Large eggs and ploidy of green frog populations in Central Europe

Abstract

AbstractGreen frogs of Central Europe consist of three taxa: Pelophylax ridibundus, P. lessonae and their natural hybridogenetic hybrid, P. esculentus, which forms as a rule mixed populations with its parental species. We examined 659 095 eggs from P. ridibundus (48 females), P. lessonae (133 females) and P. esculentus (170 females) originating from 39 populations in Austria, Denmark, Germany and Poland. Some females of each taxon laid eggs that fell into discrete size classes (small, medium and large). Large eggs were mostly diploid gametes from which triploids developed. They were found in P. esculentus (25 233 large eggs in 152 spawns), P. lessonae (81 in 10 spawns) and P. ridibundus (7 in 3 spawns). The main purpose of the paper was to demonstrate that the numbers of large eggs were clearly associated with triploid P. esculentus frogs. In pure hybrid (esculentus) populations large eggs comprised between 2.44-40.96% of all ova, while triploid adult frogs constituted between 13.9-73.2% of all individuals, in mixed ridibundus-esculentus populations the large eggs and triploid frogs ranged between 0.85-36.6% and 9.2-56.2%, respectively. However, in mixed lessonae-esculentus populations large eggs comprised only 1.74% of the spawns, whereas triploid frogs represented 2.1% of the adults in the population.