Convergence in the size and frequency of macroevolutionary peak-shifts on the adaptive landscape in vertebrates

Empirical and theoretical support is emerging for a view of macroevolution characterised by species' phenotypes tracking continually-moving adaptive peaks, interspersed with rare large shifts in the position of those peaks, likely corresponding to changes in species' adaptive zones. But we lack understanding of the factors that control these movements. We show in a sample of over 21,000 species from the five Vertebrate Classes (Mammals, Birds, Reptiles, Fish and Amphibians) repeated convergence in the magnitude and frequencies of rare shifts in body-size peaks among species inhabiting the same dominant ecology. Peak-shifts (towards becoming larger or smaller) have been largest and most frequent among aquatic species, followed by terrestrial and then smallest and least frequent among volant species, independently of phylogenetic history. All peak-shifts are small in macroevolutionary time indicating that species in the terrestrial and aerial environments could have changed more had their environments favoured it. Within-population trait-variances from independent sources are largest in aquatic, followed by terrestrial then aerial species, consistent with evolution responding to differing macroevolutionary landscapes. Our results illustrate how ecologically varying adaptive landscapes have produced convergent outcomes of vertebrate macroevolution, giving rise to predictable evolutionary patterns even among species differing in fundamental aspects of development and thermoregulation.