Latitudinal variation in suppression of flower bud formation at high temperature in four native dandelions (Taraxacum spp.) with different distributions and genetic structures in Japan

The control of the response of flowering to temperature plays a key role in successful range‐expansion of plants. A previous study showed that the suppression of flower‐bud formation at high temperature in Taraxacum officinale decreases genetically with latitude from north to south in Japan. The present study investigated whether similar trait variation occurs among populations of native Taraxacum species in Japan. Seedlings of T. albidum (a low‐ and mid‐latitude allopolyploid), T. japonicum (a mid‐latitude diploid) and T. venustum (a high‐latitude autopolyploid) were grown at three temperatures. Time to flower‐bud appearance increased with temperature in T. japonicum and T. venustum, but did not increase in T. albidum. Time to flower‐bud appearance did not differ significantly among the three species at 14°C, but it was shorter in T. albidum than in the other two species at 19°C and 24°C. The early appearance of buds of T. albidum was confirmed by another experiment in which plants of 18 populations from the three species and T. platycarpum (a mid‐latitude diploid) grown at 19°C were used. The results clearly indicate that high‐temperature suppression of flower‐bud formation was lower in low‐latitude species than in high‐latitude species. This interspecific variation is analogous to the intraspecific variation in T. officinale. Time to bud appearance of five populations in T. albidum was homogeneous within and between the populations. The results suggest that the five populations are monoclonal and lack the sensitivity of suppression of flower‐bud formation to high temperature.     

Latitudinal variation in seed weight and flower number in Prunella vulgaris

Studies of seed-weight variation across altitudinal and latitudinal gradients have led to conflicting hypotheses regarding the selective value of this traint in relation to the length of the growing season. Growing-season length may also influence the evolution of seed number, and population differentiation in seed weight may be constrained by a negative genetic correlation between seed weight and seed number within populations. We examined variation in seed weight and an estimate of seed number (flower number) and the covariance of these traits among populations of Prunella vulgaris at five latitudes between northern Michigan and South Carolina. We measured seed weight and flower number in native habitats and in a common environment to determine the extent to which patterns observed in the field reflect genetic differentiation. We observed no genetically based variation in seed weight across the latitudinal gradient, although genetic variation among populations within a latitude was observed. In contrast to the lack of variation in seed weight, flower number increased clinally from northern Michigan to Tennessee in a common environment. Population mean flowering date in a common environment was successively later from north to south. Later-flowering individuals appear to achieve a larger size before flowering and consequently possess more resources for seed production. This difference may account for the greater flower production of late-flowering, southern populations. Independence of population mean seed weight and flower number across the latitudinal gradient suggests that population differentiation in seed weight has not been constrained by a trade-off between seed size and number within populations.     

Natural phenological variation in aspen (Populus tremula): the SwAsp collection

The genus Populus is currently the main model system for genetic, genomic, and physiological research in trees. Phenotypic variation in aspen (Populus tremula) populations growing in different environments across Sweden is expected to reflect genetic variation that is important for local adaptation. To analyze such natural phenotypic and genetic variation, the Swedish Aspen (SwAsp) Collection was established. Trees were taken from 12 different populations across Sweden, from 56° to 66° latitude north and planted in two common gardens in Ekebo (55.9°N) and Sävar (63.4°N). Data related to phenological and growth traits were collected during the second year of growth. Some traits like the date of bud set and leaf area duration showed strong clinal variation patterns with latitude in both field trials, but the date of bud flush did not change along a latitudinal cline. The phenological traits showed moderate within-populations heritabilities, although growth traits showed weaker clinal patterns and lower heritabilities than the phenological traits. This research forms the starting point for the development of the SwAsp collection, a resource facilitating analysis of the natural genetic variation in aspen, the elucidation of the structure and dynamics of aspen populations, and the future identification of the genes controlling adaptive traits using association mapping of selected candidate genes.     

Latitudinal trait variation and responses to drought in Arabidopsis lyrata

Species may respond in three ways to environmental change: adapt, migrate, or go extinct. Studies of latitudinal clines can provide information on whether species have adapted to abiotic stress such as temperature and drought in the past and what the traits underlying adaptation are. We investigated latitudinal trait variation and response to drought in North American populations of Arabidopsis lyrata. Plants from nine populations collected over 13° latitude were grown under well-watered and dry conditions. A total of 1,620 seedlings were raised and 12 phenological, physiological, morphological, and life history traits were measured. Two traits, asymptotic rosette size and the propensity to flower, were significantly associated with latitude: plants from northern locations grew to a larger size and were more likely to flower in the first season. Most traits displayed a plastic response to drought, but plasticity was never related linearly with latitude nor was it enhanced in populations from extreme latitudes with reduced water availability. Populations responded to drought by adopting mixed strategies of resistance, tolerance, and escape. The study shows that latitudinal adaptation in A. lyrata involves the classic life history traits, size at and timing of reproduction. Contrary to recent theoretical predictions, adaptation to margins is based on fixed trait differences and not on phenotypic plasticity, at least with respect to drought.     

Latitudinal population differentiation in phenology,life history and flower morphology in the perennial herb Lythrum salicaria

Abstract In plants with a wide distribution, phenological characters can be expected to vary clinally along climatic gradients, whereas other characters important for adaptation to local biotic and abiotic factors may vary in a more mosaic fashion. We used common‐garden experiments and controlled crosses to examine population differentiation in phenology, life history and morphology in the perennial herb Lythrum salicaria along a latitudinal transect through Sweden (57°N to 66°N). Northern populations initiated growth and flowering earlier, flowered for a shorter period, were shorter, produced more and larger winter buds, and were older at first reproduction than southern populations. Flower morphology varied significantly among populations, but was, with the exception of calyx length, not significantly related to latitude of origin. Survival in the common garden (at 63°49′N) was positively correlated with latitude of origin and the size and number of winter buds produced in the preceding year. The results suggest that the among‐population differences in phenology and life history have evolved in response to latitudinal variation in length of the growing season. Further studies are required to determine whether population differentiation in flower morphology is maintained by selection.     

Low temperature influence on flowering in Citrus. The separation of inductive and bud dormancy releasing effects

The flowering response of Owari Satsuma mandarin ( Citrus unshiu Marc) to low temperature treatments has been determined using potted trees and in vitro bud cultures. In potted trees the chilling treatments released bud dormancy and enhanced both sprouting and flowering, but these two responses could not be separated. However, bud cultures showed no dormancy, and a specific effect of low temperature on flower induction was demonstrated. Low temperature appears to have a dual effect, releasing bud dormancy and inducing flowering. Potential flower buds have a deeper dormancy than vegetative buds, and the first stages of flower initiation seem to occur before the winter rest period.     

Correlation between time of flowering and phenotypic plasticity in Arabidopsis thaliana (Brassicaceae)

We observed substantial variation in the time of flowering among 13 populations of Arabidopsis thaliana (Brassicaceae) from an extensive latitudinal range when grown under uniform experimental conditions. The later the onset of flowering, the greater was potential reproduction. Later flowering plants also had greater plasticity in a host of morphological and physiological traits measured in nutrient-rich vs. nutrient-poor test environments. This relationship between flowering time and overall plasticity was only apparent for traits measured at the time of seed production, not at the time of flowering or earlier. At the time of seed production in this short-lived annual, the regression of a multivariate measure of overall plasticity on the time of flowering was linear and highly significant (r² = 0.90, P < 0.0001). These correlations among time of flowering, reproductive fitness, and plasticity support the idea that selection for late-flowering genotypes would select concomitantly for greater plasticity.     

Seed dormancy varies widely among Arabidopsis thaliana populations both between and within Fennoscandia and Italy

The timing of germination is a key life‐history trait in plants, which is strongly affected by the strength of seed dormancy. Continental‐wide genetic variation in seed dormancy has been related to differences in climate and the timing of conditions suitable for seedling establishment. However, for predictions of adaptive potential and consequences of climatic change, information is needed regarding the extent to which seed dormancy varies within climatic regions and the factors driving such variation.We quantified dormancy of seeds produced by 17 Italian and 28 Fennoscandian populations of Arabidopsis thaliana when grown in the greenhouse and at two field sites in Italy and Sweden. To identify possible drivers of among‐population variation in seed dormancy, we examined the relationship between seed dormancy and climate at the site of population origin, and between seed dormancy and flowering time.Seed dormancy was on average stronger in the Italian compared to the Fennoscandian populations, but also varied widely within both regions. Estimates of seed dormancy in the three maternal environments were positively correlated. Among Fennoscandian populations, seed dormancy tended to increase with increasing summer temperature and decreasing precipitation at the site of population origin. In the smaller sample of Italian populations, no significant association was detected between mean seed dormancy and climate at the site of origin. The correlation between population mean seed dormancy and flowering time was weak and not statistically significant within regions.The correlation between seed dormancy and climatic factors in Fennoscandia suggests that at least some of the among‐population variation is adaptive and that climate change will affect selection on this trait. The weak correlation between population mean seed dormancy and flowering time indicates that the two traits can evolve independently.     

Clinal variation in phyB2, a candidate gene for day-length-induced growth cessation and bud set, across a latitudinal gradient in European aspen (Populus tremula)

The initiation of growth cessation and dormancy represents a critical ecological and evolutionary trade-off between survival and growth in most forest trees. The most important environmental cue regulating the initiation of dormancy is a shortening of the photoperiod and phytochrome genes have been implicated in short-day-induced bud set and growth cessation in Populus. We characterized patterns of DNA sequence variation at the putative candidate gene phyB2 in 4 populations of European aspen (Populus tremula) and scored single-nucleotide polymorphisms in an additional 12 populations collected along a latitudinal gradient in Sweden. We also measured bud set from a subset of these trees in a growth chamber experiment. Buds set showed significant clinal variation with latitude, explaining approximately 90% of the population variation in bud set. A sliding-window scan of phyB2 identified six putative regions with enhanced population differentiation and four SNPs showed significant clinal variation. The clinal variation at individual SNPs is suggestive of an adaptive response in phyB2 to local photoperiodic conditions. Three of four SNPs showing clinal variation were located in regions with excessive genetic differentiation, demonstrating that searching for regions of high genetic differentiation can be useful for identifying sites putatively involved in local adaptation.     

Evidence of genetic change in the flowering phenology of sea beets along a latitudinal cline within two decades

Sea beets grown from seeds collected in 1989 and 2009 along the coasts of France and adjacent regions were compared for flowering date under controlled conditions. Seeds from both collection years were sown simultaneously and cultivated under the same glasshouse conditions. Date of flowering onset and year of first flowering were recorded. There was an overall northward shift in flowering time of about 0.35° latitude (i.e. 39 km) over the 20‐year period. The southern portion of the latitudinal gradient – that is, from 44.7°N to 47.28°N – flowered significantly later by a mean of 1.78 days, equivalent to a 43.2‐km northward shift of phenotypes. In the northern latitudes between 48.6°N and 52°N, flowering date was significantly earlier by a mean of 4.04 days, corresponding to a mean northward shift of 104.9 km, and this shift was apparently due to a diminished requirement of exposure to cold temperatures (i.e. vernalization), for which we found direct and indirect evidence. As all plants were grown from seed under identical conditions, we conclude that genetic changes occurred in the sensitivity to environmental cues that mediate the onset of flowering in both the northern and the southern latitudes of the gradient. Microevolution and gene flow may have contributed to this change. There was no significant change in the frequency of plants that flowered without vernalization. The lack of vernalization requirement may be associated with environmental instability rather than with climate conditions.     

Highly variable flowering time in Orchis ustulata (Orchidaceae): consequences for population dynamics

Two subspecies of Orchis ustulata differ considerably in their flowering time, but in only a few morphometric parameters; this makes the rank of these taxa problematic. The flowering time was not affected by replanting individuals to another habitat, including to the habitat of the other subspecies. In this study, populations from both subspecies were studied, measuring 464 marked genets during 5–6 years. Populations with different flowering times exhibited notable differences in their local distribution areas and the mean height of specimens. In the late-flowering populations the proportion of dormant plants is higher and the proportion of vegetatively propagated shoots lower than in the early-flowering ones. Going to (or staying) dormant is the biggest possibility in all stage groups. Flowering is more likely to be followed by dormancy than vegetative stage, but setting fruit does not affect the possibility. Vegetative propagation may play an important role in keeping the populations viable. Vegetative growth is more pronounced on stony soils.     

A resurrection study reveals limited evolution of phenology in response to recent climate change across the geographic range of the scarlet monkeyflower

Premise of the studyAs global climate change alters drought regimes, rapid evolution of traits that facilitate adaptation to drought can rescue populations in decline. The evolution of phenological advancement can allow plant populations to escape drought, but evolutionary responses in phenology can vary across a species'' range due to differences in drought intensity and standing genetic variation.Methods Mimulus cardinalis, a perennial herb spanning a broad climatic gradient, recently experienced a period of record drought. Here, we used a resurrection study comparing flowering time and stem height at first flower of pre‐drought ancestors and post‐drought descendants from northern‐edge, central, and southern‐edge populations in a common environment to examine the evolution of drought escape across the latitudinal range.Key resultsContrary to the hypothesis of the evolution of advanced phenology in response to recent drought, flowering time did not advance between ancestors and descendants in any population, though storage condition and maternal effects could have impacted these results. Stem height was positively correlated with flowering time, such that plants that flowered earlier were shorter at first flower. This correlation could constrain the evolution of earlier flowering time if selection favors flowering early at a large size.ConclusionsThese findings suggest that rapid evolution of phenology will not rescue these populations from recent climate change. Future work is needed to examine the potential for the evolution of alternative drought strategies and phenotypic plasticity to buffer M. cardinalis populations from changing climate.     

Somatic and demographic costs under different temperature regimes in the late-flowering alpine perennial herb Saxifraga stellaris (Saxifragaceae)

If reproduction involves costs, preventing reproduction one year should result in increased growth and/or reproduction the next year. Costs of reproduction in the late-flowering perennial alpine herb Saxifraga stellaris were studied in an experimental field study. To determine whether cost of reproduction differed between two contrasting temperature regimes, I examined plants in Open Top Chambers (OTCs) and control plots. One year before measurements all flower buds on the experiment plants were removed. There was no impact of the flower bud removal or the interaction between flower removal and temperature on prefloration time or seed maturation time. However, cost of reproduction influenced growth (somatic cost), vegetative propagation, flowering frequency, number of stem per ramet, number of fruits, and seed mass (demographic cost). However, significant interaction effects of flower removal and temperature on growth and fruit production revealed that the cost of reproduction differed between the two temperature regimes. The warmed plants showed reduced cost of reproduction compared to plants growing under natural temperature.     

植物开花时间: 自然变异与遗传分化

开花时间是植物的重要生活史性状。对模式植物的研究表明: 从感受内外环境信号开始到最终分化形成功能性花器官的过程涉及复杂的信号转导途径和调控网络; 开花时间受多种因子的调控, 而FT基因作为整合途径成分起到非常关键的作用。植物的花期变异在物种、群体和个体水平上具有复杂的自然变异模式, 且不同植物的花期变异随全球环境变化而具有不同的变异趋势。植物个体之间通过传粉进行的基因交流需要功能性开花时间的一致或重叠, 而花期变异会导致群体之间或群体内部亚群体之间的基因流障碍和遗传分化, 并可能导致邻域或同域的物种形成。该文分析了植物花期变异与群体遗传分化的关系, 认为决定开花时间的基因在物种分化中可能起到关键的作用, 而对开花时间自然变异模式的研究对于揭示晚近分化快速辐射物种的进化模式具有重要意义。     

The effect of LAB 173711 and ethephon on time of flowering and cold hardiness of peach flower buds

Peach flowers are often killed during bloom by spring frosts. LAB 173711, a compound with abscisic (ABA)-like activity, and ethephon delayed flowering in peach trees. In greenhouse experiments, LAB 173711, at concentrations of 10^?3–10^?2 M, was most effective in delaying bloom when applied after a 5°C cold storage period, rather than before the dormancy breaking treatment. In contrast, ethephon delayed bloom most effectively when applied before 5°C cold storage; ethephon caused flower bud abscission when treatments were made after the chilling requirement had been satisfied. In field experiments, ethephon delayed flowering by 6–7 days, which reduced bud injury after a spring frost during bloom. No flower bud injury was found on ethephon-treated trees after temperatures of ?4.3°C; whereas without ethephon 25% of the flower buds were frost damaged. LAB 173711 delayed the time to 50% bloom by 2–3 days. However, this was not long enough to avoid low-temperature injury to the flower buds.     

The Cold Awakening of <Emphasis Type="Italic">Doritaenopsis</Emphasis> ‘Tinny Tender’ Orchid Flowers: The Role of Leaves in Cold-induced Bud Dormancy Release

Massive flowering of tropical Phalaenopsis orchids is coordinated by the cold-induced release of reproductive bud dormancy. Light and temperature are the two key factors integrated by the dormancy mechanism to both stop and reactivate the meristem development of many other angiosperm species, including fruit trees and ornamental plants. It is well established that leaves and roots play a major role in inducing flower development; however, currently, knowledge of molecular events associated with reproductive bud dormancy release in organs other than the bud is limited. Using differential gene expression, we have shown that the leaves of a hybrid of Phalaenopsis species, Doritaenopsis ‘Tinny Tender’, undergo major metabolic modifications. These changes result in the production of sucrose and amino acids, both of which can sustain bud outgrowth, and auxin and ethylene, which may play important roles in awaking the dormant buds. Intake of abscisic acid and synthesis of the hormone jasmonate may also explain the inhibition of vegetative growth that coincides with bud growth. Interestingly, many genes that were upregulated by cold treatment are homologous for genes involved in flower induction and vernalization in Arabidopsis, indicating that processes regulating flowering induction and those regulating reproductive bud dormancy release may use similar pathways and effector molecules.     

Genetic differentiation of high-temperature tolerance in the kelp Undaria pinnatifida sporophytes from geographically separated populations along the Pacific coast of Japan

The kelp Undaria pinnatifida has a widespread latitudinal range in Japan, with populations exposed to very different temperature regimes. To test the hypothesis that U. pinnatifida exhibits genetic differentiation in its temperature response, juvenile sporophytes from a warmer location (Naruto, southern Japan) and two colder locations (Okirai Bay and Matsushima Bay, northern Japan) were collected and transplanted to long lines, cultivated under the environmental conditions in Matsushima Bay. These plants were bred using successive self-crossing methods for three generations and the characteristics of photosynthesis, growth, survival, and nitrogen contents of the third-generation juvenile sporophytes (2–3 cm) then were measured and compared. The plants from Naruto showed significantly higher photosynthetic activities and respiration than those from the northern populations at warmer temperatures of 20–35°C. The juvenile sporophytes from all three locations had similar growth rates below 18°C, but significant differences were observed at 18–24°C. The optimum temperatures for growth were 14–16°C in plants that originated from Okirai Bay and Matsushima Bay and 18°C in plants that originated from Naruto. These results reflected the differences in latitude. Dead plants were observed at high temperatures of 22 and 24°C in the northern population plants, whereas no plants from Naruto died. Juvenile sporophytes from Naruto exhibited the greatest capacity to accumulate high nitrogen reserves. These results suggest that the differences in high-temperature tolerance in juvenile U. pinnatifida sporophytes from geographically separated populations are due to genetic differentiation rather than phenotypic plasticity.     

Seasonal change in a pollinator community and the maintenance of style length variation in Mertensia fusiformis (Boraginaceae)

Background and Aims

In sub-alpine habitats, patchiness in snowpack produces marked, small-scale variation in flowering phenology. Plants in early- and late-melting patches are therefore likely to experience very different conditions during their flowering periods. Mertensia fusiformis is an early-flowering perennial that varies conspicuously in style length within and among populations. The hypothesis that style length represents an adaptation to local flowering time was tested. Specifically, it was hypothesized that lower air temperatures and higher frost risk would favour short-styled plants (with stigmas more shielded by corollas) in early-flowering patches, but that the pollen-collecting behaviour of flower visitors in late-flowering patches would favour long-styled plants.

Methods

Floral morphology was measured, temperatures were monitored and pollinators were observed in several matched pairs of early and late populations. To evaluate effects of cold temperatures on plants of different style lengths, experimental pollinations were conducted during mornings (warm) and evenings (cool), and on flowers that either had or had not experienced a prior frost. The effectiveness of different pollinators was quantified as seed set following single visits to plants with relatively short or long styles.

Key Results

Late-flowering populations experienced warmer temperatures than early-flowering populations and a different suite of pollinators. Nectar-foraging bumble-bee queens and male solitary bees predominated in early populations, whereas pollen-collecting female solitary bees were more numerous in later sites. Pollinators differed significantly in their abilities to transfer pollen to stigmas at different heights, in accordance with our prediction. However, temperature and frost sensitivity did not differ between long- and short-styled plants. Although plants in late-flowering patches tended to have longer styles than those in early patches, this difference was not consistent.

Conclusions

Seasonal change in pollinator-mediated selection on style length may help maintain variation in this trait in M. fusiformis, but adaptation to local flowering time is not apparent. The prevalence of short styles in these populations requires further explanation.