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Phenotypic effects of an allele causing obligate parthenogenesis in a rotifer.

Scheuerl T, Riss S, Stelzer CP - J. Hered. (2011)

Bottom Line: In this species, a polymorphism at a single locus, op, can result in transitions to obligate parthenogenesis.Thus, selective sweeps of this allele in natural populations would first require conditions favoring the generation of homozygotes.This may be given by inbreeding in very small populations or by double mutants in very large populations.

View Article: PubMed Central - PubMed

Affiliation: Institute for Limnology, Austrian Academy of Sciences, 5310 Mondsee, Austria.

ABSTRACT
Transitions to obligate asexuality have been documented in almost all metazoan taxa, yet the conditions favoring such transitions remained largely unexplored. We address this problem in the rotifer Brachionus calyciflorus. In this species, a polymorphism at a single locus, op, can result in transitions to obligate parthenogenesis. Homozygotes for the op allele reproduce strictly by asexual reproduction, whereas heterozygous clones (+/op) and wild-type clones (+/+) are cyclical parthenogens that undergo sexual reproduction at high population densities. Here, we examine dosage effects of the op allele by analyzing various life-history characteristics and population traits in 10 clones for each of the 3 possible genotypes (op/op, +/op, and +/+). For most traits, we found that op/op clones differed significantly (P < 0.05) from the 2 cyclical parthenogenetic genotypes (+/+ and +/op). By contrast, the 2 cyclical parthenogenetic genotypes were almost indistinguishable, except that heterozygote individuals were slightly but significantly smaller in body size compared with wild-type individuals. Overall, this indicates that the op allele is selectively neutral in the heterozygous state. Thus, selective sweeps of this allele in natural populations would first require conditions favoring the generation of homozygotes. This may be given by inbreeding in very small populations or by double mutants in very large populations.

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Influence of genotype on egg size (a) and body size (b). Bars represent the mean and standard deviation for each genotype (n = 9–11). For this figure, genotype means were calculated from the means for each clone (n = 8–16). For statistical analysis, see Table 2.
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fig2: Influence of genotype on egg size (a) and body size (b). Bars represent the mean and standard deviation for each genotype (n = 9–11). For this figure, genotype means were calculated from the means for each clone (n = 8–16). For statistical analysis, see Table 2.

Mentions: The second experiment was addressed to determine whether there are differences in body size and egg size among the 3 different genotypes. There were significant differences, such that the op/op genotype was always significantly smaller than the 2 CP genotypes (Figure 2 and Table 2). Closer examination of the 2 CP genotypes showed that there was no significant difference in egg size between +/op and +/+ clones, yet the difference in body size was significant (Table 2). The mean body volumes of op/op clones, +/op clones, and +/+ clones were 0.898, 1.391, and 1.527 × 106 μm3, respectively. Hence, heterozygote clones (+/op) were roughly 9% smaller than wild-type clones (+/+).


Phenotypic effects of an allele causing obligate parthenogenesis in a rotifer.

Scheuerl T, Riss S, Stelzer CP - J. Hered. (2011)

Influence of genotype on egg size (a) and body size (b). Bars represent the mean and standard deviation for each genotype (n = 9–11). For this figure, genotype means were calculated from the means for each clone (n = 8–16). For statistical analysis, see Table 2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3113615&req=5

fig2: Influence of genotype on egg size (a) and body size (b). Bars represent the mean and standard deviation for each genotype (n = 9–11). For this figure, genotype means were calculated from the means for each clone (n = 8–16). For statistical analysis, see Table 2.
Mentions: The second experiment was addressed to determine whether there are differences in body size and egg size among the 3 different genotypes. There were significant differences, such that the op/op genotype was always significantly smaller than the 2 CP genotypes (Figure 2 and Table 2). Closer examination of the 2 CP genotypes showed that there was no significant difference in egg size between +/op and +/+ clones, yet the difference in body size was significant (Table 2). The mean body volumes of op/op clones, +/op clones, and +/+ clones were 0.898, 1.391, and 1.527 × 106 μm3, respectively. Hence, heterozygote clones (+/op) were roughly 9% smaller than wild-type clones (+/+).

Bottom Line: In this species, a polymorphism at a single locus, op, can result in transitions to obligate parthenogenesis.Thus, selective sweeps of this allele in natural populations would first require conditions favoring the generation of homozygotes.This may be given by inbreeding in very small populations or by double mutants in very large populations.

View Article: PubMed Central - PubMed

Affiliation: Institute for Limnology, Austrian Academy of Sciences, 5310 Mondsee, Austria.

ABSTRACT
Transitions to obligate asexuality have been documented in almost all metazoan taxa, yet the conditions favoring such transitions remained largely unexplored. We address this problem in the rotifer Brachionus calyciflorus. In this species, a polymorphism at a single locus, op, can result in transitions to obligate parthenogenesis. Homozygotes for the op allele reproduce strictly by asexual reproduction, whereas heterozygous clones (+/op) and wild-type clones (+/+) are cyclical parthenogens that undergo sexual reproduction at high population densities. Here, we examine dosage effects of the op allele by analyzing various life-history characteristics and population traits in 10 clones for each of the 3 possible genotypes (op/op, +/op, and +/+). For most traits, we found that op/op clones differed significantly (P < 0.05) from the 2 cyclical parthenogenetic genotypes (+/+ and +/op). By contrast, the 2 cyclical parthenogenetic genotypes were almost indistinguishable, except that heterozygote individuals were slightly but significantly smaller in body size compared with wild-type individuals. Overall, this indicates that the op allele is selectively neutral in the heterozygous state. Thus, selective sweeps of this allele in natural populations would first require conditions favoring the generation of homozygotes. This may be given by inbreeding in very small populations or by double mutants in very large populations.

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