Lacrymariidae

Rajter, Ľubomír, Bourland, William & Vďačný, Peter, 2019, Morpho-molecular Characterization of the Litostomatean Predatory Ciliate Phialina pupula (Müller, 1773) Foissner, 1983 (Haptoria, Lacrymariidae), Acta Protozoologica 58 (1), pp. 53-68 : 63-64

Molecular and morphological evolution of the family Lacrymariidae

According to multiple phylogenetic analyses, the family Lacrymariidae represents a monophyletic and distinct lineage within the subclass Haptoria (e.g., Gao et al. 2008, Vďačný et al. 2011, Zhang et al. 2012, Kwon et al. 2014, Wu et al. 2017, Huang et al. 2018, Wang et al. 2019), which is also in accordance with the present results ( Figs 5 , 6 ). In the pioneer studies, the genera Phialina and Lacrymaria were each depicted as being monophyletic ( Zhang et al. 2012, Kwon et al. 2014). However, with an increasing sequence pool, both genera have become non-monophyletic ( Wu et al. 2017, Huang et al. 2018, Wang et al. 2019, present study). Although the generic home of most lacrymariid taxa is questionable and unstable (e.g., Penard 1922, Kahl 1930, Foissner 1983, Dragesco and Dragesco-Kernéis 1986, Foissner et al. 1995, Jankowski 2007), Phialina appears to be a paraphyletic stem genus while Lacrymaria seems to be polyphyletic both in the single gene and multigene phylogenetic analyses ( Figs 5 , 6 ). Therefore, we suppose that the phialinid bauplan, i.e., the anterior body end differentiated into a head-like structure directly attached to the trunk (i.e. without an intervening neck-like region), might represent the ground pattern in the family Lacrymariidae . On the other hand, the long highly contractile neck carrying the head-like structure probably evolved later and convergently in multiple Lacrymaria species from Phialina -like ancestors.

The phylogenetic home of the family Lacrymariidae within the subclass Haptoria is still uncertain (for details, see Vďačný and Rataj 2017). However, the peculiar brush structure of the family Lacrymariidae , i.e., the posterior basal body of brush dikinetids associated with an ordinary cilium ( Fig. 4A, B ), indicates a close relationship with the family Chaeneidae Kwon et al., 2014 . There are also further morphological features (e.g., body contractility, head-like anterior body end, and separation of the dorsal brush from the anterior body end by files of somatic monokinetids) corroborating the sister-group relationship of the families Lacrymariidae and Chaeneidae ( Kwon et al. 2014, Vďačný and Rataj 2017). Whether these features are synapomorphies, plesiomorphies or homoplasies, needs to be tested by further molecular markers.

Figures

Fig. 5. Phylogeny based on the 18S rRNA gene and the ITS1-5.8S-ITS2 region of 80 litostomatean taxa and two armophoreans serving as outgroup (CON-lit alignment). Posterior probabilities for the Bayesian inference and bootstrap values for maximum likelihood were mapped onto the 50%-majority rule Bayesian consensus tree. Note that monophyly of the family Lacrymariidae is moderately to strongly statistically supported. Sequences in bold face were obtained during this study. The scale bar indicates five substitutions per one hundred nucleotide positions. For GenBank accession numbers, see Supplementary Table S3.

Fig. 6. Phylogeny based on the 18S rRNA gene of 22 taxa from the family Lacrymariidae (18S-lac1 alignment). Note that the genus Phialina is paraphyletic and contains the polyphyletic genus Lacrymaria. Posterior probabilities for the Bayesian inference and bootstrap values for maximum likelihood were mapped onto the 50%-majority rule ML tree. Sequences in bold were obtained during this study. The scale bar indicates nine substitutions per one thousand nucleotide positions.

Fig. 4. Phialina pupula in the scanning electron microscope (SEM). (A) Detail of the anterior body half. The head is localized at the anterior body end and is attached directly to the trunk, as typical of the genus Phialina. The head is covered by very narrowly spaced cilia arranged in helically extending rows. Note that the cortex of the trunk is distinctly furrowed by slightly helically extending ciliary rows. According to protargol preparations, each somatic ciliary row has two to five brush dikinetids at its anterior end (see Fig. 2E). SEM observations show that the anterior basal body of a brush dikinetid bears a minute to short cilium or is unciliated, while the posterior basal body bears an or- dinary somatic cilium. Therefore, the brush is very difficult to recognize in the SEM and in vivo. (B) Detail of the anterior end of somatic ciliary rows, showing that the anterior basal body of a brush dikinetid bears a short cilium (arrowheads) or is unciliated. The posterior basal body of a brush dikinetid bears an ordinary somatic cilium. Such an inconspicuous brush is a typical feature of lacrymariids and also of the possibly related chaeneids. (C) Detail of a somatic ciliary row, showing a dikinetid (dividing basal bodies) followed by monokinetids that bear ordinary cilia. As typical for haptorians, the anterior cilium of dividing basal bodies is short and stump-like while the posterior cilium is ordinarily long. AC – anterior stump-like cilium of dividing basal bodies; G – tips of cortical granules; H – head; HC – head cilia; SC – somatic cilia; T – trunk.