Despite G-protein-coupled receptors (GPCRs) being among the most fruitful targets for marketed drugs, intense discovery efforts for several GPCR subtypes have failed to deliver selective drug candidates. Historically, drug discovery programmes for GPCR ligands have been dominated by efforts to develop agonists and antagonists that act at orthosteric sites for endogenous ligands. However, in recent years, there have been tremendous advances in the discovery of novel ligands for GPCRs that act at allosteric sites to regulate receptor function. These compounds provide high selectivity, novel modes of efficacy and may lead to novel therapeutic agents for the treatment of multiple psychiatric and neurological human disorders.

Allosteric modulators of GPCRs: a novel approach for the treatment of CNS disorders

Handbook of the Birds of Europe, the Middle East and North Africa: the Birds of the Western Palaearctic. Volume 2. Hawks to Bustards

Egg size is a widely-studied trait and yet the causes and consequences of variation in this trait remain poorly understood. Egg size varies greatly within many avian species, with the largest egg in a population generally being at least 50% bigger, and sometimes twice as large, as the smallest. Generally, approximately 70% of the variation in egg mass is due to variation between rather than within clutches, although there are some cases of extreme intra-clutch egg-size variation. Despite the large amount of variation in egg size between females, this trait is highly consistent within individuals between breeding attempts; the repeatability of egg size is generally above 0.6 and tends to be higher than that of clutch size or laying date. Heritability estimates also tend to be much higher for egg size (> 0.5) than for clutch size or laying date (< 0.5). As expected, given the high repeatability and heritability of egg size, supplemental food had no statistically significant effect on this trait in 18 out of 28 (64%) studies. Where dietary supplements do increase egg size, the effect is never more than 13% of the control values and is generally much less. Similarly, ambient temperature during egg formation generally explains less than 15% of the variation in egg size. In short, egg size appears to be a characteristic of individual females, and yet the traits of a female that determine egg size are not clear. Although egg size often increases with female age (17 out of 37 studies), the change in egg size is generally less than 10%. Female mass and size rarely explain more than 20% of the variation in egg size within species. A female's egg size is not consistently related to other aspects of reproductive performance such as clutch size, laying date, or the pair's ability to rear young. Physiological characteristics of the female (e.g. endogenous protein stores, oviduct mass, rate of protein uptake by ovarian follicles) show more promise as potential determinants of egg size. With regards to the consequences of egg-size variation for offspring fitness, egg size is often correlated with offspring mass and size within the first week after hatching, but the evidence for more long-lasting effects on chick growth and survival is equivocal. In other oviparous vertebrates, the magnitude of egg-size variation within populations is often as great or greater than that observed within avian populations. Although there are much fewer estimates of the repeatability of egg size in other taxa, the available evidence suggests that egg size may be more flexible within individuals. Furthermore, in non-avian species (particularly fish and turtles), it is more common for female mass or size to explain a substantial proportion of the variation in egg size. Further research into the physiological basis of egg-size variation is needed to shed light on both the proximate and ultimate causes of intraspecific variation in this trait in birds.

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Avian egg size: variation within species and inflexibility within individuals

This article summarises the results of 49 studies that together test the significance of 115 characteristics in 7 biological groups: birds, finfish, insects, mammals, plants, reptiles/amphibians and shellfish. Climate/habitat match, history of inva- sive success and number of arriving/released individuals are associated with establishment suc- cess in at least four independent data sets, both within and across biological groups, and none are contraindicated by other studies. In the introduced- invasive control group, two species level charac- teristics—taxon and geographic range size—were significantly associated with establishment success across two biological groups. These characteristics, however, were not supported by independent data sets, or were contraindicated by these data sets, within the biological groups examined here. In the introduced-native control group, three species level characteristics—geographic range size, leaf surface area and fertilisation system (monoecious, her- maphroditic or dioecious)—were consistently supported within plants but were either not supported by independent data sets or contraindi- cated by datasets within or across other biological groups. Climate/habitat match is the only charac- teristic that is consistently significantly associated with invasive behaviour (in this case exotic range size) across biological groups. This finding, how- ever, is not supported by two or more independent data sets within any of the biological groups examined here. Within plants there are a suite of characteristics, predominately associated with reproduction, that are significantly associated with a range of invasion metrics, predominately abun- dance in the invaded range. Nonef of these characteristics, however, are supported across any other biological groups. We note the confounding effects of phylogeny, residence time and propagule pressure and suggest that site- and taxa-specific analysis will provide further useful insights.

Are there any consistent predictors of invasion success

Evolutionary aspects of the trade-off between seed size and number in crops

1. The ecological and economic costs of introduced species can be high. Ecologists try to predict the probability of success and potential risk of the establishment of recently introduced species, given their biological characteristics.

2. In 1990 gudgeon, Gobio gobio, were released in a drainage canal of the Rhone delta of southern France. The Asian topmouth gudgeon, Pseudorasbora parva, was found for the first time in the same canal in 1993. Those introductions offered a unique opportunity to compare in situ the fate of two closely related fish in the same habitat.

3. Our major aims were to assess whether G. gobio was able to establish in what seemed an unlikely environment, to compare populations trends and life-history traits of both species and to assess whether we could explain or could have predicted our results, by considering their life-history strategies.

4. Data show that both species have established in the canal and have spread. Catches of P. parva have increased strongly and are now higher than those of G. gobio.

5. The two cyprinids have the same breeding season and comparable traits (such as short generation time, small body, high reproductive effort), so both could be classified as opportunists. The observed difference in their success (in terms of population growth and colonization rate) could be explained by the wider ecological and physiological tolerance of P. parva.

6. In conclusion, our field study seems to suggest that invasive vigour also results from the ability to tolerate environmental changes through phenotypic plasticity, rather than from particular life-history features pre-adapted to invasion. It thus remains difficult to define a good invader simply on the basis of its life-history features.

Can life‐history traits predict the fate of introduced species? A case study on two cyprinid fish in southern France

1.
The topmouth gudgeon Pseudorasbora parva Schlegel, 1842, a south-east asian cyprinid, was introduced accidentally in the Danube Delta in Romania in the 1960s and has now achieved a pan-Danubian distribution. P. parva has been introduced into other countries, such as Greece, usually inadvertently included with other species imported for fish farming. In 1984–85, during a study of the fish populations of Lake Mikri Prespa (north-west Greece), several topmouth gudgeon were caught. Our aim was to study the changes in the population size of P. parva over nearly 10 years, to study its life history traits and to assess its potential impacts on native fish species.

2.
The catch per unit effort (CPUE) in spring increased significantly between 1984 and 1992. We found evidence that P. parva has established a breeding population in the lake. P. parva combines many characteristics likely to favour a successful colonization (resistance to harsh climatic conditions, early sexual maturity, extended breeding season, broad dietary spectrum). Growth in Lake Prespa, where the oldest individuals captured were 3 years old, is very similar to that observed within its native range.

3.
There is evidence for dietary overlap between P. parva and three endemic species: Paraphoxinus epiroticus prespensis, Cobitis meridionalis and Alburnoides bipunctatus ohridanus. No decline in the populations of these three species has yet been demonstrated. Other possible impacts are discussed. The successful colonization by P. parva was certainly favoured by the absence of a true piscivorous fish in the lake and by the isolation and high level of endemism of fish communities.

4.
The conservation of the many endemic species in the lake should be a priority and the introduction of exotic species should be banned.

The establishment and impact of Pseudorasbora parva, an exotic fish species introduced into Lake Mikri Prespa (north-western Greece)

The conservation status of freshwater fish is of concern throughout the world, a third of all known species having become extinct or being endangered. Many of them have fragmented populations of small size whose future is in doubt. Conservation biology is the discipline that is used to study such populations, so that they can be managed in a way that will ensure their long-term survival. The history, development and future of conservation biology are described. Following repeated restocking of brown trout (Salmo trutta) dating from 1906, the marble trout (Salmo marmoratus) seems to have disappeared as a result of genetic pollution (hybridisation) from the lower reaches of the Soca River in Slovenia. A project for rehabilitating the marble trout has been undertaken and will serve as an example to illustrate an application of conservation biology to freshwater fish. A preliminary exploratory stage (1993-1995) that resulted in the publication in 1996 of an Action Plan, written in English and Slovenian, suggested that the cause of the disappearance of the marble trout was hybridisation, established the validity of the project in the region in question and provided us with essential information (occurrence of genetically pure populations) that could be used to define our future strategy. We chose genetic rehabilitation, i.e., the replacement of a population of introduced and introgressed fish by a population of genetically pure fish of the native species, rather than a programme of eradicating undesirable fish by chemical methods, which would have been incompatible with the region's context. Our overall strategy therefore had two main aims: to ensure the long-term survival of populations of pure marble trout (species conservation) and to rehabilitate the genes of marble trout in the hybridisation zone until foreign genes have almost been eliminated.

Conservation biology applied to fish: The example of a project for rehabilitating the marble trout (Salmo marmoratus) in Slovenia

Although being a widely introduced and successfully established species, the European catfish Silurus glanis L. (the world’s third largest freshwater fish) remains poorly studied in its introduced areas. Here we studied the trophic ecology of non-native European catfish in a large river system in south-western France using stomach content and stable isotope analyses (SIA). We used fin samples for SIA of catfish and hence tested the validity of using fin tissue as a proxy for muscle in SIA. The mean δ15N and δ13C values analysed from fin tissues did not differ from those analysed from muscle tissue and reflected strong and consistent relationships (r2 = 0.95 for carbon and r2 = 0.98 for nitrogen). The δ15N values varied almost 5‰ among the analysed catfish individuals, while δ13C values varied >5‰. Total length of these catfish ranged from 200 to 2240 mm and was correlated with δ15N and especially with δ13C values. Although catfish length and δ15N values were positively correlated, the mean trophic positions of catfish increased only slightly from smaller individuals to larger ones (4.3 to 4.7). However, larger catfish were considerably 13C-enriched in their δ13C values compared to smaller individuals and had up to 4‰ higher δ13C values than their expected aquatic prey. This might indicate frequent consumption of mammals and/or non-aquatic birds by the larger sized individuals, which were found in the catfish stomachs.

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Dietary breadth and trophic position of introduced European catfish Silurus glanis in the River Tarn (Garonne River basin), southwest France

There were significant correlations between colour pattern, LDH-5*, genotype and certain meristic characters in 59 hybrid trout Salmo, sp. from the Volarja stream, Soca River basin, Slovenia. It is concluded that panmixia between native Salmo marmoratus, and introduced S. trutta, of Atlantic, Danubian and Mediterranean origin had not been reached in this zone, despite the long period of introgression. The result is in agreement with other studies dealing with introgression in Salmo, and for management purposes certain morphological characters, especially colour pattern, can be a valuable tool in restoring the marble trout population in the Soca River.

Alain J. Crivelli

Papers

Can life‐history traits predict the fate of introduced species? A case study on two cyprinid fish in southern France

The establishment and impact of Pseudorasbora parva, an exotic fish species introduced into Lake Mikri Prespa (north-western Greece)

Conservation biology applied to fish: The example of a project for rehabilitating the marble trout (Salmo marmoratus) in Slovenia

Dietary breadth and trophic position of introduced European catfish Silurus glanis in the River Tarn (Garonne River basin), southwest France

Morphological variation in hybrids between Salmo marmoratus, and alien Salmo species in the Volarja stream, Soca River basin, Slovenia