Effects of controlled water temperatures on oviposition in a lotic‐breeding and externally fertilizing salamander (Hynobius kimurae)

Abstract

Warm or cool ambient temperatures during winter generate plasticity in the within-year timing of oviposition or breeding phenology shifts through the use of a reaction norm in many riverine ectotherms, but within-year timing of oviposition in Hynobius kimurae (Caudata: Hynobiidae) is predicted to be constant at different water temperatures of a mountain stream. To clarify this difference, by experimentally controlling water temperatures from fall to spring and thus changing durations of aquatic hibernation and dates of oviposition, we determined whether oviposition is more advanced when water temperatures increase earlier than usual or is more delayed when water temperatures increase later than usual. Oviposition was more delayed than usual with earlier exposure to high water temperatures during spring and was earlier than usual with exposing to higher water temperatures during hibernation. Days from submergence to oviposition were responsive to cumulative daily water temperatures from submergence to oviposition within a population. A rate of increase in days from submergence to oviposition was different between populations but was constant within a population even if minimal water temperatures varied each year. When running a program of a Markov chain Monte Carlo generalized linear mixed model for Bayesian computation to interpret confounding effects, neither different treatments nor different years statistically affected days from submergence to oviposition. These results suggest that a biological clock exits for days from submergence to oviposition in H. kimurae, which could allow survival in situations with either warmer or cooler environments.

A lotic‐breeding salamander (Hynobius kimurae) modifies physiological and morphological traits during wintering

“…Although it is still unknown whether male and female H. kimurae retreat to subterranean burrows (Hasumi et al., ) or under cover objects such as decaying logs and woody debris (Hasumi et al., ) in their terrestrial habitats (i.e., many references have described their retreats by guesswork: e.g., Goris & Maeda, ; Sato, ), they immigrated to aquatic hibernacula during fall in our population. This is the case in other populations examined (e.g., Akita, ; Akita & Miyazaki, ; Kakegawa & Hasumi, ; M. Kakegawa & M. Hasumi, unpublished data). Among migratory salamanders such as ambystomatids, salamandrids and hynobiids, H. kimurae is, to our knowledge, one and only species that has a prolonged period of stay in the water from fall (November) to spring (May) for hibernation and the succeeding reproduction.…”

“…In H. kimurae , independently of external stimuli such as thawing, spawning behaviour occurred 17–20 weeks (mean = 18.3 weeks) after the two sexes entered the water, with similar constant durations to change other behavioural, physiological and morphological traits such as aquatic stay, cloacal swelling, spermiation and sperm storage (Table ). These constant durations suggest the existence of biological clocks for these changes in male and female H. kimurae after entering the water (see also Kakegawa & Hasumi, ), while changes in water temperatures may induce changes in those traits. Indeed, in a natural habitat of H. kimurae , spermiation just began in males after the increase in mean daily water temperatures from the minimal base of 2.39°C (by the use of a data‐logger), and spawning just started after the abrupt increase in diurnal temperature ranges from the minimal base of 0°C (Kakegawa & Hasumi, ).…”

“…These constant durations suggest the existence of biological clocks for these changes in male and female H. kimurae after entering the water (see also Kakegawa & Hasumi, ), while changes in water temperatures may induce changes in those traits. Indeed, in a natural habitat of H. kimurae , spermiation just began in males after the increase in mean daily water temperatures from the minimal base of 2.39°C (by the use of a data‐logger), and spawning just started after the abrupt increase in diurnal temperature ranges from the minimal base of 0°C (Kakegawa & Hasumi, ).…”

“…Although HW appears to be somewhat swollen in lotic‐breeding male and female O. japonicus (figures 3a and 6 in Akita, ), the lack of increased HW is characteristic of lotic‐breeding hynobiids (Hasumi, ; Sato, ) and may depend on the lack of mating ball formation or scramble competition by other rival males in reproductive behaviour (Hasumi, , 2001a). This is likely because in this species reproductive behaviour is conducted within a limited, small space under a rock or stone in a stream (Kakegawa & Hasumi, ; Kakegawa et al., ).…”

“…Sato () stated without showing any data that Hynobius kimurae immigrates to mountain streamsides for hibernation during November. This species was then verified to hibernate in the water (Akita, ; Kakegawa & Hasumi, ; Kakegawa, Kishi, Saikawa, & Hasumi, ; M. Kakegawa & M. Hasumi, unpublished data). By contrast, fall immigration may be directional to aquatic‐breeding sites during fall and winter months in some of the counterparts of hynobiids, such as ambystomatids (e.g., Ambystoma annulatum : Anderson, Ousterhout, Peterman, Drake, & Semlitsch, ; Ambystoma macrodactylum : Verrell, ; Ambystoma talpoideum : Krenz & Sever, ) and salamandrids (e.g., Notophthalmus perstriatus : Johnson, ; Notophthalmus viridescens : Healy, ).…”