By Virginia Gewin of Nature magazine

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 Change.

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 years. 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.

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," says Ahmed Djoghlaf, executive secretary of the Convention on Biological Diversity, the United Nations treaty that commits signatories to develop national strategies to sustainably use and conserve biodiversity.

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.

Last year's adoption of a treaty to manage and share the economic benefits of the world's genetic resources with developing nations, the Nagoya Protocol, has also boosted interest in cataloging genetic diversity. "Countries are starting to invest more to document genetic aspects of species in their national jurisdictions, to better understand how to get reimbursed for their use," says Djoghlaf.

This article is reproduced with permission from the magazine Nature. The article was first published on August 18, 2011.