Mistletoes Play Different Roles in a Modular Host–Parasite Network

Abstract

Antagonistic interactions between host plants and mistletoes often form complex networks of interacting species. Adequate characterization of network organization requires a combination of qualitative and quantitative data. Therefore, we assessed the distribution of interactions between mistletoes and hosts in the Brazilian Pantanal and characterized the network structure in relation to nestedness and modularity. Interactions were highly asymmetric, with mistletoes presenting low host specificity (i.e., weak dependence) and with hosts being highly susceptible to mistletoe-specific infections. We found a non-nested and modular pattern of interactions, wherein each mistletoe species interacted with a particular set of host species. Psittacanthus spp. infected more species and individuals and also caused a high number of infections per individual, whereas the other mistletoes showed a more specialized pattern of infection. For this reason, Psittacanthus spp. were regarded as module hubs while the other mistletoe species showed a peripheral role. We hypothesize that this pattern is primarily the result of different seed dispersal systems. Although all mistletoe species in our study are bird dispersed, the frugivorous assemblage of Psittacanthus spp. is composed of a larger suite of birds, whereas Phoradendron are mainly dispersed by Euphonia species. The larger assemblage of bird species dispersing Psittacanthus seeds may also increase the number of hosts colonized and, consequently, its dominance in the study area. Nevertheless, other restrictions on the interactions among species, such as the differential capacity of mistletoe infections, defense strategies of hosts and habitat types, can also generate or enhance the observed pattern.Abstract in Portuguese is available in the online version of this article.

Range‐wide ecological niche comparisons of parasite, hosts and dispersers in a vector‐borne plant parasite system

“…According to the PNH, however, hosts would get infected only in areas climatically suitable for the parasite. Our results apparently also follow what a recent network analysis described as a non‐nested and modular interaction pattern (Genini et al ., ), in which each of four mistletoe species from the Brazilian Pantanal ( Psittacanthus cordata , Psittacanthus calyculatus , Phthirusa abdita and Phoradendron sp.) interacted with a particular set of hosts, with low host specificity, but with hosts highly susceptible to mistletoe infections.…”

“…Genini et al . () hypothesized that the modularity of infection in four mistletoe species from the Brazilian Pantanal derives from different seed dispersal systems, such that Psittacanthus species have many bird dispersers, whereas their Phoradendron species are dispersed by specialists.…”

Biotic factors associated with the spatial distribution of the mistletoe Psittacanthus calyculatus in a tropical deciduous forest of central Mexico

“…Psittacanthus seeds are dispersed by several species of birds, especially fly-catchers, thrushes, and tanagers (Genini et al, 2012). Psittacanthus calyculatus fruit production starts primarily during the dry season (Vázquez-Collazo and Geils, 2002) and begins in January and extends to May when most of TDF tree species remain leafless (Zamudio et al, 1992) and insect abundance is low.…”

Host specificity in parasitic plants—perspectives from mistletoes

“…Ecological networks most frequently fit nested or modular patterns (Genini et al 2012). Networks that are nested contain a few generalists that interact with one another and with specialist species, which allows for the persistence of specialists.…”

“…In modular networks, generalist species form sub-groups (modules) that interact more with the species within their module than they do with species in other modules. Network analysis (a test of modularity and nestedness) could be used to examine the structure of patterns of mistletoe–host interactions at the population, species, genera and family levels ( sensu Genini et al 2012) [ see Supporting Information—Appendix 1 ]. This should be supplemented by a more comprehensive reciprocal transplant analysis and a genetic study.…”