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J Evol Biol
2023 May 01;365:829-841. doi: 10.1111/jeb.14171.
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Ecology, sexual dimorphism, and jumping evolution in anurans.
Juarez BH
,
Moen DS
,
Adams DC
.
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Sexual dimorphism (SD) is a common feature of animals, and selection for sexually dimorphic traits may affect both functional morphological traits and organismal performance. Trait evolution through natural selection can also vary across environments. However, whether the evolution of organismal performance is distinct between the sexes is rarely tested in a phylogenetic comparative context. Anurans commonly exhibit sexual size dimorphism, which may affect jumping performance given the effects of body size on locomotion. They also live in a wide variety of microhabitats. Yet the relationships among dimorphism, performance, and ecology remain underexamined in anurans. Here, we explore relationships between microhabitat use, body size, and jumping performance in males and females to determine the drivers of dimorphic patterns in jumping performance. Using methods for predicting jumping performance through anatomical measurements, we describe how fecundity selection and natural selection associated with body size and microhabitat have likely shaped female jumping performance. We found that the magnitude of sexual size dimorphism (where females are about 14% larger than males) was much lower than dimorphism in muscle volume, where females had 42% more muscle than males (after accounting for body size). Despite these sometimes-large averages, phylogenetic t-tests failed to show the statistical significance of SD for any variable, indicating sexually dimorphic species tend to be closely related. While SD of jumping performance did not vary among microhabitats, we found female jumping velocity and energy differed across microhabitats. Overall, our findings indicate that differences in sex-specific reproductive roles, size, jumping-related morphology, and performance are all important determinants in how selection has led to the incredible ecophenotypic diversity of anurans.
FIGURE 1
Diversity of male and female differences in jumping velocity and energy. Males are represented as circles and females as triangles, with lines linking the sexes of each species. Shape colours indicate species' microhabitat use. Data were natural log‐transformed. Approximate (unlogged) units for velocity and energy are m1/2kg−1/2 and m3kg−1, respectively. These units differ from those typical of velocity and energy due to parameter substitutions in our approximations (see Supporting Information).
FIGURE 2
Ancestral‐state estimates of sexual dimorphism (SD) in peak jumping velocity and energy. SD was estimated as natural log (M/F). Branch colours indicate SD estimates. Root estimates for velocity and energy are 0.06 and −0.32, respectively, which include 0 within their 95% confidence intervals. Tip label colours represent microhabitat classifications. Frog images represent microhabitats, in the same order as the legend (from top to bottom): arboreal (Phyllomedusa tomopterna), leaf‐litter (Chiasmocleis bassleri), terrestrial (Epidalea calamita), burrowing (Scaphiopus hurterii), semi‐aquatic (Ptychadena mascareniensis), aquatic (Xenopus tropicalis) and torrential (Amolops tuberodepressus). The top photo (Phyllomedusa) shows a case of sexual size dimorphism (smaller male on top), whereas the middle photo (Scaphiopus) shows a species without size dimorphism (male behind female). All photos by DS Moen.
FIGURE 3
Histograms showing the degree of sexual dimorphism (SD; natural log(M/F) values) in anurans. (a) peak jumping velocity, (b) peak jumping energy, (c) snout‐vent length (SVL), (d) body mass, (e) relative Lcom (see text) and (f) relative muscle volume. Vertical solid lines at SD = 0 denote a lack of dimorphism (M = F values). Vertical dashed lines denote the median of each distribution. Jumping performance is based on anatomical approximations (see text).
FIGURE 4
Relationships between various aspects of sexual dimorphism in anurans. Red lines indicate statistically significant regression lines. SD is sexual dimorphism, r2 is the coefficient of determination and p is the p‐value. All variables are natural log‐transformed. (a) Insignificant relationship between sexual dimorphism of both estimated jumping velocity and body length (snout‐vent length). (b) Significant relationship between sexual dimorphism of both estimated jumping velocity and relative Lcom. Regression line is y = 0.020 + 0.904x. (c) Significant relationship between sexual dimorphism of both estimated jumping velocity and relative leg muscle volume. Regression line is y = 0.059 + 0.021x. (d) Significant relationship between sexual dimorphism of both relative leg muscle volume and relative Lcom. Regression line is y = −0.249 + 3.622x.
FIGURE 5Probability density functions of phylogenetically transformed sexual dimorphism (SD) in peak jumping velocity and energy across microhabitats. SD was estimated as natural log(M/F) values. Vertical grey lines are averages for each distribution. Colours follow the schematic used in other figures. Note that velocity and energy are logged ratios and thus do not have units
FIGURE 6
Probability density functions of phylogenetically transformed female peak jumping velocity across microhabitats. Vertical grey lines are averages for each distribution. Brackets on the right represent significant pairwise differences (see text). Colours follow the schematic used in other figures. Approximate units for velocity and energy are ln(m1/2kg−1/2) and ln(m3kg−1), respectively