Flowering phenology and compensation for herbivory in<Emphasis Type="Italic"> Ipomopsis aggregata</Emphasis>

The mechanisms and circumstances that affect a plant's ability to tolerate herbivory are subjects of ongoing interest and investigation. Phenological differences, and the timing of flowering with respect to pollinators and pre-dispersal seed predators, may provide one mechanism underlying variable responses of plants to herbivore damage. The subalpine wildflower, Ipomopsis aggregata, grows across a wide range of elevations and, because phenology varies with elevation, phenological delays associated with elevation may affect the ability of I. aggregata to compensate for or tolerate browsing. Thus, we examined the response of I. aggregata to herbivory across an elevation gradient and addressed the interactions among phenological delays imposed by damage, elevation, pre-dispersal seed predation and pollination, on I. aggregata's compensatory response. Among high and low elevation populations in areas near the Rocky Mountain Biological Laboratory (RMBL) in Gothic, Colorado, we compared the responses of naturally browsed, artificially browsed (clipped), and unbrowsed (control) plants of I. aggregata. We compared responses in the date of initiation of flowering, timing of peak bloom, floral display, nectar production and sugar concentration, oviposition and fruit destruction by the pre-dispersal seed predator Hylemya sp. (Anthomyiidae), fruit production, and aboveground biomass production. Clipping had the greatest effect on reproductive success and clipped plants at high elevation exhibited the lowest tolerance for herbivory. The effects of browsing appear to be mediated by flowering phenology, and both browsing and elevation delayed flowering phenology. Time needed for regrowth delays flowering, and thus affects the overlap with seed predators and pollinators. As a result of delayed flowering, naturally browsed and clipped plants incurred lower rates of seed predation. In the absence of seed predation, plants would exhibit a lower tolerance to herbivory since naturally and artificially browsed plants had fewer fruits destroyed by Hylemya larvae. We provide additional evidence that, for populations near the RMBL, clipping and natural browsing do not have the same effect on I. aggregata plants. This may be due to the selection of larger plants by herbivores. Although under some conditions plants may tolerate browsing, in areas where the growing season is short a phenological delay imposed by damage is likely to significantly reduce plant fitness. Identifying the mechanisms that allow plants to tolerate herbivore damage will help to develop a general framework for understanding the role of tolerance in plant population and community dynamics, as well as plant-herbivore interactions.     

Environmental context determines within- and potential between-generation consequences of herbivory

Plant tolerance to herbivory may depend on local environmental conditions. Models predict both increased and decreased tolerance with increasing resources. Transgenerational effects of herbivory may result in cross-generation tolerance. We evaluated within- and potential between-generation consequences of deer browsing in light-gap and understory habitats in the forest-edge herb, Campanulastrum americanum. Plants were assigned to deer-browsed, simulated-herbivory, and control (undamaged) treatments in the two light environments. In light gaps, plants were eaten earlier, more frequently, and had less vegetative recovery relative to uneaten plants than in the understory. As a result, browsed light-gap plants had a greater reduction in flowers and fruit than understory plants. This reduced tolerance was in part because deer browsing damaged plants in light gaps more than those in the understory. However, in the simulated herbivory treatment, where damage levels were similar between light habitats, plants growing in high-resource light gaps also had reduced tolerance of herbivory relative to those in the forest understory. C. americanum’s reproductive phenology was delayed by reduced light and the loss of the apical meristem. As a result, deer-browsed plants in the light gap flowered slightly later than uneaten plants in the understory. C. americanum has a polymorphic life history and maternal flowering time influences the frequency of annual and biennial offspring. The later flowering of deer-browsed plants in light gaps will likely result in a reduced frequency of high-fitness annual offspring and an increase in lower fitness biennial offspring. Therefore, additional between-generation costs of herbivory are expected relative to those predicted by fruit number alone.     

The evolution of compensation to herbivory in scarlet gilia, Ipomopsis aggregata: herbivore-imposed natural selection and the quantitative genetics of tolerance

Tolerance is the ability of plants to maintain fitness after experiencing herbivore damage. We investigated scarlet gilia tolerance to browsing in the framework of phenotypic plasticity using both an operational and candidate trait approach. Individuals from full-sib families were split into an artificial clipping treatment, a natural-damage treatment, or left as controls. We tested for genetic variation in tolerance by evaluating family x herbivory treatment interactions on fitness in a mixed model analysis of variance. In addition, we used selection analyses to assess the function of flowering phenology and compensatory regrowth (via branch production) as candidate tolerance traits. We found a strong detrimental fitness effect of browsing and considerable variation among sire half-sib families in levels of tolerance (25% to 63% of the fitness of controls). There was no evidence of overcompensation at either the population or family level and no additive genetic variation in operationally defined tolerance. Phenotypic selection analyses provide evidence that early flowering and compensatory regrowth function as tolerance characters. We found strong linear and correlational selection for early flowering and increased branch production for damaged plants and linear selection for apical dominance (reduced branchiness) and early flowering in control plants. Moreover, reduced phenological delay and increased plasticity in branch production were correlated with tolerance. We detected significant additive genetic variation in flowering phenology in both treatments and a positive genetic correlation between the phenology of control and damaged plants. We found significant additive genetic variation in branch production in undamaged and naturally damaged plants, but not in clipped plants. Damaged plants exhibited marginally significant additive genetic variance in fitness, although its heritability was very low (approximately 3.6%). We failed to find additive genetic variation in the fitness of control plants. Our results suggest that tolerance traits are under herbivore-imposed natural selection in this population, but that responses to selection are limited by available genetic variation and selective constraints.     

Assortative mating by flowering time and its effect on correlated traits in variable environments

Reproductive timing is a key life‐history trait that impacts the pool of available mates, the environment experienced during flowering, and the expression of other traits through genetic covariation. Selection on phenology, and its consequences on other life‐history traits, has considerable implications in the context of ongoing climate change and shifting growing seasons. To test this, we grew field‐collected seed from the wildflower Mimulus guttatus in a greenhouse to assess the standing genetic variation for flowering time and covariation with other traits. We then created full‐sib families through phenological assortative mating and grew offspring in three photoperiod treatments representing seasonal variation in daylength. We find substantial quantitative genetic variation for the onset of flowering time, which covaried with vegetative traits. The assortatively‐mated offspring varied in their critical photoperiod by over two hours, so that families differed in their probability of flowering across treatments Allocation to flowering and vegetative growth changed across the daylength treatments, with consistent direction and magnitude of covariation among flowering time and other traits. Our results suggest that future studies of flowering time evolution should consider the joint evolution of correlated traits and shifting seasonal selection to understand how environmental variation influences life histories.     

Microbial effects on plant phenology and fitness

Plant development and the timing of developmental events (phenology) are tightly coupled with plant fitness. A variety of internal and external factors determine the timing and fitness consequences of these life-history transitions. Microbes interact with plants throughout their life history and impact host phenology. This review summarizes current mechanistic and theoretical knowledge surrounding microbe-driven changes in plant phenology. Overall, there are examples of microbes impacting every phenological transition. While most studies have focused on flowering time, microbial effects remain important for host survival and fitness across all phenological phases. Microbe-mediated changes in nutrient acquisition and phytohormone signaling can release plants from stressful conditions and alter plant stress responses inducing shifts in developmental events. The frequency and direction of phenological effects appear to be partly determined by the lifestyle and the underlying nature of a plant–microbe interaction (i.e., mutualistic or pathogenic), in addition to the taxonomic group of the microbe (fungi vs. bacteria). Finally, we highlight biases, gaps in knowledge, and future directions. This biotic source of plasticity for plant adaptation will serve an important role in sustaining plant biodiversity and managing agriculture under the pressures of climate change.     

Effects of foliar herbivory by insects on the fitness of Raphanus raphanistrum: damage can increase male fitness

Generally, effects of herbivory on plant fitness have been measured in terms of female reproductive success (seed production). However, male plant fitness, defined as the number of seeds sired by pollen, contributes half of the genes to the next generation and is therefore crucial to the evolution of natural plant populations. This is the first study to examine effects of insect herbivory on both male and female plant reproductive success. Through controlled field and greenhouse experiments and genetic paternity analysis, we found that foliar damage by insects caused a range of responses by plants. In one environment, damaged plants had greater success as male parents than undamaged plants. Neither effects on pollen competitive ability nor pollinator visitation patterns could explain the greater siring success of these damaged plants. Success of damaged plants as male parents appeared to be due primarily to changes in allocation to flowers versus seeds after damage. Damaged plants produced more flowers early in the season, but not more seeds, than undamaged plants. Based on total seed production, male fitness measures from the first third of the season, and flower production, we estimated that damaged and undamaged plants had equal total reproductive success at the end of the season in this environment. In a second, richer environment, damaged and undamaged plants had equal male and female plant fitness, and no traits differed significantly between the treatments. Equal total reproductive success may not be ecologically or evolutionarily equivalent if it is achieved differentially through male versus female fitness. Genes from damaged plants dispersed through pollen may escape attack from herbivores, if such attack is correlated spatially from year to year.     

Density‐dependent demographic responses of a semelparous plant to natural variation in seed rain

The link between reproductive and vegetative ecology of flowering plants is rarely explored, despite its importance for understanding population processes and fitness. This link can be studied by using experimental or natural variation in seed input to the soil to assess how reproductive success affects vital rates of offspring. We previously reported for Ipomopsis aggregata that per‐seed probability of germinating is insensitive to density of seeds sown into plots, whereas per capita flower production among adults that grow from the seedlings declines in nonlinear fashion with density. Here we describe a parallel non‐experimental study. We related seedling emergence to estimated natural seed input (‘seed rain’) in three populations across ten summers and monitored seedlings that emerged in the first two summers throughout their life histories. Seedling emergence in 1996 was linearly related to seed rain from plants that flowered in 1995. This density independent seed‐to‐seedling transition recurred over the next nine summers, but the slope varied with springtime precipitation. Total numbers of 1996 seedlings that survived to flower and numbers of flowers they produced increased linearly with seed rain in one population, but did not vary detectably in the other two, consistent with negative density dependence. In consequence λ (the dominant eigenvalue of a population projection matrix) decreased from high values at low densities of seed rain to a relatively constant low value with greater seed rain. We also detected density dependence in the 1995 seedling cohort in survival and flower production. The similarity of results from natural and experimental studies supports a conclusion of nonlinear density dependence and shows that characterizing it requires the full life history. For this plant species and others, studies of pollination and fecundity alone may not suffice to draw conclusions about population change or fitness.     

Directional selection on initial flowering date in Phlox drummondii (Polemoniaceae)

The fitness effects due to initial flowering date in Phlox drummondii were determined for three populations in central Texas (USA) over 3 yr (1990-1992). Mean fitness (seed set) always decreased with the later initiation of flowering. The likelihood of a plant fruiting differed with flowering date in five of the six instances (population by year combinations). Though plants that initiated flowering later tended to have spent more time in the vegetative stage and tended to die later in the year than did earlier flowering plants, this was not sufficient to overcome the reproductive penalties of flowering late. Plants that initiated flowering later in the season spent less time in the adult phase and were smaller. The mean number of flowers, fruits, and seeds per flowering plant always decreased with later flowering. Fruit set was negatively correlated with flowering date in four of the six population by year combinations. Nonparametric fitness functions were used to summarize predicted fitness among different initial flowering dates for each population on a yearly basis. Predicted mean fitness always declined nonlinearly with later flowering; the earliest flowering plants always had the highest predicted fitness. These fitness functions describe directional selection for the early initiation of flowering.     

Scarlet gilia resistance to insect herbivory: the effects of early season browsing,plant apparency,and phytochemistry on patterns of seed fly attack

Pollen-limited plants are confronted with a difficult tradeoff because they must present showy floral displays to attract pollinators and yet must also minimize their apparency to herbivores. In these systems, traits that increase pollinator visitation may also increase herbivore oviposition and overall plant resistance may therefore be constrained to evolve largely as a correlated response to selection on plant apparency or vigor. We used a family-structured quantitative genetic experiment to evaluate the importance of ungulate browsing, flowering date and plant height (traits that are related to overall vigor), and variation in a putative phytochemical defense (cucurbitacin production) on patterns of seed fly attack in a scarlet gilia population. We found significant genetic variation in the amount of insect damage plants experience in the field, providing evidence that resistance may evolve. In addition, we found that browsing reduced seed fly attack and that oviposition is strongly related to plant size and flowering date; large, early flowering plants experience high attack. In addition, we found that high cucurbitacin production was correlated with low seed fly damage, although this effect was relatively weak.We found directional selection on final plant height and flowering date; tall, early flowering plants had the highest reproductive success. In addition, we found negative directional selection on cucurbitacin production, which may indicate a high cost of cucurbitacin or other functions of this phytochemical. Although seed fly herbivory arguably decreases plant fitness, we found an unexpected positive relationship between damage and fitness. A negative relationship between fitness and damage may be masked in this system through strong positive indirect correlations between patterns of damage and levels of pollinator visitation. Finally, we found significant genetic variation in flowering date, plant height, and cucurbitacin production. Resistance to seed flies may evolve in this population, but largely as a non-adaptive correlated response to selection on overall plant vigor. Phytochemicals may play a more important role in defense in years with high seed fly attack, or when pollen-limitation is less severe.Co-ordinating editor: J. Tuomi     

Tolerance to apical and foliar damage: costs and mechanisms in Raphanus raphanistrum

To study mechanisms underlying plant tolerance to herbivore damage, we used apical and foliar damage as experimental treatments to study whether there are similar tolerance mechanisms to different types of damage. We also studied whether tolerance to different types of damage are associated, and whether there is a cost involved in plant tolerance to different types of herbivore damage. Our greenhouse experiment involved 480 plants from 30 full-sib families of an annual weed Raphanus raphanistrum , wild radish, which were subjected to control and two different simulated herbivore damage treatments, apex removal and foliar damage of 30% of leaf area. Apical damage significantly decreased seed production, whereas foliar damage had no effect. There was a significant genetic variation for tolerance to foliar, but not apical damage. No costs were observed in terms of negative correlation between tolerance to either damage type and fitness of undamaged plants. Tolerances to apical and foliar damage were not significantly correlated with each other. We observed a larger number of significant associations between tolerance and reproductive traits than between tolerance and vegetative traits. Plant height and leaf size of damaged plants interacted in their association to tolerance to foliar damage. Inflorescence number and pollen quantity per flower of damaged plants were positively associated with tolerance to apical damage. In late-flowering genotypes, petal size of undamaged plants and pollen quantity of damaged plants were positively associated with tolerance to foliar damage. In summary, traits involved in floral display and male fitness were associated with plant tolerance to herbivore damage.     

Predicting patterns of mating and potential hybridization from pollinator behavior

Hybridization in flowering plants is determined in part by the rate at which animal pollinators move between species and by the effectiveness of such movements in transferring pollen. Pollinator behavior can also influence hybrid fitness by determining receipt and export of pollen. We incorporated information on pollinator effectiveness and visitation behavior into a simulation model that predicts pollen transfer between Ipomopsis aggregata, Ipomopsis tenuituba, and hybrids. These predictions were compared with estimates of pollen transfer derived from movement of fluorescent dyes in experimental plant arrays. Interspecific pollen transfer was relatively uncommon in these arrays, whereas transfer between hybrids and the parental species was at least as common as conspecific transfer. Backcrossing was asymmetrical; I. aggregata flowers frequently received mixed loads of hybrid and conspecific pollen. The simulation suggests that these patterns of pollen transfer are largely explained by the visitation sequences of hummingbird and insect pollinators, with little contribution from mechanical isolation. Pollen receipt by hybrids exceeded that of both parental species in a year when pollinators preferred to visit F(1) and F(2) hybrids and was intermediate in another year when they preferred to visit I. aggregata. This suggests that natural variation in pollination may produce spatiotemporal variation in hybridization and hybrid fitness.     

Interference among cotton neighbours after differential reproductive damage

In indeterminate plant species, the rate of vegetative growth usually declines during the stage of active reproductive growth. Fruit shedding, as induced by insect herbivores, could counteract this decline. Due to the relative increase in vegetative growth, plants that have suffered reproductive damage could be better able to intercept light and acquire soil resources than undamaged plants. If so, plants with damaged neighbours might grow less than their counterparts with smaller, undamaged neighbours. This hypothesis was tested in high- and low-density cotton crops subjected to three treatments: (i) undamaged controls; (ii) uniformly damaged, in which all plants were damaged; (iii) non-uniformly damaged, in which every second plant was damaged. Damaged plants had their flowerbuds and young fruits manually removed at 85 days after sowing to simulate shedding as induced by Helicoverpa spp. (Lepidoptera) and mirid bugs (Hemiptera). As expected, damaged plants had greater leaf area and more vegetative dry matter than undamaged ones. This was most pronounced at high plant density. Neighbour status did not affect vegetative growth but it had a substantial, asymmetric effect on the reproductive growth of target plants. Damaged targets recovered to the level of undamaged controls in terms of total fruit number but had a large reduction in the mass of mature fruit due to the limited time available for recovery. The effect of neighbour status, if any, on the production of mature fruit in damaged targets was overridden by the limit imposed to recovery by the duration of the growing season. In contrast, neighbour status affected the production of mature fruit of undamaged targets: undamaged targets with damaged neighbours had 34% (low density) and 56% (high density) less mature fruit mass than their counterparts with undamaged neighbours. This was because (i) reproductive allocation and (ii) the proportion of total fruit that reached maturity in target plants declined with increasing neighbour interference. Most studies dealing with changes in competitive relationships among plants subjected to differential herbivory have shown how undamaged plants may benefit from herbivores that feed on their neighbours. This study shows that differential reproductive damage can cause the opposite effect, as undamaged plants may have a significant reduction in productivity due to the influence of neighbours whose vegetative growth was stimulated by the loss of reproductive organs. Received: 2 June 1996 / Accepted: 8 September 1996     

Selection on QTL and complex traits in complex environments

Understanding genetic variation for complex traits in heterogeneous environments is a fundamental problem in biology. In this issue of Molecular Ecology, Fournier‐Level et al. ( 2013 ) analyse quantitative trait loci (QTL) influencing ecologically important phenotypes in mapping populations of Arabidopsis thaliana grown in four habitats across its native European range. They used causal modelling to quantify the selective consequences of life history and morphological traits and QTL on components of fitness. They found phenology QTL colocalizing with known flowering time genes as well as novel loci. Most QTL influenced fitness via life history and size traits, rather than QTL having direct effects on fitness. Comparison of phenotypes among environments found no evidence for genetic trade‐offs for phenology or growth traits, but genetic trade‐offs for fitness resulted because flowering time had opposite fitness effects in different environments. These changes in QTL effects and selective consequences may maintain genetic variation among populations.     

Elevated carbon dioxide concentrations indirectly affect plant fitness by altering plant tolerance to herbivory

Global environmental changes, such as rising atmospheric CO₂ concentrations, have a wide range of direct effects on plant physiology, growth, and fecundity. These environmental changes also can affect plants indirectly by altering interactions with other species. Therefore, the effects of global changes on a particular species may depend on the presence and abundance of other community members. We experimentally manipulated atmospheric CO₂ concentration and amounts of herbivore damage (natural insect folivory and clipping to simulate browsing) to examine: (1) how herbivores mediate the effects of elevated CO₂ (eCO₂) on the growth and fitness of Arabidopsis thaliana; and (2) how predicted changes in CO₂ concentration affect plant resistance to herbivores, which influences the amount of damage plants receive, and plant tolerance of herbivory, or the fitness consequences of damage. We found no evidence that CO₂ altered resistance, but plants grown in eCO₂ were less tolerant of herbivory—clipping reduced aboveground biomass and fruit production by 13 and 22%, respectively, when plants were reared under eCO₂, but plants fully compensated for clipping in ambient CO₂ (aCO₂) environments. Costs of tolerance in the form of reduced fitness of undamaged plants were detected in eCO₂ but not aCO₂ environments. Increased costs could reduce selection on tolerance in eCO₂ environments, potentially resulting in even larger fitness effects of clipping in predicted future eCO₂ conditions. Thus, environmental perturbations can indirectly affect both the ecology and evolution of plant populations by altering both the intensity of species interactions as well as the fitness consequences of those interactions.     

Leaf damage by herbivores affects attractiveness to pollinators in wild radish, Raphanus raphanistrum

 We carried out two experiments to determine the effect of leaf damage on plant attractiveness to pollinators using wild radish, Raphanus raphanistrum (Brassicaceae), a self-incompatible annual herb. Pairs of plants from 36 full-sib families were grown in pots in the greenhouse. One member of each pair was damaged by Pieris rapae larvae that were allowed to remove half of the leaf area of each of the first four rosette leaves. The plants were subsequently taken out for pollinator observations once a week from the beginning of flowering in late June until the end of August. We conducted two experiments to examine how foliar damage affected visitation by pollinators. In the first experiment, numbers of pollinators visiting plants were compared between damaged and control sibling plants. In the second experiment, the number of open flowers during observations was controlled to be the same for both damaged and undamaged sibs. Damage significantly decreased the number and size of flowers during the first observations in late June. Damaged plants received fewer visits by native bees during the first week of observations. Since damage did not affect native bee visits when the number of open flowers was equalized between treatments, flower number was probably the main cue attracting native bees to plants. In the experiment without flower number control, syrphid flies, the other abundant pollinator taxon, spent more time per flower on the undamaged than on the damaged plants. When flower number was controlled, flies probed significantly more flowers during each visit on the undamaged than on the damaged plants and had higher visitation rates to undamaged plants early in the season. Since syrphid flies preferred undamaged plants both with and without flower number control, they apparently used cues apart from flower number for visitation. The difference between undamaged and damaged plants in floral characteristics and pollinator visitation vanished within a few weeks after the start of flowering. This result suggests that early damage may not have a strong fitness effect through reduction in mating success. However, poor weather conditions can cause early mortality of plants in the field, and nutrient depletion and competition decrease fruit set of later flowers. Therefore, conditions exist under which visitation to early flowers may affect plant fitness. Received: 30 July 1996 / Accepted: 10 February 1997     

Life history strategy in herbaceous perennials: inferring demographic patterns from the aboveground dynamics of a primarily subterranean,myco‐heterotrophic orchid

Myco‐heterotrophs are non‐photosynthetic plants that parasitize mycorrhizal fungi for their nutritional requirements, especially carbon. Because green plants sprout both to photosynthesize and to reproduce, the lack of photosynthesis in myco‐heterotrophs suggests that these plants need only to sprout to reproduce. Further, they may be long‐lived, with fitness favoring high, stable survival over frequent reproduction and leading to size‐biased reproduction. We hypothesized that sprouting would be rare and would always lead to flowering in a ten‐year monitoring study of a myco‐heterotrophic plant, the autumn coral root Corallorhiza odontorhiza. We also postulated that these plants would exhibit strong size‐based flowering patterns. We tested these hypotheses by parameterizing a variety of mark–recapture models of survival, fecundity, and demographic transitions among two life history stages: flowering and non‐sprouting (vegetatively dormant). We further developed and tested novel models estimating the influence of reproduction on demographic transitions one, two, and three years after flowering. Our results suggested that this population is typically subterranean, with only a small proportion of living plants actually sprouting in any given year. Plants typically flowered and fruited when they sprouted (flowering frequency > 0.99), supporting our first hypothesis that sprouting occurs only in concert with reproduction. We also found that reproduction was associated with long‐term reproductive demographic impacts – plants that flowered more in the past three years were more likely to continue doing so than those that flowered only once. Our use of ‘memory’ mark–recapture models, in which transitions across years are allowed to vary with demographic events occurring across several previous years, proved a powerful means of testing for their long‐term impacts of reproductive events.     

Community structure of insect herbivores in a hybrid system: examining the effects of browsing damage and plant genetic variation

Abstract.  1. Using three genetic classes of willows, Salix eriocephala , Salix sericea , and their interspecific F1 hybrid, the influence of browsing damage and the importance of genetic class on insect community structure were evaluated.
2. Three-year-old plants grown from seeds generated from controlled crosses were placed in a common garden after a damage treatment was imposed on them (plants were either left undamaged during the previous winter or they had 50% of the previous year's growth removed). Clipping damage caused large increases in mean shoot length for plants.
3. The abundance of eight species of insect herbivores was determined for every plant to evaluate community structure for three genetic classes across the two damage levels. Based on manova , damage treatment had a modest effect on the relative abundance of herbivores (i.e. their proportional representation). In contrast, dramatic differences were detected among genetic classes for relative abundance; in cases where damage treatment influenced relative abundance of herbivores, the importance of genetic class was at least 20-fold greater than that of damage treatment. No interaction between genetic class and browsing treatment was detected for community structure.
4. The weak response of the herbivore community to clipping damage, contrasted to the large response to genetic class, was very surprising because mean shoot length was greatly altered by damage treatment. These findings, coupled together with previous research, suggest that plant genetic differences can act as the primary basis for herbivore community structure, while the effects of browsing may not be as common.     

Experimental icing affects growth,mortality, and flowering in a high Arctic dwarf shrub

Effects of climate change are predicted to be greatest at high latitudes, with more pronounced warming in winter than summer. Extreme mid‐winter warm spells and heavy rain‐on‐snow events are already increasing in frequency in the Arctic, with implications for snow‐pack and ground‐ice formation. These may in turn affect key components of Arctic ecosystems. However, the fitness consequences of extreme winter weather events for tundra plants are not well understood, especially in the high Arctic. We simulated an extreme mid‐winter rain‐on‐snow event at a field site in high Arctic Svalbard (78°N) by experimentally encasing tundra vegetation in ice. After the subsequent growing season, we measured the effects of icing on growth and fitness indices in the common tundra plant, Arctic bell‐heather (Cassiope tetragona). The suitability of this species for retrospective growth analysis enabled us to compare shoot growth in pre and postmanipulation years in icing treatment and control plants, as well as shoot survival and flowering. Plants from icing treatment plots had higher shoot mortality and lower flowering success than controls. At the individual sample level, heavily flowering plants invested less in shoot growth than nonflowering plants, while shoot growth was positively related to the degree of shoot mortality. Therefore, contrary to expectation, undamaged shoots showed enhanced growth in ice treatment plants. This suggests that following damage, aboveground resources were allocated to the few remaining undamaged meristems. The enhanced shoot growth measured in our icing treatment plants has implications for climate studies based on retrospective analyses of Cassiope. As shoot growth in this species responds positively to summer warming, it also highlights a potentially complex interaction between summer and winter conditions. By documenting strong effects of icing on growth and reproduction of a widespread tundra plant, our study contributes to an understanding of Arctic plant responses to projected changes in winter climatic conditions.     

Bayesian reconstruction of ancestral expression of the LEA gene families reveals propagule-derived desiccation tolerance in resurrection plants

Desiccation tolerance is a complex trait that is broadly but infrequently present throughout the evolutionary tree of life. Desiccation tolerance has played a significant role in land plant evolution, in both the vegetative and reproductive life history stages. In the land plants, the late embryogenesis abundant (LEA) gene families are involved in both abiotic stress tolerance and the development of reproductive propagules. They are also a major component of vegetative desiccation tolerance. Phylogenies were estimated for four families of LEA genes from Arabidopsis, Physcomitrella, and the desiccation tolerant plants Tortula ruralis, Craterostigma plantagineum, and Xerophyta humilis. Microarray expression data from Arabidopsis and a subset of the Physcomitrella LEAs were used to estimate ancestral expression patterns in the LEA families and to evaluate alternative hypotheses for the origins of vegetative desiccation tolerance in the flowering plants. The results contradict the idea that vegetative desiccation tolerance in the resurrection angiosperms Craterostigma and Xerophyta arose through the co-option of genes exclusively related to stress tolerance, and support the propagule-derived origin of vegetative desiccation tolerance in the resurrection plants.     

Genetics of flower initiation and development in annual and perennial plants

Flowering is an integral developmental process in angiosperms, crucial to reproductive success and continuity of the species through time. Some angiosperms complete their life cycle within a year (annual plants), and others have a longer reproductive life, which is characterized by the generation of new flowering and vegetative shoots every year (perennial plants). Despite the differences in their lifespan, the underlying genetics of flower induction and floral organ formation appears to be similar among these plants. Hence, the knowledge gained from the study of flowering mechanism in Arabidopsis thaliana can be used to better understand similar processes in other plant species, especially the perennials, which usually have a long generation time and are not amenable to genetic analysis. Using Arabidopsis as a model, we briefly discuss the current understanding of the transition from vegetative to reproductive growth and the subsequent formation of individual floral organs, and how this knowledge has been successfully applied to the identification of homologous genes from perennial crops. Although annuals appear to share many similarities with perennials in terms of gene function, they differ in their commitment to flowering. Once an annual reaches the reproductive phase, all meristems are typically converted into either floral or inflorescence meristems. In contrast, each year, each meristem of a mature perennial has the choice to produce either a vegetative or a reproductive shoot. The physiology and genetics of flowering in Citrus are used to highlight the complexity of reproductive development in perennials, and to discus possible future research directions.