Light-dependent magnetic compass in Iberian green frog tadpoles

Here, we provide evidence for a wavelength-dependent effect of light on magnetic compass orientation in Pelophylax perezi (order Anura), similar to that observed in Rana catesbeiana (order Anura) and Notophthalmus viridescens (order Urodela), and confirm for the first time in an anuran amphibian that a 90° shift in the direction of magnetic compass orientation under long-wavelength light (≥500 nm) is due to a direct effect of light on the underlying magnetoreception mechanism. Although magnetic compass orientation in other animals (e.g., birds and some insects) has been shown to be influenced by the wavelength and/or intensity of light, these two amphibian orders are the only taxa for which there is direct evidence that the magnetic compass is light-dependent. The remarkable similarities in the light-dependent magnetic compasses of anurans and urodeles, which have evolved as separate clades for at least 250 million years, suggest that the light-dependent magnetoreception mechanism is likely to have evolved in the common ancestor of the Lissamphibia (Early Permian, ~294 million years) and, possibly, much earlier. Also, we discuss a number of similarities between the functional properties of the light-dependent magnetic compass in amphibians and blue light-dependent responses to magnetic stimuli in Drosophila melanogaster, which suggest that the wavelength-dependent 90° shift in amphibians may be due to light activation of different redox forms of a cryptochrome photopigment. Finally, we relate these findings to earlier studies showing that the pineal organ of newts is the site of the light-dependent magnetic compass and recent neurophysiological evidence showing magnetic field sensitivity in the frog frontal organ (an outgrowth of the pineal).     

Effects of triclosan on gonadal differentiation and development in the frog Pelophylax nigromaculatus

Previous studies have reported that triclosan (TCS) could possess an androgenic activity. We aimed to investigate the effects of TCS on gonadal differentiation and development in the frog Pelophylax nigromaculatus, a sensitive amphibian species to androgenic chemicals. P. nigromaculatus tadpoles at stage 24 were exposed to TCS (3, 30, and 300 nmol/L) to stage 46 in a semi-static exposure system. At the end of exposure, gonadal morphology and histology, sex ratio and gonadal expression of sex-biased genes were examined in P. nigromaculatus. In each TCS treatment group, we found several individuals whose gonads exhibited morphological and/or histological abnormalities. Gonadal histological abnormalities were characterized by few oocytes and many somatic cells. Although the percentage of the individuals with abnormal gonads was low (7.8%) among all animals treated with TCS, statistical test revealed the sex ratios in the 3 and 300 nmol/L TCS treatment groups were significantly different from the solvent control. In the 30 nmol/L TCS treatment group, abnormal gonads were also observed, although the sex ratio was not changed compared with the solvent control, which was possibly due to the smaller sample size in this group. In all the TCS treatment groups, the sex ratios were not obviously male-biased, but the expression levels of some sex-biased genes were significantly altered by TCS. Altogether, our results suggest that TCS, even at environmentally relevant concentrations, could disrupt gonadal differentiation and development in P. nigromaculatus, but we are not sure whether the disrupting effects were associated with masculinization or feminization.     

Inverse Rensch's rule in a frog with female-biased sexual size dimorphism

Rensch's rule claims that sexual size dimorphism (SSD) increases with body size when males are larger but decreases with body size when males are smaller. Chinese wood frog Rana chensinensis is a medium-sized species with female-biased size dimorphism. Using data on body size and age in 27 populations covering the full known size range of the species, we tested the consistency of allometric relationships between the sexes with Rensch's rule and evaluated the hypothesis that SSD is largely a function of age differences between the sexes. The results showed that level of female-biased SSD increased with increasing mean size, supporting the inverse of Rensch's rule. Moreover, most of the variation in SSD can be explained in terms of differences in age between the sexes in populations.     

When signal meets noise: immunity of the frog ear to interference

Sound stimulates the tympanic membrane (TM) of anuran amphibians through multiple, poorly understood pathways. It is conceivable that interactions between the internal and external inputs to the TM contribute to the nonlinear effects that noise is known to produce at higher levels of the auditory pathway. To explore this issue, we conducted measurements of TM vibration in response to tones in the presence of noise in the frog Eupsophus calcaratus. Laser vibrometry revealed that the power spectra (n = 16) of the TM velocity in response to pure tones at a constant level of 80 dB sound-pressure level (SPL) had a maximum centered at an average frequency of 2,344 Hz (range 1,700–2,990 Hz) and a maximum velocity of 61.1 dB re 1 μm/s (range 42.9–66.6 dB re 1 μm/s). These TM-vibration velocity response profiles in the presence of increasing levels of 4-kHz band-pass noise were unaltered up to noise levels of 90 dB SPL. For the relatively low spectral densities of the noise used, the TM remains in its linear range. Such vibration patterns facilitate the detection of tonal signals in noise at the tympanic membrane and may underlie the remarkable vocal responsiveness maintained by males of E. calcaratus under noise interference.