The Study Of Variation In Reproductive Strategies Of Pedicularis With Elevation In The East Of Tibetan Plateau

Reproduction is the critical issue in evolution of plants, and the key point to understand any questions of biological evolution. The primary activities of plants are to uptake and use resources from natural environments, then finish reproduction. However, the resources availability in nature is pretty limited. Plants must allocate limited reources or enerty into different functions. The central question when studying reproductive strategies is to ask how plants allocate resoureces, which has been focused on since very earily. In present study, from an allocation aspect we try to detect how the reproductive strategies change with increasing elevation. As a large genus with a variety of corolla types, Pedicularis has received more and more attentions from a number of phylogists and pollination biologists, but the ecological study is very less done. We studied variation in several relatively important plant traits below with increasing elevation, and had some interesting results.1, Reproductive allometry in Pedicularis species changes with elevationPlants produce biomass and then allocate some of it to reproductive structures, so the relationship between reproductive (R) and vegetative (V) mass is a fundamental aspect of a plant's reproductive strategy.Differences in the allometric relationship between R and V have been attributed to differences in environmental conditions. One hypothesis is that genotypes adapted to more favorable environments should have a higher log R vs. log V slope. In this study, we investigated variation in allometric relationship between R-V among 44 naturally-occurring populations of 24 species of Pedicularis in the Tibetan Plateau, to ask if the populations at lower elevations (more favorable environments) have higher log R-log V slopes.We found significant positive relationship between intercept of log R-log V regressions and elevation across species, but the trends were not found among populations; there was a significant negative relationship between slope of log R-log V regression and elevation in all the analyses. We interpret this change in slope in terms of the increased costs of being larger at high elevations. In sum, the allometric slope (exponent) of the R-V relationship decreases with increasing elevation among Pedicularis populations and species, reflecting fundamental changes in the costs and benefits of increased size with elevation.2, Geographic variation in primary sex allocation per flower in Pedicularis with increasing elevationThe study of geographic variation in ecologically important traits within and among taxa is a first step towards understanding the environmental factors that contribute to population differentiation and species divergence. This study examines variation in mean sex allocation per flower (androecium mass/gynoecium mass) among 49 wild populations representing 12 Pedicularis species across an elevation gradient on the eastern Tibetan Plateau. We used population means to evaluate sources of variation in per-flower sex allocation within and across species. In particular, we evaluate the relative influence of intrinsic (i.e., plant size, estimated as above-ground stem biomass) vs. extrinsic factors affecting mean sex allocation among populations. Mean sex allocation per flower (the relative investment in male floral organs) is negatively correlated with mean plant size; populations of large plants produce relatively female-biased flowers. This relationship between mean plant size and mean sex allocation is not statistically significant, however, when the effect of elevation is controlled statistically. Among populations within and across species, mean sex allocation increases with elevation. This relationship persists even when the effect of mean plant size is controlled statistically. Factors associated with increasing elevation appear to favor genotypes and/or taxa with male-biased flowers. In sum, extrinsic environmental conditions may be more important than intrinsic resource status in determining patterns of geographic variation in mean sex allocation among populations or species of Pedicularis. We cannot conclude whether the effect of elevation on mean sex allocation is the result of environmentally-induced plasticity, genetically-based adaptation, or species-sorting, but it is only partly mediated by mean plant size.3, Geographic variation in seed mass in Pedicularis with increasing elevationWe examined geographic variation in mean individual seed mass (MISM) among 38 populations within and across nine Pedicularis species in the eastern Tibetan Plateau, measuring the effects of one extrinsic factor (elevation) and two intrinsic factors (plant size and mean seed number per fruit). Across all populations, elevation is negatively correlated with MISM; within eight of nine species, this pattern is also observed among populations. This relationship, however, is not significant when controlling for variation in plant size or seeds per fruit. High-elevation populations produce smaller plants with more seeds per fruit than low-elevation populations; controlling for these variables eliminates the negative correlation between elevation and MISM. Across all populations, the predicted trade-off between MISM and seeds per fruit is consistently strong, with or without controlling for the effects of plant size. By contrast, the trade-off between MISM and total seasonal fecundity can be detected only when controlling for plant size. Independent of plant size, populations that produce small seeds do not support individuals with particularly low reproductive yield (fecundity x MISM). Accordingly, high-elevation populations exhibit neither lower reproductive yield nor smaller seeds than expected given their lower biomass. In sum, elevation, plant size and seeds per fruit are all correlated with MISM among populations across species. Elevation is less important, however, than intrinsic factors in determining the MISM of a population; the effect of elevation on MISM disappears when the effects of intrinsic factors are controlled statistically. The observed decline in MISM with increasing elevation is partly mediated by the decline in plant size and an increase in mean seed number per fruit with elevation. Altitudinal variation in MISM across populations or species has been described before, but this is the first study to control for the effect of intrinsic factors simultaneously. This result challenges the robustness of studies that have detected geographic variation in MISM without controlling for variation in intrinsic factors.