Adult Triturus newts show spatial and temporal variation in sex ratio at the aquatic breeding site, to the extent that contrasting scenarios on the evolution of mating systems appear to be supported. I collected data for the five western European species (Triturus alpestris, Triturus cristatus, Triturus helveticus, Triturus marmoratus, and Triturus vulgaris) over 500 ponds and 27 yr in two areas in France, to test the hypothesis that the phenology of pond presence is independent of gender. Approximately equal numbers of males and females were found. However, in T. marmoratus males outnumbered females, which could be explained by a proportion of females skipping annual breeding opportunities. In the hybrid T. cristatus × T. marmoratus, females were twice as numerous as males, in accordance with Haldane's rule. A trend was observed for a male-biased sex ratio at the start of the aquatic season (late winter–early spring) and for a female bias toward the end of the aquatic season (early summer), suggesting that males mostly arrive and leave the breeding sites ahead of the females. The data do not support evolutionary scenarios selecting for the early breeding of female T. vulgaris.
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