Gunung Mulu National Park (GMNP) in northwestern Borneo is marked by high species diversity and diverse environments. We present one new amphibian and ten new reptile records from GMNP and its surrounding area. In the records, Asthenodipsas jamilinaisi and Garthius chaseni were newly recorded in the Sarawak State. We also present the first record of Cyrtodactylus muluensis from outside of GMNP and the second record of Opisthotropis typica from the park. Combined with previous information, a total of 108 amphibians and 104 reptiles are known from GMNP, and their preferred habitat types are diverse. Furthermore, observed male-male combat of Dopasia buettikoferi is the first detailed description of the genus. Two color morphs of D. buettikoferi had an identical ND2 haplotype and appeared to be the same species. The present study provides new information about Bornean amphibians and reptiles, and also emphasizes the importance of continuous monitoring.

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.