16
novel environment as a result of adaptations that have evolved under a different set
of circumstances. As applied to parasites, it means some parasites may be found in
host groups with which they did not have a long co-evolutionary history, and that
taxonomically different hosts may share similar parasites because they share similar
ecological niche and acquire similar parasite communities as a result of being
exposed to a similar suite of infective stages (Hoberg and Brooks 2008).
This is broadly comparable to convergent evolution, where phylogenetically disparate taxa evolve similar adaptations under similar circumstances. In this case,
such adaptations might have also predisposed them to being infected by similar
parasites. For example, various studies have found associations between an animal’s
diet and the composition of its parasite fauna (Poulin and Morand 2004). Many
parasites use trophic transmission, where the parasite is transmitted via the consumption of the infective stage in prey items as a mean of completing their lifecycles (Lafferty 1999), thus diet has a direct influence on the composition of their
internal parasites. Indeed, parasites can be used to infer the diet of an animal and in
contrast to stomach content, which can only provide a brief snapshot of what the
animal had recently consumed, the presence of a parasite species is a lasting indicator of an animal’s diet (e.g. Valtonen et al. 2010). In regards to fossil parasites of
extinct vertebrate hosts, this line of inference can be inverted. The likely diet of a
fossil animal might help us infer what kind of internal parasites we can expect to
find associated with it.
In some cases, the presence of parasite larvae in prey species which are consumed by many different types of predators can facilitate host switch across phylogenetically distant taxa. For example, Corynosoma australes is an acanthocephalan
commonly found in the gastrointestinal tract of pinnipeds, but they have also successfully parasitised Magellanic penguins (Spheniscus magellanicus) (HernándezOrts et al. 2017). Despite being from completely separate branches of amniotes, due
to the overlap in diet in both sea lions and penguins (in this case, fish), the latter
acquired a parasite which would usually complete its life-cycle in a marine mammal
host. Indeed, it seems that over long evolutionary time, endoparasitic helminths are
particularly apt at switching between phylogenetically distant vertebrate definitive
hosts and host-switching appear to be a common feature in their evolution (Poulin
and Morand 2004). Therefore, extant species occupying the same ecological niche
may provide a general approximation of the type of parasites that infect phylogenetically distant taxa that once occupied the same niche. For example, many of the
marine reptiles that lived during the Mesozoic filled similar ecological niches to
those occupied by extant marine mammals (Kelley and Motani 2015), and given
that some of those extinct marine reptiles such as ichthyosaurs and plesiosaurs
might have also been at least partially homeothermic (Bernard et al. 2010), there is
a strong possibility that they shared similar parasite communities to some modern
cetaceans.
Thus based on what is known about the ecology and host types of extant parasites, one can use information on the diet, habitat, morphology, physiology, phylogeny, and geological age of a given fossil taxon to infer what type of parasites were
potentially included in (or conversely, excluded from) its parasite community (see
T. L. F. Leung
novel environment as a result of adaptations that have evolved under a different set
of circumstances. As applied to parasites, it means some parasites may be found in
host groups with which they did not have a long co-evolutionary history, and that
taxonomically different hosts may share similar parasites because they share similar
ecological niche and acquire similar parasite communities as a result of being
exposed to a similar suite of infective stages (Hoberg and Brooks 2008).
This is broadly comparable to convergent evolution, where phylogenetically disparate taxa evolve similar adaptations under similar circumstances. In this case,
such adaptations might have also predisposed them to being infected by similar
parasites. For example, various studies have found associations between an animal’s
diet and the composition of its parasite fauna (Poulin and Morand 2004). Many
parasites use trophic transmission, where the parasite is transmitted via the consumption of the infective stage in prey items as a mean of completing their lifecycles (Lafferty 1999), thus diet has a direct influence on the composition of their
internal parasites. Indeed, parasites can be used to infer the diet of an animal and in
contrast to stomach content, which can only provide a brief snapshot of what the
animal had recently consumed, the presence of a parasite species is a lasting indicator of an animal’s diet (e.g. Valtonen et al. 2010). In regards to fossil parasites of
extinct vertebrate hosts, this line of inference can be inverted. The likely diet of a
fossil animal might help us infer what kind of internal parasites we can expect to
find associated with it.
In some cases, the presence of parasite larvae in prey species which are consumed by many different types of predators can facilitate host switch across phylogenetically distant taxa. For example, Corynosoma australes is an acanthocephalan
commonly found in the gastrointestinal tract of pinnipeds, but they have also successfully parasitised Magellanic penguins (Spheniscus magellanicus) (HernándezOrts et al. 2017). Despite being from completely separate branches of amniotes, due
to the overlap in diet in both sea lions and penguins (in this case, fish), the latter
acquired a parasite which would usually complete its life-cycle in a marine mammal
host. Indeed, it seems that over long evolutionary time, endoparasitic helminths are
particularly apt at switching between phylogenetically distant vertebrate definitive
hosts and host-switching appear to be a common feature in their evolution (Poulin
and Morand 2004). Therefore, extant species occupying the same ecological niche
may provide a general approximation of the type of parasites that infect phylogenetically distant taxa that once occupied the same niche. For example, many of the
marine reptiles that lived during the Mesozoic filled similar ecological niches to
those occupied by extant marine mammals (Kelley and Motani 2015), and given
that some of those extinct marine reptiles such as ichthyosaurs and plesiosaurs
might have also been at least partially homeothermic (Bernard et al. 2010), there is
a strong possibility that they shared similar parasite communities to some modern
cetaceans.
Thus based on what is known about the ecology and host types of extant parasites, one can use information on the diet, habitat, morphology, physiology, phylogeny, and geological age of a given fossil taxon to infer what type of parasites were
potentially included in (or conversely, excluded from) its parasite community (see
T. L. F. Leung