Barcoding a Quantified Food Web: Crypsis, Concepts, Ecology and Hypotheses

Abstract

The efficient and effective monitoring of individuals and populations is critically dependent on correct species identification. While this point may seem obvious, identifying the majority of the more than 100 natural enemies involved in the spruce budworm (Choristoneura fumiferana – SBW) food web remains a non-trivial endeavor. Insect parasitoids play a major role in the processes governing the population dynamics of SBW throughout eastern North America. However, these species are at the leading edge of the taxonomic impediment and integrating standardized identification capacity into existing field programs would provide clear benefits. We asked to what extent DNA barcoding the SBW food web would alter our understanding of the diversity and connectence of the food web and the frequency of generalists vs. specialists in different forest habitats. We DNA barcoded over 10% of the insects collected from the SBW food web in three New Brunswick forest plots from 1983 to 1993. For 30% of these specimens, we amplified at least one additional nuclear region. When the nodes of the food web were estimated based on barcode divergences (using molecular operational taxonomic units (MOTU) or phylogenetic diversity (PD) – the food web became much more diverse and connectence was reduced. We tested one measure of food web structure (the “bird feeder effect”) and found no difference compared to the morphologically based predictions. Many, but not all, of the presumably polyphagous parasitoids now appear to be morphologically-cryptic host-specialists. To our knowledge, this project is the first to barcode a food web in which interactions have already been well-documented and described in space, time and abundance. It is poised to be a system in which field-based methods permit the identification capacity required by forestry scientists. Food web barcoding provided an effective tool for the accurate identification of all species involved in the cascading effects of future budworm outbreaks. Integrating standardized barcodes within food webs may ultimately change the face of community ecology. This will be most poignantly felt in food webs that have not yet been quantified. Here, more accurate and precise connections will be within the grasp of any researcher for the first time.

Parasitism rate, parasitoid community composition and host specificity on exposed and semi-concealed caterpillars from a tropical rainforest

“…This is encouraging, as studies from other sites and biotopes are needed to confirm our hostspecificity analysis and they are likely to be very informative even if they do not have the resources to include both morphological and molecular species concept evidence. It also corroborates Kaartinen et al (2010) and Smith et al (2011) who showed that added molecular evidence for parasitoids had a low impact on food web parameters.…”

Complementary molecular information changes our perception of food web structure

“…The current results thus imply that the molecular methods are complementary, and that in future studies, traditional techniques such as rearing should (at the very least) be supported by these faster and less laborious molecular methods (but see SI Text, section 4 for further considerations). By determining the identity of the host (or prey) from the gut contents of the parasitoid (or predator) (30,35,61,62), and/or by directly identifying the parasitoid DNA from the host (36), molecular approaches also circumvent problems associated with the detection of the feeding event (e.g., [63][64][65], or the maturation of the parasitoid (66,67). Given the wide availability of PCR and the rapid advances in sequencing techniques, methods for detecting both hosts within parasitoids and parasitoids within hosts based on DNA barcodes is now an approach within reach for all ecologists (34,43).…”

Molecular tools reveal diets of insectivorous birds from predator fecal matter

“…Besides sequencing methodology, recent studies have expanded upon prey identification techniques to compare predator diet breadth and composition over time and across different habitats Razgour et al 2011). Further applications include revealing the prey of locally threatened species (Murray et al 2011), identifying natural predators of an economically important pest (Smith et al 2011), characterizing the microbial communities within the predators themselves (Scupham et al 2007), and quantifying prey consumption via real-time PCR techniques (Bowles et al 2011). Besides arthropod prey, molecular techniques were used to tease apart plant diets of herbivores via fecal samples enabling the separation of foraging niches (Corse et al 2010;Valentini et al 2009).…”