First report of predation on fl oral visitors by crab spiders on Croton selowii Baill . ( Euphorbiaceae )

(First report of predation on fl oral visitors by crab spiders on Croton selowii Baill. (Euphorbiaceae)). In the literature it has been extensively mentioned that crab spiders (Araneae: Thomisidae) prey on fl oral visitors of several plant species. Here we present observations of Croton selowii Baill. (Euphorbiaceae), a monoecious species harboring individuals of crab spiders in an area of coastal vegetation of Pernambuco state, Brazil. The species is visited by several invertebrate orders, and some of them were preyed upon by the spiders, mainly Diptera species. The spiders rubbed the forelimbs within the fl owers, which may constitute a strategy to camoufl age these structures. Croton selowii seems to represent a suitable foraging site for the spiders, because it has a generalist pollination system (thus being visited by a wide range of invertebrate species) and blooms in a period of low fl ower resource availability in the area.


Introduction
The crab spiders (Araneae: Thomisidae) prey on floral visitors and present the sit-and-wait strategy: they remain camouflaged in the inflorescences waiting for invertebrates (Dukas & Morse 2003;Robertson & Maguire 2005).There is evidence that the presence of crab-spiders can reduce flower visitation rates (Suttle 2003;Reader et al. 2006), and diminish pollinator density, causing a negative impact on plant reproductive success (Dukas & Morse 2003;Gonçalves-Souza et al. 2008).However, other studies discuss the beneficial effects of these flower-dwelling spiders on their host plant, such as predation on phytophagous herbivores, which can has a positive influence on seed production (Romero & Vasconcellos-Neto 2004).
Plant species of some angiosperm families were recorded as being occupied by crab spiders, such as Asteraceae (Romero & Vasconcellos-Neto 2003), Asclepiadaceae (Kareiva et al. 1989), Fabaceae (Chien & Morse 1998) and Rosaceae (Romero & Vasconcellos-Neto 2004), but to date, there are no records of this interaction in Croton L. (Euphorbiaceae) species.This short communication aims to describe general aspects of the interaction between crab spiders, C. selowii flowers and their floral visitors in an area of coastal vegetation of Pernambuco, Brazil.

Material and methods
Croton sellowii Baill. is a monoecious shrub species with restricted distribution in coastal formations of Brazil (J. S. Silva, pers.comm.).In the Reserva Particular do Patrimônio Natural "Nossa Senhora do Outeiro de Maracaípe", Ipojuca, Pernambuco, Brazil (08º31'48''S; 35º001'48''W), it occurs mainly on forest edges and gaps.Naturalistic observations were done in September 2008.To observe spiders' behavior, twenty fl owering individuals of C. selowii were observed between 9:00 and 11:00 h, and between 14:00 and 16:00 h (total of 80 h).Floral visitors were collected and identifi ed to the family level.Floral scent was recorded and the presence of regions of odor emission was tested in 20 fl owers from different individuals and populations, using the neutral red technique (Dafni 1992).Forty-fi ve individuals from different populations were checked for the presence of spiders, which were collected and identifi ed by specialists.

Results and discussion
Flowers were visited by 21 morpho-species of several invertebrate orders, such as Hymenoptera (fi ve Sphecidae, three Vespidae, one Pompilidae, two Apidae, one Megachilidae, one Adrenidae and one Formicidae morph species), Lepidoptera (two Hesperiidae), Diptera (two Bombiliidae, one Muscidae and one Syrphidae) and Heteroptera (one Coreidae).A total of 31 individuals (69%) harbored individuals of Misumenoides cf.paucispinosus, Misumenops pallens (Keyserling 1880) and/or Misumenops sp.(Araneae: Thomisidae), which prey on fl oral visitors, mainly on fl ies.It was also observed predation on bees and the phytophagous species of Coreidae.All visitors that were preyed upon touched the anthers or the stigma, being considered as potential pollinators.In most observations the spiders positioned the forelimbs perpendicularly outstretched to their bodies' axis (Fig. 1A).They resemble infl orescence structures, being easily confused with buds and fl owers (Fig. 1).Furthermore, it was observed that some individuals introduce a forelimb within the fl ower and rub on the opposite forelimb (Fig. 1F).When a visitor approaches the infl orescence, the spider attacks and consumes it immediately (Fig. 1B-E).Most fl oral visitors apparently did not perceive the spider's presence, but a bee species (Apidae) gave up the visit when it detected the spider, similarly to what was recorded by other studies (e.g., Dukas & Morse 2003;Robertson & Maguire 2005).
Studies show that these Thomisidae spiders (including species of Misumenoides F.O.P-Cambridge 1900 and Misumenops F.O.P-Cambridge 1900) can modify, gradually and reversibly, their body color to resemble the fl owers, a behavior that avoids their recognition by fl oral visitors (Schmalhofer 2000), and even may enhance fl ower attraction (Heiling et al. 2005).Some studies suggest that the forelimbs seem to be the spider trait recognized by pollinators (mainly hymenopterans), thus both the spider position in the plant and the apparent use of fl oral substances observed here seem to constitute strategies to camoufl age the forelimbs (Gonçalves-Souza et al. 2008).Croton selowii fl owers present a citric fragrance and regions of odor emission distributed on sexual elements.
Croton selowii seems to represent a suitable foraging site for the spiders in the study area.It has a generalist pollination system (thus being visited by a wide range of invertebrate species) and blooms in a period of low fl ower resource availability in the area (Medeiros et al. 2006).Consequently, it presents high visitation rates, mainly in the morning (pers.obs.).This short communication is, to our best knowledge, the fi rst report of crab spiders preying on pollinators of C. selowii.