Host taxonomy constrains the properties of trophic transmission routes for parasites in lake food webs

Abstract

Abstract. Some parasites move from one host to another via trophic transmission, the consumption of the parasite (inside its current host) by its future host. Feeding links among free-living species can thus be understood as potential transmission routes for parasites. As these links have different dynamic and structural properties, they may also vary in their effectiveness as trophic transmission routes. That is, some links may be better than others in allowing parasites to complete their complex life cycles. However, not all links are accessible to parasites as most are restricted to a small number of host taxa. This restriction means that differences between links involving host and non-host taxa must be considered when assessing whether transmission routes for parasites have different food web properties than other links. Here we use four New Zealand lake food webs to test whether link properties (contribution of a link to the predator's diet, prey abundance, prey biomass, amount of biomass transferred, centrality, and asymmetry) affect trophic transmission of parasites. Critically, we do this using both models that neglect the taxonomy of free-living species and models that explicitly include information about which free-living species are members of suitable host taxa. Although the best-fit model excluding taxonomic information suggested that transmission routes have different properties than other feeding links, when including taxonomy, the best-fit model included only an intercept. This means that the taxonomy of free-living species is a key determinant of parasite transmission routes and that food-web properties of transmission routes are constrained by the properties of host taxa. In particular, many intermediate hosts (prey) attain high biomasses and are involved in highly central links while links connecting intermediate to definitive (predator) hosts tend to be dynamically weak.

Food web structure selects for parasite host range

“…Understanding parasite host range is a longstanding goal in evolutionary ecology [1], and here I demonstrate an important role for food web structure to influence the host range of complex life cycle parasites. This neglected selective force may help to explain the observed host range of many parasitic helminth species, in combination with other factors including geography, host traits and parasite community structure [23,24]. Importantly, parasites are more than simply perturbators of the food webs of their hosts and are themselves potentially experiencing strong selection pressure from the food webs they inhabit.…”