Data from: Trait integration and macroevolutionary patterns in the pollination biology of conifers

Integration influences patterns of trait evolution, but the relationship between these patterns and the degree of trait integration is not well understood. In order to explore this further, we study a specialized pollination mechanism in conifers whose traits are linked through function but not development. This mechanism depends on interactions among three characters: pollen that is buoyant, ovules that face downward at pollination, and the production of a liquid droplet that buoyant grains float through to enter the ovule. We use a well-sampled phylogeny of conifers to test correlated evolution among these characters and specific sequences of character change. Using likelihood models of character evolution, we find that pollen morphology and ovule characters evolve in a concerted manner, where the flotation mechanism breaks down irreversibly following changes in orientation or drop production. The breakdown of this functional constraint, which may be facilitated by the lack of developmental integration among the constituent traits, is associated with increased trait variation and more diverse pollination strategies. Although this functional “release” increases diversity in some ways, the irreversible way in which the flotation mechanism is lost may eventually result in its complete disappearance from seed plant reproductive biology.性状整合影响性状演化模式，但这类演化模式与性状整合程度之间的关联仍未得到充分阐释。为进一步探究这一问题，我们针对针叶植物中一类特化传粉机制展开研究，该机制下的性状仅通过功能而非发育路径实现关联。该传粉机制依赖三类性状的协同作用：具备浮力的花粉、传粉阶段向下朝向的胚珠，以及可使浮力花粉粒游动进入胚珠的液滴分泌过程。我们借助采样覆盖度充足的针叶植物系统发育树，检验这三类性状间的协同演化关系，以及性状演化的特定序列模式。通过性状演化似然模型分析，我们发现花粉形态与胚珠性状呈现协同演化模式：当胚珠朝向或液滴产生发生改变时，该浮力传粉机制会不可逆地瓦解。这一功能约束的瓦解，其成因可能源于组成性状间缺乏发育整合，与性状变异程度提升、传粉策略多样化程度增加密切相关。尽管这种功能“释放”在某些维度上提升了多样性，但浮力传粉机制以不可逆的方式丢失这一过程，最终可能导致该机制从种子植物的生殖生物学中彻底消失。