Complementarity and discriminatory power of genotype and otolith shape in describing the fine-scale population structure of an exploited fish, the common sole of the Eastern English Channel

Abstract

Marine organisms show population structure at a relatively fine spatial scale, even in open habitats. The tools commonly used to assess subtle patterns of connectivity have diverse levels of resolution and can complement each other to inform on population structure. We assessed and compared the discriminatory power of genetic markers and otolith shape to reveal the population structure on evolutionary and ecological time scales of the common sole (Solea solea), living in the Eastern English Channel (EEC) stock off France and the UK. First, we genotyped fish with Single Nucleotide Polymorphisms to assess population structure at an evolutionary scale. Then, we tested for spatial segregation of the subunits using otolith shape as an integrative tracer of life history. Finally, a supervised machine learning framework was applied to genotypes and otolith phenotypes to probabilistically assign adults to subunits and assess the discriminatory power of each approach. Low but significant genetic differentiation was found among subunits. Moreover, otolith shape appeared to vary spatially, suggesting spatial population structure at fine spatial scale. However, results of the supervised discriminant analyses failed to discriminate among subunits, especially for otolith shape. We suggest that the degree of population segregation may not be strong enough to allow for robust fish assignments. Finally, this study revealed a weak yet existing metapopulation structure of common sole at the fine spatial scale of the EEC based on genotypes and otolith shape, with one subunit being more isolated. Our study argues for the use of complementary tracers to investigate marine population structure.

Using otoliths for fish stock discrimination: status and challenges

“…During the review of different studies, we found that a single method may not show stock discrimination because of several reasons such as the fish population is homogeneous especially in the marine environment, the marker may fail to detect changes at spatial and temporal scales, and the discrimination power of the method is very low. Therefore, two or more methods should be used complementarily to study the stock structure, and connectivity of fish populations at common breeding and feeding grounds (Randon et al 2020). The concurrent use of several stock discrimination techniques operating over broader spatial and temporal scales may provide sufficient data to understand both evolutionary and ecological processes that sustain the fish stock structure (Abaunza et al 2008;Taillebois et al 2017).…”

Sexual dimorphism in the otolith shape of shi drum, Umbrina cirrosa (L.), in the eastern Mediterranean Sea: Fish size–otolith size relationships

“…Information about the diversity of sex‐related traits is important for understanding a species' behaviour, life history and ecology (Bose et al ., 2017; Kitano et al ., 2007; Madenjian et al ., 2015; Teimori et al ., 2020). In fish, sexual dimorphism has been demonstrated in body size (Morbey, 2018; Parker, 1992), colour pattern (Esmaeili et al ., 2017; Robertson & Warner, 1978), fin morphometrics (Esmaeili et al ., 2017; Skjæraasen et al ., 2006) and otolith features (Campana & Casselman, 1993; Randon et al ., 2020). Sexual dimorphism can result from phenotypic plasticity induced by environmental and ecological variables such as diet quantity/quality and temperature (Stillwell et al ., 2007; Tsuboi et al ., 2011).…”

Directional Bilateral Asymmetry in Fish Otolith: A Potential Tool to Evaluate Stock Boundaries?

“…A previous study combined the life cycle stages, including (a) larval retention within spawning regions, (b) spatial segregation of juveniles inside separated coastal and estuarine nursery grounds, and (c) limited individual movement at the adult stages to identify three subpopulations of common sole in the eastern English Channel, with a separation between the English and the French parts [75]. Moreover, another study based on genotype and the otolith shape concluded that the structure of this species in the eastern English Channel was divided into several subunits, with noticeable isolation of the Seine River subunit [76]. The genetic and otolith shape approaches showed different discriminatory power.…”