Venom in Furs: Facial Masks as Aposematic Signals in a Venomous Mammal

Abstract

The function of colouration in animals includes concealment, communication and signaling, such as the use of aposematism as a warning signal. Aposematism is unusual in mammals, and exceptions help us to understand its ecology and evolution. The Javan slow loris is a highly territorial venomous mammal that has a distinctive facial mask and monochromatic vision. To help understand if they use aposematism to advertise their venom to conspecifics or predators with different visual systems, we studied a population in Java, Indonesia. Using ImageJ, we selected colours from the facial masks of 58 individuals, converted RBG colours into monochromatic, dichromatic and trichromatic modes, and created a contrast index. During 290 captures, we recorded venom secretion and aggressiveness. Using Non-metric Multidimensional Scaling and generalised additive models for location, scale and shape, we found that young slow lorises differ significantly from adults, being both more contrasting and more aggressive, with aggressive animals showing fewer wounds. We suggest aposematic facial masks serve multiple purposes in slow lorises based on age. Change in colouration through development may play a role in intraspecific competition, and advertise toxicity or aggressiveness to competitors and/or predators in juveniles. Aposematic signals combined with intraspecific competition may provide clues to new venomous taxa among mammals.

Special Issue: Evolutionary Ecology of Venom

“…Venom is rare in mammals but presents an interesting study system in that intraspecific competition has been proposed as a primary use in several cases (otherwise rare in other venomous animal groups) [ 2 , 22 ]. In keeping with recent evidence that slow lorises use venom primarily in intraspecific competition [ 23 ], Nekaris et al [ 24 ] present evidence that this has resulted in the evolution of contrasting face coloration that acts as an aposematic signal. Aposematic signals are usually directed at other species, so an example of warning signals directed primarily at conspecifics is unusual but may be linked to the common use of facial coloration as social signals in mammals, consistent with previous suggestions that sociality may be related to the evolution of mammal venoms [ 4 ].…”

Examining the molecular basis of coat color in a nocturnal primate family (Lorisidae)

“…We expected MC1R nucleotide changes to be associated with the more patterned and colorful Lorisinae (Loris and Nycticebus), but that was not the case. We predicted this as researchers have speculated Lorisinae patterning and coloration are adaptive (Nekaris & Bearder, 2007;Nekaris et al, 2013Nekaris et al, , 2019. Our study was unable to truly test the relationship between venom and coloration, as only Nycticebus possess venom, and the genetics of venom production in this species is still being explored.…”

Venom Use in Eulipotyphlans: An Evolutionary and Ecological Approach

“…However, following the venom definition proposed by Fry et al [ 21 ], three species of vampire bats (Chirpotera), i.e., Desmodus rotundus , Diaemus youngi and Diphylla ecuadta [ 22 , 35 , 46 , 47 , 48 , 49 ], and as many as eight species of slow lorises ( Nycticebus spp.) (Primates) can be classified as venomous, although among lorises only four species ( N. bengalensis , N. coucang , N. pygmaeus and N. javanicus ) have been confirmed as venomous so far [ 16 , 35 , 50 , 51 , 52 , 53 ]. Additionally, hedgehogs, closely related to shrews [ 54 ], have been suspected of being venomous, but studies by Mebs [ 55 ] on the biological and enzymatic activities of saliva of the European hedgehog Erinaceus europaeus have shown that hedgehogs do not produce venom in their salivary glands.…”