Data from: Physiological effects of temperature do not explain prevalence of females in populations of gynodioecious Lobelia siphilitica growing in warmer climates

PREMISE OF THE STUDY: Gynodioecy is a sexual polymorphism whereby female and hermaphroditic plants co-occur within populations. In many gynodioecious species, stressful abiotic environments are associated with higher frequencies of females. This association suggests that abiotic stress affects the relative fitness of females and hermaphrodites and, thus, the maintenance of gynodioecy.
METHODS:To test whether abiotic stress affects the fitness of females and hermaphrodites, we grew open-pollinated Lobelia siphilitica families in temperature regimes characteristic of the southern portion of the species' range (where females are common) and the northern portion of the range (where females are rare). We measured physiological and phenological traits that are indicative of heat stress, and fitness components of females and hermaphrodites that could affect the maintenance of gynodioecy.
KEY RESULTS:Contrary to expectations if growth at high temperatures is stressful, we found that the hot treatment increased leaf chlorophyll content, decreased the percentage of plants that delayed flowering initiation, and did not affect the quantum efficiency of photosystem II. Growth at high temperatures did not affect the magnitude of the difference in rosette size (a correlate of flower number) between females and hermaphrodites, or the variance in pollen viability among hermaphrodites.
CONCLUSIONS:We found that growing-season temperatures typical of high female L. siphilitica populations were not stressful and did not affect either the fitness of females compared to hermaphrodites or variation in fitness among hermaphrodites. Consequently, further research is necessary to explain correlations between abiotic environmental factors and the frequency of females in this and other gynodioecious species.

研究背景：雌全异株（gynodioecy）是一种性系统多态现象，指种群内同时存在雌性植株与两性植株（hermaphroditic plants）。在多数雌全异株物种中，非生物胁迫（abiotic stress）环境与更高的雌性植株频率相关联。这一关联提示，非生物胁迫会影响雌性与两性植株的相对适合度（relative fitness），进而维持雌全异株这一性系统。
研究方法：为验证非生物胁迫是否会影响雌性与两性植株的适合度，我们将开放授粉（open-pollinated）的美洲山梗菜（Lobelia siphilitica）家系分别种植于该物种分布区南部（雌性植株较为常见）与北部（雌性植株较为稀少）的典型温度条件中。我们测定了可表征热胁迫（heat stress）的生理与物候性状，以及可能影响雌全异株维持的雌性与两性植株的适合度组分（fitness components）。
主要结果：与“高温环境具有胁迫性”的预期相悖，我们发现高温处理提升了叶片叶绿素含量，降低了延迟开花始期的植株比例，且未影响光系统II的量子效率（quantum efficiency of photosystem II）。高温环境未改变雌性与两性植株之间莲座大小（与花数相关的指标）的差异幅度，也未影响两性植株间花粉活力（pollen viability）的变异程度。
结论：我们发现，雌性植株占比高的美洲山梗菜种群所处的生长季温度并不具有胁迫性，且既未影响雌性相较于两性植株的适合度，也未改变两性植株间的适合度变异。因此，仍需开展进一步研究，以阐释本物种及其他雌全异株物种中，非生物环境因子与雌性植株频率之间的关联。