Phalangeal bone anomalies in the European common toad Bufo bufo from polluted environments

Abstract

Every spring, many of amphibians are killed by motor vehicles on roads. These road-killed animals can be used as valuable material for non-invasive studies showing the effect of environmental pollution on amphibian populations. The aims of our research were to check whether the phalanges of road-killed toads may be useful as material for histological analysis, and whether various degrees of human impact influence the level in bone abnormalities in the common toad. We also examined whether the sex and age structure of toads can differ significantly depending in the different sites. We chose three toad breeding sites where road-killed individuals had been observed: near the centre of a city, the outskirts of a city, and a rural site. We collected dead individuals during spring migration in 2013. The sex of each individual was determined and the toes were used to determine age using the skeletochronology method. While performing age estimates, we looked for abnormalities in relation to normal bone tissue structure. In urban site, females dominate males (sex ratio 2.6:1), but in populations from rural and semi-urban sites, sex ratio was reverse (1:2.2 and 1:1.4, respectively). However, we did not find any significant differences between age structure of all populations (average age of each population: approximately 4 years). We observed abnormalities in more than 80 % of all toads from the city, compared to approximately 20 % from the rural and semi-urban sites. In particular, we found hypertrophic bone cells, misaligned intercellular substance, and irregular outer edges of bones. We suggest that these malformations are caused by different pollution, e.g. with heavy metals.

Keywords: Amphibians; Phalangeal bone; Poland; Pollution; Roadkilling; Skeletochronology; Urban area.

Fig. 1

Land covers of 1 km buffers used to quantify degrees of urbanisation around breeding side near sampling points. Land covers are tree and forest cover (dark green), paved surfaces (black), open green area (farmlands, meadows, fallow lands) (light green), illegal settlement and degraded allotment gardens (sand) and buildings or industrial plants (red)

Fig. 2

Transverse sections of third phalanx (diaphysis) of toads: after third hibernation—typical (a), fourth hibernation—with anomalies (in black frame) (b). Transverse sections of epiphysis part of toad’s phalanx: after sixth hibernation—typical (c) and anomalies in bone tissue (toad of unknown age) (d). Black arrow heads—line of arrested growth (LAG), (asterisk)—bone marrow cavity, Bm—bone marrow present in the marrow cavity, white arrow—nutrition canal, c—bone cavities. Note misaligned intercellular substance and mass of hypertrophic cells in bone structure (black arrow). In places with anomalies, LAGs are not visible. Scale bar 100 μm