Shaping communicative colour signals over evolutionary time

Abstract

Many evolutionary forces can shape the evolution of communicative signals, and the long-term impact of each force may depend on relative timing and magnitude. We use a phylogenetic analysis to infer the history of blue belly patches of Sceloporus lizards, and a detailed spectrophotometric analysis of four species to explore the specific forces shaping evolutionary change. We find that the ancestor of Sceloporus had blue patches. We then focus on four species; the first evolutionary shift (captured by comparison of S. merriami and S. siniferus) represents an ancient loss of the belly patch by S. siniferus, and the second evolutionary shift, bounded by S. undulatus and S. virgatus, represents a more recent loss of blue belly patch by S. virgatus. Conspicuousness measurements suggest that the species with the recent loss (S. virgatus) is the least conspicuous. Results for two other species (S. siniferus and S. merriami) suggest that over longer periods of evolutionary time, new signal colours have arisen which minimize absolute contrast with the habitat while maximizing conspicuousness to a lizard receiver. Specifically, males of the species representing an ancient loss of blue patch (S. siniferus) are more conspicuous than are females in the UV, whereas S. merriami males have evolved a green element that makes their belly patches highly sexually dimorphic but no more conspicuous than the white bellies of S. merriami females. Thus, our results suggest that natural selection may act more immediately to reduce conspicuousness, whereas sexual selection may have a more complex impact on communicative signals through the introduction of new colours.

Losing the trait without losing the signal: Evolutionary shifts in communicative colour signalling

“…Grey branches indicate episodes in which the male ventral blue patches were lost, as inferred by Ossip‐Drahos et al. (). Also, depicted are photos of the ventral surface (head is to the left) of a typical male of each species…”

“…The fourth loss is represented by a clade of four extant species that do not have colourful belly patches nor close sister taxa. To represent this loss, we chose one of the extant species ( S. siniferus ) and two more distantly related Sceloporus species ( S. merriami and S. graciosus ) with colourful bellies (see Ossip‐Drahos et al., for complete ancestral reconstruction of 81 species). In most colourful species, patch colour is predominantly blue with black edges; however, we include two species that have multiple colour elements in their patches: S. merriami , which has a pale green oval edged by a blue J‐shaped patch; and S. variabilis, which exhibits pink patches with blue and black borders (Figure ).…”

“…In most colourful species, patch colour is predominantly blue with black edges; however, we include two species that have multiple colour elements in their patches: S. merriami , which has a pale green oval edged by a blue J‐shaped patch; and S. variabilis, which exhibits pink patches with blue and black borders (Figure ). Two of the belly patch losses occurred relatively recently (< 12 Mya; S. virgatus and S. megalepidurus ), whereas the other two are more ancient (40–18 Mya; S. siniferus and S. cozumelae ) (Ossip‐Drahos et al., ).…”

“…detectability) of the signal (Endler, ; Osorio & Vorobyev, ). Ultimately, the expressed colour trait is a compromise between responses to sexual and natural selection (Endler, , ; Fisher, ) potentially operating through multiple pathways (Romero‐Diaz, Richner, Granado‐Lorencio, Tschirren, & Fitze, ) or at different points in time (Ossip‐Drahos et al., ). Here, we make use of natural evolutionary replication and a comprehensive spectral analysis to explore the patterns exhibited by four independent evolutionary losses of a colourful belly patch in Sceloporus lizards.…”

“…Belly colour is related to the probability of winning in staged male–male encounters in S. virgatus (Quinn & Hews, ), and patch size conveys information on body size, condition, fighting ability and parasite load in S. undulatus and S. jarrovii (Halliday, Paterson, Patterson, Cooke, & Blouin‐Demers, ; Langkilde & Boronow, ; Ossip‐Drahos et al., ). Coloured belly patches have been lost independently within the genus at least seven times (Ossip‐Drahos et al., ; Wiens, ), giving rise to white‐bellied species in which sexual dimorphism for ventral colouration is apparently absent. We now focus on four of these evolutionary losses spread across the Sceloporus genus and ask: (1) Are the spectral properties of the four losses similar, suggesting that they are examples of a similar phenotypic evolutionary phenomenon?…”