Patterns of fluctuating asymmetry in the limbs of anurans

Abstract

It has been hypothesized that fluctuating asymmetry (FA) may provide an indication of the functional importance of structures within an organism, with structures that more strongly impact fitness being more symmetric. Based on this idea, we predicted that for tetrapods in which the forelimbs and hindlimbs play an unequal role in locomotion, the less functionally important limb set should display higher levels of FA. We conducted a multispecies test of this hypothesis in anurans (frogs and toads), whose saltatory locomotor mode is powered by the hindlimbs. We also tested whether FA in the forelimbs, which play a more important role during landing, differed between families that differ in the degree of forelimb use in locomotion (Bufonidae vs. Ranidae). We calculated FA from the lengths of humeri and femora measured from disarticulated skeletal specimens of four anuran taxa (Bufonidae: Anaxyrus americanus, Rhinella marina; Ranidae: Lithobates catesbeianus, Lithobates clamitans). Our findings were consistent with the hypothesis that natural selection for increased locomotor performance may influence patterns of FA seen in vertebrate limbs, with all species displaying lower mean FA in the hindlimbs. More subtle functional roles between the forelimbs of bufonids and ranids, however, did not elicit different levels of FA.

Patterns of fluctuating asymmetry in the limbs of freshwater turtles: Are more functionally important limbs more symmetrical?

“…Our study joins a growing body of work that refutes the long‐held idea that patterns of fluctuating asymmetry are largely random (Gummer and Brigham 1995; Guillot et al. 2016; Didde and Rivera 2019). As detailed by Didde and Rivera (2019), for natural selection to be driving these patterns, several conditions must be met.…”

“…2016; Didde and Rivera 2019). As detailed by Didde and Rivera (2019), for natural selection to be driving these patterns, several conditions must be met. First, variation in fluctuating asymmetry must be heritable.…”

“…Instead, DA, defined as a consistent side‐bias in the population, is calculated as the mean of individual differences, (; Palmer and Strobeck 1986). To account for differences in size between bones, and thus facilitate comparisons between limb sets and across species, we standardized each individual measurement ( R − L ) by dividing it by the average length of the limb pair being examined (Palmer and Strobeck 1986; Palmer 1994; Palmer and Strobeck ; Didde and Rivera 2019). Expressing deviations from perfect symmetry as a dimensionless index of proportional FA, is the most common transformation used to correct for variation in trait size.…”

“…Palmer and Strobeck (1986) suggested that FA might also provide insight into the functional importance of structures within an organism, as bilaterally symmetric structures that more strongly impact fitness should display reduced asymmetry. Based on this morpho‐functional hypothesis, it has been predicted that for tetrapods in which the forelimbs and hindlimbs contribute unequally to locomotor performance, the less functionally‐important limb set should display higher levels of FA (Gummer and Brigham 1995; Didde and Rivera 2019). In bats, the forelimbs are modified into wings and used for flight, whereas hindlimbs are used primarily for roosting.…”

Superfrogs in the city: 150 year impact of urbanization and agriculture on the European Common Frog

“…Only the humerus and radio‐ulna met all the criteria (Table 1). In a recent study, selection pressure on the symmetry of functionally important characters, such as the hind limbs of anurans, has been proposed as an explanation for that observation (Didde & Rivera, 2019). Therefore, we excluded the femur and tibio‐fibula from FA analyses.…”