How many sexually reproducing species are there?

Press release: Refraining from sex also has advantages

No. 14 - January 19, 2018

(pug) Sexual reproduction is the dominant form of reproduction in the animal and plant kingdoms. Nevertheless, there are species that reproduce partially or exclusively asexually. Surprisingly, these are often more common than their closest sexual relatives. The causes of this “geographical parthenogenesis” phenomenon have so far been controversial. An international research team from the Universities of Vienna and Göttingen has now developed a new computer model. The results are in the journal Ecology Letters published.

The dominance of sexual reproduction among more highly developed forms of life is impressive evidence of the evolutionary advantages of this form of reproduction. Nevertheless, there are also widespread and therefore obviously highly successful species in today's flora and fauna that largely do without sex. The term "geographic parthenogenesis" describes the fact that asexual species have a larger, often even much larger range than closely related sexual clans - especially in regions of the earth that were glaciated during the ice ages.

A flowering plant with classic geographical parthenogenesis is the Pyrenean buttercup (Ranunculus kuepferi). There is a sexually reproducing clan and an asexual clan of this species that reproduce with the help of unfertilized seeds. The asexual clan evolved from the sexual clan and, as is often the case with flowering plants, experienced a doubling of the chromosome set. At the end of the last Ice Age, both clans were only widespread in the south-western part of the French Alps. While the sexual clan is still limited to this region today, the asexual has now spread over almost the entire Alpine range. The biologists have now developed a computer model with which the spread of both clans can be reconstructed. "This enables us to simulate how the two clans emigrated after the Ice Age and how far they got differently," explains the head of the study, Prof. Dr. Stefan Dullinger from the Department of Botany and Biodiversity Research at the University of Vienna. "And we can test different hypotheses for their different success."

The project group around Prof. Dr. For the study, Elvira Hörandl from the Albrecht von Haller Institute for Plant Sciences at the University of Göttingen recorded the number of chromosome sets and reproductive biological data of the populations from the entire distribution area, which are the prerequisites for the simulation. In addition, they created a molecular dating that enabled the temporal classification of the spread. The computer simulations suggest that the asexual clan benefited above all from their greater resistance to cold, which made it easier for them to hike through the particularly high south-west Alpine mountain ranges around Mont Blanc. “Resistance to cold is presumably a consequence of the doubling of the chromosome set and is therefore only indirectly related to the renunciation of sexual reproduction,” explains Hörandl.

Asexual reproduction also has direct advantages, for example if both clans occur together. Pollinating insects then carry part of the pollen to the “wrong” flowers, whereby the asexual clan can block the further spread of the sexual ones, while the reverse is not the case. These and other simulations in the study suggest that geographic parthenogenesis cannot be reduced to a single cause. As is so often the case, it is the interplay of several factors that causes this conspicuous biogeographical pattern and makes it a complex phenomenon.

Original publication: Bernhard Kirchheimer et al. Reconstructing geographical parthenogenesis: effects of niche differentiation and reproductive mode on Holocene range expansion of an alpine plant. Ecology Letters 2018. Doi: 10.1111 / ele.12908.

Contact:

Prof. Dr. Elvira Hörandl
Georg-August-Universität Göttingen - Faculty for Biology and Psychology

Albrecht von Haller Institute for Plant Sciences

Department for Systematics, Evolution and Diversity of Plants (with herbarium)

Untere Karspüle 2, 37073 Göttingen, phone (0551) 39-7843

Email: [email protected], Internet: www.uni-goettingen.de/de/153591.html