182
developed more specialized host infection strategies. Mucous threads secreted
through the exhalent siphon of the freshwater cyrenid (Cardiida) Corbicula fluminea are known to facilitate its downstream or even interstream transportation
because they act as a draglines, when tangled to the fish or bird (Prezant and
Chalermwat 1984; Kimura et al. 2004; Haag 2012). If such entanglement may be an
advantage of upstream dispersal, the relation between fish and glochidium may have
arose initially as a phoretic relationship (Watters 2001; Barnhart et al. 2008; Haag
2012). Strayer (2008) reports an example of rapid dispersal of Lampsilis cardium,
into the Potomac basin as a consequence of the introduction of its host, the smallmouth bass (Micropterus dolomieu). Actual dispersal due to phoresis is related to
dispersal abilities of host fish. Unionoids today often parasitize small benthic fishes,
with limited mobility, so their dispersal may be low (Watters 1992; Haag and Warren
2003; McLain and Ross 2005; Blazek and Gelnar 2006; Strayer 2008; Schwalb
et al. 2011b; Vaughn 2012). Dispersal of mussels associated with mobile or migratory species may be higher (Sepkoski and Rex 1974; Schwalb et al. 2011a; Lellis
et al. 2013; Terui et al. 2014). Still, many species of unionoids are capable of parasitizing several species of fish, ranging from mobile to mobility limited forms (e.g.
Blazek and Gelnar 2006; Van Snik Gray et al. 2009; St. John White et al. 2017).
Barnhart et al. (2008) and Haag (2012) propose that unionoids might have routinely dispersed on fish, being solely attached by the larval threads—before acquiring a firmer attachment, by clamping the valves on the fish tissue. The latter could
cause harm to the fish, initiating a wound reaction (which facilitates encapsulation),
but could also have facilitated obtaining the nutrition from tissues of their host
(Watters 2001). The crucial step for developing a parasitic mode of life is resisting
the host responses—both behavioral and cellular.
5.5.3.2 Encapsulation
Close contact with an object results in the closing of the glochidium valves, thus
larvae often attach to unsuitable hosts and even to inanimate objects (Lefevre and
Curtis 1910b; Wood 1974b; Neves et al. 1985; Jansen et al. 2001). After their valves
are closed, glochidia remain attached to the object for several hours, so they are not
able to change the place of attachment whether or not they reached their host
(Lefevre and Curtis 1910b; Wood 1974a). Within this time encapsulation by host
epithelium tissues must occur, providing both the mechanical protection and nutrients for larvae (Karna and Millemann 1978; Wächtler et al. 2001; Rogers-Lowery
and Dimock 2006; Reis et al. 2014). Mussel larva sometimes can infest and induce
the formation of a cyst even in an unsuitable host. As a result, most often the host
epithelium, which forms the capsule, is destroyed and the glochidia fall off before
they complete metamorphosis (Waller and Mitchell 1989; Watters and O’dee 1996;
Rogers-Lowery and Dimock 2006; Barnhart et al. 2008).
Jansen et al. (2001) report the observations of Pflugfelder (1951) that fish are able to
detach glochidia by rubbing their body against objects. The solution of this problem
would be quick encapsulation in host epithelium. Host epithelial cells called keratocytes
quickly cover the glochidium, instead of cell proliferation (Nezlin et al. 1994; Dodd
A. Skawina
developed more specialized host infection strategies. Mucous threads secreted
through the exhalent siphon of the freshwater cyrenid (Cardiida) Corbicula fluminea are known to facilitate its downstream or even interstream transportation
because they act as a draglines, when tangled to the fish or bird (Prezant and
Chalermwat 1984; Kimura et al. 2004; Haag 2012). If such entanglement may be an
advantage of upstream dispersal, the relation between fish and glochidium may have
arose initially as a phoretic relationship (Watters 2001; Barnhart et al. 2008; Haag
2012). Strayer (2008) reports an example of rapid dispersal of Lampsilis cardium,
into the Potomac basin as a consequence of the introduction of its host, the smallmouth bass (Micropterus dolomieu). Actual dispersal due to phoresis is related to
dispersal abilities of host fish. Unionoids today often parasitize small benthic fishes,
with limited mobility, so their dispersal may be low (Watters 1992; Haag and Warren
2003; McLain and Ross 2005; Blazek and Gelnar 2006; Strayer 2008; Schwalb
et al. 2011b; Vaughn 2012). Dispersal of mussels associated with mobile or migratory species may be higher (Sepkoski and Rex 1974; Schwalb et al. 2011a; Lellis
et al. 2013; Terui et al. 2014). Still, many species of unionoids are capable of parasitizing several species of fish, ranging from mobile to mobility limited forms (e.g.
Blazek and Gelnar 2006; Van Snik Gray et al. 2009; St. John White et al. 2017).
Barnhart et al. (2008) and Haag (2012) propose that unionoids might have routinely dispersed on fish, being solely attached by the larval threads—before acquiring a firmer attachment, by clamping the valves on the fish tissue. The latter could
cause harm to the fish, initiating a wound reaction (which facilitates encapsulation),
but could also have facilitated obtaining the nutrition from tissues of their host
(Watters 2001). The crucial step for developing a parasitic mode of life is resisting
the host responses—both behavioral and cellular.
5.5.3.2 Encapsulation
Close contact with an object results in the closing of the glochidium valves, thus
larvae often attach to unsuitable hosts and even to inanimate objects (Lefevre and
Curtis 1910b; Wood 1974b; Neves et al. 1985; Jansen et al. 2001). After their valves
are closed, glochidia remain attached to the object for several hours, so they are not
able to change the place of attachment whether or not they reached their host
(Lefevre and Curtis 1910b; Wood 1974a). Within this time encapsulation by host
epithelium tissues must occur, providing both the mechanical protection and nutrients for larvae (Karna and Millemann 1978; Wächtler et al. 2001; Rogers-Lowery
and Dimock 2006; Reis et al. 2014). Mussel larva sometimes can infest and induce
the formation of a cyst even in an unsuitable host. As a result, most often the host
epithelium, which forms the capsule, is destroyed and the glochidia fall off before
they complete metamorphosis (Waller and Mitchell 1989; Watters and O’dee 1996;
Rogers-Lowery and Dimock 2006; Barnhart et al. 2008).
Jansen et al. (2001) report the observations of Pflugfelder (1951) that fish are able to
detach glochidia by rubbing their body against objects. The solution of this problem
would be quick encapsulation in host epithelium. Host epithelial cells called keratocytes
quickly cover the glochidium, instead of cell proliferation (Nezlin et al. 1994; Dodd
A. Skawina