4 - Outliers

Summary

In contrast to the visual, auditory or olfactory senses, the sense of touch (a form of mechanoreception) has been relatively neglected in primate studies. Over the last few decades, our understanding of the ecology of touch, or how an animal explores and exploits its environment using tactile cues (or tactile information), has improved in both primates and non-primate mammals. Touch can take many forms in mammals, including vibrissal (or whisker) touch, hand touch (especially in glabrous fingertips) and skin touch. Comparative studies exploring the relative sensitivities of touch (e.g. vibrissae/face, hands, feet) in primates and non-primate mammals are often challenging without extensive behavioural training (Bauer et al., 2012; Dehnhardt and Dücker, 1996; Dehnhardt and Kaminski, 1995) or complex anatomical studies (Marshall et al., 2014; Mattson and Marshall, 2016a, 2016b; Peterson et al., 1998). We have had success in using anatomical and skeletal proxies to investigate the ecology and evolution of vibrissal touch. Indeed, there are established ecological correlates between touch sensory-end organs, like number and movement, and skeletal landmarks linked with touch acuity (Muchlinski, 2010a; Muchlinski et al., 2018). It is also possible to connect vibrissa movement to differences in behaviour (Dehnhardt and Kaminski, 1995; Grant et al., 2018; Kemble and Lewis, 1982; Muchlinski, 2010b). We have even modelled the evolution of vibrissae, discussing our findings in the context of touch (Muchlinski et al., 2013, 2018). In this chapter, we examine the ecology of face touch (i.e. vibrissal touch) among the lorisids using the above-mentioned lines of evidence. We suggest that the sensory ecology of the lorisids may be more specialised and novel than we initially thought.