Our new paper describing thermal biology of Halocaridina rubra, a small shrimp endemic to anchialine habitats of Hawaii, is now available online @ Journal of Thermal Biology.
In this work, led by PhD student Mariangel Correa-Orellana, we examined how different populations/genetic lineages of H. rubra (known in Hawaii as opae ula) respond to changes in temperature. We were especially focused on populations from new habitats created during 2018 lava flows that continue to experience high temperatures due to geothermal activity.
Here’s 5 cool things we found:
- Critical thermal limits, the upper and lower temperatures at which shrimp can continue to function, seem to be mainly determined by the temperatures shrimp are acclimated to. In other words, if they are kept at higher temps, they can tolerate higher temps. Genetics might play influence this a little, but it mostly seems to be nurture, not nature. Here’s Fig. 2 from the paper showing some data:
2. Even though the shrimp from the new, hot habitats are living at high temps (e.g., ~40 C), they can’t tolerate much higher temps. They are basically living at their maximum limit. We also never see shrimp in habitats that are much hotter than the maximum limits we measured, so we think these limits are ecologically important.
3. We also measured metabolic rates of shrimps from across the islands at room temperature. We found there was significant variability among genetic lineages, suggesting their might be a genetic component for baseline metabolic rates in this species. Here’s our data:
4. We also measured metabolic rates of different lineages that were acclimated to either a relatively warm or cool temperature. Importantly, we tested the shrimp from the different acclimation temperatures at either the cool or warm temp, so we could determine whether test or acclimation temperature was driving variation in metabolic rates. We found that metabolic rates in opae ula are almost entirely determined by test, not acclimation temperature. In other words, metabolic rates scale really fast with temperature and do not rebound if the animal is allowed to acclimate to that temperature (at least for 4 weeks). We call this a “no acclimation” response, which is fairly common across ectothermic animals, but not as common as a “partial acclimation” response where rates rebound somewhat with acclimation. Here’s the relevant figure:
5. If you look closely at the above figure, there’s no much difference among the different genetic lineages (HM, EP, P1, and SPAG) as to how their metabolic rates change with temperature. Our hypothesis was that shrimp from the new, warm habitats would show a stronger warm acclimation response – in other words their rates would not be as affected by warm temperatures as those from the old, cool habitats. But, this wasn’t really what we saw. Instead, we saw that rates were determined mostly by test temperature in all populations – none of them really showed much acclimation response.
Check out the paper if you want to learn more!