Evolvability in mammal morphology

Mammals (class Mammalia) span a tremendous range of sizes, from < 2 g for the Etruscan shrew to > 180,000 kg for the blue whale. Moreover, their shapes also vary, from the large ears of an elephant and the long limbs of an orangutan to the hundreds of similarly-shaped mice. How did this diversity arise? And why is there tremendous morphological variation in some clades but very little in others?

Appealing to the concept of evolvability, or differences in the abilities of lineages to generate phenotypic variation, may help to explain this phenomenon. Previous work has found that mammalian body size evolution has undergone a number of substantial 'jumps' towards increased evolvability; however, little is known about the history of mammalian phenotypic evolution in other body dimensions.

Using an unpublished database of morphological traits for the world's mammals (data for > 5,000 species), the student will first fill in the 'gaps' in this database with addition data collection and/or phylogenetic imputation. Using the Fabric model, the student will then search for evidence of jumps in variability (evolvability) within these traits across the history of mammals. This will determine which clades have undergone unusual bursts of morphological evolution, and at what time, and whether these changes occur across all body dimensions or just single traits (e.g., tails).

Finally, using ancestral state reconstructions, Bayesian phylogenetic mixed models, evidence from the palaeontological record, and the wealth of published and unpublished species-level social, ecological, and environmental trait data available for the world's mammals, the student will attempt to link these periods of increased or decreased morphological evolution to behavioural innovations or environmental perturbations in the history of the group. For example, the large body size of cetaceans is generally linked to aquatic lifestyles, while the highly conserved body plans of bats are attributed to their flight abilities - to what extent does locomotory mode, more generally, shape mammalian morphological evolvability?

This work will generate novel insight into the evolutionary processes shaping the morphological diversity of the word's mammals and will be well-supported by a team of experts in macroevolutionary models and in form-function evolution. There will be scope within the project to visit collaborators at the Universities of Bristol and St Andrews for additional training; depending on funding, there may also be the possibility of museum collections visits.