Lateral plate number in low-plated threespine stickleback: a study of plasticity and heritability.

Truls H Hansson,Leif Asbjørn Vøllestad,Barbara Fischer,Anna B Mazzarella,Kjetil L Voje

doi:10.1002/ece3.2020

Abstract

In the threespine stickleback Gasterosteus aculeatus model system, phenotypes are often classified into three morphs according to lateral plate number. Morph identity has been shown to be largely genetically determined, but substantial within‐morph variation in plate number exists. In this study, we test whether plate number has a plastic component in response to salinity in the low‐plated morph using a split‐clutch experiment where families were split in two, one half raised in water at 0 and the other at 30 ppt salt. We find a small salinity‐induced plastic effect on plate number in an unexpected direction, opposite to what we predicted: Fish raised in freshwater on average have slightly more plates than fish raised in saltwater. Our results confirm that heritability of plate number is high. Additionally, we find that variance in plate number at the family level can be predicted from other family level traits, which might indicate that epistatic interactions play a role in creating the observed pattern of lateral plate number variation.

Highlights

The evolutionary history of the threespine stickleback (Gasterosteus aculeatus) is a well-known example of an adaptive radiation
We find a small salinityinduced plastic effect on plate number in an unexpected direction, opposite to what we predicted: Fish raised in freshwater on average have slightly more plates than fish raised in saltwater
We tested in a split-clutch experiment whether lateral plate number of the low-plated morph of the threespine stickleback is plastic in response to salinity

Summary

Introduction

The evolutionary history of the threespine stickleback (Gasterosteus aculeatus) is a well-known example of an adaptive radiation. Saltwater populations of stickleback have independently invaded and adapted to freshwater environments recurrently since the last ice age. One of the most notable phenotypic changes seen in this radiation is the reduction of lateral bony armor plates (Bell and Foster 1994; Lescak et al 2015). Stickleback are commonly categorized into three plate morph categories: Marine fish are predominantly “fully plated” (>30 plates), fish in brackish water are commonly intermediately or “partially plated”, while freshwater fish usually have

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