Complications with body-size correction in comparative biology: possible solutions and an appeal for new approaches

Abstract

The magnitude of many kinds of biological traits relates strongly to body size. Therefore, a first step in comparative studies frequently involves correcting for effects of body size on the variation of a phenotypic trait, so that the effects of other biological and ecological factors can be clearly distinguished. However, commonly used traditional methods for making these body-size adjustments ignore or do not completely separate the causal interactive effects of body size and other factors on trait variation. Various intrinsic and extrinsic factors may affect not only the variation of a trait, but also its covariation with body size, thus making it difficult to remove completely the effect of body size in comparative studies. These complications are illustrated by several examples of how body size interacts with diverse developmental, physiological, behavioral and ecological factors to affect variation in metabolic rate both within and across species. Such causal interactions are revealed by significant effects of these factors on the body-mass scaling slope of metabolic rate. I discuss five possible major kinds of methods for removing body-size effects that attempt to overcome these complications, at least in part, but I hope that my Review will encourage the development of other, hopefully better methods for doing so.

A quantitative genetics perspective on the body-mass scaling of metabolic rate

“…Furthermore, the phenotypic scaling exponent of 0.554 based on data in Ellenby (1945) is within the 95% CI of the genetic scaling exponent, although the scaling exponent of 0.772 based on data in Ellenby (1953) is not. In addition, the genetic metabolic scaling exponent for the laboratory mouse Mus musculus (0.826±0.323) is not significantly different from the phenotypic scaling exponent (0.748±0.289) reported by Glazier (2022), based on data from 15 studies collated by Genoud et al (2018). These examples thus suggest that, with sufficient data, a match between genetic and phenotypic metabolic scaling exponents may be found.…”

Feeding behavior ofGammarus aequicaudain the presence of two prey species ofArtemiasp. andBaeotendipes noctivagus

“…had an average wet mass of 4.3 and 2.6 mg, respectively, and G. aequicauda— 23.7 mg. Before the experiments, gammarids were in vessels with filtered lake water for 3 days with aeration because such starvation standardized predators' satiety levels as shown earlier (Shadrin, Yakovenko, & Anufriieva, 2020a, b). In every experiment, one G. aequicauda male was used to avoid body‐size and sex‐related effects (Glazier, 2022; Shadrin, Yakovenko, & Anufriieva, 2021b). Different variants of prey compositions in terms of species and a number of individuals per species were used in the experiments: (1) two Artemia sp., (2) two chironomid larvae, and (3) one Artemia sp.…”

“…However, the same cannot be said about trophic relationships in extreme aquatic habitats such as hypersaline habitats, to which few works have been devoted (Carrasco & Perissinotto, 2012;Golubkov et al, 2018;N. Shadrin & Anufriieva, 2018a;Williams et al, 1995;Wurtsbaugh & Berry, 1990).…”

“…Shadrin & Anufriieva, 2018a;Williams et al, 1995;Wurtsbaugh & Berry, 1990). The species richness in these habitats is reduced, and the trophic relationships are simplified and modified (Golubkov et al, 2018;N. Shadrin & Anufriieva, 2018a;Wurtsbaugh & Berry, 1990).…”

“…Shadrin & Anufriieva, 2018a;Wurtsbaugh & Berry, 1990). Vertebrate predators are usually absent from them, and the role of predators is often performed by omnivorous invertebrates, for example, crustaceans (Amphipoda, Ostracoda, Copepoda, and so forth) or insecta (Golubkov et al, 2018;Shadrin, Yakovenko, & Anufriieva, 2019;Wurtsbaugh & Berry, 1990).…”