These aquaculture- and conservation-oriented commentaries are not abstracts written by the original authors.  They reflect the opinions of someone else -- usually Roger Doyle.  Direct quotations from the papers or abstracts are marked with inverted commas.

284.  The meta-population dynamics of recolonized trout streams
         Genetic evidence for mixed origin of recolonized sea trout populations. 2001. Knutsen, H., J.A. Knutsen, and P.E. Jorde. Heredity 87 (2):207-214.
         Trout in some of the streams along the Skagerrak coast of Norway are thought to have been extirpated by acidification, but have subsequently reappeared. Is this reappearance due to recolonization from other population units, i.e. an instance of classical metapopulation dynamics? Apparently so. The authors say "...we find evidence for a mixed origin of the recolonizing trout. Both the high levels of gametic phase disequilibrium [implying that the trout have not been breeding randomly in the same population for very long] and the clear deviation from the general pattern of increased genetic differentiation with distance that are seen in recolonized streams, are consistent with recent population admixture, and confirm the loss of the original populations of these acid streams." halvor.knutsen@bio.uio.no 

283.  How to bring back genetic diversity lost in hatcheries
         Selective recovery of founder genetic diversity in aquacultural broodstocks and captive endangered fish populations. 2001. Doyle, R.W., R. Perez-Enriquez, M. Takagi, and N. Taniguchi. Genetica 111 (1-3):291-304.
         This paper describes a way to increase the genetic diversity of a bottlenecked broodstock without bringing in new breeders. The procedure is an extension of "minimal kinship selection", which has been used to preserve diversity in broodstocks where complete pedigree records exist; for instance, in zoos (See July-August 2001 #212, November 2001 #258 & #261). Pedigrees are rarely available in fish hatcheries.
         Instead of using pedigrees to calculate kinships, we use Ritland's genetic relatedness estimator (September 2001 #227), calculated from microsatellites, to estimate the mean relatedness of each potential breeder to the whole population. A subset of breeders is then selected so as to maximize the number of founder lineages, i.e. to carry the fewest redundant copies of ancestral genes.
         Microsatellite data from a hatchery population of red sea bream for which pedigrees were independently available were used to validate the method. All standard measures of marker diversity were higher in the selected subset of breeders than in randomly chosen subsets in the bream example.
          The result in the next generation is partial reversal of the effects of genetic erosion and drift. We do not have to repeal the second law of thermodynamics do do this, we merely use embedded, inherited information to return the system to an earlier state.
         The procedure differs from marker-assisted selection (MAS) in that DNA marker data are used to identify rare pedigrees or "extended families", rather than to identify rare chromosome segments carrying QTLs. The particular application which we emphasize in this paper is recovery of the genetic diversity lost when a hatchery is founded with a small and non-representative sample of an ancestral wild population. rdoyle@genecomp.com 

282.  A new gene that turns on when tilapia are sex-reversed by temperature
         Search for genes involved in the temperature-induced gonadal sex differentiation in the tilapia, Oreochromis niloticus. 2001. D'Cotta, H., A. Fostier, Y. Guiguen, M. Govoroun, and J.F. Baroiller. Jour. Experimental Zoology 290 (6):574-585.
         Tilapia fry exposed to high temperatures before and during gonadal differentiation usually develop as phenotypic males whatever their genetic sex. In this study, genetically all female progenies (sired by  XX phenotypic males) and all male progenies (sired by YY phenotypic males) were allowed to develop at 27 and 35 degrees C. These are control and masculinizing temperatures, respectively. The authors investigated the expression of the gene for 11beta-hydroxylase, which is known to be involved in making androgens.
         Perhaps more interesting, though, they also found a new gene by looking for differential gene expression between the sex-genotypes and temperatures. The authors have so far found one very interesting differentially-expressed cDNA transcript which they named MM20C. Northern analysis of RNA and quantitative PCR analysis of the DNA both showed that this gene is hardly expressed at all at the normal temperature but is strongly expressed by both sexes at the masculinizing temperature, especially by the genetic males.
         Neither the MM20C sequence nor the protein it would generate if translated were homologous with anything in the genetic databases at the time the paper was written. "These results suggest that MM20C is a gene implicated in the testicular development of tilapia and is up-regulated with elevated temperature. At present, we do not know what the MM20C gene is ...." dcotta@beaulieu.rennes.inra.fr

281.  Is selection more important than drift?
         Comparison of genetic differentiation at marker loci and quantitative traits. 2001. Merilä, J., and P. Crnokrak. Journal of Evolutionary Biology 14 (6):892-903.
         This paper is based on a meta-analysis of 18 independent studies of " the degree of differentiation in neutral marker loci and genes coding quantitative traits with standardized and equivalent measures of genetic differentiation (FST and QST, respectively)". The authors found that quantitative trait divergence among populations was almost always larger than neutral marker divergence, leading them to infer that natural selection is the predominant driving force driving the populations toward different mean values of quantitative traits. That is, mean differences in appearance, physiology and behaviour are due to selection, not drift.
         The authors also infer from this that "selection pressures, and hence optimal phenotypes, in different populations of the same species are unlikely to be often similar". They say that natural selection is promoting unique local adaptations, not a one-suits-all phenotype, and that the unique quantitative features of local populations are primarily due to selection, not drift. (See also September 2001 #237.) This is an interesting and provocative result for genetic conservationists interested in the problem of re-habilitating populations (salmon streams, for example) with broodstock from elsewhere.
        Note that the previous paper by Merilä (January 2000 #10) on the additive variance in fitness vs. non-fitness quantitative traits which concluded that that both kinds have plenty of additive genetic variance. juha.merila@helsinki.fi

280.  Fishing mortality may reduce trout genetic diversity
         Low genetic variability in lake populations of brook trout (Salvelinus fontinalis): A consequence of exploitation? 2001. Jones, M.W., T.L. McParland, J.A. Hutchings, and R.G. Roy G. Danzmann.
         Conservation Genetics 2 (3):245-256. Populations of brook trout living in nine eastern Canadian lakes were found to have lower allozyme heterozygosities than trout in the adjacent streams. This paper demonstrates a positive correlation between the magnitude of the lake-stream difference and the distance of the lakes from the nearest all season road (!). The authors postulate a negative causal relationship between fishing mortality (angling) and heterozygosity in the lake, with bottlenecking providing the mechanism. They suggest that angling delays recovery from natural population crashes and reduces long-term effective population number. "Managers should therefore prevent human-induced mortality at any indication of a large natural mortality event to allow populations to increase in size as rapidly as possible following a decline." See December 2001 #267 for another paper on genetics of angling. matt.jones@dal.ca

279.  QTLs found in common carp
         Segregation of microsatellite alleles and residual heterozygosity at single loci in homozygous androgenetic common carp (Cyprinus carpio L.). 2001. Tanck, M.W., A.P. Palstra, M. van der Weerd, C.P. Leffering, J.J. van der Poel, H. Bovenhuis, and J. Komen. Genome 44 (5):743-751.
         Androgenetic carp are homozygous (but not identical) and carry genes only from the male parent; they are thus ideal material for linkage analysis and QTL identification. This follow-up of previous work (October 2001 #248) reports "the possible association of some microsatellites with mass, length, stress-related plasma cortisol levels, and basal plasma glucose levels". Considering that only eleven microsatellite markers were used this is a surprisingly long stride along the road to identifying QTL loci suitable for selection. The authors attribute their success to the low frequency of recombination and relatively short genetic map for common carp. michael.tanck@alg.venv.wag-ur.nl

278.  Evolutionary response may not keep up with global warming
         Constraint to adaptive evolution in response to global warming. 2001. Etterson, J.R., and R.G. Shaw. Science 294 (5540):151-154.
         This paper is a detailed analytical prediction of whether local, in situ, genetic adaptation can keep up with the rate of climate change. It is possibly the first ever example of how this challenging task can be done in an ecologically and genetically well-defined situation.
         A climate model is used to predict the changes that are expected over the next few decades in an aridity gradient in tallgrass prairie in the Great Plains of the USA. The experimental organism was an annual legume, Chamaecrista fasciculata. Breeding, transplantation and common-garden experiments were used to generate selection coefficients and matrices of genetic variances and covariances among a number of physiological and morphological traits affecting fitness. Restricted maximum likelihood (REML) was used for the genetics, and the theory of multivariate selection gradients for the selection analysis. The evolution of the traits is predicted both as a correlated ensemble (a multivariate fitness component) and in isolation (univariate evolution).
         Considered one-by-one, the physiological and morphological traits seem to be able to keep up with the changing climate. "Yet with only one exception, the multivariate prediction of evolutionary response is less in absolute magnitude than the univariate prediction; in many cases, half or less..... Numerous additive genetic correlations are antagonistic to the direction of selection jointly on pairs of traits.... In each case where the univariate analysis would indicate substantial evolutionary change but the multiple trait analysis predicts a smaller change, at least one among-trait additive genetic correlation is opposite in sign to the vector of selection...."
         The authors adopt the gloomy view that the population will be unable to evolve quickly enough to keep up with the current rate of climate change, which is one or two orders of magnitude faster than historical climate changes. An optimist will counter that their predicted multivariate evolution in not very far short of the authors's estimate of what is required. jre7e@virginia.edu

277.  Early, rapid decline in genetic variance during selection
         Evolution of genetic variability in a population of the edible snail, Helix aspersa Müller, undergoing domestication and short-term selection. 2001. Dupont-Nivet, M., J. Mallard, J.C. Bonnet, and J.M. Blanc. Heredity 87 (2):129-135.
         Theory predicts that the first generations of selection will see a large decrease in additive genetic variance, which is the raw material for future genetic gain. Whether this actually happens is rarely tested in an aquaculture or aquaculture-like context. The genetic analysis in this paper spans six generations in total: starting with wild-caught snails, there were three generations of "natural' selection in a domestic environment followed by three generations of artificial selection for weight. This is similar to the history of many of the Penaeus shrimp broodstocks now in use around the world.
         Pedigree records were maintained throughout. The most useful finding, as a model for aquaculture, was the marked decrease in the heritability and additive genetic variance for weight as well as in the genetic diversity calculated (from pedigrees) as founder genome equivalents. (See July-August 2001 #216, February 2001 #173, November 2001 # 258, this listing #283.) Most of the decrease occurred in the first generation of domestication and again in the first generation of selection (G3-G4). The result is ascribed to linkage disequilibrium (the Bulmer effect) and random drift under selection. dnivet@jouy.inra.fr

276.  Allozyme heterozygosity may be selected
         Heterozygosity-fitness correlations in rainbow trout: effects of allozyme loci or associative overdominance? 2001. Thelen, G.C., and F.W. Allendorf. Evolution 55 (6):1180-1187.
         It has been known for more than 20 years that individuals that are more heterozygous at allozyme loci (enzyme loci) are often more fit, by several measures of fitness, than individuals in the same random-mating population that are less heterozygous. Several general explanations are competing with each other: allozyme heterozygosity may itself be beneficial, which implies that allozymes are not selectively neutral; or allozymes may be neutral markers for chromosome segments carrying unknown genes which enhance fitness when heterozygous (associative overdominance); or marker heterozygosity may be an indicator of inbreeding depression.
         The controversy involves some deep genetic issues and is of practical importance as well, for example in the design and monitoring of breeding programs and the identification of "evolutionarily significant units" for conservation.
         The authors examined 10 allozyme and 10 microsatellite loci in a hatchery population of rainbow trout. Allozyme heterozygosity correlated positively with condition factor, but microsatellite (non-coding DNA) heterozygosity did not. "... the observed relationship between heterozygosity at allozyme loci and condition factor in rainbow trout appears to be due to the allozyme loci themselves, rather than associative overdominance [linkage to unidentified selected genes]. ...Regardless of the underlying mechanism, these results support the view that allozymes and microsatellites are differentially affected by natural selection." Specifically, that allozymes are selected and microsatellites are not.
Allendorf e-mail: darwin@selway.umt.edu

275.  Gene flow restores fitness
         Experimental evidence for beneficial fitness effects of gene flow in recently isolated populations. 2001. Newman, D., and D.A. Tallmon. Conservation Biology 15 (4):1054-1063.
         This is a useful experimental confirmation of the theoretical expectation that low levels of in-migration can counteract the deleterious effects of inbreeding. Experimental populations of mustard (Brassica campestris) were maintained at a census population size of N=5 for five generations with three levels of migration (0, 20 and 50%) per generation. Several measures of fitness were significantly lower in populations that had experienced no in-migration.
         "These data provide empirical evidence of the beneficial fitness effects of a small number of migrants for recently fragmented populations." This experiment is in many ways comparable to the natural experiment involving a bottlenecked population of birds reported in September 2001 #235.
Tallmon e-mail: dtat@selway.umt.edu

274.  New science website for developing countries
         "SciDev.net is free-access, Internet-based network devoted to reporting on and discussing those aspects of modern science and technology that are relevant to sustainable development and the social and economic needs of developing countries."
         Sci.Dev looks like a useful new internet resource for scientists, and not only those in developing countries. It is sponsored by Nature and Science, both of which will provide free access to some articles every week, and is financially and morally supported by international development agencies of Canada, Sweden and the UK. As we would expect of a product with this pedigree, the scientific articles are interesting and solid and the prose of the mission statement has a pleasing new-age iridescence. Recent happenings in genetics and fisheries, biotechnology and conservation are covered in a way which is particularly interesting to developing countries. The site also gives access to development-oriented organizations, granting agencies, meetings, jobs and on-line technical expertise. It is to be updated every week. http://www.scidev.net