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

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.

Elevated temperatures drive the evolution of armor loss in the threespine sticklebackGasterosteus aculeatus

“…Growth is also a plastic trait in the threespine stickleback (e.g. Mccairns and Bernatchez 2012), though plate morphotype (Colosimo et al 2005; Barrett et al 2008; Marchinko 2009) and number (Hansson et al 2016) are not. The effect demonstrated here represents a rare example of a phenotypic response to temperature change that is underpinned by genetic change.…”

Genomic signatures of the plateless phenotype in the threespine stickleback

“…), including stickleback plate number plastically responding to a change in salinity (Hansson et al. ). As such, it is possible that these or other environmental cues could be modulating the number of plates within plate morph, possibly along a reaction norm that is established by genotype ( EDA or otherwise) (Schlichting and Pigliucci ).…”

“…Plate phenotypes are clearly influenced strongly by EDA genotype (Colosimo et al 2005), but are also modified by other genes (Colosimo et al 2004). Additional modulators such as epigenetic modifications or phenotypic plasticity may also be important; indeed, it has been shown that phenotypic plasticity has a strong effect on stickleback morphology in response to different environmental cues (Day et al 1994;Wund et al 2008Wund et al , 2012Svanb€ ack and Schluter 2012;Lucek et al 2014;Mazzarella et al 2015), including stickleback plate number plastically responding to a change in salinity (Hansson et al 2016). As such, it is possible that these or other environmental cues could be modulating the number of plates within plate morph, possibly along a reaction norm that is established by genotype (EDA or otherwise) (Schlichting and Pigliucci 1998).…”

Elevated temperatures drive the evolution of armour loss in the threespine sticklebackGasterosteus aculeatus

“…Multiple genomic regions have been associated with adaptation to fresh water (Jones et al., 2012), with the ectodysplasin A locus specifically implicated in lateral plate evolution. The heritability of plate number is high (Hansson et al., 2016), with 70% of variation in plate number associated with variation in ectodysplasin A (Colosimo et al., 2005; Cresko et al., 2004). Marine populations are assumed to possess a pool of standing genetic variation, with rare variants of the ectodysplasin A locus experiencing strong selection once fish enter fresh water, where they rapidly increase in frequency (Barrett, 2010).…”