Asteroideae

Abstract: An extensive sequence comparison of the chloroplast ndhF gene from all major clades of the largest flowering plant family (Asteraceae) shows that this gene provides approximately 3 times more phylogenetic information than rbcL. This is because it is substantially longer and evolves twice as fast. The 5' region (1380 bp) of ndhF is very different from the 3' region (855 bp) and is similar to rbcL in both the rate and the pattern of sequence change. The 3' region is more A+T-rich, has higher levels of nonsynonymous base substitution, and shows greater transversion bias at all codon positions. These differences probably reflect different functional constraints on the 5' and 3' regions of ndhF. The two patterns of base substitutions of ndhF are particularly advantageous for phylogenetic reconstruction because the conserved and variable segments can be used for older and recent groups, respectively. Phylogenetic analyses of 94 ndhF sequences provided much better resolution of relationships than previous molecular and morphological phylogenies of the Asteraceae. The ndhF tree identified five major clades: (i) the Calyceraceae is the sister family of Asteraceae; (ii) the Barnadesioideae is monophyletic and is the sister group to the rest of the family; (iii) the Cichorioideae and its two basal tribes Mutisieae and Cardueae are paraphyletic; (iv) four tribes of Cichorioideae (Lactuceae, Arctoteae, Liabeae, and Vernonieae) form a monophyletic group, and these are the sister clade of the Asteroideae; and (v) the Asteroideae is monophyletic and includes three major clades.

Abstract: To assess the pollen hosts of 60 western palaearctic bee species of the genus Colletes (Colletidae), we microscopically analysed 1336 pollen loads of collected females. Twenty-six species (43.3%) were found to be specialized at the level of plant family, subfamily or genus. Thirty-four species (56.7%) proved to be pollen generalists to varying degrees, visiting the flowers of up to 15 different plant families. Flowers of the subfamily Asteroideae (Asteraceae) are by far the most important pollen source, contributing 23.6% to the pollen-plant spectrum of the whole bee genus. The high significance of Asteroideae pollen is due to the large number of specialists: 14 Colletes species belonging to four different taxonomic groups harvest pollen exclusively or predominantly on flowers of the Asteroideae. By striking contrast, Asteroideae pollen plays only a marginal role in the diets of the pollen generalists: it was recorded in only 2.7% of the pollen loads and in seven out of the 34 pollen generalists. Among the few generalists exploiting Asteroideae for pollen, three closely related species have ancestors which were possibly specialized on Asteraceae. The pattern of use of Asteroideae pollen by the Colletes bees supports recent findings that this pollen possesses unfavourable or protective properties, which render its digestion difficult, and suggests that bees need physiological adaptations to successfully utilize it. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95, 719–733.

Abstract: To determine the extent of host—plant specialization, the pollen sources of the 72 anthidiine species (family Megachilidae, subfamily Megachilinae, tribe Anthidiini) of Europe, North Africa, and Asia Minor were investigated by microscopic analysis of ≈ 1800 pollen loads of females. By this measure, 31 species (43%) were oligolectic (relatively specialized to pollen source) at the level of plant tribe, plant subfamily, or plant family. Exclusive pollen sources of these bees throughout their geographic ranges are flowers of the Cardueae (Compositae), the Asteroideae (Compositae), the Papilionoideae (Leguminosae), the Lamioideae (Labiatae), the Nepetoideae (Labiatae), the Dipsacaceae, or the Campanulaceae. Thirteen species (18%) were found to exhibit a strong, but not exclusive, preference for the Papilionoideae (Leguminosae), the Labiatae, the Cardueae (Compositae), and Zygophyllum (Zygophyllaceae), respectively, while 25 species (35%) proved to be more markedly polylectic, visiting the flowers of up to 17 different plant families for pollen. The plants exploited by three species (4%) are insufficiently known. By far the most important pollen sources of the anthidiine bees as a whole are the Compositae (41.7%) followed by the Leguminosae (23.1%) and the Labiatae (13.0%). The phylogenetic relationships of the anthidiine bees were estimated by a cladistic analysis based on 115 characters to trace possible evolutionary patterns of diet composition. Based on the estimated phylogeny, at least eight shifts of oligoleges between different plant taxa and six transitions between oligolecty and polylecty appear to have occurred. Four transitions were from oligolecty to polylecty whereas two transitions are of unknown direction, both directions being equally parsimonious. Assuming that the ancestral state in the anthidiine bees was oligolectic, the present distribution of oligolectic and polylectic species can be explained solely by switches from the oligolectic to the polylectic habit and by shifts of oligoleges between different plant taxa. Three of four transitions from oligolecty to polylecty are accompanied by a reduction in bee body size. The significance of this size reduction with respect to the polylectic habit is discussed. The oligolectic anthidiine species visit significantly fewer flower species for pollen during a single foraging bout than the polylectic species. On average, 1.4 plant species were recorded in the loads of specialists compared to 2.2 for generalists. Two monophyletic groups of bees belonging to the genus Anthidium are equipped with a pollen—collecting apparatus consisting of specialized hairs localized either on the face or on the underside of the thorax. It is used to remove pollen from the raised anthers of flowers of the Labiatae and the Scrophulariaceae and to brush pollen from the flat inflorescences of some Compositae, respectively. The observation of flower—visiting females of several anthidiine species revealed that pollen uptake is far from an accidental process. Basic pollen—harvesting techniques have reached a high degree of efficiency: females of a given bee species worked flowers of a certain plant species in a fixed manner, the structures used for pollen uptake from the same flower type were found to be largely the same among anthidiine bees of different taxonomic groups, and no distinct differences with respect to the basic pattern of pollen removal from flowers of the same architecture were obvious when comparing oligolectic and polylectic species. On the other hand, polyleges showed a high intraspecific flexibility regarding the organs used for pollen uptake from flowers of a different architecture.