Diversification dynamics of rhynchostomatian ciliates: the impact of seven intrinsic traits on speciation and extinction in a microbial group

Abstract

Ciliates are a suitable microbial model to investigate trait-dependent diversification because of their comparatively complex morphology and high diversity. We examined the impact of seven intrinsic traits on speciation, extinction, and net-diversification of rhynchostomatians, a group of comparatively large, predatory ciliates with proboscis carrying a dorsal brush (sensoric structure) and toxicysts (organelles used to kill the prey). Bayesian estimates under the binary-state speciation and extinction model indicate that two types of extrusomes and two-rowed dorsal brush raise diversification through decreasing extinction. On the other hand, the higher number of contractile vacuoles and their dorsal location likely increase diversification via elevating speciation rate. Particular nuclear characteristics, however, do not significantly differ in their diversification rates and hence lineages with various macronuclear patterns and number of micronuclei have similar probabilities to generate new species. Likelihood-based quantitative state diversification analyses suggest that rhynchostomatians conform to Cope’s rule in that their diversity linearly grows with increasing body length and relative length of the proboscis. Comparison with other litostomatean ciliates indicates that rhynchostomatians are not among the cladogenically most successful lineages and their survival over several hundred million years could be associated with their comparatively large and complex bodies that reduce the risk of extinction.

A Proposed Timescale for the Evolution of Armophorean Ciliates: Clevelandellids Diversify More Rapidly Than Metopids

“…Nevertheless, Bayesian diversification analyses favors a birth‐death model over a pure‐birth model both in the metopid‐clevelandellid group (present study) and in rhynchostomatians (Vďačný et al. ), suggesting attrition of some lineages via extinction. Diversification patterns of spathidiid ciliates might be, however, comparatively different from those of metopids, clevelandellids, pleurostomes and rhynchostomatians.…”

“…Diversification dynamics is only rarely examined in ciliates due to the lack of fossil records (Rajter and Vďačný ; Vďačný ; Vďačný et al. ; Wright and Lynn ). However, this problem could be overcome by the fossil appearance of hosts of the exclusively endosymbiotic clevelandellids, whose origin cannot precede that of their host groups.…”

Taxonomy and Phylogeny of the Dileptid Ciliate Genus Paradileptus (Protista: Ciliophora), With a Brief Review and Redescriptions of Two Species Isolated From a Wetland in Northern China

“…Rhynchostomatia was established by Jankowski (1980) as one of three subclasses of the class Litostomatea. This subclass comprises two orders, Tracheliida and Dileptida ( Vd’ačný et al, 2017 ). Phylogenetic analyses based on 18S, 5.8S, and ITS rDNA sequence data demonstrated that each of these two orders is monophyletic ( Figures 6A , 7 , 8 ), which is consistent with previous studies ( Vd’ačný et al, 2011b , 2014 ; Jang et al, 2014 ; Vd’ačný and Rajter, 2015 ; Huang et al, 2018 ).…”

“…Rhynchostomatians are raptorial feeders whose predatory lifestyle has led to the development of special structures for prey recognition and capture. The primary feature is the apical proboscis which carries a dorsal brush that may be used for sensory feedback, extrusomes (toxicysts) to paralyze and/or kill prey organisms, and differentiated kineties such as the circumoral kinety (∼paroral membrane) and preoral kineties (∼adoral zone of membranelles) to aid feeding ( Visscher, 1923 ; Dragesco, 1962 ; Vd’ačný and Foissner, 2012 ; Vd’ačný et al, 2017 ; Chi et al, 2021 ). Furthermore, differences in hunting strategies and preferred prey among dileptids ( Vd’ačný and Foissner, 2012 ) seem to be related to these differentiated structures.…”

“…Ciliated protists (ciliates) are a diverse group of morphologically differentiated eukaryotic microorganisms that play critical roles in aquatic and terrestrial ecosystems by maintaining energy flow and nutrient cycles ( Lynn, 2008 ; Song et al, 2009 ; Gao et al, 2016 ; Hu et al, 2019 ). Rhynchostomatians are a large group of raptorial ciliates with a conspicuous proboscis that bears well-developed extrusomes and a dorsal brush ( Vd’ačný and Rajter, 2015 ; Vd’ačný et al, 2017 ). They occur in marine, limnetic, terrestrial, and anaerobic environments including both benthic and planktonic habitats ( Lynn, 2008 ; Vd’ačný and Foissner, 2012 ).…”