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.
Highlights
The evolutionary function of colouration in vertebrates includes physiological aspects, concealment, courtship, species recognition, and intra- and interspecific communication and signalling [1,2]
Considering the colour values in Munsell system in a monochromatic scheme, we found no separation among age classes in the Non-metric Multidimensional Scaling (NMDS) (Figure 1) and no relationship between the colour values and the individual ages in days (E-value (E) = −0.008, Standard Error (SE) = 0.0006, t-value = −1.39, coefficient of determination (r2 ) = 0.08, p = 0.17)
In both dichromatic and trichromatic schemes, we found no separation among age classes in the NMDS (Figure 1) (p < 0.05) and no relationship between the colours and the individual ages in days
Summary
The evolutionary function of colouration in vertebrates includes physiological aspects, concealment, courtship, species recognition, and intra- and interspecific communication and signalling [1,2]. The latter includes the use of aposematism (bright or conspicuous colouration) as a warning signal to deter predators or to emphasise an animals’ unpalatability, which includes toxicity [3,4]. Toxins 2019, 11, 93 ultimate mimicry of one or more defensive properties, including aggressive behaviour, warning calls, unpalatability or toxicity [7]. In the case of mammals, stripes or patches may point towards areas of the body that deliver these toxic defences [3]
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