Evolution of morphological differences with moderate genetic correlations among traits as exemplified by two flycatcher species (Ficeduia; Muscicapidae)

Theoretical work on multivariate evolution predicts that genetic correlations can act to constrain the rate at which new adaptive peaks are reached, but there is very limited empirical information available on this issue so far. To evaluate the importance of genetic correlations for evolutionary change, we studied the morphological differences between two flycatcher species (Ficeduia albicollis and F. hypoleuca) using both univariate and multivariate quantitative genetic models. Comparison of the results obtained using these different models revealed that even relatively low genetic correlations between traits will considerably increase the net selection forces needed for evolutionary changes in morphology. In particular, the divergence in wing and tail length, which are positively genetically correlated, would require a considerable amount of antagonistic selection. Because of the genetic correlations, strong selection will be needed to retain certain traits unchanged while others are changing. Based on these results, we argue that it is unlikely that small morphological differences such as between these two species could have evolved during a short (200 years) time period, i.e. the period of sympatry of these species in Sweden. These findings support the hypothesis that even relatively low genetic correlations may constrain short-term adaptive evolution in natural populations.     

Antennal glands in Psylliodes chrysocephala, and their possible role in reproductive behaviour

Abstract. The antennal morphology of Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae), an important pest of oilseed rape ( Brassica napus ), was studied. Two types of tricellular, integumentary glands were found. The common antennal glands are distributed under all sensilla-bearing parts of male and female antennae. The male-specific antennal glands are only located under a glabrous area found on antennomeres 6–10 of male beetles. The common antennal glands are synthetically active in both pre- and post-diapause adults, but the male specific antennal glands are only active in post-diapause (reproductively active) males. During studies of mating behaviour, the antennae of the males were highly active at the beginning and end of copulation, and in response to increased female activity. The male specific antennal glands may secrete a sex pheromone, and the glabrous area on the male antennae could be the release site for such a pheromone.     

Ethylene Release from Leaves of Xanthium strumarium L. and Zea mays L.

The release of ethylene into sealed Erlenmeyer flasks by intactleaves and leaf discs of Xanthium strumarium L. a C₃ plant andZea mays L. a C₄ plant were compared both in white light andin darkness. The effects of the presence or absence of addedCO₂ (in the form of sodium bicarbonate) the photosynthetic inhibitor3-[3,4-dichlorophenyl]-l, l-dimethyl urea (DCMU) and 1-aminocyclopropane-1-carboxylicacid (ACC), the precursor of ethylene in higher plants, werealso investigated. The rate of ethylene release from leaf tissue of Xanthium inthe absence of added CO₂ was markedly reduced in the light (i.e.at the CO₂ compensation point). Treatments that would enhancethe CO₂ availability to the tissue (i.e. added bicarbonate,darkness, treatment with DCMU) allowed higher levels of ethylenerelease. Incubation of the tissue with ACC considerably enhancedthe release of ethylene compared to that from the correspondingcontrol tissue without ACC. However, the pattern of ethylenerelease induced by the various treatments was similar with orwithout added ACC. When tissue, in the absence of added CO₂, was transferred fromlight to darkness, and back to light for 90 min periods, theethylene release rates Increased during the interposed darkperiod but resumed the lower rate during the final light period.The addition of CO₂ in the light resulted in a similar rateof ethylene release to that found in the dark. The overall pattern of ethylene release from Zea leaf tissuesubjected to light and dark in the presence or absence of addedCO₂ was similar to that of Xanthium. However, two or three timesmore ethylene was released from maize leaves in the light whenCO² was added compared to that generated in the dark. This isin marked contrast to Xanthium, where, under the light conditionsused, the ethylene release rate in the dark equalled or exceededthat occurring in the light, even in the presence of high levelsof CO₂. A very low rate of ethylene release was observed atthe CO₂ compensation point of maize. A speculative model is presented to explain how photosyntheticactivity might act as a key factor in regulating ethylene evolutionfrom leaf tissue in these experiments. It invokes the conceptof an inhibition by CO₂ of ethylene retention or breakdown thuspermitting more ethylene to be released from the leaves.     

Permeability of Bacteria to Inorganic Cations. A Comparison between a Psychrophilic Achromobacter Strain and Escherichia coli

The permeability of a psychrophilic Acbromobacter strain to the chlorides of Na, K, Mg and Ca was investigated with light-scattering technique. Comparisons, were made with cells of Escherichia coli B. Cells of both strains suspended in “water were plasmolyzed by 0.1 or 0.2 M solutions of MgCl₂ or CaCl₂ without subsequent deplasmolysis. NaCl or KCl also plasmolyzed the cells, but deplasmolysis followed.” When suspended in growth medium E. coli became completely de-plasmolyzed., whereas the psychrophile still excluded MgCl₂ and CaCl₂ to a great extent. The plasmolysis and deplasmolysis were reversible. Electron micrographs of the psychrophile exposed to CaCl₂ confirmed the presence of plasrnolysis.     

Genetic determination of honeybee (Apis mellifera L.) foraging preferences

Progeny from different honeybee queens that were reared in, and foraged from, the same colony sometimes differed in their floral preferences, confirming that these are to some extent innately determined.     

Gas exchange patterns of Pterostichus niger (Carabidae) in dry and moist air

Gas exchange patterns of adult male Pterostichus niger Schaller after hydration (i.e. given access to food and water) are compared in dry air [5–7% relative humidity (RH)] and moist air (90–97% RH) by means of flow‐through CO₂ respirometry combined with infrared probe actography. Of thirty beetles examined, slightly more than 50% showed continuous gas exchange and are not considered further. Of the remaining beetles, the majority (approximately 71%) display a pattern of cyclic gas exchange in both dry and moist air (i.e. CO₂ gas is released in bursts, with a low level of CO₂ release during the interburst periods). A minority of the beetles (four out of 30) are found to exhibit discontinuous gas exchange in both dry and moist air; this is characterized by three clearly separated states of the spiracles: closed (C), flutter (F) and open (O) phases. The pattern of cyclic gas exchange is associated with weak abdominal pulsations. After switching from moist to dry air, a small modulation of the discontinuous gas exchange cycles (maximum mean CO₂ production rate) occurs, providing no clear support for the hygric theory of discontinuous gas exchange in this species (i.e. that it serves to restrict respiratory water loss).     

ABSOLUTE AND RELATIVE PITCH PRODUCTION IN THE SONG OF THE WHITE-THROATED SPARROW (ZONO TRICHIA ALBICOLLIS)

ABSTRACT

The songs of white-throated sparrows consist of 5 notes of very pure tonal quality. In ascending song, the pitch increases substantially from Note 1 to Note 2; whereas, in descending song, pitch decreases substantially from Note 2 to Note 3. Variability in the absolute pitch of each note is considerable among birds, but much less within individuals. Analysis of the major pitch changes in these songs shows that the pitch interval (ratio of the higher to the lower frequency), a measure of relative pitch constancy, predicts the frequency of the higher note in the pitch change more precisely than does the difference between the frequencies of the two notes, a measure of absolute pitch constancy. We conclude that white-throated sparrows produce relative rather than absolute pitch constancy during the major frequency changes in their songs and suggest that pitch interval may be an important cue in species recognition.     

Litter decomposition in grasslands of Central North America (US Great Plains)

One of the major concerns about global warming is the potential for an increase in decomposition and soil respiration rates, increasing CO₂ emissions and creating a positive feedback between global warming and soil respiration. This is particularly important in ecosystems with large belowground biomass, such as grasslands where over 90% of the carbon is allocated belowground. A better understanding of the relative influence of climate and litter quality on litter decomposition is needed to predict these changes accurately in grasslands. The Long‐Term Intersite Decomposition Experiment Team (LIDET) dataset was used to evaluate the influence of climatic variables (temperature, precipitation, actual evapotranspiration, and climate decomposition index), and litter quality (lignin content, carbon : nitrogen, and lignin : nitrogen ratios) on leaf and root decomposition in the US Great Plains. Wooden dowels were used to provide a homogeneous litter quality to evaluate the relative importance of above and belowground environments on decomposition. Contrary to expectations, temperature did not explain variation in root and leaf decomposition, whereas precipitation partially explained variation in root decomposition. Percent lignin was the best predictor of leaf and root decomposition. It also explained most variation in root decomposition in models which combined litter quality and climatic variables. Despite the lack of relationship between temperature and root decomposition, temperature could indirectly affect root decomposition through decreased litter quality and increased water deficits. These results suggest that carbon flux from root decomposition in grasslands would increase, as result of increasing temperature, only if precipitation is not limiting. However, where precipitation is limiting, increased temperature would decrease root decomposition, thus likely increasing carbon storage in grasslands. Under homogeneous litter quality, belowground decomposition was faster than aboveground and was best predicted by mean annual precipitation, which also suggests that the high moisture in soil accelerates decomposition belowground.