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Coexistence of diploid and triploid hybrid water frogs: population differences persist in the apparent absence of differential survival.

Christiansen DG, Jakob C, Arioli M, Roethlisberger S, Reyer HU - BMC Ecol. (2010)

Bottom Line: As the relative survival and proportion of LLR, LR and LRR did not correlate within ponds, this study provided no evidence for the selection hypothesis in adults.The result was a weak preference for the gamete pattern hypothesis.Moreover, the study provided valuable data on genotype-specific body lengths, adult survival and sex ratios.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, Zurich, Switzerland. ditte.christiansen@ieu.uzh.ch

ABSTRACT

Unlabelled: The role of differential selection in determining the geographic distribution of genotypes in hybrid systems has long been discussed, but not settled. The present study aims to asses the importance of selection in structuring all-hybrid Pelophylax esculentus populations. These populations, in which the parental species (P. lessonae with genotype LL and P. ridibundus with genotype RR) are absent, have pond-specific proportions of diploid (LR) and triploid (LLR and LRR) genotypes.

Results: With data from 12 Swedish ponds, we first show that in spite of significant changes in genotype proportions over time, the most extreme ponds retained their differences over a six year study period. The uneven distribution of genotypes among ponds could be a consequence of differential selection varying among ponds (selection hypothesis), or, alternatively, of different gamete production patterns among ponds (gamete pattern hypothesis). The selection hypothesis was tested in adults by a six year mark-recapture study in all 12 ponds. As the relative survival and proportion of LLR, LR and LRR did not correlate within ponds, this study provided no evidence for the selection hypothesis in adults. Then, both hypotheses were tested simultaneously in juvenile stages (eggs, tadpoles, metamorphs and one year old froglets) in three of the ponds. A gradual approach to adult genotype proportions through successive stages would support the selection hypotheses, whereas the presence of adult genotype proportions already at the egg stage would support the gamete pattern hypothesis. The result was a weak preference for the gamete pattern hypothesis.

Conclusions: These results thus suggest that selection is of little importance for shaping genotype distributions of all-hybrid populations of P. esculentus, but further studies are needed for confirmation. Moreover, the study provided valuable data on genotype-specific body lengths, adult survival and sex ratios.

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Related in: MedlinePlus

Genotype distributions at four stages of the 2006 cohort in three ponds. a) pond 001 (LLR-rich), b) pond 011 (LR-rich) and c) pond 089 (LRR-rich). The four stages are eggs, tadpoles, metamorphs and one year-olds. Regression lines for LLR, LR and LRR are added for comparison of slopes and intercepts. The line is drawn solid for the genotype that is dominant among adults in the particular pond; the lines for the remaining genotypes are dashed.
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Figure 6: Genotype distributions at four stages of the 2006 cohort in three ponds. a) pond 001 (LLR-rich), b) pond 011 (LR-rich) and c) pond 089 (LRR-rich). The four stages are eggs, tadpoles, metamorphs and one year-olds. Regression lines for LLR, LR and LRR are added for comparison of slopes and intercepts. The line is drawn solid for the genotype that is dominant among adults in the particular pond; the lines for the remaining genotypes are dashed.

Mentions: The genotype distribution of the offspring sampled is shown in Figure 6. A GLM was fitted for each genotype, LLR, LR and LRR (residual deviance = 81, 73 and 20 for LLR, LR and LRR respectively, with 27 df). Two of the three GLMs were significant for pond (LLR: t27 = 8.51, P = 0.003*; LR: t27 = 3.65, P = 0.047; LRR: t27 = 10.03, P = 0.001*; Bonferroni-corrected α2 = 0.025), but there was neither significance for stage nor for the interaction between pond and stage (data not shown).


Coexistence of diploid and triploid hybrid water frogs: population differences persist in the apparent absence of differential survival.

Christiansen DG, Jakob C, Arioli M, Roethlisberger S, Reyer HU - BMC Ecol. (2010)

Genotype distributions at four stages of the 2006 cohort in three ponds. a) pond 001 (LLR-rich), b) pond 011 (LR-rich) and c) pond 089 (LRR-rich). The four stages are eggs, tadpoles, metamorphs and one year-olds. Regression lines for LLR, LR and LRR are added for comparison of slopes and intercepts. The line is drawn solid for the genotype that is dominant among adults in the particular pond; the lines for the remaining genotypes are dashed.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2902419&req=5

Figure 6: Genotype distributions at four stages of the 2006 cohort in three ponds. a) pond 001 (LLR-rich), b) pond 011 (LR-rich) and c) pond 089 (LRR-rich). The four stages are eggs, tadpoles, metamorphs and one year-olds. Regression lines for LLR, LR and LRR are added for comparison of slopes and intercepts. The line is drawn solid for the genotype that is dominant among adults in the particular pond; the lines for the remaining genotypes are dashed.
Mentions: The genotype distribution of the offspring sampled is shown in Figure 6. A GLM was fitted for each genotype, LLR, LR and LRR (residual deviance = 81, 73 and 20 for LLR, LR and LRR respectively, with 27 df). Two of the three GLMs were significant for pond (LLR: t27 = 8.51, P = 0.003*; LR: t27 = 3.65, P = 0.047; LRR: t27 = 10.03, P = 0.001*; Bonferroni-corrected α2 = 0.025), but there was neither significance for stage nor for the interaction between pond and stage (data not shown).

Bottom Line: As the relative survival and proportion of LLR, LR and LRR did not correlate within ponds, this study provided no evidence for the selection hypothesis in adults.The result was a weak preference for the gamete pattern hypothesis.Moreover, the study provided valuable data on genotype-specific body lengths, adult survival and sex ratios.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, Zurich, Switzerland. ditte.christiansen@ieu.uzh.ch

ABSTRACT

Unlabelled: The role of differential selection in determining the geographic distribution of genotypes in hybrid systems has long been discussed, but not settled. The present study aims to asses the importance of selection in structuring all-hybrid Pelophylax esculentus populations. These populations, in which the parental species (P. lessonae with genotype LL and P. ridibundus with genotype RR) are absent, have pond-specific proportions of diploid (LR) and triploid (LLR and LRR) genotypes.

Results: With data from 12 Swedish ponds, we first show that in spite of significant changes in genotype proportions over time, the most extreme ponds retained their differences over a six year study period. The uneven distribution of genotypes among ponds could be a consequence of differential selection varying among ponds (selection hypothesis), or, alternatively, of different gamete production patterns among ponds (gamete pattern hypothesis). The selection hypothesis was tested in adults by a six year mark-recapture study in all 12 ponds. As the relative survival and proportion of LLR, LR and LRR did not correlate within ponds, this study provided no evidence for the selection hypothesis in adults. Then, both hypotheses were tested simultaneously in juvenile stages (eggs, tadpoles, metamorphs and one year old froglets) in three of the ponds. A gradual approach to adult genotype proportions through successive stages would support the selection hypotheses, whereas the presence of adult genotype proportions already at the egg stage would support the gamete pattern hypothesis. The result was a weak preference for the gamete pattern hypothesis.

Conclusions: These results thus suggest that selection is of little importance for shaping genotype distributions of all-hybrid populations of P. esculentus, but further studies are needed for confirmation. Moreover, the study provided valuable data on genotype-specific body lengths, adult survival and sex ratios.

Show MeSH
Related in: MedlinePlus