Desert tortoise scat microsatellite results

Sampling fecal droppings (scat) to genetically identify individual animals is an established method for monitoring mammal populations and could be highly useful for monitoring reptile populations. Whereas existing protocols for obtaining DNA from reptile scat focus on analyses of whole, fresh scat deposited during animal handling, the collection of scat naturally deposited by reptiles in situ, as required for non-invasive population monitoring, requires protocols to extract highly degraded DNA. Using surface swabs from such scats can reduce logistical challenges, ecological impacts, and zoonotic risks. We report on three related but independently designed studies of DNA analyses from scat swabs of herbivorous reptiles under natural desert conditions: two free-ranging desert tortoise species (Agassiz's desert tortoise, Gopherus agassizii, California, US, and Morafka's desert tortoise, G. morafkai, Arizona, US) and the common chuckwalla (Sauromalus atar) (Arizona, US, and Sonora, MX). We analyzed samples from both tortoise species with the same set of 16 microsatellites and chuckwalla samples with four mtDNA markers; studies also varied in swab preservation medium and DNA extraction method. Microsatellite amplification success, defined as ≥9 loci with amplification varied by species: 15% of samples for Agassiz's desert tortoise and 42% Morafka's desert tortoise. For chuckwallas, we successfully amplified and sequenced 50% of samples. Fragments up to 400 bp for tortoises and 980 bp for chuckwallas were successfully recovered from scat swab samples. This study demonstrates that genotypes can successfully be obtained from swabs of herbivorous reptile scat collected in the field under natural environmental conditions and emphasizes that repeat amplifications are necessary for estimating population genetic parameters.