Seasonally varying marine influences on the coastal ecosystem detected through molecular gut analysis

Abstract

Terrestrial predators on marine shores benefit from the inflow of organisms and matter from the marine ecosystem, often causing very high predator densities and indirectly affecting the abundance of other prey species on shores. This indirect effect may be particularly strong if predators shift diets between seasons. We therefore quantified the seasonal variation in diet of two wolf spider species that dominate the shoreline predator community, using molecular gut content analyses with general primers to detect the full prey range. Across the season, spider diets changed, with predominantly terrestrial prey from May until July and predominantly marine prey (mainly chironomids) from August until October. This pattern coincided with a change in the spider age and size structure, and prey abundance data and resource selection analyses suggest that the higher consumption of chironomids during autumn is due to an ontogenetic diet shift rather than to variation in prey abundance. The analyses suggested that small dipterans with a weak flight capacity, such as Chironomidae, Sphaeroceridae, Scatopsidae and Ephydridae, were overrepresented in the gut of small juvenile spiders during autumn, whereas larger, more robust prey, such as Lepidoptera, Anthomyidae and Dolichopodidae, were overrepresented in the diet of adult spiders during spring. The effect of the inflow may be that the survival and growth of juvenile spiders is higher in areas with high chironomid abundances, leading to higher densities of adult spiders and higher predation rates on the terrestrial prey next spring.

High-throughput sequencing for community analysis: the promise of DNA barcoding to uncover diversity, relatedness, abundances and interactions in spider communities

“…Examples include trophic niche differentiation within an adaptive radiation ( Fig. 4; Kennedy et al 2019), the effect of grazers on prey communities (Schmidt et al 2018), ontogenetic shifts in diet (Verschut et al 2019), and a stable diet despite differences in available prey communities along an elevational gradient (Eitzinger et al 2019). Improved resolution is often achieved by combining HTS-based gut content screening with stable isotope analysis (Hambäck et al 2016;Kennedy et al 2019).…”

“…These technologies enable simultaneous processing of DNA barcodes for thousands of specimens (Shokralla et al 2015;Srivathsan et al 2019;Meier et al 2016) with considerably improved phylogenetic resolution (Krehenwinkel et al 2019a). Metabarcoding makes it possible to characterize the species composition of whole communities (Cristescu 2014;Yu et al 2012) and identify the makeup of the predators' diets in an unprecedented detail (Piñol et al 2014;Verschut et al 2019). Recent developments even enable mobile DNA barcoding under remote field conditions (Menegon et al 2017;Pomerantz et al 2018).…”

Introduction: Special issue on species interactions, ecological networks and community dynamics – Untangling the entangled bank using molecular techniques

“…Thus, this microbial ecology example reveals new dimensions in the structuring of ecological interaction networks: Species groups can be linked by one group preparing the metabolic substrate for another, a concept perhaps less familiar to those of us working with macroscopic taxa. Verschut et al () address how local interactions may be affected by not just one environment, but by the flow of individuals and matter between neighboring realms. Targeting terrestrial spiders living on the sea shore, these authors show how spider diets change from predominantly terrestrial prey in early summer to predominantly marine prey (non‐biting midges) in late summer and autumn.…”

“…In terms of the types of interactions addressed, this Special Issue shows how molecular techniques can be applied to resolving mutualistic interactions such as pollen transport (Bell et al, ; Tiusanen et al, ) and seed dispersal (González‐Varo et al, ), antagonistic interactions including predator–prey interactions (Deagle et al, ; Eitzinger et al, ; Mata et al, ; Sint, Kaufmann, Mayer, & Traugott, ; Verschut, Strandmark, Esparza‐Salas, & Hambäck Walters et al, ), predator–prey‐and‐detritus interactions (Siegenthaler, Wangensteen, Benvenuto, Campos, & Mariani, ), host–parasitoid interactions (Gariepy et al, ; Kitson et al, ), host–symbiont interactions (Doña, Proctor, et al, ; Doña, Serrano, Mironov, Montesinos‐Navarro, & Jovani, ), plant–herbivore interactions (Bhattacharyya, Dawson, Hipperson, & Ishtiaq, ), plant–fungus interactions (Schröter et al, ; Sepp et al, ), plant–prey interactions (Littlefair, Zander, de Sena Costa, & Clare, ), fungus–fungivore interactions (Koskinen et al, ) and multifaceted interactions (Clare et al, ).…”

“…Verschut et al (2019) address how local interactions may be affected by not just one environment, but by the flow of individuals and matter between neighboring realms. Targeting terrestrial spiders living on the sea shore, these authors show how spider diets change from predominantly terrestrial prey in early summer to predominantly marine prey (non-biting midges) in late summer and autumn.…”