The evolution of life-history strategies should increase reproductive success and fitness of individuals. Alternative life history strategies like the offspring number – size trade-off, bet hedging or phenotypic plasticity should evolve, if species develop in unpredictable environments and face a high risk of reproductive failure. We used a wild population of the European common frog as a model system to ask the following questions. Are some mothers more successful than others in reproduction by spreading the risk of reproductive failure? Do metamorphic traits differ between and within specific matrilines? How does multiple paternity influence variability in metamorphic traits? We sampled all clutches of Rana temporaria in one pond and used microsatellite analyses to genotype them. When metamorphs started to emigrate, we fenced the pond and collected all emerging froglets. We recorded their size, weight and took DNA swabs for microsatellite analyses. With the program COLONY we assigned froglets to their respective mother (matriline), taking full and half-sib relations into account. Afterwards, we compared metamorphic traits between and within matrilines, as well as the influence of multiple paternity on the variability of half-sibs.
Results/Conclusions
We identified 40 matrilines with a total of 439 offspring within one natural pond. The timing of metamorphosis did not correlate with body size or body condition. Some mothers had a higher number of offspring and bigger metamorphs than others, indicating higher reproductive success and different life-history strategies. Developmental time was the most variable trait for metamorphs within and between matrilines, which could be the trait under natural selection in that pond. The other metamorphic traits, size and body condition differed as well, but on a much smaller scale. We identified multiple paternity in 80% off all matrilines, which increased the variability of developmental time, but not the variability of the other metamorphic traits. Mothers seem to follow different strategies to spread the risk of reproductive failure in an unpredictable environment by hedging their bets, expressed as high variability of metamorphic traits within a matriline. Additionally, larvae exhibited phenotypic plasticity mediated by environmental conditions, which presumably allows them to adapt and survive in these unpredictable environments. These strategies could ensure the maintenance of local population, when they lead to higher variability and therefore higher survival chances, at least for some offspring, in unpredictable environments.