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Projeto de investigação
Multigenerational adaptation of ascidians to ocean warming and acidification
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Impacts of deoxygenation and hypoxia on shark embryos anti-predator behavior and oxidative stress
Publication . Varela, Jaquelino; Martins Rebocho, Sandra; Court, Melanie; Santos, Catarina Pereira; Paula, José Ricardo; Ferreira, Inês João; Diniz, Mário; Repolho, Tiago; Rosa, Rui
Simple Summary Despite their importance, sharks are among the most endangered ocean species. In addition to overexploitation and the destruction of their natural habitat, climate change is also known to pose a serious threat to them. Among the physico-chemical changes associated with climate change, oxygen loss has been the least studied in terms of its effect on shark physiology and behavior. In this study, we evaluated the impact of deoxygenation (93% air saturation) and hypoxia (26% air saturation) on the anti-predatory behavior and physiology of temperate shark embryos. We found that hypoxia caused a high mortality (44%), significantly increased embryo movement within capsules, and, consequently, reduced the freezing response behavior (a behavior that allows embryos to be unnoticed by predators). Regarding oxidative stress, most biomarkers analyzed were not impacted by the experimental treatments. Overall, our results suggest that the temperate shark's early life stages showed a certain degree of resilience to deoxygenation but not to hypoxia. Climate change is leading to the loss of oxygen content in the oceans and endangering the survival of many marine species. Due to sea surface temperature warming and changing circulation, the ocean has become more stratified and is consequently losing its oxygen content. Oviparous elasmobranchs are particularly vulnerable as they lay their eggs in coastal and shallow areas, where they experience significant oscillations in oxygen levels. Here, we investigated the effects of deoxygenation (93% air saturation) and hypoxia (26% air saturation) during a short-term period (six days) on the anti-predator avoidance behavior and physiology (oxidative stress) of small-spotted catshark (Scyliorhinus canicula) embryos. Their survival rate decreased to 88% and 56% under deoxygenation and hypoxia, respectively. The tail beat rates were significantly enhanced in the embryos under hypoxia compared to those exposed to deoxygenation and control conditions, and the freeze response duration showed a significant opposite trend. Yet, at the physiological level, through the analyses of key biomarkers (SOD, CAT, GPx, and GST activities as well as HSP70, Ubiquitin, and MDA levels), we found no evidence of increased oxidative stress and cell damage under hypoxia. Thus, the present findings show that the projected end-of-the-century deoxygenation levels elicit neglectable biological effects on shark embryos. On the other hand, hypoxia causes a high embryo mortality rate. Additionally, hypoxia makes embryos more vulnerable to predators, because the increased tail beat frequency will enhance the release of chemical and physical cues that can be detected by predators. The shortening of the shark freeze response under hypoxia also makes the embryos more prone to predation.
Hypoxia impairs survival and alters immune and iron metabolism gene expression during shark early ontogeny
Publication . Martins, Sandra; Varela, Jaquelino; Félix, Rute; Santos, Catarina Pereira; Paula, José Ricardo; Power, Deborah Mary; Rosa, Rui
The global oxygen inventory has been declining worldwide, primarily due to climate change. The importance of oxygen for aerobic respiration and its homeostasis makes declining oxygen levels a concern, particularly during energy demanding lifecycle stages. The effects of low oxygen levels on neuroendocrine responses and immune competence of developing sharks were studied in the head and trunk tissues of early (EE; before pre-hatching) and late embryos (LE) of small-spotted catshark (Scyliorhinus canicula) under six days of deoxygenation (93 % O2 of air saturation) and hypoxic conditions (26 % O2). Catshark embryos were resilient to deoxygenation, with only a 10 % decline in survival compared to the control, and only the gene expression of melanotransferrin changed. Under hypoxia, growth was unaffected, but survival decreased by 31 % compared to the control in LE, highlighting an inadequate physiological response. Developmental stage affected the expression of hypoxiainducible factor 1 alpha (hif1a), iron metabolism and immune-related genes, pointing to critical response mechanisms. The EE stage had an optimised stress response under hypoxia compared to LE, with the upregulation of the hif1a gene. The lack of a protective response and compromised immune-related functions under hypoxia in LE raise concerns about species survival under climate change. These findings highlight the need for further research on the likely resilience of sharks to environmental challenges.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
9471 - RIDTI
Número da atribuição
PTDC/BIA-BMA/28609/2017