“Phylogenetic analysis supports the aerobic capacity model for the evolution of endothermy”

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Roberto F. Nespolo, Jaiber J. Solano-Iguaran, and Francisco Bozinovic

Researchers apply analysis of evolutionary optima to test the aerobic model for evolution of endothermy

The evolution of endothermy and comparative phylogenetics: exploring the signatures of selection on physiological data

The authors’ working phylogenetic tree: a sub-tree of the Global Timetree of Life, with silhouettes were kindly drawn by Alejandra Tejada.

Perhaps the most heated debates among paleontologists, physiologists, and palaeo-ecologists are about the tempo and mode of evolution of endothermy in vertebrates: in other words, how warm-blooded animals (“endotherms”) evolved from supposedly cold-blooded (“ectotherms”) ancestors. This is a tough question, as endotherms have to eat many times the amount of food at day of a similarly sized ectotherm, which represents an important cost. So what are the advantages?

Birds and mammals travel very long distances to forage, to reach better habitats, or to escape from predators. These animals can maintain sophisticated systems such as a centralized nervous system or four-chambered hearts. However, these are long-term advantages. The short-term consequences of endothermy are just costs: energetic costs.

A solution to this conundrum was given three decades ago by Bennett and Ruben, who proposed the aerobic model for the evolution of endothermy. This idea posits that selection acted on aerobic capacity (the capacity to maintain sustained activity), and resting metabolism was elevated (together with body temperature) as a correlated response. The basic assumption of this hypothesis is that resting and maximum metabolic rate are correlated across all vertebrates. Since then, several authors have gathered experimental data on individual species, or a few of them. Although theoretical models and single-species studies supported the idea, explicit studies based on evolutionary theory were lacking.

Working with large phylogenetic trees (sketches of evolutionary histories), Nespolo and colleagues have applied a group of comparative models to test this hypothesis on 176 vertebrates species, from fish and frogs to mammals and birds. They applied a number of statistical analyses that explicitly test the consequences of selection on diversification. Their results show that the correlation between resting and maximum rates is a general feature of vertebrates, supporting the aerobic model for the evolution of endothermy. Read the Article