Blown by the wind: the ecology of male courtship display behavior in orchid bees

Abstract

Many insects rely on chemical signals to transmit precise information on the location, identity, and quality of potential mates. Chemical signals are often broadcasted at sites with physical properties that maximize signal propagation and signal transmission. Male neotropical orchid bees (Euglossini) perch and display on vertical branches and tree trunks in the forest to expose volatile blends (perfumes) that they previously collected from their environment. Previous studies have shown that the chemical composition of perfume blends is highly differentiated even between closely related species. However, variation in behavioral components of perfume exposure and male display remain poorly understood. We conducted a four-year study on orchid bee display sites (8 species) in pacific Costa Rica, using field observations along with chemical analysis and cage experiments to assess display niche partitioning among sympatric species. We evaluated the influence of physical factors (terrain, wind, light) on the distribution of perch sites and on display behavior, and tested a prediction of the sex pheromone-analogue hypothesis, i.e., that displaying males have above-average quantities or qualities of acquired perfumes. Males of different species displayed in the same general area and sometimes in close proximity to each other, but partitioned the display niche by selecting different perch diameters, display heights, and by displaying at different times of the day. Most perch sites were located inside the forest on elevated ground, especially along ridges, where stronger winds may help disperse perfume signals. Furthermore, the angular position of displaying males on perches was narrowly determined by wind direction, with males being positioned on the downwind side of the perch, where they would be most conspicuous to conspecifics approaching on an odor trail. Although our results generally support the hypothesis that perfumes serve as pheromone analogues, we did not find differences in the perfume composition of males caught at display perches and males captured at chemical baits. This suggests that, while chemical communication is an integral part of orchid bee display, male display activity is not determined by the history of, and success in, volatile acquisition.

Experimental trait mismatches uncover specificity of evolutionary links between multiple signaling traits and their interactions in hummingbirds*

“…), and cicadas (Bennet‐Clark and Young ) and chemical signals that are directionally transmitted through wind (Pokorny et al. ) or water flow (Atema ). Therefore, our results can be interpreted across multiple signal modalities, demonstrating that the need for signalers to behaviorally alter, position, and/or orient themselves or their signals relative to their intended receiver and environment, and these behaviors should closely coevolve with the directional aspects of their signals for optimal presentation and transmission through the environment.…”

“…Further, some colorful ornaments are only observable due to specific behavioral manipulations, such as uncovering a colorful patch (e.g., lifting a wing and showing an underwing color patch; (Hansen and Rohwer 1986;Zanollo et al 2013), positioning the color patch toward the receiver (e.g., male Harbronattus jumping spiders ensuring they directly face a female throughout their courtship display; (Echeverri et al 2017), or repositioning various body parts to create a color-display not possible in a natural body position (e.g., superb bird-of-paradise, Lophorina superba; Laman and Scholes 2012). Thus, for many animals, behaviors are important to optimizing color presentations during displays and/or coloration is important to accentuating behavioral (Rosenthal 2007;Patricelli et al 2016), such as the directional acoustic signals of blackbirds (Larsen and Dabelsteen 1990;Patricelli et al 2007), treehoppers (Cocroft et al 2000), and cicadas (Bennet-Clark and Young 1998) and chemical signals that are directionally transmitted through wind (Pokorny et al 2017) or water flow (Atema 1995). Therefore, our results can be interpreted across multiple signal modalities, demonstrating that the need for signalers to behaviorally alter, position, and/or orient themselves or their signals relative to their intended receiver and environment, and these behaviors should closely coevolve with the directional aspects of their signals for optimal presentation and transmission through the environment.…”

Wind drives temporal variation in pollinator visitation in a fragmented tropical forest

“…Despite its likely importance in dispersing scents, the role of wind in orchid bee ecology is not well understood, although previous observers have noted temporary increases in orchid bee arrivals at baits after wind gusts [39]. Recent work has also shown that male orchid bees performing mating displays strongly prefer to orient on the downwind side of trees, presumably to maximize the dispersal of odor plumes [40]. However, to our knowledge, quantitative studies of the impacts of wind (or turbulence) on spatial or temporal variation in orchid bee abundance and visitation rates at scent sources have not been made.…”

Sexual dimorphism in visual and olfactory brain centers in the perfume‐collecting orchid beeEuglossa dilemma(Hymenoptera, Apidae)

“…Orchid bee males collect scents from floral and nonfloral sources to concoct a complex species-specific chemical "perfume" blend (Dressler, 1982;Eltz, Whitten, Roubik, & Linsenmair, 1999;Roubik & Hanson, 2004;Weber, Mitko, Eltz, & Ramírez, 2016;Zimmermann, Ramírez, & Eltz, 2009). The perfume is subsequently released during a stereotypical display behavior at perching sites (Pokorny et al, 2017). It is only in combination with perfume display behavior that mating occurs (Dodson, 1966;Kimsey, 1980;Pokorny et al, 2017;Stern, 1991;Zimmermann, Roubik, & Eltz, 2006).…”

“…The perfume is subsequently released during a stereotypical display behavior at perching sites (Pokorny et al, 2017). It is only in combination with perfume display behavior that mating occurs (Dodson, 1966;Kimsey, 1980;Pokorny et al, 2017;Stern, 1991;Zimmermann, Roubik, & Eltz, 2006). Although the exact function of perfume bouquets is still unclear, they are most likely involved in sexual selection, presumably by enabling species-specific recognition or the discrimination of males within a species.…”