Freshwater influence is associated with differences in bone mineral density and armour configuration in threespine stickleback (Gasterosteus aculeatus)

Heather A Jamniczky,Sean M Rogers,Amie Le,Tegan N Barry,Steven J Cooke

doi:10.1139/facets-2017-0120

Abstract

Threespine stickleback ( Gasterosteus aculeatus Linnaeus, 1758) exhibit a well-documented reduction in plate number associated with adaptation to freshwater environments. We tested the hypothesis that changes in plate number are accompanied by changes in plate bone mineral density and plate shape, reflecting the presence of a complex plate “armour” phenotype and a complex adaptive response to different selective pressures in changing habitats. We used traditional and novel morphometric techniques to characterize armour traits from stickleback occupying three marine habitats and one tidally influenced freshwater stream in southwestern British Columbia. Stickleback inhabiting marine environments share a conserved plate phenotype that includes a full complement of highly mineralized plates that exhibit a characteristic density profile along the plate. Stickleback inhabiting tidally influenced fresh water display an average reduction in plate number along with increased variation in number and reduced total mineralization despite maintenance of a marine-like density profile. Further, we found that although mineralization and armour shape are correlated with size, after accounting for size variation in both traits remains attributable to habitat. Our results hint at an important role for development in structuring phenotypic variation during the process of adaptive change in stickleback.

Highlights

Published: June 25, 2018Published by: Canadian Science Publishing the incorporation of genetic theory and genomic approaches have resulted in substantial gains toward understanding the processes that produce phenotypic variation in nature, it is clear that considerable work remains to be done to understand the nature and complexity of the links between genotype, phenotype, and environmental context that produce the phenotypes upon which selection can act (Travisano and Shaw 2013)
The nature of the genetic and environmental mechanisms that underlie the maintenance of phenotypic variation in sticklebacks in the marine environment remains poorly understood, and we propose that this may be, in part, due to the inability of relatively superficial trait descriptions to adequately describe features of organisms that selection sees
Size was a significant source of variance, there was no interaction between size and Bone mineral density (BMD) across the plate and an interaction term was not included in the final model (Tables 2 and 3)

Summary

Introduction

The incorporation of genetic theory and genomic approaches have resulted in substantial gains toward understanding the processes that produce phenotypic variation in nature, it is clear that considerable work remains to be done to understand the nature and complexity of the links between genotype, phenotype, and environmental context that produce the phenotypes upon which selection can act (Travisano and Shaw 2013). Threespine stickleback are known to exhibit parallel changes in plate phenotype, as since the last major glaciation they have repeatedly moved from a marine environment to colonize freshwater lakes and streams (Bell and Foster (1994)). This phenotypic variation has largely been characterized by a reduction in plate number. Plates tend to be lost from the back and the middle of the fish, whereas anterior plates are largely retained to support the spines (Reimchen 1983)

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