Genetic effects of roads on Northern Chihuahuan Desert populations of the lizard Uta stansburiana

Background/Question/Methods

Urbanization can have significant ecological effects on natural populations, including habitat fragmentation through increased road density. The effect of roads is of concern due to their potential impacts on wildlife movements. Roads may increase mortality rates, leading to inbreeding and decreased genetic diversity. In addition roads may isolate populations, causing disruption of gene flow among populations and eventually resulting in genetic differentiation. In this study we investigate how roads affect genetic diversity of side-blotched lizards (Uta stansburiana) in the northern Chihuahuan desert of New Mexico. We examined the genetic effects of two types of roads with expected differences in permeability to movement: an interstate highway (I-10) with heavy traffic and a rural country road (NM-9) with low traffic. Lizards were trapped on both sides of the road at three sites per road, plus one control site/road located 1000 m from the road. DNA was extracted and nine microsatellite loci were amplified. Microsatellite genotypes were examined for signatures of disrupted gene flow across roads. Genetic diversity was estimated by mean effective allelic richness and levels of heterozygosity. Genetic differentiation was estimated by pairwise F_ST values and Nei’s genetic distances between subpopulations.

Results/Conclusions

Genotypes were obtained for 144 individuals on both sides of each road from three sites, one from I-10 (n=63) and two from NM-9 (n=31, 50), a total of six sub-populations. Preliminary results indicate similar levels of genetic diversity within sub-populations. Mean effective allelic richness ranged from 1.9 to 2.3 alleles/locus. Mean heterozygosities over all loci ranged from 0.33 to 0.42. Pairwise F_ST values ranged from 0.008 to 0.023, indicating negligible genetic differentiation between all six sub-populations. Nei’s genetic distance also indicated low levels of differentiation, ranging from 0.01 to 0.032. Genetic isolation caused by roads is not supported by our results. Results indicated that all populations are genetically indistinguishable from each other, even populations separated by 50 km. Individuals from the control sites located away from the roads will help determine if genetic diversity is decreased near both roads. Genotypes from additional individuals from the remaining sites on both roads will provide further information about levels of population differentiation across the landscape. These results, combined with those from an associated demographic study, will aid in our understanding of how roads impact movement of individuals, and how those impacts affect genetic diversity of natural populations.