DOI: 10.5061/dryad.6rg87
title: Data from: Post-zygotic selection against parental genotypes during larval development maintains all-hybrid populations of the frog Pelophylax esculentus

description: Background: Hybridization between two species usually leads to inviable or
 infertile offspring, due to endogenous or exogenous selection pressures.
 Yet, hybrid taxa are found in several plant and animal genera, and some of
 these hybrid taxa are ecologically and evolutionarily very successful. One
 example of such a successful hybrid is the water frog, Pelophylax
 esculentus which originated from matings between the two species P.
 ridibundus (genotype RR) and P. lessonae (LL). At the northern border of
 the distribution all-hybrid populations consisting of diploid (LR) and one
 or two triploid (LLR, LRR) frog types have been established. Here, the
 hybrid has achieved reproductive independence from its sexual ancestors
 and forms a self-sustaining evolutionary unit. Based on the gamete
 production of these hybrids, certain mating combinations should lead to LL
 and RR offspring, but these parental forms are absent among the adults.
 Results: In order to investigate the mechanisms that maintain such an
 all-hybrid system, we performed a field study and a crossing experiment.
 In the field we sampled several ponds for water frog larvae at different
 developmental stages. Genotype compositions were then analysed and
 life-history differences between the genotypes examined. In the experiment
 we crossed diploid and triploid males and females from different ponds and
 determined fertilization success as well as development speed and survival
 rates of the offspring under high, medium and low food availability. In
 both parts of the study, we found numerous LL and RR offspring during the
 egg and early larval stages; but the frequency of these parental genotypes
 decreased drastically during later stages. In natural ponds almost all of
 them had disappeared already before metamorphosis; under the more benign
 experimental conditions the last ones died as juveniles during the
 following year. Conclusions: From the combined results we conclude that
 the absence of parental genotypes in all-hybrid populations is due to
 post-zygotic selection against them, rather than to pre-zygotic mechanisms
 that might prevent their formation in the first place. For this
 post-zygotic selection, genetic mechanisms resulting from low genetic
 diversity and fixation of deleterious mutations seem to be a more likely
 explanation than ecological factors.
description: Reyer_et_al_Fig-3This file provides the data base for Table 1 and Fig. 3, namely the absolute numbers and proportions of 7 genotypes (LL, LLR, LLRR, LR, LRR, RR and uncertain) sampled in natural ponds at 5 developmental stages (eggs, tadpoles, metamorphs, juveniles and adults).Reyer_et_al_Fig-4This file presents the numbers of gamete types produced by the crossed LR, LLR and LRR males and females. Data base for Table 2 and Fig. 4.Reyer_er_al_Fig-5Fertilization success and hatching rates of offspring from different crossing types. Data base for Table 3 and Fig. 5.Reyer_et_al_Fig-6+7aThis file provides the data basis for Table 4a and Figs. 6 and 7a, which analyze and depict tadpole development under different food treatments from the start of the raising Experiment (SURVA0) to shortly before metamorphosis (SURVA10).Reyer_et_al_Fig-7bNumber of surviving froglets from shortly after metamorphosis (Aug 04) to the next summer (July 05). The category "Hyb" includes all hybrid types (LR, LLR, LRR) and the category "Par" the two parental species (LL, RR). Data base for Table 4b and Fig. 7b.