These aquaculture-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.

72. Growth of GIFT tilapia compared with two other strains
The culture performance of monosex and mixed-sex new-season and overwintered fry in three strains of Nile tilapia (Oreochromis niloticus) in northern Vietnam. 2000. Dan, N.C., and D.C. Little. Aquaculture 184:221-231.
         This is one of the all-too-rare independent comparisons of the performance of tilapia strains.  It was done in northern Vietnam to choose a strain suited to the local, extensive cultivation procedures.  Eight combinations of grow-out procedures were tried: using pond or cage-in-pond culture, using new-season fry or fry which had been overwintered in submerged cages, using fry with and without hormonal sex reversal.  A Vietnamese strain, a Thai strain and the GIFT strain were compared under these 8 conditions.
         The GIFT strain grew about 10% better when the fry were overwintered in ponds and cages.  Although the 3 strains were statistically indistinguishable under the other conditions GIFT was a little larger at harvest in all but one of the 8 tests.  The authors end their paper on a note of surprise at this result.  "This growth differential is much less than reported for this selected strain compared to unselected controls...[Eknath, 1995. The Nile Tilapia. In: Thorpe, J., Lannan, J., Nash, C. (Eds), Conservation of Fish and Shellfish Resources. Academic Press, London. pp. 177-194]."
         This comment about selection and GIFT does not take note of the composition of GIFT before selection was begun.  Broodstocks that contain genetic material recently collected from Egypt grow very well, and this would include GIFT whether or not the GIFT selection programme has further improved it.  The statistical power to distinguish strains is probably reduced by the limited number of cages deployed in the Vietnam experiment and the heterogeneity of the environment "in the windy lake".  The authors of this very useful paper properly compensated for this by adding "cage effects" to their analysis, but this solution increases the number of parameters to be estimated and thus diminishes the power of the (main) test for strain differences.
         So, was the GIFT strain the best of the three?  If we consider the Vietnamese experiment as a whole the daily growth of GIFT was on average about 7% better than the next strain, which should be economically meaningful.  Was the 7% advantage statistically significant as well?   The probability that any one of the 3 strains would come out tops in 7 of the 8 tests solely by chance is only about 0.001.  Furthermore, given that GIFT was significantly better in 2 of the tests, the probability that this same strain would also be at least a bit better in 5 of the other 6 tests solely by chance is about 0.004.   ncdan@ftp.vn

71. Inbreeding depression in a penaeid shrimp
Microsatellite-associated heterosis in hatchery-propagated stocks of the shrimp Penaeus stylirostris. 2000. Bierne, N., I. Beuzart, V. Vonau, F. Bonhomme, and E. Bédier. Aquaculture 184:203-219.
         The P. stylirostris used in this study had been propagated in a closed population for 22 generations, during the last 5 as two separate subpopulations.  Allele frequency differences have appeared between the subpopulations.  Microsatellite heterozygosity of individual shrimp was positively correlated with their growth rates.  Both of these genetic phenomena are thought to be caused by the small effective size of the broodstocks.  Effective size was estimated from the breeding records and from the genetic data in various ways.  The authors interpret the correlation between heterozygosity and growth as a general indicator of inbreeding depression, rather than an artifact or the direct effect of the 3 dinucleotide microsatellite marker loci or loci linked to them.  (See similar inferences from similar correlations in wild populations in March list #32 and #24, and February list #9.)
         The average depression associated with one locus in our case is above or equivalent to the amount observed for a 10% increase of inbreeding in other species.  These results suggest that heterozygosity at neutral marker loci is sufficiently well correlated with individual inbreeding coefficients to reveal a significant residual inbreeding load for growth rate in Tahitian P. stylirostris stocks."   n-bierne@univ-montp2.fr

70. Caution about detecting inbreeding depression "the easy way"
Fluctuating asymmetry and fitness in Drosophila melanogaster. 2000. Bourget, D. Journal of Evolutionary Biology 13:515-521.
         Fluctuating asymmetry, or FA, is a measure of how physically similar the right side of the body is to the left side.  Fluctuating asymmetry is often taken as an indirect indicator of inbreeding depression or other genetic problems and has been applied both to aquacultural populations and small, endangered, wild populations with considerable success.  Since the two halves of an embryo are almost always genetically identical the random side-to-side variation ("asymmetry") can be ascribed to the failure of the genotype to adequately regulate the development of the phenotype.  Non-random and systematic differences in development like right/left handedness in people are discounted in the FA analysis, hence the qualifying word "fluctuating".  FA is potentially a convenient indicator of broodstock fitness in applied situations because it is easy to measure.  However, whilst the idea that fluctuating asymmetry indicates diminished genetic fitness is intuitively appealing it not yet well supported by scientific observation.  This is mainly because FA is easy to measure but fitness is not.
         The author of this paper measured the fluctuating asymmetry of abdominal bristles in 32 fruit fly lines.  "Two measures of fitness were made for each line: productivity (a combined measure of fecundity and egg-to-adult survivorship) and competitive male mating success.  Fluctuating asymmetry was correlated with neither of these two components of fitness.  This suggests that generalizations about fluctuating asymmetry must be taken with care."   bourget@jouy.inra.fr .

69. A big, new tilapia gene pool
Breeding new strains of tilapia: development of an artificial center of origin and linkage map based on AFLP and microsatellite loci. 2000. Agresti, J.J., S. Seki, A. Cnaani, S. Pompuang, E.M. Hallerman, N. Umiel, G. Hulata, G.A.E. Gall, and B. May. Aquaculture 185:43-56.
         This paper is a progress report on an international project (Israel & U.S.A.) that aims to increase the genetic diversity of the tilapia gene pool as a preliminary for divergent selection for environment-specific traits.  The composite tilpia population (artificial centre of origin) includes Sarotherodon galilaeus, Oreochromis aureus, O. mossambicus and several strains of O. niloticus.
         The idea is to base selective improvement on the identification of quantitative trait loci (QTLs), and to this end a linkage map for a total of 229 genetic markers has been constructed.  It was not possible to assign linkage groups to physical chromosomes but the authors report that genetic mapping of centromeres will be completed soon (Tom Kocher lab) and linkage groups will then be associated with specific chromosomes.  Progress has been made in uniting the information gathered in this project with other, published, linkage information for tilapia but the union is by no means complete.  This is due in part to chromosome-arm differences among tilapia species.  The breeding work has been done in Israel at the Department of Aquaculture, Agricultural Research Organization.
         Challenge tests for cold and salinity tests are underway and are expected to identify QTL that might then be used for marker assisted selection.  The potential environmental impact of extended-range tilapias will have to be assessed very carefully at some point, but actual strain improvements based on QTLs are not likely to appear terribly soon (I think). In the meantime linkage maps, or locus assignment to linkage groups, will be extremely useful for many purposes including statistical analyses of inbreeding and admixture at the population level.   jjagresti@ucdavis.edu .

68. Biogeography of virulence in white spot syndrome virus
Per os challenge of Litopenaeus vannamei postlarvae and Farfantepenaeus duorarum juveniles with six geographic isolates of white spot syndrome virus. 1999. Wang, Q., White, B.L., Redman, R.M. and D. V. Lightner. Aquaculture 170:179-194
         "The virulence of six geographic isolates of WSSV was compared using Litopenaeus vannamei postlarvae and Farfantepenaeus duorarum juveniles.  The six geographic isolates of WSSV originated from China, India, Thailand, Texas, South Carolina, as well as from crayfish maintained at the USA National Zoo."  The pathogen was delivered to the test animals in their feed.  All the L. vannamei died under the test but the Texas pathogen isolate killed them faster than the others.  "The findings suggest that slight differences in virulence exist among geographic isolates of WSSV... ." This paper shows that functional differences follow the genetic pattern of variation in WSSV which has also been reported by this laboratory (May list #54).  See also March list #31.   qwang@aruba.u.arizona.edu .

67. Attempting to purge the depressive effects of inbreeding is risky
Inbreeding depression and genetic load in laboratory metapopulations of the butterfly Bicyclus anyana. 2000. van Oosterhout, C., W.G. Zijlstra, M.K. van Heuven, and P.M. Brakefield. Evolution 54:218-225.
         Each of the six experimental metapopulations consisted of four very small subpopulations, N=6 or N=12, which would not be unreasonably small for some endangered Atlantic salmon populations. There were two levels of migration among populations.  Pedigrees were recorded for 7 generations, by which time inbreeding depression had become so severe that further survival was in doubt.  There was large variation in individual inbreeding coefficients at generation 7.  The authors conclude that "the genetic load remained higher than that of many outbreeding species: approximately two lethal equivalents were detected for egg sterility, one for zygote survival, one for juvenile survival, and one for longevity. ... This finding suggests that the purging of genetic load by intentional inbreeding cannot be recommended for the genetic conservation of species with a high number of lethal equivalents".    c.van-oosterhout@biosci.hull.ac.uk .

66. Population viability analysis works!
Predictive accuracy of population viability analysis in conservation biology. 2000. Brook, B.W., J.J. O'Grady, A.P. Chapman, M.A. Burgman, H. R. Akçakaya, and R. Frankham. Nature 404:385-387.
         The authors have completed what they say is the first real-world study of the ability of population viability analysis (PVA) to predict the future of an endangered species.  They used a type of cross-validation approach on published data from 21 long-term ecological studies.  The first half of the data from each study was used to construct the PVA prediction and the second half was used to see whether the universe proceeded to unfold as it should. To the authors surprise, it did!  "The risk of population decline closely matched observed outcomes, there was no significant bias, and population size projections did not differ significantly from reality.  Furthermore, the predictions of the five PVA software packages were highly concordant.  We conclude that PVA is a valid and sufficiently accurate tool for categorizing and managing endangered species."    barry.brook@ntu.edu.au .

65. Unsuccessful selection for tolerance to cold and heat in a fish
Direct and correlated responses to artificial selection on acute thermal stress tolerance in a livebearing fish. 2000. Baer, C.F., and J. Travis. Evolution 54:238-244.
         The fish was the poeciliid Heterandria formosa and the authors, to their surprise, did NOT observe a response to selection for cold or heat tolerance.  The two source populations studied came from different thermal backgrounds, one warm and one cold.  The experimenters encountered numerous technical difficulties including the dying out of a substantial number of selection lines from one of the populations and uncontrollable environmental variation in the experimental grow-out environments of the lines.  However, these problems were just what one would expect to encounter in an aquaculture-oriented selection programme with the same objectives.
         The authors concluded that heritability of tolerance is low and included a statistical power analysis of the maximum heritability consistent with their results.  The low estimate agrees with the observed lack of selection response.  Since there was no selection response at all there was no "trade-off" -- i.e. a loss of cold tolerance as the lines evolved to be more heat tolerant, or vice versa.
         The authors do not believe that the two populations are genetically identical in their thermal tolerance, but they found that straightforward selection did not magnify or otherwise change any pre-existing genetic differences.  Geneticists planning to extend the thermal habitat range of aquacultural species by selection involving acute stress response might be somewhat unnerved by this result.   cbaer@darkwing.uoregon.edu .

64. Which loci tell the best story?
Concordance of genetic divergence among sockeye salmon populations at allozyme, nuclear DNA and mitochondrial DNA markers. 2000. Allendorf, F.W., and L.W. Seeb. Evolution 54:640-651.
         The authors studied a rather large number of allozyme and nuclear DNA polymorphisms (21 and 15, respectively) plus mtDNA variation in four Alaskan populations of Oncorhynchus nerka.  This is as big or bigger than most samples of the genome used for biogeographic studies on fish up to this point.  They "found concordance among markers in the amount of genetic variation within and among populations, with the striking exception of one allozyme locus (sAH), which exhibited more than three times the amount of among-population differentiation as other loci".  From this they conclude that information should be gathered on many loci for this type of work, but that the type of locus is of secondary importance.  darwin@selway.umt.edu [Allendorf]

63. Can population managers manage emergent properties?
Does population stability evolve? 1999. Mueller, L.D., A. Joshi, and D.J. Borash. Ecology 81:1273-1285.
         This experimental study on the evolution of Drosophila may have long-term implications for population management, or rather, considering the implied time scales, population stewardship.  The authors asked whether the evolutionary response to natural selection on individual fitness also increases the stability (= population fitness = long-term survival) at the level of the population.  In this limited experimental case the answer was no.
         Replicated populations of fruit flies were grown for many generations in two types of selective environment; one with low larval food which causes population cycling or chaotic fluctuations, the other with abundant larval food in which populations are stable.  "While we could document phenotypic evolution in these [low larval food] populations for several characters due to density-dependent natural selection, there was no detectable change in the population stability characteristics. ... This result is consistent with either no evolution of population stability, or very slow change.  Thus, while evolution in these populations affects important [density-dependent] life-history characteristics, these changes appear to have no detectable effects on population stability."   ldmuelle@uci.edu .

62. Triploid salmon to reduce environmental impact
         An evaluation of the use of triploid Atlantic salmon (Salmo salar L.) in minimising the impact of escaped farmed salmon on wild populations. 2000. Cotter, D., V. O'Donovan, N. O'Maoiléidigh, G. Rogan, N. Roche, and N.P. Wilkins. Aquaculture 186:61-75.
         Farmed salmon that escape their hatcheries or cages may interfere with native populations either genetically or ecologically, or both.  Since triploid salmon don't breed the farming of triploids could solve the genetic problem.  If triploids don't even migrate to the spawning areas some of the ecological problems could be averted as well.
         The authors produced and released diploid and triploid salmon in a controlled experiment and found that "The return of triploid salmon from each of the release groups, both to the coast and to fresh water, was significantly reduced compared to diploid salmon. ... The reduced return of triploid salmon to the coast and to fresh water, together with their inability to produce viable offspring, demonstrates the potential for triploidy as a means of eliminating genetic interactions between cultured and wild populations, and of reducing the ecological impact of escaped farmed fish."   smoltunit@sra.iol.ie [Cotter].

61. Successful genetic management of a salmon supplementation programme
The impact of supplementation in winter-run chinook salmon on effective population size. 2000. Hedrick, P.W., D. Hedgecock, S. Hamelberg, and S.J. Croci. Journal of Heredity 91:112-116.
         A state hatchery has been breeding and releasing winter-run Chinook salmon into the Sacramento river in California for almost 10 years.  This type of programme is usually expected to have negative genetic side effects, especially loss of genetic variation.  However, in this hatchery the breeding protocol was designed to maximise the effective population size by equalizing the contribution made by all the spawners.  The authors have recently checked on this and found that "the releases in 1994 and 1995 appear not to have decreased the overall effective population size and may have increased it somewhat."  This should count as a genetic success for a salmon supplementation programme.   philip.hedrick@asu.edu .

60. Inbreeding and strain-crossing hit reproductive traits especially hard
Inbreeding and outbreeding depression in male courtship song characters in Drosophila montana. 2000. Aspi, J. Heredity 84:273-282.
         In Drosophila montana, the frequency of the male courtship song is closely related to the male's success in attracting mates and also to the survival of his offspring.  Inbred flies showed strong inbreeding depression of song frequency, as expected for an important component of fitness (see also May list #48).  What is equally important if we think of this as a possible model for aquaculture or genetic conservation, is that there was also noticeable outbreeding depression when strains from different geographical locations were hybridized.  The outbreeding depression was evident in the F2 as well as the F1 hybrid generations.
         Given the extreme importance of mating and reproductive performance to successful aquaculture (particularly shrimp) and to propagation of endangered populations, we should note the significance of this inbreeding and outbreeding depression even though it was observed in fruit flies. jouni.aspi@oulu.fi .