Effects of heating rate and shell colour on the cardiac thermal performance in a polymorphic gastropod Batillaria attramentaria.

Heating rate has gained extensive attention in mechanistic understanding of physiological responses to changing thermal conditions in the context of climate change. In polymorphic gastropods, differences in the absorption of solar energy between dark- and light-coloured individuals lead to supposable differences in their heating rates and body temperatures in sunshine. In the present study, we examined the effect of heating rate on heart rate (HR) in a polymorphic gastropod Batillaria attramentaria. By using biomimetic models, we found that daily maximum temperature of snails with a dark unbanded shell (D-type morph) was higher than snails with a white line on the upper side of each whorl (UL-type morph) by 0.6 °C when exposed to sunlight, but there was no apparent difference in heating rates between D- and UL-type models. We measured HR of snails at various heating rates from 3.0 to 9.0 °C h ^-1 . Faster heating rates significantly increased maximum thermal tolerance in both D- and UL-type snails, highlighting the importance to have thorough knowledge on the heating rate in the field to obtain accurate maximum thermal limit of gastropods. Critical temperature at which HR precipitously declines was higher in D-type snails than UL-type snails. Our results suggested that the impacts of heating rate as well as the shell colour should be considered to gain a mechanistic understanding of the population dynamics of polymorphic gastropods.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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