A study reveals how marine adaptations explain the longevity of whales and oceanic birds.

Barcelona (Spain), May 12 (EFE).- Living at sea requires a series of adaptations that improve individual survival and, therefore, promote longevity, according to a study by several scientific organizations from universities that sheds light on the mystery of the long lifespans of whales and other marine animals.

The research, published in the journal Nature Communications , was coordinated by the Institute of Evolutionary Biology (IBE) and CREAF (Center for Ecological Research and Forestry Applications), affiliated with the Autonomous University of Barcelona (UAB), with the participation of experts from CEAB-CSIC and the University of Barcelona (UB).

The research concludes that when terrestrial mammals and birds made the transition from land to sea, they evolved toward increasingly slower life strategies.

In nature, growing quickly and reproducing young is the most common life strategy because it reduces the risk of dying without leaving offspring, but not all animals follow this rule.

Humpback whales, for example, don't mature until they are 10 or 15 years old, and have only one calf every few years, so understanding the evolution of such slow life strategies remains one of the great enigmas of evolutionary biology.

Living in the sea requires a series of adaptations

This slowing of life is explained by the fact that living in the sea requires a series of adaptations that improve individual survival and promote a long life.

Researchers have shown that the ability to have a long reproductive life makes it possible to sustain low fertility and slower development.

According to Daniel Sol, first author of the study and a researcher at IBE and CREAF, the research demonstrates that "the evolution of slow lifespans is not simply the result of increasing mortality or reducing mortality risk, but also has to do with the colonization of new environments."

In the case of the marine ecosystem, he points out, "it poses major challenges, such as the difficulty of finding food in such a vast space," and these challenges "favor adaptations that protect individuals from the risk of dying from external factors."

Examining the present to understand the past

Since life strategies leave no trace in the fossil record, the study's authors had to investigate past evolutionary changes using phylogenetic information and evolutionary models.

The first step was to reconstruct the transitions from terrestrial and freshwater habitats to marine environments, using phylogenetic information from more than 90% of the bird and mammal species currently living on Earth.

They then combined this information with evolutionary models and were able to confirm that these transitions have been accompanied by adaptive adjustments in longevity, fertility, and development time.

According to Daniel Sol, "Although we understand quite well why some organisms live fast and die young, the reasons behind slower life strategies are less clear, although we do know that larger animals have a low metabolism, which slows aging."

"We also know that a reduced mortality risk favors longer lives because it allows selection to eliminate harmful genes and boost investment in body maintenance," he adds.

The challenges of living at sea

Life at sea is not easy, especially for animals whose ancestors lived on land, and finding food is particularly complicated, since prey is distributed over very large areas, and some live at inaccessible depths.

Marine species have had to "invent" new ways of feeding, often in the inhospitable and extreme environments of the planet's coldest oceans.

Adaptive innovations take a long time to develop, but once they do, they provide animals with a survival advantage that allows them to enjoy long lives.

Modern dangers for ancient survivors

The same traits that helped marine mammals and birds thrive for millions of years now make them vulnerable, the study notes, because the slow-moving lives of marine birds and mammals make their populations highly vulnerable to threats that affect adult survival.

These threats include ship collisions, noise pollution, entanglement in fishing nets, oil spills, and commercial fishing and hunting, and they have had little opportunity to adapt to these threats.

To make matters worse, since they also reproduce at a slow rate and the time between each generation is very long, this means that population recovery is slow and any evolutionary adjustment—if it's possible—takes a long time to occur. EFE

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