Comparison of Patterns of Genetic Variation and Demographic History in the Greater Sage-Grouse (Centrocercus urophasianus): Relevance for Conservation

Robert M Zink

doi:10.2174/1874453201407010019

Abstract

The greater sage-grouse (Centrocercus urophasianus) was once widespread in western North America but its range has contracted by an uncertain degree owing to anthropogenic and natural causes. Concern over population declines has led to its proposed listing as threatened under the U.S. Endangered Species Act. Detailed genetic and demographic analyses of this species throughout its range are available but heretofore have not been compared. Reduced genetic variability is often taken as a proxy for declining populations, but rarely are there quantitative population estimates with which to compare. I compared published mitochondrial DNA (mtDNA) control region sequences, microsatellite allele frequencies at seven loci, and estimates of numbers of males per lek, number of active leks, percent decline in the best population models, and the probability (P) of Ne < 50 in 30 years and P(Ne < 500) in 100 years, at two spatial scales, 45 local population samples and 16 larger aggregates of samples. When excluding the populations from the Columbia Basin, which show little genetic diversity and are statistical outliers, there were no consistent relationships between estimates of genetic variation and demographic trends across the remainder of the range at either spatial scale. A measure of inbreeding derived from microsatellite data was also not related to population trends. Thus, despite habitat reduction and range fragmentation, the greater sage-grouse does not exhibit expected genetic signatures of declining populations. Possibly, the mtDNA and microsatellite data are insufficiently sensitive to detect population declines that have occurred over the span of a half century. Alternatively, only when populations are reduced to the levels seen in the Columbia Basin will genetic effects be seen, suggesting that the bulk of the range of the greater sage-grouse is not currently in genetic peril.

Highlights

Many sources of biological information can guide management of threatened and endangered species
Lower than average levels of genetic variability are typically inferred to be a result of population declines
The variability in degree of decline provides an opportunity for assessing the congruence of estimates of population trends and genetic variation

Summary

Introduction

Many sources of biological information can guide management of threatened and endangered species. Measures of genetic variability and differentiation provide indirect historical information on whether populations have experienced bottlenecks or inbreeding, or have been isolated from exchanging individuals with other populations. Measures of demographic fluctuations through long-term population monitoring provide evidence on more recent population fluctuations. In theory, these two types of information should be complementary. Lower than average levels of genetic variability are typically inferred to be a result of population declines. 1293] noted that such populations “can suffer from inbreeding effects and can be more susceptible to parasitic agents and disease.”. Small populations can lose genetic diversity, which could hamper their ability to respond to new (or current) environmental challenges [2]. Slightly deleterious alleles might increase in frequency and result in lower individual fitness. Given the potential for genetic and demographic information jointly to inform conservation efforts, it is

Results

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Conclusion