Differential growth of naturally and sexually selected traits in an Anolis lizard

Abstract

Sexual dimorphism may be indicative of differential natural and/or sexual selection pressures acting on males and females. Although similar degrees of adult sexual dimorphism may be observed among populations and species, underlying physiological, developmental and ecological processes driving growth during the juvenile stages may vary. Unraveling how and when differences arise during ontogeny is important to our understanding of the evolutionary patterns observed among adults. In addition, growth patterns may differ among traits within a single individual. Anolis lizards vary greatly in the degree of adult sexual size and shape dimorphism. Ultimate hypotheses (e.g. sexual selection, habitat partitioning) have been put forward to explain this variation, but proximate mechanisms operating during the juvenile stages remain largely unknown. Herein, we aim at elucidating the proximate mechanisms of sexual dimorphism in head and limb shape, performance and dewlap size in Anolis baracoae, a crown-giant anole. We used a longitudinal approach and raised 23 captive-bred juvenile A. baracoae lizards through adulthood. By quantifying body size, head and limb dimensions, dewlap size and bite performance, we obtained growth trajectories that were compared between the sexes and among traits. Our results show that the growth of head and limb shape is similar in males and females, whereas dewlap size and bite performance diverge at a specific age. Based on these results, we hypothesize that, whereas selection favors a similar head and limb shape in males and females, selection pressures on dewlap size and bite performance likely differ between the sexes. In addition, dewlap size starts diverging around the time the animals reach sexual maturity, whereas bite performance diverges much earlier in (sexually) immature males.

The brown anole dewlap revisited: do predation pressure, sexual selection, and species recognition shape among-population signal diversity?

“…First, sexual selection is simply not acting on dewlap traits. This sounds highly improbable, because the dewlap has all the characteristics of a sexually secondary trait: it is highly dimorphic in adult individuals, and exhibits the typical developmental pattern with sex-specific growth trajectories once the age of maturity is reached ( Vanhooydonck et al, 2015 ). Several studies have shown that male brown anoles use their dewlap during territorial disputes ( Scott, 1984 ) and/or during courtship ( Simon, 2011 ; Driessens, Vanhooydonck & Damme, 2014 ).…”

Signal detection shapes ornament allometry in functionally convergent Caribbean Anolis and Southeast Asian Draco lizards

“…Males use a conspicuous throat fan, or dewlap, as part of a visual display used to establish and maintain territories that encompass several trees (Jenssen et al, 2000;Nicholson et al, 2007;Ord, 2021;Ord et al, 2007;Ord & Stamps, 2008). The size of this dewlap in males has previously been shown to be positively correlated with bite force within species (Lailvaux & Irschick, 2007;Vanhooydonck et al, 2005) and has also been shown to be correlated with indices of sexual size dimorphism across species (Fitch & Hillis, 1984;Vanhooydonck et al, 2015). This implies male dewlap size could provide an honest indicator of potential fighting ability and reflect differences in the intensity of competition for territories among species.…”