Influence of each host species on cross-species transmission
Some host species were more central in the networks of overlapping
epidemics (Figure 4), suggesting they might be more important for the
cross-species transmission of particular parasites. The eigenvector
centrality values depended on the host species and parasite species.
Only three parasite species, P. ramosa, B. paedophthorum, andS. cienkowskii , were sufficiently common to create epidemic
overlap networks large enough to calculate centrality values. Of those
parasites, cross-species transmission networks of P. ramosashowed some hosts (D. dentifera and D. retrocurva ) were
more central in the network (Fig. 4A, Kruskal–Wallis test, p = 0.01),
suggesting they may be more important for driving cross-species
transmission. For B. paedophthorum , host species also varied in
their centrality (Fig. 4B, Kruskal–Wallis test, p = 0.01). However, forS. cienkowskii , host species had indistinguishable centralities
(Fig. 4C, Kruskal–Wallis test, p = 0.46). Thus, although each parasite
(P. ramosa, B. paedophthorum, and S. cienkowskii ) commonly
infected multiple host species, the cross-species transmission dynamics
might be different because host centrality patterns differ across
parasite species; more specifically, in some cases (S.
cienkowskii ) the hosts all seem equally important, while in others
(e.g., P. ramosa ) only some hosts seem important for
cross-species transmission.
D. dentifera and D. retrocurva consistently had the
highest centrality values (Figure 4), suggesting they are more important
for cross-species transmission of certain parasite species. On the other
hand, the host species that were least central tended to vary depending
on parasite species (note letters in Fig. 4, and see Table S1 for a full
list of significant pairwise comparisons). D. parvula , D.
pulicaria , and Ceriodaphnia were all less important for
transmitting at least one parasite species. Besides D. dentiferaand D. retrocurva , no other host species had significantly higher
centrality than another. Thus, these two host species might be of
particular interest for future work on cross-species transmission in
these communities.
Broadly speaking, the three common multihost parasites—P.
ramosa, B. paedophthorum, and S. cienkowskii — appear to have
different patterns of cross-species transmission. For P. ramosa ,
two host species (D. dentifera and D. retrocurva ) were
likely most important for cross-species transmission because they had
higher centrality values on average (Figure 4A). For B.
paedophthorum only one host species (D. dentifera ) had higher
centrality values on average, while two different species (compared toP. ramosa ) had lower centrality values (Figure 4B). However, withS. cienkowskii , there were no differences across host species,
suggesting that host species identity is not an important driver of
patterns of cross-species transmission.