Genomic convergence underlying high-altitude adaptation in alpine plants

Evolutionary convergence is one of the most striking examples of adaptation driven by natural selection.However, genomic evidence for convergent adaptation to extreme environments remains scarce.Here, we assembled reference genomes of two alpine plants, Saussurea obvallata(Asteraceae)and Rheum alexandrae(Polygonaceae), with 37,938 and 61,463 annotated protein-coding genes. By integrating an additional five alpine genomes,we elucidated genomic convergence underlying high-altitude adaptation in al...     

Plant size influences abundance of floral visitors and biomass allocation for the cushion plant Thylacospermum caespitosum under an extreme alpine environment

Variation in size may influence the abundance of visitors and reproductive allocation for cushion plants in the extreme alpine environments. To assess effects of plant size on the abundance of main visitors and reproductive allocation in Thylacospermum caespitosum populations at two altitudes, the abundance of the visitors, visiting frequency, total number of flowers, number of fruits, number of unseeded flowers, and reproductive allocation were investigated during the period of reproductive growth. Concurrently, the effects of plant size on the visitors' contributions to fruit setting rate were assessed by a bagging experiment. Our results showed that flies (Musca domestica and Dasyphora asiatica) were the main pollinating insects of T. caespitosum, and they could obvious facilitate (p < 0.05) the fruit setting rate of this cushion plant. Seed set and floral visitation were significantly influenced (p < 0.001) by plant size. Moreover, the reproductive allocation and fruit setting rate of T. caespitosum was influenced (p < 0.001) by plant size. More biomass was allocated to reproduction in plants of greater diameter. There is an increase in reproductive success (increases of fruit number with increase in plant size) in relation to plant size. In conclusion, the extent of M. domestica and D. asiatica to facilitate the fruit setting rate mainly depended on the size of T. caespitosum. Size‐dependent reproductive allocation occurred in T. caespitosum and was the chief factor affecting the contribution of flies to fruit setting rate. These traits reflect reproductive fitness of T. caespitosum related to plant size in extreme alpine environments.     

Fitness of Bt‐resistant cabbage loopers on Bt cotton plants

Development of resistance to the insecticidal toxins from Bacillus thuringiensis (Bt) in insects is the major threat to the continued success of transgenic Bt crops in agriculture. The fitness of Bt‐resistant insects on Bt and non‐Bt plants is a key parameter that determines the development of Bt resistance in insect populations. In this study, a comprehensive analysis of the fitness of Bt‐resistant Trichoplusia ni strains on Bt cotton leaves was conducted. The Bt‐resistant T. ni strains carried two genetically independent mechanisms of resistance to Bt toxins Cry1Ac and Cry2Ab. The effects of the two resistance mechanisms, individually and in combination, on the fitness of the T. ni strains on conventional non‐Bt cotton and on transgenic Bt cotton leaves expressing a single‐toxin Cry1Ac (Bollgard I) or two Bt toxins Cry1Ac and Cry2Ab (Bollgard II) were examined. The presence of Bt toxins in plants reduced the fitness of resistant insects, indicated by decreased net reproductive rate (R₀) and intrinsic rate of increase (r). The reduction in fitness in resistant T. ni on Bollgard II leaves was greater than that on Bollgard I leaves. A 12.4‐day asynchrony of adult emergence between the susceptible T. ni grown on non‐Bt cotton leaves and the dual‐toxin‐resistant T. ni on Bollgard II leaves was observed. Therefore, multitoxin Bt plants not only reduce the probability for T. ni to develop resistance but also strongly reduce the fitness of resistant insects feeding on the plants.     

Host specificity of two pollinating seed‐consuming fly species is not related to soil moisture of host plant in the high Himalayas

Studying the drivers of host specificity can contribute to our understanding of the origin and evolution of obligate pollination mutualisms. The preference–performance hypothesis predicts that host plant choice of female insects is related mainly to the performance of their offspring. Soil moisture is thought to be particularly important for the survival of larvae and pupae that inhabit soil. In the high Himalayas, Rheum nobile and R. alexandrae differ in their distribution in terms of soil moisture; that is, R. nobile typically occurs in scree with well‐drained soils, R. alexandrae in wetlands. The two plant species are pollinated by their respective mutualistic seed‐consuming flies, Bradysia sp1. and Bradysia sp2. We investigated whether soil moisture is important for regulating host specificity by comparing pupation and adult emergence of the two fly species using field and laboratory experiments. Laboratory experiments revealed soil moisture did have significant effects on larval and pupal performances in both fly species, but the two fly species had similar optimal soil moisture requirements for pupation and adult emergence. Moreover, a field reciprocal transfer experiment showed that there was no significant difference in adult emergence for both fly species between their native and non‐native habitats. Nevertheless, Bradysia sp1., associated with R. nobile, was more tolerant to drought stress, while Bradysia sp2., associated with R. alexandrae, was more tolerant to flooding stress. These results indicate that soil moisture is unlikely to play a determining role in regulating host specificity of the two fly species. However, their pupation and adult emergence in response to extremely wet or dry soils are habitat‐specific.     

Comparative floral biology of Rhynchospora ciliata (Vahl) Kukenth and R. pubera (Vahl) Boeckeler (Cyperaceae): the role of white involucral bracts in attracting pollinating insects

Although Cyperaceae are considered anemophilous, some species exhibit features that are attractive to pollinators, such as the white UV‐reflecting involucral bracts of Rhynchospora ciliata. But how effective are these conspicuous adaptations? To address this question, we tested the hypothesis that species such as R. ciliata are visited by greater numbers of pollinating insects than similar species with green involucral bracts, such as R. pubera. We compared the floral biology of both species and the number of visits to sympatric populations of each species, associating them with the availability of pollen and the pollination system. We verified that species with white involucral bracts are preferred, because there were more visits to R. ciliata in the first 2 h the flowers were open. The peak visitation in R. pubera was 2 h after the flowers opened, when the pollen of R. ciliata was exhausted. Although the involucral bracts of R. pubera are green, the spikelet scales and anthers are white and reflect ultraviolet light. Overall, flowers of R. pubera exhibit fewer white or reflective surfaces and are probably less conspicuous to a bee than those of R. ciliata. It is possible that R. pubera is a second option for visitors after the first 2 h of anthesis. The two different peaks in visitation minimize interspecific competition for pollinators, suggesting that R. ciliata and R. pubera together could attract more generalist pollinators and, instead of competing, facilitate the pollination of both species. Although R. pubera is autogamous and self‐compatible, both wind and insects are important to its reproductive success.     

Optical and anatomical characteristics of bracts from the Chinese "glasshouse" plant, Rheum alexandrae Batalin (Polygonaceae), in Yunnan, China

Bracts that lacked chlorophyll were compared with rosette leaves on the Chinese glasshouse plant Rheum alexandrae Batalin. The structures were analyzed anatomically and with photospectrometry. Histological features were significantly different between the bracts and the rosette leaves. Epidermal pavement cells and palisade cells were larger in the bracts than in the rosette leaves, but the ratio of the intercellular spaces to the cells in the palisade layer was the same in the two structures. Absorption spectrum analyses of the half-translucent bracts showed that, despite their thinner structure, they absorbed ultraviolet (UV) radiation more efficiently than did the green rosette leaves. The characteristics of the R. alexandrae bracts were different from those of the Himalayan glasshouse plant Rheum nobile. These results suggest that R. alexandrae evolved bracts as an adaptive strategy to protect the inflorescence from UV radiation. Received: August 22, 2001 / Accepted: October 15, 2001     

Friend or foe? A parasitic wasp shifts the cost/benefit ratio in a nursery pollination system impacting plant fitness

Nursery pollination systems are species interactions where pollinators also act as fruit/seed herbivores of the plant partner. While the plants depend on associated insects for pollination, the insects depend on the plants’ reproductive structures for larval development. The outcome of these interactions is thus placed on a gradient between mutualism and antagonism. Less specialized interactions may fluctuate along this gradient with the ecological context, where natural enemies can play an important role. We studied whether a natural enemy may impact the level of seed consumption of a nursery pollinator and how this in turn may influence individual plant fitness. We used the plant Silene latifolia, its herbivore Hadena bicruris, and its ectoparasitoid Bracon variator as a model plant–herbivore–natural enemy system. We investigated seed output, germination, survival, and flower production as proxies for individual plant fitness. We show that B. variator decreases the level of seed consumption by H. bicruris larvae which in turn increased seed output in S. latifolia plants, suggesting that parasitism by B. variator may act as a regulator in the system. However, our results also show that plant survival and flower production decrease with higher seed densities, and therefore, an increase in seed output may be less beneficial for plant fitness than estimated from seed output alone. Our study should add another layer to the complex discussion of whether parasitoids contribute to plant fitness, as we show that taking simple proxies such as seed output is insufficient to determine the net effect of multitrophic interactions.     

A non‐pollinating moth inflicts higher seed predation than two co‐pollinators in an obligate pollination mutualism

1. Mutualisms are relationships of mutual exploitation, in which interacting species receive a net benefit from their association. In obligate pollination mutualisms (OPMs), female pollinators move pollen between the flowers of a single plant species and oviposit eggs within the female flowers that they visit. 2. Competition between co‐occurring pollinator species is predicted to increase pollinator virulence, i.e. laying more eggs or consuming more seeds per fruit. Plants involved in OPMs frequently host various non‐pollinating seed parasites and parasitoids that may influence the outcome of the mutualism. Quantifying the prevalence of parasites and parasitoids and competition between pollinators is important for understanding the factors that influence OPM evolutionary stability. 3. This study investigated the pollination mutualism occurring between the leaf flower plant, Breynia oblongifolia, and its co‐pollinating Epicephala moths. A third moth, Herpystis, also occurs in B. oblongifolia fruits as a non‐pollinating seed parasite. 4. Breynia oblongifolia fruits were collected to quantify seed predation and compare seed predation costs between the three moth species. Results showed that the larvae of the two pollinator species consume similar numbers of seeds, and that adults deposit similar numbers of eggs per flower. As such, no evidence of increases in virulent behaviours was detected as a result of competition between co‐pollinators. 5. By contrast, the seed parasite Herpystis consumed more seeds than either pollinator species, and fruit crops with a high proportion of Herpystis had significantly lower net seed production. 6. This work adds to the growing understanding of the ecology and dynamics of plant–pollinator mutualisms.     

Evolution of seed dispersal in North American <Emphasis Type="Italic">Ephedra</Emphasis>

Related plants often produce seeds that are dispersed in very different ways, raising questions of how and why plants undergo adaptive shifts in key aspects of their reproductive ecology. Here we analyze the evolution of seed dispersal syndromes in an ancient group of plants. Ephedra (Gymnospermae; Gnetales; Ephedraceae) is a genus containing ≈50 species in semiarid ecosystems worldwide and with three distinct types of cones. We collected mature cones and seeds of ten species of Ephedra in southwestern United States and measured nine morphological traits for each species. Principal component analysis and other data characterized three types of Ephedra cones and seeds. Species with dry, winged cone bracts are dispersed by wind (i.e., E. torreyana and E. trifurca), those with succulent, brightly-colored cone bracts are dispersed by frugivorous birds (i.e., E. antisyphilitica), and those with small, dry cone bracts and large seeds are dispersed by seed-caching rodents (e.g., E. viridis and E. californica). Two species (E. funerea and E. nevadensis) have cone and seed morphologies intermediate between two seed dispersal syndromes. Seed and cones traits were mapped onto two recent phylogenies to help reveal the evolutionary history of seed dispersal syndromes. Bird dispersal is thought to be the ancestral form of seed dispersal in ephedras as it is common in the Old World where Ephedra originated, but the three North American species dispersed by birds are not monophyletic. The two wind dispersed species in North America also do not cluster together, suggesting separate origins. Seed dispersal by seed-caching rodents is common in North America and appears to have evolved several times, but this syndrome is absent form other continents. The evolutionary history of Ephedra in North America suggests that the means of seed dispersal has been malleable. Evolutionary shifts were likely linked to changes in ecological conditions.     

Agri‐environment schemes targeting farmland bird populations also provide food for pollinating insects

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Tracking the elusive history of diversification in plant–herbivorous insect–parasitoid food webs: insights from figs and fig wasps

The food webs consisting of plants, herbivorous insects and their insect parasitoids are a major component of terrestrial biodiversity. They play a central role in the functioning of all terrestrial ecosystems, and the number of species involved is mind‐blowing (Nyman et al. 2015 ). Nevertheless, our understanding of the evolutionary and ecological determinants of their diversity is still in its infancy. In this issue of Molecular Ecology, Sutton et al. ( 2016 ) open a window into the comparative analysis of spatial genetic structuring in a set of comparable multitrophic models, involving highly species‐specific interactions: figs and fig wasps. This is the first study to compare genetic structure using population genetics tools in a fig‐pollinating wasp (Pleistodontes imperialis sp1) and its main parasitoid (Sycoscapter sp.A). The fig‐pollinating wasp has a discontinuous spatial distribution that correlates with genetic differentiation, while the parasitoid bridges the discontinuity by parasitizing other pollinator species on the same host fig tree and presents basically no spatial genetic structure. The full implications of these results for our general understanding of plant–herbivorous insect–insect parasitoids diversification become apparent when envisioned within the framework of recent advances in fig and fig wasp biology.     

Multifunctional bracts enhance plant fitness during flowering and seed development in Rheum nobile (Polygonaceae), a giant herb endemic to the high Himalayas

Specialized bracts are thought to be important for the successful reproduction of some plants and are regarded as adaptations to diverse driving forces. However, few empirical studies have quantified the adaptive significance of bracts within a cost–benefit framework. We explored the adaptive significance of large and showy bracts for reproduction in Rheum nobile, a giant herb endemic to the high Himalayas. We examined whether the bracts enhance reproductive success during flowering and seed development. Bracts increased flower and fruit temperature on sunny days, greatly decreased the intensity of ultraviolet-B (UV-B) radiation reaching flowers and fruits, and prevented pollen grains being washed away by rain. Experiments indicated that high temperature could promote pollen germination, while pollen grains exposed to rain and UV-B radiation at ambient levels were seriously damaged. Furthermore, bract removal decreased the number of pollinators visiting flowers. When bracts were removed before or after flowering, fecundity and progeny quality were adversely affected, but seed predation by larvae of pollinators decreased. A cost–benefit analysis demonstrated that the cost of bracts, i.e., increased seed predation, is modest. Our results suggest that the bracts of R. nobile promote pollen germination, protect pollen grains from rain and intense UV-B radiation, enhance pollinator visitation during flowering, and facilitate the development of fertilized ovules during seed development. We conclude that multifunctional bracts of R. nobile are an effective adaptive strategy in alpine environments and might have been selected for because of abiotic environmental conditions as well as for enhancing pollination success.     

Fragment size does not matter when you are well connected: effects of fragmentation on fitness of coexisting gypsophiles

Most habitat fragmentation studies have focused on the effects of population size on reproductive success of single species, but studies assessing the effects of both fragment size and connectivity, and their interaction, on several coexisting species are rare. In this study, we selected 20 fragments along two continuous gradients of size and degree of isolation in a gypsum landscape in central Spain. In each fragment, we selected 15 individuals of each of three dominant gypsophiles (Centaurea hyssopifolia, Lepidium subulatum and Helianthemum squamatum, 300 plants per species, 900 plants in total) and measured several reproductive traits: inflorescence number, fruit set, seed set and seed mass. We hypothesised that plant fitness would be lower on small and isolated fragments due to an interaction between fragment size and connectivity, and that response patterns would be species‐specific. Overall, fragment size had very little effect on reproductive traits compared to that of connectivity. We observed a positive effect of fragment connectivity on C. hyssopifolia fitness, mediated by the increased seed predation in plants from isolated fragments, resulting in fewer viable seeds per capitulum and lower seed set. Furthermore, seed mass was lower in plants from isolated fragments for both C. hyssopifolia and L. subulatum. In contrast, few reproductive traits of H. squamatum were affected by habitat fragmentation. We discuss the implications of species‐specific responses to habitat fragmentation for the dynamics and conservation of gypsum plant communities. Our results highlight the complex interplay among plants and their mutualistic and antagonistic visitors, and reinforce the often‐neglected role of habitat connectivity as a key component of the fragmentation process.     

Mismatches between breeding phenology and resource abundance of resident alpine ptarmigan negatively affect chick survival

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Faunal influences on New Zealand seed dispersal characteristics

A range of distinctive dispersal features have been recognised within the New Zealand flora, and a wide range of fauna are involved in the dispersal of seed in New Zealand, either by consuming fruit or seed, or as transporters of adhesive seed. In this study the composition of New Zealand’s zoochorous fauna (except insects) was examined using both trait matching within environmental, morphological and behavioural variables, and compared to the trait pattern of the groups of plant species they disperse. The importance of the different dispersal groups to the plant species they disperse varies with habitat, landform, region of New Zealand, foraging behaviour, and morphology. Over half of New Zealand’s vertebrate fauna are involved in fruit dispersal, though only 6% are considered frugivorous—the remainder include varying quantities of insects and other plant material in their diets. Flighted species are over-represented in wooded environments and higher strata and flightless species predominate in low alpine and grassland habitats. The frugivore-fruiting plant interaction group shows some indications of ecological generalism as frugivorous species consume a range of fruit sizes across all vegetation strata and fruit-bearing plants have lower species diversity and occupy a wide range of habitats. Granivores are over-represented in wetland habitats and the eastern South Island. The importance of species which unintentionally disperse adhesive seed depends on whether they are volant (higher importance in coastal environments) or flightless (higher importance dry grasslands and in low alpine areas). A subgroup of birds, such as the ratite Apteryx spp. and the now extinct Dinornithiform moa, with loose feathers (“velcro” species) are over-represented in lower vegetation strata and this matches the zone where many attachment-dispersed plant species present their seed.     

Demographic consequences of greater clonal than sexual reproduction in Dicentra canadensis

Clonality is a widespread life history trait in flowering plants that may be essential for population persistence, especially in environments where sexual reproduction is unpredictable. Frequent clonal reproduction, however, could hinder sexual reproduction by spatially aggregating ramets that compete with seedlings and reduce inter‐genet pollination. Nevertheless, the role of clonality in relation to variable sexual reproduction in population dynamics is often overlooked. We combined population matrix models and pollination experiments to compare the demographic contributions of clonal and sexual reproduction in three Dicentra canadensis populations, one in a well‐forested landscape and two in isolated forest remnants. We constructed stage‐based transition matrices from 3 years of census data to evaluate annual population growth rates, λ. We used loop analysis to evaluate the relative contribution of different reproductive pathways to λ. Despite strong temporal and spatial variation in seed set, populations generally showed stable growth rates. Although we detected some pollen limitation of seed set, manipulative pollination treatments did not affect population growth rates. Clonal reproduction contributed significantly more than sexual reproduction to population growth in the forest remnants. Only at the well‐forested site did sexual reproduction contribute as much as clonal reproduction to population growth. Flowering plants were more likely to transition to a smaller size class with reduced reproductive potential in the following year than similarly sized nonflowering plants, suggesting energy trade‐offs between sexual and clonal reproduction at the individual level. Seed production had negligible effects on growth and tuber production of individual plants. Our results demonstrate that clonal reproduction is vital for population persistence in a system where sexual reproduction is unpredictable. The bias toward clonality may be driven by low fitness returns for resource investment in sexual reproduction at the individual level. However, chronic failure in sexual reproduction may exacerbate the imbalance between sexual and clonal reproduction and eventually lead to irreversible loss of sex in the population.     

CONSEQUENCES OF EMERGENCE PHENOLOGY FOR REPRODUCTIVE SUCCESS IN RANUNCULUS ADONEUS (RANUNCULACEAE)

This study explores the effects of emergence time and reproductive phenology on seed number, seed size, and seedling survival in a population of the alpine buttercup, Ranunculus adoneus. Phenology in this snow bowl population is structured by snow depth. Plants in late melting interior portions of the bowl emerged and flowered 3 to 4 wk after those in early melting zones at the bowl perimeter during the summers of 1988 and 1989. Flowering time differences of buttercups across the bowl were consistent from one year to the next. In 1988, late flowering plants tended to set fewer seeds than early flowering ones; in 1989 no decrease in seed number accompanied flowering date. Path analysis showed that equal fecundity in early and late emerging portions of the bowl population during 1989 resulted from balancing spatial and temporal constraints on seed production. Spatial aspects of habitat quality improved toward the interior of the bowl, but temporal regimes deteriorated in these late melting sites. In both 1988 and 1989 seed size declined with delays in flowering. Path analysis of 1989 data showed that because of reduced time for seed growth, plants in late melting portions of the bowl set smaller seeds than those in earlier melting zones. Differences in seed size due to parental phenology are likely to influence fitness in snow buttercups. Under natural conditions, seedlings from large seeds (>;0.65 mg) have sixfold higher survival than do those from smaller seeds (<;0.65 mg). We conclude that seedling recruitment may be infrequent in late-melting portions of the snow bowl due to delayed parental phenology.     

Self-pollination in Euphrasia willkommii Freyn (Scrophulariaceae), an endemic species from the alpine of the Sierra Nevada (Spain)

 The reproductive ecology of Euphrasia willkommii (Scrophulariaceae), an endemic species from the Mediterranean alpine environments of the SE Spain, has been experimentally studied during two reproductive seasons. The flowers of this plant species were visited by very few insects belonging only to two generalist taxa, thrips and ants. Nevertheless, reproduction is not pollen limited in E. willkommii. Hand-pollinations demonstrated that this plant species is capable of selfing, reproductive success being similar in autogamous and allogamous crosses. Moreover, pollinator-exclusion experiments also showed that, under natural conditions, this plant relies predominantly on selfing, seed production being similar in presence or absence of pollinators. Selfing in E. willkommii is presumably an ecological mechanism to ensure successful reproduction in a harsh environment where pollinator availability is extremely low. Received May 2, 2001 Accepted December 6, 2001     

Non‐pollinating Fig Wasps Decrease Pollinator and Seed Production in Ficus andicola (Moraceae)

Fig trees ( Ficus spp.) and Agaonine fig‐wasps participate in an obligate mutualism. Fig wasps can only develop within fig inflorescences (syconia) and they are the only organisms capable of pollinating fig flowers. Other non‐pollinating wasps that lay eggs by inserting their ovipositors from the outside can also develop in syconia. These parasitic wasps may be parasitoids of either pollinating or other non‐pollinating wasps, or form galls in fig flowers or other tissues. Depending on this interaction, parasitic wasps may have various effects on the production of pollinating wasps and seeds. Wasps in the genus Idarnes, which parasitize New World figs (subgenus Urostigma), have an effect on wasp production but not on seed production. Heterandrium spp., which have short ovipositors and lay on external flowers, are infrequent and no effect on seed production has been documented. In the Colombian Andes, Idarnes spp. and Heterandrium spp. are the most frequent parasites of the Ficus andicola — Pegoscapus sp. mutualism, affecting 62 and 43 percent of syconia, respectively. Controlling for other factors that influence wasp and seed production, such as number of foundresses, syconium size and tree, we found that Idarnes reduced pollinator production by almost half but did not reduce seed production, whereas Heterandrium reduced seed production by 40 percent, and marginally affected pollinator production. Our results provide the first clear documentation of Heterandrium spp. impact on fig seed production. Whether the relative abundance of this genus is a generalized phenomenon in montane forest remains to be determined.