Composition of the essential oils of Ocimum urticifolium (Lamiaceae) chemotypes grown in Rwanda

NTEZURUBANZA, L., SCHEFFER, J. J. C. & SVENDSEN, A. B., 1988. Composition of the essential oils of Ocimum urticifolium (Lamiaceae) chemotypes grown in Rwanda. Leaves and flowers of 48 specimen of Ocimum urticifolium (synonym: O. suave), Lamiaceae, were collected in different parts of Rwanda. The volatile components of each specimen were isolated by hydrodistillation under standardized conditions, and the 48 essential oils analysed by thin-layer chromatography. This preliminary analysis showed six different oil compositions. Thereafter, six oil samples were fractionated by liquid—solid chromatography. The fractions thus obtained, and all other oil samples were then analyzed by capillary gas chromatography. In this way 46 compounds were identified in the various oil samples. Eight components, which amounted to more than 10% in at least one oil sample, were used to characterize the oils. Twelve oil types were distinguished, three of which were dominated by one component only: eugenol, methyleugenol and transmethylisoeugenol respectively. The other types were more complex. In some parts of Rwanda almost one oil type seemed to occur, whereas in other areas a more heterogeneous collection of types was found. Eugenol was quantitatively most important in 31 of the 48 oil samples, in 22 of which this component amounted to more than 50%.     

Eleven polymorphic microsatellite loci in Lindera benzoin,Lauraceae

Microsatellite markers were developed for studies of the genetic diversity and population substructure of Lindera benzoin, Lauraceae (spicebush). Nuclear microsatellite sequences were obtained from DNA libraries that were enriched for (CA), (GA), (AAG) and (ATG) repeat motifs. From 69 microsatellite sequences, 20 primer sets were developed. Of these, 11 primer pairs resulted in amplified polymorphic loci. In 29 samples of eastern Pennsylvania spicebush plants, the number of microsatellite alleles ranged from two to 16 per locus with observed heterozygosity values ranging from 0.10 to 0.82.     

Uncovering tropical diversity: six sympatric cryptic species of Blepharoneura (Diptera: Tephritidae) in flowers of Gurania spinulosa (Cucurbitaceae) in eastern Ecuador

Diversification of phytophagous insects is often associated with changes in the use of host taxa and host parts. We focus on a group of newly discovered Neotropical tephritids in the genus Blepharoneura , and report the discovery of an extraordinary number of sympatric, morphologically cryptic species, all feeding as larvae on calyces of flowers of a single functionally dioecious and highly sexually dimorphic host species ( Gurania spinulosa ) in eastern Ecuador. Molecular analyses of the mitochondrial cytochrome oxidase-I gene from flies reared from flowers of G. spinulosa reveal six distinct haplotype groups that differ by 7.2–10.1% bp (uncorrected pairwise distances; N  = 624 bp). Haplotype groups correspond to six distinct and well-supported clades. Members of five clades specialize on the calyces of flowers of a particular sex: three clades comprise male flower specialists; two clades comprise female flower specialists; the sixth clade comprises generalists reared from male and female flowers. The six clades occupy significantly different morphological spaces defined by wing pigmentation patterns; however, diagnostic morphological characters were not discovered. Behavioural observations suggest specific courtship behaviours may play a role in maintaining reproductive isolation among sympatric species. Journal compilation  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 779–797. No claim to original US government works.     

Microscale vegetation-soil feedback boosts hysteresis in a regional vegetation–climate system

It has been hypothesized that a positive feedback between vegetation cover and monsoon circulation may lead to the existence of two alternative stable states in the Sahara region: a vegetated state with moderate precipitation and a desert state with low precipitation. This could explain the sudden onset of desertification in the region about 5000 years ago. However, other models suggest that the effect of vegetation on the precipitation may be insufficient to produce this behavior. Here, we show that inclusion of the microscale feedback between soil and vegetation in the model greatly amplifies the nonlinearity, causing alternative stable states and considerable hysteresis even if the effect of vegetation on precipitation is moderate. On the other hand, our analysis suggests that self‐organized vegetation patterns known from models that only focus at the microscale plant–soil feedback will be limited to a narrower range of conditions due to the regional scale climate‐feedback. This implies that in monsoon areas such as the Western Sahara self‐organized vegetation patterns are predicted to be less common than in areas without monsoon circulation such as Central Australia.     

Wintering Snowy Owls Bubo scandiacus integrate plumage colour,behaviour and their environment to maximize efficacy of visual displays

For a comprehensive understanding of the evolution of animal signals, it is necessary to understand how the performance of visual displays is maximized to get the most possible attention from receivers. We assessed whether the white plumage of Snowy Owls Bubo scandiacus functioned as a social signal and, if so, how coloration and behavioural adaptations enhance signal efficacy. Signalling theory predicts that: (1) the colour properties of plumage should vary across the body, with the brightest parts being those involved in visual display performance; (2) specific displays calling attention to or enhancing detection or conspicuousness to conspecifics should be evident; and (3) location of the signallers should be such that signal efficacy is optimized. All three predictions were supported. The brightest areas of the plumage (particularly the face, throat and upper breast) were always unspotted, and white is particularly effective in open habitats characteristic of this species. The birds displayed a specific posture and orientated toward the sun preferentially on sunny days, and Owls with the whitest (least spotted) plumage displayed more and signalled more frequently from perches on the ground, where albedo from the snow may enhance the visual display. Snowy Owls integrate coloration, behaviour and environment through habitat selection to maximize the efficacy of their visual displays.     

Ambiguous climate impacts on competition between submerged macrophytes and phytoplankton in shallow lakes

1. Shallow lakes may switch from a state dominated by submerged macrophytes to a phytoplankton‐dominated state when a critical nutrient concentration is exceeded. We explore how climate change may affect this critical nutrient concentration by linking a graphical model to data from 83 lakes along a large climate gradient in South America. 2. The data indicate that in warmer climates, submerged macrophytes may tolerate more underwater shade than in cooler lakes. By contrast, the relationship between phytoplankton biomass [approximated by chlorophyll‐a (chl‐a) or biovolume] and nutrient concentrations did not change consistently along the climate gradient. In warmer climates, the correlation between phytoplankton biomass and nutrient concentrations was overall weak, especially at low total phosphorus (TP) concentrations where the chl‐a/ TP ratio could be either low or high. 3. Although the enhanced shade tolerance of submerged plants in warmer lakes might promote the stability of their dominance, the potentially high phytoplankton biomass at low nutrient concentrations suggests an overall low predictability of climate effects. 4. We found that near‐bottom oxygen concentrations are lower in warm lakes than in cooler lakes, implying that anoxic P release from eutrophic sediment in warm lakes likely causes higher TP concentrations in the water column. Subsequently, this may lead to a higher phytoplankton biomass in warmer lakes than in cooler lakes with similar external nutrient loadings. 5. Our results indicate that climate effects on the competitive balance between submerged macrophytes and phytoplankton are not straightforward.     

Effects of resources and mortality on the growth and reproduction of Nile perch in Lake Victoria

1. A collapse of Nile perch stocks of Lake Victoria could affect up to 30 million people. Furthermore, changes in Nile perch population size‐structure and stocks make the threat of collapse imminent. However, whether eutrophication or fishing will be the bane of Nile perch is still debated. 2. Here, we attempt to unravel how changes in food resources, a side effect of eutrophication, and fishing mortality determine fish population growth and size structures. We parameterised a physiologically structured model to Nile perch, analysed the influence of ontogenetic diet shifts and relative resource abundances on existence boundaries of Nile perch and described the populations on either side of these boundaries. 3. Our results showed that ignoring ontogenetic diet shifts can lead to over‐estimating the maximum sustainable mortality of a fish population. Size distributions can be indicators of processes driving population dynamics. However, the vulnerability of stocks to fishing mortality is dependent on its environment and is not always reflected in size distributions. 4. We suggest that the ecosystem, instead of populations, should be used to monitor long‐term effects of human impact.     

Molecular phylogeny and systematics of leaf‐mining flies (Diptera: Agromyzidae): delimitation of Phytomyza Fallén sensu lato and included species groups,with new insights on morphological and host‐use evolution

Abstract Phytomyza Fallén is the largest genus of leaf‐mining flies (Agromyzidae), with over 530 described species. Species of the superficially similar genus Chromatomyia Hardy have been included in Phytomyza by some authors and the status of the genus remains uncertain. Using 3076 bp of DNA sequence from three genes [cytochrome oxidase I (COI), CAD (rudimentary), phosphogluconate dehydrogenase (PGD)] and 113 exemplar species, we identified and tested the monophyly of host‐associated species groups in Phytomyza and Chromatomyia and investigated the phylogenetic relationships among these groups. Chromatomyia is polyphyletic and nested largely within Phytomyza; two small groups of species, however, are related more closely to Ptochomyza and Napomyza. Therefore, we synonymize Chromatomyia syn.n. , Ptochomyza syn.n. , and Napomyza syn.n. with Phytomyza, recognizing Ptochomyza, Napomyza and Phytomyza sensu stricto as subgenera of Phytomyza. We recognize five major clades within Phytomyza sensu stricto that comprise the majority of species ascribed previously to Chromatomyia and Phytomyza. Many species groups recognized previously were recovered as monophyletic, or virtually so, but some (e.g. robustella and atomaria groups) required emendation. On the basis of the proposed phylogeny and recent taxonomic literature, we present a preliminary revision of 24 species groups within Phytomyza, but leave many species unplaced. Evolution of internal pupariation (within the host’s tissue), regarded as a defining character of the former Chromatomyia, is discussed with regard to the new phylogeny, and we suggest a correlation with stem or leaf midrib mining. The large size of the Phytomyza lineage and an inferred pattern of host family‐specific species radiations make it a promising candidate for the study of macroevolutionary patterns of host shift and diversification in phytophagous insects. The proposed generic synonymies necessitate a number of new combinations. The following 46 species described in Chromatomyia are transferred to Phytomyza: P. actinidiae (Sasakawa) comb.n. , P. alopecuri (Griffiths) comb.n. , P. arctagrostidis (Griffiths) comb.n. , P. beigerae (Griffiths) comb.n. , P. blackstoniae (Spencer) comb.n. , P. centaurii (Spencer) comb.n. , P. chamaemetabola (Griffiths) comb.n. , P. cinnae (Griffiths) comb.n. , P. compta (Spencer) comb.n. , P. cygnicollina (Griffiths) comb.n. , P. doolittlei (Spencer) comb.n. , P. elgonensis (Spencer) comb.n. , P. eriodictyi (Spencer) comb.n. , P. flavida (Spencer) comb.n. , P. fricki (Griffiths) comb.n. , P. furcata (Griffiths) comb.n. , P. griffithsiana (Beiger) comb.n. , P. hoppiella (Spencer) comb.n. , P. ixeridopsis (Griffiths) comb.n. , P. kluanensis (Griffiths) comb.n. , P. leptargyreae (Griffiths) comb.n. , P. linnaeae (Griffiths) comb.n. , P. luzulivora (Spencer) comb.n. , P. mimuli (Spencer) comb.n. , P. mitchelli (Spencer) comb.n. , P. montella (Spencer) comb.n. , P. nigrilineata (Griffiths) comb.n. , P. nigrissima (Spencer) comb.n. , P. orbitella (Spencer) comb.n. , P. paraciliata (Godfray) comb.n. , P. poae (Griffiths) comb.n. , P. pseudomilii (Griffiths) comb.n. , P. qinghaiensis (Gu) comb.n. , P. rhaetica (Griffiths) comb.n. , P. scabiosella (Beiger) comb.n. , P. seneciophila (Spencer) comb.n. , P. shepherdiana (Griffiths) comb.n. , P. spenceriana (Griffiths) comb.n. , P. styriaca (Griffiths) comb.n. , P. subnigra (Spencer) comb.n. , P. suikazurae (Sasakawa) comb.n. , P. symphoricarpi (Griffiths) comb.n. , P. syngenesiae (Hardy) comb.n. , P. thermarum (Griffiths) comb.n. , P. torrentium (Griffiths) comb.n. and P. tschirnhausi (Griffiths) comb.n. Furthermore, we transfer all species of Napomyza to Phytomyza, resulting in the following new combinations: P. achilleanella (Tschirnhaus) comb.n. , P. acutiventris (Zlobin) comb.n. , P. angulata (Zlobin) comb.n. , P. arcticola (Spencer) comb.n. , P. bellidis (Griffiths) comb.n. , P. carotae (Spencer) comb.n. , P. cichorii (Spencer) comb.n. , P. curvipes (Zlobin) comb.n. , P. dubia (Zlobin) comb.n. , P. filipenduliphila (Zlobin) comb.n. , P. flavivertex (Zlobin) comb.n. , P. flavohumeralis (Zlobin) comb.n. , P. genualis (Zlobin) comb.n. , P. grandella (Spencer) comb.n. , P. humeralis (Zlobin) comb.n. , P. immanis (Spencer) comb.n. , P. immerita (Spencer) comb.n. , P. inquilina (Kock) comb.n. , P. kandybinae (Zlobin) comb.n. , P. lacustris (Zlobin) comb.n. , P. laterella (Zlobin) comb.n. , P. manni (Spencer) comb.n. , P. maritima (Tschirnhaus) comb.n. , P. merita (Zlobin) comb.n. , P. mimula (Spencer) comb.n. , P. minuta (Spencer) comb.n. , P. montanoides (Spencer) comb.n. , P. neglecta (Zlobin) comb.n. , P. nigriceps (van der Wulp) comb.n. , P. nugax (Spencer) comb.n. , P. pallens (Spencer) comb.n. , P. paratripolii (Chen & Wang) comb.n. , P. plumea (Spencer) comb.n. , P. plumigera (Zlobin) comb.n. , P. prima (Zlobin) comb.n. , P. pubescens (Zlobin) comb.n. , P. schusteri (Spencer) comb.n. , P. scrophulariae (Spencer) comb.n. , P. suda (Spencer) comb.n. , P. tanaitica (Zlobin) comb.n. , P. tenuifrons (Zlobin) comb.n. , P. vivida (Spencer) comb.n. , P. xizangensis (Chen & Wang) comb.n. and P. zimini (Zlobin) comb.n. Phytomyza asparagi (Hering) comb.n. and P. asparagivora (Spencer) comb.n. are transferred from Ptochomyza. In Phytomyza ten new names are proposed for secondary homonyms created by generic synonymy: P. echo Winkler nom.n. for P. manni Spencer, 1986; P. californiensis Winkler nom.n. for C. montana Spencer, 1981 ; P. griffithsella Winkler nom.n. for C. griffithsi Spencer, 1986; P. vockerothi Winkler nom.n. for C. nigrella Spencer, 1986; P. kerzhneri Winkler nom.n. for N. nigricoxa Zlobin, 1993; P. asteroides Winkler nom.n. for N. tripolii Spencer, 1966; P. minimoides Winkler nom.n. for N. minima Zlobin, 1994; P. nana Winkler nom.n. for N. minutissima Zlobin, 1994; P. ussuriensis Winkler nom.n. for N. mimica Zlobin, 1994 and P. zlobini Winkler nom.n. for N. hirta Zlobin, 1994.     

Strong growth limitation of a floating plant (Lemna gibba) by the submerged macrophyte (Elodea nuttallii) under laboratory conditions

1. The asymmetric competition for light and nutrients between floating and submerged aquatic plants is thought to be key in explaining why dominance by either of these groups can be stable and difficult to change. 2. Although the shading effect of floating plants on submerged plants has been well documented, the impact of submerged plants on floating plants has been poorly explored hitherto. 3. Here, we used laboratory experiments to examine how submerged plant (Elodea nuttallii) alter nutrient conditions in the water column and how this affects the growth of floating plants (Lemna gibba). 4. We demonstrate that, at higher nutrient concentrations, Lemna is increasingly likely to outcompete Elodea. 5. Under low nutrient concentrations (0.1–2 mg N L^?1) Elodea can strongly reduce the growth of Lemna. Growth of floating plants virtually stopped in some of the experiments with Elodea. 6. Extremely reduced tissue N, Mn, chlorophyll and elongated roots indicated that the growth inhibition of Lemna by Elodea was predominantly caused by the latter’s impact on the nutrient conditions for floating plants. 7. These results strengthen the hypothesis that submerged plants can prevent colonization of a lake by floating plants.