Payoff matrix and four evolutionary stable strategies (ESS) from the game theory model [12].

W: egg without care; w: egg with care; P0: egg survival without parental care; P1: egg survival with uni-parental care; P2: egg survival with bi-parental care; P2> P1> P0; p: male deserts and then obtains another mating opportunity. ESS1: both sexes show care; wP2> WP1, otherwise female deserts; wP2> wP1 (1+p), otherwise male deserts. ESS2: female deserts and male cares; WP1 > wP2, otherwise female cares; WP1 > WP0 (1+P), otherwise male deserts. ESS3: female cares and male deserts; wP1 > WP0, otherwise female deserts; wP1 (1+p) > wP2 otherwise male cares. ESS4: both sexes desert; WP0 > wP1, otherwise the female cares; WP0 (1+p) > WP1, otherwise the male cares.