What were the authors trying to test, and what predictions did they make?
The authors were trying to test the effects of road networks on genetic diversity and connectivity of populations. They predicted that roads and highways would reduce connectivity among populations of flora and fauna. The large number of roads is expected to hinder gene flow, and facilitate genetic drift. Under these conditions, species isolated by roads would likely lose genetic diversity. Population extinction rates are also expected to increase due to inbreeding and reduced evolutionary potential.
What, exactly, did the authors do?
The authors studied 27 populations of desert bighorn sheep. Over three years genetic samples of the sheep were collected across the study area, primarily by means of fecal pellets. Fourteen different microsatellite loci were genotyped. Female dispersal rates were also studied by examining mitochondrial DNA. Female bighorn sheep are less likely to disperse, so maternally transmitted mitochondrial DNA was used to study dispersal rates.
What did the authors find (i.e, what were their data)?
The authors found that “the amount of gene flow among populations was strongly and negatively correlated with barriers at interpopulation distances of less than 15 km.” Furthermore, gene flow was weakly and negatively correlated with barriers at distances between 15 and 30 km. The two variables were not correlated after distances of 30km. There was a low correlation of mitochondrial DNA diversity with both barriers and distance. Genetic simulations were also used, and showed that the genetic distance between populations could be influenced by barriers constructed only 40 years ago.
How did the authors interpret their findings?
The authors concluded that genetic diversity for bighorn sheep was negatively correlated with barriers, such as roads and highways. From the results, the authors estimate that genetic diversity had decreased by 15%, for populations completely isolated by barriers. The low correlation of mitochondrial DNA diversity with both barriers and distance may be due to low dispersal rates of the female sheep. Finally, the authors highlight the significance of their finding in a world with a rapidly increasing number of man made barriers “These results suggest that anthropogenic barriers constitute a severe threat to the persistence of naturally fragmented populations.” Underpasses and overpasses have been used successfully to aid in gene flow and help mitigate this issue.
Recent comments