Plasticity of foot muscle and cardiac thermal limits in the limpet Lottia limatula from locations with differing temperatures

Abstract

Species distributions are shifting in response to increased habitat temperatures as a result of ongoing climate change. Understanding variation in physiological plasticity among species and populations is important for predicting these distribution shifts. Interspecific variation in intertidal ectotherms' short-term thermal plasticity has been well established. However, intraspecific variation among populations from differing thermal habitats remains a question pertinent to understanding the effects of climate change on species' ranges. In this study, we explored upper thermal tolerance limits and plasticity of those limits using a foot muscle metric and 2 cardiac metrics (Arrhenius breakpoint temperature, ABT, and flatline temperature, FLT) in adult file limpets Lottia limatula. Limpets were collected from thermally different coastal and inland-estuarine habitats and held for 2 wk at 13, 17 or 21°C prior to thermal performance assays. Compared to limpets from the warm estuary site, limpets from the cold outer coast site had similar foot muscle critical thermal maxima (CT max ; 35.2 vs. 35.6°C) but lower cardiac thermal tolerances (ABT: 30.5 vs. 35.1°C). Limpets from the cold coast site had higher acclimation responses in foot muscle CT max (0.22°C per 1°C rise in acclimation) than those of the warm estuary site (0.07°C per 1°C rise in acclimation), but lower acclimation responses in cardiac thermal tolerance (ABT: −0.85°C per 1°C rise in acclimation) than those of the estuary site (ABT: 0.10°C per 1°C rise in acclimation). Since outer coast populations had lower cardiac plasticity and higher mortalities in the warm acclimation, we predict L. limatula from colder habitats will be more susceptible to rising temperatures. Our findings illustrate the importance of population-specific variation in short-term thermal plasticity when considering the effects of climate change on ectotherms.

Mussels' acclimatization to high, variable temperatures is lost slowly upon transfer to benign conditions

“…Limpets from the site with the highest daily temperature fluctuations had the largest changes in T crit with heat acclimation (i.e. the greatest physiological plasticity), while limpets from the most thermally stable environment actually had a decrease in thermal tolerance with heat acclimation (Wang et al, 2019). The idea that physiological plasticity is dependent on an animal's thermal history is in line with findings in mussels showing that living in different intertidal locations (e.g.…”

“…Moreover, our low-zone mussels are immersed for a much larger percentage of their day (around two-thirds of the day) compared with our highzone mussels, which are immersed for approximately one-third of each day (Tide Predictions -NOAA Tides and Currents, 2019). In general, animals that experience less temperature variability (like our low-zone mussels) appear to have less physiological plasticity (Denny and Dowd, 2012;Seebacher et al, 2015), and as a result, are often less able to acclimatize to temperatures or conditions outside their normal temperature range (Wang et al, 2019). For example, Wang et al (2019) heat-acclimated limpets (Lottia limatula) from three locations with very different thermal profiles, and then conducted thermal tolerance tests.…”

“…In general, animals that experience less temperature variability (like our low-zone mussels) appear to have less physiological plasticity (Denny and Dowd, 2012;Seebacher et al, 2015), and as a result, are often less able to acclimatize to temperatures or conditions outside their normal temperature range (Wang et al, 2019). For example, Wang et al (2019) heat-acclimated limpets (Lottia limatula) from three locations with very different thermal profiles, and then conducted thermal tolerance tests. Limpets from the site with the highest daily temperature fluctuations had the largest changes in T crit with heat acclimation (i.e.…”

“…Gleason et al (2018) found that the thermal performance of both high-and low-zone juvenile mussels' (as assessed by the temperature at which 50% of mussels died, LT 50 ) decreased after 28 days of constant submersion, while the LT 50 of adult mussels did not change (Gleason et al, 2018). Research on other organisms suggests that adult mussels with different thermal histories might respond differently to constant submersion (Burggren, 2018;Jimenez et al, 2015;Wang et al, 2019;Williams and Somero, 1996) an avenue that Gleason et al (2018) explored only in juvenile, but not adult, mussels. Moreover, based on previous literature in other ectotherms like fish (Corey et al, 2017;Healy and Schulte, 2012;Huey and Bennett, 1990), it may take longer than the 28 days of constant submersion used by Gleason et al (2018) to cause a downward shift in thermal performance, and whereas LT 50 values may change with constant submersion, it is unclear whether constant submersion affects cardiac thermal performance, a trait which (unlike LT 50 , i.e.…”

Limited plasticity in thermally tolerant ectotherm populations: evidence for a trade-off

“…Selection on heat tolerance may also be moderated by the Bogert effect, where behavioural thermoregulation buffers against selection on physiological traits [108][109][110]. The importance of the Bogert effect is supported by the fact that upper thermal limits and acclimation capacity vary relatively little with latitude in terrestrial ectotherms, but do vary with latitude in marine taxa which have fewer options for Dong et al [70] ecosystem freshwater marine terrestrial Kellerman et al [76] Chen et al [67] Wang et al [81] Healy et al [74] Philips et al [79] Enriquez-urzelai et al [71] Jensen et al [75] Weldon et al [82] Diamond et al…”