2012-08-30 | Press Release
Short-winged grasshoppers support new explanation of evolution
Darwin explained evolution through focusing on individuals which were most suited to surviving and reproducing the next generation of offspring. A research group under the leadership of Professor Anders Forsman at Linnaeus University reports that it is not just natural selection but differences in the animals' ability to disperse which can function as spatial filters and lead to rapid evolutionary changes. The results have been published in the Journal of Evolutionary Biology.
Pygmy grasshoppers are small insects which exhibit great variation in colour, form and behaviour, particularly with regards to flying ability. Individuals with long wings are able to fly to more favourable areas if local conditions undergo deterioration. The short-winged variant can however only disperse within a smaller area by hopping short distances. Researchers have discovered that the proportion of long and short-winged individuals varies greatly between different areas. The proportion of long-winged individuals also changes over time or following environmental / habitat destruction such as in the case of a forest fire for example.
Researchers caught grasshoppers from many different places in Sweden over a period of several years. The proportion of long-winged grasshoppers was considerably greater in the recently disturbed and altered areas in comparison with more stable habitats. In areas undergoing change, the proportion of long-winged grasshoppers fell as a function of the length of time following the disturbance. The proportion of long-winged individuals did not however change over time in the stable areas.
– As the pattern has been repeated in many populations we are certain that it depends on discrepancies in the grasshoppers' habitats, says Professor Forsman.
Why aren't all pygmy grasshoppers long-winged? The ability to fly costs a great deal of energy and it has therefore long been regarded the case that long-winged individuals need to pay a price in the form of lower reproductive ability. Short-winged individuals should therefore have an advantage in certain habitats.
– We don't however find any difference in the total number of offspring reproduced between the short and long-winged forms, explains Hanna Berggren whose independent degree project provided the basis for the now published study.
By following marked individuals in their natural environment, researchers discovered that pygmy grasshoppers do not stray far from their home environment which usually extends to a few meters over a period of several days. With the help of experiments, researchers could additionally show that the long-winged grasshoppers make use of their flight ability only in inhospitable environments.
– The variation in the ability and inclination to fly can explain the changes and differences we see between grasshoppers in different environments, explains Professor Forsman.
Researchers checked to see whether the differences in wing frequency between populations were hereditary by maintaining grasshoppers in a laboratory. Long-winged grasshopper females reproduced more long-winged offspring compared with short-winged variants. In addition, grasshoppers from areas which had undergone disturbance reproduced more long-winged offspring compared with grasshoppers from stable habitats despite the fact that immature grasshoppers developed under similar conditions. The differences in grasshopper wing size between places and over time are therefore hereditary and are not the result of access to food or other factor in the growth environment.
– This involves extremely rapid evolutionary changes, explains PhD student Jon Tinnert who has also worked with the study.
– What was most interesting with our study was the finding that the genetic differences between different types of environment can be explained by variation in the grasshoppers' dispersal ability and that evolutionary changes are thought to take place even when there has been a total absence of natural selection, says Professor Forsman.
Link to the journal website
Anders Forsman works at the Linnaeus University Centre for Ecology and Evolution in Microbial model Systems, one of Linnaeus University's cutting edge research group. You can read more about the group by following the link here.
Link to Anders Forsman's personal website
For pictures in printable format, contact christina.dahlgren_AT_lnu.se
Berggren, H., Tinnert, J. and Forsman, A. 2012. Spatial sorting may explain evolutionary dynamics of wing polymorphism in pygmy grasshoppers. Journal of Evolutionary Biology.
Anders Forsman, Professor, +46 (0)480-44 61 73, +46 (0)706-27 27 38, anders.forsman_AT_lnu.se
Christina Dahlgren, press officer, +46 (0)470-70 85 51, +46 (0)70-572 26 56