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Behavioral biologists have long been fascinated with the diversity of animal signals produced in the contexts of courtship and same-sex competition. In these contexts many lizards engage in conspicuous bobbing displays, and numerous studies have been devoted to describing these displays. Traditionally, bobbing displays are partitioned into units whose durations (and sometimes head amplitudes) are measured. Recently, Macedonia et al. (2019) introduced use of the Discrete Fourier Transform (DFT) as an alternative to unit-based variables for characterizing species-specific traits in display structure of Galapagos Lava Lizards (Microlophus spp.). The relative success of the two methods was not compared directly, however, because the homology of display units among species was uncertain. Here we overcome this problem using the “grahami series” of Anolis lizards—a monophyletic radiation of seven species on Jamaica and Grand Cayman. Our study had three primary goals. Our first goal was to discover whether DFT-based measures, unit-based measures, or their combination provided the best means to capture taxon-specific distinctiveness in display structure. To this end, we quantified bobbing displays and used nested analyses of variance (ANOVAs) to determine if particular variables were reliably superior at differentiating populations within a species. We then used principal components analysis to reduce the number of measurement variables, and entered the components into discriminant function analyses to determine which approach best discriminated among taxa. Results showed that no one type of measurement, or measurement combination, emerged as being consistently better at discriminating taxa across comparisons. Our second goal was to test a hypothesis that arose from our findings in Galapagos Lava Lizards—that the DFT may decrease in effectiveness as bobbing display structure increases in complexity. For this test we used four simple and compound display types from the species Anolis reconditus. Results of discriminant function analyses provided mixed support for the hypothesis, and we suggest that a definitive test of DFT performance and display complexity should utilize synthetic displays in which attributes of display structure are varied systematically. Last, we show how bobbing display structure maps onto alternative DNA-based phylogenies of the grahami series anoles. Whereas some species produced derived display types unanticipated from displays of more basal species in this adaptive radiation, others exhibited features that linked them to a particular population of a species in their clade.

In many species, outcomes of male duels determine access to females and, ultimately, male reproductive success. Ritualization of behavior in male contests can reduce the probability of injury, which benefits both contestants. Components of ritualized combat often include postures and displays that showcase a male’s quality in a sequential assessment of fighting ability. Among the most common contest acts in iguanine lizards are bobbing displays. Investigations of bobbing display dynamics often include experimental “playbacks,” in which video or robotic representations of conspecifics are presented to subjects. In most “playback” research, pre-programmed stimuli exhibit behavior that is independent of subjects’ responses, despite the fact that actual animal contests are highly interactive. In the present study, we utilized a robotic Galapagos lava lizard (Microlophus bivittatus) to investigate the importance of interaction in simulated contests under field conditions. Using a matched pairs design where each subject experienced two behavioral variants of the robotic stimulus, we tested the effect of a robot that displayed immediately following a subject’s display versus when the same robot display was postponed 30 s. Results showed that immediate response from the robot stimulated subjects to display significantly more often than when the stimulus was delayed. We speculate that subjects perceived a rapid response from their robotic contestant as being more aggressive than a delayed response. We discuss our results in light of relevant previous work, and we suggest possibilities for future research using interactive lizard robots. Some of the most impressive examples of ritualized animal behavior can be observed in male contests for access to reproductive females. The use of stereotyped displays in such duels allows males to assess one another’s quality while avoiding dangerous fighting that can lead to injury. For example, males in many lizard species perform bobbing displays where contestants respond to each other in reciprocal fashion. In this study, we used a realistic lizard robot as a stand-in for a contestant in simulated contests. We found that an immediate display response by the robot to a subject’s bobbing display stimulated subjects to display significantly more often than when the robot’s response was delayed by 30 s. To our knowledge, this is the first interactive robot “playback” experiment with lizards. Future research will further explore the “rules” underlying display behavior in lizard contests.

Differentiation in the structure of animal signals and displays among closely related species has intrigued biologists for centuries. Such divergence is often attributed to behavioural premating isolation, where sexual selection has favoured species recognition in environments containing sympatric congeners. However, in some cases closely related taxa have undergone speciation and display differentiation in isolation, in the apparent absence of benefits afforded by species recognition. Such is the case for the lava lizards (Microlophus spp.) endemic to the Galapagos Islands, where no two species overlap in distribution and all are thought to have evolved in allopatry from congeners. To test alternative evolutionary models, we used several phylogenetic comparative methods to assess how Microlophus displays have evolved. Results showed some potential for the influence of genetic drift, but little evidence of sexual selection (via male–male competition) or colonization history on the way displays have diverged among taxa. We then used lizard robots to test whether two representative Galapagos lava lizard species, Microlophus grayii and Microlophus indefatigabilis, would respond preferentially to a robot performing conspecific displays over those of the congener. We predicted that, in the absence of reinforcing selection, neither species would show a preference for conspecific displays. Results were mixed: whereas M. grayii showed no discrimination of conspecific over heterospecific displays, male M. indefatigabilis showed significantly stronger responses to their own displays than to those of the heterospecific. We then conducted the same experiment with a mainland congener, Microlophus occipitalis, to provide a broader view of potential responses across the group. Results revealed significant discrimination against heterospecific displays. We discuss our findings in light of hypotheses of signal differentiation, and suggest alternative interpretations for recognition of conspecific displays in species that are thought to have evolved in isolation.

Green Anoles (Anolis carolinensis) are comprised of red-dewlapped (RD) forms that are found throughout the southeastern USA and a gray-dewlapped (GD) form that is restricted to southwest Florida. Prior research has shown that RD A. carolinensis produce headbob displays of three distinct types that differ primarily in their temporal patterns. Based on known morphological, physiological, and genetic differences between GD and RD populations, we hypothesized that these populations also would differ in headbob display structure. To test this hypothesis we quantified 440 displays from 39 males (24 GD and 15 RD) and assigned displays to type using numerical decision criteria. Although comparison of the same display types between GD and RD males revealed differences in the durations of several homologous display units (i.e., bobs or interbob pauses), only one unit differed following statistical correction for multiple comparisons. By taking into account all display variation in both populations simult...

Some of the most striking behaviors of animals are displays used in courtship, territorial behavior, and in defense against predators. Among reptiles, lizards exhibit enormous diversity in...

Many animal species use stereotyped displays to attract the opposite sex and to intimidate same-sexed rivals. Research aimed at understanding display recognition, function, and usage can be aided through the use of animal robots that allow one side of signaler–receiver interactions to be controlled. Manipulation of displays in ways that do not occur in nature has the potential to determine the boundaries of display recognition, as well as to provide insights into the manner in which animal display contests are structured. We describe two experiments that extend previous work on display recognition in the lizard Anolis grahami. In the first experiment, we used robots to determine the relative importance of body coloration and headbob display structure for species recognition. The results showed that subjects responded more strongly to robots having both conspecific appearance and display structure than to robots that deviated in those characteristics from the conspecific stimulus. In the second ...