. M. Vaira. CONICET, Museo de Ciencias Naturales, Universidad Nacional de Salta, Mendoza 2, Salta 4400, Argentina. 1 Corresponding author (e-mail: jgoldberg@argentina.com). 699 Can. J. Zool. 84: 699–705 (2006) doi:10.1139/Z06-038 # 2006 NRC Canada