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
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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
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