Increased frequency of scale anomalies and loss of genetic variation in serially bottlenecked populations of the dice snake, Natrix tessellata

Abstract

Documented demographic bottlenecks resultingfrom introductions of the dice snake to severallakes in Switzerland provide a rare opportunityto study the effect of serial bottlenecks onthe genetic properties of Natrixtessellata populations. We investigated twointroduced populations using informationderived from eight microsatellite markers. Bothintroduced populations had significantlyreduced levels of allelic diversity relative tonon-bottlenecked populations. The severity ofthe bottlenecks was underlined by thesignificant reduction in observed and expectedheterozygosity. The loss of allelic diversityand observed heterozygosity was stronger in theserially bottlenecked population than in thepopulation that was bottlenecked only once.From previous studies, scale anomalies wereknown to be more common in introducedpopulations relative to native populations. Weinvestigated whether the higher occurrence ofscale anomalies in introduced populations isassociated with individual heterozygosity andmean genomic diversity d 2. We founda significant relationship between theoccurrence of scale anomalies and individualheterozygosity but no significant relationshipbetween scale anomalies and the microsatellitespecific measurement, d 2, was found.Because of their known history, introducedpopulations in Switzerland may serve as a modelto demonstrate the effect of severe populationbottlenecks on genetic variability anddevelopmental stability in N. tessellata.The results therefore help to device strategiesfor the management and protection of endangerednatural N. tessellata populations.