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.

174.  News flash! Selected fish grow as fast as transgenics.
        Growth of domesticated transgenic fish. 2001. Devlin, R.H., C.A. Biagi, T.Y. Yesaki, D.E. Smailus, and J.C. Byatt. Nature 409 (781-78):781-782.
        The authorss inserted a growth-hormone gene into two very different strains of rainbow trout: a fast-growing, highly domesticated strain and a much slower-growing wild strain. The new gene had very little effect on the domesticated fish but the growth of the wild fish speeded up 17-fold.[!] In the end they were about equal.
        "The growth response is strongly influenced by the intrinsic growth rate and genetic background of the host strain, and that inserting growth-hormone transgenes into highly domesticated fish does not necessarily result in further growth enhancement. ...These results indicate that similar alterations of growth rate can be achieved both by selection and by transgenesis in rainbow trout, but that the effects are not always additive."
        Cranial abnormalities were seen in the transgenic but not the domesticated animals. "Transgenesis can affect growth pathways outside the range supported by the homeostatic processes that maintain the fish's normal morphology and viability".
        The authors conclude that "the effect of introducing a growth-hormone gene construct into fish to increase growth rates appears to be dependent on the degree to which earlier enhancement has been achieved by traditional genetic selection. Such effects are likely to be specific for different species, strains and transgenes — in selected mice or in domesticated, rapidly growing farm animals, for example, growth-hormone transgenesis can have little effect on growth or it can induce pathological effects, as we have seen in transgenic salmonids." [See April list #43 for a related paper on transgenic mice.]  devlinr@pac.dfo-mpo.gc.ca 

173.  Excellent analysis of a living gene bank
        Genealogical analysis of a closed herd of black hairless Iberian pigs. 2000. Toro, M.A., J. Rodrigañez, L. Silio, and C. Rodriguez. Conservation Biology 14 (6):1843-1851.
        This paper is a fine example of the use of pedigree records to produce information which are useful for maintaining the genetic quality of a captive population. The population has been stabilized at 1000 breeding animals since 1945 in a herd that began with 24 founders. The authors track, through the successive generations, variables such as inbreeding and coancestry, the effective number of founders and nonfounders, the founder genome equivalents, and expected number of founders' surviving alleles. "Finally, the effect of family structure and mating tactics on the evolution of coancestry was also analyzed. The greatest rates of coancestry per cohort were attributable to unbalanced family sizes, and the use of minimum coancestry matings effectively delayed the increase in inbreeding." toro@inia.es 

172.  Variable populations are more likely to crash
        Population variability and extinction risk. 2000. Vucetich, J.A., T.A. Waite, L. Qvarnemark, and S. Ibargüen. Conservation Biology 14 (6):1704-1714.
        The authors note that while theoretical population models generally predict that populations which fluctuate in numbers are more likely to go extinct than stable populations (i.e. when they fluctuate down to zero), some laboratory and field studies appear to have shown otherwise. Why the contradiction?
        Vucetich et al. demonstrate that there is a statistical artifact which tends to obscure the underlying positive relationship, when one exists, between extinction risk and variability. "Without exception, [the authors'] simulation results, experimental findings, reanalysis of published data, and analysis of quasiextinction risk all contradict previous reports of negative or equivocal relationships. Valid analysis of meaningful data provides strong evidence that increased population variability leads to increased extinction risk." javuceti@mtu.edu 

171.  Critical population size for "mutational meltdown"
        Fixation of new alleles and the extinction of small populations: drift load, beneficial alleles, and sexual selection. 2000. Whitlock, M.C. Evolution 54 (6):1855-1861.
        When populations are very small, chance events -- random drift -- have a stronger influence on the ultimate fate of a mutant gene than selection, unless selection is very strong. Deleterious genes and beneficial genes can both be fixed by chance, but there are generally more bad mutations than good ones. Consequently a small population tends to drift downhill, so to speak, on the fitness peak which Darwin said it ought to be climbing under the influence of natural selection. "Mutational meltdown" of small populations may end with extinction.
        "This paper derives the overall change in fitness due to fixation of new deleterious and beneficial alleles, as a function of the distribution of effects of new mutations and the effective population size. There is a critical effective size below which a population will on average decline in fitness, but above which beneficial mutations allow the population to persist. With reasonable estimates of the relevant parameters, this critical effective size is likely to be a few hundred." The authors also find that sexual selection can reduce the risk of extinction of small populations. whitlock@zoology.ubc.ca 

170.  New migration patterns may evolve very quickly
        Heritability of arrival date in a migratory bird. 2000. Møller, A.P. Proceeding of the royal Society (U.K.): Series B. 268 (1463):203-206.
        The author obtained field data on the heritability of arrival date of the barn swallow, Hirundo rustica, in Denmark and estimated it to be 0.54 (s.e. = 0.15). Heritabilities were obtained in the field through tagging and careful observation. With 54% of the variance being heritable the trait should respond rapidly to selection under changing environmental conditions, as has in fact been noted earlier by W.J Sutherland (1988. Nature 334: 471-472). Variation in the migratory behaviour of salmon has also been proven to be highly heritable and responsive to selection (October list #115). amoller@hall.snv.jussieu.fr 

169.  Heritability of salmon reproductive traits measured in nature
        Genetic variation of fecundity and egg size in anadromous pink salmon Oncorhynchus gorbuscha Walbaum. 2000. Smoker, W.W., A.J. Gharrett, M.S. Stekoll, and S.G. Taylor. Alaska Fishery Research Bulletin 7:44-50.
        The heritability of traits closely related to fitness are now thought to be relatively low because non-heritable sources of variation are relatively high for such traits. The conclusion of this field study of pink salmon in Alaska is therefore unexpected. "Additive genetic variation contributed significantly to variation of fecundity, a trait closely related to fitness, but not to variation of egg size (another trait closely related to fitness) in families drawn from an anadromous population of salmon and measured after growing to maturity in the wild. ... Heritability (estimated from the paternal component of variation) of number of eggs was 0.8 "(standard error, SE = 0.3). [That's high! ]
        "Our observations suggest that variations of fitness-related traits can be maintained from generation to generation in fluctuating environments by genetic variation and are important to the adaptability and persistence of salmon populations." bill.smoker@uaf.edu 

168.  Local population differentiation in shrimp
        Identification of genetic populations of the Pacific blue shrimp Penaeus stylirostris of the Gulf of California, Mexico. 2000. Aubert, H., and D.V. Lightner. Marine Biology 137 (5/6):875-885.
        The authors found that six morphologically-distinguishable populations of stylirostris from different locations in the Gulf of California are genetically distinguishable as well. This raises the possibility -- or probability --- that stylirostris from different places will differ in their genetic suitability for aquaculture. This study is based on neutral RAPD loci. The authors comment that "The finding that genetically discrete stocks of P. stylirostris can be found in a small portion of the geographic distribution range of the species, disagrees with the long-held perception that this resource is panmictic in nature." aubert@dakotacom.net 

167.  Fluctuating asymmetry is not heritable. And that's good.
       Heritability of fluctuating asymmetry for multiple traits in Chinook salmon (Oncorhynchus tshawytscha).  Bryden, C.A., and D.D. Heath. 2000. Can. J. Fish. Aquat. Sci. 57:2186-2192.
        The authors conducted a rather large breeding experiment which involved both an aquacultural stock and an "enhanced but large" natural population; the purpose was to find out whether fluctuating asymmetry (a measure of developmental instability) is heritable in this fish. They conclude that, for the meristic and quantitative traits they measured, it probably isn't heritable. "We found no significant heritability of FA for any of the individual traits examined or for a composite FA index. Our results indicate that FA estimates in chinook salmon will not be confounded by appreciable additive genetic contributions and thus can be reliably used as an environmental and genetic stress indicator." dheath@uwindsor.ca

166.  Complex dynamics of IHNV strains and salmon populations
        Molecular epidemiology reveals emergence of a virulent infectious hematopoietic necrosis (IHN) virus strain in wild salmon and its transmission to hatchery fish. 2000. Anderson, E.D., H.M. Engelking, E.J. Emmenegger, and G. Kurath. Journal of Aquatic Animal Health 12:85-99.
       This paper contains detailed genetic detective work on IHNV viral epidemics among kokanee salmon in the Deschutes River watershed in Oregon, USA. " Analysis of the 16 identified composite haplotypes suggested that both virus evolution and introduction of new IHNV strains contributed to the genetic diversity observed. The results indicated that the 1991–1995 epidemics ... were due to a newly introduced IHNV type that was first detected in spawning adult kokanee in 1988 and that this virus type was transmitted from the wild kokanee to hatchery fish downstream in 1991.
        Twelve IHNV haplotypes were found at Round Butte Fish Hatchery, indicating a series of virus displacement events during the 20-year period examined." The authors conclude that traffic between hatchery and wild populations can be much more complex than one might think. The view that hatcheries introduce diseases to naive and vulnerable wild salmon is too simplistic in this case. gael-kurath@usgs.gov

165.  Multi-generation bottleneck didn't reduce genetic diversity
        Intact genetic structure and high levels of genetic diversity in bottlenecked sockeye salmon (Oncorhynchus nerka) populations of the Fraser River, British Columbia, Canada. 2000. Withler, R.E., K.D. Le, R.J. Nelson, K.M. Miller, and T.D. Beacham. Canadian Journal of Fisheries and Aquatic Sciences 57:1985-1998.
       "Analysis of six microsatellite loci in 5800 sockeye salmon (Oncorhynchus nerka) from 29 Fraser River populations provided little evidence of genetic bottlenecks or mass straying in upper Fraser sockeye salmon resulting from reduced abundances following 1913-1914 rockslides in the Fraser canyon and successive decades of high exploitation. Upper Fraser populations were not characterized by a paucity of rare alleles, a sensitive indicator of populations in which effective size has been recently reduced. Heterozygosity and allelic diversity did not differ consistently between lower and upper Fraser populations." withlerr@dfo-mpo.gc.ca

164.  Genetic variation in susceptibility to a shellfish disease
        Protease inhibitory activity in selectively bred families of eastern oysters. 2000. Oliver, J.L., P.M. Gaffney, S.K. Jr. Allen, M. Faisal, and S.L. Kaattari. Journal of Aquatic Animal Health 12:136-145.
        "In an effort to identify potential biochemical markers for resistance to Dermo, a disease that afflicts eastern oysters Crassostrea virginica, [10 families were] assessed for protease inhibitory (PI) activity against proteases of Perkinsus marinus, the causative agent of Dermo." The three families which had the highest PI activity were also best at surviving Dermo challenge tests both in the lab and in the field. Evidently there is a genetic component to the resistance to this shellfish disease. kaattari@vims.edu

163.  Supportive breeding did reduce effective population size
        Genetic monitoring of supportive breeding in brown trout (Salmo trutta L.), using microsatellite DNA markers. 2000. Hansen, M.M., E.E. Nielsen, D.E. Ruzzante, C. Bouza, and K.-L.D. Mensberg. Can. Jour. Fisheries and Aquatic Sciences 57:2130-2139.
        It is commonly thought that if wild populations of salmon or trout need to be supplemented with fish produced in a hatchery, the hatchery should use as parents fish that are captured in the wild. The idea is to avoid contaminating wild populations with genes adapted to domestic environments.
        If the wild population is small enough to require this type of supportive breeding, however, it may also be small enough to lose absolute population fitness from inbreeding depression, genetic drift away from a local fitness optimum because of the reduced effective population size, and mutational meltdown -- the dreaded extinction vortex. The authors of this paper studied 8 microsatellite loci in 3 brown trout populations that had been supported by a hatchery in Denmark.
        "In two populations subject to supportive breeding, there were strong indications of reduced effective population sizes, and significant genetic differentiation was observed between different samples from the same population." So, supportive breeding does lead to changes at these neutral loci and probably, by a variety of mechanisms, to loci involved in adaptation as well. [Compare the report on supplementation of salmon in the Sacramento river, June list #61, January list #158.]
        The paper includes a careful comparison of the strengths and weakness of several well-known techniques for detecting population bottlenecks and stable effective population sizes. mmh@dfu.min.dk