By pulling together more than ninety thousands publicly available data of genetic sequences from amphibians and terrestrial mammals, scientists from the Centre for Macroecology, Evolution and Climate at the University of Copenhagen developed the first global distribution map of intraspecific genetic diversity for terrestrial mammals and amphibians. The study, published on 30 September in the journal Science, shows that genetic diversity is generally higher in the tropics than in higher latitudes. It also shows that areas more impacted by humans, as urban areas and croplands, have reduced genetic diversity when compared to wilder regions.
Understanding what determines biodiversity is a major scientific challenge for the 21st century, especially in the light of global change. Biodiversity encompasses diversity at all levels of biological organization, from genetic diversity within populations, to species diversity within communities and the diversity of ecosystems in a landscape. However, most of the studies to date on the global patterns of biodiversity have been conducted at the species and ecosystem diversity levels. This is best illustrated by the fact that, despite recent rapid advances in sequencing technology and the availability of an ever-increasing amount of genetic sequence data in public repositories, we still lack crucial baseline information on genetic diversity, such as a global map of its distribution.
The scientists from the Centre for Macroecology, Evolution and Climate at the University of Copenhagen address this gap by providing the first global distribution map of intraspecific genetic diversity for terrestrial mammals and amphibians.
To achieve this they took advantage of the immense wealth of publicly available genetic sequences in GenBank and BOLD Systems repositories. They then developed bioinformatic tools to attach geographic coordinates to a total of 92,801 mitochondrial sequences (31,029 for amphibians and 61,772 for terrestrial mammals) and adapted a widely-used genetic diversity metric, nucleotide diversity, to explore how this diversity is distributed across the globe.
Andreia Miraldo, lead author, postdoctoral researcher, Centre for Macroecology, Evolution and Climate, University of Copenhagen »
They were able to calculate genetic diversity in hundreds of localities throughout the world, allowing the team to map, for the first time, the distribution of genetic diversity on Earth. This map and its functionalities have been made publicly available as a beta version via a webpage including instructions to understand full functionality of the mapping tool. One can use this tool to see the diversity of one or several species on a map of the world. It lets you explore the data underlying the paper in an interactive manner. Additionally, the site is based on google maps, so any functionality that google maps supports (such as zooming, terrain and national boundaries) can be used in this map.
Tropical regions (i.e., tropical Andes, Amazonia and the tropics of East Asia) not only contain the highest number of species on Earth, they also turn out to hold the highest amount of genetic diversity, the study shows. While the tropics constitute hotspots of genetic diversity, the study shows that it decreases when moving towards the Polar Regions. Co-author and Associate Professor David Nogués-Bravo, elaborates:
“Our results make it clear that the tropics really are the richest regions in terms of biodiversity at all levels, ranging from tiny genes to major ecosystems. On the contrary, we found very low levels of genetic diversity for amphibians in Western Europe. This suggests that the region’s long history of human presence and heavy alteration of nature, has taken its toll on genetic diversity. This leaves species in Europe and other areas altered by humans extra vulnerable to environmental change because low genetic diversity entails a higher risk of becoming extinct.”
Human activity has already transformed the surface of the Earth. Now it also seems to reduce genetic diversity within animals — putting them at higher risk of extinction. Mammals and amphibians living in areas heavily altered by humans, as urban areas and croplands, have reduced genetic diversity when compared to wilder regions. Therefore they have less prospects of adapting to changes in their environment. Lead author Andreia Miraldo explains:
“Having genetic variation within a population means that whilst some individuals die from changed conditions in their living environment, like an increase in temperature, others are able to survive because they are different at the genetic level and therefore possess different traits. In this sense, genetic diversity within species determines their ability to survive the increasing human impacts on the environment like climate change.”
(Source: Centre for Macroecology, Evolution and Climate press release, 29.09.2016)