POLLEN DISPERSAL DYNAMICS IN AN ALPINE WILDFLOWER,POLEMONIUM VISCOSUM

The alpine wildflower, Polemonium viscosum, depends on insect visitors for effective pollination. Here, I examine experimentally the effects of pollinator visitation on pollen removal, pollen dispersal success, paternity, and gene flow. Bumble bee pollinators visited donor individuals homozygous for marker alleles at an isozyme (GOT-2) encoding locus and then were presented with arrays of recipient plants lacking the marker alleles. Four aspects of male fitness were estimated for each donor: the number of pollen grains dispersed to flowers of the first recipient visited, the number of offspring sired on that recipient, the proportion of offspring sired in the full array, and the proportion of mates in the array bearing seeds of the donor. Pollen removal was strongly influenced by the number of bee visits to donor flowers. The amount of pollen removed in turn significantly affected the number of pollen grains reaching flowers of the first recipient. However, because seed production decelerates with stigma pollen load, the relationship between pollen export and paternal success at this proximate scale showed diminishing returns. The probability of reaching mates within the array also increased with pollen export. These findings show that floral characters enhancing pollinator visitation rate in P. viscosum have positive effects on paternity and gene flow.     

The Effect of Light Regime on Source–Sink Relations in the Shade-Enduring Ajuga reptans Plant

A quantitative approach to the evaluation of source–sink relations in Ajuga reptans plants grown under the forest canopy (shade plants) and on an open plot (sun plants) was worked out in terms of growth characteristics, CO₂ exchange, and carbon balance. Shade plants developed leaves with the relative and specific areas twice exceeding those of sun plants. Sun plants assimilated more carbon, using a significant part of it for the development of numerous runners. During a day, shade and sun plants produced 0.03 and 0.67 g of substrate, respectively. At the same time, forest (shade) plants spent 48% of assimilates for the respiration, in comparison with plants from the open plot that spent almost 70% of assimilates for respiration as they were greater in size. It was concluded, that light controls source–sink relations, which is a way of realization of the life strategy and a coordination mechanism of functional integrity of the plant organism. Light not only controls photosynthesis (source activity) but morphophysiological characteristics of plants with their hierarchical structure of sinks too.     

Cell Cultures of Ecdysteroid-Containing Ajuga reptansand Serratula coronata Plants

Cell suspension cultures of Ajuga reptans L. and Serratula coronata L. were derived from long-cultured calluses. Their growth patterns and morphophysiological characteristics indicated that these cells adapted well to grow in suspensions. During the growth cycle of cell suspension, the main ecdysteroid, among others present in plants, was 20-hydroxyecdyson (20E) for both cell lines. The content of 20E in cell suspension of A. reptans was 4–8 times higher than in the intact plant. After long culturing, the ecdysteroid profile in cell suspensions of S. coronata (20E, inokosterone, makisterone A, ecdyson, and a nonidentified metabolite) became similar to that of the intact plant. The ecdysteroids accumulated with a periodicity during subculturing cycle.     

Experimental life-history evolution: selection on the allocation to sexual reproduction and its plasticity in a clonal plant

Abstract.— Allocation to sexual reproduction is an important life-history trait in clonal plants. Different selection pressures between competitive and competition-free environments are likely to result in the evolution of specialized genotypes and to maintain genetic variation in reproductive allocation. Moreover, selection may also result in the evolution of plastic allocation strategies. The necessary prerequisite for evolution, heritable genetic variation, can best be studied with selection experiments. Starting from a base population of 102 replicated genotypes of the clonal herb Ranunculus reptans , we imposed selection on the proportion of flowering rosettes in the absence of competition (base population: mean = 0.391, broad-sense heritability = 0.307). We also selected on the plasticity in this trait in response to competition with a naturally coexisting grass in a parallel experiment (base population: 14% lower mean in the presence of competition, broad-sense heritability = 0.072). After two generations of bidirectional selection, the proportion of flowering rosettes was 26% higher in the high line than in the low line (realized heritability ± SE = 0.205 ± 0.017). Moreover, genotypes of the high line had 11% fewer carpels per flower, a 22% lower proportion of rooted rosettes, and a 39% smaller average distance between rosettes within a clone. In the second experiment, we found no significant responses to selection for high and low plasticity in the proportion of flowering rosettes (realized heritability ± SE =–0.002 ± 0.013). Our study indicates a high heritability and potential for further evolution of the proportion of flowering rosettes in R. reptans , but not for its plasticity, which may have been fixed by past evolution at its current level. Moreover, our results demonstrate strong genetic correlations between allocation to sexual reproduction and other clonal life-history characteristics.     

Genetic isolation of fragmented populations is exacerbated by drift and selection

Reduced genetic variation at marker loci in small populations has been well documented, whereas the relationship between quantitative genetic variation and population size has attracted little empirical investigation. Here we demonstrate that both neutral and quantitative genetic variation are reduced in small populations of a fragmented plant metapopulation, and that both drift and selective change are enhanced in small populations. Measures of neutral genetic differentiation (F(ST)) and quantitative genetic differentiation (Q(ST)) in two traits were higher among small demes, and Q(ST) between small populations exceeded that expected from drift alone. This suggests that fragmented populations experience both enhanced genetic drift and divergent selection on phenotypic traits, and that drift affects variation in both neutral markers and quantitative traits. These results highlight the need to integrate natural selection into conservation genetic theory, and suggests that small populations may represent reservoirs of genetic variation adaptive within a wide range of environments.     

Clonal integration in Ranunculus reptans: by‐product or adaptation?

We studied fitness consequences of clonal integration in 27 genotypes of the stoloniferous herb Ranunculus reptans in a spatially heterogeneous light environment. We grew 216 pairs of connected ramets (eight per genotype) with mother ramets in light and daughter ramets in shade. In half of the pairs we severed the stolon connection between the two ramets at the beginning of the experiment. During the experiment, 52.7% of the ramet pairs with originally intact connection physically disintegrated. We detected significant variation among genotypes in this regard. Survival of planted ramets was 13.3% higher for originally connected pairs. Moreover, there was significant variation among genotypes in survival, in the difference in survival between plant parts developing from mother and daughter ramets, and in the effect of integration on this difference. In surviving plants connection between ramets decreased size differences between mother and daughter parts. Variation among genotypes was significant in growth and reproduction and marginally significant in the effect of physiological integration on growth and reproduction. Connected daughter ramets had longer leaves and internodes than daughters in severed pairs indicating that integration stimulated plant foraging in both the vertical and the horizontal plane. Observed effects of integration on fitness components in combination with genetic variation in maintenance and effects of connection indicate that clonal integration in R. reptans has the capability to evolve, and therefore suggest that clonal integration is adaptive. If genetic variation in integration is common, future studies on clonal integration should always use defined genetic material and many clones to allow extrapolation of results to population and wider levels.     

Wise flies: a pre‐dispersal seed predator prefers hermaphrodites over females in the gynodioecious Polemonium foliosissimum

1. Oviposition choices can profoundly affect offspring performance. Oviposition decisions of the dipteran pre‐dispersal seed predator, Hylemya sp. (Diptera: Anthomyiidae), when choosing among sex morphs of their host‐plant—Polemonium foliosissimum Hook—were evaluated. Polemonium foliosissimum is gynodioecious, with female and hermaphrodite sex morphs that differ in flower size. 2. It was asked: Do female flies preferentially oviposit on hermaphrodite plants and, if so, are oviposition choices correlated with flower size? Is larval survivorship higher on hermaphrodite plants and, if so, is larval success correlated with flower size? Can the differences in oviposition and/or larval success be explained by slight differences in flowering phenology between the sexes? 3. Hermaphrodite flowers received 45% more Hylemya eggs than females. Although hermaphrodites had larger petals and sepals than females, egg loads were not correlated with petal or sepal size. Larval survival was 30% greater on hermaphrodites than females and higher on plants with larger sepals. However, the difference in sepal area between genders did not fully explain larval survival differences. Egg numbers declined over weeks, but differences in egg loads between the sex morphs were not attributable to a slight phenological delay of females. Larval survival declined over the season; however, larval survival differences between sex morphs were consistent. 4. Hylemya preferentially oviposited on hermaphrodites where their larvae had a significantly greater survival rate compared with females. The present results add to the knowledge that intra‐specific choices have consequences for phytophagous insects and that the relationship between antagonists and their gynodioecious host plants is complex.     

Pigment apparatus in <Emphasis Type="Italic">Ajuga reptans</Emphasis> plants as affected by adaptation to light growth conditions

Mechanisms of adaptation of the photosynthetic apparatus at the level of pigment complex in a shade-tolerant bugle plant (Ajuga reptans L.) grown at full solar irradiation in an open plot were studied. In “sun” plants, the content of photosynthetic pigments decreased markedly as compared to “shade” plants grown under a forest canopy at 5–10% of the full solar irradiation. In leaves of sun plants, the portion of β-carotene and lutein in the carotenoid spectrum was higher than in shade plant leaves, antheraxanthin and zeaxanthin were present, and de-epoxidation of violaxanthin was by an order of magnitude higher in sun plant leaves reaching 40%. The data obtained indicate the role of the violaxanthin cycle in the protection of photosynthetic apparatus in a shade-tolerant plant against destruction under excessive irradiation.     

DOWN THE TUBE: POLLINATORS, PREDATORS, AND THE EVOLUTION OF FLOWER SHAPE IN THE ALPINE SKYPILOT, POLEMONIUM VISCOSUM

Abstract We address how a conflict between pollinator attraction and avoidance of flower predation influences the evolution of flower shape in Polemonium viscosum. Flower shape in P. viscosum is the product of an isometric relationship between genetically correlated (r_A= 0.70) corolla flare and length. Bumblebee pollinators preferentially visit flowers that are more flared and have longer tubes, selecting for a funnel‐shaped corolla. However, flower shape also influences nectar‐foraging ants that sever the style at its point of attachment to the ovary. Surveys of ant damage show that plants having flowers with flared, short corollas are most vulnerable to ant predation. Consistent with this result, the ratio of corolla length to flare is significantly greater in a krummholz (high predation risk) population than in a tundra (low predation risk) population. To explicitly test whether the evolution of a better defended flower would exact a cost in pollination, we created tubular flowers by constricting the corolla during development. Performance of tubular flowers and natural controls was compared for defensive and attractive functions. In choice trials, ants entered control flowers significantly more often than tubular ones, confirming that the evolution of tubular flowers would reduce the risk of predation. However, in a bumblebee‐pollinated population, tubular flowers received significantly less pollen and set fewer seeds than controls. A fitness model incorporating these data predicts that in the absence of the genetic correlation between corolla length and flare, intermittent selection for defense could allow tubular flowers to spread in the krummholz population. However, in the tundra, where bumblebees account for nearly all pollination, the model predicts that tubular flowers should always confer a fitness disadvantage.     

资源异质性环境中三种匍匐茎草本植物克隆内资源共享和分株功能特化

研究了3种来自中国北方林下、草地和碱化草甸匍匐茎型克隆草本植物绢毛匍匐委陵菜 (Potentilla reptans L. var. sericophylla Franch.)、鹅绒委陵菜 (P. anserina L.) 和金戴戴 (Halerpestes ruthenica (Jacq.) Qvcz.) 对由高光照低养分斑块和低光照高养分斑块组成的资源交互斑块性生境的适应性对策.当生长于高光照低养分条件下分株 (HL分株) 与生长于低光照高养分条件下分株 (LH分株) 之间的匍匐茎连接时, 3种克隆植物HL分株、LH分株以及整个分株对系统 (HL分株 + LH分株) 的生物量均得到显著提高.同时, LH分株根冠比显著增加, 而HL分株根冠比显著下降.这表明, 当互连分株置于由低光照高养分斑块和高光照低养分斑块组成的异质性环境中时, 3种植物克隆分株均发生了环境诱导的功能特化.克隆内资源共享以及克隆内不同分株的功能特化有利于整个分株系统对局部丰富资源的获取, 从而能够缓解资源交互斑块性生境对克隆植物的不利影响.