Data from: Seasonal genetic variation associated with population dynamics of a poecilogonous polychaete worm

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.Seasonal_genetic_structure_Pygospio_elegansThe file 'Seasonal_genetic_structure_Pygospio_elegans.xlsx' contains information about samples used in this study including: SampleID Sampling.Data (population codes include location name and a 2 digit code for the sampling month) Phenotypic.Data (Length is measured in mm; cohort refers to cohort assignments described in Thonig et al. 2016 Invertebrate Biology 135(4): 370–384) Microsatellite.Data (11 microsatellite loci, 2 columns for each) Structure: Cluster Membership Coefficients (results of the structure analysis presented in the paper: membership coefficients and final cluster assignment for each individual