Measuring the flow of transgenes from GM crops into wild plants

Gene flow under contrasting levels of human disturbance

Gene flow under con­trast­ing levels of human disturbance

Rapid devel­op­ment of bio­tech­no­logy offers new oppor­tun­it­ies to ensure our future food sup­ply. Novel traits can be intro­duced into crops by trans­gene tech­no­logy more effi­ciently than by con­ven­tional crop breed­ing. Since the first com­mer­cial­iz­a­tion of a genet­ic­ally mod­i­fied (GM) crop in 1996, the global area of GM crops has grown stead­ily and reached 170·3 mil­lion hec­tares in 2012. Increasing num­bers of GM crops with dif­fer­ent traits are being pro­duced and released into the envir­on­ment. The intro­duc­tion of new trans­genes into crops has raised con­cerns about pos­sible neg­at­ive effects on the envir­on­ment. Transgenes could move from crops into wild rel­at­ives via gene flow. Depending on the nature of the trans­gene and its product, such trans­gene flow may lead to unwanted eco­lo­gical and evol­u­tion­ary con­sequences in wild populations

The pro­cess of trans­gene flow from crops into wild rel­at­ives involves sev­eral steps: first, the form­a­tion of crop–wild hybrids with a trans­gene through hybrid­iz­a­tion between crops and wild pop­u­la­tions; second, the estab­lish­ment of the trans­gene in local wild pop­u­la­tions through back­cross­ing with wild plants; third, the spread of the trans­gene across the whole meta­pop­u­la­tion of the wild spe­cies via pol­len and seed dis­persal. The major­ity of pre­vi­ous stud­ies have focused only on eval­u­at­ing the first two steps of trans­gene intro­gres­sion. A recent paper in Annals of Botany exam­ines the role of meta­pop­u­la­tion dynam­ics in trans­gene spread.

Wild pop­u­la­tions close to crop fields are usu­ally strongly affected by human dis­turb­ance. Habitat loss and frag­ment­a­tion due to human dis­turb­ance may alter the level of gene flow among patches and the rate of patch turnover. If gene dis­persal becomes lim­ited under strong human dis­turb­ance, the dis­tri­bu­tion pat­tern of genetic diversity may change dra­mat­ic­ally in the meta­pop­u­la­tion. In this case, a newly emerged gene, such as a trans­gene in a local wild pop­u­la­tion, may not be able to spread through the meta­pop­u­la­tion. Conversely, human-mediated dis­persal may enhance con­nectiv­ity among pop­u­la­tions in areas where anthro­po­genic dis­turb­ance is high, which would lead to increased spread of an escaped trans­gene. However, it is dif­fi­cult to study the effects of human dis­turb­ance and asso­ci­ated hab­itat changes on gene flow, because find­ing intact wild pop­u­la­tions as con­trols is hard and the effects of other factors may inter­fere with those of human disturbance.

The authors com­pared his­tor­ical and con­tem­por­ary pat­terns of gene flow in a wild car­rot meta­pop­u­la­tion, test­ing the null hypo­thesis that human dis­turb­ance did not change gene flow in the meta­pop­u­la­tion and that con­tem­por­ary gene flow was sim­ilar to his­tor­ical gene flow in wild car­rots and aim­ing to answer the fol­low­ing questions:

  1. What is the rate of gene flow in the wild car­rot metapopulation?
  2. Is con­tem­por­ary gene flow equal to his­tor­ical gene flow in the wild car­rot metapopulation?
  3. How does the rate of gene flow affect the chance of trans­gene intro­gres­sion into the wild car­rot metapopulation?

They found that the con­tem­por­ary gene flow was five times higher than the his­tor­ical estim­ate, and the cor­rel­a­tion between them was very low. Moreover, the con­tem­por­ary gene flow in road­sides was twice that in a nature reserve, and the cor­rel­a­tion between con­tem­por­ary and his­tor­ical estim­ates was much higher in the nature reserve. Mowing of road­sides may con­trib­ute to the increase in con­tem­por­ary gene flow.

AJ Cann. ORCID 0000-0002-9014-3720

Alan Cann is a Senior Lecturer in the School of Biological Sciences at the University of Leicester and Internet Consulting Editor for AoB.