Beyond the Behavioural Syndrome: Functional Integration of Physiology, Behaviour, and Cognition among Squamates

Abstract

Understanding the mechanisms driving the patterns of organismal diversity is a central aim of evolutionary biology. When fitness relies upon the synergistic effect of multiple traits, they become functionally integrated, giving rise to complex phenotypes, also referred to as syndromes. Patterns of phenotypic integration are shaped by both extrinsic as well as intrinsic factors, and occur across taxonomic levels. Current syndrome research focuses primarily on behaviour with only one, the Pace-of-Life Syndrome (POLS), incorporating components of physiology. Despite the strong effect temperature has on behaviour and cognition, thermal physiology has yet to be considered within a syndrome framework. Accordingly, I propose the POLS be extended to include a new dimension, the cold-hot axis, characterized by a suite of inter-correlated thermal traits. Under this premise, it is predicted that individuals would be similarly positioned along five axes encompassing physiological, behavioural, and cognitive traits. At one extreme of the continuum are Hot-Fast Thermal Types characterized as having high thermal traits; a fast, inaccurate, stereotypical cognitive style; and high levels of activity, boldness, exploration, and anti-social behaviour. Conversely, the Cold-Slow Thermal Type is instead associated with low thermal traits; a slow, accurate, reactive cognitive style; and low activity, exploratory behaviour, and boldness levels. My thesis takes a multi-scale approach to test the predictions put forth by the extended POLS. I begin by employing a phylogenetic framework to model the evolutionary patterns of phenotypic integration among squamate reptiles (chapter 2). In the ensuing chapters, I focus on a single lizard species, the delicate skink (Lampropholis delicata) to first examine the stability and correlation among physiological traits to detect the presence of thermal types (chapter 3) followed by investigations into the correlation between thermal traits, behaviour (chapter 4), and cognition (chapter 5). My overall results indicated that physiological and behavioural traits are functionally integrated at both the inter- as well as intra-specific level among lizards. Broadly, it was shown that across Sauria, physiological and behavioural traits have become functionally integrated and that the primary selective agent dictating the evolution of this complex phenotype is environmental temperature (chapter 2). When focussing on a single species, L. delicata, I found clear evidence in support of the incorporation of the thermal axis within the POLS (chapters 3). Lizards were found to exhibit a ‘thermal type’ where Hot-Fast types had quicker sprint speeds and higher optimal and preferred body temperatures whereas Cold-Slow types performed slower and selected lower body temperatures. Behavioural and cognitive traits were also found to be component axes of the syndrome paralleling this physiological continuum (chapters 4 and 5). Boldness, activity, exploratory behaviour, sociability, and learning speed all increased with thermal traits while learning accuracy decreased. As a whole, my thesis not only highlights the need to incorporate physiology within the syndrome concept, but also serve to provide a comprehensive examination of how thermal traits, as the links between the external environment and organismal fitness, may be what underlies phenotypic evolution.