Human influence on brown trout juvenile body size during metapopulation expansion.

Change in body size can be driven by social (density) and non-social (environmental and spatial variation) factors. In expanding metapopulations, spatial sorting by means of dispersal on the expansion front can further drive the evolution of body size. However, human intervention can dramatically affect these founder effects. Using long-term monitoring of the colonization of the remote Kerguelen islands by brown trout, a facultative anadromous salmonid, we analyse body size variation in 32 naturally founded and 10 human-introduced populations over 57 years. In naturally founded populations, we find that spatial sorting promotes slow positive changes in body size on the expansion front, then that body size decreases as populations get older and local density increases. This pattern is, however, completely different in human-introduced populations, where body size remains constant or even increases as populations get older. The present findings confirm that changes in body size can be affected by metapopulation expansion, but that human influence, even in very remote environments, can fully alter this process.

The context dependence of assortative mating: a demonstration with conspecific salmonid populations.

Assortative mating is thought to play a key role in reproductive isolation. However, most experimental studies of assortative mating do not take place in multiple natural environments, and hence, they ignore its potential context dependence. We implemented an experiment in which two populations of brown trout (Salmo trutta) with different natural flow regimes were placed into semi-natural stream channels under two different artificial flow regimes. Natural reproduction was allowed, and reproductive isolation was measured by means of parentage assignment to compare within-population vs. between-population male-female mating and relative offspring production. For both metrics, reproductive isolation was highly context dependent: no isolation was evident under one flow regime, but strong isolation was evident under the other flow regime. These patterns were fully driven by variance in the mating success of males from one of the two populations. Our results highlight how reproductive isolation through assortative mating can be strongly context dependent, which could have dramatic consequences for patterns of gene flow and speciation under environmental change.

The role of body size versus growth on the decision to migrate: a case study with Salmo trutta.

In a population exhibiting partial migration (i.e. migration and residency tactics occur in the same population), the mechanisms underlying the tactical choice are still unclear. Empirical studies have highlighted a variety of factors that could influence the coexistence of resident and migratory individuals, with growth and body size considered to be key factors in the decision to migrate. Most studies suffer from at least one of the two following caveats: (1) survival and capture probabilities are not taken into account in the data analysis, and (2) body size is often used as a proxy for individual growth. We performed a capture-mark-recapture experiment to study partial migration among juvenile brown trout Salmo trutta at the end of their first year, when a portion of the population emigrate from the natal stream while others choose residency tactic. Bayesian multistate capture-recapture models accounting for survival and recaptures probabilities were used to investigate the relative role of body size and individual growth on survival and migration probabilities. Our results show that, despite an apparent effect of both size and growth on migration, growth is the better integrative parameter and acts directly on migration probability whereas body size acts more strongly on survival. Consequently, we recommend caution if size is used as a proxy for growth when studying the factors that drive partial migration in juvenile salmonid species.

Characterization of X-ray-generated floral mutants carrying deletions at the S-locus of distylous Turnera subulata.

To investigate the genetic architecture of distyly in Turnera subulata and test the hypothesis that a supergene determines distyly, we used X-ray mutagenesis to generate floral mutants. Based upon the crossing design, all progeny were expected to be short-styled. Of 3982 progeny screened, 10 long-styled mutants, one long homostyle and one short homostyle were recovered. Assays for molecular markers tightly linked to the S-locus showed that the mutants were missing 1-3 markers indicating they are deletion mutants. We investigated the incompatibility phenotype of the mutants and found that both their styles and pollen behaved like those of the long-styled morph. There was a variation in the absolute length of styles, stamens and pollen size of the long-styled mutants. Furthermore, long-styled mutants possessing larger deletions tended to have their anthers and stigmas in closer proximity. We explored the inheritance of the S-locus mutations and found that only one of the deletion mutations was transmitted to progeny where we recovered seven such progeny. Remarkably, our data are consistent with the supergene model (GPA/gpa) of Primula. The long homostyle mutant appears to have deletions involving both the G and P loci. The other mutants appear to have deletions of the entire S-locus. The mutants generated will serve as a valuable resource for the molecular dissection of the S-locus region, and in the identification of genes determining distyly.

Construction of a first genetic map of distylous Turnera and a fine-scale map of the S-locus region.

As a prelude to discovery of genes involved in floral dimorphism and incompatibility, a genetic map of distylous Turnera was constructed along with a fine-scale map of the S-locus region. The genetic map consists of 79 PCR-based molecular markers (48 AFLP, 18 RAPD, 9 ISSR, 4 RAMP), 5 isozyme loci, one additional gene, and the S-locus, spanning a total distance of 683.3 cM. The 86 markers are distributed in 5 linkage groups, corresponding to the haploid chromosome number. Molecular markers tightly linked or co-segregating with the S-locus in an initial mapping population of 94 individuals were used to assay an additional 642 progeny to construct a map of the S-locus region. The fine-scale map consists of 2 markers (IS864a and RP45E9) flanking the S-locus at distances of 0.41 and 0.54 cM, respectively, and 3 additional markers (OPK14c, RP45G18, and RP81E18) co-segregating with the S-locus in the total mapping population of 736 individuals. The genetic map constructed will serve as a framework for localization of genes outside the S-locus affecting distyly, while molecular markers of the fine-scale map will be used to initiate chromosome walking to find the genes residing at the S-locus.

Meiotic recombination in Turnera (Turneraceae): extreme sexual difference in rates, but no evidence for recombination suppression associated with the distyly (S) locus.

To explore the rate of recombination resulting from male vs female meiosis, crosses were performed using distylous Turnera subulata as well as a cross involving the introgression of genes from T. krapovickasii into T. subulata. We assayed four loci on the chromosome bearing the S-locus as well as two loci on each of two other linkage groups. Substantial and consistent dimorphism in recombination rates was found with female meiosis resulting in as much as a approximately 6-fold increase relative to male. Aberrant single locus segregation ratios occurred for some loci, particularly when the male (pollen) parent was heterozygous and the cross involved introgressed genes. The extreme trend of greater recombination resulting from female meiosis was, however, maintained in crosses where no aberrant ratios occurred, indicating that the sex dimorphism in recombination is not the result of aberrant segregation. We also exploited this distylous species and tested whether there is recombination suppression around the S-locus because of an inversion or other chromosome rearrangement(s). We found no significant evidence for recombination suppression.

Studies on trachoma. 11. Evaluation of laboratory diagnostic methods under field conditions.

The severity of trachoma in endemic areas has, in general, a tendency to decrease as a consequence of control measures and gradual improvements in sanitation and living conditions. The number of mild cases seen where the disease is prevalent is thus increasing and it is becoming more difficult to establish a differential diagnosis in certain cases, and to determine the degree of endemicity of the disease in a given area or community.In order to ascertain whether available laboratory methods could contribute useful data from this point of view, a clinical and laboratory study was carried out on the school population of the island of Djerba, off the south coast of Tunisia, during the school year 1963-64.The ophthalmological findings confirmed that, notwithstanding the large-scale treatment campaigns which had been in operation for 10 years, trachoma was then still highly endemic in the island, but relatively mild.The laboratory studies included microscopical examination of conjunctival scrapings for inclusion bodies, complement-fixation tests on serum specimens and-on a subsample of the populations studied-attempts to isolate the trachoma agent. The results indicated that the tests are more likely to be positive when the clinical signs are more pronounced. In individual cases, laboratory tests can at best confirm an already established clinical diagnosis and contribute little to the differential diagnosis of borderline cases.However, this study also indicated that the laboratory tests may provide useful quantitative indications on the endemicity of the disease in a community or in an area, from the point of view of the density of the agent and of the response to its presence. The techniques used must obviously be uniform enough to allow for a comparison with results obtained elsewhere or at different times.