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（trait integration）会影响性状演化的模式，但此类演化模式与性状整合程度之间的关联尚未得到充分阐明。为进一步探究这一问题，本研究聚焦于针叶树（conifers）的特化传粉机制：该机制中各性状仅存在功能关联，而非发育整合。此传粉机制依赖三类性状的协同作用：具有漂浮能力的花粉、传粉期向下朝向的胚珠，以及可使漂浮花粉通过并进入胚珠的液滴产生过程。我们采用一套采样充分的针叶树系统发育（phylogeny）数据集，检验这三类性状间的协同演化关系及性状变化的特定时序。通过性状演化似然模型（likelihood models）分析，本研究发现花粉形态与胚珠性状以协同模式演化：当胚珠朝向或液滴产生性状发生改变后，漂浮传粉机制会不可逆地瓦解。这类功能约束的瓦解——或可因组成性状间缺乏发育整合而得以促进——与性状变异程度升高以及传粉策略愈发多样相关。尽管这种功能“解放”在某些维度上提升了多样性，但漂浮传粉机制丧失的不可逆性，最终或导致其从种子植物（seed plant）的生殖生物学中彻底消失。