ECOSPHERE NATURALIST No guts, no glory: Gut content metabarcoding unveils the diet of a flower-associated coastal sage scrub predator PAUL MASONICK , MADISON HERNANDEZ, AND CHRISTIANE WEIRAUCH Department of Entomology, University of California, Riverside, 900 University Avenue, Riverside, California 92521 USA Citation: Masonick, P., M. Hernandez, and C. Weirauch. 2019. No guts, no glory: Gut content metabarcoding unveils the diet of a flower-associated coastal sage scrub predator. Ecosphere 10(5):e02712. 10.1002/ecs2.2712 Abstract. Invertebrate generalist predators are ubiquitous and play a major role in food-web dynamics. Molecular gut content analysis (MGCA) has become a popular means to assess prey ranges and specificity of cryptic arthropods in the absence of direct observation. While this approach has been widely used to study predation on economically important taxa (i.e., pests) in agroecosystems, it is less frequently used to study the broader trophic interactions involving generalist predators in natural communities such as the diverse and threatened coastal sage scrub communities of Southern California. Here, we employ DNA metabarcoding-based MGCA and survey the taxonomically and ecologically diverse prey range of Phymata pacifica Evans, a generalist flower-associated ambush bug (Hemiptera: Reduviidae). We detected predation on a wide array of taxa including beneficial pollinators, potential pests, and other predatory arthropods. The success of this study demonstrates the utility of MGCA in natural ecosystems and can serve as a model for future diet investigations into other cryptic and underrepresented communities. Key words: biodiversity; blocking primers; DNA detectability half-life; Eriogonum fasciculatum; food webs; intraguild predation; natural enemies. Received 24 January 2019; accepted 11 February 2019. Corresponding Editor: Karen A. Haubensak. Copyright: © 2019 The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. E-mail: [email protected] INTRODUCTION and endangered species (Polis and Holt 1992, Bampfylde and Lewis 2007, Hurd 2008, Gagnon Predatory arthropods can have profound et al. 2011, Chisholm et al. 2014). Fundamentally, it impacts on pollinator–plant communities as their enables biologists to unravel the complex dynamics presence may alter the behavior and abundance of and functions of ecosystems (Agrawal 2000). other flower-visiting insects and indirectly affect While much research has been devoted to natu- plant fitness (Dukas 2005, Jones 2010, Wirsing et al. ral enemies that specialize on pests (Sheehan 1986, 2010, Huey and Nieh 2017). Generalist ambush Landis et al. 2000, Snyder and Ives 2003, Choate predators can engage in a variety of trophic inter- and Lundgren 2015, Morgan et al. 2017), trophic actions, ranging from direct predation on both interactions involving generalist arthropod preda- pests and beneficial organisms to complex trophic tors in natural systems remain vastly understud- cascades through intraguild predation (Polis and ied. One such system is the coastal sage scrub McCormick 1987, Rosenheim et al. 1993, Finke and (CSS) or soft chaparral of Southern California. Denno 2004, Gagnon et al. 2011). A refined under- With a great diversity of endemic flora and fauna, standing of trophic interactions not only has impli- this habitat covers lower elevation portions of a cations for pest management, but also has complex Mediterranean-type scrub ecoregion that implications for the conservation of biodiversity is part of one of Earth’s biodiversity hotspots ❖ www.esajournals.org 1 May 2019 ❖ Volume 10(5) ❖ Article e02712 ECOSPHERE NATURALIST MASONICK ET AL. (Cowling et al. 1996, Myers et al. 2000). Once widespread perennial of CSS that serves as an widespread, CSS communities have become important resource for many arthropods includ- increasingly fragmented and altered through ing over 30 bee species (Kremen et al. 2002a,Mon- anthropogenic disturbance and the introduction of talvo and Beyers 2010). This plant is commonly, non-native species over the past two centuries although patchily, frequented by Phymata pacifica (Westman 1981, Minnich and Dezzani 1998, Lam- Evans (Hemiptera: Reduviidae), an ambush bug brinos 2000). As a result, many endemics of CSS native to CSS and a presumed generalist predator have become rare and some even endangered such of other flower-associated arthropods. Like crab as the California gnatcatcher, Polioptila californica spiders (Thomisidae; Llandres and Rodrıguez- californica Brewster (McCormack and Maley 2015), Girones 2011, Llandres et al. 2013, Huey and Nieh and the Quino checkerspot butterfly, Euphydryas 2017) and weaver ants (Gonzalvez et al. 2013), editha editha (Boisduval; Parmesan et al. 2015). ambush bugs can alter the foraging behavior of Coastal sage scrub and surrounding communi- other flower visitors. For example, pollinators will ties support a particularly high number of unique spend significantly less time foraging on flowers arthropods. Approximately 500 native bee species harboring these ambush predators than on vacant have been documented here (Michener 1979), flowers (Elliott and Elliott 1991, 1994). Given their many of which provide important services for flower-dwelling niche, a diverse range of prey natural, urban, and agricultural landscapes taxa are available to ambush bugs in CSS. Despite (Kremen et al. 2002b, Hernandez et al. 2009). this, the composition of their diet remains unclear. Despite recent concerns surrounding the general Over the past two decades, novel methods to decline of pollinators (Committee on the Status of delineate food-web linkages have been devised Pollinators in North America 2007, Potts et al. that eliminate the need for direct observation or 2010), little is known about the current status of the visual inspection of gut or fecal matter (King native pollinator populations in CSS. The fitness et al. 2008, Pompanon et al. 2012, Gonzalez- of many flowering plants relies largely on interac- Chang et al. 2016, Birkhofer et al. 2017). Among tions with pollinating insects; mutually, many the most commonly applied and successful insects require pollen and/or nectar from flowers approaches for gathering qualitative prey data is for sustenance and development (Tepedino 1979, DNA-based MGCA; Seric Jelaska et al. 2014, Kearns and Inouye 1997). Flowering plants which Rondoni et al. 2015, Roubinet et al. 2015, Sch- have evolved mutualistic relationships with speci- midt et al. 2016, Curtsdotter et al. 2018, Eitzinger fic pollinating insects are particularly vulnerable et al. 2018). This method provides a reliable to environmental changes (Gilman et al. 2012), means to examine the diets of small, cryptic and a reduction in the services provided by a arthropods that pre-orally digest their food such unique pollinator can negatively impact plant as spiders and true bugs (Heteroptera). To cap- populations (Wilcock and Neiland 2002, Romero ture the wide taxonomic range of a generalist and Koricheva 2011). Predatory arthropods are predator’s diet, DNA metabarcoding can be used also diverse and ubiquitous in CSS and influence to accumulate large amounts of prey data ecosystem dynamics (Burger et al. 2001, 2003). (Ji et al. 2013, Brandon-Mong et al. 2015). In Predation on pollinators may have strong indirect metabarcoding, large numbers of amplicon effects given that pollinators provide essential ser- sequences are derived via high-throughput vices for natural communities and help maintain sequencing and compared to existing barcode healthy ecosystems (Klein et al. 2007). The occur- databases for identification (Blaxter 2016). Of rence of predators on flowers may reduce pollina- studies on terrestrial arthropods that have uti- tor visitation, causing some pollinators to spend lized MGCA, many have focused on one or sev- less time at or avoid certain flowers, or potentially eral specific prey taxa (often pests) and relied on diminish the numbers of pollinators that share prey-specific primers to determine which natural mutualisms with rare native plants (Elliott and enemies are consuming those taxa in agroecosys- Elliott 1991, 1994, Reader et al. 2006, Romero tems (Harwood et al. 2007, Fournier et al. 2008, et al. 2011, Tan et al. 2013). Juen et al. 2011, Szendrei et al. 2014, Gomez-Polo California buckwheat, Eriogonum fasciculatum et al. 2015). A disproportionately small number Bentham (Polygonaceae), is a dominant and of studies have attempted to assess the diet range ❖ www.esajournals.org 2 May 2019 ❖ Volume 10(5) ❖ Article e02712 ECOSPHERE NATURALIST MASONICK ET AL. of generalist predators in natural communities (http://research.amnh.org/pbi/heteropteraspecies (Seric Jelaska et al. 2014). page). Non-reduviid buckwheat-associated arth- For this study, our attention focused on four ropods were also mounted and identified to the main objectives: I. determine whether native bees lowest taxonomic level possible using reference constitute the main group of prey of ambush specimens from UCR’s Entomology Research bugs in a CSS community; II. document the diet Museum, online searches (BugGuide.net), taxo- breadth of P. pacifica with respect to (1) the taxo- nomic keys (Goulet and Huber 1993, Triplehorn nomic diversity of prey (i.e., the number of dif- and Johnson 2005, Lawrence et al. 2010), and ferent families, genera, and species consumed) advice from specialists of various groups. These and (2) the