February 22, 2024

How elasmobranches adapt to a warmer world

Elasmobranches (which include sharks, rays and rays) have thrived for more than 450 million years and have survived Earth’s most dramatic climate shifts, including the five mass extinction events. Yet in today’s world of rapidly warming oceans, they face a new and enormous challenge.

Climate change.

A taboo word for some, climate change has revealed the importance of species’ ability to adapt to changing conditions, either by redistributing to more suitable thermal habitats or by demonstrating phenotypic plasticity and adaptation. The key to understanding this challenge lies in the context of their ecology and mobility, as the extent to which a species can move and adapt to new environments plays a crucial role.

This also applies to sharks and their relatives. Elasmobranchs range from the elusive tiger shark to the resilient epaulette shark, the versatile blacktip reef shark and the adaptable Atlantic stingray. With more than 1,000 species under the “elasmobranch” label, each creature brings its unique strategies to the table to combat rising temperatures and changing environments.

Recent research suggests that the ability to redistribute to optimal thermal habitats and exhibit phenotypic plasticity or adaptation is often related to a species’ ecology, with mobility being a key factor. At the forefront of adaptation is behavioral plasticity, the authors emphasize. A strategy used by many elasmobranchs to navigate a changing world, the tiger shark (Galeocerdo cuvier), known for its worldwide distribution in tropical and temperate waters, illustrates this beautifully. These majestic creatures choreograph their oceanic movements based on temperature gradients, ensuring they stay in conditions that approximate their thermal optimal conditions. This kind of precision in behavioral thermoregulation allows them to optimize their performance and maintain desired body temperature.

But what if a shark doesn’t undergo the long-distance migrations that tiger sharks do? Well, that doesn’t mean they can’t exhibit behavioral thermoregulation too! The blacktip reef shark (Carcharhinus melanopterus), which prefers shallow coral reefs, is a good example of behavioral thermoregulation that matches the thermal variability of its environment. They optimize their living conditions and maintain a relatively narrow thermal window that suits their specific needs. This adaptation makes these sharks resilient in their native ecosystems, allowing them to find the perfect balance between temperature and performance.

In contrast, species such as the epaulette shark (Hemiscyllium ocellatum), located in Australia’s Great Barrier Reef, emphasize physiological plasticity as a means of coping with temperature fluctuations. This remarkable species has become accustomed to harsh conditions, including dramatic daily temperature changes. As a result, their physiology exhibits robustness when faced with low oxygen levels, high carbon dioxide concentrations and significant thermal fluctuations. This adaptability is key to their survival and helps them maintain their performance under rapidly changing conditions.

Although some elasmobranchs exhibit behavioral plasticity and others exhibit physiological plasticity, some species can use both strategies. These are the sharks and rays that live in estuaries and experience large temperature fluctuations, such as the Atlantic stingray (Hypanus sabinus). These animals have a combination of traits that allow them to thrive in conditions ranging from 33.26°F to 109.4°F (0.7°C to 43°C) and demonstrate adaptability not just through their own actions, but also across generations. Pregnant females are known to regulate their temperature during pregnancy to accelerate embryonic development, preferring warmer temperatures. However, some individuals migrate seasonally to deeper waters during the winter months, indicating some degree of behavioral plasticity when necessary.

What mechanisms drive these incredible adaptations in elasmobranchs, allowing them to navigate our planet’s warming waters? The answers lie at different levels of biological organization. At the organismal level, metabolic rates are a central aspect of adaptation. Elasmobranches adapt their metabolic properties, blood oxygen transport capacity, and ability to reduce reactive oxygen species in response to changing environmental conditions. This fine-tuning of metabolic processes is crucial for survival in times of warming oceans.

At the cellular level, mitochondria play a crucial role in the response to temperature stress. Elasmobranches exhibit modified mitochondrial structures and functions as part of their adaptive strategy. These subtle changes at the cellular level allow them to maintain critical metabolic functions even as their environment warms. Furthermore, gene regulation (at the molecular level) is an essential mechanism underlying phenotypic plasticity. The ability to upregulate genes related to metabolic functions, stress responses, and immune responses in response to changing conditions is a powerful tool for adaptation. For elasmobranchs, these genetic responses can help them survive and thrive in the face of environmental stressors.

Despite the important role that elasmobranchs play in marine ecosystems, we know surprisingly little about their responses to climate change, the authors point out. Their long lifespan, limited mobility, and the logistical challenges of studying them have made it difficult to collect comprehensive data. However, with modern technology and innovative research approaches, scientists are beginning to bridge the gap in our understanding of elasmobranchs’ ability to adapt and acclimate. By studying these remarkable creatures, we can not only gain insight into their evolutionary history, but also valuable information for conservation efforts and ecosystem management. Elasmobranchs are often hailed as one of the most important stewards of our oceans, and their ability to adapt to a changing climate is not just a matter of survival for them – it is also a key factor in the health of the most extensive and critical areas in the world. ecosystems. As climate change continues to threaten marine ecosystems, the lessons we learn from these ancient survivors will be invaluable in shaping our future.

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