Negative maternal or paternal effects on tactic inheritance under a conditional strategy

Alternative behavioral and life-history tactics are common in animal populations. The conditional strategy model provides a powerful explanation for the evolution and persistence of such tactics, as it allows alternative tactics to be perpetuated even if there is tactic inheritance and tactics yield unequal mean fitness. In many biological systems negative maternal or paternal effects complicate the inheritance of condition and, hence, the inheritance of alternative tactics. Indeed, the inheritance of condition may result in the alternation of tactics across generations. In this paper, we show that the conditional strategy is robust to these effects on progeny condition. There is a unique and stable proportion of tactics under standard inheritance and unequal tactic fitness, and these two important properties of the conditional strategy hold even if negative maternal or paternal effects on progeny condition cause tactics to alternate across generations. However, the dynamics of tactic proportions pursuant to a perturbation of the equilibrium tactic proportions depend on the form of tactic inheritance. An application of our theoretical results to data from a population of smallmouth bass (Micropterus dolomieu) in which negative paternal effects dictate progeny condition reveals that age at first reproduction in males alternates regularly across generations. Furthermore, the model indicates that the population would return rapidly to equilibrium if the proportions of males that mature early or late in life were perturbed from the equilibrium within the system. This example shows how the model of the conditional strategy can be used to gain insight into tactic dynamics in situations where some of the model parameters are difficult or impossible to measure empirically.