The aim of this study was to evaluate how the summer and winter conditions affect the photosynthesis and water relations of well-watered orange trees, considering the diurnal changes in leaf gas exchange, chlorophyll (Chl) fluorescence, and leaf water potential (Ψ) of potted-plants growing in a subtropical climate. The diurnal pattern of photosynthesis in young citrus trees was not significantly affected by the environmental changes when compared the summer and winter seasons. However, citrus plants showed higher photosynthetic performance in summer, when plants fixed 2.9 times more CO2 during the diurnal period than in the winter season. Curiously, the winter conditions were more favorable to photosynthesis of citrus plants, when considering the air temperature (< 29 °C), leaf-to-air vapor pressure difference (< 2.4 kPa) and photon flux density (maximum values near light saturation) during the diurnal period. Therefore, low night temperature was the main environmental element changing the photosynthetic performance and water relations of well-watered plants during winter. Lower whole-plant hydraulic conductance, lower shoot hydration and lower stomatal conductance were noticed during winter when compared to the summer season. In winter, higher ratio between the apparent electron transport rate and leaf CO2 assimilation was verified in afternoon, indicating reduction in electron use efficiency by photosynthesis. The high radiation loading in the summer season did not impair the citrus photochemistry, being photoprotective mechanisms active. Such mechanisms were related to increases in the heat dissipation of excessive light energy at the PSII level and to other metabolic processes consuming electrons, which impede the citrus photoinhibition under high light conditions. and R. V. Ribeiro ... [et al.].
The seasonal changes of the nematode Camallanus anabantis Pearse, 1933, in the climbing perch (Anabas testudineus) from the freshwater swamps near Kalyani town, West Bengal, India were studied during the period from February 1988 to August 1989. The nematode exhibited a one-year cycle. Larvated females occurred in the fishes from October to February at a water temperature of 12“-29 °C. New infection of fishes occurred from February to May and occasionally in September. The fourth-stage larvae, the males, and the young females (without eggs), although irregularly, were found present throughout the year. Egg-laden females occurred in the fishes in August, October to February, and March.
This is the first study detailing the microhabitat specificity of the monogenean parasite, Paradiplozoon ichthyoxanthon Avenant-Oldewage in Avenant-Oldewage et al., 2014. Samples of the monogenean were collected from the gills of the smallmouth yellowfish Labeobarbus aeneus (Burchell) from the Vaal Dam, South Africa, over four seasons with the use of gill nets. Host condition factor fluctuated between the different seasons, with the highest values recorded in summer. Adults and diporpas of P. ichthyoxanthon were found in all four seasons. Adult parasites predominantly infect the first gill arch, whereas diporpas were found on the second and fourth arches. In utero eggs were also found throughout the sampling seasons and their number negatively correlated with the condition factor of the host. The occurrence of adults and diporpas of P. ichthyoxanthon correlated with the size of the host but not the condition factor. Water quality of the study site also had little correlational relationship with the occurrence of the parasites and fluctuations were related to season. The main factor that may drive the microhabitat specificity of P. ichthyoxanthon is the flow of water over the surfaces of the gills and chances of the parasites becoming dislodged. Size of the attachment organs has also been shown to play a role in this specificity, because smaller attachment structures favour stronger holdfast to areas where flow might be stronger compared to larger attachment structures., Beric M. Gilbert, Annemariè Avenant-Oldewage., and Obsahuje bibliografii
Data are presented on the variable patterns of the seasonal dynamics of Ixodes ricinus L. ticks seen questing on the vegetation and feeding on small rodents (mice and voles) and squirrels within a British woodland focus of Lyme borreliosis. Information on tick infestation levels on pheasants is also presented. The results show a prolonged, unimodal pattern of tick activity, with ticks feeding throughout the year in this sheltered habitat. If host density is taken into account, squirrels are quantitatively more important than small mammals as hosts for larval ticks from April until July, and overwhelmingly so for nymphal ticks throughout the year. The observed inter- and intraspecific differences in tick infestation levels are related to the behaviour of both hosts and ticks. Squirrels, as competent hosts for Borrelia burgdorferi and frequent occupants of habitats closely associated with man, will contribute significantly to the risk of Lyme disease.
In this paper the seasonality of summer, winter and annual maximum discharges in mid-sized catchments of Slovakia was analysed. The seasonality measure represents an important indicator of flood processes and can be used as a pooling characteristic in regional flood frequency analysis. The seasonality characteristics such as mean date of flood occurrence (DQ) and seasonal concentration index (r) were derived in 142 Slovak catchments, with the lengths of observation 20 to 70 years. The DQ value represents the fictive centre of the occurrence of Qmax within a year and the weighted value of all dates of Qmax occurrence; the index r expresses a measure of the variability of the date of occurrence and it is based on the principles of directional statistics. The analysis of summer, winter and annual flood seasonality in the territory of Slovakia showed that a majority of the catchments show higher potential for summer floods than winter floods. Catchments with high flood risk are located mainly in the flysch region of Slovakia, the Spis Region and the Laborec Mountains, the Slovenske Rudohorie, the Slovenske stredohorie Mts. and the Fatra Region. and Predložený príspevok sa zaoberá analýzou charakteristík sezónnosti letných, zimných a ročných maximálnych prietokov na vybraných povodiach Slovenska. Charakteristiky sezónnosti sú významným ukazovateľom procesu tvorby povodní, a sú často typizačnou hodnotou pre následné regionalizačné analýzy. Do procesu vyhodnocovania sezónnosti letných, zimných a ročných maximálnych prietokov bolo vybraných 142 povodí Slovenska s radom pozorovaní do roku 2001 s dĺžkou časového radu od 20 do 70 rokov. Sezónnosť bola definovaná dvoma charakteristikami: priemerným dňom výskytu povodní (DQ) a indexom sezónnej koncentrácie r. Veličina DQ charakterizuje fiktívne ťažisko výskytov Qmax v kalendárnom roku a v jej hodnote sú vážené všetky dátumy výskytov prietokov. Index sezónnej koncentrácie maximálnych ročných prietokov (r) indikuje rozptyl dní výskytu maximálnych prietokov v priebehu roka a jeho výpočet je založený na princípoch teórie centroidných dát (directional statistics). Na základe vykonanej analýzy bolo možné začleniť povodia Slovenska z hľadiska náchylnosti na výskyt povodní v jednotlivých ročných sezónach do viacerých oblastí. Za najrizikovejšie oblasti sa javia povodia západného flyšového pásma, povodia v oblasti Spiša, Šariša, Slovenského Rudohoria, Slovenského stredohoria a FatranskoTatranskej oblasti, a to z hľadiska výskytu letných ako aj ročných maximálnych prietokov.
The aim of this study is to understand the seasonalities of runoff and precipitation and their controls along two transects in Peru and one transect in Austria. The analysis is based on daily precipitation data at 111 and 61 stations in Peru and Austria, respectively, and daily discharge data at 51 and 110 stations. The maximum Pardé coefficient is used to quantify the strength of the seasonalities of monthly precipitation and runoff. Circular statistics are used to quantify the seasonalities of annual maximum daily precipitation and annual maximum daily runoff. The results suggest that much larger spatial variation in seasonality in Peru is because of the large diversity in climate and topography. In the dry Peruvian lowlands of the North, the strength of the monthly runoff seasonality is smaller than that of precipitation due to a relatively short rainy period from January to March, catchment storage and the effect of upstream runoff contributions that are more uniform within the year. In the Peruvian highlands in the South, the strength of the monthly runoff seasonality is greater than that of precipitation, or similar, due to relatively little annual precipitation and rather uniform evaporation within the year. In the Austrian transect, the strength of the runoff seasonality is greater than that of precipitation due to the influence of snowmelt in April to June. The strength of monthly regime of precipitation and runoff controls the concentration of floods and extreme precipitation in Peruvian transects. The regions with strong monthly seasonality of runoff have also extreme events concentrated along the same time of the year and the occurrence of floods is mainly controlled by the seasonality of precipitation. In Austria, the monthly runoff maxima and floods occur in the same season in the Alps. In the lowlands, the flood seasonality is controlled mainly by summer extreme precipitation and its interplay with larger soil moisture.
The analyses of precipitation and runoff data along topographic gradients in Peru and Austria showed that, overall, in Peru the spatial variation in seasonality is much larger than in Austria. This is because of the larger diversity in climate and topography.
Components of daily and seasonal timing systems in insects are reviewed. Photoperiod indicates seasonal position reliably, but signals can be much modified by habitat, latitude and season. Several receptor features and pigment systems are known, with different daily, seasonal and general functions, including differences between circadian and seasonal reception. Clocks can serve several different purposes, functioning as daily oscillators, interval timers or through successive requirements. The molecular functioning of circadian clocks is best known, but even so there is considerable complexity and diversity and much remains to be discovered. We know relatively little about the internal states that provide information for timed responses (such as the photoperiodic "counter"), about the central controlling mechanism, or about the effectors that transmit output signals. Nevertheless, temporal responses serve a very great range of purposes in insects, and the reported complexity in all of the components of timing systems reflects complex ecological needs across daily and seasonal intervals. The variety of components and the complexity of interactions reported (even within species), as well as the diversity of such elements as photosensitive pigments, molecular clock function and potential neurotransmitters, suggests that - unlike some earlier expectations - there is no single master clock for all timing functions in insects.
Insect photoperiodism and rhythmicity have been studied by both observational or direct approaches (examination of system elements or devices, and qualities such as survival), and by inferential or indirect approaches (such as interpretation of various responses to photoperiod, modelling, and estimating fitness). Many students work with only one approach, but the power of different approaches is not equal, and knowledge at one level may not give answers at another. These difficulties tend to limit our understanding of the linkages among components.
This overview suggests several lessons for the study of photoperiodism and rhythmicity. There are multiple elements, complex integration and a diversity of clocks, showing that different processes serve different purposes. The diversity of findings also results from the fact that different investigative approaches, which depend on the question being asked and on the perspective of the investigator, can influence the outcome of the investigation. Given these complexities, I believe that the key to interpreting photoperiodic and circadian responses is their ecological value. Notwithstanding the interest of timing mechanisms or their parts and of specific responses, daily rhythms and seasonal timing are best understood through the essential context provided by the ecological demands on the actual organisms under study.
Glochidia are the larval stage of freshwater unionid mussels that parasitize the fins and gill apparatus of fish. A total of 22 fish species were examined for the presence of glochidia whose distribution on individual hosts was studied on three common fish species, the roach Rutilus rutilus (L.), perch Perca fluviatilis L. and bitterling Rhodeus sericeus (Pallas). Between 1997 and 1999, the fish were obtained from the rivers Morava and Kyjovka and surrounding water pools in the Czech Republic. The glochidia of two genera, Unio and Anodonta, were found. Anodonta glochidia were observed on 10 fish species, Unio glochidia on 17 fish species. There was a difference in spatial distribution of glochidia on the body of the host fish. Unio glochidia were predominantly located on the gills, whereas most Anodonta glochidia were found on the fins, with the highest numbers of glochidia were observed on the margin of the pectoral fins. For the gill apparatus, Unio glochidia were found predominantly on the second and third arch. Anodonta glochidia were predominantly found during winter and spring (November-May), whereas Unio glochidia were more abundant during May and June. The number of glochidia was positively correlated with fish length in perch highly infected by Anodonta glochidia and perch infected by Unio glochidia. Of the three fish species, the highest occurrence of parasites was found on perch with fewer observed on roach. In spite of the close relationship between bitterling and unionid mussels, glochidiosis was rare on this fish species.
The objective of this study is to analyse the spatial variability of seasonal flood occurrences in the Upper Danube region for the period 1961-2010. The analysis focuses on the understanding of the factors that control the spatial variability of winter and summer floods in 88 basins with different physiographic conditions. The evaluation is based on circular statistics, which compare the changes in the mean date and in the seasonal flood concentration index within a year or predefined season. The results indicate that summer half-year and winter half-year floods are dominant in the Alps and northern Danube tributaries, respectively. A comparison of the relative magnitude of flood events indicates that summer half-year floods are on average more than 50% larger than floods in winter. The evaluation of flood occurrence showed that the values of seasonal flood concentration index (median 0.75) in comparison to the annual floods (median 0.58) shows higher temporal concentration of floods. The flood seasonality of winter events is dominant in the Alps; however, along the northern fringe (i.e. the Isar, Iller and Inn River) the timing of winter half-year floods is diverse. The seasonal concentration of summer floods tends to increase with increasing mean elevation of the basins. The occurrence of the three largest summer floods is more stable, i.e. they tend to occur around the same time for the majority of analysed basins. The results show that fixing the summer and winter seasons to specific months does not always allow a clear distinction of the main flood generation processes. Therefore, criteria to define flood typologies that are more robust are needed for regions such as the Upper Danube, with large climate and topographical variability between the lowland and high elevations, particularly for the assessment of the effect of increasing air temperature on snowmelt runoff and associated floods.