175
Rectidentinae, Nearctic and Neotropical Ambleminae (comprising Lampsilini and
Pleurobemini in which advanced strategies of host attraction evolved), together with
mostly Holarctic paraphyletic assemblage of species “Gonideinae” (Whelan et al.
2011; Bolotov et al. 2017a, b; Lopes-Lima et al. 2017; Huang et al. 2019; Pfeiffer
et al. 2019). According to Bolotov et al. (2017a) the most species rich family
Unionidae possibly originated during the Middle Jurassic in an evolutionary hotspot in Southeast and East Asia, then colonized North America (not earlier than in
mid-Cretaceous), and later Europe and India (since Paleocene).
5.4.3 Phylogeny
The phylogeny of Unionida is under active research, and no consensus about the
phylogenetic relationships among families is reached yet (Fig. 5.7). Nevertheless
recently Combosch et al. (2017) for bivalvia (including unionoids) and Lopes-Lima
et al. (2017) for Unionidae (and the other families of the order) proposed a phylogenetic scenario at a family level on the basis of molecular datasets. They both confirm
trigoniids as a sister group to monophyletic unionoids, and Hyriidae as sister group
to all the other unionoid families (Fig. 5.7a, b). Similar results were obtained by e.g.
Hoeh et al. (2001), Whelan et al. (2011), Graf et al. (2015), Pfeiffer and Graf (2015),
Huang et al. (2018, 2019), although they differ in reconstructing phylogenetic relations between the remaining five families (Fig. 5.7a, b, d). Most authors however
place Unionidae as sister group to Margaritiferidae (Fig. 5.7c, d, f). Above reconstructions require that families that have glochidia (Hyriidae, Unionidae and
Margaritiferidae) are paraphyletic, and a glochidium is an ancestral larva for lasidium. The alternative is that glochidia-bearing families are monophyletic as well as
lasidia-bearing families (superfamily Etherioidea). This alternative was erected (on
the basis of morphology and life history) by Parodiz and Bonetto (1963), who
directly excluded a possibility that such different larvae could be derived from each
other. This scenario was recently supported by several authors on the basis of analyses of the mitochondrial genome (Bolotov et al. 2017b; Guerra et al. 2017; Pfeiffer
et al. 2019) which in unionoids (like in some other bivalves) may come from both
sexes of the parents (DUI: doubly uniparental inheritance) depending on the method.
There are however differences depending on the method (Whelan et al. 2011;
Huang et al. 2018, 2019; Fig. 5.7c, e). Also, Combosch et al. (2017) noticed that
assessing the main divisions within the Unionida is sensitive to methodologies and
needs more data.
The molecular clock—the idea of dating the separation of two taxa on the basis
of their molecular sequences (more precisely the number of substitutions which
accumulated between their DNA sequences) provides a powerful tool in estimations
of phylogeny of taxa (Warnock and Engelstädter 2021). Nevertheless, because
molecular clocks vary between evolutionary lineages, such phylogeny usually
requires the comparison of clock-based data with the other sources of time information, e.g. fossils (Pulquerio and Nichols 2007). Recently, several attempts at the
estimation of divergence of evolutionary traits of unionoid lineages were performed
5 Evolutionary History of Bivalves as Parasites
Rectidentinae, Nearctic and Neotropical Ambleminae (comprising Lampsilini and
Pleurobemini in which advanced strategies of host attraction evolved), together with
mostly Holarctic paraphyletic assemblage of species “Gonideinae” (Whelan et al.
2011; Bolotov et al. 2017a, b; Lopes-Lima et al. 2017; Huang et al. 2019; Pfeiffer
et al. 2019). According to Bolotov et al. (2017a) the most species rich family
Unionidae possibly originated during the Middle Jurassic in an evolutionary hotspot in Southeast and East Asia, then colonized North America (not earlier than in
mid-Cretaceous), and later Europe and India (since Paleocene).
5.4.3 Phylogeny
The phylogeny of Unionida is under active research, and no consensus about the
phylogenetic relationships among families is reached yet (Fig. 5.7). Nevertheless
recently Combosch et al. (2017) for bivalvia (including unionoids) and Lopes-Lima
et al. (2017) for Unionidae (and the other families of the order) proposed a phylogenetic scenario at a family level on the basis of molecular datasets. They both confirm
trigoniids as a sister group to monophyletic unionoids, and Hyriidae as sister group
to all the other unionoid families (Fig. 5.7a, b). Similar results were obtained by e.g.
Hoeh et al. (2001), Whelan et al. (2011), Graf et al. (2015), Pfeiffer and Graf (2015),
Huang et al. (2018, 2019), although they differ in reconstructing phylogenetic relations between the remaining five families (Fig. 5.7a, b, d). Most authors however
place Unionidae as sister group to Margaritiferidae (Fig. 5.7c, d, f). Above reconstructions require that families that have glochidia (Hyriidae, Unionidae and
Margaritiferidae) are paraphyletic, and a glochidium is an ancestral larva for lasidium. The alternative is that glochidia-bearing families are monophyletic as well as
lasidia-bearing families (superfamily Etherioidea). This alternative was erected (on
the basis of morphology and life history) by Parodiz and Bonetto (1963), who
directly excluded a possibility that such different larvae could be derived from each
other. This scenario was recently supported by several authors on the basis of analyses of the mitochondrial genome (Bolotov et al. 2017b; Guerra et al. 2017; Pfeiffer
et al. 2019) which in unionoids (like in some other bivalves) may come from both
sexes of the parents (DUI: doubly uniparental inheritance) depending on the method.
There are however differences depending on the method (Whelan et al. 2011;
Huang et al. 2018, 2019; Fig. 5.7c, e). Also, Combosch et al. (2017) noticed that
assessing the main divisions within the Unionida is sensitive to methodologies and
needs more data.
The molecular clock—the idea of dating the separation of two taxa on the basis
of their molecular sequences (more precisely the number of substitutions which
accumulated between their DNA sequences) provides a powerful tool in estimations
of phylogeny of taxa (Warnock and Engelstädter 2021). Nevertheless, because
molecular clocks vary between evolutionary lineages, such phylogeny usually
requires the comparison of clock-based data with the other sources of time information, e.g. fossils (Pulquerio and Nichols 2007). Recently, several attempts at the
estimation of divergence of evolutionary traits of unionoid lineages were performed
5 Evolutionary History of Bivalves as Parasites