Effects of temperature and aquatic Po-2 on the physiology and behaviour ofApalone ferox and Chrysemys picta

Softshell turtles overwinter in the same bodies of water as some emydids, b ut their reduced shell and increased non-pulmonary gas exchange may contrib ute to a different mechanism of overwintering. The dynamics of bimodal resp iration, diving behaviour and blood acid-base status in Apalone ferox and C hrysemys picta were investigated under two different temperatures combined with three different aquatic P-O2 levels, Both species obtained oxygen thro ugh pulmonary and non-pulmonary routes. Apalone ferox obtained more oxygen through non-pulmonary routes and increased its non-pulmonary (V) over dot(O 2) in response to both higher aquatic P-O2 and lower temperatures. Both spe cies increased pulmonary P-O2 in response to higher temperatures. As a cons equence of the greater reliance of A. ferox on pulmonary (V) over dot(O2), warmer temperatures caused plasma P-CO2 and [HCO3-] values to increase sign ificantly compared with C, picta, Apalone ferox, which is efficient at bimo dal respiration, displayed a high degree of plasticity with respect to both its respiratory and acid-base profiles, behaving more like an aquatic air- breathing fish in bimodal respiration at low temperature and more like a te rrestrial air-breather at high temperature. Chrysemys picta, which is poor at bimodal respiration, was highly dependent on aerial gas exchange at both temperatures. Aquatic P-O2 did not change any of the behavioural variables measured. At warm temperatures, A. ferox met O-2 demands by increasing the rate of lung ventilation, which resulted in a significantly greater number of breathing bouts per hour and breaths per emersion period. However, the number of breaths per bout was not affected by temperature, As temperatures decreased, A. ferox utilized its non-pulmonary respiration ability and sig nificantly increased its dive duration. Apalone ferox became less active at colder temperatures by significantly increasing the duration of inactive p eriods (from 4 to 18 min) and by significantly decreasing the frequency of activity bursts. Chrysemys picta also met the higher gas-exchange demands a ssociated with increased temperature by increasing the rate of lung ventila tion; however, this increase was not as large as that measured in A. ferox, Chrysemys picta displayed multiple rhythmic breaths per bout. These result s indicate that, unlike aquatic P-O2, temperature is an important factor in the regulation of diving and ventilatory behaviour in turtles. The species responded to temperature in dissimilar ways because of differences in thei r bimodal respiration ability.