Abstract
Poecilogonous species show variation in developmental mode, with larvae that differ both morphologically and ecologically. The spionid polychaete Pygospio elegans shows variation in developmental mode not only between populations, but also seasonally within populations. We investigated the consequences of this developmental polymorphism on the spatial and seasonal genetic structure of P. elegans at four sites in the Danish Isefjord‐Roskilde‐Fjord estuary at six time points, from March 2014 until February 2015. We found genetic differentiation between our sampling sites as well as seasonal differentiation at two of the sites. The seasonal genetic shift correlated with the appearance of new size cohorts in the populations. Additionally, we found that the genetic composition of reproductive individuals did not always reflect the genetic composition of the entire sample, indicating that variance in reproductive success among individuals is a likely explanation for the patterns of chaotic genetic patchiness observed during this and previous studies. The heterogeneous, unpredictable character of the estuary might maintain poecilogony in P. elegans as a bet‐hedging strategy in the Isefjord‐Roskilde‐Fjord complex in comparison with other sites where P. elegans are expected to be fixed to a certain mode of development.
Highlights
Phenotypic variation within a single population or species is a classical focus of ecology and evolution, and both the causes and consequences of polymorphism are actively investigated (e.g., Schwander & Leimar, 2011; Wennersten & Forsman, 2012)
We examine population genetic structure at the four sites from samples collected at six time points in order to determine whether genetic differences can be detected between size cohorts and how variation in developmental mode is related to the spatial and temporal population genetic structure
We investigated the genetic structure of the poecilogonous polychaete P. elegans from four sites in the Isefjord-Roskilde-Fjord estuary complex using six temporal samples collected over 1 year
Summary
Phenotypic variation within a single population or species is a classical focus of ecology and evolution, and both the causes and consequences of polymorphism are actively investigated (e.g., Schwander & Leimar, 2011; Wennersten & Forsman, 2012). Different developmental modes in P. elegans are found both between populations and within populations, at times showing seasonal switches (Gudmundsson, 1985; Rasmussen, 1973; Thonig et al, 2016), suggesting a possible environmental influence. Median grain size and sorting of the sediment correlated with the spatial differences, where higher densities of P. elegans and larger specimens were observed at sites with coarse and poorly sorted sediment (Herslev and Vellerup) In this part of the study, we analyzed the population genetic structure of P. elegans using seven microsatellite loci to genotype individuals sampled from the same four locations at six different time points over 1 year. We compare genotypes and phenotypes of individuals sampled both spatially and temporally to describe consequences of poecilogony on the population genetic structure of P. elegans
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