Data and analysis scripts for: Asymmetrical reproductive barriers in sympatric Jewelflowers: are floral isolation, genetic incompatibilities, and floral trait displacement connected?

Floral visitors influence reproductive interactions among sympatric plant species, either by facilitating assortative mating and contributing to reproductive isolation, or by promoting heterospecific pollen transfer, potentially leading to reproductive interference or hybridization. We assessed preference and constancy of floral visitors on two co-occurring Jewelflowers (Streptanthus breweri and S. hesperidis, Brassicaceae) using field arrays, and quantified two floral rewards potentially important to foraging choice – pollen production and nectar sugar concentration – in a greenhouse common garden. Floral visitors made an abundance of conspecific transitions between S. breweri individuals, which thus experienced minimal opportunities for heterospecific pollen transfer from S. hesperidis. In contrast, behavioral isolation for S. hesperidis was essentially absent due to pollinator inconstancy. This pattern emerged across multiple biotic environments and was unrelated to local density dependence. S. breweri populations that are sympatric with S. hesperidis had higher nectar sugar concentrations than their sympatric congeners, as well as allopatric conspecifics. Previous work shows that S. breweri suffers a greater cost to hybridization than S. hesperidis, and here we find that it also shows asymmetrical floral isolation and floral trait displacement in sympatry. These findings suggest that trait divergence may reduce negative reproductive interactions between sympatric but genetically incompatible relatives.花访客（floral visitors）可影响同域分布植物物种间的生殖互作，具体可分为两类路径：一是促进选型交配（assortative mating），助力生殖隔离（reproductive isolation）的形成；二是推动异种花粉传递（heterospecific pollen transfer），进而可能引发生殖干扰（reproductive interference）或杂交（hybridization）事件。 本研究借助野外样方实验，针对两种同域分布的宝石花（Jewelflowers）——布雷尔扭果花（Streptanthus breweri）与西部扭果花（S. hesperidis，十字花科Brassicaceae）——评估了花访客的觅食偏好与恒常性；同时在温室同质园（greenhouse common garden）中量化了两类对传粉者觅食选择具有关键作用的花部报酬（floral rewards）：花粉产量与花蜜糖浓度。 花访客在布雷尔扭果花植株间频繁发生同种转移行为，因此后者从西部扭果花处获得异种花粉传递的概率极低。与之相对，由于传粉者恒常性缺失，西部扭果花几乎不存在行为生殖隔离。该模式在多种生物环境中均有体现，且与本地种群密度依赖效应无关。 与西部扭果花同域分布的布雷尔扭果花种群，其花蜜糖浓度显著高于同域的近缘类群以及异域分布的同种种群。已有研究显示，布雷尔扭果花面临的杂交代价高于西部扭果花；而本研究发现，其在同域分布状态下同时表现出不对称花部隔离与花部性状位移。 上述研究结果表明，花部性状分化可降低同域分布但遗传不相容的近缘类群间的负面生殖互作。