Mangroves brave the northern cold despite reduced genetic variation

Climate change continues to alter the global environment. One common effect is that existing areas where a species lives can become inhospitable, while other areas become more suitable for the same species to move into. These changes in the liveable environment are most often seen at the edges of a species’ distribution, areas known as range margins. Range margins can be stressful places for organisms to live, as the conditions experienced are often at the limit of what a species can tolerate. At range margins, we also expect that species possess less genetic diversity than in areas where they are common. This lower genetic variation is thought to limit the ability of species to adapt to environmental changes. In research recently published in Molecular Ecology, John Paul Kennedy (a PhD student in the Ecological Genetics lab under the supervision of Dr Jennifer Rowntree and Prof. Richard Preziosi) used the cold-sensitive neotropical black mangrove (Avicennia germinans) to test this theory. John Paul worked with Dr Ilka Feller at the Smithsonian Institute, USA. He used a combination of genetic markers and leaf measurements to evaluate changes in genetic variation and cold tolerance in three currently-expanding, northern range margins across the southeast United States. He found that, although range margins did possess reduced genetic diversity, they also developed leaf traits to endure colder temperatures (thicker, shorter leaves).

“Responses to climate change at range margins have wide-reaching repercussions that extend from the level of the species itself to entire ecosystems. These changes have direct impacts on human well-being. Our research highlights that, for certain species, limited genetic variation at range margins may not prevent responses to climate change,” said John Paul Kennedy, lead author on this research. This open-access publication is available here. Kennedy, J. P., Preziosi, R. F., Rowntree, J. K., Feller, I. C. (2020). Is the central‐marginal hypothesis a general rule? Evidence from three distributions of an expanding mangrove species, Avicennia germinans (L.) L. Molecular Ecology. 2020;29: 704-719.

Figure © J. P. Kennedy 2020. Evaluation of the central‐marginal hypothesis (CMH) in Avicennia germinans from three distribution ranges in the United States (USA)