Experimental insight into the process of parasite community assembly

Abstract

Community assembly is a fundamental process that has long been a central focus in ecology. Extending community assembly theory to communities of co-infecting parasites, we used a gastrointestinal nematode removal experiment in free-ranging African buffalo to examine the community assembly patterns and processes. We first asked whether reassembled communities differ from undisturbed communities by comparing anthelmintic-treated and control hosts. Next, we examined the temporal dynamics of assembly using a cross-section of communities that reassembled for different periods of time since last experimental removal. Next, we tested for evidence of assembly processes that might drive such reassembly patterns: environmental filtering based on host traits (i.e. habitat patches), interspecific interactions, priority effects and chance dispersal from the environmental pool of infective stages (i.e. the regional species pool). On average, reassembled parasite communities had lower abundance, but were more diverse and even, and these patterns varied tightly with reassembly time. Over time, the communities within treated hosts progressively resembled controls as diversity and evenness decreased, while total abundance increased. Notably, experimental removal allowed us to attribute observed differences in abundance, diversity and evenness to the process of community assembly. During early reassembly, parasite accumulation was biased towards a subordinate species and, by excluding stochastic assembly processes (i.e. chance dispersal and priority effects), we were able to determine that early assembly is deterministic. Later in the reassembly process, we established that host traits, as well as stochastic dispersal from the environmental pool of infective stages, can affect the community composition. Overall, our results suggest that there is a high degree of resiliency and environmental dependence to the worm communities of buffalo. More generally, our data show that both deterministic and stochastic processes may play a role in the assembly of parasite communities of wild hosts, but their relative importance may vary temporally. Consequently, the best strategy for managing reassembling parasite communities may also need to shift over time.

Within-Host Priority Effects Systematically Alter Pathogen Coexistence

“…Our work illustrates how between-host processes (prevalence and transmission) alter within-host dynamics via withinhost priority effects. To fully apply this framework to pathogen communities in other natural systems, we must understand how within-host priority effects function in species-rich pathogen and parasite assemblages (Budischak et al 2016). Further, we need to study whether within-host priority effects function in a discreet or continuous manner.…”

Tracking the assembly of nested parasite communities: Using β‐diversity to understand variation in parasite richness and composition over time and scale

“…spatial variation in exposure risk; Calabrese, Brunner, & Ostfeld, 2011) or interactions between dispersal and drift (e.g. priority effects; Budischak et al, 2016). Overall, parasite interactions and variation in host competency or exposure risk did not appear to be important processes in this system.…”

“…For example, by partitioning variance in community composition across scale and over time, Costello et al (2009) showed that temporal variation in gut microbiomes within the same individual was smaller than among‐individual variation, even on the same day, suggesting that different hosts selected particular microbial communities that remained distinct from other hosts’ microbiota over time. Temporal analyses of parasite community composition are still relatively rare (but see Budischak, Hoberg, Abrams, Jolles, & Ezenwa, 2016; Cohen et al, 2015; Fallon, Ricklefs, Latta, & Bermingham, 2004; Vidal‐Martínez & Poulin, 2003), and even fewer studies have longitudinally tracked parasite community composition across multiple distinct scales to infer the general processes driving assembly.…”

Bovine tuberculosis disturbs parasite functional trait composition in African buffalo

“…While the tick-borne parasites (e.g., TP, Anaplasma spp.) (22), Coccidia, nematodes, and flukes (21,46,47) were diagnosed by the presence of the parasite itself, the remaining parasites were considered present when a buffalo's antibody status went from negative to positive between 2 captures (48). Because buffalo are not known to clear Br (49) or BVDV (50,51), once an animal seroconverted, it was considered positive for the remainder of the study.…”

“…Investigators have begun to apply community ecological principles to the field of disease ecology to understand parasite interactions within a host (4,(11)(12)(13)(14)(15), although most studies still break existing networks of parasites into isolated pairwise comparisons (e.g., refs. [16][17][18][19][20][21][22] that may fail to capture the true dynamics of coinfection.…”