Limits...
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.

Show MeSH
Ternary plots of genotype compositions. a) Proportions of LLR, LR and LRR among males and females of P. esculentus in 12 Swedish ponds (numbers 001-138) over six years (2002-2007). Each point represents the sum of two catching rounds per year; labels indicate the year (02-07). b) 95% confidence intervals around three fictive samples of 30 individuals with different genotype compositions.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2902419&req=5

Figure 3: Ternary plots of genotype compositions. a) Proportions of LLR, LR and LRR among males and females of P. esculentus in 12 Swedish ponds (numbers 001-138) over six years (2002-2007). Each point represents the sum of two catching rounds per year; labels indicate the year (02-07). b) 95% confidence intervals around three fictive samples of 30 individuals with different genotype compositions.

Mentions: The genotype proportions obtained in the 12 Swedish ponds over the six years are illustrated in Figure 3a. The two annual catching rounds were pooled to increase the sample sizes, which thus became mean 28.3 (range 6-64) for males and mean 41.8 (range 9-97) for females. As expected (see Background), LRR were rare among males, which is the main reason for the clear difference between male and female genotype proportions. By providing examples of 95% confidence intervals for similar sample sizes, Figure 3b suggests that most of the year-to-year variation observed within ponds and sex is due to sampling stochasticity. From inspection of Figure 3a it is evident that ponds 001, 011 and 089 were the most different ponds with non-overlapping genotype distributions for both sexes.


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)

Ternary plots of genotype compositions. a) Proportions of LLR, LR and LRR among males and females of P. esculentus in 12 Swedish ponds (numbers 001-138) over six years (2002-2007). Each point represents the sum of two catching rounds per year; labels indicate the year (02-07). b) 95% confidence intervals around three fictive samples of 30 individuals with different genotype compositions.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: Ternary plots of genotype compositions. a) Proportions of LLR, LR and LRR among males and females of P. esculentus in 12 Swedish ponds (numbers 001-138) over six years (2002-2007). Each point represents the sum of two catching rounds per year; labels indicate the year (02-07). b) 95% confidence intervals around three fictive samples of 30 individuals with different genotype compositions.
Mentions: The genotype proportions obtained in the 12 Swedish ponds over the six years are illustrated in Figure 3a. The two annual catching rounds were pooled to increase the sample sizes, which thus became mean 28.3 (range 6-64) for males and mean 41.8 (range 9-97) for females. As expected (see Background), LRR were rare among males, which is the main reason for the clear difference between male and female genotype proportions. By providing examples of 95% confidence intervals for similar sample sizes, Figure 3b suggests that most of the year-to-year variation observed within ponds and sex is due to sampling stochasticity. From inspection of Figure 3a it is evident that ponds 001, 011 and 089 were the most different ponds with non-overlapping genotype distributions for both sexes.

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