The population genetics of two orchid bees suggests high dispersal,low diploid male production and only an effect of island isolation in lowering genetic diversity

Orchid bees (Hymenoptera, Apidae, Euglossini) are important pollinators of many plant families in Neotropical forests, habitats that have become increasingly degraded and fragmented by agricultural practices. To understand the extent to which loss of natural habitat and isolation has affected the genetic diversity and diploid male production (DMP) of two orchid bee species, Euglossa dilemma and Euglossa viridissima, we collected and genotyped 1686 males at five microsatellite loci and tested for differences in allelic richness, heterozygosity and DMP across three different types of land use (natural, agricultural and urban) and between mainland and island populations in the Yucatan Peninsula of Mexico. We also investigated the impact of land use and geographic isolation on gene flow. Euglossa dilemma and E. viridissima seemed to be particularly resilient to loss of natural habitat; in locations with human impact, we did not find reduced genetic diversity, and populations generally showed very little population genetic structure. Only on islands did E. dilemma show significantly reduced genetic diversity. Even after accounting for putative null alleles, DMP was very low (0.2–1.3%) across all sampling sites, including on islands. We therefore suggest that DMP is an insensitive measure of inbreeding and population decline in our two study species.     

Potential distribution of orchid bees outside their native range: The cases of Eulaema polychroma (Mocsáry) and Euglossa viridissima Friese in the USA (Hymenoptera: Apidae)

Aim This study aimed to evaluate the probability of suitable habitats in the USA for two adventive orchid bee species (Eulaema polychroma (Mocsáry) and Euglossa viridissima Friese), one of which has become established in southern Florida despite the absence of its associated orchid hosts. Location North and Central America, northern South America and the Caribbean. Methods Using positive occurrence data within the native range of both orchid bee species, Maxent species distribution modelling was employed to evaluate the probability of suitable habitats in the USA. The power of predictability for the model was tested using partitions of the data. Results Our results show the absence of suitable habitat in southern Arizona for E. polychroma to maintain populations there, as well as establishing the northernmost limit for the species at around 29°N in north‐western Mexico. Suitable habitat was found for E. viridissima in various locations throughout southern Florida. This species is predicted to spread to occupy roughly the southern half of the Florida Peninsula. Main conclusions The findings indicate that species distribution modelling is useful for evaluating records of species occurrence outside of their native range. Our results indicate that the isolated record of a male of E. polychroma from southern Arizona should not be considered representative of an established population in the absence of further males and females from the same region. Conversely, E. viridissima has successfully become established in south‐eastern Florida after a seemingly accidental introduction first noticed in the summer of 2003. We discuss the naturalization of E. viridissima in Florida, the probability of suitable habitat across the Caribbean (where orchid bees are otherwise natively absent today) and the absence of perfume orchids (Orchidaceae). Lastly, we discuss the implications of these results for understanding the biology and biogeography of Euglossini.     

Solitary invasive orchid bee outperforms co-occurring native bees to promote fruit set of an invasive Solanum

Our understanding of the effects of introduced invasive pollinators on plants has been exclusively drawn from studies on introduced social bees. One might expect, however, that the impacts of introduced solitary bees, with much lower population densities and fewer foragers, would be small. Yet little is known about the potential effects of naturalized solitary bees on the environment. We took advantage of the recent naturalization of an orchid bee, Euglossa viridissima, in southern Florida to study the effects of this solitary bee on reproduction of Solanum torvum, an invasive shrub. Flowers of S. torvum require specialized buzz pollination. Through timed floral visitor watches and two pollination treatments (control and pollen supplementation) at three forest edge and three open area sites, we found that the fruit set of S. torvum was pollen limited at the open sites where the native bees dominate, but was not pollen limited at the forest sites where the invasive orchid bees dominate. The orchid bee’s pollination efficiency was nearly double that of the native halictid bees, and was also slightly higher than that of the native carpenter bee. Experiments using small and large mesh cages (to deny or allow E. viridissima access, respectively) at one forest site indicated that when the orchid bee was excluded, the flowers set one-quarter as many fruit as when the bee was allowed access. The orchid bee was the most important pollinator of the weed at the forest sites, which could pose additional challenges to the management of this weed in the fragmented, endangered tropical hardwood forests in the region. This specialized invasive mutualism may promote populations of both the orchid bee and this noxious weed. Invasive solitary bees, particularly species that are specialized pollinators, appear to have more importance than has previously been recognized. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Subtle visits despite guards: Theft from nest of stingless bee (Meliponini) by orchid bee (Euglossini)

The theft of food items and building materials from nests of stingless bees (Hymenoptera: Apidae: Meliponini) is most commonly carried out by other Meliponini bee species, especially by those related to genus Lestrimelitta Friese, 1903. In this note, we recorded the theft of cerumen and propolis made by a species of the orchid bee, Euglossa annectans Dressler, 1982 (Apidae: Euglossini) from the nest of the stingless bee Tetragonisca angustula (Latreille, 1811). We noticed that the guard workers of T. angustula did not attack the thief bee even though it did not come sufficiently close to the entrance tube of the nest.     

Phylogeny,diversification patterns and historical biogeography of euglossine orchid bees (Hymenoptera: Apidae)

The orchid bees constitute a clade of prominent insect pollinators distributed throughout the Neotropical region. Males of all species collect fragrances from natural sources, including flowers, decaying vegetation and fungi, and store them in specialized leg pockets to later expose during courtship display. In addition, orchid bees provide pollination services to a diverse array of Neotropical angiosperms when foraging for food and nesting materials. However, despite their ecological importance, little is known about the evolutionary history of orchid bees. Here, we present a comprehensive molecular phylogenetic analysis based on ～4.0 kb of DNA from four loci [cytochrome oxidase (CO1), elongation factor 1‐α (EF1‐α), arginine kinase (ArgK) and RNA polymerase II (Pol‐II)] across the entire tribe Euglossini, including all five genera, eight subgenera and 126 of the approximately 200 known species. We investigated lineage diversification using fossil‐calibrated molecular clocks and the evolution of morphological traits using disparity‐through‐time plots. In addition, we inferred past biogeographical events by implementing model‐based likelihood methods. Our dataset supports a new view on generic relationships and indicates that the cleptoparasitic genus Exaerete is sister to the remaining orchid bee genera. Our divergence time estimates indicate that extant orchid bee lineages shared a most recent common ancestor at 27–42 Mya. In addition, our analysis of morphology shows that tongue length and body size experienced rapid disparity bursts that coincide with the origin of diverse genera (Euglossa and Eufriesea). Finally, our analysis of historical biogeography indicates that early diversification episodes shared a history on both sides of Mesoamerica, where orchid bees dispersed across the Caribbean, and through a Panamanian connection, thus reinforcing the hypothesis that recent geological events (e.g. the formation of the isthmus of Panama) contributed to the diversification of the rich Neotropical biota. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 552–572.     

Raising the Sugar Content – Orchid Bees Overcome the Constraints of Suction Feeding through Manipulation of Nectar and Pollen Provisions

Unlike most other bees, the long-tongued orchid bees ingest nectar using suction feeding. Although long tongues allow exploitation of flowers with deep spurs, the energy intake rate is optimal at 10–20% lower nectar sugar concentrations compared to that of lapping bees. This constraint might be compensated by a higher digestive throughput. Additionally, orchid bees might evaporate water from regurgitated droplets of crop contents. We found male Euglossa championi (n = 10) and Euglossa dodsoni (n = 12) to regularly regurgitate droplets of crop content to the base of their proboscis, generating a fluid film between the proximal parts of the galeae, glossa and labial palps. Rhythmic movements of the proboscis may help to increase convection. There was a significant change in sugar concentration between the initially imbibed solution and the resulting crop content (P<0.05) and the time individual bees had engaged in this liquid exposure behavior was positively correlated with the resulting crop sugar concentration. Female Euglossa townsendi and Euglossa viridissima showed the same behavior. Additionally, they manipulated their nectar-enriched pollen provisions for extensive periods of time before deposition in brood cells. The deposited pollen loads (n = 14) showed a significantly higher sugar concentration than the sugar-water available to the bees (P<0.001). Thus, both male and female euglossines show behaviors that promote evaporative water loss from nectar. We suggest that the behaviors have evolved in concert with suction feeding on dilute nectar from deep floral tubes.     

Revision of the orchid bee subgenus Euglossella (Hymenoptera, Apidae), Part I, The decorata species group

Euglossella, one of the most distinctive subgenera of orchid bees of the genus Euglossa, is composed of two characteristic assemblages of species, one of them comprising bees bearing the strongly metallic integument trademark of the genus (viridis species group), and the other consisting of bees with a brown integument shaded with metallic iridescence (decorata species group). Here we provide the first of two parts of a revision of Euglossella, providing diagnostic definitions for the subgenus, the decorata species group, and all the species included therein. Six species are included in the decorata group, one new: Euglossa (Euglossella) aurantia, sp. n.; Euglossa (Euglossella) apiformis Schrottky, resurrected status; Euglossa (Euglossella) decorata Smith, revised status; Euglossa (Euglossella) singularis Mocsáry, revised status; Euglossa (Euglossella) cosmodora Hinojosa-Díaz and Engel; and Euglossa (Euglossella) perpulchra Moure and Schlindwein. Euglossa meliponoides Ducke and Euglossa urarina Hinojosa-Díaz and Engel are newly synonymized under Euglossa decorata, Euglossa decorata ruficauda Cockerell is synonymized under Euglossa singularis, and a neotype is designated for Euglossa apiformis.     

Are body size and volatile blends honest signals in orchid bees?

Secondary sexual traits may convey reliable information about males’ ability to resist pathogens and that females may prefer those traits because their genes for resistance would be passed on to their offspring. In many insect species, large males have high mating success and can canalize more resources to the immune function than smaller males. In other species, males use pheromones to identify and attract conspecific mates, and thus, they might function as an honest indicator of a male's condition. The males of orchid bees do not produce pheromones. They collect and store flower volatiles, which are mixed with the volatile blends from other sources, like fungi, sap and resins. These blends are displayed as perfumes during the courtship. In this study, we explored the relationship between inter‐individual variation in body size and blend composition with the males’ phenoloxidase (PO) content in Euglossa imperialis. PO content is a common measure of insect immune response because melanine, its derived molecule, encapsulates parasites and pathogens. Body size and blend composition were related to bees’ phenolic PO content. The inter‐individual variation in body size and tibial contents could indicate differences among males in their skills to gain access to some compounds. The females may evaluate their potential mates through these compounds because some of them are reliable indicators of the males’ capacity to resist infections and parasites.     

Seasonal stability and species specificity of environmentally acquired chemical mating signals in orchid bees

Traits that mediate reproductive isolation between species, such as those involved in mate choice and/or recognition, are predicted to experience stabilizing selection towards the species mean. Male orchid bees collect chemical compounds from many sources, such as plants and fungi, which they use as a perfume signal (pheromone) during courtship display, and are suggested to contribute to reproductive isolation between species. Environmentally acquired signals are more prone to variation as source availability can vary through space and time. If orchid bee perfumes are important for reproductive isolation between species, we expect them to exhibit stable species-specific differences in time and space. Here, we describe phenotypic patterns of inter- and intraspecific variation in the male perfumes of three sympatric species of Euglossa orchid bees across an entire year, investigating both their seasonality and species specificity. Our analysis revealed considerable within-species variation in perfumes. However, species specificity was maintained consistently throughout the year, supporting the idea that these perfumes could play an important role in reproductive isolation and are experiencing stabilizing selection towards a species mean. Our analysis also identified strong correlations in the abundance of some compounds, possibly due to shared collection sources between species. Our study suggests that orchid bee perfumes are robust in the face of environmental changes in resource availability and thus can maintain reproductive isolation between species.     

The behaviour of male orchid bees (Apidae,Hymenoptera, Insecta) and the question of leks

The male territories of two species of orchid bees, Eulaema meriana and Euglossa imperialis, are described. These territories consist of a perch, where the males display on the trunk of a tree, and a route flown from and back to the perch. Territories are located in treefalls or other large light gaps in tropical forest. The territories of these two species differ in the height of the perch and amount of light reaching it, size of the perch tree, and period of activity. A definition of lek is given. These male euglossines form facultative leks in large treefalls. The relationships between male territories, female foraging ranges, and collection of aromatic material by males are discussed.     

Three new cryptic species of Euglossa from Brazil (Hymenoptera,Apidae)

Three new species of orchid bees are described and figured from the Amazon and Atlantic forests of Brazil. Euglossa clausi sp. n., Euglossa moratoi sp. n., and Euglossa pepei sp. n. are distinguished from their close congeners Euglossa crassipunctata Moure, Euglossa parvula Dressler, and Euglossa sapphirina Moure, previously placed in the subgenus Euglossa (Glossurella) Dressler, 1982, a demonstrably paraphyletic assemblage requiring serious reconsideration. Their affinities with related species are discussed and pertinent characters are figured.     

Sociality in <Emphasis Type="Italic">Euglossa</Emphasis> (<Emphasis Type="Italic">Euglossa</Emphasis>) <Emphasis Type="Italic">viridissima</Emphasis> Friese (Hymenoptera,Apidae, Euglossini)

Euglossa viridissima is an orchid bee that forms both solitary and multiple female nests, making it a suitable species for the study of factors leading to diverse degrees of sociality in Euglossines. We conducted observations in eight reused nests (where a first generation of bees had been produced) kept in artificial boxes from the Yucatan Peninsula, Mexico. Five nests were reused (reactivated) by a single female (SFN), two nests reused by a mother and one daughter (MFN1) and one nest reused by the mother and two daughters (MFN2). No single nest was reactivated by unrelated females. The number of foraging trips, their duration and the duration of cell provisioning was not different between SFN and MFN. The overall production of cells per female was not different either between both types of nest. However, in MFN although all females did lay eggs, there was a reproductive skew in favor of the mother (95 and 45% of the brood produced in MFN1 and MFN2 respectively). She showed reproductive control of her daughters through oophagy and displaying threatening behavior when the daughters tried to open a cell where she had laid an egg. Brood losses to parasites (Anthrax sp. (Bom-byliidae) and Hoplostelis bivittata (Megachilidae)) were only found in SFN which possibly reflects and advantage of MFN in this respect. Our results coupled with other studies in Euglossa, reveal that a wide range of social behaviors occur in this genus, from solitary and communal to primitive reproductive division of labor. Multiple factors involving different levels of pressure imposed by food availability and parasites may favor such a diverse range of nesting behaviors. Interestingly, female associations in E. viridissima seem a result of kin selection that is enforced by coercion from mother females on their daughters. More studies are needed to shed light upon the social organization of Euglossa and other Euglossines and on their phylogenetic relationships in order to trace the origins of eusociality in Apidae. Received 12 February 2008; revised 25 June 2008; accepted 17 July 2008.     

Searching for Euglossa cyanochlora Moure, 1996 (Hymenoptera: Apidae), one of the rarest bees in the world

Euglossa cyanochlora Moure, 1996 (Hymenoptera: Apidae: Euglossina) is known from only two specimens and is considered as one of the rarest bees. An intensive search for this species in its expected area of occurrence in eastern Brazil was carried out during three consecutive summers and involved over 1,000?h of active sampling in 50 sites distributed among 20 forest remnants. Almost 15,000 orchid bee males were attracted to scent baits and collected, but only 24 of them belonged to E. cyanochlora. Some degree of mitochondrial gene (COI, cytB, and 16S) variation was observed in this species. Although no intra-specific variation was identified at the 16S locus, three and six haplotypes were characterized at the COI and cytB genes, respectively. Combined data from field work and molecular analysis suggest that the species southernmost distribution limit is close to its type locality, near Parque Nacional do Monte Pascoal, in southern Bahia. The conservation status of E. cyanochlora is discussed and measures for its protection are here proposed.     

Molecular identification of species of the genus Euglossa Latreille (Hymenoptera: Apidae, Euglossini)

Euglossine bees interact with more than 60 plant families of the Neotropical region. The richness and abundance of these bees have been intensively studied in different ecosystems using the methodology of capturing males with chemical baits. Females are poorly known for most of the species and morphological characters for their taxonomic classification have not yet been described. The purpose of this study was to use allozymes and restriction patterns of the mitochondrial regions 16S and Cyt b to identify species of Euglossa Latreille. Bees were collected while visiting Thevetia peruviana (Apocynaceae) flowers in five cities of the state of S?o Paulo, Brazil. Three Euglossa species were identified among the 305 individuals collected. Euglossa cordata (L.) was the only species found in all cities, while E. securigera Dressler and E. townsendi Cockerell were restricted to two and one cities respectively. EST-3 was a diagnostic marker, whereas ICD, MDH, ME and PGM were informative for species identification when used in combination. Restriction by VspI of the amplified 16S fragment differentiated the three species and showed intraspecific polymorphism for E. cordata and E. securigera. The Cyt b region showed distinctive patterns for E. townsendi but it was not possible to differentiate the other two species. Our results describe potentially useful genetic markers for the identification of Euglossa spp. at the species and group level.     

Shared reproduction and sex ratio adjustment to clutch size in a socially polymorphic orchid bee

Nests of the primitively eusocial orchid bee Euglossa viridissima are generally founded by a solitary female but can be reactivated by female offspring, in the presence or absence of the mother. The population therefore exists of solitary and social nests that co-occur in an area. A female can stay as a subordinate helper under a dominant female or disperse to become a solitary foundress. Yet, the costs and benefits of the different social phenotypes are so far little understood. Here, we compared solitary and social nests of orchid bees. We used offspring of solitary and social nests to calculate offspring sex ratio, and applied molecular markers to calculate intranidal relatedness, infer maternity and test whether sociality may have a genetic component. We found that social nests had on average more brood than solitary nests. The overall sex ratio in the population did not differ from 1:1. However, social nests tended to produce a split sex ratio with some nests producing mainly males and others mainly female offspring. Regardless of social phenotype, the number of offspring was correlated with the sex ratio, with smaller nests having a more female-biased offspring. In social nests, not all offspring resulted from a single-mated mother, which was also the case for some solitary nests. This suggests shared reproduction in social nests and may be an indication that intraspecific parasitism and nest takeover are not uncommon. Structure analyses did not reveal different genetic background of the two social phenotypes. Our results suggest that there is no clear benefit that favours one of the two social phenotypes over the other and that the population is kept at balance in terms of sex ratio.     

Mimetic colour pattern evolution in the highly polymorphic Bombus trifasciatus (Hymenoptera: Apidae) species complex and its comimics

Müllerian mimetic systems have uncovered some of the dynamic processes by which natural selection can drive the radiation of convergent and divergent phenotypes. We examined evolution involving Müllerian mimicry in bumble bees by documenting the distribution and evolution of colour patterns amongst three colour‐polymorphic lineages –Bombus trifasciatus Smith, Bombus haemorrhoidalis Smith, and Bombus breviceps Smith – that mimic each other across ～14 colour groups in South‐East Asia. Using mitochondrial DNA sequence data, we estimated relationships within each lineage to infer the processes that gave rise to the colour diversity and develop hypotheses on species recognition. We expanded on our assessment of species delineation in the B. trifasciatus lineage using three nuclear gene fragments and morphometrics. Comparison of colour patterns amongst georeferenced specimens showed considerable variation in the degree and geographical range of mimicry amongst mimicry groups. Phylogenetic estimates show high rates of colour pattern evolution, with colour variation often exceeding variation within the fast‐evolving mitochondrial genes. The molecular data, and to some degree the morphometric data, support unique histories for several taxa recognized previously within the B. trifasciatus lineage, which may include several species. Early vicariant events within the B. trifasciatus lineage are likely to have occurred ～2.2 Mya in the mountains of south‐west China. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 166 , 805–826.     

Climate,physiological tolerance and sex‐biased dispersal shape genetic structure of Neotropical orchid bees

Understanding the impact of past climatic events on the demographic history of extant species is critical for predicting species' responses to future climate change. Palaeoclimatic instability is a major mechanism of lineage diversification in taxa with low dispersal and small geographical ranges in tropical ecosystems. However, the impact of these climatic events remains questionable for the diversification of species with high levels of gene flow and large geographical distributions. In this study, we investigate the impact of Pleistocene climate change on three Neotropical orchid bee species (Eulaema bombiformis, E. meriana and E. cingulata) with transcontinental distributions and different physiological tolerances. We first generated ecological niche models to identify species‐specific climatically stable areas during Pleistocene climatic oscillations. Using a combination of mitochondrial and nuclear markers, we inferred calibrated phylogenies and estimated historical demographic parameters to reconstruct the phylogeographical history of each species. Our results indicate species with narrower physiological tolerance experienced less suitable habitat during glaciations and currently exhibit strong population structure in the mitochondrial genome. However, nuclear markers with low and high mutation rates show lack of association with geography. These results combined with lower migration rate estimates from the mitochondrial than the nuclear genome suggest male‐biased dispersal. We conclude that despite large effective population sizes and capacity for long‐distance dispersal, climatic instability is an important mechanism of maternal lineage diversification in orchid bees. Thus, these Neotropical pollinators are susceptible to disruption of genetic connectivity in the event of large‐scale climatic changes.     

Mandibular postcanine dentition from the Shungura Formation,Ethiopia: Crown morphology,taxonomic allocations,and Plio-Pleistocene hominid evolution

Over 200 hominid specimens were recovered by the International Omo Expedition of 1967–1976. Despite the fragmentary nature of this primarily dental collection, these hominid remains represent a major body of evidence about hominid evolution in eastern Africa during the 2–3 myr time period. Our analysis of the Omo dental collection is based on a large comparative sample of 375 quantifiable mandibular postcanine teeth of A. afarensis, A. africanus, A. aethiopicus, A. boisei, A. robustus, and early Homo. A total of 48 isolated mandibular premolars and molars of the Omo collection spanning the 2–3 myr time period is sufficiently preserved to allow reliable serial allocations and intertaxon comparisons and is the object of study in this paper. We present taxonomic identifications of these teeth and seven other mandibular specimens preserving tooth crowns. Metric analyses of this study include cusp area and crown shape variables taken on occlusal view diagrams. Nonmetric analyses were based on simultaneous observations of all relevant material to ensure accuracy of categorical evaluations. First, a combined metric and morphological evaluation was conducted to allocate each Omo tooth to either robust or nonrobust categories. Further taxonomic affinities were then examined. Our results indicate that nonrobust and robust lineages cooccur by circa 2.7 myr. We consider the Shungura robust specimens from Members C through F to represent A. aethiopicus. A significant phenetic transformation occurs at circa 2.3 myr, with the mosaic emergence of the derived A. boisei morphology across Member G times. Characterization of the East African nonrobust lineage is more difficult because of the comparatively subtle morphological differences seen among the dentitions of A. afarensis, A. africanus, and early Homo. The earlier Members B and C nonrobust specimens are difficult to evaluate and are considered indeterminate to genus or species. Both molars and premolars from Members E through G exhibit phenetic similarities to the early Homo condition and are considered as aff. Homo sp. indet. At present, there is no indication of multiple species in the Omo nonrobust sample at any time horizon. The 2–2.4 myr Omo nonrobust specimens exhibit some similarities to the stated Homo “rudolfensis” condition in size and morphology and are likely to represent the ancestral condition of the genus Homo. The bearing of these results on interpretations of early hominid evolution and diversification is considered. © 1996 Wiley-Liss, Inc.     

Orchid Bee (Apidae: Euglossini) Communities in Atlantic Forest Remnants and Restored Areas in Paraná State,Brazil

In this study, we compare orchid bee communities surveyed in four forest remnants of the Atlantic Forest and four reforested areas characterized by seasonal semi-deciduous forest vegetation in different successional stages (mature and secondary vegetation), located in southern Brazil. The sizes of forest remnants and reforested areas varied from 32.1 to 583.9 ha and from 11.3 to 33.3 ha, respectively. All reforested areas were located near one forest remnant. During samplings, totaling nine per study area, euglossine males were attracted to eight scent baits and captured with bait trap and entomological nets. Each forest remnant and its respective reforested area were sampled simultaneously by two collectors. We collected 435 males belonging to nine species of orchid bees distributed in four genera. The number of individuals and species did not differ significantly between different areas, except for a reforested area (size 33.3 ha), which was located far from its respective forest remnant. Our findings also revealed an apparent association between an orchid bee species (Euglossa annectans Dressler 1982) and the most preserved area surveyed in our study, suggesting that this bee is a potential indicator of good habitat quality in recuperating or preserved areas. Our results suggest that reforested habitats located near forest remnants have a higher probability of having reinstated their euglossine communities.