Isogamy in large and complex volvocine algae is consistent with the gamete competition theory of the evolution of anisogamy.

Although the gamete competition theory remains the dominant explanation for the evolution of anisogamy, well-known exceptions to its predictions have raised doubts about the completeness of the theory. One of these exceptions is isogamy in large or complex species of green algae. Here, we show that this exception may be explained in a manner consistent with a game-theoretic extension of the original theory: a constraint on the minimum size of a gamete may prevent the evolution of continuously stable anisogamy.