Abstract
Despite much theoretical work, the molecular-genetic causes and evolutionary consequences of asexuality remain largely undetermined. Asexual animal species are rare, evolutionarily short-lived, and thought to suffer mutational meltdown as a result of lack of recombination. Whole-genome analysis of 11 sexual and 11 asexual genotypes of Daphnia pulex indicates that current asexual lineages are in fact very young, exhibit no signs of purifying selection against accumulating mutations, and have extremely high rates of gene conversion and deletion. The reconstruction of chromosomal haplotypes in regions containing SNP markers associated with asexuality (chromosomes VIII and IX) indicates that introgression from a sister species, Daphnia pulicaria, underlies the origin of the asexual phenotype. Silent-site divergence of the shared chromosomal haplotypes of asexuals indicates that the spread of asexuality is as recent as 1,250 y, although the origin of the meiosissuppressing element or elements could be substantially older. In addition, using previous estimates of the gene conversion rate from Daphnia mutation accumulation lines, we are able to age each asexual lineage. Although asexual lineages originate from wide crosses that introduce elevated individual heterozygosities on clone foundation, they also appear to be constrained by the inbreeding-like effect of loss of heterozygosity that accrues as gene conversion and hemizygous deletion expose preexisting recessive deleterious alleles of asexuals, limiting their evolutionary longevity. Our study implies that the buildup of newly introduced deleterious mutations (i.e., Muller's ratchet) may not be the dominant force imperiling nonrecombining populations of D. pulex, as previously proposed.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 15740-15745 |
| Number of pages | 6 |
| Journal | Proceedings of the National Academy of Sciences of the United States of America |
| Volume | 110 |
| Issue number | 39 |
| DOIs | |
| State | Published - Sep 24 2013 |
| Externally published | Yes |
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Keywords
- Evolution of sex
- Parthenogenesis
ASJC Scopus subject areas
- General
Cite this
Population-genomic insights into the evolutionary origin and fate of obligately asexual Daphnia pulex. / Tucker, Abraham E.; Ackerman, Matthew S.; Eads, Brian D.; Xu, Sen; Lynch, Michael.
In: Proceedings of the National Academy of Sciences of the United States of America, Vol. 110, No. 39, 24.09.2013, p. 15740-15745.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Population-genomic insights into the evolutionary origin and fate of obligately asexual Daphnia pulex
AU - Tucker, Abraham E.
AU - Ackerman, Matthew S.
AU - Eads, Brian D.
AU - Xu, Sen
AU - Lynch, Michael
PY - 2013/9/24
Y1 - 2013/9/24
N2 - Despite much theoretical work, the molecular-genetic causes and evolutionary consequences of asexuality remain largely undetermined. Asexual animal species are rare, evolutionarily short-lived, and thought to suffer mutational meltdown as a result of lack of recombination. Whole-genome analysis of 11 sexual and 11 asexual genotypes of Daphnia pulex indicates that current asexual lineages are in fact very young, exhibit no signs of purifying selection against accumulating mutations, and have extremely high rates of gene conversion and deletion. The reconstruction of chromosomal haplotypes in regions containing SNP markers associated with asexuality (chromosomes VIII and IX) indicates that introgression from a sister species, Daphnia pulicaria, underlies the origin of the asexual phenotype. Silent-site divergence of the shared chromosomal haplotypes of asexuals indicates that the spread of asexuality is as recent as 1,250 y, although the origin of the meiosissuppressing element or elements could be substantially older. In addition, using previous estimates of the gene conversion rate from Daphnia mutation accumulation lines, we are able to age each asexual lineage. Although asexual lineages originate from wide crosses that introduce elevated individual heterozygosities on clone foundation, they also appear to be constrained by the inbreeding-like effect of loss of heterozygosity that accrues as gene conversion and hemizygous deletion expose preexisting recessive deleterious alleles of asexuals, limiting their evolutionary longevity. Our study implies that the buildup of newly introduced deleterious mutations (i.e., Muller's ratchet) may not be the dominant force imperiling nonrecombining populations of D. pulex, as previously proposed.
AB - Despite much theoretical work, the molecular-genetic causes and evolutionary consequences of asexuality remain largely undetermined. Asexual animal species are rare, evolutionarily short-lived, and thought to suffer mutational meltdown as a result of lack of recombination. Whole-genome analysis of 11 sexual and 11 asexual genotypes of Daphnia pulex indicates that current asexual lineages are in fact very young, exhibit no signs of purifying selection against accumulating mutations, and have extremely high rates of gene conversion and deletion. The reconstruction of chromosomal haplotypes in regions containing SNP markers associated with asexuality (chromosomes VIII and IX) indicates that introgression from a sister species, Daphnia pulicaria, underlies the origin of the asexual phenotype. Silent-site divergence of the shared chromosomal haplotypes of asexuals indicates that the spread of asexuality is as recent as 1,250 y, although the origin of the meiosissuppressing element or elements could be substantially older. In addition, using previous estimates of the gene conversion rate from Daphnia mutation accumulation lines, we are able to age each asexual lineage. Although asexual lineages originate from wide crosses that introduce elevated individual heterozygosities on clone foundation, they also appear to be constrained by the inbreeding-like effect of loss of heterozygosity that accrues as gene conversion and hemizygous deletion expose preexisting recessive deleterious alleles of asexuals, limiting their evolutionary longevity. Our study implies that the buildup of newly introduced deleterious mutations (i.e., Muller's ratchet) may not be the dominant force imperiling nonrecombining populations of D. pulex, as previously proposed.
KW - Evolution of sex
KW - Parthenogenesis
UR - http://www.scopus.com/inward/record.url?scp=84884638276&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84884638276&partnerID=8YFLogxK
U2 - 10.1073/pnas.1313388110
DO - 10.1073/pnas.1313388110
M3 - Article
C2 - 23959868
AN - SCOPUS:84884638276
VL - 110
SP - 15740
EP - 15745
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
SN - 0027-8424
IS - 39
ER -