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Floral Biology of the federally threatened Apios priceana (Fabaceae)
Abstract
Apios priceana B. L. Rob. is federally threatened and little is known about its pollination biology. At the Redstone Arsenal population, Alabama, we studied its breeding system, determined major floral visitors and their pollination effectiveness, and explored pollen limitation of fruit and seed production. Fruit initiation was low (3.9%) for cross-pollinated flowers but only marginally greater than for self-pollinated or nonpollinated flowers (none initiated a fruit). Most floral visits (97%) were by bees with 43% of visits by large bees (> 1.5 cm in length) and 51% by medium bees (1-1.5 cm in length). Keel petals of A. priceana flowers enclose the style and stamens: flowers must be "tripped" for pollination to occur. Large and medium bees were equally effective in tripping flowers, whereas small bees (< 1 cm in length) did not trip flowers. Success of large and medium bee species (several Bombus species and Megachile sculpturalis Smith) in initiating legumes after a single floral visit ranged from 17-35% but did not differ significantly among species. Pollen supplementation showed legume production was pollen-limited: 24% of supplemented flowers produced fruits versus 6% of nonsupplemented flowers. Seed counts revealed a marginally nonsignificant trend for more seeds in legumes from pollen-supplemented flowers. We conclude that this rare plant species is dependent on medium and large bees for pollination, and that reproduction is partially pollen-limited. Conservation efforts should include measures to protect bee pollinators of this species to ensure that managed populations of this rare plant continue to reproduce sexually.
Iris verna L. var. smalliana Fernald ex M.E. Edwards (Family Iridaceae, hereafter referred to as Iris verna) is currently listed as endangered in Pennsylvania. The six extant populations in Pennsylvania are all located in one state forest and represent the northern end of the range for the species. There is little known about the basic biology of I. verna throughout its range, making preservation of threatened populations difficult. Iris verna was tested for self-compatibility and the ability to autonomously self-pollinate in 2016. Pollinator limitation studies were conducted on three of the Pennsylvania populations in 2015 and 2016 by comparing hand-pollinated and naturally pollinated flowers. Potential animal pollinators or seed dispersers were identified through in-person observation and video camera use. Iris verna was found to be self-compatible, with no significant reduction in seed production in selfed flowers, but the species does require a pollinator for pollen transfer. Seed production in I. verna was limited by pollinators during both years of the study and seed production in both control and hand-pollinated flowers was variable across years, suggesting resource availability also limits sexual reproduction. Ants were the only observed animals potentially coming in contact with reproductive organs while visiting flowers, and were also identified as seed dispersers. Our findings suggest that pollinators can be an important limiting factor to sexual reproduction in these endangered populations of I. verna in Pennsylvania.
Apios priceana, commonly known as Price’s potato-bean, is a perennial species native to the Southeastern US. Habitat destruction has caused A. priceana to become rare, and it is federally listed as threatened. Protocols developed for in vitro germination, shoot micropropagation, in vitro rooting, shoot establishment in soil, and seed cryopreservation will assist in the safeguarding and conservation of dwindling natural populations. Seeds were germinated in vitro on plant growth regulator (PGR)-free Murashige and Skoog (MS) medium after seed sterilization in H2O2 and seed nicking. Greatest shoot multiplication occurred on MS medium with BAP/IBA/GA3 at 2.22/0.49/1.44 μM with 2.0 g/l Phytagel and pH adjusted to 5.7. Shoots rooted in vitro in MS medium with 3.2 μM IBA. Shoots rooted in vitro rapidly established in greenhouse potting mix, usually showing new growth within 2 wk, with tuber formation by the end of the growing season. Plants transferred to a forest setting in late winter survived, grew throughout the summer, and became dormant in the fall. In small post cryopreservation tests with A. americana and A. priceana seeds, air or desiccant-dried to water contents below 10% but above 2.5%, germination reached 87–90%.
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Bumblebees (Bombus spp.) are efficient pollinators of many flowering plants, yet the pollen deposition performance of individual bees has not been investigated. Worker bumblebees exhibit large intraspecific and intra-nest size variation, in contrast with other eusocial bees; and their size influences collection and deposition of pollen grains.
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Laboratory studies with B. terrestris workers and Vinca minor flowers showed that pollen grains deposited on stigmas in single visits (SVD) were significantly positively related to bee size; larger bees deposited more grains, while the smallest individuals, with proportionally shorter tongues, were unable to collect or deposit pollen in these flowers. Individuals did not increase their pollen deposition over time, so handling experience does not influence SVD in Vinca minor.
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Field studies using Geranium sanguineum and Echium vulgare, and multiple visiting species, confirmed that individual size affects SVD. All bumblebee species showed size effects, though even the smallest individuals did deposit pollen, whereas there was no detectable effect with Apis with its limited size variation. Two abundant hoverfly species also showed size effects, particularly when feeding for nectar.
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Mean size of foragers also varied diurnally, with larger individuals active earlier and later, so that pollination effectiveness varies through a day; flowers routinely pollinated by bees may best be served by early morning dehiscence and visits from larger individuals.
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Thus, while there are well-documented species-level variations in pollination effectiveness, the fine-scale individual differences between foragers should also be taken into account when assessing the reproductive outputs of biotically-pollinated plants.
Apios americana Medicus (Leguminosae; Phaseoleae), a tuberous, herbaceous vine, consists of diploid and triploid clones which are morphologically nearly identical. Although A. americana is widespread in eastern North America and flowers profusely throughout its range, fruit set is low. In part, this is because populations north of Connecticut consist almost exclusively of sterile triploid individuals. Although triploid populations occur south of this region, diploids predominate. Fruit set is also low in diploids. We attribute this to partial self-incompatibility and to a low rate of floral visits by leaf-cutter bees (Megachile spp.), the only legitimate pollinator. Visitation is easily measured because flowers have a nonrepetitive explosive tripping mechanism which must be triggered by insects. In two Connecticut populations only 10% of 299 flowers were tripped, and on average only about one-half of these set fruit. We conclude that A. americana maintains populations by vegetative propagation, but expands its range and retains variability through sexual reproduction of diploids.
Mutualistic networks are key for the creation and maintenance of biodiversity, yet are threatened by global environmental change. Most simulation models assume that network structure remains static after species losses, despite theoretical and empirical reasons to expect dynamic responses. We assessed the effects of experimental single bumblebee species removals on the structure of entire flower visitation networks. We hypothesized that network structure would change following processes linking interspecific competition with dietary niche breadth. We found that single pollinator species losses impact pollination network structure: Resource complementarity decreased, while resource overlap increased. Despite marginally increased connectance, fewer plant species were visited after species removals. These changes may have negative functional impacts, as complementarity is important for maintaining biodiversity-ecological functioning relationships and visitation of rare plant species is critical for maintaining diverse plant communities.
Visitation rates and assemblage composition of pollinators have often been related to environmental, ecological and phenotypic variables. However, the interaction between flowers and pollinators has not been evaluated in a biomechanical context. Floral rewards in keel flowers (Fabaceae, Faboideae) are concealed behind four joined petals, the keel-wing unit, and are accessible only if pollinators open this unit by exerting force on it. Force needed to open the flower is expected to affect the interaction with pollinators because pollinators must invest time and energy to open the keels. Consequently, plants with stiff flowers should be expected to experience diminished visitation frequency, particularly by weak visitors. To test this expectation of diminished visitation rates and of assemblage composition biased by pollinator strength, we measured the force needed to open the keel flowers of five co-occurring legume species and, using a canonical correspondence analysis (CCA), we tested their association with pollinator visitation rates and assemblage composition. We additionally included a size flag variable in CCA to test the effect of attractiveness on pollinator visits. There was no association between flower stiffness and visitation frequency. According to the CCA, pollinator assemblage compositions were associated with the force needed to open the keel and not flag size. As a general pattern, weak flowers are pollinated by an uneven assemblage of weak bees while the stiffest flowers are pollinated by an even assemblage of large and strong bees. These results supports the idea that force has an effect in controlling pollinator assemblage composition.
Background and aims – Apios priceana is a rare flowering plant that can only be found in parts of the Southeastern United States. Little is known about the reproductive biology of this plant and only a few insect flower visitors have been previously documented. The aim of this study was to further document the insect flower visitors of A. priceana in North Alabama. Methods – Cameras and observers recorded flower visitors during the 2014 blooming season of a large North Alabama population of A. priceana. Key results – Although fifteen different species of insects were documented on flowers of A. priceana, most performed a single or very few visits. Bumble bees (Bombus spp.), two species of Megachilidae (Megachile sculpturalis and Megachile campanulae), and the hummingbird clearwing (Hemaris thysbe) were the most common visitors. Interestingly, the giant resin bee, M. sculpturalis, is considered to be an invasive species but in this case may be pollinating a native and Federally threatened plant. Conclusion – Although A. priceana flowers are visited by numerous insects, Bombus spp. and, surprisingly, an invasive species (Megachile sculpturalis) are probably the most important pollinators of this plant. © 2016 Botanic Garden Meise and Royal Botanical Society of Belgium.
Explosive pollen release is documented in many plant families, including the Fabaceae. Desmodium setigerum E. Mey (Fabaceae) is a perennial herb with single trip explosive pollen release found in eastern Africa, and the unique ability to reverse floral colour change if insufficient pollination has occurred. However, little else is known about the pollination ecology of this species, what visitors can trigger explosive pollen release, and whether bee body size is related to pollination efficiency. We investigated: 1) the breeding system of D. setigerum, and whether it is pollen limited; 2) whether flowers are visited early in the day allowing sufficient time for a second opportunity for pollination; and 3) what insect species visit D. setigerum and the relative efficacy of different flower visitors in relation to visitor size and pollination success. We found that although self-compatible, D. setigerum requires insect visitation to set seed as explosive pollen release is needed even for selfing. Most flowers are initially visited before 1400h, and by 1800h nearly all flowers have been tripped. Flowers were not pollen limited in this study, and were visited primarily by bees. We observed 16 visiting species, and there was a wide variation (0-404 grains) in the amount of pollen deposited on stigmas. Although almost all bees deposited some pollen, the mean number of pollen grains deposited in a single visit per species was negatively related to body size. However, one particular megachilid species deposited significantly more pollen grains than any other visitor and so is likely an important pollinator of this species. This provides insights into the pollination biology of this unique plant species, and adds to increasing literature on the relationships between bee body size, explosive pollen release and pollination effectiveness.
Wild bee declines have been ascribed in part to neonicotinoid insecticides. While short-term laboratory studies on commercially bred species (principally honeybees and bumblebees) have identified sub-lethal effects, there is no strong evidence linking these insecticides to losses of the majority of wild bee species. We relate 18 years of UK national wild bee distribution data for 62 species to amounts of neonicotinoid use in oilseed rape. Using a multi-species dynamic Bayesian occupancy analysis, we find evidence of increased population extinction rates in response to neonicotinoid seed treatment use on oilseed rape. Species foraging on oilseed rape benefit from the cover of this crop, but were on average three times more negatively affected by exposure to neonicotinoids than non-crop foragers. Our results suggest that sub-lethal effects of neonicotinoids could scale up to cause losses of bee biodiversity. Restrictions on neonicotinoid use may reduce population declines.
The conservation of plants has not generated the sense of urgency—or the funding—that drives the conservation of animals, although plants are far more important for us. There are an estimated 500,000 species of land plants (angiosperms, gymnosperms, ferns, lycophytes, and bryophytes), with diversity strongly concentrated in the humid tropics. Many species are still unknown to science. Perhaps a third of all land plants are at risk of extinction, including many that are undescribed, or are described but otherwise data deficient. There have been few known global extinctions so far, but many additional species have not been recorded recently and may be extinct. Although only a minority of plant species have a specific human use, many more play important roles in natural ecosystems and the services they provide, and rare species are more likely to have unusual traits that could be useful in the future. The major threats to plant diversity include habitat loss, fragmentation, and degradation, overexploitation, invasive species, pollution, and anthropogenic climate change. Conservation of plant diversity is a massive task if viewed globally, but the combination of a well-designed and well-managed protected area system and ex situ gap-filling and back-up should work anywhere. The most urgent needs are for the completion of the global botanical inventory and an assessment of the conservation status of the 94% of plant species not yet evaluated, so that both in and ex situ conservation can be targeted efficiently. Globally, the biggest conservation gap is in the hyperdiverse lowland tropics and this is where attention needs to be focused.
Background:
Megachile (Callomegachile) sculpturalis Smith, the giant resin bee, is an adventive species in the United States. First established in the United States during the early 1990s, records currently exist from most states east of the Mississippi River along with Iowa and Kansas.
New information:
New distributional records are presented for Megachile (Callomegachile) sculpturalis Smith, an introduced bee. Additional records presented here expand the known distribution southwest through Arkansas, Louisiana, Mississippi, Missouri, and Texas. An updated host plant list containing new records is also presented, expanding the number of known floral associations.
Premise of research. Apios is a perennial twining herbaceous plant genus with a disjunct distribution between eastern Asia and North America. Some of its species have shown great economic potential as a tuber crop and a source of useful flavonoids. However, the phylogenetics of Apios has not been studied using molecular data. Several questions remain unanswered, including the monophyly of Apios, species boundaries, interspecific relationships, the pattern and timing of the intercontinental disjunct distribution, and the evolution of tuber formation. Methodology. Phylogenetic analyses were conducted on the basis of sequences from nuclear and plastid genomes using both maximum parsimony and maximum likelihood methods. Species trees were inferred via Bayesian analysis in BEST. Divergence times were estimated using BEAST with multiple calibration points, and ancestral areas were inferred with S-DIVA. Pivotal results. Our DNA sequence data recognize the five species of Apios, including A. carnea, A. fortunei, A. delavayi, A. americana, and A. priceana. Apios species form a clade in the basal position of the phaseoloid group, and within Apios, A. carnea is sister to the remaining species. The two North American species (A. americana and A. priceana) are more closely related to each other than either is to any of the Asian species, and their ancestral populations may have migrated from Asia in the late Miocene and early Pliocene via the Bering land bridge. Well-developed tuber is a derived trait in Apios that may function as assisting vegetative reproduction. Parapatric speciation may have happened in both eastern Asia and North America, adapting to specific habitats or pollinators. Conclusions. Apios is a monophyletic lineage that diverged early in the phaseoloid group. Within Apios, the two North American species form a clade that was derived from Asian ancestral populations in the late Miocene. Unequal range of distribution of species in both eastern Asia and North America may be explained by parapatric speciation.
Biodiversity is declining, with direct and indirect effects on ecosystem functions and services that are poorly quantified. Here we develop the first global assessment of trends in pollinators, focusing on pollinating birds and mammals. A Red List Index for these species shows that, overall, pollinating bird and mammal species are deteriorating in status, with more species moving towards extinction than away from it. On average, 2.4 species per year have moved one Red List category towards extinction in recent decades, representing a substantial increase in extinction risk across this set of species. This may be impacting the delivery of benefits to people that these species provide. We recommend that the index is expanded to include taxonomic groups that contribute more significantly to pollination, such as bees, wasps and butterflies, thereby giving a more complete picture of the state of pollinating species worldwide.
The future health of ecosystems is arguably as dependent on urban sprawl as it is on human-caused climatic warming. Urban sprawl strongly impacts the urban ecosystems it creates and the natural and agro-ecosystems that it displaces and fragments. Here, we project urban sprawl changes for the next 50 years for the fast-growing Southeast U.S. Previous studies have focused on modeling population density, but the urban extent is arguably as important as population density per se in terms of its ecological and conservation impacts. We develop simulations using the SLEUTH urban growth model that complement population-driven models but focus on spatial pattern and extent. To better capture the reach of low-density suburban development, we extend the capabilities of SLEUTH by incorporating street-network information. Our simulations point to a future in which the extent of urbanization in the Southeast is projected to increase by 101% to 192%. Our results highlight areas where ecosystem fragmentation is likely, and serve as a benchmark to explore the challenging tradeoffs between ecosystem health, economic growth and cultural desires.
The relative importance of specialized and generalized plant‐pollinator relationships is contentious, yet analyses usually avoid direct measures of pollinator quality (effectiveness), citing difficulties in collecting such data in the field and so relying on visitation data alone.
We demonstrate that single‐visit deposition ( SVD ) of pollen on virgin stigmas is a practical measure of pollinator effectiveness, using 13 temperate and tropical plant species. For each flower the most effective pollinator measured from SVD was as predicted from its pollination syndrome based on traditional advertisement and reward traits. Overall, c . 40% of visitors were not effective pollinators (range 0–78% for different flowers); thus, flower–pollinator relationships are substantially more specialized than visitation alone can reveal.
Analyses at species level are crucial, as significant variation in SVD occurred within both higher‐level taxonomic groups (genus, family) and within functional groups.
Other measures sometimes used to distinguish visitors from pollinators (visit duration, frequency, or feeding behaviour in flowers) did not prove to be suitable proxies.
Distinguishing between ‘pollinators’ and ‘visitors’ is therefore crucial, and true ‘pollination networks’ should include SVD to reveal pollinator effectiveness ( PE ). Generating such networks, now underway, could avoid potential misinterpretations of the conservation values of flower visitors, and of possible extinction threats as modelled in existing networks.
The effect of climate change on the frequency and intensity of droughts across the contiguous United States over the next century is assessed by applying Standardized Precipitation Indices and the Palmer Drought Severity Index to the full suite of 22 Intergovernmental Panel on Climate Change General Circulation Models for three IPCC-SRES emissions scenarios (B1, A1B, and A2 from the Special Report on Emissions Scenarios (SRES) listed in order of their emissions through 2100 from high to low). The frequency of meteorological drought based on precipitation alone is projected to increase in some parts of the US, for example the southwestern states, and decrease in others. Hydrological drought frequencies based on precipitation and temperature are projected to increase across most of the country, however, with very substantial and almost universally experienced increases in drought risk by 2050. For both measures, the southwestern US and the Rocky Mountain states are projected to experience the largest increases in drought frequency, but these areas may be able to exploit existing excess storage capacity. Drought frequencies and uncertainties in their projection tend to increase considerably over time and show a strong worsening trend along higher greenhouse gas emissions scenarios, suggesting substantial benefits for greenhouse gas emissions reductions.
The only hard evidence from field studies in the natural range ofApios americana (Leguminosae) indicates that this species is frequently triploid and seed sterile, and that the only legitimate pollinators are Megachilid bees. Claims of fly pollination based exclusively on examination of floral features of a European botanic garden specimen are unwarranted.
A growing number of studies on naturally occurring plant species have shown that plant-plant interactions for pollination vary from competitive to facilitative. In reviewing the seven published studies on how alien species can affect the pollination success in natives, we found that all authors suggest competitive effects to dominate, either through reduced pollinator visitation rates or through increased heterospecific pollination of native flowers. Although certain pollinator interactions were competitive, the reproductive output in the native species was not always reduced. This implies that natives are not pollen limited, and/or that they compensate for the loss of pollinators by other animals. However, the few studies on pollination interactions between alien and native plant species show differing results. We therefore discuss other properties that can cause aliens to be strong interactors for pollination, and can modify how alien species affect the reproductive success in natives. We also emphasize the spatial scales addressed in the reviewed studies, as alien plant species may represent valuable food resources for many pollinators. Such plant species tend to be interpreted as competitive plants for pollination, whereas we stress their facilitative ability that may occur on a landscape scale by increasing pollinator densities. Additionally, while most studies tend to work within a shorter temporal scale, the impacts of the alien plant introductions may differ depending on the year or seasonal time leading to the differing results reported.
A test was made of the hypothesis that papilionate legume flowers filter pollinators according to their ability to exert strength to open flowers to access rewards. In addition, interactions with pollen vectors were expected to explain the structural complexity of the architecture of these flowers since operative flower strength may be determined by a combination of morphological traits which form part of an intrafloral functional module.
Six papilionate species were studied: Collaea argentina, Desmodium uncinatum, Galactia latisiliqua, Lathyrus odoratus, Spartium junceum and Tipuana tipu. Measurements were made of the strength needed to open keels and the strength that pollinators were capable of exerting. Morphological traits of all petals were also measured to determine which of them could be either mutually correlated or correlated with operative strength and moment of strength and participated in a functional module.
It was observed that pollinators were capable in all cases of exerting forces higher and often several times higher than that needed to access floral rewards, and no association could be detected between floral operative strength and strength exerted by the corresponding pollinators. On the other hand, strong and significant correlations were found among morphometric traits and, of these, with operative strength and moment. This was particularly evident among traits of the keel and the wings, presumably involved in the functioning of the floral moveable mechanism.
Though visitors are often many times stronger than the operative strength of the flowers they pollinate, exceptionally weak bees such as Apis mellifera cannot open the strongest flowers. On the other hand, strong correlations among certain petal morphometric traits (particularly between the keel and wings) give support to the idea that an intrafloral module is associated with the functioning of the mechanism of these legume flowers. In addition, the highly significant correlations found across petals support the view of functional phenotypic integration transcending the ontogenetic organization of flower structure.
Bumble bees (Bombus) are vitally important pollinators of wild plants and agricultural crops worldwide. Fragmentary observations, however, have suggested population declines in several North American species. Despite rising concern over these observations in the United States, highlighted in a recent National Academy of Sciences report, a national assessment of the geographic scope and possible causal factors of bumble bee decline is lacking. Here, we report results of a 3-y interdisciplinary study of changing distributions, population genetic structure, and levels of pathogen infection in bumble bee populations across the United States. We compare current and historical distributions of eight species, compiling a database of >73,000 museum records for comparison with data from intensive nationwide surveys of >16,000 specimens. We show that the relative abundances of four species have declined by up to 96% and that their surveyed geographic ranges have contracted by 23– 87%, some within the last 20 y. We also show that declining populations have significantly higher infection levels of the microsporidian pathogen Nosemabombi and lower genetic diversity compared with co-occurring populations of the stable (nondeclining) species. Higher pathogen prevalence and reduced genetic diversity are, thus, realistic predictors of these alarming patterns of decline in North America, although cause and effect remain uncertain.
Includes Supporting Information.
The effects of forager body size and floral display size on pollinator behaviour were assessed in a relatively specialised plant-pollinator system. Cytisus scoparius, which has structurally complex, nectarless flowers is pollinated by foraging bumblebees. Variations in bee body size affected the proportion of open flowers visited, the ability of bees to trigger the pollination mechanism of flowers and handling times on open flowers. Smaller bees handled flowers more successfully and efficiently than larger ones. Contrary to previous reports, all bees preferred to visit open flowers and possible explanations for this are discussed. Floral display size also affected behaviour as bees visited more flowers per plant on larger plants, but visited a lower proportion of the available flowers. There was no interaction between body size and floral display size, suggesting that bees of all sizes respond in a similar manner to variations in floral display sizes. The potential impacts of variations in bumblebee behaviour on plant reproductive success are discussed.
There is increasing evidence that human disturbance can negatively impact plant-pollinator interactions such as outcross pollination. We present a meta-analysis of 22 studies involving 27 plant species showing a significant reduction in the proportion of seeds outcrossed in response to anthropogenic habitat modifications. We discuss the evolutionary consequences of disturbance on plant mating systems, and in particular whether reproductive assurance through selfing effectively compensates for reduced outcrossing. The extent to which disturbance reduces pollinator versus mate availability could generate diverse selective forces on reproductive traits. Investigating how anthropogenic change influences plant mating will lead to new opportunities for better understanding of how mating systems evolve, as well as of the ecological and evolutionary consequences of human activities and how to mitigate them.
Breeding systems are important, and often neglected, aspects of the natural biology of organisms, affecting homozygosity and thus many aspects of their biology, including levels and patterns of genetic diversity and genome evolution. Among the different plant mating systems, it is useful to distinguish two types of systems: 'sex systems', hermaphroditic versus male/female and other situations; and the 'mating systems' of hermaphroditic populations, inbreeding, outcrossing or intermediate. Evolutionary changes in breeding systems occur between closely related species, and some changes occur more often than others. Understanding why such changes occur requires combined genetical and ecological approaches. I review the ideas of some of the most important theoretical models, showing how these are based on individual selection using genetic principles to ask whether alleles affecting plants' outcrossing rates or sex morphs will spread in populations. After discussing how the conclusions are affected by some of the many relevant ecological factors, I relate these theoretical ideas to empirical data from some of the many recent breeding system studies in plant populations.
Apios priceana (Fabaceae) is a rare herbaceous perennial vine. Seed collection for ex situ conservation is difficult because seed production is sporadic. We investigated propagation by cuttings of A. priceana at Redstone Arsenal, Alabama. Two experimental factors were investigated: donor plant size (small vs. large) and month of cutting (May vs. June 2013). We also documented impact of cutting collection on donor plants by recording size and reproductive variables from both cut and uncut (control) plants. About one-third of cuttings formed tubers by May 2014; success did not differ due to donor plant size or month of cutting. However, May cuttings produced two-fold more tubers and had five-fold greater total tuber mass. Large donor plants grew more, and produced significantly more inflorescences and legumes than small donors. Cutting treatment alone did not significantly affect any donor plant variable, showing that donor plants recovered quickly after cuttings were taken. Significant interactions (for stem diameter and inflorescence production of donor plants) suggested that cutting more greatly stimulated regrowth of large plants cut in June. We conclude that propagation by cuttings can rapidly produce plants of this species for ex situ conservation, but there are trade-offs in outcomes. Cuttings taken in May have an advantage for tuber production (producing more tubers and greater tuber mass), whereas cuttings taken in June affect donor plants less (although this effect was modest). Overall, propagation by cuttings is a useful technique for this rare species as it produces new plants yet minimally impacts wild populations.
Bee species that are effective pollinators of sunn hemp (Crotalaria juncea L.: Fabaceae: Crotalarieae) are few in number because of the large size and papilionaceous structure of the plant’s blossom. Seed for this potentially valuable cover crop is largely unavailable due to the paucity of pollinators and to the plant’s self-incompatibility. The introduced Megachile (Callomegachile) sculpturalis Smith (Megachilidae: Megachilinae), the giant resin bee, has the anatomy and behavior to be a most effective pollinator. While holding onto the upper vexillum petal of the blossom with her mandibles, this bee has the strength to depress the lower keel causing pollen to be expelled by the style through the small opening at the end. The bee is long enough for its metasoma to extend over the end of the keel, and, as a member of the family Megachilidae, has scopal hairs on the venter of the metasoma, which are thus in an optimal position to contact the pollen. Honey bees (Apis mellifera L.: Apidae) are common visitors to sunn hemp flowers but are too small to be effective pollinators. A honey bee worker robs the pollen by inserting her proboscis into the end of the keel and extracting the adhering pollen. Possible problems could result from mutual enhancement of populations of an exotic bee and an exotic plant.
Successful management of rare plant species requires understanding of reproductive life history. To assess reproductive attrition, the status of all reproductive units (expressed in seven stages) on 40 plants at The Nature Conservancy's Keel Mountain Preserve (Madison County, Alabama) was recorded throughout 4 yr (2009-12). Floral herbivory by Lepidopteran larvae (Geometridae) and abortion of reproductive units was common, with few flower buds (< 12%) producing mature fruits and the greatest attrition occurring during the smallest flower bud stage. Reproductive output was positively correlated with peak growth season rainfall (April-June); plants produced more fruits in wet years (2009 and 2011) than in drought years (2010 and 2012). Postdispersal achene predation assessed in a high-density Clematis area and a low-density Clematis area reached 15% after 1 wk and increased to 30% after 4 mo but did not significantly differ between high-density and low-density areas. Germination was documented by planting achenes in cages in high-density and low-density areas. Seeds remained dormant the first year and germinated in significantly greater amounts the second year (23%) compared to the third year (9%) after planting. Germination did not differ between high-density and low-density areas. This study documented high levels of floral herbivory, demonstrated the importance of growing season rainfall, revealed moderate levels of postdispersal achene predation, and confirmed the existence of a short-lived seed bank. Land managers can use these results to design management strategies to boost reproductive success of plants in declining or small populations.
Bumble bees (Bombus spp.) are important pollinators of both crops and wildflowers. Their contribution to this essential ecosystem service has been threatened over recent decades by changes in land use, which have led to declines in their populations. In order to design effective conservation measures, it is important to understand the effects of variation in landscape composition and structure on the foraging activities of worker bumble bees. This is because the viability of individual colonies is likely to be affected by the trade-off between the energetic costs of foraging over greater distances and the potential gains from access to additional resources. We used field surveys, molecular genetics, and fine resolution remote sensing to estimate the locations of wild bumble bee nests and to infer foraging distances across a 20-km2 agricultural landscape in southern England, UK. We investigated five species, including the rare B. ruderatus and ecologically similar but widespread B. hortorum. We compared worker foraging distances between species and examined how variation in landscape composition and structure affected foraging distances at the colony level. Mean worker foraging distances differed significantly between species. Bombus terrestris, B. lapidarius, and B. ruderatus exhibited significantly greater mean foraging distances (551, 536, and 501 m, respectively) than B. hortorum and B. pascuorum (336 and 272 m, respectively). There was wide variation in worker foraging distances between colonies of the same species, which was in turn strongly influenced by the amount and spatial configuration of available foraging habitats. Shorter foraging distances were found for colonies where the local landscape had high coverage and low fragmentation of seminatural vegetation, including managed agri-environmental field margins. The strength of relationships between different landscape variables and foraging distance varied between species, for example the strongest relationship for B. ruderatus being with floral cover of preferred forage plants. Our findings suggest that management of landscape composition and configuration has the potential to reduce foraging distances across a range of bumble bee species. There is thus potential for improvements in the design and implementation of landscape management options, such as agri-environment schemes, aimed at providing foraging habitat for bumble bees and enhancing crop pollination services.
Cotton is the most economically and culturally important fiber crop worldwide. Though cotton may potentially benefit from animal mediated pollination, it is unknown if the species is indeed pollen limited across agroecological landscapes. Our study had three objectives: (1) identify the land use attributes that impact wild pollinator abundance and diversity, (2) investigate the relationship between pollinator community composition and cotton pollen limitation and (3) determine the extent of direct and indirect effects of land use on pollinator community composition and pollination service. To address these objectives, we used a combination of pollinator community surveys, GIS analysis, and pollen limitation experiments across 12 cotton landscapes in South Texas. Overall, we found that pollinator community composition was closely related to the abundance of natural areas (250 m radius). We also found evidence of substantial cotton pollen limitation, as significantly larger bolls were produced with the addition of outcross pollen. Further, we reveal that pollen limitation was negatively correlated with pollinator abundance and richness. Path analysis confirmed the two direct effects of land use composition on pollinator community and pollinator community composition on pollen limitation. Overall, our results reveal potential for increased crop yields via wild pollinator-mediated fruit set, equivalent to more than 1.1 million USD. Further, our research provides insight into the specific land management practices that support pollinator communities within cotton agroecosystems. Cotton landscapes that maintain natural areas promote wild pollinator abundance and diversity, and subsequently experience reduced pollination limitation and increased crop yields.
Megachile (Callomegachile) sculpturalis Smith has been found in several parts of North Carolina, prompting our surveys for it in other states. Including the reports of others, the bee is in South Carolina, Georgia, Virginia, Maryland, the District of Columbia, Pennsylvania, West Virginia, Ohio, Tennessee, New Jersey, Connecticut, Delaware, New York, and Alabama. We also found it in southern Ontario, which is the first Canadian record. Its host plants include Koelreuteria paniculata, Sophora japonica, Ligustrum Iucidum, Ligustrum vulgare, Oxydendrum arboreum, Catalpa speciosa, Lathyrus latifolius, Lythrum salicaria, Buddleia, spp., Vitex spp., and Asclepias spp. When foraging on L. latifolius and S. japonica, M. sculpturalis sometimes punctures the standard petal with its mandibles, leaving a distinctive mark that is useful for surveys. Over half of the host plants reported here originate from Asia, which is also the native range of M. sculpturalis. Perhaps this favorable foraging environment has, in part, aided the establishment and spread of M. sculpturalis in the United States.
Flowers from diverse angiosperm families conceal their pollen within a keel. Visitors in search of nectar enter the narrow entrance between the movable keel and the opposed immovable flag. Thus, they secondarily release (doses of) pollen from its cover. As bees are the only visitors able to handle these flowers and thus their essential pollinators on one hand and the only pollen foragers on the other hand, keel blossoms are best understood as an adaptive response of plants to the dilemma of strong competition for pollen between flowers and bees.
Flowering invasive plants can potentially reduce pollination rates in co-flowering native plant species by attracting shared flower visitors. We investigate the effect of a prolifically flowering invasive species, Acacia saligna (Fabaceae), on native insect–flower interactions in surrounding communities. We surveyed flower visitation to A. saligna and selected native species at invaded and uninvaded areas and assessed the extent of flower visitor overlap of A. saligna and native species across four sites in South Africa’s Cape Floristic Region. Median visitation rates of bees and all insects were significantly lower to one native species (Roepera fulva) in both field seasons at the same site when A. saligna was present. This native species also had the highest flower visitor overlap with A. saligna which was driven primarily by the native honeybee, Apis mellifera subsp. capensis. Observational data showed that A. saligna inflorescences were visited most frequently by minute beetles and the native honeybee. Our findings indicate that native honeybees are important visitors to A. saligna, and that at least one native plant species experiences reduced flower visitation due to competition with A. saligna for honeybee visits. Flowering A. saligna could have wide-reaching effects on native plants by competing for visits from a super generalist flower visitor – the native honeybee – which may jeopardize the reproductive success of natives whose flowering time overlaps with that of A. saligna. Our study further highlights the importance of understanding the effect of a flowering invasive species on native species and the potentially important mutualism between A. saligna and honeybees.
Kudzu, Pueraria montana (Lour.) Merr. variety lobata (Willd.) was introduced into the United States at the 1876 Centennial Exposition in Philadelphia, PA. Subsequently, it was planted widely to reduce soil erosion by the Soil Erosion Service and Civilian Conservation Corp. Over 85 million seedlings of kudzu were provided to landowners by government agencies in the southeast in the first half of the 20th century. In 1953, kudzu was removed from the list of approved plants for erosion control, in 1970 it was officially labeled a weed, and in 1997 it was placed on the Federal Obnoxious Weed List. Its rapid elongation rates, high leaf area indices, high photosynthetic rates, and frequent rooting at stem nodes make kudzu an aggressive competitor with native shrubs and trees. Estimates are that kudzu currently covers 3 million hectares throughout the eastern United States and is spreading by 50,000 ha per year. Despite widespread anecdotal statements, little quantitative information is available regarding the ecological effects of kudzu. The ability of kudzu to overtop and shade forest trees, fix atmospheric nitrogen, and emit isoprene suggest that it may have substantial effects on native forest biodiversity, forest nitrogen cycles, watershed nitrogen saturation, freshwater eutrophication, and regional air quality. Kudzu's growth rate increases strongly in response to increased CO2, and without the constraint of allocation to woody tissue this response may increase the competitive dominance of kudzu as atmospheric levels of CO2 increase. This fact, combined with its sensitivity to cold temperatures, implies that kudzu may increase its range in future warmer, high-CO2 environments. The lack of quantitative investigations on the ecological effects of kudzu is a severe impediment to our understanding of its current and future effects on native plant and animal communities and forest ecosystems.
Two sonatic chromosome numbers were found for the leguminous plant Apios americana Medikus, i.e., 22 and 33. The former was interpreted as diploid, and the latter, as triploid. The triploid form predominated in the northern range of the species. The diploid was represented in northern material by a single collection (from Medoc, Ontario). A collection of plants produced from seeds obtained from a site in Tennessee was uniformly diploid. A combination of triploidy and self-incompatibility is suggested as the cause of the apparent complete sterility of the species over much of its range. Characterization of individual clones indicated that at least three different triploids were in existence. One of these was distributed over much of the northern range of the species. Chromosome counts of Apios priceana Robinson, a rare and the only other known American species in the genus, showed it to be a diploid with 22 somatic chromosomes.
The revision of Apios in North America is based on morphological analysis of herbarium specimens as well as field and greenhouse observations. The genus is herein recognized as consisting of two distinct species in North America. Apios priceana was described by Robinson in 1898. Currently it is listed as threatened by the United States Fish and Wildlife Service and is known from 47 populations in 22 counties in Alabama, Kentucky, Mississippi and Tennessee. The other species, A. americana, widely distributed in eastern North America, was first described by Cornut in 1633 and has been regarded as consisting of six infraspecific taxa, which are not recognized in the present treatment. Demarcation is based primarily on reproductive features as vegetative characteristics, both within and between species, exhibits a significant amount of variation. In addition to the taxonomic descriptions, dichotomous keys, illustrations and distribution maps are presented for each species.
s Abstract Bees are generally regarded as beneficial insects for their role in pol-lination, and in the case of the honeybee Apis mellifera, for production of honey. As a result several bee species have been introduced to countries far beyond their home range, including A. mellifera, bumblebees (Bombus sp.), the alfalfa leafcutter bee Megachile rotundata, and various other solitary species. Possible negative conse-quences of these introductions include: competition with native pollinators for floral resources; competition for nest sites; co-introduction of natural enemies, particularly pathogens that may infect native organisms; pollination of exotic weeds; and disrup-tion of pollination of native plants. For most exotic bee species little or nothing is known of these possible effects. Research to date has focused mainly on A. mellifera, and has largely been concerned with detecting competition with native flower visitors. Considerable circumstantial evidence has accrued that competition does occur, but no experiment has clearly demonstrated long-term reductions in populations of native or-ganisms. Most researchers agree that this probably reflects the difficulty of carrying out convincing studies of competition between such mobile organisms, rather than a genuine absence of competitive effects. Effects on seed set of exotic weeds are easier to demonstrate. Exotic bees often exhibit marked preferences for visiting flowers of exotic plants. For example, in Australia and New Zealand many weeds from Europe are now visited by European honeybees and bumblebees. Introduced bees are primary pollinators of a number of serious weeds. Negative impacts of exotic bees need to be carefully assessed before further introductions are carried out.
In contrast to other social bees, bumble‐bees exhibit considerable size variation within the worker caste. This size variation has not been adequately explained, although it is known that larger workers tend to be foragers and smaller bees spend more time in the nest. We quantify size variation and mean size for foragers of 22 bumble‐bee species inhabiting climates ranging from arctic and montane to the lowland tropics.
Mean size was larger in bee species from cold climates compared with temperate bumble‐bees. Within species, individuals from Scotland tended to be larger than those from southern England. However, tropical bumble‐bees (mostly belonging to the subgenus Fervidobombus ) were largest of all. We suggest that although a lower limit to size may be imposed by inhabiting cold climates, overheating does not constrain large size in bumble‐bees from hot climates, perhaps because they have efficient mechanisms for heat loss through shunting heat to their extremities.
Tropical bees had shorter thoracic setae than species from cooler climates, while B. terrestris from Greece had shorter setae than those from southern UK. Presumably shorter setae enhance heat loss in warm climates.
Larger workers of B. terrestris were found to have smaller extremities, in proportion to their size, than small workers. We suggest that heat retention is more important in large bees that spend more of their time foraging, than in small bees which spend much of their time in the nest where incubation of the brood requires them to lose heat.
In the temperate climate of southern UK, we found no evidence for ambient temperature having a differential effect on activity of workers of B. terrestris according to their size. We suggest that, at least in temperate climates, size variation in bumble‐bee foragers is probably not an adaptation to temperature variation. Instead it may improve colony foraging efficiency since foragers of different sizes are suited to, and tend to visit, different flower species.
In the flowers ofApios americana the vexillum remains in its bud position. In this way, a dark cavity is formed displaying a bright window at its base. Insect visitors are attracted to the hidden inflorescences by scent. In their attempt to reach the window they trigger an explosive release of stigma and pollen. Stigmatic fluid glues pollen to the visitor. All characters of the flower fit well into the myiophilous syndrome and thus flies are expected to be the proper pollinators.Apios americana seems to be the only myiophilous exception within the predominantly melittophilousFabaceae.
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