Data from: Fine-scale environmental control of hybridization in oaks

Natural hybridization is attracting much interest in modern speciation and conservation biology studies, but the underlying mechanisms remain poorly understood. In particular, it is unclear why environmental changes often increase hybridization rates. To study this question, we surveyed mating events in a mixed oak stand and developed a spatially-explicit individual-based hybridization model. This model, where hybridization is frequency dependent, pollen is non-limiting and which allows immigrant pollen to compete with local pollen, takes into account species-specific pollen dispersal and sexual barriers to hybridization. The consequences of pollen limitation on hybridization were studied using another simple model. The results indicate that environmental changes could increase hybridization rates through two distinct mechanisms. First, by disrupting the spatial organisation of communities, they should decrease the proportion of conspecific pollen available for mating, thus increasing hybridization rates. Second, by decreasing the density of conspecifics, they should increase pollen limitation and thus hybridization rates, as a consequence of chance pollination predominating over deterministic pollen competition. Altogether, our results point to a need for considering hybridization events at the appropriate level of organisation and provide new insights into why hybridization rates generally increase in disturbed environments.

自然杂交在现代物种形成与保护生物学研究中备受关注，但其内在机制仍未得到充分阐释。尤为关键的是，学界尚未明确环境变化为何常会提升杂交发生率。为解答这一问题，本研究对一片混交栎林内的交配事件开展了调查，并构建了基于个体的空间显式杂交模型（spatially-explicit individual-based hybridization model）。该模型具备三项核心特征：杂交过程呈频率依赖（frequency dependent）特性、花粉供给不受限制，且允许外来花粉与本地花粉展开竞争；同时模型纳入了物种特异性的花粉扩散规律与杂交生殖障碍。此外，本研究还通过另一简化模型，探究了花粉限制（pollen limitation）对杂交过程的影响。研究结果显示，环境变化可通过两种截然不同的机制提升杂交发生率：其一，环境变化会破坏群落的空间结构，减少可用于交配的同种花粉（conspecific pollen）占比，进而推高杂交发生率；其二，环境变化会降低同种个体的种群密度，加剧花粉限制效应——此时随机授粉将取代确定性花粉竞争占据主导，从而进一步提升杂交发生率。综上，本研究结果表明，需在恰当的组织层级上开展杂交事件研究，同时也为受干扰环境中杂交发生率普遍升高的现象提供了全新的解释视角。