Conspecifics of the Striped Lava Lizard are able to distinguish sex and male colour morphs in apparently homogeneous dull dorsal colouration

Abstract

Animal colouration plays a key role in inter and intraspecific interactions, pre-eminently in mate signalling. When multiple types of colouration occur within sexes it is possible that they show alternative reproductive strategies. In lizards, most colouration studies do not incorporate how colour is perceived by conspecifics. Here, we used unbiased colour analysis methods (spectrophotometry and visual modelling) to test for sexual dimorphism and within male dichromatism in the Striped Lava Lizard. We found that males express two distinct colourations that are different from females in several dorsal and ventral body regions. Our results showed UV reflection at the throat, an important body region for signalling. Ventral patches, the coloured badge seen in adult males of Tropidurus spp., have two distinct colour classes within males (Y and B males). Morphs are best discriminated by blue and yellow chroma, and brightness. Body size had little influence on colouration, suggesting that colour may be linked to inheritance rather than growth. Our study clearly shows sexual dichromatism and the existence of colour morphs in this species. Moreover, morph differences in colouration are perceptible by conspecifics. These differences are not only between ventral patches, but also in other body parts such as the dorsum, previously considered as cryptic by human observers. We suggest that colouration at the ventral patches and throat might play a role in intraspecific interactions. Patches increase colour intensity during breeding season and are likely to be costly by pigment-based expression, whereas throat’s UV reflection might have a cost infringed by conspicuousness.

Chemical signalling behaviour in intrasexual communication of lizards lacking femoral pores

“…Melanistic coloured patches in the ventral thighs and pre‐cloacal flaps of adult males are diagnostic traits of the genus (Bruinjé, Coelho, et al, 2019; Bruinjé, Moura, et al, 2019; Ribeiro et al, 2012) but, to date, no chemical signalling function of these structures has been shown. Such patches can also be yellow coloured in T. semitaeniatus (Bruinjé, Coelho, et al, 2019; Bruinjé, Moura, et al, 2019), T. hispidus , T. oreadicus (A. C. Bruinjé, personal observation) and T. torquatus (Pinto et al, 2005). Pinto et al, (2005) reported ontogenetic changes in the colouration of femoral patches of T. torquatus , suggesting that patches were used in visual communication for sex recognition and hierarchy establishment.…”

“…Such visual signalling could occur during the behaviour of lifting the body, which were reported for the species (Pinto et al, 2005). In addition, in T. semitaeniatus , ventral patches become more evident during the breeding season (Ribeiro, Kolodiuk, & Freire, 2010) and intensity of ventral patches’ colouration in males of this species are correlated to increased levels of aggression (Bruinjé, Coelho, et al, 2019; Bruinjé, Moura, et al, 2019). On the other hand, Harvey and Gutberlet (1998) described these patches as a diagnostic trait of the genus and proposed that its colouration results from the production and secretion of chemical compounds, thus suggesting that it is of little importance for visual signalling.…”

“…Lizards from the genus Tropidurus do not have femoral pores. Melanistic coloured patches in the ventral thighs and pre-cloacal flaps of adult males are diagnostic traits of the genus (Bruinjé, Coelho, et al, 2019;Bruinjé, Moura, et al, 2019;Ribeiro et al, 2012) but, to date, no chemical signalling function of these structures has been shown. Such patches can also be yellow coloured in T. semitaeniatus (Bruinjé, Coelho, et al, 2019;Bruinjé, Moura, et al, 2019), T. hispidus, T. oreadicus (A.…”

“…The genus Tropidurus (Wied‐Neuwied, 1825) is one of the best represented among tropidurids, with at least 31 described species (Reptile Database, 2018). A marked trait of this genus (and other genera) of this family is the presence of dark‐coloured patches (Figure 1d,f) at ventral thighs and pre‐cloacal flaps of adult males (Bruinjé, Coelho, Paiva, & Costa, 2019; Bruinjé, Moura, et al, 2019; Frost et al, 2001; Stebbins, Lowenstein, & Cohen, 1967). A primary premise of its function is that its colouration would play a role in visual communication (Pinto, Wiederhecker, & Colli, 2005), although it was also suggested that coloured patches could be just a consequence of chemical secretions produced by glandular scales (Carvalho et al, 2016; Harvey & Gutberlet, 1998; Kuns & Borges‐Martins, 2013).…”

Convergence and divergence in lizard colour polymorphisms

“…1). An exception is the striped lava lizard ( Tropidurus semitaeniatus ), in which males are either black or yellow (Bruinjé, Leivas, & Costa, 2018; Bruinjé et al ., 2019 b ). The Roze's gecko ( Gonatodes rozei ) also has strikingly different male morphs, with throats that are orange‐yellow, dull yellow, grey‐brown with pale yellow markings, or grey‐brown with black suffusions between yellow markings (Rivero‐Blanco & Schargel, 2012).…”