Phylogenetic analysis of Chloraeinae (Orchidaceae) based on plastid and nuclear DNA sequences

The phylogenetic relationships of subtribe Chloraeinae, a group of terrestrial orchids endemic to southern South America, have not been satisfactorily investigated. A previous molecular phylogenetic analysis based on plastid DNA supported the monophyly of Chloraeinae and Gavilea, but showed that Chloraea is non‐monophyletic and that the sole species of Bipinnula analysed is sister to Geoblasta. However, that analysis included only 18 of the 73 species belonging to this subtribe. Here, the phylogenetic relationships of Chloraeinae were assessed by analysing aproximately 7500 bp of nucleotide sequences from nuclear ribosomal internal transcribed spacer (ITS) and plastid DNA (rbcL, matK, trnL‐trnF, rpoB‐trnC) for 42 species representing all four currently accepted genera of Chloraeinae and appropriate outgroups. Nuclear and plastid data were analysed separately and in combination using two different methods, namely parsimony and Bayesian inference. Our analyses support the monophyly of Chloraeinae and their inclusion in an expanded concept of Cranichideae, but none of the genera of Chloraeinae that includes more than one species is monophyletic. Gavilea and Bipinnula are paraphyletic, with Chloraea chica nested in Gavilea and Geoblasta penicillata in Bipinnula. As currently delimited, Chloraea is polyphyletic. The taxonomic changes proposed recently are for the most part not justifiable on phylogenetic grounds, except for recognition of the monotypic genus Correorchis. The lack of resolution for the relationships among species of ‘core’Chloraea suggests a relatively recent diversification of this group. The current generic classification is in need or revision, but additional study is advisable before carrying out further taxonomic changes. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 168 , 258–277.     

Correlates and Consequences of Body Size in Nectar-Feeding Birds

Nectar-feeding birds are among the smallest birds and the largestpollinators. Energetic costs of maintenance, temperature regulation,foraging and reproduction increase in direct proportion to bodymass raised to fractional exponents, which may vary from 0.5to 1.0; overall costs probably vary with an exponent of 0.75.Avian nectarivores acquire most of their energy from flowernectar; in so doing they compete with other nectar feeders andpollinate plants. Larger pollinators are more reliable and movepollen greater distances, but to attract them plants must secretemore nectar and protect it from utilization by smaller animals.Minimum body size of avian nectarivores (2g) appears to reflectboth competition with insects and the limited capacity of thesmallest birds to acquire and store energy relative to the demandsof fasting, temperature regulation, and reproduction. Hummingbirdshave attained significantly smaller size than other nectar feedingbirds because lower metabolic rates and use of hypothermic torporreduce their energy expenditure relative to income. Maximumbody size of avian nectarivores (approximately 80g) apparentlyreflects the upper limit of plant energy expenditure for reliable,long distance pollination. Between these limits, size variationreflects divergence to reduce interspecific competition andcoevolution with plants to promote specificity     

The Stigma of Dendrobium speciosum Sm. (Orchidaceae): A New Stigma Type Comprising Detached Cells Within a Mucilaginous Matrix

The stigma of Dendrobium speciosum does not correspond to anymorphological category previously described. The stigma lieson the lower surface of the column as an oval, bowl-shaped depressioncontaining a wet, jelly-like, viscid material, which comprisesa large number of elongated, detached cells suspended in a matrix.The stigmatic cells are thick walled and have a vacuolated cytoplasmcontaining amyloplasts. These cells give a positive reactionto fluorescein diacetate indicating that the plasma membraneis intact; this evidence points to the conclusion that the stigmaticcells are not detached, senescent or necrotic papillae. Histochemical staining of the matrix shows high levels of acidicpolysaccharides with low levels of lipids and proteins. Biochemicalanalysis shows this matrix to comprise around 80 per cent uronicacids. This highly specialized stigma may be a further evolutionarydevelopment of the wet papillate stigma resulting from the specialneeds of both pollination and the nutritional support of thelarge number of developing pollen tubes. Stigma, Dendrobium speciosum, Orchidaceae     

Genetic divergence and assortative mating between colour morphs of the sea urchin Paracentrotus gaimardi

Some species of sea urchins feature large variation in pigmentation. This variability may be the result of phenotypic plasticity or it may be associated with genetic divergence between morphs. Paracentrotus gaimardi exhibits five colour morphs (pink, brown, green, grey and black), which often occur side by side on the same rock. We studied genetic divergence between these morphs in three populations on the coast of Brazil. A fragment of the region encoding the mitochondrial ATPase 8 and 6 mitochondrial genes, a fragment of the intron of a nuclear histone and the entire nuclear gene coding for the sperm protein bindin were analysed. Mitochondrial DNA was differentiated between the pink and all other morphs, but the histone intron was similar in all colour morphs. In bindin, nine codons were found to be under positive selection and significant differences of allelic frequencies were observed in almost all pairwise comparisons between colour morphs. Although the molecular differentiation in bindin is not large enough to suggest reproductive isolation, some degree of assortative mating within morphs seems to be occurring in this species.     

Electrical Impedance Studies on Potato and Alfalfa Tissue

Small pulses of alternating current have been found to be conductedchiefly in the channels of the cell walls of tubers of potato(Solatium tuberosum), the roots and stems of alfalfa (Medicagosativa), and similar plant tissue. Impedance measurements mayusefully detect the state of water relations in these channelswhen the frequency of the measuring A.C. is low (around 60 c/s),when chlori-dized silver probes are used and when the cell-wallresistance is low compared to the cell membranes in series.Activation energies have been calculated for the conductivityof these tissues. Over the temperature and soil moisture rangesinvestigated, the log impedance has been found to be approximatelylinear with the reciprocal of these parameters. Impedance changeshave also been found to accompany endogenous and other changesin the plant. In particular, pulses of light or heat causedchanges of impedance which reflect a change of internal waterrelations and possibly transport. Suitable light and potassiumfertilizer treatments at temperatures around 4 °C enhancedthe impedance of alfalfa and its apparent resistance to frost.