Phenotypic and genetic variabilities of nine meristic traits (in threespine stickleback, Gasterosteus aculeatus) were calculated for 33 full-sib families raised under controlled laboratory conditions and for 33 pairs caught in nature. Heritabilities were measured using three methods: regression (across environments, laboratory–nature), full sib (laboratory), and minimum estimate (nature). Evolvabilities, as an alternative measure of genetic variability, were computed from the genetic coefficient of variation across environments, in the laboratory, and in nature. In general terms, phenotypic variability was smaller in laboratory-reared fish than in wild fish. Results applying both parameters (heritability and evolvability) suggest that in the natural environment, there is a relevant presence of additive genetic variability for lateral-plate number and, to a lesser extent, for lower gill rakers, as well as maternal effects on caudal and abdominal vertebrae and paternal effects on dorsal fin rays. Some of the meristic traits examined are bilateral. Heritabilities across environments and in the laboratory for fluctuating asymmetry values were calculated according to conventional methods and also employing method 2 of Falconer. Qualitatively, the results were almost the same using the two methods: most heritability values were around zero, even taking into account overall measures of fluctuating asymmetry.

Growth rates of populations of the freshwater pearl mussel, Margaritifera margaritifera (L., 1758), in northwestern Spain were analysed based on measurements of annual annuli and using two nonlinear functions for length-at-age data sets: von Bertalanffy's growth model and a hyperbolic function. These populations reach the smallest maximum shell length (90.5 mm) and have the shortest life-span (35 years) and the highest growth rate (k in von Bertalanffy's model >0.1·year–1, on average) known for this species. The two models were similar in performance and were well fitted (around 99%) to shell-length-at-age data, although the hyperbolic function appears to be applicable only from 6 years of age. The growth rate (either k or k' from the hyperbolic function) showed a large and significant variation across populations, both among and within drainages.

A genetic analysis of freshwater pearl mussel Margaritifera margaritifera populations from NW Spain, a peripheral area of its European distribution, was carried out using microsatellite markers. These populations were formerly reported as genetically differentiated on the basis of growth and longevity studies. Ten loci previously characterized in populations from central Europe were used to comparatively analyze the genetic variability at the southern edge of the species' range. Iberian pearl mussel populations showed very low genetic variability and significant high genetic differentiation. Half of the total genetic diversity observed appeared to be distributed between populations, which suggested a highly structured adaptive potential in pearl mussel at the southern peripheral distribution of the species. Population distinctiveness was evidenced by assignment tests, which revealed a high accuracy of individual assignments to their population of origin. All data suggested low effective population size and major effects of genetic drift on population genetic structure. In order to avoid further loss of genetic variation in biologically distinctive populations from NW Spain, prioritization of genetic resources of this species is required for conservation and management.

To study the relative importance of inbreeding depression and the loss of adaptive diversity in determining the extinction risk of small populations, we carried out an experiment in which we crossed and self-fertilized founder plants from a single, large population of shore campion (Silene littorea Brot.). We used the seeds these plants produced to colonize 18 new locations within the distribution area of the species. The reintroduced populations were of three kinds: inbred and genetically homogeneous, each made up of selfed seed from a single plant; inbred and mixed, made up of a mixture of selfed seeds from all founder plants; and outbred and mixed, made up of a mixture of seeds obtained in outcrosses between the founders. We compared the inbred homogeneous populations with the inbred mixed to measure the effect of genetic diversity among individuals and the inbred mixed with the outbred mixed to measure the effect of inbreeding. Reintroduction success was seriously limited by inbreeding, whereas it was not affected by genetic diversity. This observation and the nonsignificant interaction between family and reintroduction location for individual plant characters suggest that the fixation of overall deleterious genes causing inbreeding depression posed a more serious threat to the short-term survival of the populations than the loss of genes involved in genotype and environment interactions. Thus, reintroduction success was related to adaptive diversity. Preventing such fixation might be the most important consideration in the genetic management and conservation of shore campion populations.

No abstract

No abstract

1. The European freshwater pearl mussel, Margaritifera margaritifera (Bivalvia: Unionoida), is one of the most threatened mussels. The Iberian populations of this species are considered peripheral because their distinct characters such as growth rate and longevity, and require development of effective conservation strategies. 2. We assessed population density and age structure of pearl mussels in two Galician rivers (Eo and Masma in north-west Spain). Four sampling sites were selected in each river to cover stretches of 100 m. The mean density of mussels in each of these sampling transects was estimated using the adaptive sampling technique, given that mussels occur at low densities and are highly aggregated in these rivers. 3. Age structure was inferred for each population using length-age keys. The empty shells encountered during sampling were used to determine the length of the specimens at different ages (years), together with length-at-age data from shells previously analysed for computing growth rates from the same rivers. Water samples from both rivers were analysed for typical physicochemical parameters. 4. Mean densities were very variable, even within the same river (from 0.27 to 6.55 m )2 in the River Eo and from 0.98 to 2.38 m )2 in the River Masma). Individuals in the 0-to 5-year age class were scarce in both rivers. 5. Margaritifera margaritifera showed a preference for the strip of river bed within 1.5 m from the river bank and avoided sites at greater distances. The species also showed a preference for sites with more than 80% tree cover and avoided sites with <50% cover. 6. Iberian populations exhibit the highest growth rate, together with the lowest maximum age and maximum length known for M. margaritifera. Detailed knowledge about these peripheral Iberian populations will contribute to developing strategies for conservation and management of this endangered species.

Aim At what spatial extent are biotic interactions discernible influences on the distribution and abundance of species in river networks? We address this question with analyses of data from river networks for Margaritifera margaritifera, a freshwater mussel that passes its larval stage attached to a host fish.Location Twenty river networks in Galicia, north-western Spain.Methods A maximum-entropy approach was implemented to model the species' distribution. Geostatistical mixed models were used to analyse the mussel's abundance in dendritic river networks. Predictor variables included the abundance and biomass of host fish (biotic interactions) and abiotic predictors for climate, geology and land-form.Results Maxent models of species distribution were improved by 4.5% in terms of the area under the receiver-operating characteristic curve (AUC) by the inclusion of biotic interactions. Host-fish predictors contributed 63% of the Maxent model prediction of mussel presence. A geostatistical mixed model explained 52% of the variance in mussel abundance when including all the mussel abundance sites in the study area; abiotic predictors had no significance and salmonid biomass and resident trout population density were the only significant biotic predictors, together explaining 2.4% of the variance. An autocovariate representing biotic interactions between mussels and fish explained 11.7% of the variance. Using only sites where migratory host fish were present (n = 149), a mixed model explained more variance (78%) and the contribution from the autocovariate for parasite-host interactions was about three times larger than for the model including all sites (n = 419). The spatial autocorrelation from mussel-fish interactions had a spatial extent (geostatistical range) greater than 15 km.Main conclusions Interactions between mussels and their larval hosts in river networks are manifested in spatial patterns of species distribution and abundance in this region, encompassing 20 river networks. The directional topology of dendritic river networks strongly supports the upstream dispersal of mussels by parasitized host fish as a component of spatial autocorrelation in mussel abundance.