Privation and uncertainty in the small nursery of Peruvian laughing frogs: Larval ecology shapes the parental mating system
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Haugen, L. 2002. Privation and uncertainty in the small nursery of Peruvian laughing frogs: Larval ecology shapes the parental mating system. University of Oklahoma, PhD Thesis.
Abstract:
I investigated the life history traits of a Neotropical hylid, Osteocephaus planiceps, in relation to the stochastic nature of its larval microhabitat. This anuran deposits eggs in the water-filled leaf axils of bromeliads and palms. To determine the features that allow this species to exploit such larval habitats, I studied a free-living population of O. planiceps within a 3600 m2 area of the upper Amazon Basin, Departamento Loreto, Peru that contained both natural and artificial oviposition sites (water-filled plastic cups). The artificial sites allowed me to track survivorship of larvae and reproductive effort of breeding females (as frequency of egg depositions and clutch sizes). I also conducted laboratory experiments to determine how egg density affects tadpole survivorship, developmental time, and body size at emergence. Each female distributed 3 to 5 subsets of her clutch across several catchments, depositing eggs according to water volume (ca 2 - 2.5 eggs/ml). Clutch size increased with inter-clutch intervals and females adjusted their inter-clutch intervals to rainfall amounts by preferentially ovipositing on days after substantial rainfalls, when water oxygen levels are highest in the catchments. When choices were available, females tended to oviposit in larger volume nurseries and their egg masses fared better in such sites. Throughout tadpole development, females returned periodically to the oviposition sites, paired with males, and deposited additional fertilized eggs. Most of these secondary eggs were eaten immediately by resident tadpoles. In addition to oophagy, tadpoles were cannibalistic on siblings. Cannibalism appeared to be density-dependent. Tadpole density declined with larval cannibalism, resulting in more available food (i.e., nutritive eggs) per tadpole. Larval mortality was extremely high due to factors other than cannibalism (e.g., heterospecific predation). When a clutch failed, or when all individuals had metamorphosed, the subsequent deposition of eggs by the female essentially became the new primary clutch. The reproductive strategy of this species differs from most other anuran trophic feeders in that the secondary eggs are fertilized. Through over-production of young, females provide a food source for subsets of their initial clutches and automatically create replacement offspring in the event of unpredictable loss.
To determine how ecological factors of both offspring and adults can influence the adult mating system, I studied the parental care and mating behavior of the laughing frog, Osteocephalus planiceps. This species uses the water-filled leaf axils of bromeliads as larval nurseries. Both male and female laughing frogs are site-faithful, return? ing again and again throughout tadpole development to remate at the same sites, thereby providing their young with needed nutrients in the form of eggs. Whereas males tend to remain at the oviposition sites continuously and defend them against conspecific males, females leave the sites immediately after mating and do not return until their next egg deposition (roughly a week later). Due to the uneven spatial distribution of the oviposition sites, some individuals mate at clumped sites, while others use more isolated sites. Although there were no differences in mating success for both sexes at clumped vs. isolated sites, the diversity of breeding partners was greater at clumped sites, which featured polygynandrous mating systems, while at isolated sites, frogs tended to be monogamous. At the isolated sites, misdirected paternal care was uncommon, resulting primarily from females physically recruiting new partners to assist in oviposition for existing broods. Such borrowed males thus contributed overwhelmingly to unrelated tadpoles, but the great majority (81 %) of trophic eggs were consumed by both parents' own offspring. Male laughing frogs appear to be constrained in their ability to monopolize females by three factors: (i) the limited space in nurseries, (ii) the physiological needs of embryos and tadpoles, and (iii) the tendency of females to breed synchronously in response to rainfall. These generally result in a facultatively monogamous mating system.
Keywords: anuran, bromeliad, cannibalism, development, facultative monogamy, larvae, mating system, oophagy, Osteocephalus, over-production, parental care, reproduction