Detecting predation and scavenging by DNA gut-content analysis: a case study using a soil insect predator-prey system

Abstract

White grubs (larvae of Coleoptera: Scarabaeidae) are abundant in below-ground systems and can cause considerable damage to a wide variety of crops by feeding on roots. White grub populations may be controlled by natural enemies, but the predator guild of the European species is barely known. Trophic interactions within soil food webs are difficult to study with conventional methods. Therefore, a polymerase chain reaction (PCR)-based approach was developed to investigate, for the first time, a soil insect predator-prey system. Can, however, highly sensitive detection methods identify carrion prey in predators, as has been shown for fresh prey? Fresh Melolontha melolontha (L.) larvae and 1- to 9-day-old carcasses were presented to Poecilus versicolor Sturm larvae. Mitochondrial cytochrome oxidase subunit I fragments of the prey, 175, 327 and 387 bp long, were detectable in 50% of the predators 32 h after feeding. Detectability decreased to 18% when a 585 bp sequence was amplified. Meal size and digestion capacity of individual predators had no influence on prey detection. Although prey consumption was negatively correlated with cadaver age, carrion prey could be detected by PCR as efficiently as fresh prey irrespective of carrion age. This is the first proof that PCR-based techniques are highly efficient and sensitive, both in fresh and carrion prey detection. Thus, if active predation has to be distinguished from scavenging, then additional approaches are needed to interpret the picture of prey choice derived by highly sensitive detection methods.

Diversity and Antimicrobial Resistance of Salmonella enterica Isolates from Surface Water in Southeastern United States

“…However, detection of Salmonella in water samples can be complicated by factors such as fecal in- hibitors in nucleic acid-based detection assays (34), inhibitors from soil suspension in water samples (35), and a low number of cells requiring a large volume of sample. Thus, a key aspect of obtaining accurate assessments of the prevalence of Salmonella in irrigation water relies greatly on the availability of sensitive and specific detection methodologies.…”

Predation or scavenging? Thoracic muscle pH and rates of water loss reveal cause of death in arthropods

“…The importance of carrion in the diets of scavenging predators cannot be determined solely through gut content analysis. Although consumed carrion can be detected in gut contents (Foltan et al, 2005;Juen and Traugott, 2005), PCR-based methods cannot distinguish this class of resource from prey. Although information about the availability of fresh carcasses in the field might improve estimates of how much carrion predators consume (Foltan et al, 2005;Juen and Traugott, 2005), measuring predator number, carcass removal rates and carrion availability in the field poses logistic difficulties (Foltan et al, 2005), and may be infeasible for small taxa such as arthropods.…”

“…Although consumed carrion can be detected in gut contents (Foltan et al, 2005;Juen and Traugott, 2005), PCR-based methods cannot distinguish this class of resource from prey. Although information about the availability of fresh carcasses in the field might improve estimates of how much carrion predators consume (Foltan et al, 2005;Juen and Traugott, 2005), measuring predator number, carcass removal rates and carrion availability in the field poses logistic difficulties (Foltan et al, 2005), and may be infeasible for small taxa such as arthropods. The approach developed in this study could indicate the relative frequency of scavenging versus predation by central-place invertebrate foragers (Kasper et al, 2004;Tillberg et al, 2007;Wilson et al, 2009) because diet items can be obtained from returning individuals prior to consumption.…”

“…For these reasons, ecologists rely heavily on PCR-based methods (Symondson, 2002;Sheppard et al, 2004;Foltan et al, 2005;King et al, 2008) and stable isotope analyses (Kelly, 2000;Fiedler et al, 2007;Hood-Nowotny and Knols, 2007) to characterize species interactions and to infer trophic level. A major shortcoming of such methods, however, is their inability to differentiate killed prey from scavenged carrion for consumers that engage in both behaviors (Morris et al, 1999;Foltan et al, 2005;Juen and Traugott, 2005;Tillberg et al, 2007;King et al, 2008).…”

“…Considering that invertebrates comprise much of the global terrestrial animal biomass (Williams, 1960;May, 2000), the importance of invertebrate carrion as a resource for scavenging predators has received surprisingly little attention. Many predatory invertebrates can engage in facultative scavenging, including Amphipoda (Ide et al, 2006), Coleoptera (Sunderland and Sutton, 1980;Juen and Traugott, 2005), Decapoda (Wolcott, 1978), Dermaptera (Sunderland and Sutton, 1980), Diptera (Foltan et al, 2005), Hemiptera (Velasco and Millan, 1998), Hymenoptera ), Isopoda (Barradas-Ortiz et al, 2003, Litobiomorpha (Sunderland and Sutton, 1980), Neuroptera (Foltan et al, 2005) and Opiliones (Sunderland and Sutton, 1980). Several studies have identified ants as key scavengers of small invertebrate carrion (Fellers and Fellers, 1982;Fellers, 1987;Retana et al, 1991).…”