| Summary: | When several male snakes dispute over one female in the breeding season, two major male-male rivalries are known to occur: male-male combat and multimale breeding aggregation. The roles of male body size and the degree of sexual size dimorphism are different between these rivalries. We report field observations of mating behaviour including a multimale breeding aggregation of pseudoxyrhophiins, Dromicodryas bernieri and D. quadrilineatus, in northwestern Madagascar, which have a local name, “Maro longo”, meaning “many friends”. To examine the relationships between sexual size dimorphism and mating strategies of males, we also analysed the body size of the two species of Dromicodryas and two other pseudoxyrhophiins, Leioheterodon madagascariensis and L. modestus, which are known to exhibit the male-male combat. Our data obtained during a long-term field study showed that D. bernieri and D. quadrilineatus have female-biased sexual size dimorphism, whereas L. madagascariensis and L. modestus have male-biased sexual size dimorphism. This result conforms to the general tendency of the relationship between body size and male-male rivalry in snakes.
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