Metabolic scaling in modular animals

Abstract

Abstract. Metabolic scaling is the relationship between organismal metabolic rate and body mass. Understanding the patterns and causes of metabolic scaling provides a powerful foundation for predicting biological processes at the level of individuals, populations, communities, and ecosystems. Despite intense interest in, and debate on, the mechanistic basis of metabolic scaling, relatively little attention has been paid to metabolic scaling in clonal animals with modular construction, such as colonial cnidarians, bryozoans, and colonial ascidians. Unlike unitary animals, modular animals are structural individuals subdivided into repeated morphological units, or modules, each able to acquire, process, and share resources. A modular design allows flexibility in organism size and shape with consequences for metabolic scaling. Furthermore, with careful consideration of the biology of modular animals, the size and shape of individual colonies can be experimentally manipulated to test competing theories pertaining to metabolic scaling. Here, we review metabolic scaling in modular animals and find that a wide range of scaling exponents, rather than a single value, has been reported for a variety of modular animals. We identify factors influencing variation in intraspecific scaling in this group that relate to the general observation that not all modules within a colony are identical. We highlight current gaps in our understanding of metabolic scaling in modular animals, and suggest future research directions, such as manipulating metabolic states and comparisons among species that differ in extent of module integration.

Influence of food, body size, and fragmentation on metabolic rate in a sessile marine invertebrate

“…Modular animals are useful for testing theories of metabolic scaling, as it is possible to manipulate their size and shape (reviewed in Burgess et al., ). In a colonial ascidian, Nakaya, Saito, and Motokawa () found that metabolic scaling switched from allometry to isometry during the takeover stage of the colony, in which the zooids of the parent generation in a colony degenerate and zooids of a new generation develop in unison.…”

“…Modular animals are useful for testing theories of metabolic scaling, as it is possible to manipulate their size and shape (reviewed in Burgess et al, 2017). In a colonial ascidian, Nakaya, Saito, and…”

“…In colonial organisms (i.e., clonal organisms that are subdivided into functionally autonomous or semi‐autonomous, multicellular modules, Vuorisalo & Tuomi, ), feeding differs from that in unitary organisms in the way that colonial animals take up and transform resources. Most studies indicate that feeding rates scale isometrically or superlinearly in colonial animals (e.g., Okamura, , ; Pratt, ), whereas metabolic scaling is allometric in most species (Barneche, White, & Marshall, ; Burgess et al., ; Hartikainen, Humphries, & Okamura, ). Hence, as colonies increase in size, their capacity to capture food increases more quickly than the rate at which they expend energy.…”

“…Colonial animals provide an opportunity to manipulate size independently of other factors, thereby minimizing potentially confounding effects (e.g., those associated with age). Size manipulation approaches in several recent studies show how size can be manipulated to test predictions of competing theories (Barneche et al., ; Nakaya, Saito, & Motokawa, ; White, Kearney, Matthews, Kooijman, & Marshall, ; reviewed in Burgess et al., ).…”

Rediscovering and Reviving Old Observations and Explanations of Metabolic Scaling in Living Systems

“…In keeping with the overall theme of my article, this discovery of metabolic scaling diversity was rediscovered many times during the 1900s (e.g., [23,32,[261][262][263]), but largely ignored in favor of a 3/4-power law. Only during the last two decades, has a true appreciation of the broad diversity of metabolic scaling relationships been spreading widely (see e.g., [19,20,24,26,27,33,34,39,44,46,50,[54][55][56][57][58]103,[105][106][107]117,118,121,132,142,143,147,149,153,182,193,219,225,260,264,265]), thus helping to stimulate the development of multi-mechanistic explanatory models (see Section 3.1). The recognition of diversity is not necessarily a hindrance to the development of general theory, as sometimes thought (cf.…”