Evolutionary loss of a signalling colour is linked to increased response to conspecific chemicals

Abstract

Behavioural responses to communicative signals combine input from multiple sensory modalities and signal compensation theory predicts that evolutionary shifts in one sensory modality could impact the response to signals in other sensory modalities. Here, we conducted two types of field experiments with 11 species spread across the lizard genus Sceloporus to test the hypothesis that the loss of visual signal elements affects behavioural responses to a chemical signal (conspecific scents) or to a predominantly visual signal (a conspecific lizard), both of which are used in intraspecific communication. We found that three species that have independently lost a visual signal trait, a colourful belly patch, responded to conspecific scents with increased chemosensory behaviour compared to a chemical control, while species with the belly patch did not. However, most species, with and without the belly patch, responded to live conspecifics with increased visual displays of similar magnitude. While aggressive responses to visual stimuli are taxonomically widespread in Sceloporus , our results suggest that increased chemosensory response behaviour is linked to colour patch loss. Thus, interactions across sensory modalities could constrain the evolution of complex signalling phenotypes, thereby influencing signal diversity.

Signaler’s Vasotocin Alters the Relationship between the Responder’s Forebrain Catecholamines and Communication Behavior in Lizards (<b><i>Anolis carolinensis</i></b>)

“…Specifically, AVT had no impact on the motivation to perform the first visual display in untreated responders, while AVT altered the relationship between the latency to perform a tongue flick and DA concentrations in the FB. Trade-offs between visual and chemical communication occur over evolutionary time scales [Romero-Diaz et al, 2021], and plasticity in the behavioral responses of receivers may help maintain complex and multimodal signals [Martins et al, 2018]. We found that at lower DA concentrations (<0.02), AVT responders were faster to perform a tongue flick than SAL responders, but at higher DA concentrations (>0.02), SAL lizards were faster to perform a tongue flick.…”

Brain transcriptomic responses of Yarrow's spiny lizard, Sceloporus jarrovii, to conspecific visual or chemical signals

“…data) and male S . jarrovii significantly increase the frequency of territorial patrolling and aggressive displays within seconds to minutes following a staged territorial intrusion by a live conspecific male 29–31 . Similarly, femoral gland secretions from male conspecifics elicit increased chemosensory behavior in S .…”

“…However, visual stimuli elicit increased frequency ofpush-up displays while scents preferentially trigger a chemosensory response. 29,31,32,54 Visual-encounter territory intrusions may represent a more immediate threat to male residents and more frequently result in a quick escalation of aggressive displays leading to physical combat. 17,55 In contrast, scent marks deposited in the substrate may be detected long after the intruder has left the territory 56,57 and elicit comparatively tamer responses.…”

“…jarrovii , visual and chemical conspecific signals increase agonistic displays and territory patrolling of resident males. However, visual stimuli elicit increased frequency of push‐up displays while scents preferentially trigger a chemosensory response 29,31,32,54 . Visual‐encounter territory intrusions may represent a more immediate threat to male residents and more frequently result in a quick escalation of aggressive displays leading to physical combat 17,55 .…”

“…data) and male S. jarrovii significantly increase the frequency of territorial patrolling and aggressive displays within seconds to minutes following a staged territorial intrusion by a live conspecific male. [29][30][31] Similarly, femoral gland secretions from male conspecifics elicit increased chemosensory behavior in S. jarrovii in identical laboratory conditions. 32 Because of this well-established paradigm, we did not record behavioral responses in this experiment.…”