Unraveling the Olfactory Biases of Male Euglossine Bees: Species-Specific Antennal Responses and Their Evolutionary Significance for Perfume Flowers

Male euglossine bees exhibit unique adaptations for the acquisition and accumulation of chemical compounds from “perfume flowers” and other sources. During courtship display, male bees expose perfume mixtures, presumably to convey species-specific recognition and/or mate choice signals to females. Because olfaction regulates both signal production (in males) and signal detection (in females) in this communication system, strong selective pressures are expected to act on the olfactory system, which could lead to sensory specialization in favor of an increased sensitivity to specific chemical compounds. The floral scents of euglossine-pollinated plants are hypothesized to have evolved in response to the preexisting sensory biases of their male euglossine bee pollinators. However, this has never been investigated at the peripheral olfactory circuitry of distinct pollinating genera. Here, we present a comparative analysis using electroantennography (EAG) of males across the phylogeny of 29 euglossine bee species, among them Euglossa and Eulaema species. First, we tested whether antennal responses differ among different euglossine genera, subgenera and species. Secondly, we conducted a comparative phylogenetic analysis to investigate the macroevolutionary patterns of antennal responses across the euglossine bee phylogeny. We found that antennal response profiles are very unique on the species level and differ on the subgenus and the genus level. The differences can be explained by chemical compounds typically found in the floral scent bouquets of perfume flowers and specific compounds of species either pollinated by Euglossa (e.g., ipsdienol) or Eulaema bees (e.g., (−)-(E)-carvone epoxide). Also, we detected a phylogenetic signal in mean antennal responses and found that especially at the species level of our simulation the overall antennal responses exhibit greater disparity relative to a null model of pure Brownian-motion across the phylogeny. Altogether, our results suggest that (1) euglossine bee species exhibit species-specific antennal responses that differ among euglossine genera and subgenera, (2) antennal responses diverge early after speciation events, and (3) scent composition of perfume flowers evolved in response to pollinator-mediated selection imposed by preexisting sensory biases in euglossine bees.

Reproductive Ecology of Euglossine Bee-pollinated Orchid Catasetum Integerrimum Hook (Ochidaceae)

Catasetum is a dimorphic and dioecious genus of orchids with a pollinaria release mechanism triggered by pollinator visitation. The reproductive ecology of Catasetum integerrimum Hook (Orchidaceae) was characterized in Central Veracruz, Mexico. For that, it was determined whether floral senescence and fruit production are resulted of pollination efficiency in the species, and if so, to what extent present reproductive event constraint the investment in subsequent reproductive event. In the sampled population, efficient pollinaria removal/deposition triggered floral senescence. Eulaema polychroma bee visited earlier and with lower frequency the staminate than pistillate flowers. Alleviating pollen limitation increased fruit production but it caused a reduction in flower and fruit production in the subsequent reproductive event. C. integerrimum seemed to exhibit reproductive cost-saving mechanisms linked to the pollinator identity and behavior, whereas pollinator efficiency appeared to be mediated by dioecism and dimorphism in floral traits. This study highlights the importance to understand the adaptive significance of dimorphic floral traits in animal-pollinated plants, stimulating new research avenues on the role of pollinators in maintaining safe reproduction threshold of plants.

Sexual dimorphism in floral scents of the neotropical orchid Catasetum arietinum and its possible ecological and evolutionary significance

Dioecy in angiosperms is often associated with sexual dimorphism in floral traits other than the sexual organs. Species of the neotropical orchid genus Catasetum produce unisexual flowers characterized by a remarkable morphological sexual dimorphism. Catasetum species emit strong floral perfumes that act as both signal and reward for male euglossine bee pollinators. Although the role of floral perfumes of Catasetum in attracting euglossine pollinators is well investigated, little is known about whether perfumes differ between floral sexes and, if they do, whether this chemical dimorphism influences the pollination ecology of the plants. Taking Catasetum arietinum as a model species, our aim was to observe the behaviour of pollinators on male and female flowers and to compare scent properties (i.e. chemical composition, total amount and temporal fluctuation) of male and female flowers. Floral scent samples were collected by using dynamic headspace methods and were analysed via gas chromatography coupled with mass spectroscopy (GC-MS). Catasetum arietinum is pollinated by males of two Euglossa species (i.e. E. nanomelanotricha and E. securigera). Bees approached male and female inflorescences of C. arietinum in similar proportions but landed significantly more often and spent more time on female flowers, which emitted more scent than male flowers. Furthermore, the amount of scent emitted varied across the different times of sampling, corresponding to the pattern of the diel foraging activity of pollinating bees on male and female flowers. The chemical composition of scents differed significantly between sexes. The two major compounds (Z)-methyl-p-methoxycinnamate and (E)-geranyl geraniol contributed most to this difference. This is the first case of sexual dimorphism reported in orchid floral perfumes. We discuss the influence of sex-specific floral scents on the behaviour of euglossine pollinators and offer new insights into the ecological and evolutionary significance of divergence in floral scents among dioecious plants.

Different Physiognomies and the Structure of Euglossini bee (Hymenoptera: Apidae) Communities

Our aim was to evaluate the occurrence of orchid bees in remnants of the Atlantic Forest. We sampled specimens from five regions of Southeast Brazil, covering three different physiognomies of the Atlantic Forest (mixed Araucaria forests with high altitude fields, Atlantic Semi-deciduous Forest and Atlantic Rain Forest). The distances between the sampling sites ranged from 24 to 746 km. Male orchid bees attracted by fragrances were actively sampled monthly during one year using entomological nets and aromatic traps. A total of 1,482 bees were captured, including four genera and at least 31 species. We observed differences in the abundance and richness of species sampled among sites. Climatic variables, mostly relative humidity, explained twice more of the observed differences in the Euglossini communities than simple spatial variation. Our study found differences in the composition of euglossine bee communities as well as in their patterns of abundance and dominance among different vegetation formations. However, the level of pairwise similarity among the Euglossini communities sampled, although highly variable, was not related to climatic factors or geographical distances between the sampling sites. The greatest dissimilarities in the composition of the orchid bee communities were observed between sites around 400 km from each other rather than among sites that were further apart. A possible explanation is that the sampled areas that were 400 km from each other were also highly dissimilar regarding climate, especially altitude.

Molecular phylogenetics and generic concepts in the Maxillarieae (Orchidaceae)

<div class="page" title="Page 1"><div class="layoutArea"><div class="column"><p><span>Tribe Maxillarieae account for approximately 10% (&gt;2800 species) of Orchidaceae and are a major com- ponent of the Neotropical epiphytic flora. Pollination systems include 1) male euglossine-bee fragrance rewards in four subtribes, 2) oil reward systems and mimicry in some groups, 3) nectar rewards in a wide range of taxa, and 4) pseudocopulation in some Maxillariinae and some Oncidiinae. </span></p></div></div></div>

Two common species dominate the species-rich Euglossine bee fauna of an Atlantic Rainforest remnant in Pernambuco, Brazil

Nowadays, the northern part of the Atlantic Rainforest of Brazil is largely destroyed and forest remnants rarely exceed 100 ha. In a 118 ha forest fragment within a state nature reserve of Pernambuco (Reserva Ecológica Gurjaú), we surveyed the orchid bee fauna (Apidae, Euglossini) using eight different scent baits to attract males. Once a month during one year, the bees were actively collected with entomological nets, from November 2002 to October 2003 by two collectors. We collected 2,908 orchid bee males belonging to 23 species, one of the highest richness values of the Northern Atlantic Rainforest. Bees of only two species, Euglossa carolina (50%) and Eulaema nigrita (25%), which occurred throughout the year, accounted for three quarter of the collected individuals. Both species are typical for open or disturbed areas. Rainforest remnants like those of Gurjaú within the predominant sugar cane monocultures in the coastal plains of the northern Atlantic Rainforest play an important role in orchid bee conservation and maintenance of biodiversity.