Pollination failure in mediterranean Ruscus aculeatus L.

The reproductive biology of Ruscus aculeatus L. was studied at a mediterranean site during 1996–1999. Field observations showed that reproductive success was very low, because only 3% of the marked flowers developed fruits in 1996 and none in 1997 and 1998. Several experiments were performed to investigate the reasons for reproductive failure in this species. Pollen viability was on average 85%, showing that reproductive failure is not due to poor pollen quality. Two hand-pollination experiments showed that all flowers are potentially able to develop fruits throughout the flowering period, suggesting that no aberration occurs in sporogencsis, fertilization or post-zygote processes in R. aculeatus and that low reproductive success in the field occurs because of lack of pollination. This hypothesis was tested by looking for pollen on the stigmatic surface of randomly sampled flowers, but without success. Moreover, the bodies of insects trapped in the proximity of the female plants were carefully checked for pollen but none was found. The number of pollen grains produced per flower is lower than that reported for wind-pollinated species. Nevertheless, we showed with empirical probes that the possibility of wind pollination cannot be ruled out. The breeding system and reproductive characteristics of R. aculeatus seem to match the traits of the sclerophyllous taxa remnants of the tropical Tertiary flora. Moreover, the climatic fluctuation of the Quaternary and the establishment of the mediterranean climate might have changed the conditions of a good pollination process. At present, the low sexual reproduction of R. aculeatus is due to the lack of pollen transport. Within a population of R. aculeatus , genetic variability is revealed by seeds from the few developed fruits which have been shown to be viable. However, maintenance of the individual plants in the population relies on the resprouting capacity of the species in question.     

Divergence of mate recognition systems among conspecific populations of the plethodontid salamander Desmognathus santeetlah (Amphibia: Plethodontidae)

The disjunct geographic distribution of plethodontid salamanders of the genus Desmognathus provides excellent opportunities to test whether populations diverge in mate recognition systems so as to result in sexual incompatibility. Previous work has shown that sexual incompatibility may exist both among conspecific populations and between different species in this genus. Populations of the Santeetlah dusky salamander, Desmognathus santeetlah , are found at higher elevations in three mountain ranges in the southern Appalachian Mountains of eastern North America, where they are sympatric with congeneric species of similar body size. We report that statistically significant levels of sexual incompatibility exist among populations of D. santeetlah collected from across the species' range. Contrary to popular belief, but in accord with a growing body of empirical literature, aspects of mate recognition systems can diverge among conspecific populations of salamanders, resulting in incidental sexual incompatibility.     

The Galactan Sulphates of the Conchocelis Phases of Porphyra leucostricta and Bangia atropurpurea (Rhodophyta)

Galactan sulphates have been extracted from mechanically isolatedcell walls of laboratory cultured conchocelis phases of Porphyraleucostricta and Bangia atropurpurea and their structure establishedby chemical methods and ¹³C-n.m.r. spectroscopy. The polysaccharidesrepresent an extreme structure for porphyran-type polymers inthat they consist almost entirely of 3-linked ß-D-galactosylresidues alternating with 4-linked -L-galactose-6-sulphate residues,the molar ratio of D to L units being approximately 1: 1. ¹³C-n.m.r.and gas-liquid and paper chromatography gave no indication of6-O-methyl-D-galactose in these polymers. Conchocelis galactansare chemically distinct from porphyrans of generic phases ofPorphyra and Bangia. Key words: Rhodophyta, Galactans, Cell walls     

Acetate Metabolism by an Obligate Phototrophic Strain of Pandorina morum1

SYNOPSIS. Acetate metabolism was studied in 2 strains of the green alga Pandorina morum. Both strains were capable of mixotrophic growth in the light, but only one strain was capable of heterotrophic growth in the dark. ¹⁴C-2-acetate uptake by both strains was studied in the light and dark, in the presence and absence of CO₂ and 3(3,4-dichlorophenyl)-1,1-dimethylurea (10^?5M). The distribution of radioactivity incorporated into the insoluble, aqueous and chloroform soluble fractions of the cells was determined. The strain incapable of heterotrophic growth in the dark was found to incorporate very little acetate in the dark, and its ability to incorporate acetate into the insoluble fraction was severely limited under all conditions. Incorporation into the aqueous and chloroform-soluble fractions in the light was similar in both strains. The reduced incorporation into the insoluble fraction was almost totally the result of limited incorporation of acetate into polysaccharides by the obligate phototrophic strain.     

Land clearing reduces gene flow in the granite outcrop‐dwelling lizard,Ctenophorus ornatus

An important question for the conservation of species dwelling in fragmented habitats is whether changes to the intervening landscape create a barrier to gene flow. Here, we make use of the spatial distribution of the granite outcrop‐dwelling lizard, Ctenophorus ornatus, to compare inferred levels of gene flow between outcrops in a nature reserve with that between outcrops in the adjacent agricultural land. Genetic variation, relatedness and subdivision were compared within groups of individuals from different outcrops similar in size and distance apart at each site. In the agricultural land, we found significantly lower genetic variation within outcrops and greater genetic differentiation between outcrops than in the reserve. Further, the rate at which genetic divergence between outcrops increased over geographical distance was significantly greater in the agricultural land than in the reserve. We also found that individuals were more closely related within outcrops but more distantly related between outcrops in the cleared land. These effects occur over a small spatial scale with an average distance between outcrops of less than five kilometres. Thus, even though land clearing around the outcrops leaves outcrop size unchanged, it restricts gene flow, reducing genetic variation and increasing population structure, with potentially negative consequences for the long‐term persistence of the lizards on these outcrops.     

Driving forces of soil organic carbon evolution at the landscape and regional scale using data from a stratified soil monitoring

Soil monitoring programmes face significant challenges as there is an important trade‐off between detecting significant changes in soil properties on the one hand (which can be achieved by minimizing variability by higher sampling density or stratification approaches), and identifying the driving forces responsible for these changes on the other hand (which requires enough variability). This study aims to reconcile these two objectives by identifying the driving forces of soil organic carbon (SOC) evolution over a long period, based on an extensive but stratified soil monitoring programme. Data at both the finest level (questionnaires to the farmers) and the large scale (agricultural census, climate and soil databases for southern Belgium) were used in a cluster analysis, multiple linear regressions and mixed odels in order to discriminate between the driving forces involved. Results indicated that the negative ‘baseline effect’ (i.e. the inversely proportional effect of the initial SOC content on the SOC evolution) was responsible for an important part of the SOC variability. Consequently, the systems are not at steady state when starting the observations, although this assumption is used by most SOC dynamic models. Moreover, the baseline effect resulted in a trend of the soils to converge towards a regional SOC stock which significantly differed according to land use (36.4 t C ha^?1 for the plough depth of cropland and 92.2 t C ha^?1 for the 0–30 cm layer of grassland). Despite this strong effect, the main driving forces of the SOC decrease of cropland (?0.2 t C ha^?1 yr^?1) and SOC increase of grassland (+0.2 t C ha^?1 yr^?1) over a period of 50 years were discriminated. The agricultural management (cropland) and the clay content (grassland), together with the change in precipitation (to a lesser degree for cropland) were highlighted as the predominant factors involved in SOC evolution, when land use change is excluded. The use of questionnaires allowed to better understanding the impact of an intensive agricultural management on the SOC content, as the lowest SOC stocks were associated to the most intensively managed fields. The mixed models partly succeeded in predicting SOC evolution as they presented still large uncertainties after validation (mean error from 3% to 25%, root mean square error of prediction from 21% to 242%). While SOC monitoring schemes are increasingly being implemented, our results will likely apply to those using a similar design. It was shown that this strategy succeeded to reconcile both the SOC change detection and the distinction of the driving forces involved at the regional scale.     

Impact of HIV Comprehensive Care and Treatment on Serostatus Disclosure among Cameroonian Patients in Rural District Hospitals

This work aimed to analyze the rate of disclosure to relatives and friends over time and to identify factors affecting disclosure among seropositive adults initiating antiretroviral therapy (ART) in rural district hospitals in the context of decentralized, integrated HIV care and task-shifting to nurses in Cameroon. Stratall was a 24-month, randomized, open-label trial comparing the effectiveness of clinical monitoring alone with laboratory plus clinical monitoring on treatment outcomes. It enrolled 459 HIV-infected ART-naive adults in 9 rural district hospitals in Cameroon. Participants in both groups were sometimes visited by nurses instead of physicians. Patients with complete data both at enrolment (M0) and at least at one follow-up visit were included in the present analysis. A mixed Poisson regression was used to estimate predictors of the evolution of disclosure index over 24 months (M24).The study population included 385 patients, accounting for 1733 face-to-face interviews at follow-up visits from M0 to M24. The median [IQR] number of categories of relatives and friends to whom patients had disclosed was 2 [1]–[3] and 3 [2]–[5] at M0 and M24 (p-trend<0.001), respectively. After multiple adjustments, factors associated with disclosure to a higher number of categories of relatives and friends were as follows: having revealed one’s status to one’s main partner, time on ART, HIV diagnosis during hospitalization, knowledge on ART and positive ratio of follow-up nurse-led to physician-led visits measuring task-shifting. ART delivered in the context of decentralized, integrated HIV care including task-shifting was associated with increased HIV serological status disclosure.