Metabarcoding analysis of different portions of the digestive tract of scorpions (Scorpiones, Arachnida) following a controlled diet regime shows long prey DNA half-life

Abstract

Molecular analysis of gut content is one of the widest used methods to investigate diet in arthropods. Stomach content analysis in some arthropods is particularly difficult, e.g., in arachnids, because they have external digestion and a low foraging frequency. Scorpions have a particularly low feeding frequency, and their diet information is scarce. In this work we explore a DNA metabarcoding approach to detect prey DNA in Vietnamese forest scorpions (Heterometrus laoticus) under a controlled diet regime. A different type of prey (crickets, mealworms, and cockroaches) was offered once every 3 weeks for a total of 9 weeks. To assess the most suitable part of the digestive system and extraction method to use for molecular diet analysis, we separately analyzed three different portions of the digestive tract of scorpions (mid-gut, hepatopancreas, and hindgut) using two different extraction methods (salt-out method and a customized beads-based protocol). We calculated the detectability half-life of the prey DNA for each digestive tract section. We detected all three targeted prey items, showing that in scorpions multiple predation events can be distinguished in the same specimen within its last 9 weeks of foraging activity. The hepatopancreas was the portion of the digestive tract that provided the best prey detection and the longest DNA detectability half-life (51 days), followed by the mid-gut (22 days) and the hindgut (16 days). We found no significant difference between the extraction methods used. However, the salt-out method was less effective in some of the PCRs and is therefore not recommended for molecular diet analysis.