Question: What explains the differences in ratios of diploid (LR) and two types of triploid
frogs (LLR, LRR) among all-hybrid frog populations?
Hypothesis: Ecological conditions favouring one (LL) or the other (RR) parental species also
favour those triploids that carry two copies of the respective genome (dosage effect), whereas
diploids dominate under intermediate conditions.
Organism: European water frog (Pelophylax esculentus).
Field site: Thirty-four natural ponds in the province of Skåne, southern Sweden.
Methods: We caught more than 3000 frogs, determined their genotypes with microsatellites,
and related the ploidy composition to several uncorrelated ecological parameters, including
pond morphology, vegetation, and physical and chemical water parameters.
Conclusions: We found a shift from predominantly LLR in small isolated ponds to more LRR
in large wetland ponds. This parallels the preferences of the parental species LL and RR
for small and large bodies of water, respectively. The effects that pond vegetation and
physico-chemical water parameters exert on the parental species were not found in all-hybrid
populations. This suggests that environmental parameters affect the genotype composition of
all-hybrid populations less than populations containing the parental species. Pond-to-pond
differences in LR, LLR, and LRR proportions seem to be better explained by differences in
gamete production and thus inheritance patterns.