Running with the Red Queen: Host-Parasite Coevolution Selects for Biparental Sex
Levi T. Morran*, Olivia G. Schmidt, Ian A. Gelarden, Raymond C. Parrish II, Curtis M. Lively
Most organisms reproduce through outcrossing, even though it comes with substantial costs. The Red Queen hypothesis proposes that selection from coevolving pathogens facilitates the persistence of outcrossing despite these costs. We used experimental coevolution to test the Red Queen hypothesis and found that coevolution with a bacterial pathogen (Serratia marcescens) resulted in significantly more outcrossing in mixed mating experimental populations of the nematode Caenorhabditis elegans. Furthermore, we found that coevolution with the pathogen rapidly drove obligately selfing populations to extinction, whereas outcrossing populations persisted through reciprocal coevolution. Thus, consistent with the Red Queen hypothesis, coevolving pathogens can select for biparental sex.
Levi T. Morran*, Olivia G. Schmidt, Ian A. Gelarden, Raymond C. Parrish II, Curtis M. Lively
Most organisms reproduce through outcrossing, even though it comes with substantial costs. The Red Queen hypothesis proposes that selection from coevolving pathogens facilitates the persistence of outcrossing despite these costs. We used experimental coevolution to test the Red Queen hypothesis and found that coevolution with a bacterial pathogen (Serratia marcescens) resulted in significantly more outcrossing in mixed mating experimental populations of the nematode Caenorhabditis elegans. Furthermore, we found that coevolution with the pathogen rapidly drove obligately selfing populations to extinction, whereas outcrossing populations persisted through reciprocal coevolution. Thus, consistent with the Red Queen hypothesis, coevolving pathogens can select for biparental sex.
Science 8 July 2011: Vol. 333 no. 6039 pp. 216-218
Why is this cool?
If you are like me, sometimes you will stare at someone while they talk and think about something...anything. You may look at their body and wonder if anyone finds them attractive and then you wonder what it means to be attracted. Why is there attraction? Why can't we reproduce without a partner? Why do we need women? Why is love so cruel?
Today's researcher's may have ideas about the last question, but their work focuses on why two sexes ever evolved. The abstract states the following "The Red Queen hypothesis proposes that selection from coevolving pathogens facilitates the persistence of outcrossing despite these costs." They tested this with nematodes (Caenorhabditis elegans) which can reproduce asexually or with a mate. The nematodes were separated into two groups and one was grown in the presence of a pathogenic bacteria (Serratia marcescens) and the other was not. They found that the bacterially infected nematodes ceased to asexually reproduce and shifted to mating with a partner.
As a teenager, I often wondered why I yearned for love and that "other." You know, the someone who completes me and boils my thin blood. I am drawn towards the perfect Her not because I philosophically believe that someone else is necessary, but because my biology is pre-programmed that way.
It is startlingly to me that this compulsion for someone else is an evolutionary accident. Great poetry and prose are all the indirect result of some pathogen changing our evolutionary trajectory. Clint Eastwood may appear to be pretty bad ass in his movies, but he always comes off as some unnatural creature. He fights, revenges, and smokes, but he never has a partner dangling off his arm. His lack of partner feels off. In a world where humans reproduced asexually, Clint Eastwood would always have a mate.
