Scaling limits of bisexual Galton–Watson processes

Bisexual Galton–Watson processes are discrete Markov chains where reproduction events are due to mating of males and females. Owing to this interaction, the standard branching property of Galton–Watson processes is lost. We prove tightness for conveniently rescaled bisexual Galton–Watson processes, based on recent techniques developed in [V. Bansaye, M.E. Caballero, and S. Méléard, Scaling limits of population and evolution processes in random environment, Electron. J. Probab. 24(19) (2019), pp. 1–38]. We also identify the possible limits of these rescaled processes as solutions of a stochastic system, coupling two equations through singular coefficients in Poisson terms added to square roots as coefficients of Brownian motions. Under some additional integrability assumptions, pathwise uniqueness of this limiting system of stochastic differential equations and convergence of the rescaled processes are obtained. Two examples corresponding to mutual fidelity are considered.