Heat hardening as a function of developmental stage in larval and juvenile Bufo americanus and Xenopus laevis

Abstract

1. We studied heat hardening in tadpoles and juveniles of the temperate Bufo americanus and the subtropical Xenopus laevis by comparing the critical thermal maxima (CTMax) of heat-pretreated animals with the CTMax of control (non-pretreated) animals of the same developmental stages. 2. While premetamorphic tadpoles (Gosner stages 26-43) of both species exhibited heat hardening, metamorphosing B.americanus tadpoles (stages 44-45) were unable to heat harden and, in fact, exhibited a decrease in CTMax following pretreatment while metamorphosing X. laevis tadpoles still exhibited heat hardening. 3. This difference may reflect the more stressful nature of the more extensive metamorphosis of Bufo compared to that of Xenopus.

Heat hardening of a larval amphibian is dependent on acclimation period and temperature

“…The group with the lowest mean CT max (36.5°C) had the greatest hardening effect (0.9°C), while the group with the highest mean CT max (39.0°C) had a minimal hardening effect (0.1°C). While the 0.9°C hardening effect was comparable with larval American toads ( Anaxyrus americanus ) and African clawed frogs ( Xenopus laevis ) (Sherman & Levitis, 2003), the remaining groups had a minor hardening response (≤0.4°C) that was similar with values reported for larval bullfrogs ( Lithobates catesbeianus ) (Menke & Claussen, 1982). Additionally, the bullfrogs in the earlier study showed no evidence of the trade‐off hypothesis as CT max increased positively with acclimation temperatures while the hardening effect was unchanged.…”

Heat hardening of a larval amphibian is dependent on acclimation period and temperature

“…The group with the lowest mean CT max (36.5°C) had the greatest hardening effect (0.9°C), while the group with the highest mean CT max (39.0°C) had a minimal hardening effect (0.1°C). While the 0.9°C hardening effect was comparable with larval American toads ( Anaxyrus americanus ) and African clawed frogs ( Xenopus laevis ) (Sherman & Levitis, 2003), the remaining groups had a minor hardening response (≤0.4°C) that was similar with values reported for larval bullfrogs ( Lithobates catesbeianus ) (Menke & Claussen, 1982). Additionally, the bullfrogs in the earlier study showed no evidence of the trade‐off hypothesis as CT max increased positively with acclimation temperatures while the hardening effect was unchanged.…”

Immediate and Persistent Effects of Temperature on Oxygen Consumption and Thermal Tolerance in Embryos and Larvae of the Baja California Chorus Frog, Pseudacris hypochondriaca

“…Thermal tolerance of larval P. hypochondriaca is within the range measured in similar species, but was more responsive to acclimation compared to previous studies. Our CTMax values at an acclimation temperature of 20°C (38–39°C) were similar to Pseudacris triseriata , R. sylvatica , R. temporaria , and Xenopus laevis , but lower than values (41–43°C) observed in Bufo americanus , B. woodhousei , B. marinus , and Gastrophryne carolinenus at the same acclimation temperature (Cupp, 1980; Floyd, 1983; Sherman and Levitis, 2003; Enriquez-Urzelai et al, 2019). Thus, thermal tolerance of P. hypochondriaca larvae tends to match other species that breed during the winter months.…”

Methodological assessment of the Critical Thermal Maximum (CTmax) of anuran larvae: interaction among the experimental heating rates, ontogeny and body mass

“…Neurohormonal, behavioral and ecological observations also agree with the notion of anuran metamorphosis as a stressful process (Arnold and Wassersug, 1978;Denver, 1997;Floyd, 1984;Wilbur, 1980). Thus, metamorphosing tadpoles are hypothesized to be less able to mobilize mechanisms to cope with high temperatures when compared with premetamorphic tadpoles (Sherman and Levitis, 2003). However, our results in metamorphosing tadpoles of P. nattereri challenge the previous claim, for the degree of the thermal exposure may be a determinant for the scope of responses in these 'naturallystressed' individuals.…”

“…Experimental heating rates (∆T's) affected the upper thermal limits of P. nattereri along ontogeny. Previous contributions also observed a diminishing on the upper thermal tolerance at the end of metamorphosis in other anuran species (Cupp, 1980;Floyd, 1983;Sherman, 1980;Sherman and Levitis, 2003). However, we showed that in P. nattereri this trend was dependent of the ∆T.…”

Heat hardening of a larval amphibian is dependent on acclimation period and temperature

“…The group with the lowest mean CT max (36.5°C) had the greatest hardening effect (0.9°C), while the group with the highest mean CT max (39.0°C) had a minimal hardening effect (0.1°C). While the 0.9°C hardening effect was comparable with larval American toads ( Anaxyrus americanus ) and African clawed frogs ( Xenopus laevis ) (Sherman & Levitis, 2003), the remaining groups had a minor hardening response (≤0.4°C) that was similar with values reported for larval bullfrogs ( Lithobates catesbeianus ) (Menke & Claussen, 1982). Additionally, the bullfrogs in the earlier study showed no evidence of the trade‐off hypothesis as CT max increased positively with acclimation temperatures while the hardening effect was unchanged.…”

Immediate and Persistent Effects of Temperature on Oxygen Consumption and Thermal Tolerance in Embryos and Larvae of the Baja California Chorus Frog, Pseudacris hypochondriaca

“…Thermal tolerance of larval P. hypochondriaca is within the range measured in similar species, but was more responsive to acclimation compared to previous studies. Our CTMax values at an acclimation temperature of 20°C (38–39°C) were similar to Pseudacris triseriata , R. sylvatica , R. temporaria , and Xenopus laevis , but lower than values (41–43°C) observed in Bufo americanus , B. woodhousei , B. marinus , and Gastrophryne carolinenus at the same acclimation temperature (Cupp, 1980; Floyd, 1983; Sherman and Levitis, 2003; Enriquez-Urzelai et al, 2019). Thus, thermal tolerance of P. hypochondriaca larvae tends to match other species that breed during the winter months.…”

Methodological assessment of the Critical Thermal Maximum (CTmax) of anuran larvae: interaction among the experimental heating rates, ontogeny and body mass

“…Neurohormonal, behavioral and ecological observations also agree with the notion of anuran metamorphosis as a stressful process (Arnold and Wassersug, 1978;Denver, 1997;Floyd, 1984;Wilbur, 1980). Thus, metamorphosing tadpoles are hypothesized to be less able to mobilize mechanisms to cope with high temperatures when compared with premetamorphic tadpoles (Sherman and Levitis, 2003). However, our results in metamorphosing tadpoles of P. nattereri challenge the previous claim, for the degree of the thermal exposure may be a determinant for the scope of responses in these 'naturallystressed' individuals.…”

“…Experimental heating rates (∆T's) affected the upper thermal limits of P. nattereri along ontogeny. Previous contributions also observed a diminishing on the upper thermal tolerance at the end of metamorphosis in other anuran species (Cupp, 1980;Floyd, 1983;Sherman, 1980;Sherman and Levitis, 2003). However, we showed that in P. nattereri this trend was dependent of the ∆T.…”

Heat hardening of a larval amphibian is dependent on acclimation period and temperature

“…The group with the lowest mean CT max (36.5°C) had the greatest hardening effect (0.9°C), while the group with the highest mean CT max (39.0°C) had a minimal hardening effect (0.1°C). While the 0.9°C hardening effect was comparable with larval American toads ( Anaxyrus americanus ) and African clawed frogs ( Xenopus laevis ) (Sherman & Levitis, 2003), the remaining groups had a minor hardening response (≤0.4°C) that was similar with values reported for larval bullfrogs ( Lithobates catesbeianus ) (Menke & Claussen, 1982). Additionally, the bullfrogs in the earlier study showed no evidence of the trade‐off hypothesis as CT max increased positively with acclimation temperatures while the hardening effect was unchanged.…”

Immediate and Persistent Effects of Temperature on Oxygen Consumption and Thermal Tolerance in Embryos and Larvae of the Baja California Chorus Frog, Pseudacris hypochondriaca

“…Thermal tolerance of larval P. hypochondriaca is within the range measured in similar species, but was more responsive to acclimation compared to previous studies. Our CTMax values at an acclimation temperature of 20°C (38–39°C) were similar to Pseudacris triseriata , R. sylvatica , R. temporaria , and Xenopus laevis , but lower than values (41–43°C) observed in Bufo americanus , B. woodhousei , B. marinus , and Gastrophryne carolinenus at the same acclimation temperature (Cupp, 1980; Floyd, 1983; Sherman and Levitis, 2003; Enriquez-Urzelai et al, 2019). Thus, thermal tolerance of P. hypochondriaca larvae tends to match other species that breed during the winter months.…”

Methodological assessment of the Critical Thermal Maximum (CTmax) of anuran larvae: interaction among the experimental heating rates, ontogeny and body mass

“…Neurohormonal, behavioral and ecological observations also agree with the notion of anuran metamorphosis as a stressful process (Arnold and Wassersug, 1978;Denver, 1997;Floyd, 1984;Wilbur, 1980). Thus, metamorphosing tadpoles are hypothesized to be less able to mobilize mechanisms to cope with high temperatures when compared with premetamorphic tadpoles (Sherman and Levitis, 2003). However, our results in metamorphosing tadpoles of P. nattereri challenge the previous claim, for the degree of the thermal exposure may be a determinant for the scope of responses in these 'naturallystressed' individuals.…”

“…Experimental heating rates (∆T's) affected the upper thermal limits of P. nattereri along ontogeny. Previous contributions also observed a diminishing on the upper thermal tolerance at the end of metamorphosis in other anuran species (Cupp, 1980;Floyd, 1983;Sherman, 1980;Sherman and Levitis, 2003). However, we showed that in P. nattereri this trend was dependent of the ∆T.…”