335
14. Rhinonyssidae are another group of nasal mites, this time found in the respiratory tract of various birds (de Rojas et al. 2001).
15. Entonyssidae are endoparasites found in the lungs of snakes (Stiller et al. 1977).
9.5 The Origins of Parasitic Behaviour
Early derivative lineages of both acariform and parasitiform mites are not parasitic
and as noted above this lifestyle has clearly evolved several times independently
(Fig. 9.3, Table 9.1). This begs the question of how, and when, parasitism evolved.
The origins of lineages which infest specific groups of arthropods or vertebrates
may be constrained by the time when the host first appeared; see also De Baets and
Littlewood (2015); Warnock and Engelstädter (2021). Thus there has been considerable debate about which vertebrates were the original hosts of ticks, and correspondingly diverse estimates for tick origins from as young as the Devonian to as
late as the Cretaceous; see Chitimia-Dobler et al. (2018) for a review. The fossil
record of mites and ticks is largely unhelpful here as the few relevant fossils of parasitic lineages are restricted to amber deposits from the mid-Cretaceous onwards.
Earlier origins and/or radiations remain obscure.
Alternatively, the fossil record of the host, or molecular clock data for their likely
origins, could be used as a proxy here. For example, the monotypic mesostigmatid
family Manitherionyssidae lacks a fossil record and today is only found on pangolins. These unusual mammals have a fossil record going back to the Eocene and
molecular data suggests divergence from their sister group a little earlier in the Late
Cretaceous (Meredith et al. 2009). This data could be used to constrain the origins
of the mites as well. The problem with this line of reasoning is the implicit assumption that early members of parasitic clades used the same hosts as today. As noted
for flatworms (De Baets et al. 2015), biogeography and/or fossils calibrations if
available may represent more reliable guides to the origination of a given parasite—
as opposed to the fossil record of its modern host(s). Furthermore, we cannot
exclude the possibility of host switching (reviewed by Poulin 2011) in the past or
the utilisation of now extinct groups. A case in point would be bird ticks (Argasidae:
Argasinae), which are estimated to have split off from the other argasid subfamily
(the mammal parasites, Ornithodorinae) during the Triassic (234 Ma: Mans et al.
2012). This obviously predates the oldest definitive bird (Archaeopteryx: ca.
150 Ma), but perhaps earlier argasid ticks lived on [feathered?] dinosaurs; see also
Chitimia-Dobler et al. (2018).
Within hard ticks (Ixodidae) there is an estimated split between the so-called
prostriates (the genus Ixodes) and all other hard ticks (the Metastriata) which corresponds with the end-Permian mass extinction event (reviewed by Chitimia-Dobler
et al. 2018). This event in turn led to a major shift in vertebrate faunas. Ixodes ticks
are usually found on mammals today and we might speculate (Chitimia-Dobler
et al. 2018) that during the Triassic the prostriate (Ixodes) ticks became associated
with cynodonts, from which mammals eventually evolved, while the metastriates
9 Chelicerates as Parasites
14. Rhinonyssidae are another group of nasal mites, this time found in the respiratory tract of various birds (de Rojas et al. 2001).
15. Entonyssidae are endoparasites found in the lungs of snakes (Stiller et al. 1977).
9.5 The Origins of Parasitic Behaviour
Early derivative lineages of both acariform and parasitiform mites are not parasitic
and as noted above this lifestyle has clearly evolved several times independently
(Fig. 9.3, Table 9.1). This begs the question of how, and when, parasitism evolved.
The origins of lineages which infest specific groups of arthropods or vertebrates
may be constrained by the time when the host first appeared; see also De Baets and
Littlewood (2015); Warnock and Engelstädter (2021). Thus there has been considerable debate about which vertebrates were the original hosts of ticks, and correspondingly diverse estimates for tick origins from as young as the Devonian to as
late as the Cretaceous; see Chitimia-Dobler et al. (2018) for a review. The fossil
record of mites and ticks is largely unhelpful here as the few relevant fossils of parasitic lineages are restricted to amber deposits from the mid-Cretaceous onwards.
Earlier origins and/or radiations remain obscure.
Alternatively, the fossil record of the host, or molecular clock data for their likely
origins, could be used as a proxy here. For example, the monotypic mesostigmatid
family Manitherionyssidae lacks a fossil record and today is only found on pangolins. These unusual mammals have a fossil record going back to the Eocene and
molecular data suggests divergence from their sister group a little earlier in the Late
Cretaceous (Meredith et al. 2009). This data could be used to constrain the origins
of the mites as well. The problem with this line of reasoning is the implicit assumption that early members of parasitic clades used the same hosts as today. As noted
for flatworms (De Baets et al. 2015), biogeography and/or fossils calibrations if
available may represent more reliable guides to the origination of a given parasite—
as opposed to the fossil record of its modern host(s). Furthermore, we cannot
exclude the possibility of host switching (reviewed by Poulin 2011) in the past or
the utilisation of now extinct groups. A case in point would be bird ticks (Argasidae:
Argasinae), which are estimated to have split off from the other argasid subfamily
(the mammal parasites, Ornithodorinae) during the Triassic (234 Ma: Mans et al.
2012). This obviously predates the oldest definitive bird (Archaeopteryx: ca.
150 Ma), but perhaps earlier argasid ticks lived on [feathered?] dinosaurs; see also
Chitimia-Dobler et al. (2018).
Within hard ticks (Ixodidae) there is an estimated split between the so-called
prostriates (the genus Ixodes) and all other hard ticks (the Metastriata) which corresponds with the end-Permian mass extinction event (reviewed by Chitimia-Dobler
et al. 2018). This event in turn led to a major shift in vertebrate faunas. Ixodes ticks
are usually found on mammals today and we might speculate (Chitimia-Dobler
et al. 2018) that during the Triassic the prostriate (Ixodes) ticks became associated
with cynodonts, from which mammals eventually evolved, while the metastriates
9 Chelicerates as Parasites