Risky business in ephemeral waters: the reproductive ecology of the Sandpaper Frog, Lechriodus fletcheri

Many amphibian species have evolved to exploit temporary aquatic systems, such as ephemeral pools, for the purposes of reproduction. These systems may be selected as they offer a refuge from the competition and predation pressures faced in more permanent systems. However, given that they hold onto water intermittently, these are akin to vanishing islands that are only available for egg deposition on some occasions. As such, though there use may offer some benefits during the aquatic stage of the amphibian life cycle, it may also carry an increased risk of complete reproductive failure as hydroperiods vary unpredictably and may be too short for tadpoles to complete development before desiccation occurs. Understanding the life history and ecological trade-offs involved in exploiting these ephemeral habitats offer an opportunity to test and understand many aspects of life history evolution. Two key threats to survival in the tadpole phase can be identified: (1) Ephemerality of aquatic breeding habitats. Ephemerality exposes spawn and tadpoles to variable aquatic conditions, food resources and hydroperiod. The greatest risk for offspring in temporary aquatic breeding habitats is the risk of mortality from desiccation if hydroperiods are below a critical threshold for them to reach metamorphosis. This risk is highest under circumstances where rainfall is variable, unpredictable and intermittent, as adults are more likely to mistime spawning trying to match optimal rainfall period or make non-viable breeding site choices (where hydroperiods are too short). (2) Cannibalism. Short hydroperiods in aquatic systems often lead to food resource limitations. Under such conditions, selection for cannibalism may be a strong mechanism to increase nutritional availability when large conspecific spawning events occur. Such variability in both hydroperiods and the presence of conspecifics are strong selection pressures that have driven the evolution of a diverse array of strategies, both in the reproducing adults and their offspring, to improve the chances of reproductive success. This thesis explores these strategies and their adaptive function in temporary aquatic systems, by exploring the reproductive biology of the sandpaper frog, Lechriodus fletcheri. This species almost exclusively reproduces in small, highly ephemeral pools on the forest floor that dry within a matter of days or weeks after rainfall has ceased, making it an ideal model for exploring adaptation in the face of variability. The thesis begins by examining the effects of variable hydroperiod on offspring survival, before moving on to possible adaptations that have evolved in this species to improve the odds of reproductive success, including bet-hedging through iteroparity, multi-clutching and adaptive oviposition site selection in response to conspecific presence. We describe cannibalism of unhatched L. fletcheri embryos by previously hatched conspecific tadpoles. This leads to an analysis of the possible effect cannibalism has had on oviposition site selection in relation to the presence of conspecifics at various life history stages, which likely involves a complex game were individuals try and take advantage of their fellow conspecifics as food while simultaneously avoiding becoming food to these conspecifics themselves. Finally, we test whether facial skin features of L. fletcheri adults can be used to identify individuals in the field, as a substitute for more expensive and labour intensive marking techniques in capture-mark-recapture studies undertaken to investigate the ecology of L. fletcheri. For many amphibian species, the ways in which individuals deal with the effects of environmental variability in terms of their reproductive regimes has not been investigated in detail. We conclude that studies that shed a light on the adaptive mechanisms of reproductive strategies that evolve in direct response to environmental variability are critical, not only from a natural history perspective, but to assess the possible vulnerability of species that exploit these systems to possible changes in patterns of environmental variability as a result of climate change.