The effect of temperature on sea lamprey (Petromyzon marinus): ecological and cellular implications
Understanding how species respond to thermal challenges is important for forecasting future species distributions, and to provide information for population management. Sea lamprey (Petromyzon marinus), a jawless representative of a basal branch of the vertebrates, successfully invaded the Laurentian Great Lakes in the 20th century to the detriment of the local fishery, resulting in an intensive population control effort since the late 1950s. Sea lamprey are therefore an excellent study species not only for the practical implications of population management, but also as an outgroup to the vertebrates and for testing predictions of invasion theory. Here, the critical thermal maximum (CTMax) of a native population of sea lamprey larvae from New Brunwick was determined in individuals acclimated to 5 °C, 13.5 °C, and 20 °C, and gene expression profiles were determined via reverse-transcription quantitative polymerase chain reaction (qPCR) for genes involved in the cellular stress response (CSR) in response to an acute thermal shock. Subsequently, similar experiments were performed on an invasive landlocked population of sea lamprey larvae acclimated to similar temperatures, and a population comparison was performed. The CTMax results demonstrated that sea lamprey possess a relatively low acclimation capacity, as their CTMax increased only 0.12 °C for each 1 °C increase in acclimation temperature in both populations; however, the landlocked population had a consistently higher CTMax temperature. Sublethal thresholds appear to exist at ~24 °C – 26 °C and ~30 °C in the New Brunswick population , where the CSR is initiated and then shifts to an extreme response, respectively. Invasion theory predicts increased plasticity in invasive populations, and evidence for this was found in the transcription profiles of heat shock proteins in the landlocked population relative to the New Brunswick population. Temperatures above 30 °C are already being recorded in historical sea lamprey spawning streams in the southern end of their native distribution, suggesting that a northerly range shift may occur. Despite their greater upper thermal tolerance, this suggests the landlocked population may be more susceptible for future warming, as they already exploit their entire range in the Great Lakes Basin .
Thermal biology, Cellular stress, Gene expression, Sea lamprey, Fisheries, Conservation, Invasion biology