Maternal quality, paternal effects, and sibling interactions influence seed size in the eelgrass, Zostera marina

Seed size is an essential determinant of germination and survival in angiosperms. Zostera marina, one of few marine angiosperms, is a key foundation species present in coastal marine ecosystems, and edge-of-range population persistence is increasingly reliant on seed production. While environmental conditions have been invoked to explain regional patterns of seed size variation, far less is known about seed size differences within a plant. In this study, we genotype and measure individual seeds across parent plants to investigate the relative contributions of maternal, paternal and offspring traits on seed weight. Specifically, we investigate how parent heterozygosity, paternal siring success, outcrossing, a size-number tradeoff, and sibling interactions influence both seed weight (mg) and cross-sectional area (mm2). Here, we provide all necessary files to conduct the entirety of analyses used in the manuscript. 

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1. Study Sites and Sample Collection  

Three seagrass meadows in the intracoastal waters of Topsail Sound, North Carolina were sampled to characterize Zostera marina seed size variation. Meadows were on a narrow shelf classified as shallow subtidal (depth < 2m MLLW) between the Intracoastal Waterway and the adjacent shoreline (34.22 N, 77.37 W; Fig. S1). On 4 May 2021, near the end of the eelgrass reproductive season, flowering shoots were haphazardly collected at least 5m apart, yielding 35 shoots total. Samples were transported on ice to UNCW’s Center for Marine Science, and the morphological characteristics of each shoot were recorded. Specifically, each rhipidium (branching reproductive structure), spathe (seed-containing branch within a rhipidium), and seed position was labeled in order of decreasing proximity to the rhizome (i.e., basal positions were given a value of 1; Fig. S2). 

 

2. Seed Measurements and Genotyping 

Seeds were removed from ..., , # Seed size variation in the eelgrass, *Zostera marina*

[https://doi.org/10.5061/dryad.6t1g1jx7p](https://doi.org/10.5061/dryad.6t1g1jx7p)

# Data Collection & Description

## 1. Study Sites and Sample Collection 

*Zostera marina* shoots were sampled in the intracoastal waters of Topsail Sound, North Carolina. The morphological characteristics of each shoot were recorded. Specifically, each rhipidium (branching reproductive structure), spathe (seed-containing branch within a rhipidium), and seed position was labeled in order of decreasing proximity to the rhizome (i.e., basal positions were given a value of 1; Fig. S2).

## 2. Seed Measurements and Genotyping 

Viable seeds were removed from spathes, weighed (mg) with a microbalance, and photographed at ×10 magnification on a stereo microscope. Length (mm), width (mm), and cross-sectional area (mm^2) were measured for each seed using ImageJ software. Cross-sectional area of seeds was then calculated from the following equation: *v* = ...,

种子大小是被子植物萌发与存活的核心决定因子。大叶藻（Zostera marina）是少数海洋被子植物类群之一，作为沿海海洋生态系统的关键建群物种，其分布边缘种群的存续愈发依赖种子生产。尽管已有研究通过环境条件阐释了种子大小变异的区域格局，但针对同株植物内部的种子大小差异，目前所知甚少。本研究对不同亲本植株的单粒种子开展基因分型与表型测量，以探究母本、父本以及子代性状对种子重量的相对贡献。具体而言，本研究旨在解析亲本杂合度、父本授粉成功率、异交率、大小-数量权衡效应以及同胞间相互作用，如何同时影响种子重量（单位：毫克，mg）与横截面积（单位：平方毫米，mm²）。本文提供了支撑论文全部分析所需的全部必要文件。

# 鳗草（大叶藻，Zostera marina）种子大小变异
数据集DOI链接：https://doi.org/10.5061/dryad.6t1g1jx7p

# 数据采集与描述
## 1. 研究地点与样本采集
在北卡罗来纳州托普西尔湾的沿岸水域中，共选取3片海草床，用于表征大叶藻的种子大小变异。该海草床坐落于内陆水道与邻近岸线之间的狭窄浅海架上，属于潮下浅生境（以平均低潮水位为基准，水深小于2米），坐标为34.22°N，77.37°W（图S1）。2021年5月4日，正值鳗草繁殖季末期，研究人员随机采集间距至少5米的开花枝条，最终获得35份枝条样本。样本以冰鲜方式运输至北卡罗来纳大学威尔明顿分校（UNCW）海洋科学中心，并记录每份枝条的形态特征。具体操作如下：按照距根茎由近及远的顺序（即基部位置赋值为1；图S2），对每个复伞形生殖枝（rhipidium，分枝状生殖结构）、佛焰苞（spathe，复伞形枝内包含种子的分枝）以及种子位置进行标记。

## 2. 种子测量与基因分型
从佛焰苞中剥离出存活种子，使用微量天平称量其重量（单位：毫克），并在体视显微镜下以10倍放大倍率进行拍照。利用ImageJ软件测量每粒种子的长度（单位：毫米）、宽度（单位：毫米）与横截面积（单位：平方毫米）。种子横截面积通过以下公式计算：v = ……