Ambient temperature fluctuations are detected via the thermosensory system which allows animals to seek preferable thermal conditions or escape from harmful temperatures. Evolutionary changes in thermal perception have thus potentially played crucial roles in niche selection. The genus Xenopus (clawed frog) is suitable for investigating the relationship between thermal perception and niche selection due to their diverse latitudinal and altitudinal distributions. Here we performed comparative analyses of the neuronal heat sensors TRPV1 and TRPA1 among closely related Xenopus species (X. borealis, X. muelleri, X. laevis, and X. tropicalis) to elucidate their functional evolution and to assess whether their functional differences correlate with thermal niche selection among the species. Comparison of TRPV1 among four extant Xenopus species and reconstruction of the ancestral TRPV1 revealed that TRPV1 responses to repeated heat stimulation were specifically altered in the lineage leading to X. tropicalis which inhabits warmer niches. Moreover, the thermal sensitivity of TRPA1 was lower in X. tropicalis than the other species, although the thermal sensitivity of TRPV1 and TRPA1 was not always lower in species that inhabit warmer niches than the species inhabit cooler niches. However, a clear correlation was found in species differences in TRPA1 activity. Heat-evoked activity of TRPA1 in X. borealis and X. laevis, which are adapted to cooler niches, was significantly higher than in X. tropicalis and X. muelleri which are adapted to warmer niches. These findings suggest that the functional properties of heat sensors changed during Xenopus evolution, potentially altering the preferred temperature ranges among species.
Data for Fig 2 & Fig3a-c
Electrophysiological data used for Fig 2 and Fig 3a-c. The file include data for current amplitudes and normalized responses obtained by repeated heat stimulation (five times) from Xenopus laevis oocytes expressing TRPV1 from extant and ancestral clawed frog species. A basal current amplitude was obtained in a five-second duration just before each heat stimulation. If the maximum current amplitude was smaller than 0.5 μA, the current data obtained from such oocytes was excluded from analysis since we could not precisely judge the responses of TRPV1 to repeated heat stimulation.
Data for Fig2&Fig3a-c.xlsx
Data for Fig 3e
Thermal activation thresholds estimated by an Arrhenius plot using data obtained from Xenopus laevis oocytes expressing TRPV1 from extant and ancestral clawed frog species. The data for currents and temperatures were obtained at the first heat stimulation from Xenopus laevis oocytes expressing TRPV1 from extant and ancestral clawed frog species. Then, Arrhenius plots were performed as shown in Fig S2.
Data for Fig3e.xlsx
Data for Fig 5c
Thermal activation thresholds estimated by an Arrhenius plot using data obtained from Xenopus laevis oocytes expressing TRPA1 from Xenopus species. The data for currents and temperatures were obtained at the first heat stimulation from Xenopus laevis oocytes expressing TRPA1 from Xenopus species. Then, Arrhenius plots were performed as shown in Fig S5.
Data for Fig5c.xlsx
Data for Fig 5d & 5e
Electrophysiological data used for Fig 5d & 5e. The file include data for current amplitudes and normalized responses obtained by heat stimulation, then 0.3 mM cinnamaldehyde stimulation from Xenopus laevis oocytes expressing TRPA1 from Xenopus species. A basal current amplitude was obtained in a five-second duration just before each stimulation. The current amplitude elicited by heat stimulation was normalized to that elicited by 0.3 mM cinnamaldehyde stimulation.
Dose-dependent responses for Xbo-TRPA1a and Xmu-TRPA1a were obtained by applying different concentrations of cinnamaldehyde (0.01, 0.3, 1, and 2 mM) to Xenopus laevis oocytes expressing TRPA1a from each species. 2 mM cinnamaldehyde was applied to oocytes at the last in all the case to normalize current amplitudes evoked by lower concentrations of cinnamaldehyde.
Data for Fig5d&e.xlsx
Data for Fig 6
Electrophysiological data used for Fig 6. The file include data for current amplitudes and normalized responses obtained by heat stimulation, then 0.3 mM cinnamaldehyde stimulation from Xenopus laevis oocytes expressing TRPA1a or TRPA1b from Xenopus laevis. Basal current amplitudes were obtained in a five-second duration just before each stimulation. The current amplitude elicited by heat stimulation was normalized to that elicited by 0.3 mM cinnamaldehyde stimulation.
Dose-dependent responses for TRPA1a or TRPA1b from Xenopus laevis were obtained by applying different concentrations of cinnamaldehyde (0.01, 0.3, 1, and 2 mM) to Xenopus laevis oocytes expressing TRPA1a or TRPA1b. 2 mM cinnamaldehyde was applied to oocytes at the last in all the case to normalize current amplitudes evoked by lower concentrations of cinnamaldehyde.
Data for Fig6.xlsx
Nucleotide sequences for Xenopus TRPV1
Aligned nucleotide sequences for TRPV1 from extant and ancestral clawed frog species.
Nucleotide sequences for Xenopus TRPA1
Aligned nucleotide sequences for TRPA1 from Xenopus species.
