How closely do measures of mitochondrial DNA control region diversity reflect recent trajectories of population decline in birds?

Monitoring levels of genetic diversity in wild- life species is important for understanding population sta- tus and trajectory. Knowledge of the distribution and level of genetic diversity in a population is essential to inform conservation management, and help alleviate detrimental genetic impacts associated with recent population bottle- necking. Mitochondrial DNA (mtDNA) markers such as the control region have become a common means of sur- veying for within-population genetic diversity and detect- ing signatures of recent population decline. Nevertheless, little attention has been given to examining the mtDNA control region’s sensitivity and performance at detecting instances of population decline. We review genetic studies of bird populations published since 1993 that have used the mtDNA control region and reported haplotype diversity, number of haplotypes and nucleotide diversity as measures of within-population variability. We examined the extent to which these measures reflect differences in known demo- graphic parameters such as current population size, severity of any recent bottleneck and IUCN Red List status.Overall, significant relationships were observed between two measures of genetic diversity (haplotype diversity and the number of haplotypes), and population size across a number of comparisons. Both measures gave a more accurate reflection of recent population history in com- parison to nucleotide diversity, for which no significant associations were found. Importantly, levels of diversity only correlated with demographic declines where popula- tion sizes were known to have fallen below 500 individu- als. This finding suggests that measures of mtDNA control region diversity should be used with a degree of caution when inferring demographic history, particularly bottle- neck events at population sizes above N = 500.