Tadpole morphology features of different Pelophylax esculentus complex forms

Abstract

Complicated relationships between different forms of Pelophylax esculentus complex are strongly connected to their reproduction modes. Stability of the hemiclonal population systems including variety of hybrids is provided by balance between gamete production patterns and selective death of offspring portion. A direct way to study such mechanisms is to investigate the ontogeny of different forms – that means studying their tadpoles. However, there are still no suitable methods to morphologically distinguish the known diversity of hybrid forms (2n and 3n of different genomic composition) from the naturally diverse parental species at the tadpole stage. The present work is aimed to investigate external quantitative (measurements-based) and coloration features for tadpoles of parental species (P. lessonae, P. ridibundus “pure” and triploid-born) and of two P. esculentus forms (progeny of unusual LLR-females and diploid hybrids). For this purpose, the set of experimental artificial crossings were established and larvae were reared under similar conditions (equal water volume, light, temperature and feeding regimes). Species and ploidy of experimental frogs were identified using external morphology features, microscopic cytometry of blood cells, karyology of intestine mitotic cells and microsatellite analysis. Coloration of different body parts were scored visually using microscope; measuring was performed by microscopic photographing with scale and further measuring using AxioVision soft. Measurements were analyzed via multidimensional analyses (PCA, discriminant, canonical), and appeared weakly applicable taken both together and separately. It allowed us only to partly separate progeny of two parental species from each other and from progeny of unusual triploid hybrids. States combinations of coloration features appeared to be specific for each form taken into analysis, but only at the particular age range. Specificities of triploid and different P. ridibundus groups can be explained by natural variability as well as by peculiar processes in hybridogenetic systems.

Keywords

• water frogs, larvae, development, progeny, hybrid, triploid