Consuming alternative prey does not influence the DNA detectability half-life of pest prey in spider gut contents

Abstract

BackgroundKey natural enemy-pest interactions can be mapped in agricultural food webs by analysing predator gut content for the presence of a focal pest species. For this, PCR-based approaches are the most widely used methods providing the incidence of consumption of a focal pest in field sampled predators. To interpret such data the rate of prey DNA decay in the predators’ gut, described by DNA detectability half-life (t1/2), is needed. DNA decay may depend on the presence of alternative prey in the gut of generalist predators, but this effect has not been investigated in one of the major predatory arthropod groups, spiders.MethodsIn a laboratory feeding experiment, we determined t1/2 of the key cereal pest virus vector leafhopper Psammotettix alienus in the digestive tracts of its natural enemy, the spider Tibellus oblongus. We followed the fate of prey DNA in spiders which received only the focal prey as food, or as an alternative prey treatment they also received a meal of fruit flies after leafhopper consumption. After these feeding treatments, spiders were starved for variable time intervals prior to testing for leafhopper DNA in order to establish t1/2.ResultsWe created a PCR protocol that detects P. alienus DNA in its spider predator. The protocol was further calibrated to the digestion speed of the spider by establishing DNA decay rate. Detectability limit was reached at 14 days, where c. 10% of the animals tested positive. The calculated t1/2 = 5 days value of P. alienus DNA did not differ statistically between the treatment groups which received only the leafhopper prey or which also received fruit fly. The PCR protocol was validated in a field with known P. alienus infestation. In this applicability trial, we showed that 12.5% of field collected spiders were positive for the leafhopper DNA. We conclude that in our model system the presence of alternative prey did not influence the t1/2 estimate of a pest species, which makes laboratory protocols more straightforward for the calibration of future field data.

Molecular diet analysis enables detection of diatom and cyanobacteria DNA in the gut of Macoma balthica

“…Unlike previous studies that looked at the prevalence of prey DNA in e.g. insect and spider consumers [ 25 , 29 , 33 , 35 – 38 ], we found no consistent increase in phytoplankton detection or linear decrease in the guts of the clam M . balthica following feeding.…”

“…balthica following feeding. Additionally, we likely required more sampling time points such as sooner after feeding (within 30 minutes) to detect initial increases in phytoplankton DNA [ 32 ], as well as longer than one week after feeding to capture the decrease in phytoplankton DNA detection [ 33 ]. For example, [ 33 ] still detected prey DNA in spiders after 14 days, while [ 36 ] and [ 38 ] did not detect prey DNA in spiders after 5 days.…”

“…Additionally, we likely required more sampling time points such as sooner after feeding (within 30 minutes) to detect initial increases in phytoplankton DNA [ 32 ], as well as longer than one week after feeding to capture the decrease in phytoplankton DNA detection [ 33 ]. For example, [ 33 ] still detected prey DNA in spiders after 14 days, while [ 36 ] and [ 38 ] did not detect prey DNA in spiders after 5 days. As our study is the first investigation into benthic detritivore feeding by qPCR that we are aware of, and most work involving time of prey detection (from a few hours to 14 days) has been performed on terrestrial invertebrates (insects and spiders; [ 23 ]), the gut residence time detection in benthic invertebrates will require further calibration.…”

“…This is important for understanding food web energetics, and for any future studies that use molecular methods to determine diet, as the length of time prey DNA is detectable has been shown to depend on: predator species identity [ 24 , 25 ]; prey species identity [ 26 , 27 ]; temperature [ 28 , 29 ]; and meal size [ 30 , 31 ]. Other studies have found that prey DNA is detectable in predators from only a few hours to several weeks [ 32 , 33 ]. qPCR has increased our knowledge of diet and trophic links in terrestrial invertebrates [ 24 , 27 , 34 – 38 ], aquatic vertebrates [ 21 , 29 , 39 , 40 ] and pelagic invertebrates [ 32 , 41 – 45 ].…”

Different groups of ground‐dwelling spiders share similar trophic niches in temperate forests

“…The simultaneous consumption of several prey types usually does not distort the amplification results for each single prey group (Fülöp et al ., 2019), but we cannot confidently say that all possible positive trophic relationships were revealed considering the high rates of DNA degradation in guts (Pompozzi et al ., 2019). This is especially true for external digestive system of spiders (Juen & Traugott, 2005; Sheppard et al ., 2005; Kuusk et al ., 2008), where digestion time is also affected by many external factors, including the amount and composition of consumed prey.…”