The Crow Corvus corone hybrid zone in southern Denmark and northern Germany

In hybrid zones genetically differentiated populations meet and interbreed. As they result from ongoing divergence and potential speciation, such zones provide opportunities to study how different factors affect this process. One well-known avian hybrid zone is that between the Hooded Crow Corvus corone cornix and Carrion Crow C. c. corone , which extends throughout much of Europe. We compare the current position and width of the zone in southern Denmark and northern Germany with that described in detail by Meise in 1928. A GPS technique was used to determine the geographical position of more than 1000 Crows in established pairs in which all individuals were classified as either Carrion, Hooded or hybrid phenotype. The data show that the Carrion Crow has expanded northwards and that this is most pronounced at the eastern side of the study area. Here the hybrid zone has moved around 19 km. However, the width of the zone seems to have remained stable over time. Possible reasons for why the zone may have moved are discussed.     

Fixed wavelength fluorescence (FF) of bile as a monitoring tool for polyaromatic hydrocarbon exposure in fish: an evaluation of compound specificity,inner filter effect and signal interpretation

Fixed wavelength fluorescence (FF) of bile has been evaluated as a monitoring tool for the screening of polyaromatic hydrocarbon (PAH) contamination in fish. The methodology was studied through laboratory and field experiments with Atlantic cod (Gadus morhua L.) and flounder (Platichthys flesus L.) exposed to various forms of PAH contamination. The present study demonstrates the ability of FF screening to discriminate between 2-, 4- and 5-ring PAH metabolites by using the wavelength pairs 290/335 nm, 341/383 nm and 380/430 nm, respectively. In general, the degree of fluorescence interference between these metabolite groups appears to be low. Dose- and time-response patterns of the FF signals were shown to give a good reflection of the PAH exposure. Further, the necessity of an appropriate dilution of bile samples prior to fluorescence measurements is demonstrated by a study of inner filter effect. Normally a dilution of 1000-2000-fold is necessary. Individual differences in the bile density, e.g. measured as the concentration of the bile pigment biliverdin, have to be allowed for when applying the FF method. However, it is shown that normalizing the FF signals to biliverdin concentrations on an individual basis added extra error to the data set. The simple, rapid and cost-effective FF method is found to be well suited for screening fish for PAH contamination.     

Editor's column: Tnternational Geological Correlation Programme

The International Geological Correlation Programme (IGCP) offers great opportunities to geologists but suffers from a marked lack of identity in both public and professional perspective. This can be remedied by organizing the programme into a number of reasonably large projects with an identity of their own. Such a structure has to be attained according to a differentiated pattern, adjusted to accommodate groups and persons with initiative and dedication. The Board of the IGCP now has its great chance to act creatively by structurizing the programme. Now that the IGCP has become more widely known, geologists should make increased use of their formal powers to influence the programme, through the IUGS and individually.     

Migration, stopover and moult of the Great Reed Warbler Acrocephalus arundinaceus in Ghana, West Africa

We studied Great Reed Warblers Acrocephalus arundinaceus at two localities in Ghana during the winter. In the north (Tono), the birds arrived from late September and conducted a rapid moult soon after arrival. Towards the end of moult, birds accumulated fat and disappeared from the site. In the south (Tafo), birds arrived from mid-November in fresh plumage. This seemed to be the final wintering area as birds stayed there during the winter. In March-April they again accumulated fat, although only small amounts, before spring migration back to breeding areas.     

Tumor Gene Expression and Interphase Chromatin Appearance in Xiphophorus

SYNOPSIS. Xiphophorus maculatus (platyfish) exhibits spots whichconsist of neoplastically transformed pigment cells (T-cells).The spots actually represent extreme benign melanomas. Transformationto T-cells is mediated by a "tumor gene" (Tu). Platyfish whichdevelop from X-irradiated embryos reveal an increase of Tu-expressionresulting in an overproduction of T-cells to benign melanomaswhich can be compared to that observed in certain hybrids betweenthe platyfish and Xiphophorus helleri (swordtail). Both theX irradiation-induced and the crossing conditioned increaseof Tu-expression represent a heritable alteration which mightbe related to a conversion from dispersed to condensed chromatinin the interphase nuclei.     

How is host egg mimicry maintained in the cuckoo (Cuculus canorus)?

To investigate the evolutionary mechanism (host specificity vs. random searching) maintaining mimicry between cuckoo egg appearance and that of different European cuckoo Cuculus canorus hosts, we studied the level of mimicry between the appearance of C. canorus eggs and that of their hosts' eggs in different habitats in southern Finland by using ultraviolet-visible reflectance spectrophotometry. In the main habitat used by C. canorus for reproduction, eggs laid in nests of different host species differed in appearance. Host use by C. canorus was not related to the abundance of hosts, and the level of mimicry was not related to host abundance in the habitat. Furthermore, a close match between C. canorus egg appearance and that of host eggs within habitats was detected after removing the potentially confounding effect of host abundance. In the only two suitable host species nesting in trees (namely chaffinch Fringilla coelebs and brambling Fringilla montifringilla ) we detected changes in C. canorus egg appearance that paralleled those of the two host species. Thus our findings suggest the existence of a correlation between the appearance of C. canorus eggs and that of their hosts' eggs within different habitat types, and suggest that mimicry is maintained by strict host preferences by each C. canorus female when laying.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 57–68.     

The moult of Barred Warblers Sylvia nisoria in Kenya—evidence for a split wing-moult pattern initiated during the birds' first winter*

The moult of Barred Warblers Sylvia nisoria was studied during three winter seasons in southeastern Kenya at a southward passage site (Ngulia) and a wintering site (Mtito Andei). Most Barred Warblers migrating through Ngulia in November had yet to commence winter moult. These birds probably moulted subsequently in winter in northern Tanzania. In December, birds were found in heavy moult at Mtito Andei, and some of these birds were known to stay throughout the winter. By contrast, most birds reaching southeastern Kenya from late December onwards had already completed part or all of their winter moult, presumably at stopover sites in northern and eastern Kenya or in Ethiopia. Thus, winter moult in Barred Warblers takes place mainly in late November and December, either just before or soon after the final leg of autumn migration. In general, first-year birds renewed all tertials and tail feathers, about three to five secondaries per wing and commonly also the outer one to four large primaries per wing. Adults renewed all tertials and tail feathers, almost all secondaries and only occasionally an outer primary. The replacement of relatively fresh juvenile secondaries during the birds' first winter implies that the split moult pattern of this species (secondaries, tertials and tail moulted in winter; primaries and tertials in summer) is endogenously controlled.