How Biological Responses May Help Avert Another Mass Extinction of Species

By Raghu Murtugudde

A recently published study in the journal Proceedings of the National Academy of Science documents how sea stars resort to rapid genetic selection when subjected to the shock of mortality due to a wasting disease. The ‘genetic selection’ in response to massive perturbation led to rapid evolution of a resilient genetic variant that will survive for many generations. Each species carries genes that may help it survive a perturbation like global warming. In some species, those genes begin to appear more frequently in newborns in response to the perturbation. This is called genetic selection – an increased frequency of a particular gene in response to environmental change or increased predation. Such biological response to ecological disturbance is a constant reminder that nature makes the rules while biology finds the loopholes.

Human activities, particularly increased carbon emissions and global warming combined with habitat alteration and destruction, are an inexorable perturbation to the ecosystem and species. Human-induced, or anthropogenic, distress is so rapid that many species fail to respond fast enough to survive. The anthropogenic extinction of many species is now called the ‘sixth extinction’. The previous five mass extinctions wiped out as many as 90% or more of extant species at the time and were caused by natural drivers like basalt floods (magma flows that last for millions of years like the process that formed the Deccan Plateau in India) or meteorite strikes.

Each of the historical mass extinctions opened up new environmental niches, which were quickly occupied by new species, leading to an increase in biodiversity. The response of species in the ‘sixth extinction’ will not be known for many centuries or millennia hence. A number of species like the sea stars do respond within our lifetime, and such responses provide excellent insights into evolutionary processes and their timescales as well as potential pathways to apply the advances in genetic science to mitigate the sixth extinction.

The drivers of the sixth extinction include decimation of megafauna, such as of the mammoth by hunter-gatherers, as well as the disappearance of many species of birds, insects and large animals due to global warming, urbanisation, habitat loss due to deforestation, forest degradation, pesticide use, air and water pollution, etc. There is documentary evidence of biological responses that correspond to each of these environmental changes that are either genetic selection or morphological changes.

It is important to focus on the negative ecological responses – from the dwindling polar bear population due to decreasing Arctic ice cover to the mysterious drop in bee population. At the same time, there are species that respond resiliently or even thrive under anthropogenic perturbations.

The wasting disease that struck the sea stars may not be directly attributable to humans but we do know that warming brings increased disease pressure because many microbes and pathogens respond positively to warmer temperatures. Biological responses more directly related to human perturbations are worth noting.

Coral bleaching due to warming and ocean acidification has been reported widely. Some corals on the other hand, such as those in the Gulf of Aqaba, are resistant to warming and acidification. This is similar to the species of corn that does well in hot and dry climate compared to others, which can survive only in relatively cooler and wetter climates. Rapid urbanisation has also elicited rapid evolution in resilience or adaptation among various birds and insects – from the feather colour of pigeons due to increased melanin, the wing span of sparrows reduced to manoeuvre through urban traffic and buildings, the altered notes of great tits to be heard over the urban din and the reduced attraction of moths to harmful artificial light.

Another example is a study (of which this author was a part) of how global warming itself produces unexpected environmental niches that are beneficial to some species. For example, warming’s effects on winds have been found to expand the region of upwelling or upward movement of colder, deeper waters around Isla Isabela, the largest island in the Galápagos archipelago. This expansion of local upwelling is associated with nutrient supply from the deep ocean and is thus rich in fish. This bounty of fish has led to a recovery of the Galápagos penguins, which were on the path to extinction.

While the sixth extinction may well be a justified narrative for human impact on biodiversity, it is important to use advances in genetics to explore novel ways to mitigate its scope. Can the genetic traits from the resilient species of corals or corn or sea stars be transplanted into their cousins that are less resilient or slower to adapt to human and natural environmental disturbances? Can artificial habitats be created following the example of Isla Isabela to provide shelter to species teetering on the edge of extinction? Many such efforts are underway at terrestrial and marine protected zones but the natural genetic resilience and capacity for adaptation of many species may offer bolder ways to expedite the slowing of the sixth extinction.

Raghu Murtugudde is a professor at the Earth System Science Interdisciplinary Centre, University of Maryland, and a visiting faculty member at IISER, Pune, and IIT Bombay.