Search results for "systematics."
showing 10 items of 4966 documents
Olfactory response of two aphid parasitoids, Lysiphlebus testaceipes and Aphidius colemani, to aphid-infested plants from a distance
2004
The role of volatile stimuli in the host-searching behaviour of the two parasitoid species Lysiphlebus testaceipes Cresson and Aphidius colemani Viereck (Hymenoptera: Braconidae) was studied in relation to the host Aphis gossypii Glover (Homoptera: Aphididae) on cucumber plants, Cucumis sativa L. (Cucurbitaceae). Experiments were carried out in the laboratory in a wind tunnel, exposing individual parasitoids to signals from three sources simultaneously: (1) a complex of cucumber plants, Cucumis sativa , and A. gossypii ; (2) uninfested cucumber plants; and (3) dummy cardboard plants. The flight response of the female parasitoids was considered oriented when they landed on plants and non-ori…
Warning coloration can be disruptive: aposematic marginal wing patterning in the wood tiger moth
2015
Warning (aposematic) and cryptic colorations appear to be mutually incompatible because the primary function of the former is to increase detectability, whereas the function of the latter is to decrease it. Disruptive coloration is a type of crypsis in which the color pattern breaks up the outline of the prey, thus hindering its detection. This delusion can work even when the prey’s pattern elements are highly contrasting; thus, it is possible for an animal’s coloration to combine both warning and disruptive functions. The coloration of the wood tiger moth (Parasemia plantaginis) is such that the moth is conspicuous when it rests on vegetation, but when it feigns death and drops to the gras…
Will legal international rhino horn trade save wild rhino populations?
2020
Wild vertebrate populations all over the globe are in decline, with poaching being the second-most-important cause. The high poaching rate of rhinoceros may drive these species into extinction within the coming decades. Some stakeholders argue to lift the ban on international rhino horn trade to potentially benefit rhino conservation, as current interventions appear to be insufficient. We reviewed scientific and grey literature to scrutinize the validity of reasoning behind the potential benefit of legal horn trade for wild rhino populations. We identified four mechanisms through which legal trade would impact wild rhino populations, of which only the increased revenue for rhino farmers cou…
Holocephalan (Chondrichthyes) dental plates with hypermineralized dentine as a substitute for missing teeth through developmental plasticity.
2020
All extant holocephalans (Chimaeroidei) have lost the ability to make individual teeth, as tooth germs are neither part of the embryonic development of the dental plates, nor of their continuous growth. Instead, a hypermineralized dentine with a unique mineral, whitlockin, is specifically distributed within a dentine framework into structures that give the dental plates their distinctive, species-specific morphology. Control of the regulation of this distribution must be cellular, with a dental epithelium initiating the first outer dentine, and via contact with ectomesenchymal tissue as the only embryonic cell type that can make dentine.\ud Chimaeroids have three pairs of dental plates with…
Planktivorous vendace (Coregonus albula ) utilise algae-derived fatty acids for biomass increase and lipid deposition
2017
Spatial and seasonal variation in the abundance and composition of phytoplankton and other basal resources (bacteria, terrestrial detritus) influence the availability of essential polyunsaturated fatty acids (PUFA) for upper trophic levels in lake food webs. We studied accumulation, composition and content of fatty acids in planktivorous vendace (Coregonus albula) muscle tissue during the summer feeding period (May to late September) in six boreal lakes. Vendace muscle fatty acid content increased from ~17.7 mg/g DW to ~28.1 mg/g DW from spring to summer, corresponding to a ~59% increase in total fatty acids. PUFA accounted for 45%–65% of all fatty acids, and the most abundant fatty acid wa…
Riella heliospora (Riellaceae) a new monoicous species of Riella subgenus Trabutiella from California
2012
14 páginas, 8 figuras, 1 tabla.
Taxonomic revision of Riella subgenus Trabutiella (Riellaceae, Sphaerocarpales)
2014
The genus Riella (Riellaceae, Sphaerocarpales) includes some 24 species of thalloid aquatic liverworts with unique morphological and ecological features among hepatics. These include the development of sporophytes enclosed within involucres and growing submerged in seasonal fresh or brackish water ponds. Riella subgenus Trabutiella includes species with winged involucres. Seven taxa have been described, however, four to five taxa have been recognized at a time depending on authors. In this study we have conducted a morphological revision of the species of this subgenus, based on 59 traits measured under light and Scanning Electron Microscopy analyses and that were the subject of statistical…
Variability in δ13C values between individual Daphnia ephippia: Implications for palaeo-studies
2018
The stable carbon isotope ratio (δ13 C value) of Daphnia spp. resting egg shells (ephippia) provides information on past changes in Daphnia diet. Measurements are typically performed on samples of _20 ephippia, which obscures the range of values associated with individual ephippia. Using a recently developed laser ablation-based technique, we perform multiple δ13 C analyses on individual ephippia, which show a high degree of reproducibility (standard deviations 0.1e0.5‰). We further measured δ13 C values of 13 ephippia from surface sediments of three Swiss lakes. In the well-oxygenated lake with low methane concentrations, δ13 C values are close to values typical for algae (_31.4‰) and the …
Ultraviolet radiation exposure of a high arctic lake in Svalbard during the Holocene
2014
Long-term fluctuations in lake-water optical properties were examined using a Holocene sediment sequence and multi-proxy palaeolimnological approach in Lake Einstaken, Nordaustlandet, Svalbard. UV-absorbance of sedimentary cladoceran remains provided information on underwater UV exposure and changes in lake-catchment coupling processes were inferred from sediment geochemistry. In addition, aquatic community succession was used as an indicator for lake-water bio-optical properties and a Holocene record of sun activity (sunspots) was utilized to evaluate long-term solar forcing. The results indicated that the UV-absorbance of cladoceran remains was highest (i.e. maximum UV-induced pigmentatio…
Climate signal age effects in boreal tree-rings: Lessons to be learned for paleoclimatic reconstructions
2016
Abstract Age-related alternation in the sensitivity of tree-ring width (TRW) to climate variability has been reported for different forest species and environments. The resulting growth-climate response patterns are, however, often inconsistent and similar assessments using maximum latewood density (MXD) are still missing. Here, we analyze climate signal age effects (CSAE, age-related changes in the climate sensitivity of tree growth) in a newly aggregated network of 692 Pinus sylvestris L. TRW and MXD series from northern Fennoscandia. Although summer temperature sensitivity of TRW ( r All = 0.48) ranges below that of MXD ( r All = 0.76), it declines for both parameters as cambial age in…