The origin of bird pollination in Macaronesian Lotus (Loteae, Leguminosae).

The four red-flowered, apparently bird-pollinated Lotus species from the Canary Islands have previously been classified in their own genus, Rhyncholotus. Currently, they are considered as a separate section within genus Lotus, distinct from other herbaceous Canarian congeners which are yellow-flowered and bee-pollinated. A combined analysis of four nuclear regions (including ITS and three homologues of CYCLOIDEA) and three plastid regions (CYB6, matK and trnH-psbA) nests the four bird-pollinated species within a single extant species of bee-pollinated Lotus (L. sessilifolius), in a very extreme example of species paraphyly. Therefore, our data compellingly support the hypothesis that the Macaronesian Lotus species with a bird pollination syndrome are recently derived from entomophilous ancestors. Calibration of the phylogenetic trees using geological age estimates of the most recent islands (La Palma and El Hierro) together with oldest ages of Fuerteventura indicates that bird pollination evolved ca. 1.7 Ma in the Canarian Lotus. These four bird-pollinated species share a most recent common ancestor (MRCA) with L. sessilifolius that dates to about 2.2 Ma. Our analyses further suggest that the evolution of the bird pollination syndrome was likely triggered by the availability of new niches in La Palma and Tenerife as a result of recent volcanic activity.

Evolution of petal epidermal micromorphology in Leguminosae and its use as a marker of petal identity.

BACKGROUND AND AIMS: The legume flower is highly variable in symmetry and differentiation of petal types. Most papilionoid flowers are zygomorphic with three types of petals: one dorsal, two lateral and two ventral petals. Mimosoids have radial flowers with reduced petals while caesalpinioids display a range from strongly zygomorphic to nearly radial symmetry. The aims are to characterize the petal micromorphology relative to flower morphology and evolution within the family and assess its use as a marker of petal identity (whether dorsal, lateral or ventral) as determined by the expression of developmental genes. METHODS: Petals were analysed using the scanning electron microscope and light microscope. A total of 175 species were studied representing 26 tribes and 89 genera in all three subfamilies of the Leguminosae. KEY RESULTS: The papilionoids have the highest degree of variation of epidermal types along the dorsiventral axis within the flower. In Loteae and genistoids, in particular, it is common for each petal type to have a different major epidermal micromorphology. Papillose conical cells are mainly found on dorsal and lateral petals. Tabular rugose cells are mainly found on lateral petals and tabular flat cells are found only in ventral petals. Caesalpinioids lack strong micromorphological variation along this axis and usually have only a single major epidermal type within a flower, although the type maybe either tabular rugose cells, papillose conical cells or papillose knobby rugose cells, depending on the species. CONCLUSIONS: Strong micromorphological variation between different petals in the flower is exclusive to the subfamily Papilionoideae. Both major and minor epidermal types can be used as micromorphological markers of petal identity, at least in papilionoids, and they are important characters of flower evolution in the whole family. The molecular developmental pathway between specific epidermal micromorphology and the expression of petal identity genes has yet to be established.

Bird-pollinated flowers in an evolutionary and molecular context.

Evolutionary shifts to bird pollination (ornithophily) have occurred independently in many lineages of flowering plants. This shift affects many floral features, particularly those responsible for the attraction of birds, deterrence of illegitimate flower visitors (particularly bees), protection from vigorous foraging by birds, and accurate placement of pollen on bird's bodies. Red coloration appears to play a major role in both bee-deterrence and bird-attraction. Other mechanisms of bird-attraction include the production of abundant dilute nectar and the provision of secondary perches (for non-hovering birds). As a result of selection for similar phenotypic traits in unrelated bird-pollinated species, a floral syndrome of ornithophily can be recognized, and this review surveys the component floral traits. The strong convergent evolution evident in bird-pollinated flowers raises a question about the nature of the genetic mechanisms underlying such transitions and whether the same gene systems are involved in most cases. As yet there is too little information to answer this question. However, some promising model systems have been developed that include closely related bee and bird-pollinated flowers, such as Ipomoea, Mimulus, and Lotus. Recent studies of floral developmental genetics have identified numerous genes important in the development of the floral phenotype, which are also potential candidates for involvement in shifts between bee-pollination and bird pollination. As more whole-genome information becomes available, progress should be rapid.

Legume comparative genomics: progress in phylogenetics and phylogenomics.

The legumes are the focus of numerous rapidly expanding genomic projects, all of which involve members of one part of the Leguminosae, the subfamily Papilionoideae. This subfamily is monophyletic, and recent studies concur on a series of clades within it that are well supported and have received informal names. These include the Cladrastis clade, the genistoids (including Lupinus), the mirbelioids, the dalbergioids (including Arachis), the millettioids (including Glycine and Phaseolus), and the hologalegina (galegoid) legumes, which comprise the robinioids (including Lotus) and the inverted repeat loss (IRL) clade (including Medicago and Pisum). The canavanine-accumulating legumes appear to fall into a single clade, consistent with the idea that the production of this toxic amino acid evolved only once. Recent advances in analytical techniques for dating phylogenies support an 'early explosion hypothesis', suggesting that much of the morphological diversity of the legume family evolved rapidly around 50-60 million years ago. Within the papilionoids, the divergence between Glycine and Medicago is estimated to have taken place around 54 million years ago. There is strong evidence for a palaeoduplication event that affected both Glycine (a millettioid) and Medicago (from the IRL clade). As more genomic data are forthcoming for Arachis, it will be possible to test whether this event extends to the dalbergioids.