Embryonic life histories in annual killifish: adapted to what?

Adaptation requires an evolving strategy and an environment. Given an environment, we predict or estimate which strategies are adapted. Given a strategy, we want to know in which environments it might be adapted. Example calculations aiming to determine such environments, named evolutionarily singular environments ESE, are presented using lab data on embryonic life histories of Austrolebias annual killifish. Annual killifish embryos can arrest development and survive desiccation of temporary ponds in the soil. They might implement diversified bet-hedging, generally seen as an adaptation to uncertain environments. Using parameter estimates and parsimonious assumptions, a population dynamical model is constructed with explicit developmental stages. Using invasion fitness gradients of rates of development and hatching probabilities, it is investigated whether these could be adapted to pond filling regimes with gradual filling and drying and deterministic within-year variation only. The life history as a whole is not adapted to the regular within-year annual cycles investigated, with one or two periods where reproduction can occur. Faster development rates were always favoured, just as in constant environments. Only for hatching probabilities, pond filling regimes were found which made their invasion fitness sensitivities zero. However, the observed trait values did not have long-term evolutionary stability in these ESE. Therefore, neither the developmental rates nor the hatching strategy seem adapted to within-year patterns of environmental change.