Ploidy and Pollinators

Polyploidy (having more than two sets of chromosomes) has allowed plants to do some incredible things from an evolutionary perspective. It is now widely believed that polyploidy has played a role in the evolution of 45% - 70% of the flowering plants we know and love today. Having extra sets of chromosomes allows mutations to occur without harming important cellular processes. Despite this knowledge, very little has been done to investigate exactly how polyploidy manifests in terms of ecological interactions. Recently, however, research into this has unveiled some very interesting ways in which polyploidy may lead to speciation. One of these has to do with pollination.

You are probably more familiar with the effects of polyploidy in plants that you realize. Polyploid plants are often much larger and more robust than their diploid relatives and many of the horticultural species we plant in our gardens have been bred for this genetic quirk. Polyploids happen in nature as well and it has long been known that polyploid populations often naturally segregate themselves out in the wild. This has led to observations that polyploid plants are often more resistant to things like parasites and herbivores. Recently, researchers from the University of California, Santa Cruz took a look at diploid and polyploid populations of a plant called Heuchera grossulariifolia.

They wanted to see if naturally occurring populations of each experienced differences in pollinators. After observing flower visitation rates between each population, they found some surprising differences. Diploid plants were more often visited by small bees in the genus Lasioglossum whereas the polyploid populations were more often visited by bumblebees (genus Bombus). Though this may seem inconsequential, differences in pollinators can have huge effects on reproduction.

If different pollinators are visiting these separate populations then they are essentially reproductively isolated from each other. With little to no gene transfer between diploids and polyploids, each population may follow its own evolutionary trajectory. This very well could lead to speciation. How pollinators distinguish between the populations is not yet known. There are some morphological differences, however, subtle differences in chemical cues may also play a role. Either way, research like this is opening up some exciting new avenues for investigation.

Photo Credit: Paul Slichter (http://bit.ly/1IDFVo3) and Science and Plants for Schools (http://bit.ly/1yQykCu)

Further Research:
http://www.ncbi.nlm.nih.gov/pubmed/18724730