Host repertoire: Host evolution shapes community structure
We inferred two main predictors of cichlid-Cichlidogyrusinteractions: host phylogenetic relationships and host environment. The
hosts’ evolutionary history can have a significant impact on the
structure of host-parasite networks (e.g. Mouillot et al. 2008a;
Braga et al. 2014, 2020). Here, we show that the realised host
repertoire of most species of Cichlidogyrus is determined more by
the hosts’ evolutionary history than their environment. First, host
repertoires differed more regarding the ecological niche than the
phylogenetic relationships as evidenced by a reduction of the mean
functional-phylogenetic distances (FPDist) with increasing phylogenetic
weight (Fig. 4). Second, FPDist estimates rarely differed from the null
distribution for increasing functional weight (but see C. sp.
‘nyanza’ ; Fig. 4). Third, estimates outside the null distribution
were underdispersed (clustered), i.e. lower than expected at random at
both the ancient and recent evolutionary scale (measured as MPD and MNTD
respectively). The strong phylogenetic influence and underdispersion are
associated with co-divergent evolution (Clark & Clegg 2017).
Co-divergence assumes that host and parasite phylogenies are
phylogenetically congruent (Page 2003; Hoyal Cuthill & Charleston
2012), a pattern that has already been observed for a number of species
of Cichlidogyrus (Vanhove et al. 2015). Congruence might
arise especially in younger parasite lineages that have experienced a
phase of isolation resulting in co-divergence (Agosta & Brooks 2020),
e.g. species of Cichlidogyrus infecting tropheine cichlids
(Vanhove et al. 2015), which arose 4.5–6.5 MYA (Schedel et
al. 2019).
Additionally, phylogenetic tracking might explain the role of the host
phylogeny on host repertoires. Even within the same ecosystem, parasites
are constrained to compatible ecological niches created by host
speciation (Russo et al. 2018). Consequently, phylogenetic
relationships are determinants of neotropical (Braga et al. 2014)
and Mediterranean (Desdevises et al. 2002) monogenean-fish
communities but also plant-pollinator, plant-frugivore (Rezende et
al. 2007), plant-mycorrhiza (Jacquemyn et al. 2011), and other
host-parasite networks (Mouillot et al. 2008). Yet natural (Birgi
& Euzet 1983; Birgi & Lambert 1986) and invasion-induced
(Jiménez-García et al. 2001; Šimková et al. 2019; Jorissenet al. 2020) host switches of species of Cichlidogyrushighlight that fundamental host repertoires might differ considerably
from the realised host repertoires estimated here. Monogeneans have the
capacity to infect new hosts and adapt to new environments (Bragaet al. 2014; Messu Mandeng et al. 2015; Nack et al.2016). Thus, conclusions drawn based solely on analyses of host
repertoires should be treated with caution.