genetic diversity

Climate change will hit genetic

diversity

Probable loss of 'cryptic' variation a challenge for conservationists.

Climate change represents a threat not only to the existence of individual species,

but also to the genetic diversity hidden within them, researchers say. The finding

promises to complicate assessments of how climate change will affect biodiversity,

as well as conservationists' task in preserving it.

DNA studies have revealed that traditional species, as defined by taxonomists,

contain a vast amount of 'cryptic' diversity — such as different lineages, or even

species within species. Carsten Nowak, a conservation biologist at the Senckenberg

Research Institutes and Natural History Museum in Gelnhausen, Germany, and his

colleagues have made a first attempt to understand how global warming might

affect this form of diversity. Their findings are published in Nature Climate Change1.

The team looked at aquatic insects living in the mountain streams of central Europe

— seven species of caddisfly, a mayfly and a stonefly. The insects were chosen

because they are likely to be especially vulnerable to rising temperatures — they

need cold water, and have limited ability to travel large distances.

To measure genetic diversity, Nowak's team sequenced genes in the animals'

mitochondria — energy-generating cellular organelles that have their own small

genome. This allowed the authors to divide each species into a number of

evolutionary significant units (ESUs) — the technical term for a population within a

species that is genetically distinct from the rest of its kind.

On the basis of where in Europe each ESU is found, the researchers then analysed

whether the associated insect would be able to tolerate higher temperatures or

move to somewhere cooler, using two models developed by the Intergovernmental

Panel on Climate Change (IPCC).

Lost potential

Under the IPCC's business-as-usual climate scenario, 79% of ESUs included in the

study are projected to become extinct by 2080; for a reduced-emissions scenario

this fell to 59%. ESUs suffered a much greater rate of extinctions than species.

This lost evolutionary potential could hinder species' ability to adapt to change.

"This genetic diversity is the most fundamental form of biodiversity — essentially,

it's the substrate for evolution," says Nowak. The study "shows how global climate change may lead to the loss of significant

amounts of hidden diversity, even if some of the traditionally defined species will

persist," says Michael Balke, an entomologist at the Bavarian State Collection of

Zoology in Munich, Germany.

What is not clear is how to extend this approach to other species with different

powers of migration or dispersal. "If researchers can figure out how to factor in

dispersal capacity — an attribute often not well-defined for individual species — the

potential impact on genetic diversity becomes a lot more applicable," says Jim

Provan, a molecular geneticist at Queen's University in Belfast, UK.

Study co-author Steffen Pauls of the Biodiversity and Climate Research Centre in

Frankfurt, Germany, agrees that such factors are also important. "We hope that this

approach will be developed further to incorporate different migratory abilities, types

of dispersal and thermal adaptability," he says.

Diversity danger zone

"For Europe, it turns out that the most genetically diverse regions are also the most

endangered," says Nowak. The study predicts that loss of genetic diversity in the

study insects will be greatest in the Mediterranean region, where all but two

populations are projected to become extinct. This is also the region with the

greatest genetic diversity.

This combination of genetic diversity and vulnerability has been found for other

Mediterranean species, such as the seaweed, Chondrus crispus, which has already

shifted northward during the past 40 years2. Many European species retreated to

the Mediterranean during past ice ages, meaning that their southerly populations

are especially ancient and diverse. The loss of these populations might compromise

species' ability to adapt to future warming.

Combining genetics and ecology should aid conservation efforts. "This study

highlights the huge potential of DNA-sequencing initiatives to reveal high levels of

cryptic diversity, of utmost importance to informed conservation decision making,"

says Balke.

Genetic diversity is gaining increased attention in conservation circles. "Through our

work to determine climate-adaptation strategies, we realize that genetics is one

way to get an overall better view of how species are affected by climate change,"