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.

187.  Pre-adapted salmon are better colonizers
        Genetic contribution of three introduced life history forms of sockeye salmon to colonization of Frazer Lake, Alaska. 2000. Burger, C.V., K.T. Scribner, W.J. Spearman, C.O. Swanton, and D.E. Campton. Canadian Jour. Fisheries and Aquatic Sciences 57:2096-2111.
        Sockeye eggs, fry and adults were introduced into the lake a number of times between 1951 and 1971. The source populations were adapted to a variety of different spawning habitats and spawning seasons. The authors used "six nuclear DNA (nDNA) microsatellite loci and mitochondrial DNA (mtDNA) to determine which donor population(s) had colonized the principal spawning habitats of Frazer Lake: three shoreline areas and four inlet tributaries." Mitochondrial DNA evidence suggested significant female founder effects and subsequent drift. The authors concluded that "life history adaptations of donor populations were critically important for successful colonization of Frazer Lake, thus underscoring the need to consider life history traits in other introduction and recovery programs." carl_v_burger@fws.gov

186.  Unlimited effective population number? Merely eliminate sampling error
        Application of reproduction technologies to the conservation of genetic resources. 2000. Santiago, E., and A. Caballero. Conservation Biology 14:1831-1836.
        The authors point out that genetic drift in finite populations is mostly due to random loss of alleles during meiotic segregation, in well-managed populations where family sizes are equal and survival is high. So, they suggest eliminating this random dropping of alleles by using high-tech reproductive techniques which produce more than one daughter cell per meiosis. Theoretical analysis leads to the conclusion, " With this technology it is possible to reduce or even completely cancel the genetic drift caused by segregation of heterozygotes. We evaluated the theoretical benefits of the use of such technologies to conservation biology. The effective population size can be increased enormously and, consequently, the amount of drift can be greatly reduced if manipulations in reproduction are made." [This is a wonderful idea but it does sound like the advice given forestry students. Don't waste time measuring a lot of trees to find their average diameter. Just walk over to the average tree, and measure it.] armando@uvigo.es

185.  An extinction vortex
        Experimental confirmation that inbreeding depression increases extinction risk in butterfly populations. 2001. Nieminen, M., M.C. Singer, W. Fortelius, K. Schöps, and I. Hansk. American Naturalist 157:237-244.
        Most people agree that inbreeding reduces the viability of small, endangered populations but controversy surrounds the question, "how much?". A field study of a butterfly population that exhibited increased extinction rates with inbreeding, where inbreeding was indirectly indicated by heterozygosity, was noted in a previous list (March 2000 #32). The present paper is an experimental follow-up in which inbred and outbred families were outplanted and monitored over the course of a year. The conclusions of the previous indirect analysis were confirmed, which is itself useful information. The mechanism appears to involve an extinction vortex. "The most severe effects of inbreeding depression [on reproduction and winter survival] ... result in small larval groups, which are known to have reduced survival. Consequently, inbreeding creates a negative cascade effect that is amplified by environmental stress: low-egg-hatching rate in inbred females leads to small larval groups, which leads to low survival of larvae, especially under unfavorable conditions. Therefore, genetic, demographic, and environmental causes of local extinction cannot be easily separated in M. cinxia nor, most likely, can they be in many other species with small local populations." This butterfly project is turning out to be one of the most convincing examples of an inbreeding problem in nature. marko.nieminen@helsinki.fi.

184.  Genetics of parasite resistance in oysters
        Influence of parentage upon growth in Ostrea edulis: evidence for inbreeding depression. 2000. Naciri-Graven, Y., S. Launey, N. LeBayon, A. Gerard, and J.P. Baud. Genetical Research 76:159-168.
        The authors examined genetic variability of growth in three lines selected for resistance to the protozoan parasite Bonamia ostreae, and the crosses between the lines. Genetic growth effects were highly significant at the population and family levels. "Estimates of inbreeding depression (relative to the mean, for complete inbreeding) were high ..., which correlates with the apparent heterosis for growth observed in the crossbred population." They also found that heritability of resistance was high. February list #164 notes a comparable result. yamama.Naciri-Graven@cjb.ville-ge.ch

183.  Trout QTL genes for disease resistance
        Quantitative trait loci (QTLs) associated with resistance/susceptibility to infectious pancreatic necrosis virus (IPNV) in rainbow trout (Oncorhynchus mykiss). 2001. Ozaki, A., T. Sakamoto, S. Khoo, K. Nakamura, M.R.M. Coimbra, T. Akutsu, and N. Okamoto. Molecular Genetics and Genomics 265:23-31.
        The salmonid disease infectious pancreatic necrosis (IPN) causes major losses in aquaculture. The authors used backcrosses between resistant and susceptible strains to identify several chromosome regions containing putative QTL genes which affect disease resistance. Fifty-one microsatellite markers were used for the linkage analysis. The authors comment that the results may lead to the cloning of resistance genes as well as to marker assisted selection. nokamoto@tokyo-u-fish.ac.jp

182.  QTL mappers -- watch out for mixed populations!
        Population admixture: detection by Hardy-Weinberg test and its quantitative effects on linkage-disequilibrium methods for localizing genes underlying complex traits. 2001. Deng, H.-W. , W.-M. Chen, and R.R. Recker. Genetics 157:885-897.
        Aquaculture geneticists are using, or plan to use, genetic markers in breeding populations to search for associations between markers and complex quantitative traits such as growth and disease resistance. This paper is a useful warning about what happens when mixtures of populations or broodstocks with somewhat different gene frequencies are used in the search for QTLs or major genes. The authors show (a) that H-W disequilibrium is not a powerful tool for detecting admixtures, (2) that if populations are mixed you get a lot of false positive associations. This is one of the rare instances in aquaculture when type I error wastes more money than type II error. It sends you chasing after genes that aren't there. deng@creighton.edu

181.  Frankenmice don't grow faster if they already grow fast
        Correlated responses to selection for large body size in oMt1a-oGH mice: growth, feed efficiency and body composition. 2000. Parks, K.R., E.J. Eisen, and J.D. Murray. Journal of Animal Breeding and Genetics 117 (6):385-405.
        This interesting work on mice examined what happens when you insert a transgene that increases growth and then select the transgenic population for a further increase in growth. If you can arrange matters so that the transgene can be switched on or off at will, should selection be done when the gene is activated or when it is not activated? The experiment was done in lines of mice which carried the sheep metallothionein 1-a growth hormone transgene, which was activated during selection by adding ZnSO4 to the drinking water. The results were complicated and depended among other things on whether the mouse line had already been selected for high growth. This work should be pondered by those who are wondering how to improve their lines further once their Frankenfish are up and running. It is also directly related to the work on transgenic trout, February list #174, which showed that a growth-hormone transgene had little effect in a strain which had already achieved high growth after many generations of selection. genejeisen@ncsu.edu

180.  Genetic variation in crustacean parasite resistance
        The cause of parasitic infection in natural populations of Daphnia Crustacea: Cladocera): the role of host genetics. 2000. Little, T.J., and D. Ebert . Proceedings Royal Society (B) 267 (1457):2037-3042.
        A crustacean model system (Cladocera) was studied to find out whether genetic variation among individual animals contributes to variation in their resistance to a bacterial parasite. Taking advantage of the infamous sexual behaviour of cladocera, they carried out an ingenious experiment in which clonally produced great-granddaughters of animals which were observed to be infected when collected in the wild were compared with the great-granddaughters of animals which were naturally healthy. In three of the four populations studied, "hosts that were healthy in the field had greater genetic-based resistance than hosts that were infected in the field, unambiguously showing the effect of host genetic factors on the expression of disease in the wild". It is perhaps important for aquaculture (by analogy) that not only was there variation in resistance among individual daphnia, there was variation among populations too. tom.little@ed.ac.uk

179.  Outcrossing may help, if you don't stray too far
        Inbreeding and outbreeding depression in natural populations of Chamaecrista fasciculata (Fabaceae). 2000. Fenster, C.B., and L.F. Galloway. Conservation Biology 14 (5):1406-1412.
        The authors crossed wild populations of the partridge pea (a native N.A. legume) and measured the performance of several generations of the hybrids under natural conditions. The objective was to see whether outcrossing does actually restore the fitness of populations that suffer from inbreeding depression. " We found almost universal F1 superiority over the parents. The F3 hybrids suffered a loss of fitness compared to the F1 hybrids [caused by] loss of heterozygosity and the disruption of coadapted gene complexes." In the longest range crosses, about 1000 km, the fitness of some of the F3 dropped below that of either parent, indicating true outbreeding depression. It appears that outcrossing always provided a short-term benefit but that deleterious effects often showed up later, especially in wide crosses. See January list #155 another paper on deleterious outcrossing in plants. cf25@umail.umd.edu

178.  How many animals needed to define an ESU?
        Sample size for the diagnosis of conservation unit. 2000. Walsh, P.D. Conservation Biology 14 (5):1533-1537.
        The author discusses what happens when a small sample of individuals is studied and, because the individuals are identical for a particular trait, the inference is made that the entire population is identical for that trait. "Use of the phylogenetic species concept in defining conservation units is based on the assumption that the fixation of a particular character state in a population is diagnostic of a long history of reproductive isolation.... [Walsh's] results suggest that confident diagnosis requires sample sizes much larger than those commonly used when the phylogenetic species concept is applied to defining conservation units." The sampling problem doesn't appear to be totally intractable, however. A sample of around 60 identical individuals is required to reject with 95% confidence the hypothesis that 5% of the population is actually different. walshpd@aol.com

177.  Designing a selection program to minimize inbreeding
        Optimal mass selection policies for schemes with overlapping generations and restricted inbreeding. 2000. Villanueva, B., P. Bijma, and J.A. Woolliams. Genetics Selection and Evolution 32:339-355.
        This is an interesting analysis of the trading-off between inbreeding and selection in species which, like salmonids, may undergo selection in small broodstocks with overlapping generations. Inbreeding can be restricted by increasing the number of parents and/or by increasing the generation interval. "Optimization of schemes when restricting the rate of inbreeding per generation leads to shorter generation intervals than optimization when restricting the rate of inbreeding per year." The details should be of practical importance in hatcheries. b.villanueva@ed.sac.ac.uk

176.  Population substructure makes DNA fingerprint matches more likely
        Estimating the probability of identity among genotypes in natural populations: cautions and guidelines. 2001. Waits, L.P., G. Luikart, and P. Taberlet. Molecular Ecology 10:249-256.
        There are many situations in conservation genetics and ecological genetics -- and forensics, including fishery forensics -- when one needs to know the probability of sampling identical genotypes from two individuals that are, in fact, different ("match probability"). The authors of this paper point out that population substructure can increase this probability by several orders of magnitude, so one ought to take substructure into account. "To help researchers and managers avoid potential problems associated with this bias, we introduce an equation for P(ID) between sibs. This equation provides an estimator that can be used as a conservative upper bound for the probability of observing identical multilocus genotypes between two individuals sampled from a population. " lwaits@uidaho.edu

175.  Frankencrops don't overwhelm the ecosystem
        Transgenic crops in natural habitats. 2001. Crawley, M.J., S.L. Brown, R.S. Hails, D.D. Kohn, and M. Rees. Nature 409:682-683.
        Several papers have been noted on this website that suggest that transgenic fish have metabolic peculiarities which should make them relatively uncompetitive in the wild. Here is a brief report on a long-term experiment designed to see how transgenic crops fare under natural conditions. The crops carried various transgenes that made them herbicide tolerant or insecticidal. "Four different crops (oilseed rape, potato, maize and sugar beet) were grown in 12 different habitats and monitored over a period of 10 years. In no case were the genetically modified plants found to be more invasive or more persistent than their conventional counterparts." m.crawley@ic.ac.uk