Showing papers by "Alex Widmer published in 2000"

Evolution of gall morphology and host‐plant relationships in willow‐feeding sawflies (hymenoptera: tenthredinidae)

Abstract: There are over 200 species of nematine sawflies that induce galls on willows ( Salix spp.). Most of the species are mono- or oligophagous, and they can be separated into seven or eight different groups based on the type of gall that they induce. We studied the evolution of different gall types and host plant associations by reconstructing the phylogeny of five outgroup and 31 ingroup species using DNA sequence data from the mitochondrial cytochrome b gene. Maximum-parsimony and maximum-likelihood analyses resulted in essentially the same phylogeny with high support for important branches. The results show that: (1) the galling species probably form a monophyletic group; (2) true closed galls evolved only once, via leaf folders; (3) with the possible exception of leaf rollers, all gall type groups are mono- or paraphyletic; (4) similar gall types are closer on the phylogeny than would be expected by a random process; (5) there is an apparent evolutionary trend in galling site from the leaf edge towards the more central parts of the host plant; and (6) many willow species have been colonized several times, which excludes the possiblity of parallel cladogenesis between willows and the gallers; however, there are signs of restrictions in the evolution of host use. Many of the patterns in the evolutionary history of nematine gallers have also been observed in earlier studies on other insect gallers, indicating convergent evolution between the independent radiations.

Genetic evidence for host specificity in the hemi-parasitic Viscum album L. (Viscaceae).

Abstract: Nuclear ribosomal DNA (nrDNA) ITS sequences and partial sequences of three non-coding chloroplast DNA (cpDNA) introns and spacers were used to assess genetic variation within and among three presumed host races of the hemi-parasite Viscum album L. Currently, identification of host races occurs via the host trees, and morphological differences are minute at best. cpDNA and nrDNA ITS sequences revealed little sequence variation, but the variation found consistently supported the distinction of three host races. cpDNA and ITS sequences were not incongruent, as assessed by the incongruence length difference test. A combined analysis supported the sister group relationship between mistletoes from deciduous trees and fir.

Molecular analysis of orchid pollinaria and pollinaria-remains found on insects.

Abstract: Direct observations of pollinator visits to orchids are often difficult and time consuming, especially in orchids with a deceptive pollination system where seed set is typically pollinator-limited. This lack of direct observations greatly inhibits our understanding of orchid-pollinator relationships and especially the degree of pollinator-specificity. Here we describe a molecular approach to the study of orchid-pollinator relationships based on the analysis of DNA recovered from pollinaria found on insects. The insects were collected from nectar-rich plants flowering near natural orchid populations, or taken from museum collections. Sequence analysis of the nuclear ribosomal ITS region allowed the identification of the orchid species or species-group from which the pollinaria originated. Four out of eight orchid-pollinator relationships established with this approach have not been reported previously, which highlights the value of molecular tools for the study of orchid pollination biology.

A molecular phylogenetic analysis of the neotropical dart-poison frog genus Phyllobates (Amphibia: Dendrobatidae).

Abstract: A phylogenetic analysis of the Neotropical dart-poison frogs, genus Phyllobates, was performed based on mitochondrial cytochrome b sequences. Members of Phyllobates from South and Central America were found to form each an evolutionary lineage. Among the South American lineage, species with uniform dorsal coloration as adults form a derived monophyletic clade.