Progress 03/01/00 to 09/30/04
Outputs
The goals of this project were to measure: (1) the average genomic number of early-acting recessive lethals per wild-caught individual, and (2) the rate that such harmful mutations arise, both in the vertebrate model organism, the zebrafish. The first of these measurements was made by a genetic experiment: wild-caught fish were crossed and for each of the resulting F1 families, we did 5-10 sib-crosses to generate F2 offspring, then scored for early-acting recessive lethal mutations. From our F1 sib crosses, we scored ~5700 F2 offspring (twice daily for up to 21 days) derived from 86 successful crosses across 13 F1 families. According to these data, the average genomic number of recessive lethal mutations is 1.4 (95 percent confidence limits 1.0-2.0). These results, and very similar results from an experiment done on killifish in another lab, are unexpectedly low and the same as for Drosophila, despite the 2-3 fold difference in genome sizes. Given the much lower than
expected N, it was not logistically feasible to measure the rate of spontaneous lethal mutation as intended. Instead, we used the F1 families from wild-caught fish to examine the effects of inbreeding and food on growth and mortality. For this experiment, we produced and measured the growth/mortality of 20 clutches (10 inbred and 10 outbred). Mortality was 33 percent greater for inbred fish, implying at least 3.6 lethal equivalents of deleterious recessive alleles per zygote. There was no significant inbreeding depression in the growth, perhaps because the surviving inbred fish lived under less crowded conditions. In contrast to alleles causing embryonic and early larval mortality in the same population, alleles responsible for late larval and early juvenile mortality did not result in any gross morphological abnormalities. An unexpected result of the first experiment was the high frequency of mutations involving loss or non-inflation of the gas bladder. By doing the requisite
complementation tests and morphological studies, we were able to show that there were 18-22 genetically distinct bladderless mutations. The high frequency of the bladderless phenotype is of particular interest given the high frequency of gas bladder loss among teleost fishes.
Impacts
This study has provided the first careful measurement of the average genomic number of early-acting recessive lethals carried in a wild population of vertebrates. This is an important parameter value for modeling in population biology, conservation, and assessing health risks of mutation in vertebrates, including humans. Among animals, such data had previously only been available for fruit flies and for a sample of 8 salamanders. Our subsequent work shows that deleterious recessive alleles which segregate in a wild zebrafish population appear to belong to two sharply distinct classes: early-acting, morphologically overt, unconditional lethals and later-acting, morphologically cryptic, and presumably milder alleles. While this result is thought to be the case for flies, it has not been shown before for vertebrates. Over the last twenty years, adaptation and developmental biases in the production of phenotypes have often been considered as alternatives. Our study of
bladderless mutations in zebrafish provides empirical support for synthesis of these two viewpoints: convergence (usually considered to be evidence of adaptation) may originate from complementary processes of adaptation and biased production of phenotypes, acting together.
Publications
- McCune, A. R. and Carlson, R. 2004. Twenty ways to lose your bladder: Common natural mutants in zebrafish and widespread convergence of swim bladder loss among teleost fishes. Evolution and Development 6 (4):246-259.
- McCune, A. R., Houle, D., McMillan, K., Annable, R., and Kondrashov, A. 2004. Two classes of deleterious recessive alleles in a natural population of zebrafish. Proceedings of the Royal Society of London 271:2025-2033.
- McCune, A. R. 2004. Diversity and speciation of semionotid fishes in Mesozoic rift lakes. Pp.362-379. In: U. Dieckman, M. Doebli, and J.A. J Metz, editors. Adaptive Speciation. Cambridge University Press.
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Progress 01/01/03 to 12/31/03
Outputs
The goals of this project are to measure: (1) the average genomic number of early-acting recessive lethals per wild-caught individual, and (2) the rate that such harmful mutations arise, both in the vertebrate model organism, the zebrafish. The first of these measurements has been made by the following genetic experiment: wild-caught fish were crossed and for each of the resulting F1 families, we did 5-10 sib-crosses to generate F2 offspring, which were then scored for early-acting recessive lethal mutations. We first made F1 families. Then we began F1 sib crosses and scored about 5700 F2 offspring (twice daily for periods of up to 21 days) derived from 86 successful crosses across 13 F1 families. According to these data, the average genomic number of recessive lethal mutations is 1.4 (95 percent confidence limits 1.0-2.0). These results, and very similar results from an experiment done on killifish in another lab, are unexpectedly low and the same as for Drosophila,
despite the 2-3 fold difference in genome sizes. Given the much lower than expected N, it was not logistically feasible to measure the rate of spontaneous lethal mutation as originally intended. Instead, we then used the already-made F1 families from wild-caught fish to examine whether there are differential effects of inbreeding and food on growth and mortality. For this experiment, we produced and measured the growth/mortality of 20 clutches (10 inbred and 10 outbred). Mortality was 33 percent greater for inbred fish, implying at least 3.6 lethal equivalents of deleterious recessive alleles per zygote. There was no significant inbreeding depression in the growth, perhaps because the surviving inbred fish lived under less crowded conditions. In contrast to alleles which cause embryonic and early larval mortality in the same population, alleles responsible for late larval and early juvenile mortality did not result in any gross morphological abnormalities.
Impacts
This study has provided the first careful measurement of the average genomic number of early-acting recessive lethals carried in a wild population of vertebrates. This is an important parameter value for modeling in population biology, conservation, and assessing health risks of mutation in vertebrates, including humans. Among animals, such data had previously only been available for fruit flies and for a sample of 8 salamanders. Our subsequent work shows that deleterious recessive alleles which segregate in a wild zebrafish population appear to belong to two sharply distinct classes: early-acting, morphologically overt, unconditional lethals and later-acting, morphologically cryptic, and presumably milder alleles. While this result is thought to be the case for flies, it has not been shown before for vertebrates.
Publications
- McCune, A. R. and McClure, M. M. 2003. Evidence for developmental linkage of pigment patterns with body size and shape in danios (Teleostei: Cyprinidae). Evolution 57(8):1863-1875.
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Progress 01/01/02 to 12/31/02
Outputs
The goals of this project are to measure: (1) the average genomic number of early-acting recessive lethals per wild-caught individual, and (2) the rate that such harmful mutations arise, both in the vertebrate model organism, the zebrafish. The first of these measurements has been made by the following genetic experiment: wild-caught fish were crossed and for each of the resulting F1 families, we did 5-10 sib-crosses to generate F2 offspring, which were then scored for early-acting recessive lethal mutations. In the first year of the project, we set up a new rearing facility, hired personnel, and began making F1 families. In this second year of the project we began F1 crosses and scored about 5700 F2 offspring (twice daily for periods of up to 21 days) derived from 86 successful crosses across 13 F1 families. According to these data, the average genomic number of recessive lethal mutations is 1.4 (95 percent confidence limits 1.0-2.0). These results, and very similar
results from an experiment done on killifish in another lab, are unexpectedly low and the same as for Drosophila, despite the 2-3 fold difference in genome sizes. Given the much lower than expected N, it is not logistically feasible to measure the rate of spontaneous lethal mutation as originally intended. Instead, in this third year of the project, we have been using the already-made F1 families from wild-caught fish to do an experiment to examine whether there are differential effects on growth of lowered feeding regime on inbred versus outbred fish. For this experiment, we have now produced and measured the growth of 14 clutches (7 inbred and 7 outbred).
Impacts
This study has provided the first careful measurement of the average genomic number of early-acting recessive lethals carried in a wild population of vertebrates. This is an important parameter value for modeling in population biology, conservation, and assessing health risks of mutation in vertebrates, including humans. Among animals, such data had previously only been available for fruit flies and for a sample of 8 salamanders.
Publications
- McCune, A. R., R. C. Fuller, A. A. Aquilina, R. M. Dawley, J. M. Fadool, D. Houle, J. Travis, and A. S. Kondrashov. 2002. A low genomic number of recessive lethals in natural populations of bluefin killifish and zebrafish. Science 296:2398-2401.
- Sanger, T. J. and A. R. McCune. 2002. Comparative osteology of the Danio (Cyprinidae: Ostariophysi) axial skeleton with comments on Danio relationships based on molecules and morphology. Zoological Journal of the Linnean Society 135:529-546.
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Progress 01/01/01 to 12/31/01
Outputs
The goals of this project are to measure: (1) the average genomic number of early-acting recessive lethals per wild-caught individual, N, and (2) the rate that such harmful mutations arise. These measurements are to be made using a vertebrate model organism, the zebrafish. The average genomic number of lethal mutations per fish is being measured by the following genetic experiment: wild-caught fish are being crossed and for each of the resulting F1 families, we are doing a set of sib-crosses to generate F2 offspring which will be scored for early-acting recessive lethal mutations. The rate at which lethal mutations arise was to be measured by making individuals in which both copies of the genome are identical (and thus carry no recessive lethals) and then measuring the number of lethals that arise in the next generation. In the first year of the project, we set up a new rearing facility, hired personnel, and began making F1 families. In this second year of the project
we began F1 crosses and scored about 5700 F2 offspring (twice daily for periods of up to 21 days) derived from 86 successful crosses across 13 F1 families. According to data thus far, the average genomic number of recessive lethal mutations (N) in these wild-caught zebrafish is much lower than expected. Given the lower than expected N, it may not be logistically feasible to measure the rate of spontaneous lethal mutation.
Impacts
This study will provide the first measurement of the average genomic number of early-acting recessive lethals carried in a wild population of vertebrates. This is an important parameter value for modeling in population biology, conservation, and assessing health risks of mutation in vertebrates, including humans. Among animals, such data are available only for fruit flies.
Publications
- No publications reported this period
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Progress 03/01/00 to 12/31/00
Outputs
The goals of this project are to measure: (1) the number of early-acting recessive lethals in the genome of wild-caught individuals and (2) the rate that such harmful mutations arise. Both measurements will be made using a vertebrate model organism, the zebrafish. The number of lethal mutations carried in the genome is being measured by the following genetic experiment: wild-caught fish are being crossed and for each of the resulting F1 families, we are doing a set of sib-crosses to generate F2 offspring which will be scored for early-acting lethals. The rate at which lethal mutations arise will be measured by making individuals in which both copies of the genome are identical (and thus carry no recessive lethals) and then measuring the number of lethals that arise in the next generation. In this partial first year of the project, we have set up a new rearing facility, hired personnel, and begun making F1 families. We are about to begin sib-crosses to generate F2s for
scoring lethals.
Impacts
This study will provide the first measurement of (1) the number of early-acting lethals carried in a wild population of vertebrates and (2) genomic rate at which new harmful mutations arise in any vertebrate. These are important measured quantities for modeling in population biology, conservation, and assessing health risks of mutation in vertebrates, including humans. Among animals, data on the genomic rate of the new appearance of harmful mutations is available only for fruit flies.
Publications
- No publications reported this period
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