SIZE-DEPENDENT MALE REPRODUCTIVE SUCCESS AND SIZE-ASSORTATIVE MATING IN THE MIDWIFE TOAD ALYTES OBSTETRICANS

In a field population of the midwife toad, Alytes obstetricans, a temp erate zone species with extensive paternal care, size-assortative mati ng was observed. During the more favourable mating season of 1987, lar ger males carried bigger single clutches, as expected from assortative matings. Furthermore, larger males experienced higher mating success over the whole season as well as during single egg carrying intervals. However, during the extraordinarily dry breeding period of 1988, no s ize-related male mating success was found. Males were in both years hi ghly successful caretakers as far as hatching success of the tadpoles was concerned. Brood care was associated with conditional costs for eg g-carrying males in 1988, but not in 1987. Neither hatching success no r hatching size of the tadpoles were correlated with male size. Possib le causes, leading to the observed mating advantage of larger-sized ma les in some years, but not in others, are discussed.