PhD: Complexity and the Evolution of Arthropod Diversity

Why are some groups of animals super diverse, while their sister groups are species poor? Understanding the forces that shape past and present patterns of diversity is now a major agenda in evolutionary biology and conservation. In this project, we will focus on arthropods, because the heterogeneity of species richness is particularly striking. For example, there are about a million described species of insect but only 30 species of remipede, their closest relatives. What is the relationship between species richness and the complexity and flexibility of the bodyplan? Counterintuitively, remipedes have numerous (16-32) similar limb pairs (a flexible but low complexity bodyplan), while insects have three pairs of walking limbs and strongly regionalized bodies (a less flexible but more complex bodyplan). We will use time-calibrated supertrees and data on body and limb segment specialization to quantify complexity and identify significant shifts in its evolution across arthropods through time.

Project aims -

Is complexity and the flexibiity of bodyplan design a driver of clade diversity?
1. To understand the relationship between the bodyplan complexity of arthropods and their species richness.
2. To quantify shifts in rates of diversification through time, and relate this to changes in complexity.
3. To quantify the relationship between morphological disparity and complexity.

Project methods -

We will use published supertrees and construct new ones using the Supertree Toolkit. We will time calibrate these (nodes and tips using Strap and Paleotree) using the literature and online resources (fossilworks). Shifts in diversification rate will be quantified using BAMM.
Complexity will be quantified using indices of serial differentiation in the body, limbs and limb podomeres (see Adamowicz et al., 2008) and rate shifts quantified using Auteur, Giga and Motmot.

Disparity will be quantified using discrete characters and morphometric parameters, so that we will be able to investigate multiple aspects of morphospace filling (Ruta & Wills, 2016).

We will then compare levels of complexity, diversity and disparity in independent sister group clades. We will also investigate the correlation between limb and body complexity using phylogenetic least squares regression throughout our trees.

Candidate -

The ideal candidate will have experience in phylogenetics, with either a Biology or Earth Sciences background. He/She will be computer literate, with a reasonable knowledge of basic statistics and possibly some scripting ability.

Training -

The student will be trained in phylogenetic analysis using parsimony, likelihood and Bayesian inference (PAUP*, Mesquite, TNT, RAXML, MrBayes). They will be taught to construct supertrees (STK) and to time calibrate these (PaleoTree, Strap, Giger). We will cover basic scripting in R, and the use of a variety of R packages for manipulating trees and looking for rate shifts (Auteur, BAMM). We will also cover disparity and morphospace analyses using discrete character and morphometric data.