Alpine Gingers Research Articles

The evolution of flower-pollinator trait matching, and why do some alpine gingers appear to be mismatched?

Morphological matching between flower and pollinator traits has been documented in diverse plant lineages. Indeed, the matching of corolla tube length and pollinator tongue length has been cited repeatedly as a classic case of coevolution. However, there are many possible evolutionary routes to trait matching. Our aim here is both to review the evolutionary mechanisms of plant-pollinator trait matching and to investigate a specific case of trait matching/mismatching in a genus of alpine gingers. Roscoea gingers with long corolla tubes in the western Himalayas have pollinators with correspondingly long tongues, but the match between corolla tube and pollinator tongue lengths is not seen in the eastern Himalayas. Six floral traits were measured, including corolla tube depth, an internal trait controlling pollinator access to nectar. We calculated coefficients of variation and phylogenetically controlled correlation patterns of these traits in six Roscoea species in order to gain possible insights into stabilizing selection and modularization of these traits. The distal (nectar-containing) portion of the corolla tube exhibited lower coefficients of variations than did the basal portion. This is consistent with the hypothesis that pollinators mediate stabilizing selection on the distal, but not basal, portion of the corolla tube. This result, combined with phylogenetic data, suggests that the elevated liquid level of nectar in the distal tube evolved subsequent to dispersal into the eastern Himalayan region and loss of long-tongue pollinators. After accounting for phylogeny, corolla tube length, anther length, style length and labellum width were all intercorrelated. Corolla-tube depth was not part of this covariational module, however, suggesting separate adaptation to short-tongued pollinators. The reduction in functional corolla tube depth in the Roscoea appears to be related to the loss of long-tongued pollinators associated with dispersal to the eastern Himalayas and pollination by short-tongued pollinators. The apparent mismatch between floral tubes and pollinator tongues is a case of cryptic trait matching between flowers and pollinators, underscoring the importance of combining floral anatomy with pollination ecology in assessing plant-pollinator trait matching.

Plant diversity and ecology on the Qinghai–Tibet Plateau

Plant diversity and ecology on the Qinghai–Tibet Plateau

A new locality record for the narrowly endemic alpine ginger (Roscoea tumjensis Cowley) of the Nepalese Himalayas

A new locality record for the narrowly endemic alpine ginger (Roscoea tumjensis Cowley) of the Nepalese Himalayas

The complete chloroplast genome of Roscoea tibetica, an alpine ginger species

Roscoea tibetica is a most widespread and extensively phenotypic-variable alpine ginger species. Here, we reported the complete chloroplast (cp) genome sequence of R. tibetica. The complete chloroplast genome is 163,515 base pairs (bp) in length, containing two inverted repeat (IRa and IRb) regions of 29,781 bp, which was separated by a large single-copy (LSC) region of 88,090 bp and a small single-copy (SSC) region of 15,863 bp. The overall GC content of the plastid genome was 36.06%. In total, 113 unique genes were annotated, including 79 protein-coding genes, 30 tRNA genes, and 4 rRNA genes. Phylogenetic analysis based on 22 chloroplast genomes indicates that R. tibetiaca is closely related to R. humeana, forming a monophyletic group with high value.

Geographic isolation, pollination syndromes, and pollinator generalization in HimalayanRoscoeaspp. (Zingiberaceae)

AbstractThe pollination syndromes have been widely used to predict effective pollinators of plant species and provide the mechanistic explanation of floral diversity. However, in recent years, the predictive applicability of pollination syndromes has been frequently questioned. The accuracy of the syndromes among the closely related plant species may vary temporally and spatially. This suggests the need for the standardized, comprehensive evaluation of factors influencing the matching of a pollination syndrome of a plant species to the predominant pollinator community. We studied the pollination biology of three geographically/phenologically isolated alpine gingers (Roscoea auriculata,Roscoea capitata, andRoscoea tumjensis) exhibiting the correlated suites of floral traits that suggest long‐tongued insects as major pollinators, to test for the predictive power of the respective pollination syndrome. We also tested if geographical and temporal isolation affects interspecies breeding system and extent of pollinator generalization. We demonstrate that the threeRoscoeaspecies are self‐compatible but lack autonomous selfing, and thus completely rely on pollinators for pollination success. Five years of observations demonstrate that only diurnal insect visitors foraged on the flowers of the threeRoscoeaspecies. Estimates of the pollinator importance (pollen deposition) of the observed floral visitors indicate that morphologically mismatched bumblebees contribute more than 90% of pollination service in all the threeRoscoeaspecies, while long‐tongued butterflies and moths function as nectar robbers. We found that geographical isolation and temporal variation in flowering period does not affect the breeding system and pollinator generalization in the threeRoscoeaspecies. The three geographically and phenologically isolated HimalayanRoscoeaspp., with long‐tongued insect pollination syndrome, exhibit generalized pollination system and primarily rely on the morphologically mismatchedBombusspecies for pollination success. While, for threeRoscoeaspp., our result suggests that pollination syndromes are a weak predictor of efficient contemporary pollinator community, it also substantiates the role of non‐pollinator agents for the evolution of floral traits. The evolution ofBombuspollination in these alpine gingers suggests how the mismatch between plant and pollinator phenology can lead to the emergence of novel reproductive strategies among the congeners, which ultimately seems to play a key role for the speciation and diversification of the genusRoscoeain the Himalayas.

The effect of elevational gradient on alpine gingers (Roscoea alpina and R. purpurea) in the Himalayas.

There is currently enormous interest in how morphological and physiological responses of herbaceous plants may be affected by changing elevational gradient. Mountain regions provide an excellent opportunity to understand how closely related species may adapt to the conditions that rapidly change with elevation. We investigated the morphological and physiological responses of two Himalayan alpine gingers (Roscoea alpina and R. purpurea) along two different vertical transects of 400 m, R. purpurea between 2,174–2,574 m a.s.l and R. alpina between 2,675–3,079 m a.s.l. We measured the variables of plant height, leaf length, leaf area, specific leaf area, and stomata density at five plots, along the vertical transect at an elevational gap of ca. 100 m. Results revealed that with increased elevation plant height, and leaf area decreased while stomata density increased, whereas changes in specific leaf area, were not correlated with the elevation. Our results reveal that these alpine gingers undergo local adaptation by modifying their plant height, leaf area and stomata density in response to the varying selection pressure associated with the elevational gradient. Thus, the findings of this research provide valuable information on how a narrow range of elevational gradient affects the herbaceous plants at the alpine habitat of the Himalayas.

The complete chloroplast sequence of Roscoea humeana (Zingiberaceae): an alpine ginger in the Hengduan Mountains, China

The complete chloroplast genome sequence of Roscoea humeana (Zingiberaceae), an alpine ginger in the Hengduan Mountains, China is reported in this study. The complete chloroplast genome is 160,288 base pairs (bp) in length, containing two inverted repeat (IRa and IRb) regions of 26,852 bp, which was separated by a small single-copy region of 18,788 bp and a large single-copy region of 87,796 bp. The overall GC contents of the plastid genome were 36.1%. In total, 116 unique genes were annotated and they were consisted of 82 protein-coding genes, 30 tRNA genes, and four rRNA genes. Phylogenetic analysis based on 33 chloroplast genomes indicates that R. humeana is closely related to Zingiber spectabile and Z. officinale.

Reproductive isolation in alpine gingers: How do coexisting Roscoea (R. purpurea and R. tumjensis) conserve species integrity?

Multiple barriers may contribute to reproductive isolation between closely related species. Understanding the relative strength of these barriers can illuminate the ecological factors that currently maintain species integrity and how these factors originally promoted speciation. Two Himalayan alpine gingers, Roscoea purpurea and R. tumjensis, occur sympatrically in central Nepal and have such similar morphology that it is not clear whether or how they maintain a distinct identity. Our quantitative measurements of the components of reproductive isolation show that they are, in fact, completely isolated by a combination of phenological displacement of flowering, earlier for R. tumjensis and later for R. purpurea, and complete fidelity of visitation by different pollinator species, bumblebees for R. tumjensis and a long-tongued fly for R. purpurea. Furthermore, the nectar of R. tumjensis flowers is available to the shorter tongued bumblebees while R. purpurea nectar is less accessible, requiring deep probing from long-tongued flies. Although flowering phenology is a strong current barrier that seemingly obviates any need for pollinator discrimination, this current pattern need not reflect selective forces occurring at the initial divergence of R. tumjensis. There has been considerable pollinator switching during the radiation of the Himalayan Roscoea, and the association of flowering time with type of pollinator in these sympatric species may have originated among the earliest or latest flowering individuals or populations of an ancestor to exploit either bumblebee activity early in the breeding season or long-tongued fly abundance later in the season. These two sympatric Roscoea species add to accumulating evidence of the primacy of prezygotic pollination traits in speciation among angiosperms even in the absence of postzygotic incompatibility.

Ginger and the beetle: Evidence of primitive pollination system in a Himalayan endemic alpine ginger (Roscoea alpina, Zingiberaceae).

The Himalayan endemic alpine genus Roscoea, like other members of ginger family, exhibits the combination of floral traits that would fit pollination by long distant foragers such as bees, birds or flies. We studied the pollination biology of Roscoea alpina, observed potential floral visitors and determined their foraging behaviour, visitation frequency and pollination efficiency, to seek evidence in support of the pollination syndrome hypothesis. We also measured the floral spectra of R. alpina flowers to evaluate if signals fit with the currently known framework for observed floral visitors. We found that R. alpina have autonomous selfing and pollinator-mediated crossing, but lack apomixis. We observed that a beetle (Mylabris sp.), and a moth (Macroglossum nycteris) visit the flowers of R. alpina for pollen and nectar feeding respectively. Our field observations, the stigmatic pollen count and fruit set data indicated that the visit by the beetle was legitimate, while that of the moth was illegitimate. Emasculated flowers visited by beetles set as many fruits and seeds/fruit as auto-selfed and naturally pollinated flowers, while emasculated flowers excluded from beetle visits did not set fruit and seed; indicating that a single visit of a beetle to the flowers of R. alpina can facilitate pollination. We found that flower spectral signal of R. alpina does not fit typical spectra previously reported for beetle or bee-visited flowers. Our results suggest that, to ensure reproductive success in alpine habitat, R. alpina has evolved autonomous selfing as a predominant mode of reproduction, while beetle pollination would promote genetic diversity of this plant species. The visitation of beetles to the flowers of R. alpina, despite floral signal mismatch with the classically associated beetle vision, suggests that a different visual processing may operate in this plant-pollinator interaction at high altitudes.

Coevolutionary elaboration of pollination-related traits in an alpine ginger (Roscoea purpurea) and a tabanid fly in the Nepalese Himalayas.

Geographical variation in the interacting traits of plant-pollinator mutualism can lead to local adaptive differentiation. We tested Darwin's hypothesis of reciprocal selection as a key driving force for the evolution of floral traits of an alpine ginger (Roscoea purpurea) and proboscis length of a tabanid fly (Philoliche longirostris). We documented the pattern of trait variation in R.purpurea and P.longirostris across five populations.At each site, we quantified pollinator-mediated selection on floral display area, inflorescence height and corolla length of R.purpurea by comparing selection gradients for flowers exposed to natural pollination and to supplemental hand pollination. Reciprocal selection between plant and fly was examined at two sites via the relationship between proboscis length and nectar consumption (fly benefit) and corolla length and pollen deposition (plant benefit). Local corolla tube length was correlated with local fly proboscis length among the five sites. We found strong linear selection imposed by pollinators on corolla tube length at all sites, but there was no consistent relationship of fitness to inflorescence height or floral display area. Selection between corolla length and proboscis length was reciprocal at the two experimental sites examined. The geographical pattern of trait variation and the evidence of selection is consistent with a mosaic of local, species-specific reciprocal selection acting as the major driving force for the evolution of corolla length of R.purpurea and proboscis length of P.longirostris.

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Increasing temperature causes flowering onset time changes of alpine ginger Roscoea in the Central Himalayas

Recent herbarium-based phenology assessments of many plant species have found significant responses to global climate change over the previous century. In this study, we investigate how the flowering phenology of three alpine ginger Roscoea species responses to climate change over the century from 1913 to 2011, by comparing between herbarium-based phenology records and direct flowering observations. According to the observations, flowering onset of the three alpine ginger species occurred either 22 days earlier or was delayed by 8–30 days when comparing the mean peak flowering date between herbarium-based phenology records and direct flowering observations. It is likely that this significant change in flowering onset is due to increased annual minimum and maximum temperatures and mean annual temperature by about 0.053°C per year. Our results also show that flowering time changes occurred due to an increasing winter–spring minimum temperature and monsoon minimum temperature, suggesting that these Roscoea species respond greatly to climate warming resulting in changes on flowering times.

Evolutionary diversification of alpine ginger reflects the early uplift of the Himalayan–Tibetan Plateau and rapid extrusion of Indochina

The evolutionary diversifications of many taxonomic groups, especially those with limited dispersal ability, are often driven by key geological events, such as tectonic drift, continental collisions, and uplifts of mountains. Here, we use full range geographic sampling to create a dated molecular phylogeny for two genera of alpine gingers (Cautleya and Roscoea) in the Pan-Himalaya, and test the correlations between evolutionary diversification of this group and major geological events in the studied region. Our results revealed that the origination of their common ancestor and evolutionary split between the two genera occurred during the middle Eocene and the late Eocene to the early Oligocene, corresponding well to the proposed two early uplifts of the Himalayan–Tibetan Plateau. Roscoea species, the highest elevation gingers known, were then divided into distinct Himalayan and Indochinese clades, simultaneous with the rapid extrusion of Indochina and accompanied by the third Himalayan uplift around the Oligocene/Miocene boundary. This study highlights the importance of evolutionary diversification of plants as an independent line of evidence to reflect tectonic events in the Himalayan–Indochinese region.

Reproductive biology of two Himalayan alpine gingers (Roscoea spp., Zingiberaceae) in China: pollination syndrome and compensatory floral mechanisms

According to the concept of pollination syndromes, floral traits reflect specialisation to a particular pollinator or set of pollinators. However, the reproductive biology of endemic, and often specialised, plants may require increased attention as climate change accelerates worldwide. Species of Roscoea endemic to the Himalayan region have striking orchid-like flowers with long corolla tubes, suggesting pollination by long-tongued insects. Until now, the reproductive biology of species of Roscoea has been poorly documented. We investigated the floral biology, breeding system and pollination ecology of R. cautleoides and R. humeana, from Hengduan Mountains, a global biodiversity hotspot in southwest China. We also tested whether floral longevity increases pollination success. Pollination experiments showed that the two species were self-compatible and depended on insects for fruit production. Over several flowering seasons we did not observe any potential pollinators with long tongues that matched the corolla tube visiting flowers in centres of distribution. The principal pollinators observed were pollen-collecting generalist bees, with low visitation frequencies. In general, members of the ginger family are characterised by short-lived (usually 1 day) flowers, but flowers of R. cautleoides and R. humeana last 8 and 6 days, respectively. Removing stigmas decreased fruit set in both study populations. Our results suggest that the original pollinators may have been long-tongued insects that are now absent from the Chinese Himalayas because habitats have responded to climate change. However, long-lived and self-compatible flowers, coupled with the presence of generalist pollinators, are traits that have allowed these gingers to reproduce and continue to persist in the alpine habitats.

Autonomous Selfing Provides Reproductive Assurance in an Alpine Ginger Roscoea schneideriana (Zingiberaceae)

Reproductive assurance, the ability to produce seeds when pollinators or mates are scarce, is thought to be the major advantage of selfing in flowering plants. However, few studies have performed a direct cost-benefit analysis of the selective advantage of selfing, particularly given a long-term perspective among populations or across several flowering seasons within population. This study examined the fertility consequences of autonomous selfing in Roscoea schneideriana (Zingiberaceae), a small perennial Himalayan ginger typically found in habitats at around 3000 m a.s.l. The floral biology of R. schneideriana was studied in natural populations; the capacity for autonomous selfing was estimated using pollinator exclusion experiments; the timing of selfing was quantified by anther removal at different times during flowering; whether autonomous selfing increases seed production was tested by emasculating flowers; and the magnitude of inbreeding depression was estimated by comparing relative performance of progeny from self- and cross-pollinations. Pollinator observations were also conducted in the natural populations. The hooked stigmas of most flowers curl towards the anther and can contact pollen grains at an early stage of anthesis. Flowers with potential pollinators excluded set of as many seeds per fruit as hand-selfed and opened flowers. Autonomous selfing mostly occurs within 2 d of anthesis and can increase seed production by an average of 84 % in four populations during the flowering seasons of 2005-2007. Visits by effective pollinators were extremely rare. The cumulative inbreeding depression of R. schneideriana was 0.226. Autonomous selfing in R. schneideriana is achieved by stigmas curling towards the anthers early in flowering. It is suggested that under the poor pollination conditions, autonomous selfing has been selected for in this alpine ginger because it provides substantial reproductive assurance with very low costs.