Dear MarMamers My coauthors and I would like to share our new publication on conditioned heart rate responses in dolphins (https://www.frontiersin.org/articles/10.3389/fphys.2020.604018/abstract). In this study we show that the change in heart rate during diving varies depending on anticipation. This suggest that dolphins conditionally reduce their heart rate, and these results provide further evidence for the Selective Gas Exchange hypothesis (https://royalsocietypublishing.org/doi/full/10.1098/rspb.2018.0482) that explains how marine mammals can selective exchange oxygen and carbon dioxide without exchange of nitrogen and thereby maximize aerobic dive duration and also minimize the risk of the bends (see below for short video explaining this hypothesis). For more information, the title and abstract is below and also a link to the open access article. In addition, we have also included a video abstract of the paper, and also a link to an educational video explaining the Selective Gas Exchange hypothesis. If you have any questions, please do not hesitate to get in contact: afahlman@whoi.edu Title: Conditioned variation in heart rate during static breath-holds in the bottlenose dolphin (Tursiops truncatus) Authors: Fahlman,A., Cozzi, B., Manley, M., Jabas, S., Malik, M., Blawas A., and Janik, V.M.. DOI: 10.3389/fphys.2020.604018 URL: https://www.frontiersin.org/articles/10.3389/fphys.2020.604018/abstract Abstract: Previous reports suggested the existence of direct somatic motor control over heartrate (fH) responses during diving in some marine mammals, as the result of a cognitive and/or learning process rather than being a reflexive response. This would be beneficial for O2 storage management, but would also allow ventilation-perfusion matching for selective gas exchange, where O2 and CO2 can be exchanged with minimal exchange of N2. Such a mechanism explains how air breathing marine vertebrates avoid diving related gas bubble formation during repeated dives, and how stress could interrupt this mechanism and cause excessive N2 exchange. To investigate the conditioned response, we measured the fH-response before and during static breath-holds in three bottlenose dolphins (Tursiops truncatus) when shown a visual symbol to perform either a long (LONG) or short (SHORT) breath-hold, or during a spontaneous breath-hold without a symbol (NS). The average fH (ifHstart), and the rate of change in fH (difH/dt) during the first 20 s of the breath-hold differed between breath-hold types. In addition, the minimum instantaneous fH (ifHmin), and the average instantaneous fH during the last 10 s (ifHend) also differed between breath-hold types. The difH/dt was greater, and the ifHstart, ifHmin, and ifHend were lower during a LONG as compared with either a SHORT, or an NS breath-hold (P < 0.05). Even though the NS breath-hold dives were longer in duration as compared with SHORT breath-hold dives, the difH/dt was greater and the ifHstart, ifHmin, and ifHend were lower during the latter (P < 0.05). In addition, when the dolphin determined the breath-hold duration (NS), the fH was more variable within and between individuals and trials, suggesting a conditioned capacity to adjust the fHresponse. These results suggest that dolphins have the capacity to selectively alter the fH-response during diving and provide evidence for significant cardiovascular plasticity in dolphins. Video summary: https://www.youtube.com/watch?v=666zieqGv0A Explanation of the Selective Gas Exchange hypothesis: https://www.youtube.com/watch?v=sfBOpUuJv1c