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.

273.  News flash: how to make transgenic shrimp (and guppies too)
         Production of transgenic live-bearing fish and crustaceans with replication-defective pantropic retroviral vectors. 2001. Sarmasik, A., C.Z. Chun, I.-K. Jang, J.K. Lu, and T.T. Chen. Marine Biotechnology 3:177-184.
         Standard techniques for inserting foreign genes have been difficult to apply to shrimp species of aquacultural interest. This is because embryos of Penaeus, for example, are released from their mothers at a relatively advanced stage. Newly-fertilized eggs are essentially unavailable at the appropriate stage for microinjection or electroporation. The authors of this paper have found a clever way around this problem and produced transgenic crayfish and topminnows (Poeciliposis lucida). This appears to be the first time this has been done. They expect their procedure will work in other crustaceans and live-bearing fish.
         The foreign gene is carried into the host by an extensively engineered viral vector. One engineered feature of the vector makes it unable to replicate. Other features, derived from the hepatitus B virus and the vesicular stomatitis virus (a strange pathogen similar to hoof and mouth disease which infects mammals, insects and possibly plants), enable the vector to stick to the cell membrane of practically anything. Another feature is the transgene itself, which in this case was a "reporter gene" that lets you know when it is working in the host genome, but which in principle could be a foreign gene that usefully enhances growth, reproduction or disease resistance in shrimp.
         Immature gonads of the crayfish were injected with a solution of the vector about one month before the normal age of first reproduction. When they matured the injected individuals were mated with normal individuals. About 50% of the resulting offspring were transgenic, as predicted. The paper provides proof of integration, expression and transmission of the reporter transgene for at least three generations.
         "Therefore, we believe that pantropic retroviral vectors will allow the transfer of superior genetic traits, such as fast somatic growth or disease resistance, into economically important crustacean species for commercial aquaculture. Furthermore, these gene transfer vectors will facilitate the generation of transgenic model live-bearing fish with reporter genes for studies in environmental toxicology and cancer research." tchen@uconnvm.uconn.edu

272.  Salmon MHC diversity selects locally, drifts globally
         Comparative analysis of population structure across environments and geographical scales at major histocompatability complex and microsatellite loci in Atlantic salmon (Salmo salar). 2001. Landry, C., and L. Bernatchez. Molecular Ecology 10 (10):2525-2539.
         This is an interesting extension of earlier work which showed that genetic diversity at the major histocompatability locus (MHC) in Atlantic salmon is maintained by a sort of balancing selection. This presumably increases the flexibility of the antigenic response (a good thing) and probably includes mate selection as a mechanism (opposites attract; July-August list #226). The new paper shows that this diversifying selection is a major influence on MHC gene frequency distributions only at the local population level, i.e. within rivers.
         This makes sense in light of the proposed balancing selection mechanisms. Over larger geographical distances, however, migration and random drift are the dominant evolutionary process at the MHC locus, as shown by the similar geographical pattern of MHC and neutral microsatellite variation.
         This conclusion fits in nicely with a recent paper by Garrigan & Hedrick (2001, Immunogenetics 53(6):483-9) on MHC in the endangered Chinook salmon of the Sacramento river. Apparently balancing selection has maintained MHC diversity for millions of years in these fish, and continues to counteract the potential random loss of diversity (drift) caused by the recent, local population bottleneck. Louis.Bernatchez@bio.ulaval.ca

271.  Different HPV strains imply need for multiple PCR primers
         Different reactions obtained using the same DNA detection reagents for Thai and Korean hepatopancreatic parvovirus of penaeid shrimp. 2001. Phromjai, J., W. Sukhumsirichart, C. Pantoja, D.V. Lightner, and T.W. Flegel. Diseases of Aquatic Organisms 46 (2):153-158.
         Three types of DNA molecule were used in this study. The first was the genomic DNA of the hepatopancreatic parvovirus (HPV), a major shrimp pathogen. The second was the short sections of DNA used to prime the PCR amplification of this HPV in the laboratory. The third type of DNA was the probe used to indicate the presence of HPV DNA in the PCR amplified product and/or infected shrimp tissue. The authors found that probes and PCR primers developed for detecting HPV in Penaeus chinensis did not work very well with the HPV infections in another species of shrimp, P. monodon. Furthermore the sequence of the amplified viral DNA was different in the two shrimp species. From this the authors conclude that there are actually two viral species or varieties at work even though the histopathology is the same, and that " multiple primers or degenerate primers may be necessary for general detection of HPV varieties". This is important practical information for the many shrimp farmers who have set up a PCR capability on their farms. sctwf@mahidol.ac.th

270.  Managing a hatchery to minimize inbreeding
         Minimization of rate of inbreeding for small populations with overlapping generations. 2001. Sonesson, A.K., and T.H.E. Meuwissen. Genetical Research 77:285-292.
         Everyone who manages hatcheries knows that every breeder -- fish or shrimp -- should contribute the same number of offspring to the next generation in order to minimize the accumulation of inbreeding. This is often impossible to achieve in practice, but it is recognized as optimal. But is it really optimal? Well no, actually. Other procedures such as selecting breeders to minimize multi-generation coancestry of the parents are much better, when pedigree records are available. Even this method is less than optimal, however, when generations overlap as they do in many hatcheries. Hatcheries which are primarily intended for genetic conservation will normally have many generations on site at any given time.
         The scheme presented here and examined by simulation favours selection of older breeders out of the age-class mixture. Over the long term it considerably reduces the rate of accumulation of coancestry and inbreeding. The method appears to be practical when mature mortality rates are reasonably low and there is good control over family size. The details depend on both of these factors. a.k.sonesson@id.wag-ur.nl .

269. More evidence that mates are chosen to maximize diversity
         The influence of parental relatedness on reproductive success. 2001. Amos, W., J.W. Wilmer, K. Fullard, B. Burg, J.P. Croxall, D. Bloch, and T. Coulson. Proceedings of the Royal Society UK (Ser. B) 268 (1480):2021-2027.
         "Examination of three long-lived vertebrates, the long-finned pilot whale, the grey seal and the wandering albatross reveals significant negative relationships between parental similarity and genetic estimates of reproductive success." Parental relatedness was estimated from neutral marker data in several ways, including Queller & Goodnight's estimator and Coulson's d2 estimator, and in one case from pedigrees. The authors come to the conclusion that the negative correlation between parental relatedness and fitness is not merely the result of inbreeding depression caused by the mating of close relatives. The correlation extends to low levels of relatedness where conventional inbreeding depression is unlikely. In fact there seems to be a positive advantage to finding a dissimilar mate. Note that the evidence that Atlantic salmon may choose mates to maximize MHC diversity (July-Aug 2001 #221, and this month #272). w.amos@zoo.cam.ac.uk

268.  Distinguishing between structured mating and structured populations
         A method for distinguishing consanguinity and population substructure using multilocus genotype data. 2001. Overall, A.D.J., and R.A. Nichols. Molecular Biology and Evolution 18 (11):2048-2056.
         When an excess of homozygotes is observed in a sample it is usually ascribed either to non-random mating in the population or to the pooling of individuals from two or more (somewhat different) populations. External non-genetic evidence may favour one of these explanations over the other, but papers that report homozygous excess often conclude on a note of uncertainty. One can think of situations in aquaculture and conservation when it is important to have the correct explanation; when assigning individuals to population groups for instance, or when estimating genetic relatedness from microsatellite data.
         The authors of this paper have developed a maximum-likelihood procedure for distinguishing the two main causes of homozygote excess using marker data. It worked well on two Asian immigrant populations in the UK, one of which is characterized by a high frequency of cousin mating and the other by a caste-dependent mating system -- effectively multiple populations. andy.overall@ed.ac.uk

267.  Fishing reduces the fitness of released hatchery fish
         Evidence for selective angling of introduced trout and their hybrids in a stocked brown trout population. 2001. Mezzera, M., and C.R. Largiadèr. Journal of Fish Biology 59 (2):287-301.
         Microsatellite identification showed that fishing (angling) a stocked population selectively removed hatchery trout and their hybrid offspring as well. The authors suggest that angling might therefore be used to reduce the genetic impact of supplementary breeding programs. In other words, that angling increases the difference in fitness between wild and hatchery trout, and that this could be useful for preserving the wild gene pool. largiader@zoo.unibe.ch

266.  Adaptive growth-predation tradeoff in fish
         Evolution of intrinsic growth and energy acquisition rates. I. Trade-offs with swimming performance in Menidia menidia. 2001. Billerbeck, J.M., T.E. Lankford Jr., and D.O. Conover. Evolution 55 (9):1863-1872.
         A paper reviewed here last year (March 2000 #28) described a "common-garden" experiment in which silversides from Nova Scotia (NS) ate more food, used it more efficiently and grew faster than a population from South Carolina (SC). The review noted the significance of such natural adaptations when choosing broodstocks for aquaculture. Now the same authors have followed up with two papers in Evolution which together explain why South Carolina silversides remain slow-growing even when faster growth is evolutionarily possible.
         The first Evolution paper shows that rapid growth has a trade-off: low swimming speed. "Maximum prolonged and burst swimming speeds of NS fish were significantly lower than those of SC fish, and swimming speeds of fast-growing phenotypes were lower than those of slow-growing phenotypes within populations."
         The second paper (Evolution 55 (9):1873–1881) shows that slow swimming speed has a fitness cost: vulnerability to predation. The authors exposed silversides to several common predators and found that NS fish were more vulnerable than SC fish, and that predation increased with growth rate and feeding rate both within and between populations. "Differences in predation vulnerability were likely due to swimming performance, not attractiveness to predators. [The authors'] findings demonstrate that maximization of energy intake and growth rate engenders fitness costs in the form of increased vulnerability to predation." dconover@notes.cc.sunysb.edu.

265.  Prior inbreeding did not prevent extinction
         Inbreeding and extinction: Effects of purging. 2001. Frankham, R., D.M. Gilligan, D. Morris, and D.A. Briscoe. Conservation Genetics 2 (3):279-284.
         There is a long-standing, sometimes rather heated, controversy over whether it might be a good idea to deliberately inbreed small, captive populations to eliminate inbreeding depression. Inbreeding exposes the alleles to selection so they can be removed ("purged") quickly from the population. After that they are gone forever, except for new mutation, so the population manager never has to worry about inbreeding depression again no matter how long the population stays small. The controversy includes questions about whether purging actually works, what the effects on genetic diversity might be, and other matters. Fundamental disagreements about the genetic basis of heterosis and inbreeding depression quickly become part of every discussion on this issue.
         In this experimental study on fruit flies two types of populations were closely inbred (brother-sister mating) for 12 generations. One type had been outbred until the inbreeding started and was presumably genetically variable. The second type had been inbred for 20 generations and then multiply hybridized just prior to the final inbreeding experiment. Therefore it too was genetically variable, because of the hybridization, but purged of deleterious alleles because of the prior inbreeding. Each type of population was replicated many times.
         So did the purged type of population do better than the non-purged during the twelve generations of inbreeding that followed these pre-treatments? No, it didn't. "There was a small and non-significant difference between the extinction rates at an inbreeding coefficient of 0.93 in the non-purged (0.74 ± 0.03) and purged (0.69 ± 0.03) treatments. This is consistent with other evidence indicating that the effects of purging are often small.
         Purging using rapid inbreeding in very small populations cannot be relied upon to eliminate the deleterious effects of inbreeding." There are a multitude of hypothetical reasons why purging -- a very attractive idea -- might or might not work, so empirical results like this are very useful. Unfortunately they may not be generalizable (See September list #228. The paper in May list #193 emphasizes that small populations are unpredictable in their response to inbreeding.). rfrankha@Rna.bio.mq.edu.au

264.  Genetics of black blotches on red tilapia
         Experimental evaluation of mass selection to improve red body colour in Fijian hybrid tilapia (Oreochromis niloticus × Oreochromis mossambicus). 2001. Mather, P.B., S.N. Lal, and J. Wilson. Aquaculture Research 32 (5):329-336.
         The authors mass-selected a "red" hybrid of Oreochromis niloticus × Oreochromis mossambicus to reduce the incidence of black spots. "The results show clearly that red phenotype can be improved significantly by applying mass selection, without affecting growth performance. [The authors] propose that black spots on an otherwise red phenotype could represent the allelic products of a second genetic locus influencing skin colour, which can be expressed in red individuals (genotype Rr) but which may be masked in black individuals (genotype rr)." p.mather@qut.edu.au

263.  QTL action may be much more complex than we would like
         Genome-wide epistatic interaction analysis reveals complex genetic determinants of circadian behavior in mice. 2001. Shimomura, K., S.S. Low-Zeddies, D.P. King, T.D.L. Steeves, A. Whiteley, J. Kushla, P.D. Zemenides, A. Lin, M.A. Vitaterna, G.A. Churchill, and J.S. Takahashi. Genome Research 11:959-980.
         There is vastly more genetic information about the mouse than about any aquacultural species, so mouse genetics may tell us something about what lies ahead for aquacultural QTL mappers. The authors dissected the genetics of circadian behaviour of mice. Let us willingly suspend our disbelief for a moment and suppose this is a typical quantitative trait with relevance to aquaculture.
         There are nine known "clock" genes in mice which ought to be candidate QTL genes. However, few or none of the fourteen circadian QTL they found were, in fact, clock genes.
         After finishing their search for ordinary (additive) QTLs, the authors proceeded to look for QTL interactions. They found two additional pairs of QTL loci that had strong effects together but not separately. Thus variation in behaviour is determined to a considerable extent not by single [QTL] genes acting additively but by multiple genes acting interactively. These would not respond to marker assisted selection (MAS) as MAS is usually envisaged.
         This experiment brings to mind the papers on transgenic trout (February 2001 #174) and mouse Mar-Apr 2001 #181 in which growth hormone transgenes (candidate genes by definition) had little effect on strains that are already fast growing because of other genetic characteristics. This may be a hint that it may not be at all easy to exploit the full genetic variance of QTLs by marker assisted selection. j-takahashi@northwestern.edu

262.  Calculating the economic and social cost of evolution
         Humans as the world's greatest evolutionary force. 2001. Palumbi, S.R. Science 293 (5536):1786-1790.
         Pests evolve pesticide resistance, bacteria grow tolerant to antibiotics, invading species adapt physiologically and behaviorally to new environments, fish evolve to escape the fishery. Everyone knows this but Palumbi has gone further and put a price on it. The "cost of evolution" in the USA alone adds up to $33 billion to $55 billion per year.
         Some of the examples are arguable and dated (fisheries anyway) but that doesn't detract from the main point of Palumbi's article. Our civilization has set us up for an evolutionary arms race with every other creature in the world. Palumbi suggests several ways to slow evolution down, including reducing unwanted selective pressures and fitness variances in species that affect us (and vice versa). That means a lot of species because is hard to think of a single one that 21st century humans genuinely fear that isn't evolving to overwhelm us. Or a wild species we approve of that isn't becoming inaccessible or falling into an extinction vortex. This would be a good paper for classroom discussion. palumbi@oeb.harvard.edu