Is Malaysia’s “mystery monkey” a hybrid between Nasalis larvatus and Trachypithecus cristatus? An assessment of photographs

Abstract

Interspecific hybridization in primates is common but hybridization between distantly related sympatric primate species is rarely observed in the wild. We present evidence for a possible hybridization event between Nasalis larvatus and Trachypithecus cristatus in the Lower Kinabatangan Wildlife Sanctuary, Sabah, through assessment of photographs. We used a set of categorical characters and metric measurements to compare the putative hybrid with the likely parent species. Nonmetric comparison showed that this “mystery monkey” is intermediate in several characters. Measurements of limb proportions on photographs showed that the brachial, humerofemoral, and intermembral indexes are above 100 for N. larvatus and below 100 for T. cristatus on all photographs, whereas the crural index is higher than 100 in both species and the distributions of this index in the two species overlap. Brachial and intermembral indices of the putative hybrid were similar to those of N. larvatus . Crural and humerofemoral indices were closer to the values for T. cristatus than those of N. larvatus . Multiple observers confirmed the occurrence of mixed-species groups in the area, and interspecific mating has been photographed. The putative hybrid is now an adult female and was last photographed in September 2020 with an infant and swollen breast, suggesting lactation. We propose further noninvasive fecal sampling for genetic analyses to confirm the origins of this “mystery monkey.” This case of hybridization may be related to anthropogenic changes to the landscape, whereby expansion of oil palm plantations confines N. larvatus and T. obscurus to narrow riverine forest patches along the Kinabatangan. This observation therefore also may have conservation implications, indicating limited mate access and dispersal opportunities for these threatened primates. Supplementary Information The online version contains supplementary material available at 10.1007/s10764-022-00293-z.

Mixed-species association and a record of a hybrid offspring between Trachypithecus pileatus and Trachypithecus phayrei in Bangladesh

“…Several cases of hybridization have been found in langurs, e.g. Trachypithecus geei × Trachypithecus pileatus (Choudhury 2008 ), Semnopithecus entellus × Semnopithecus johnii (Hohmann and Herzog 1985 ; Hohmann 1989 ), and Nasalis larvatus × Trachypithecus cristatus (Lhota et al 2022 ). In the present study, we found an adult male immigrant in all the mixed-species groups.…”

“…Found in birds, mammals and fish, these mixed-species groups often comprise species from closely related taxa, i.e. the same genus or family, with some exceptional cases where groups involve members from different orders or even classes (Powell 1985 ; Heymann and Buchanan-Smith 2000 ; Stensland et al 2003 ; Rehg 2006 ; Kelm et al 2021 ; Lhota et al 2022 ). The interaction between the group members of mixed-species groups varies from passive association with little interaction to coordinated behaviours (Kelm et al 2021 ).…”

Distribution, social organization, and management of Semnopithecus johnii: An umbrella species of fragmented landscape of the Western Ghats

“…in India (Chetan et al., 2014). Mixed species groups are often reported from such overlapping ranges, for example, S. priam and S. johnii (Hohmann, 1988; Nag, 2020; Oates, 1982), S. priam thersites and S. vetulus philbricki (Lu et al., 2021), Trachypithecus pileatus and T. geei (Choudhury, 2008), Nasalis larvatus and T. cristatus (Lhota et al., 2022) and T. pileatus and T. phayrei (Al‐Razi et al., 2023). In some of these cases, hybridization between the mixed species was reported (Lu et al., 2021).…”