Asymmetry in threespine stickleback lateral plates

Abstract

The study of asymmetry can provide insights into genetic and environmental influences on organismal development. Directional asymmetry (DA) can be either adaptive or non‐adaptive, whereas fluctuating asymmetry (FA) – defined as small non‐directional departures from symmetry in bilateral traits – is thought to be an indicator of genetic or environmental stress experienced during development. Using data from 28 European populations, we assessed the degree of DA and FA in the lateral plates of threespine sticklebacks Gasterosteus aculeatus and surveyed the direction of DA and differences in levels of DA and FA in different habitat types (viz. marine, lake and river populations). DA differed between habitats, with right‐biased DA found in the marine populations and no directional bias found in lake and river populations. Differences in DA among habitats may be a by‐product of habitat‐specific developmental instability resulting in asymmetry, or it may indicate habitat‐specific differences in selection against/for symmetry, as has been proposed in previous research of sticklebacks. Also, the presence of FA varied depending upon habitat type, but it also depended on plate morph – a variable confounded with the habitat effect. While we cannot rule out factors such as stress as a cause of population differences in FA, it may also simply be a by‐product of other evolutionary processes (e.g. lateral plate number reduction) without functional basis.

Heterozygosity and asymmetry: Ectodysplasin as a form of genetic stress in marine threespine stickleback

“…(4) Plate position asymmetry differed between structural and nonstructural plates. In contrast to observations made in freshwater populations (Bergstrom and Reimchen 2000;Loehr et al 2013), only a single individual exhibited structural asymmetry among all marine individuals. (5) Finally, asymmetry did not vary significantly with standardized genome-wide heterozygosity, but was clearly associated with Eda genotype, even in genotype-phenotype mismatched individuals.…”

“…That is an occurrence of 0.35%, as opposed to freshwater reports varying from 1.1% to 4.8% (Bergstrom and Reimchen ; Loehr et al. ). This contrast suggests that canalization of structural plates may be under relaxed selection in the freshwater environment (Trokovic et al.…”

“…The structural plates are hypothesized to develop early due to their defensive role, particularly in spine deflection (Reimchen 1983). Consistent with this expectation, symmetric and asymmetric loss of structural plates is less common than loss of nonstructural plates in Haida Gwaii and Scandinavian sticklebacks (Reimchen 1983;Bergstrom and Reimchen 2000;Loehr et al 2013), presumably due to selection. Our results confirmed this association.…”

“…; Reimchen and Bergstrom ; Loehr et al. , , but see Van Dongen et al. ), but not tested in threespine stickleback—such a correlation in marine stickleback could potentially explain the maintenance of SGV in oceanic populations.…”

Constant fluctuating asymmetry but not directional asymmetry along the geographic distribution of Drosophila antonietae (Diptera, Drosophilidae)

“…Directional asymmetry is not a rare effect in Diptera Pélabon and Hansen, 2008;Soto et al, 2010), as well in other invertebrate (Graham et al, 1998;Schneider et al, 2003) and vertebrate groups (Kark, 2001;Marchand et al, 2003;Loehr et al, 2013). In Diptera, suggested that the genetic basis of DA has been conserved over evolutionary time due to the existence of a left-right axis determining the position of imaginal disks (developmental precursors of wings) on each side of the body.…”