Reproductive effort and phenology of seed production of savanna grasses with different growth form and life history

The phenology of seed production in natural savanna grasslands was studied in the grass speciesAristida congesta, Cymbopogon plurinodis, Cynodon dactylon, Digitaria eriantha ssp.pentzii, Eragrostis rigidior, Eragrostis superba, Panicum coloratum, Schmidtia pappophoroides, Tragus berteronianus andUrochloa panicoides. Maximum seed production varied according to life history strategy and growth form from 0.03 mg seed g^-1 shoot dry weight in the perennialD. eriantha ssp.pentzii which produces long stolons and 14.8 mg seed g^-1 shoot inE rigidior, which produces short geniculate stolons, to 169.1 mg g^-1 in the annualT. berteronianus. Seed production was in most species divided over several peaks during the season. Peaks of seed production were observed 3 to 7 months after the onset of the growth season depending on the start of the rains and the life history strategy and growth form of the species. Seed production varied from maxima of 180 seeds m^-2 inD. eriantha ssp.pentzii to 47000 seeds m^-2 in annual stands ofT. berteronianus. Except for annual grasslands withU. panicoides, seedling emergence data reported are smaller by at least a factor of 10 than the observed seed production. Among other factors, a low quality of produced seeds, predation by birds and insects and previous grazing by livestock may have contributed to this difference.     

Trade-offs between phenology,relative growth rate,life form and seed mass among 22 Mediterranean woody species

Mediterranean woody plants exhibit a wide phenological diversity which cannot be explained just on the basis of climatic constraints. We assessed the role of relative growth rate (RGR), life form, seed and fruit mass as potential constraints of plant phenology. In a comparison of traits of 22 Mediterranean woody plant species, the duration of the primary shoot growing period decreased from climbers to shrubs and to trees. A hypothesised negative association between RGR and primary shoot growth duration did not emerge in our species set. The mechanism underlying phenological differences between plant life forms might relate to differences in the proportion of respiring to photosynthetic tissues, which decreases from climbers to trees. It is suggested that the degree of shoot preformation within the bud correlates with primary shoot growth duration, but not with RGR. Development of big fruits and seeds competes for carbon with vegetative growth. Indeed, species with bigger seeds and fruits exhibited shorter primary shoot growing periods, which tended to overlap with flower bud formation and flowering periods. We suggest that duration of primary shoot growth allow to short out the species between two extreme growth strategies: The conservative one would be characterised by a concentration of the primary shoot growth into a short period, free of frosts and droughts, and by a diversion of part of the current resources to assure next year's growth. The opportunistic strategy, on the other extreme, would be defined by the allocation of resources to current growth whenever they are available, achieving longer growing periods at the expense of higher risk of tissue damage. These strategies should have been selected for in environments of predictable and unpredictable resource availability, respectively.     

Annual cycle of activity of the neurocytes of the ventral lateral septum in the brainof Rana esculenta L.∗

Abstract

Sexually mature male and femaleRana esculenta L. were captured in their natural habitat in six phases of the annual cycle. Nuclear volumes of neurocytes in the ventral lateral septum (VLS) were found to fluctuate distinctly in the course of the year. In both sexes nuclear volumes of neurocytes were maximal in the phases preceding the breeding season (3rd decade of January, and 1st decadeof April), and minimal in the phaseat the beginning of hibernation (3rd decade of October). The results lead to the assumption that the VLS ofRana esculenta may have an active role in controlling gonadotropin release.     

Genetic diversity within mer genes directly amplified from communities of noncultivated soil and sediment bacteria

Individual merRTΔP regions were amplified from DNA directly isolated from soil and sediment samples using consensus primers derived from the conserved mer sequences of Tn501, Tn21 and pMER419. Soil and sediment samples were taken from four sites in the British Isles; one ‘pristine’ (SB) and three polluted (SO, SE, T2) with respect to mercury. The sizes of the PCR products amplified (= 1 kb) were consistent with their generation from mer determinants related to the archetypal elements found in Gram negative bacteria. Forty-five individual clones of sequences obtained from these four sites were isolated which hybridized (> 70% homology) to a merRTΔP probe from Tn501. The diversity of these amplified mer genes was analysed using Restriction Fragment Length Polymorphism (RFLP) profiling. Fourteen RFLP classes were distinguished, 12 of which proved to be novel and only two of which had been identified in an earlier study of 40 Gram negative mercury resistant bacteria cultured from the same four sites. UPGMA analysis was used to examine the relationships between the 22 classes of determinant identified. The T2 site, which has the longest history of mercury exposure, was found to have the greatest level of diversity in terms of numbers of classes of determinant, while the SO site, which had the highest mercury levels showed relatively low variation. Variation of mer genes within and between the sequences from cultivated bacteria and from total bacterial DNA shows clearly that analysing only sequences from cultivated organisms results in a gross underestimation of genetic variation.     

Genet Distribution of Ectomycorrhizal Fungus Suillus grevillei Populations in Two Larix kaempferi Stands over Two Years

Suillus grevillei in two Larix kaempferi stands was determined over two years by inter-simple sequence repeat (ISSR) polymorphism analysis using primers, (GTG)₅, (GCC)₅ and (GACA)₄. Thirty-five genets were identified from 67 sporocarps at the older stand (stand A in which the distribution of S. grevillei genet in 1997 was analyzed previously) in 1998, and 14 genets from 52 sporocarps at the younger stand (stand B) in 1997 and 1998. The characteristics of S. grevillei genets in stand A in 1998 were similar to those in 1997. A single genet was represented by 1.8 and 3.7 sporocarps on average in stands A and B, respectively. In stand A, 42 out of 61 genets, i.e., about 70% were represented by individual sporocarps compared to five out of 14 genets, i.e., about 35% in stand B. The largest and the average genet sizes was 6.8 m and less than 1 m in stand A, and 11 m and 2.3 m in stand B, respectively. A t-test showed the genet size in stand A to be significantly smaller than that in stand B. The above results indicate that the smaller genets of the S. grevillei population in stand A might be due to environmental conditions not genetic traits specific to this species. Observations over two years showed that although some genets formed sporocarps in both 1997 and 1998, many formed sporocarps only in one of the two years. Emerging positions of sporocarps in 1997 and 1998, which belonged to the same genet, were similar but not identical, about 2 m apart, suggesting mobility in the subterranean parts of ECM fungal genets. Received 10 April 2000/ Accepted in revised form 31 August 2000     

Induction of sister chromatid exchanges by heavy metal salts in root meristem cells ofAllium cepa L.

Four heavy metal salts, nickel sulphate, mercuric chloride, cadmium sulphate and zinc sulphate, were tested for induction of sister chromatid exchange (SCE) in root meristem cells ofAllium cepa. A simple modified Feulgen staining procedure was employed for SCE-analysis. Maleic hydrazide and paraquat were included for comparison. An evaluation of genotoxicity of the above test chemicals made on the basis of SCE-assay was found positive for all the test chemicals with exception of zinc sulphate which gave a weak positive result.     

Spatial organisation of European wildcats (Felis silvestris silvestris) in an agriculturally dominated landscape in Central Europe

For the first time, a telemetry study of European wildcats was conducted outside heavily forested habitats, in an agriculturally-dominated landscape, which is assumed to be a suboptimal habitat in Central Europe. According to the current knowledge of morphological and genetic diagnoses all captured wildcats were purebred, without any hint of recent interbreeding. Our results confirmed the regular use of open landscape habitats also by resident individuals. Sex and age ratios of wildcats, using the open landscapes, were balanced, and one successful reproduction event was recorded. Female annual home-ranges were smaller compared to those recorded in forested habitats. Male annual home-ranges were similar in size, whereas the core areas were smaller than those recorded in adjacent forested habitats. Males had the largest home-ranges during spring and the smallest in summer, whereas females had the largest home-ranges during summer and the smallest during winter/spring. The structure of the apparently purebred population with resident individuals and a reproduction event in an open cultivated landscape may be related to the close proximity (3.5–5 km) of a wildcat core distribution area. As a consequence of our results, the potential range of the European wildcat is increased, because it may occur in agricultural landscapes where sufficient shelter is available. This should be considered in environmental impact analyses and species monitoring.     

Mercury Concentrations in Tissues of Osprey From the Carolinas,USA

Abstract: Mercury (Hg) contamination is believed to be one of the most significant pollution hazards to wildlife in the southeastern United States, yet comprehensive studies of Hg contamination of piscivorous raptors are rare in this region. We analyzed total Hg (THg) concentration in tissues of 39 osprey (Pandion haliaetus) primarily from coastal counties of South Carolina, USA, to describe tissue distribution of Hg and to determine whether age or sex influenced Hg accumulation. To determine whether Hg poses health risks to osprey breeding in this region, we also measured selenium in all tissues and the percentage of THg that was methylated in a subset of individuals. Osprey with adult plumage tended to have higher and more variable Hg concentrations in their tissues than younger birds. Whereas highest concentrations of Hg were found in liver and kidney of older birds, chicks had highest concentrations in keratinized tissues. Mercury concentrations were correlated between feathers and soft tissues, but talon concentrations of Hg were better correlated with organs than to feathers in most cases. Contrary to previous studies on birds, we found no relationship between Hg concentration in primary feathers and the sequence in which the feather was molted. We attribute this observation to the irregular and protracted molting pattern of osprey. Also contrary to other studies, feather concentrations of Hg were considerably lower than concentrations in liver and kidney. Osprey with high concentrations of Hg in their livers and kidneys accumulated as much as 99% of it as Hg(II), suggesting that demethylation and sequestration of Hg(II) may be even more critical to mitigating adverse effects than it is for other birds that eliminate most of their Hg burden in feathers. In addition, selenium was co-sequestered with Hg in the liver and kidneys and may further mitigate any adverse effects. Based on these findings, we suggest that most osprey in this region are not currently at risk of Hg toxicosis, but recommend that additional ecotoxicological studies be performed to monitor risk to osprey in this coastal region facing heavy development. We also suggest that concentrations of Hg in talon and claw may serve as important indicators of previous exposure and provide useful information for natural resource managers seeking to assess health risks to birds.     

Reproductive cycle and gonadal development of the Atlantic sea urchin Arbacia punctulata in the Gulf of Mexico: changes in nutritive phagocytes in relation to gametogenesis

ABSTRACT

The annual reproductive cycle comprises steady gametogenic activities that synchronize gonadal maturation and spawning rhythms, which are important for aquatic organisms including marine echinoderms (Echinodermata, Echinoidea). In this study, we report the annual reproductive cycle, gonadal development, and changes in nutritive phagocytes (NPs, which accumulate nutrients in germ cells) in relation to gametogenesis of the Atlantic sea urchin (Arbacia punctulata, an edible echinoid) in the Gulf of Mexico. Monthly changes in gonadal development and maturation were observed morphologically and histologically. We calculated gonadosomatic index (GSI) and compared the stages of gonadal development in order to determine the NPs index, and characteristics of germ cells (eggs and sperm) during the annual reproductive cycle. According to GSI and histological analyses, gametogenic activities were classified into four stages of both sexes: mature (June–August), spent (September–November), recovery (December–March), and growing (April–May). The GSI values in both sexes were high during summer months. In males, testicular lobules were densely packed with sperm from June to August. In females, however, mature eggs first appeared in some ovaries in May, numerically increased from June to July, and decreased in August. During gametogenesis, on the other hand, NPs in both testes and ovaries were depleted from June to August. Collectively, our results suggest that the Atlantic sea urchin spawns during summer months in the Gulf of Mexico. This is the first report, to the best of our knowledge, on gonadal development and changes in NPs during the annual reproductive cycle of any Arbacia species in the Gulf of Mexico.