Proboscis Length Research Articles

Morphological approaches to community structure in hoverflies (Diptera, Syrphidae)

Simulation techniques are used to generate random communities of hoverflies that can be com pared with observed communities: both the species composition and morphological size ratios are compared. Patterns of morphology are also examined through the study of size ratios within taxa. Three sites were surveyed, two man-made garden habitats, and one ancient woodland. The man-made habitats contained assemblages of species indistinguishable from species assembled randomly from those present in the county (area = 3400 km 2 ) as a whole, given the assumptions of the random model. The ancient woodland site contained significantly fewer species in common with the man-made habitats than expected from the random model. Size ratios (of both absolute and relative proboscis length) show a similar pattern, with non-random (constant) ratios observed among the common species in ancient woodland. Significantly constant proboscis length ratios were detected in two genera, Eristalis and Platycheirus . In the former, these are due to regular ratios of general body size. In Platycheirus , species have significantly regular differences in relative as well as absolute proboscis length.

Morphometric patterns in hoverflies (Diptera, Syrphidae)

Multivariate techniques are used to elucidate the main patterns of variation in morphology between and within species. The major difference between species lies in proboscis length relative to body size, and only secondarily in aspects of body size uncorrelated with this. Within species, sexual dimorphism is associated with differences in abdomen width, and variation between individuals of one sex is predominantly of size differences.

Estimating Corolla Length in the Study of Bumble Bees and their Food Plants

SummaryDead worker Bombus honorum and queen B. terrestris bumble bees representing the narrowest elongate head and the broadest short head likely to be present in the local bumble bee population, were mounted as probes with their proboscides folded in the non-feeding position. The probes were inserted into the corollae of 60 plant species and the distance from the distal tip of the labrum to the bottom of the functional corolla tube, or spur, was recorded at each insertion. The measurements gave a minimum and maximum ‘exclusive corolla length’—the part of the corolla tube that can only be probed by the proboscis, because it cannot be entered by the bee's body. The mean exclusive corolla length varied from 0·8 mm for Anthriscus sylvestris to 18·9 mm for Mimulus guttatus in the species studied. The technique is intended to facilitate the interspecific collation of corolla lengths, proboscis lengths and bee sizes in studies of food resource availability.

Pollination system and its significance on isolation and hybridization in JapaneseEpimedium (Berberidaceae)

Observations on native populations of JapaneseEpimedium have revealed that two types of effective pollinators can be recognized. One of the two types, which consists of small bees (mainlyAndrena spp. andLasioglossum spp.), is characterized by nondiscriminating behavior for collecting pollen and is commonly found inEpimedium. The other type, which comprises medium sizedTetralonia nipponensis and largerBombus diversus queens as main components, showed flower-dependent foraging fidelity associated with nectar-sucking behavior.T. nipponensis with a shorter proboscis pollinated flowers with a shorter spur ofE. trifoliatobinatum and of a part ofE. s sempervirens, while the queen ofB. diversus with a longer proboscis pollinated longer spurred flowers ofE. grandiflorum andE. sempervirens. In the populations of putative hybrid-derivatives which show gradational variations of spur length, bees of the pollencollecting type pollinated any flower non-discriminately while bees of the nectar-foraging type tended to visit the flowers with spur lengths corresponding to their proboscis length. These observations suggest that the pollen-collecting bees play an important role for gene flow among theEpimedium species, and the nectar-foraging bees reinforce the isolation between the species by their selective pollination. Reproductive isolation between species ofEpimedium is discussed in relation with some practical behavior, such as flying power, of the pollinators.

Proboscis Length and the Coexistence of Bumblebee Species

Proboscis length spacings were studied among species in local and regional communities of bumblebees in Europe and North America. A simple numerical method has been developed which takes into account abundances of the species. Species in local and regional communities were arranged by descending abundance, and observed spacings in proboscis lengths were then calculated for increasing number (k) of species ranked by abundance. Observed spacings are compared with those obtained by making all possible k species combinations of the species pool of S species. Observed and expected spacings are compared by dividing their difference by the standard deviation of the expected spacing. In most of the studied communities the proboscis lengths of the most abundant species are more similar than expected on the basis of competition theory. The observed clustering of proboscis length of the 2 to 5 most abundant species in the communities is most likely the result of uneven availability of flower resources, classified by depth of corolla tubes of individual flowers.

THE POLLINATION DYNAMICS OF SYMPATRIC SPECIES OF PEDICULARIS (SCROPHULARIACEAE)

Sympatric populations ofPedicularis oederi, P. cystopteridifolia, andP. groenlandicaon the Beartooth Plateau (Montana) were obligately dependent onBombuspollinators. Their corolla colors were mutually distinct to insect vision, but their nectars had identical sugar components. Analysis of corbicular pollen loads of pollinating insects indicated a high degree of polylecty. Queen/worker ratios of pollinators on plant species corresponded to the parallel phenological sequences of plant blooming and insect caste development. The total number of individual pollinators of eachBombusspecies on all plants was directly related to the number of plant species it pollinated, but a comparable relationship between the number of pollinators on a plant species to the number ofBombusspecies pollinating it was not found. Morphological and behavioral correspondence of floral mechanisms and pollinators form an integral part of the general pattern of coadaptive evolution of the floral ecology ofPedicularisin North America known from previous studies. Reproductive isolation betweenPedicularisspecies in this study is attributed to internal barriers. Wide overlaps of blooming seasons, proboscis lengths of bumblebee species and castes, and pollinator species onPedicularisspecies suggest resource sharing, rather than resource partitioning or competition for resources among plant and insect species and individuals.

Behavior of Hawkmoths on Flowers of Datura meteloides

Datura meteloides is pollinated mainly by long-tongued hawkmoths: Manduca quinquemaculata, M. sexta, and Hyles lineata. The most abundant and important of these species in the Arizona and New Mexico populations studied is M. quinquemaculata. There is good correspondence between the proboscis length of M. quinquemaculata (10 ± 1.2 cm) and corolla tube length of D. meteloides (10.5-11.0 cm) The Manduca moths feeding on D. meteloides flowers in the Arizona populations behaved in an intoxicated manner All parts of this plant, including the flowers, are known to contain tropane alkaloids, and such alkaloids may well occur in the nectar also. Intoxicating substances in nectar or other floral tissues could represent a new or little known type of floral reward to look for in other plant groups

Measurement and estimation of functional proboscis length in bumblebees (Hymenoptera: Apidae)

Analysis of a 16-mm cinefilm of feeding bumblebees (Bombus) indicated that the glossa is the functional unit of proboscis length. This was corroborated by observations of the depth to which wild bees probed Impatiens biflora and by data presented in the literature. Accurate measurement of the glossa length of bees that died with their proboscides folded is facilitated by straightening the labium by dissection. Regression equations describing the relation between glossa and wing length, derived from bees from a single colony, provide sufficient accuracy to allow prediction of glossa length for that species in a field study.

Local Geographic Distributions of Bumblebees Near Crested Butte, Colorado: Competition and Community Structure

It was hypothesized that the local geographic distributions of bumblebees near Crested Butte, Colorado and the community patterns exhibited by these bumblebees are the products of competition for plants. To evaluate this hypothesis several transects were established and at regular intervals throughout a summer growing season, data were collected along each transect on how many bumblebees of each species and caste were visiting the various plant species. The distributions and abundances of the plant species involved were recorded qualitatively. Seven species of bumblebees accounted for 97% of all bumblebees observed and in this paper attention is restricted to these species. Five other species were observed in very low numbers. Each bumblebee species had a different distributional pattern. The seven bumblebee species form four groups in terms of both their proboscis lengths and the corolla lengths of the plants they preferentially visit. Long—, medium—, and short—tongued groups were most often observed foraging at flowers with long, medium, and short corollas, respectively. Furthermore proboscis lengths of bumblebees tended to be very similar within each group but quite dissimilar between groups. The fourth group consisted of a single short—tongued species which has well—developed mandibles which enable it to rob nectar from many plants with long corollas. It also feeds legitimately on short—corolla flowers. Some anomalies in the above groupings are mentioned and discussed. When the data on bumblebees and plant distributions are combined with data on flower preferences, a pattern consistent with the competition hypothesis emerges. Within each proboscis—length group, bumblebee species tend to replace one another altitudinally in a manner consistent with the hypothesis. The nectar—robbing species is most abundant in areas where a plant that is usually visited by hummingbirds is most common. Other species of bumblebees are unable to gain access to the nectar of this plant. In any uniform well—isolated area, similar floristically to the present study area, only three or four species of bumblebees appear to be able to coexist. Furthermore, a bumblebee community in such an area will apparently consist of a short—, a medium—, and a long—tongued species and in some cases a short—tongued nectar—robber. These patterns are also consistent with the competition hypothesis, as similarity in proboscis length reflects similarity in diet and the intensity of competition should, for these bumblebees, be closely related to diet similarity. It is possible that the observed distributional patterns could also be explained on the basis of different distributions of suitable nest sites for each bumblebee species or different responses to local variations in climatic conditions. Neither alternative seems able, however, to explain the observed patterns.

Species Structure of North European Bumblebee Communities

The structure of North European bumblebee communities was studied on regional and local scales. As the bumblebee proboscis has a potentially important role in resource partitioning, the structure of bumblebee communities was analysed in terms of proboscis length relationships. The regional numbers of bumblebee species in 100-km squares in NW Europe were frequently between 11 and 15. No obvious south to north gradient in species richness was found. The slightly lower regional numbers of species in Finland are suggested to be due to the lack of alpine habitats with associated species. England and Ireland have fewer species than equally sized areas in Scandinavia. Most of the bumblebee species (25/29) in Northern Europe have proboscises shorter than 12 mm. Short-tongued species tend to be more widely distributed than those with long tongues. B. hortorum, a long-tongued species, deviates clearly from this trend by being more widely distributed than the other species with a long proboscis, all of which are either habitat (alpine) or food specialists. Local communities consist of a number of coexisting species, most of which differ only slightly in terms of proboscis length. Only a few species (1-3 per community) have long proboscises and these species are seldom abundant. When species in the realized communities were compared in terms of proboscis length distances, no statistically significant differences were revealed from distances expected on the basis of random sampling from the local species pool. The same was the case also when only the abundant species were taken into account. Thus, propositions advocating proboscis length differences and food competition as the single assembly rule of bumblebee communities should be supported by good evidence. Other conceivable factors include competition for nesting sites, nest predation, and other mechanisms that shape the present-day local communities and regional species pools.

Structure in seven bumblebee communities in eastern Finland in relation to resource availability

The structure of seven local bumblebee communities was studied in eastern Finland. The number of species in the study sites varied from 5 to 10, 11 being the number in the species pool. Most of the species (queens) had proboscis lengths of 8–11 mm. When floral resources were analysed on the basis of corolla tube depths, a group was found between 4 and 8 mm. In terms of flower utilization, species with similar proboscises had higher pairwise niche overlaps than species differing by their proboscis lengths.Spacing between neighbouring species along the proboscis length dimension was not more uniform in the realized communities than what was expected on the basis of random draws from the local species pool. The results were the same for all species observed in the communities and for the abundant species only (frequency >5%), although competition among species in the latter group is expected to be more intense.When the structure of bumblebee communities and of floral resources was expressed in terms of diversity of proboscis lengths and corolla tube depths, respectively, a positive correlation was found. Data suggest that species with similar proboscis tend to co‐occur on fields with availability of appropriate corolla tubes.

Resource utilization by bumblebee queens, workers and males in a subarctic area

We studied the seasonal dynamics of food niche width and annual niche relations of queens, workers and males of six abundant bumblebee species living on a slope of a subarctic hill in North Sweden. The basic data consist of analyses of pollen contents in nectar loads of individual foragers. At any given time of the season individual foragers utilized frequently more than one flower species during each trip, concentrating, however, most of their efforts on one species only. These “major” species varied between individuals thus widening the foraging niche of the species. No obvious differences were observed in niche widths of the sexes and castes of the species (neither day‐to‐day nor annual observations). Queens had highest niche overlaps and males the lowest ones. Sexes and castes were separated into groups by their foraging patterns. Differences in proboscis lengths are not obvious niche separating factors at the study area. The environmental uncertainty (in time and space) may occasionally lead to excess of resources, which, in turn, may open possibilities of wide utilization of available flower species, thus rendering close fit between proboscis length and corolla tube depths of the foraged flowers unnecessary.

Why Are There So Many Species? Spatio-Temporal Heterogeneity and Northern Bumblebee Communities

It is proposed that (1) the different body sizes and proboscis lengths of bumblebee species lead to different optimal foraging patterns in different species. The morphological differences affect niche relations, depending on the pattern of the resource environment. Tongue morphology allows only a basic set of three to four species per community, differing by proboscis length and frequency in indulging in robbery. To explain considerably higher community species numbers (frequently between six and eleven species), (2) the effect of superabundant resources was examined. Data suggest that species-rich bumblebee communities exist locally by the Schlaraffenland effect. As few of the bumblebee communities are located at fields of superabundant resources, or in non-competitive environments, other coexistence mechanisms were sought for. (3) Intensified intraspecific competition relative to interspecific competition may theoretically allow coexistence, but supporting evidence is still lacking. (4) Spatio-temporal heterogeneity was advocated as the main coexistence mechanism: the energy available for colony growth changes seasonally and depends to a large extent on the location of the nest relative to dynamically changing resources. This may lead to temporal reversions in the competitive relations between the colonies and species. All three tests available suggested that spatio-temporal heterogeneity suffices in explaining the high species numbers in northern bumblebee communities. However, specific features of bumblebee foraging behaviour call for measurements of withinand between-colony competition.

Patterns of Resource Utilization in Two Fennoscandian Bumblebee Communities

We studied seasonal changes in food niche relations among species in two Fennoscandian bumblebee communities. A community in southern Finland composed of 8 species utilized altogether 59 flower species during the whole summer. Corresponding figures for a community in northern Sweden were 9 bumblebee species and 50 flower species. Three bumblebee species were common to both communities. The flowering periods of the resource plants were longer in the southern community than in the northern one. In the southern community, but not in the northern one, the observed weekly niche overlaps were smaller than those to be expected assuming random foraging. During the whole season most species utilized more than 15-20 flower species in both areas, concentrating, however, most of their visits to a few of them. Niche overlaps (whole season combined) and differences between the frequency distributions of proboscis length and utilized corolla tube depths, respectively, were smaller in the southern community than in the northern one. These discrepancies may be due to a more stable resource production in the southern community contributing to a more intensive competition between species.

Resource Partitioning in Bumblebees: The Significance of Differences in Proboscis Length

The resource utilization by nine species of bumblebees in a subarctic community was studied by analysing the distribution of the depths of the corolla tubes of the visited flower species. When measured in this way, the food niches of the bumblebee species showed a wide overlap. Species with a long proboscis could use flowers with short corolla tubes for feeding, whereas the reverse was rare. We postulate that foraging efficiency is maximal when the proboscis length of a species corresponds to the corolla tube depth of the flower visited. An analysis of published data supports this hypothesis. The paucity of plant species with deep corolla tubes thus explains the small number and low abundance of bumblebee species with long proboscis. The continuously changing pattern of corolla tube depths due to the seasonal succession of plant species facilitates the coexistence of many bumblebee species in a community in spite of small differences in proboscis length.

The effect of proboscis and corolla tube lengths on patterns and rates of flower visitation by bumblebees.

The rates at which bumblebees of different proboscis lengths forage on flowers of a series of corolla tube lengths were determined. The results indicate significant correlations between proboscis length and time spent by bees on flowers. Bumblebees of long proboscis length can forage significantly faster than bees of shorter proboscis length on flowers with long corolla tubes. There is also evidence which suggests that bumblebees of short proboscis length prefer and are more efficient on short corolla tubes. These results support the use of proboscis length as a morphological indicator of resource utilization in bumblebees.

Geographic and Host-Related Variation among Species of Fessisentis (Acanthocephala) and Confirmation of the Fessisentis fessus Life Cycle

Specimens of the 4 known species of Fessisentis, acquired through new collections in 6 states and laboratory infections, were compared with existing descriptions and collections. It was concluded that the number od longitudinal rows of proboscis hooks and lengths of proboscis receptacles, largest proboscis hooks, and reproductive systems are not useful in distinguishing the species. Egg size is of limited usefulness. Regardless of host or geographical locality, proboscis shape and length, the number of proboscis hooks in each longitudinal row, hook shape and size distribution, number of testes, number of cement glands, and female genital pore position are consistent differences. Cystacanths of Fessisentis fessus occurred in aquatic isopods, Asellus forbesi and Lirceus lineatus, in Jackson County, Illinois, where Siren intermedia is the usual definitive host. Laboratory infections confirmed the life cycle of this species.

Meristogram Analysis of the Acanthocephalan Genus Pomphorhynchus in North America

Meristogram analysis revealed that specimens of Pomphorhynchus bulbocolli and P. rocci can be easily distinguished by measuring the length of one hook in the 60-80 region of the proboscis. Percent-position of a hook is calculated by multiplying the counted posteriad position number of the hook by 100 and then dividing by 1 + the number of hooks in that longitudinal row. Hooks in the 60-80 percent-position region are longer than 37 aum in P. rocci and shorter than 37 ,um in P. bulbocolli. P. rocci was found not only in the coastal marine fishes to which it was formerly thought to be restricted, but also in freshwater fishes of coastal brackish and freshwaters. The Pomphorhynchus fauna of North American fishes is generally thought to consist of two species, P. bulbocolli Linkins in Van Cleave 1919, and P. rocci Cordonnier and Ward 1967. Pomphorhynchus bulbocolli was first described from fishes of the Illinois River by Linkins in an unpublished thesis. Van Cleave (1919) later published the description but did not provide diagnostic hook drawings and apparently did not designate type and paratype specimens. Cordonnier and Ward (1967) described Pomphorhynchus rocci from Morone (= Roccus) saxatilis caught commercially near Elizabeth City, North Carolina. Informative hook drawings accompanied the description and a type collection was deposited in the USNM Helm. Coll. P. rocci was distinguished as a new species primarily on the basis of possessing longer necks and bodies than P. bulbocolli and in having proboscides armed with 15-18 hooks in each longitudinal row rather than the 12-14 hooks/row reported in Van Cleave's description of P. bulbocolli. When subsequent collections produced Pomphorhynchus specimens from freshwater hosts with more than 14 hooks/row and specimens from marine hosts with fewer than 15 hooks/row, and the purported differences in neck and trunk lengths were shown not to exist (Samuel, Nickol, and Mayes, 1976), the validity of P. rocci was questioned. Samuel et al. (1976) studied Pomphorhynchus specimens from several hosts and localities in the hope that the additional morphological Received for publication 7 February 1978. data would provide characters that would distinguish P. bulbocolli from P. rocci. However, they were unable to sort the specimens into two groups using conventional characters such as number of longitudinal rows of proboscis hooks, number of hooks in each row, proboscis length, and trunk length, and were forced to assume that all specimens from freshwater hosts were P. bulbocolli. As will be shown later, this led to inclusion of some data from P. rocci specimens in their redescription of P. bulbocolli. Jensen (1952) found Pomphorhynchus larvae infecting Hyalella azteca. Johnson and Harkema (1971) found larvae in Gammarus tigrinus. Attempts by Johnson (1973, pers. comm.) to cross-infect were futile, suggesting that two distinct Pomphorhynchus populations were involved in spite of morphological similarity. A similar problem involving morphologically indistinguishable species of Echinorhynchus from the fishes of New England was resolved by meristogram analysis (Huffman and Bullock, 1975). Consequently, this technique was applied to several Pomphorhynchus collections with the hope that reliable morphological distinctions between the two Pomphorhynchus species could be discovered. MATERIALS AND METHODS Thirteen collections of North American Pomphorhynchus were exposed to meristogram analysis. Table I lists the code name, locality, and number of specimens analyzed for each collection. In order for a specimen to be suitable for meristo-

Resource Partitioning in Bumblebees: Experimental Studies of Foraging Behavior

A system comprising 2 species of bumblebess (Bombus appositus and Bombus flavifrons) and 2 species of flowers (Delphinium barbeyi and Aconitum columbianum) in Gothic, Colorado, USA, was manipulated to determine whether resource utilization by each bumblebee species was influenced by the presence of the other species of bumblebee. Each bumblebee species concentrated its foraging efforts on a different flower species, apparently choosing the species whose corolla tube length matched its proboscis length most closely. When each bumblebee species was temporarily removed from its preferred flower species, the remaining bumblebee species increased visitation to the other, previously less—utilized, flower species. The remaining bumblebees visited more flowers per stay in the patch, suggesting that they were finding greater amounts of nectar in the absence of other bumblebee species. These removal experiments demonstrated that the bumblebees were sampling flowers frequently enough and were flexible enough in their foraging behavior to respond rapidly to short—term changes in nectar availability. In another area, where its preferred flower species and the other bumblebee species were absent, B. flavifrons foraged actively on the flower species it rarely used in Gothic. This observation and the experiments demonstrate that resource utilization by a bumblebee species is influenced by the presence of other species and suggest that the phenomenon of competitive release can be observed in bumblebees. In this system,interspecific exploitation competition appears to be the primary mechanism involved in resource partitioning.

Pollination Ecology of Vernal Angiosperms

Pollination interrelationships of vernal, herbaceous angiosperms in a deciduous forest in southwestern Ohio, USA, were studied for 3 seasons with particular emphasis on phonological integration of the bionomics of flowers and the annual colonies of Bombus pollinators. Except for Corydalis flavula, all plants were insect or bird-dependent for pollination. In general, the spectrum of Bombus species on flowers was related to time of emergence from hibernation of bumblebee queens, sequence of anthesis, depth of nectariferous tubes or spurs of flowers in relation to measured proboscis lengths of bumblebee foragers, and site preference for pollinator nesting and foraging. Spectral reflectance from corollas measured spectrophotometrically indicated general correspondence of corolla color and visual spectra of pollinators. Analysis of nectars by refractometry and thin-layer chromatography revealed no preference of pollinators for particular sugars in nectar nor for particular sugar concentrations. Such preference is considered to be related to availability and abundance of nectar. As determined by analysis of corbicular pollen loads from pollinators, fidelity of bumblebee queens to specific flowers was 60%. Only 9.5% of 1457 queens investigated foraged for pollen. Close correspondence of floral form and insect behavior was indentified by means of cinematography and stereophotographic analysis of pollinator activity. Except for possible interactions between Dicentra species and Corydalis, no clear evidence for competition between pollinators for forage or between plant species for pollinators was observed. The pollination system of the vernal flora is considered to reflect a high degree of coadaptive integration of phenological, ethological, and morphological phenomena in dynamic homeostasis involving constant, but very gradual, change.