The ecological role of extremely long-proboscid Neotropical butterflies (Lepidoptera: Hesperiidae) in plant-pollinator networks

Arthropod-Plant Interactions, Jun 2015

Extremely long proboscides of insect flower visitors have been regarded as an example of a coevolutionary arms race, assuming that these insects act as efficient pollinators for their nectar host plants. However, the effect of proboscis length on generalized or specialized flower use remains unclear and the efficiency of butterfly pollination is ambiguous. Neotropical Hesperiidae feature a surprising variation of proboscis length, which makes them a suitable study system to elucidate the role of extremely long-proboscid insects in plant-pollinator networks. The results of this study show that skippers with longer proboscides visit plant species with deep-tubed flowers to take up food, but do not pollinate them. Skippers equipped with extremely long proboscides seldom include short-tubed flowers in their diet nor visit more plant species than those with shorter proboscides. Our observations indicate that the extremely long-proboscid skippers steal nectar from their preferred nectar host plants, Calathea sp., instead of contributing to their pollination. Finally, we discuss the impact of nectar robbery by these butterflies on their nectar host plants and their legitimate pollinators, euglossine bees.

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The ecological role of extremely long-proboscid Neotropical butterflies (Lepidoptera: Hesperiidae) in plant-pollinator networks

The ecological role of extremely long-proboscid Neotropical butterflies (Lepidoptera: Hesperiidae) in plant-pollinator networks J. A.-S. Bauder 0 1 2 A. D. Warren 0 1 2 H. W. Krenn 0 1 2 Handling Editor: Katja Hogendoorn. 0 McGuire Center for Lepidoptera and Biodiversity, Florida Museum of Natural History, University of Florida , Gainesville, FL , USA 1 Department of Integrative Zoology, University of Vienna , Vienna , Austria 2 & J. A.-S. Bauder Extremely long proboscides of insect flower visitors have been regarded as an example of a coevolutionary arms race, assuming that these insects act as efficient pollinators for their nectar host plants. However, the effect of proboscis length on generalized or specialized flower use remains unclear and the efficiency of butterfly pollination is ambiguous. Neotropical Hesperiidae feature a surprising variation of proboscis length, which makes them a suitable study system to elucidate the role of extremely long-proboscid insects in plant-pollinator networks. The results of this study show that skippers with longer proboscides visit plant species with deep-tubed flowers to take up food, but do not pollinate them. Skippers equipped with extremely long proboscides seldom include short-tubed flowers in their diet nor visit more plant species than those with shorter proboscides. Our observations indicate that the extremely long-proboscid skippers steal nectar from their preferred nectar host plants, Calathea sp., instead of contributing to their pollination. Finally, we discuss the impact of nectar robbery by these butterflies on their nectar host plants and their legitimate pollinators, euglossine bees. interaction; Skippers; Calathea; Insect-plant; Foraging behavior; Coevolution - Many scientists have pondered over the evolutionary processes that led to the development of particularly elongate proboscides in flower-visiting insects (Darwin 1862; Johnson 1997; Johnson and Anderson 2010; Muchhala and Thomson 2009; Nilsson 1988, 1998; Pauw et al. 2009; Rodr´ıguez-Girone´s and Llandres 2008; Rodr´ıguez-Girone´s and Santamar´ıa 2007; Wasserthal 1997, 1998; Whittall and Hodges 2007). The most widely accepted hypothesis for the evolution of extreme mouthpart lengths is that they coevolved with long nectar spurs of angiosperms. In this way, the plant partner secures its pollination and the insect partner gains exclusive access to plenty of nectar (Darwin 1862; Nilsson 1998). Although the majority of butterflies feed on floral nectar (Krenn 2010), their role as effective pollinators remains doubtful in many examples (Courtney et al. 1982; Wiklund 1981; Wiklund et al. 1979). A mutualistic coevolutionary relationship between particular butterfly species and their preferred nectar host plants has only been demonstrated in two cases (Gilbert 1972, 1975; Grant and Grant 1965; Levin and Berube 1972). In fact, some authors regard butterflies as opportunistic flower visitors that use resources as they become available during the season (Shreeve 1992; Stefanescu and Traveset 2009; Tudor et al. 2004). The effect of proboscis length on generalized or specialized flower use remains contradictory and to date has been investigated mainly in temperate butterfly communities (Corbet 2000; Porter et al. 1992; Stefanescu and Traveset 2009; Tiple et al. 2009; Tudor et al. 2004). Here, we investigated Neotropical skipper butterflies (Hesperiidae) with a wide range of proboscis lengths to test the hypothesis that insects equipped with extremely long mouthparts specialize on flowers with deep nectar spurs. Alternatively, the hypothesis could be forwarded that extremely long-proboscid butterflies use a wide variety of flowers regardless of nectar spur length in an opportunistic way: The longer the proboscis, the more flowers which can be visited. Finally, we raise the question whether extremely long-proboscid butterflies act as pollinators of their nectar plants and thus constitute another example of a coevolved pollination mutualism, as in extremely long-proboscid hawk moths and orchids. Materials and methods Flower use, study area and species sampling We chose four flowering plant species (Verbenaceae: Lantana camara, Stachytarpheta frantzii; Marantaceae: Calathea crotalifera, Calathea lutea) growing in the garden and surroundings of the Tropical Station La Gamba (Costa Rica, Puntarenas, Piedras Blancas National Park, 8 450N, 83 100W; 81 m a.s.l.) for recording skipper visitation (Fig. 1a, b) during an overall observation time of approximately 240 h (September–October 2012, January– February 2013). All four plant species flowered during both observation periods in the seminatural garden area, which borders on natural forest habitats. The plant species grew in close proximity to each other and within reach of the butterfly species foraging in this area. The study area offers a rich nectar supply throughout the year that is highly attractive to a great variety of butterflies colonizing the s (...truncated)


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J. A.-S. Bauder, A. D. Warren, H. W. Krenn. The ecological role of extremely long-proboscid Neotropical butterflies (Lepidoptera: Hesperiidae) in plant-pollinator networks, Arthropod-Plant Interactions, 2015, pp. 415-424, Volume 9, Issue 4, DOI: 10.1007/s11829-015-9379-7