A method for estimating population sex ratio for sage-grouse using noninvasive genetic samples

Area of Science:

• Wildlife ecology
• Conservation genetics
• Molecular ecology

Background:

• Population sex ratio is crucial for wildlife management and conservation.
• Estimating sex ratios can be challenging, especially for sexually monomorphic species or those with sex-specific detection probabilities.
• Noninvasive genetic sampling (NGS) offers a promising method for sex identification from various biological samples.

Purpose of the Study:

• To assess Polymerase Chain Reaction (PCR) success and error rates for sex identification in greater sage-grouse (Centrocercus urophasianus) using fecal samples.
• To investigate the impact of fecal sample exposure time on PCR success and error rates.
• To evaluate the precision and bias of different sex assignment criteria for population sex ratio estimation using simulation models.

Main Methods:

• Collected greater sage-grouse fecal samples and measured PCR success and error rates for W and Z chromosome amplification.
• Assessed how PCR success and error rates varied with sample exposure time.
• Employed simulation models to test three sex assignment criteria under various sample sizes and PCR replication levels.

Main Results:

• PCR success rates were found to be higher for female greater sage-grouse than for males.
• The choice of sex assignment criteria significantly influenced the bias and precision of sex ratio estimates.
• Simulation results highlighted the critical interplay between sex-biased PCR success, genotyping replicates, sample size, and true population sex ratio.

Conclusions:

• Noninvasive genetic sampling from fecal DNA holds significant potential for estimating sage-grouse population sex ratios.
• Careful consideration of sex-biased PCR success and appropriate sex assignment rules is essential for accurate sex ratio estimation.
• The methodology, with minor adaptations, could be applicable to numerous other species for sex ratio determination.