Digital malformation and chromosomal abnormality in Rana tigirina – the warning signal of declining amphibian population

Abstract

Amphibians are in most cases, diverse and sensitive to environmental variability. They are considered reliable bioindicators of environmental pollution. In recent years, much attention has been given towards the detection of genotoxic agents in the aquatic environment. The presence of such agents is suggested to have adverse effects on animal as well as human health via the food chain. Previous studies on reproductive toxicology in amphibians showed that different types of pesticides adversely affect larval development and induce complete feminization. The present study demonstrates the phenomenon of hermaphroditism and digital malformation in adult amphibians. The morphology of reproductive system of abnormal male Rana tigirina was studied which comprised of testis with well developed long oviduct. Histological structures of kidney, testis and ovary were investigated by examining the sections of the organs in both sexes. The studies indicated that particularly the outer part of the section of kidney in male abnormal individual revealed the ovarian structure which is an indication of hermaphroditism. Somatic chromosomes of both male and female specimens were prepared from intestinal epithelium by mitotic division inhibition technique. Conventional Giemsa stained metaphase chromosomes of both male and female Rana tigirina revealed the existence of 2n = 26 biarmed chromosomes. An examination of well spread metaphase stages in both sexes revealed a variety of chromosomal abnormalities. Comparative analysis of chromosomal abnormalities in both normal and morphologically abnormal (with digital malformation) individuals revealed that the frequencies of chromosomal abnormalities were maximum in morphologically abnormal individuals. Germ cell cytotoxicity was also assessed by studying the different types of sperm shape abnormalities in the morphologically abnormal individuals. So this study emphasizes that excessive genome damage caused by genotoxic agents in aquatic environment may be an important factor for such reproductive consequences as well as digital malformation.