Map showing the position of Lampedusa Island in the Mediterranean basin, and the studied area in the island. 

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Context 1

... & Venter 2001), which result from lack of separation of pollen grains during pollen production (Harder & Johnson 2008). Pollen of Asclepiadoideae is usually a coherent mass, the pollinium (Ollerton & Liede 1997), which consists of single, inaperturate pollen grains surrounded by a pollinium wall. Within the two subfamilies both tetrads and pollinia are placed onto specialized transportation devices, the translators. The translators play a fundamental role in pollination. In Periplocoideae, the translator consists of three parts: spoon, stipe and adhesive disc. The spoon has an adhesive surface which carries the pollen tetrads ( Verhoeven & Venter 2001). In Asclepiadoideae, the translator has a rather uniform structure, composed of a corpusculum and two caudicles to which the pollinia are attached and form the pollinarium. In the genus Caralluma, the two pollinia are each attached to the upper region of the corpusculum by a short obscure caudicle as described by Verhoeven and Venter (2001) for the entire subfamily. In Asclepiadoideae, at the last stage of pollinarium development, when the anther wall dehisces, the pollinium comes into contact with, and becomes attached to, the translator apparatus (Kunze 1994). The two subfamilies use a different mechanism to attach the translators to the pollinators: in Periplocoideae, the translator is attached to the insect by means of an adhesive disc, while in Asclepiadoideae the corpusculum clips either the proboscis, body hairs or a leg of the pollinator. Both genera contain nectar according to Sennblad et al. (1998) for Periploca and Meve and Liede (1994) for Caralluma. Although bees (Hymenoptera: Apoidea) are widely recognized as the most important anthophiles and pollinators, flies (Diptera) certainly rank second. At least 71 dipteran families have been recorded as pollinators or regular visitors of some 555 species of flowering plant (Larson et al. 2001). Diptera are known as pollinators of several genera in at least two subfamilies of Apocynaceae: Periplocoideae and Asclepiadoideae (Ollerton & Liede 1997). In this article we present field data on pollinators of two co-occurring taxa of Apocynaceae: Periploca laevigata subsp. angustifolia (Labill.) Markgraf (Periplocoideae) and Caralluma europaea (Guss.) N.E.Br. (Asclepiadoideae) with the aim to identify pollinators at specific level and to verify whether beside the phenotypic flower specialization the studied taxa are ecologically generalist or specialist. Furthermore the co-occurring of two taxa of Apocynaceae of two different subfamilies may give information on the presence of overlapping pollinators. Lampedusa Island lies in the Mediterranean Sea and is 20.2-km 2 wide, 11-km long (East-West). It is an emergence of the African Continental platform and is 195 km from the Sicilian coast and 120 km from Tunisia (Agnesi & Federico 1995). The geographic position of Lampedusa makes the island a biogeo- graphical bridge between Sicily and North Africa. Geological studies date back its definitive isolation from north Africa to about 18,000 B.P. It is arguable that besides colonization due to dispersal, either active or passive, dispersion of some species took place through North Africa after the last glaciation, between 23,000 and 18,000 years ago, and remained isolated in the island where some speciation occurred. The Lampedusa flora testifies the connections that the Island had with Sicily and North Africa. Circum- Mediterranean species are predominant and constitutes 41.9% of the flora (Bartolo et al. 1990). The zoological aspects confirm the connections with the Mediterranean basin (Massa 1995): some species of Arthropoda with scarce dispersal capacity are sig- nificantly relevant to indicate a very probable dispersion from north African coast. Venturi (1960), on the basis of the few data on the dipterofauna, noted that some species belongs to the North African region and others to the Italian one. A relevant aspect of the biological diversity of the Pelagie Archipelago is the presence of North African elements beside a high level of endemic species. For instance, the herpetofauna of Lampedusa includes two North African species: Macroprotodon cucullatus Geoffroy de St-Hilaire, 1827 (Carranza et al. 2004) and Malpolon monspessulanus Hermann, 1804 (Corti et al. 2001). P. laevigata ssp. angustifolia and C. europaea are widespread along the coast of Lampedusa Island where only these two taxa of Apocynaceae grow wild. Their distribution is discontinuous, with some areas of major abundance and two localities, Isola dei Conigli and Albero Sole (Figure 1) where they grow in mixed populations. P. laevigata subsp. angustifolia is a thermophilic, perennial, deciduous shrub widespread in Spain, Morocco, Algeria, Tunisia, Libya, Egypt, Crete and Karpathos, Malta, Sicily (Greuter et al. 1984). For Sicily, it is reported only for Egadi Islands, Pantelleria, Lampedusa, and Linosa (Pignatti 1982). P. laevigata subsp. angustifolia generally grows on alkaline substrate, regardless of soil composition (Ferchichi 1995). In particular, in Lampedusa it dominates summer-deciduous xeromorphic vegetation ascribed to Periploco angustifoliae - Euphorbietum dendroidis Brullo, Di Martino et Marceno ` 1977, specialized to colonized sunny slopes; it also occurs with Juniperus turbinata Guss., forming nuclei of vegetation referred to Periploco angustifoliae - Juniper- etum turbinatae Bartolo, Brullo, Minissale et Spampinato 1990. C. europaea ( Apteranthes europaea (Guss.) Plowes) is a stem-succulent plant originally described ...

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... Island of Lampedusa (Gussone 1839). Since then, it has been reported from the southernmost Iberian Peninsula, Morocco and, with some inter- ruptions, along the northern coast of the African continent up to the Sinai, Israel, and Jordan (Meve & Heneidak 2005). As it is typical for most stapeliads, C. europaea prefers shaded stands such as the base of bushes wherein the plants are often scrambling (e.g. Jonkers & Walker 1993). The individuals vary considerably in their general habit depending on the edaphic situa- tion. In deep, sandy soil there is a strong tendency to form rhizomes. On rocks, the plants usually form compact clumps of rather thick stems (up to 30 mm in diameter). In Lampedusa, the species grows on rocky slopes and pavements, especially in rocky crevices within the local garrigue, dominated by Thymus capitatus (L.) Hoffmanns. et Link or in overgrazed grasslands communities with Urginea maritima (L.) Baker and Asphodelus ramosus L. It also occurs in the lithophilous vegetation subject to salt-spray ascribed to Limonietum lopadusani Bartolo et al. 1990. Fieldwork was carried out every month from January 2007 to November 2008. Most of the observations were diurnal, with limited nocturnal surveillance. Sampling areas were chosen for sites with the maximum abundance of the two studied taxa (Figure 1): Isola dei Conigli and Casa Teresa for P. laevigata subsp. angustifolia , and Isola dei Conigli, Albero Sole, Cala Galera and Capo Grecale for C. europaea . For each visit to the island, captures were done during 3 days, simultaneously by two teams of researchers, 2 h in the morning from 10 to mid-day, and 2 hours in the afternoon from 14 to 16. In total, 408 man hours were spent observing and collecting insects. On average, three specimens of C. europaea and three of P. laevigata subsp. angustifolia for each area were selected for observation of visitors and captures. Visitors were recorded with field notes and photographs. Captures were done using an entomological net and specimens were kept separately in plastic test-tubes with cork shavings imbued with ethyl acetate until they could be prepared for identification. Captures were carried out following two techniques: (1) stalking near plants waiting for arrival of flower visitors, (2) random captures in the sampling area. Flowers of the two taxa and samples of insect visitors were returned to the laboratory for closer observations and analysis of pollen loads. Translators were identified by comparison with those previously removed from flowers of P. laevigata subsp. angustifolia (Figure 2) and C. europaea (Figure 3). Insects with at least one specimen captured with pollen of the studied plants were considered legimitate pollinators according to Ollerton et al. (2003) and identified at specific level. Insects were dry mounted and observed using a binocular microscope (Wild M3B) with a 6 40 extension to check for the presence of translators. The mounted specimens with translators were then identified down to specific level. Voucher specimens are stored in entomological boxes and kept at the Entomological Collection of the Dipartimento di Coltivazione e Difesa delle Specie Legnose ‘‘G. Scaramuzzi’’, University of Pisa, and at the Dipartimento di Scienze Botaniche, University of Palermo. Each record of pollination was ranked on the basis of the quality of the information using ...