The relationship between stimulus intensity and response amplitude for the photopic negative response of the flash electroretinogram

The aim of this study was to investigate the relationship between stimulus intensity and response amplitude for the photopic negative response (PhNR) of the flash ERG. Specific aims were (i) to determine whether a generalized Naka-Rushton function provided a good fit to the intensity-response data and (ii) to determine the variability of the parameters of the best-fitting Naka-Rushton models. Electroretinograms were recorded in 18 participants, on two occasions, using both DTL fibre and skin active electrodes, in response to Ganzfeld red stimuli (Lee filter "terry red") ranging in stimulus strength from -1.30 to 0.53 log cd.s.m(-2) (0.28-2.11 log phot td.s) presented over a steady blue background (Schott glass filter BG28; 3.9 log scot td). PhNR amplitude was measured from b-wave peak and from pre-stimulus baseline. The Naka-Rushton function was fitted to all intensity-response data, and parameters, 'n', 'Vmax' and 'K' were obtained. Coefficients of variation (CoV), and inter-ocular and inter-session limits of agreement (LoA) were calculated for both Naka-Rushton parameters. A generalized Naka-Rushton function was found to provide a good fit to the intensity-response data, except at the highest stimulus intensity, where a reduction in amplitude occurred in many individuals. The 'Vmax' parameter was less variable than 'K' for all intensity-response data. Variability was lower for DTL than skin electrodes, and for peak-to-trough PhNR measurements, compared to baseline-to-trough. This study has demonstrated for the first time that the Naka-Rushton model provides a useful means of quantifying the intensity-response relationship of the PhNR

Conservation and Management of the Habitats of Two Relict Butterflies in the Belgian Ardenne: Proclossiana eunomia and Lycaena helle

Habitat preservation and restoration are crucial for species conservation and to tackle its main challenges. In many cases, this implies management actions, especially for seminatural ecosystems. We address here the question of management actions suitable for maintaining viable populations of two relict butterfly species inhabiting wet meadows and peat bogs in the Belgian Ardenne: the bog fritillary Proclossiana eunomia and the violet copper Lycaena helle. Habitat loss due to natural vegetation succession towards forest can be prevented either by mowing (traditional way of management) or by extensive grazing (with cattle or horses). Results from field studies and experiments conducted on several sites in the Belgian Ardenne led to two conclusions. Mowing can strongly affect the populations of both species, the impact being particularly pronounced on larval stages due to the removal of grass tussocks and the export of hay containing host plant on which caterpillars feed. Grazing also has a negative effect on both species, with adult density being lower on grazed biotopes compared to abandoned ones. However, the negative impact is more limited for grazing than for mowing. As both management methods have more or less pronounced negative impacts on populations of these two butterfly species, they should be applied with caution. We suggest that mowing should be applied in long-term rotation, with the preservation of sufficient refuge areas every year, and that grazing should be applied in late summer, every other year, with a low stocking rate (< 0.2 LU/ha/year). More particularly, to ensure their effectiveness in maintaining a favorable state, both the biotope and the associated populations using it as their habitat, managementactions must be designed according to the species habitat requirements, and adapted to carefully monitor their implementatio

The importance of ecological and behavioural data in studies of hybridisation among marine fishes

Natural hybridisation is a widespread phenomenon, particularly well documented in terrestrial and freshwater ecosystems, where it has been ascribed substantial evolutionary and adaptive relevance. Hybridisation has received comparatively less attention in marine systems, though there has been a recent surge of reported marine hybrids, particularly among corals and fishes. This review summarises the current knowledge of hybridisation in marine fishes, with a focus on ecological and behavioural factors that may play a role in hybridisation processes. Rarity of one or both parental species within the hybrid zone, overlap in habitat use, dietary overlap and the breakdown in assortative mating appear to have a role in facilitating hybridisation. Despite this, most of the recent literature on marine fish hybridisation has a strong genetic focus, with little or no quantitative information about the ecological and behavioural factors that initiate or facilitate hybridisation. Future studies should attempt to gather ecological and behavioural data from hybrid zones, thus teasing out which processes are most relevant to overcoming pre-zygotic barriers to reproductive isolation. Not only will this advance our understanding of the adaptive and evolutionary relevance of hybridisation in marine fishes, but it will also provide unique insights into the maintenance of reproductive isolation and the process of speciation in the marine environment