Both natural selection and isolation by distance explain phenotypic divergence in bill size and body mass between South Australian little penguin colonies.

Diane Colombelli‐Négrel

doi:10.1002/ece3.2516

Abstract

Morphological variation between populations of the same species can arise as a response to genetic variation, local environmental conditions, or a combination of both. In this study, I examined small‐scale geographic variation in bill size and body mass in little penguins (Eudyptula minor) across five breeding colonies in South Australia separated by <150 km. To help understand patterns driving the differences, I investigated these variations in relation to environmental parameters (air temperature, sea surface temperature, and water depth) and geographic distances between the colonies. I found substantial morphological variation among the colonies for body mass and bill measurements (except bill length). Colonies further located from each other showed greater morphological divergence overall than adjacent colonies. In addition, phenotypic traits were somewhat correlated to environmental parameters. Birds at colonies surrounded by hotter sea surface temperatures were heavier with longer and larger bills. Birds with larger and longer bills were also found at colonies surrounded by shallower waters. Overall, the results suggest that both environmental factors (natural selection) and interpopulation distances (isolation by distance) are causes of phenotypic differentiation between South Australian little penguin colonies.

Highlights

Understanding mechanisms of population divergence is important for both evolutionary biologists and conservationists
This study focused on morphological variation in little penguins (Eudyptula minor; Figure 1), the smallest of all penguin species (Marchant & Higgins, 1990)
Multivariate analysis of variance (MANOVA) was used to compare the morphological measurements taken by the three researchers: the results showed that the measurements were comparable and not statistically different (MANOVA: all p > .28), and all data were combined

Summary

| INTRODUCTION

Understanding mechanisms of population divergence is important for both evolutionary biologists and conservationists. The roles of these genetic and environmental factors are not mutually exclusive (e.g., Barbraud & Jouventin, 1998; Darwin, 1859), and their importance for population divergence still remains to be examined for many species (see Pfennig et al, 2010; West-Eberhard, 1989), with additional studies from different geographic areas necessary to fully understand mechanisms of morphological variation (Waugh, Prince, & Weimerskirch, 1999; Wojczulanis-Jakubas et al, 2011). I expected that (1) birds breeding in conditions of low air temperatures and/or at sites surrounded by lower sea surface temperatures would be larger than individuals breeding in areas experiencing milder conditions (Bergmann, 1848; Blackburn et al, 1999; James, 1970) and (2) larger individuals would be found at colonies surrounded by shallower waters because they would have access to more accessible prey and have developed larger bodies (Wiebkin, 2012)

| METHODS

Findings

| DISCUSSION