The East African lakes: specialised and saturated communities?
Explosive speciation in cichlids has resulted in distinctively
structured cichlid-Cichlidogyrus communities in Eastern Africa.
Meta-communities in Lake Tanganyika (LT ) and the Lake Victoria
region (LV ) are more specialised, and less nested and connected
than those inferred for species elsewhere (Fig. 3; Appendix S1). Few
additional interactions were predicted (Fig. 5b) suggesting that most
are already known for the sampled species. This saturation of
interactions might be expected as new ecological opportunities, an
important determinant of interactions at the global scale, arise less in
comparatively stable lake ecosystems such as LT (Salzburgeret al. 2014). Newcomers to these systems might find little
opportunity to radiate (e.g. Koch et al. 2007). Furthermore,
simulations suggest that specialisation in a network can be a by-product
of adaptive radiation (Maynard et al. 2018).
Specialisation was particularly high for LT . Notably, host
repertoires were frequently not estimated for these parasite species as
many infect only single host species. These restricted host repertoires
(Fig. 5b) might also be an explanation for the poor performance of NLP
for the LT network as the input variables are by design identical
for duplicate interactions. The algorithms performed well for LVlikely because of the higher nestedness (Fig. 3). For instance, only one
recorded monogenean species infects deepwater cichlids from theLT tribe Bathybatini (Kmentová et al. 2016) whereas
co-infections for 36 host species in the LV community are
reported (Fig. 2b, Appendix S1.2). Species of LV might be more
interconnected than LT due the younger age of the host radiation
(0.4 M years; see, Salzburger et al. 2014), which left the
network less saturated. The Lake Victoria region has also experienced
rapid ecosystem degradation over the past century including the
introduction of a novel predator, Lates niloticus (L.), and
eutrophication causing the decline and extinction of many native fishes
(Marshall 2018). Environmental disturbance might have promoted the
expansion of host repertoires as new ecological opportunities arise and
parasites increase their change of survival through ecological fitting
(Brooks et al. 2019). For instance, Cichlidogyrus sp.
‘nyanza’ is one of the few species with a host repertoire more
determined by ecological parameters than the host evolution at least at
the recent evolutionary scale (Fig. 4), although this pattern might
emerge from the comparatively low genetic differentiation of theLV radiation (Salzburger et al. 2014). In conclusion,
cichlid-Cichlidogyrus communities in the East African lakes
appear more stable and saturated than those elsewhere. Yet the younger
age and environmental degradation might make LV a less stable
system than LT . Limitations of the dataset call for more
extensive sampling of host-parasite communities in these lakes to better
understand these interactions. Other lake systems, e.g. Lake Malawi
could be of particular interest for future comparative studies mirroring
the research conducted on the cichlid radiations in this region (e.g.
Duponchelle et al. 2008).