The long-tongued hawkmoth pollinator niche for native and invasive plants in Africa

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

BACKGROUND AND AIMS

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.

METHODS

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.

KEY RESULTS

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.

CONCLUSIONS

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.

The iconic cactus of the Caatinga dry forest, Cereus jamacaru (Cactaceae) has high sphingophily specialization and pollinator dependence

Cereus jamacaru is a cactus distributed in Northeastern Brazil, with high symbolic value to this region. However, the interaction, behavior and the role of pollinators remains poorly understood. Here, we investigate the reproductive biology, addressing the ecological significance of floral attributes, including details about floral signaling. The study was carried at three areas of the Caatinga, in 2015, 2017 and 2021. We analyzed the floral morphometry, volume and concentration of the nectar, and characterized the colour and scent of flowers. Additionally, we described the pollinator behavior and performed controlled pollination experiments. The 'Mandacaru' is self-incompatible, has nocturnal anthesis and the nectar is accumulated as droplets in a long hypanthial tube. The flowers have a reflective pattern with a dark outer surface and a white inner surface. (E)-nerolidol is the major component (87.4%) of its floral perfume. We registered the sphingid moth Cocytius antaeus visiting the flowers. The floral attributes, attractants and rewards drives to a sphingophily, and the pollination treatments showed the dependence to fruit set by C. antaeus, the pollinator registered. In this case, if the apparent lack of pollinator diversity encompasses its entire range, the loss of the hawkmoth could severely impact the reproductive success of the cactus.

Intrafloral patterns of color and scent in Capparis spinosa L. and the ghosts of its selection past

PREMISE

Capparis spinosa is a widespread charismatic plant, in which the nocturnal floral habit contrasts with the high visitation by diurnal bees and the pronounced scarcity of hawkmoths. To resolve this discrepancy and elucidate floral evolution of C. spinosa, we analyzed the intrafloral patterns of visual and olfactory cues in relation to the known sensory biases of the different visitor guilds (bees, butterflies, and hawkmoths).

METHODS

We measured the intrafloral variation of scent, reflectance spectra, and colorimetric properties according to three guilds of known visitors of C. spinosa. Additionally, we sampled visitation rates using a motion-activated camera.

RESULTS

Carpenter bees visited the flowers eight times more frequently than nocturnal hawkmoths, at dusk and in the following morning. Yet, the floral headspace of C. spinosa contained a typical sphingophilous scent with high emission rates of certain monoterpenes and amino-acid derived compounds. Visual cues included a special case of multisensory nectar guide and color patterns conspicuous to the visual systems of both hawkmoths and bees.

CONCLUSIONS

The intrafloral patterns of sensory stimuli suggest that hawkmoths have exerted strong historical selection on C. spinosa. Our study revealed two interesting paradoxes: (a) the flowers phenotypically biased towards the more inconsistent pollinator; and (b) floral display demands an abundance of resources that seems maladaptive in the habitats of C. spinosa. The transition to a binary pollination system accommodating large bees has not required phenotypic changes, owing to specific eco-physiological adaptations, unrelated to pollination, which make this plant an unusual case in pollination ecology.

Evolutionary functional morphology of the proboscis and feeding apparatus of hawk moths (Sphingidae: Lepidoptera)

The morphology of the proboscis and associated feeding organs was studied in several nectar-feeding hawk moths, as well as a specialized honey-feeder and two supposedly nonfeeding species. The proboscis lengths ranged from a few millimeters to more than 200 mm. Despite the variation in proboscis length and feeding strategy, the principle external and internal composition of the galeae, the stipes pump, and the suction pump were similar across all species. The morphology of the smooth and slender proboscis is highly conserved among all lineages of nectar-feeding Sphingidae. Remarkably, they share a typical arrangement of the sensilla at the tip. The number and length of sensilla styloconica are independent from proboscis length. A unique proboscis morphology was found in the honey-feeding species Acherontia atropos. Here, the distinctly pointed apex displays a large subterminal opening of the food canal, and thus characterizes a novel type of piercing proboscis in Lepidoptera. In the probably nonfeeding species, the rudimentary galeae are not interlocked and the apex lacks sensilla styloconica; galeal muscles, however, are present. All studied species demonstrate an identical anatomy of the stipes, and suction pump, regardless of proboscis length and diet. Even supposedly nonfeeding Sphingidae possess all organs of the feeding apparatus, suggesting that their proboscis rudiments might still be functional. The morphometric analyses indicate significant positive correlations between galea lumen volume and stipes muscle volume as well as the volume of the food canal and the muscular volume of the suction pump. Size correlations of these functionally connected organs reflect morphological fine-tuning in the evolution of proboscis length and function.

Mutualist- and antagonist-mediated selection contribute to trait diversification of flowers

Flowers are generally short-lived, and they all face a multidimensional challenge because they have to attract mutualists, compel them to vector pollen with minimal investment in rewards, and repel floral enemies during this short time window. Their displays are under complex selection, either consistent or conflicting, to maximize reproductive fitness under heterogeneous environments. The phenological or morphological mismatches between flowers and visitors will influence interspecific competition, resource access, mating success and, ultimately, population and community dynamics. To better understand the effects of the plant visitors on floral traits, it is necessary to determine the functional significance of specific floral traits for the visitors; how plants respond to both mutualists and antagonists through adaptive changes; and to evaluate the net fitness effects of biological mutualisms and antagonism on plants. In this review, we bring together insights from fields as diverse as floral biology, insect behavioral responses, and evolutionary biology to explain the processes and patterns of floral diversity evolution. Then, we discuss the ecological significance of plant responses to mutualists and antagonists from a community perspective, and propose a set of research questions that can guide the research field to integrate studies of plant defense and reproduction.

Sravan Kumar, L. Kala Grace, K. Punny, Raliengoane TP, K. Prathyusha. Zoophily and nectar-robbing by sunbirds in Gardenia latifolia Ait. (Rubiaceae)

Gardenia latifolia is a semi-deciduous tree species which blooms during the dry season. Its flowers are hermaphroditic, strongly fragrant, nectariferous, and specialized with a narrow corolla tube and concealed deep seated nectar. Thrips act as resident pollinators while bats and carpenter bees act as non-resident pollinators.  Sunbirds act as nectar robbers and have no role in pollination.  The flowers are milky white and fragrant on  days 1 and 2; they cease fragrance and change color to golden yellow on day 3. Bats visit newly open, day 1 fragrant flowers for pollen collection while thrips use day 1 and day 2 flowers. Carpenter bees and sunbirds visit only day 2 flowers. The flower visiting activity of all these foragers indicates that they do not visit non-fragrant, golden yellow colored flowers although they possess nectar. Fruit is an indehiscent berry with seeds placed in pulp inside; the birds are the most likely seed dispersal agents when they break the pericarp and feed on the fruit pulp.

Local Insect Availability Partly Explains Geographical Differences in Floral Visitor Assemblages of Arum maculatum L. (Araceae)

Geographical variation in abundance and composition of pollinator assemblages may result in variable selection pressures among plant populations and drive plant diversification. However, there is limited knowledge on whether differences in local visitor and pollinator assemblages are the result of site-specific strategies of plants to interact with their pollinators and/or merely reflect the pollinator availability at a given locality. To address this question, we compared locally available insect communities obtained by light-trapping with assemblages of floral visitors in populations of Arum maculatum (Araceae) from north vs. south of the Alps. We further investigated whether and how the abundance of different visitors affects plants' female reproductive success and examined the pollen loads of abundant visitors. Local insect availability explained inter-regional differences in total visitor abundance, but only partly the composition of visitor assemblages. Northern populations predominantly attracted females of Psychoda phalaenoides (Psychodidae, Diptera), reflecting the high availability of this moth fly in this region. More generalized visitor assemblages, including other psychodid and non-psychodid groups, were observed in the south, where the availability of P. phalaenoides/Psychodidae was limited. Fruit set was higher in the north than in the south but correlated positively in both regions with the abundance of total visitors and psychodids; in the north, however, this relationship disappeared when visitor abundances were too high. High pollen loads were recorded on both psychodids and other Diptera. We demonstrate for the first time that the quantitative assessment of floral visitor assemblages in relation to locally available insect communities is helpful to understand patterns of geographical variation in plant-pollinator interactions. This combined approach revealed that geographical differences in floral visitors of A. maculatum are only partly shaped by the local insect availability. Potential other factors that may contribute to the geographical pattern of visitor assemblages include the region-specific attractiveness of this plant species to flower visitors and the population-specific behavior of pollinators.

Geographical and temporal distribution of hawkmoth (Lepidoptera: Sphingidae) species in Africa

Background

Hawkmoths consist of species where most adults are nocturnal, but there are some day-flying genera. Hawkmoth species have a wide variety of life-history traits, comprising species with adults (mostly nectarivorous though with some exceptions, honey-feeding), but there are also species that do not feed at all. The nectarivorous species are an important component of tropical ecosystems, with significant roles as major pollinators of both crops and wild flora with the pollination done by the adult stage. Pollinators are in decline world-wide and there is need for baseline data to provide information about their conservation strategies. Species occurrence data from Museum collections have been shown to be of great value as a tool for prioritising conservation actions in Africa. The National Museums of Kenya (NMK) have a large and active entomology collection that is in continuous growth. The NMK’s collection of hawkmoths had not been digitised prior to 2017. This moth family Sphingidae includes about 1,602 species and 205 genera worldwide (Kitching et al. 2018) with the majority of these species occurring in Africa. These moth species can also be used as indicators in biodiversity assessments as they can be easily sampled and identified. However, hawkmoths have rarely been surveyed over the long term for this purpose. Long-term datasets are of unquestionable significance for understanding and monitoring temporal changes in biodiversity. These hawkmoth data have addressed one of the most significant challenges to insect conservation, the lack of baseline information concerning species diversity and distribution and have provided key historic hawkmoth species diversity and distribution data that can be used to monitor their populations in the face of climate change and other environmental degradation issues that are facing the world today. The publication of the hawkmoth species occurrence data records in GBIF has enhanced data visibility to a wider audience promoting availability for use.

New information

The hawkmoth (Lepidoptera: Sphingidae) collection at the National Museums of Kenya was digitised from 2017 – 2020 and this paper presents details of species occurrence records as in the insect collection at the NMK, Nairobi, Kenya.

The collection holds 5,095 voucher specimens consisting of 88 genera and 208 species. The collection covers the period between 1904 and 2020.

The geographical distribution of the hawkmoths housed at the NMK covers East Africa at 81.41%, West Africa at 7.20%, Southern Africa at 6.89%, Central Africa at 4.02% and North Africa at 0.2%.

Floral Nectar Chemistry in Orchids: A Short Review and Meta-Analysis

Nectar is one of the most important flower traits, shaping plant-pollinator interactions and reproductive success. Despite Orchidaceae including numerous nectariferous species, nectar chemistry in this family has been infrequently studied. Therefore, the aim of this study is to compile data about nectar attributes in different orchid species. The scarcity of data restricted analyses to sugar concentration and composition. Our results suggest that the most important factor shaping nectar traits in orchids is the pollinator type, although we also found differentiation of nectar traits according to geographical regions. In spurred orchids, the length of the spur impacted nectar traits. We recommend the development of studies on nectar chemistry in orchids, including a wider range of species (both in taxonomic and geographical contexts), as well as extending the analyses to other nectar components (such as amino acids and secondary metabolites). The nectar biome would be also worth investigating, since it could affect the chemical composition of nectar. This will enrich the understanding of the mechanisms of plants-pollinators interactions.

Flower Diversification Across "Pollinator Climates": Sensory Aspects of Corolla Color Evolution in the Florally Diverse South American Genus Jaborosa (Solanaceae)

Flower phenotype may diverge within plant lineages when moving across "pollinator climates" (geographic differences in pollinator abundance or preference). Here we explored the potential importance of pollinators as drivers of floral color diversification in the nightshade genus Jaborosa, taking into account color perception capabilities of the actual pollinators (nocturnal hawkmoths vs. saprophilous flies) under a geographic perspective. We analyzed the association between transitions across environments and perceptual color axes using comparative methods. Our results revealed two major evolutionary themes in Jaborosa: (1) a "warm subtropical sphingophilous clade" composed of three hawkmoth-pollinated species found in humid lowland habitats, with large white flowers that clustered together in the visual space of a model hawkmoth (Manduca sexta) and a "cool-temperate brood-deceptive clade" composed of largely fly-pollinated species with small dark flowers found at high altitudes (Andes) or latitudes (Patagonian Steppe), that clustered together in the visual space of a model blowfly (Lucilia sp.) and a syrphid fly (Eristalis tenax). Our findings suggest that the ability of plants to colonize newly formed environments during Andean orogeny and the ecological changes that followed were concomitant with transitions in flower color as perceived by different pollinator functional groups. Our findings suggest that habitat and pollination mode are inextricably linked in the history of this South American plant lineage.

Diel scent and nectar rhythms of an African orchid in relation to bimodal activity patterns of hawkmoth pollinators

BACKGROUND AND AIMS

The temporal dimensions of floral adaptation to pollinators are not yet well understood, partly because we lack accurate information on the diel rhythms of flower visitation for many pollinators. We investigated whether diel patterns of pollinator visitation to flowers of the African woodland orchid Bonatea polypodantha are synchronized with rhythms of floral anthesis, scent emission and nectar availability.

METHODS

Direct observations and motion-activated cameras were used to identify pollinators of B. polypodantha and to document their activity periods. The timing of pollinaria removal from flowers, emission of scent and availability of nectar was also measured.

RESULTS

We found that B. polypodantha is pollinated exclusively by short-tongued hawkmoths. Pollinaria of the orchid are affixed between the labial palps of the moths and brush over the protruding stigmatic arms. The flowers also receive visits by long-tongued hawkmoths, but these act as nectar thieves. Tracking of pollinaria removal from flowers confirmed that pollination occurs only at night. Camera footage revealed a striking crepuscular pattern of foraging by short-tongued hawkmoths with peaks of activity during the twilight periods at dusk and at dawn. In contrast, long-tongued hawkmoths were found to visit flowers throughout the night. Flowers of B. polypodantha exhibit unimodal peaks of anthesis, scent emission (dominated by nitrogenous aromatics) and nectar availability before or around dusk.

CONCLUSIONS

Flowers of B. polypodantha are pollinated exclusively by short-tongued hawkmoths, which show crepuscular foraging activity at dusk and dawn. Floral phenophases of the orchid are closely synchronized with the peak of pollinator activity at dusk.

Measuring proboscis length in Lepidoptera: a review

Mouthpart morphologies relate to diet range. Differences among or within species may result in resource partitioning and speciation. In plant-pollinator interactions, mouthpart length has an important role in foraging efficiency, resource partitioning and pollination, hence measuring nectarivorous insect mouthparts’ morphological variation is important. Most adult lepidopterans feed on nectars and participate in pollination. Although a vast range of studies applied morphometric measurements on lepidopteran proboscis (tongue) length, general recommendations on methodologies are scarce. We review available proboscis length measurement methodologies for Lepidoptera. Focusing on how proboscides have been measured, how accurate the measurements were, and how were these constrained by sampling effort, we searched for research articles investigating lepidopteran proboscis length and extracted variables on the aims of measurements, preparation and measurement methodology, and descriptive statistics. Different methods were used both for preparation and measurements. Many of the 135 reviewed papers did not provide descriptions of the procedures applied. Research aims were different among studies. Forty-four percent of the studies measured dead specimens, 13% measured living specimens, and 43% were unclear. Fifteen percent of the studies used callipers, 9% rulers, 1% millimetre scales, 4% ocular micrometers, 3% drawings and 14% photographs; 55% were non-informative. We emphasise the importance to provide detailed descriptions on the methods applied. Providing guidelines for future sampling and measurements, we encourage fellow researchers planning measurements to take into account the effect of specimen preparation techniques on the results, define landmarks, consider resolution, accuracy, precision, choose an appropriate sample size and report details on methodology.

Trait matching and phenological overlap increase the spatio-temporal stability and functionality of plant-pollinator interactions

Morphology and phenology influence plant-pollinator network structure, but whether they generate more stable pairwise interactions with higher pollination success remains unknown. Here we evaluate the importance of morphological trait matching, phenological overlap and specialisation for the spatio-temporal stability (measured as variability) of plant-pollinator interactions and for pollination success, while controlling for species' abundance. To this end, we combined a 6-year plant-pollinator interaction dataset, with information on species traits, phenologies, specialisation, abundance and pollination success, into structural equation models. Interactions among abundant plants and pollinators with well-matched traits and phenologies formed the stable and functional backbone of the pollination network, whereas poorly matched interactions were variable in time and had lower pollination success. We conclude that phenological overlap could be more useful for predicting changes in species interactions than species abundances, and that non-random extinction of species with well-matched traits could decrease the stability of interactions within communities and reduce their functioning.

Importance of Pollinator-Mediated Interspecific Pollen Transfer for Angiosperm Evolution

Understanding how pollen moves between species is critical to understanding speciation, diversification, and evolution of flowering plants. For co-flowering species that share pollinators, competition through interspecific pollen transfer (IPT) can profoundly impact floral evolution, decreasing female fitness via heterospecific pollen deposition on stigmas and male fitness via pollen misplacement during visits to heterospecific flowers. The pollination literature demonstrates that such reproductive interference frequently selects for reproductive character displacement in floral traits linked to pollinator attraction, pollen placement, and mating systems and has also revealed that IPT between given pairs of species is typically asymmetric. More recent work is starting to elucidate its importance to the speciation process, clarifying the link between IPT and current and historical patterns of hybridization, the evolution of phenotypic novelty through adaptive introgression, and the rise of reproductive isolation. Our review aims to stimulate further research on IPT as a ubiquitous mechanism that plays a central role in angiosperm diversification.

Floral adaptations of two lilies: implications for the evolution and pollination ecology of huge trumpet-shaped flowers

PREMISE

Evolutionary transitions among floral morphologies, many of which provide evidence for adaptation to novel pollinators, are common. Some trumpet-shaped flowers are among the largest flowers in angiosperms, occurring in different lineages. Our goal was to investigate the role of pollinators in the evolution of these flowers using Lilium.

METHODS

We investigated floral traits and pollinators of L. primulinum var. ochraceum and L. brownii var. viridulum and reviewed reports of visitors to huge trumpet-shaped flowers. Using a published phylogeny of Lilium, we reconstructed ancestral floral morphological states in Lilium to elucidate the origins of trumpet-shaped lilies.

RESULTS

Both lilies are largely self-incompatible and show floral syndromes indicative of hawkmoth pollination. The short trumpet-shaped lily can be pollinated by short-tongued (<40 mm) but not long-tongued hawkmoths (>65 mm), while the huge trumpet-shaped lily can be pollinated by both. A literature review including 22 species of trumpet-shaped flowers suggests that their pollinator guilds commonly include both short- and long-tongued moths. A phylogenetic reconstruction indicates that trumpet-shaped lilies possibly have multiple origins from tepal-reflexed ancestors, at least six of which have evolved huge flowers (>50 mm).

CONCLUSIONS

Adaptation to short-tongued hawkmoths may have initiated the evolution of trumpet-shaped lilies. Huge trumpet-shaped lilies may have evolved as a response to selection by long-tongued hawkmoths, without excluding the short-tongued ones. This evolutionary pathway leads to a functionally more generalized pollination system instead of an increasingly specialized one and is not necessarily associated with pollinator shifts.

High niche diversity in Mesozoic pollinating lacewings

Niche diversity of pollinating insects plays a vital role in maintaining extant terrestrial ecosystems. A key dimension of pollination niches refers to the insect proboscis length that commonly matches the floral tube length. Here we describe new kalligrammatid lacewings (an iconic Mesozoic pollinating insect lineage) from late Cretaceous Burmese amber and Mesozoic sediments in China. Kalligrammatids display complex configurations of elongate mouthpart elements consisting of well-developed maxillae, labium and their palps. The mouthpart lengths vary among species, from 0.6 to 18.0 mm, suggesting corresponding variability in the floral tube lengths of Mesozoic plants. With the diversification of pollinating habits, the kalligrammatids presented highly divergent traits related to chemical communication and defence mechanisms. Together with other Mesozoic long-proboscid insects, these fossils not only reveal the high niche diversity of Mesozoic pollinating insects but also highlight the diversity of Mesozoic pollinator-dependent plants prior to the rise of angiosperms.

Pollination niche availability facilitates colonization of Guettarda speciosa with heteromorphic self-incompatibility on oceanic islands

Obligate out-breeding plants are considered relatively disadvantageous comparing with self-breeding plants when colonizing oceanic islets following long-distance dispersal owing to mate and pollinator limitation. The rarity of heterostyly, a typical out-breeding system, on oceanic islands seems a good proof. However, a heterostylous plant, Guettarda speciosa, is widely distributed on most tropical oceanic islets. Our research demonstrates that its heteromorphic self-incompatibility, plus herkogamy and long flower tube make it rely on pollinator for sexual reproduction, which is generally considered "disadvantageous" for island colonization. We hypothesize that available pollination niche will be a key factor for its colonization on islands. Our studies on remote coral islands show that G. speciosa has built equilibrium population with a 1:1 morph ratio. It could obtain pollination niche from the hawkmoth Agrius convolvuli. A pioneer island plant Ipomoea pes-caprae sustain the pollination niche by providing trophic resource for the larvae of the pollinator. Geographic pattern drawn by Ecological Niche Modelling further indicates the interaction between G. speciosa, A. convolvuli and I. pes-caprae can be bounded on those remote oceanic islands, explaining the colonization of G. speciosa distylous population. These findings demonstrated obligate out-breeding system could be maintained to acclimatize long distance dispersal, if the pollination niche is available.

Diversification of Trait Combinations in Coevolving Plant and Insect Lineages

Closely related species often have similar traits and sometimes interact with the same species. A crucial problem in evolutionary ecology is therefore to understand how coevolving species diverge when they interact with a set of closely related species from another lineage rather than with a single species. We evaluated geographic differences in the floral morphology of all woodland star plant species (Lithophragma, Saxifragaceae) that are pollinated by Greya (Prodoxidae) moths. Flowers of each woodland star species differed depending on whether plants interact locally with one, two, or no pollinating moth species. Plants of one species grown in six different environments showed few differences in floral traits, suggesting that the geographic differences are not due significantly to trait plasticity. Greya moth populations also showed significant geographic divergence in morphology, depending on the local host and on whether the moth species co-occurred locally. Divergence in the plants and the moths involved shifts in combinations of partially correlated traits, rather than any one trait. The results indicate that the geographic mosaic of coevolution can be amplified as coevolving lineages diversify into separate species and come together in different combinations in different ecosystems.

The long and the short of it: a global analysis of hawkmoth pollination niches and interaction networks

1. Proboscis length has been proposed as a key dimension of plant pollination niches, but this niche space has not previously been explored at regional and global scales for any pollination system. Hawkmoths are ideal organisms for exploring pollinator niches as they are important pollinators in most of the biodiverse regions of the earth and vary greatly in proboscis length, with some species having the longest proboscides of all insects. 2. Using datasets for nine biogeographical regions spanning the Old and New World, we ask whether it is possible to identify distinct hawkmoth pollination niches based on the frequency distribution of proboscis length, and whether these niches are reflected in the depths of flowers that are pollinated by hawkmoths. We also investigate the levels of specialization in hawkmoth pollination systems at the regional and community level using data from interaction network studies. 3. We found that most regional hawkmoth assemblages have bimodal or multimodal distributions of proboscis length, and that these are matched by similar distributions of floral tube lengths. Hawkmoths, particularly those with longer proboscides, are polyphagous and at the network level show foraging specialization equivalent to or less than that of bees and hummingbirds. In the case of plants, shorter-tubed flowers are usually visited by numerous hawkmoth species, while those that are longer-tubed tend to exclude shorter-proboscid hawkmoths and thus become ecologically specialized on longer-proboscid hawkmoth species. Longer-tubed flowers tend to have greater nectar rewards and this promotes short-term constancy by long-proboscid hawkmoths. 4. Our results show that pollinator proboscis length is a key niche axis for plants and can account for patterns of evolution in functional traits such as floral tube length and nectar volume. We also highlight a paradoxical trend for nectar resource niche breadth to increase according to proboscis length of pollinators, while pollinator niche breadth decreases according to the tube length of flowers.

Orchid conservation: further links

BACKGROUND

Due in great part to their often complex interactions with mycorrhizal fungi, pollinators and host trees, Orchidaceae present particular challenges for conservation. Furthermore, orchids, as potentially the largest family of angiosperms with >26000 species, species complexes and frequent hybrid formation, are complex to catalogue. Following a highlight in 2015, a further seven papers focusing on orchids, their interactions with beneficial organisms, pollinators and mycorrhiza, and other factors relating to their conservation, including threats from human utilization and changing land use, are presented here.

CONCLUSIONS

The production of an online flora of all known plants and an assessment of the conservation status of all known plant species as far as possible, to guide conservation action are the first two targets of the Global Strategy for Plant Conservation Without knowing how many species there are and how they should be circumscribed, neither of these targets is achievable. Orchids are a fascinating subject for fundamental research with rapid species evolution, specific organ structure and development, but they also suffer from high levels of threat. Effective orchid conservation must take account of the beneficial interactions with fungi and pollinators and the potentially detrimental effects of over-collection and changes in land use.