Abstract
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.
Highlights
Many scientists have pondered over the evolutionary processes that led to the development of 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; Rodrıguez-Girones and Llandres 2008; Rodrıguez-Girones and Santamarıa 2007; Wasserthal 1997, 1998; Whittall and Hodges 2007)
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
According to this hypothesis of competition avoidance, extremely long-proboscid skippers should specialize in visiting flowers that correspond to their mouthpart lengths and avoid short corolla flowers
Summary
Many scientists have pondered over the evolutionary processes that led to the development of 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; Rodrıguez-Girones and Llandres 2008; Rodrıguez-Girones and Santamarıa 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). 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. Bauder et al. 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. We raise the question whether extremely long-proboscid butterflies act as pollinators of their nectar plants and constitute another example of a coevolved pollination mutualism, as in extremely long-proboscid hawk moths and orchids
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