The biomechanical basis of evolutionary change in a territorial display

Abstract

Summary1. Few studies have examined how the anatomy of an animal signal contributes to, or limits, the evolution of signal differentiation among closely related species. 2. In Anolis lizards, adult males extend a large, conspicuous dewlap as part of a territorial advertisement display. Males of species from the island of Jamaica rely on the rapid extension of the dewlap to facilitate display detection by territorial neighbours and conspecific females. Males of other species on the island of Puerto Rico extend the dewlap at considerably slower speeds and instead rely on other strategies to maintain an effective display. What initially prompted this divergence in display between the islands is unknown, but evidence suggests that it may have something to do with the way the dewlap is extended during display. 3. Our goal was to determine whether an innovation in the dewlap lever in Jamaican lineages, but absent in Puerto Rican lineages, accounted for the evolution of the high-speed dewlap on Jamaica. We began by modelling the performance of the Anolis dewlap as a first-order lever system. We then simulated changes to this system relating to its morphology, articulation and input force in biologically realistic ways to predict how such changes impact dewlap speed. Finally, we compared these predictions with data on the morphology of the dewlap lever system from museum specimens and actual dewlap speed recorded for lizards in the field. 4. This investigation revealed that changes to the dewlap lever have affected the performance of the dewlap display in at least two ways. Within islands, structural changes to the hyoid morphology seem to have led to differences in dewlap speed among species. Between islands, however, differences in dewlap speed were most likely the result of a major increase in muscle contraction velocity that powers the dewlap extension in Jamaican species, but has not originated in species on Puerto Rico. 5. Our study shows how the biomechanics of a social signal can have important implications for understanding why closely related species might differ in signal behaviour, despite apparent similarities in the selection pressures that act on the signal.

Modular color evolution facilitated by a complex nanostructure in birds

“…However, very few studies have explored how the proximate mechanisms of functional traits (like color) influence their evolution (Emlen et al. ; Maia et al ; Ord et al ). With colorful ornaments, different spectral variables may convey unique messages to other individuals.…”

“…The macroevolutionary consequences of sexual selection on ornamental diversity and speciation have long been central to evolutionary studies, both from an empirical and a theoretical standpoint (West-Eberhard 1983;Ritchie 2007). However, very few studies have explored how the proximate mechanisms of functional traits (like color) influence their evolution (Emlen et al 2007;Maia et al 2013b;Ord et al 2013). With colorful ornaments, different spectral variables may convey unique messages to other individuals.…”

“…Changes in form-function relationships can increase morphological diversity in biomechanical and ecological traits (Alfaro et al 2005;Stayton 2006;Wainwright 2007), but whether this holds true in ornamental traits is less understood (Ord et al 2013;Maia et al 2013b). Ornamental traits are often more diverse than ecological traits (Andersson 1994;Emlen et al 2005), potentially because of the increased strength and constancy of sexual selection compared to natural selection (Hoekstra et al 2001) or the greater potential for rapid divergence by a runaway process of coevolution between trait and preference (Prum 2010).…”

Repeated evolution of exaggerated dewlaps and other throat morphology in lizards

“…Based on previous biomechanical modelling (Ord et al ., ) and detailed investigations of the action of the hyoid as the dewlap is extended by adult male Anolis lizards (Font & Rome, ), there are several key components that govern the performance of the dewlap mechanism that also clearly delineate the overall appearance of the hyoid in Anolis (a genus with a notable moving dewlap) from most other iguanid lizards (genera that do not possess an extendible dewlap; this study).…”

Variation in Display Behavior, Ornament Morphology, Sexual Size Dimorphism, and Habitat Structure in the Fan-Throated Lizard (Sitana, Agamidae)

“…Conversely, conspicuousness also may be selected against in habitats where lizards suffer high rates of predation (e.g., in Ctenophorus lizards [Stuart-Fox et al, 2003] and Crotaphytus lizards [Husak et al, 2008]), leading to geographic variation in coloration that corresponds to variation in predation risk (McLean et al, 2014). Finally, anatomical and biomechanical constraints affect variation in motion signaling between closely related species of anoles (Ord et al, 2013). Variation across lizard taxa, in not only the ornaments themselves but also in the proximate and ultimate causes for ornament diversification, makes lizards an interesting group in which to examine ornament evolution.…”