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

Peter Vďačný,Mann Kyoon Shin,Shahed Uddin Ahmed Shazib,Seok Won Jang,Ľubomír Rajter

doi:10.1038/s41598-017-09472-y

Peter Vďačný, Mann Kyoon Shin + Show 3 more

Open Access

https://doi.org/10.1038/s41598-017-09472-y

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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.

Highlights

The subclass Rhynchostomatia was divided into two fundamental lineages, the order Tracheliida and the order Dileptida, whose monophylies were strongly statistically supported by both analyses
According to the classification framework of Vďačný et al.[20], there are over 250 species in the order Spathidiida[21], more than 100 species in the order Pleurostomatida[22,23,24,25,26], about 66 species in the Rhynchostomatia[14], and only several dozens of species in the orders Haptorida, Didiniida, and Lacrymariida[24, 27, 28]
This cursory appraisal indicates that rhynchostomatians are not among the cladogenically most successful litostomateans

Summary

Introduction

Ciliates seem to be a suitable microbial model to explore trait-dependent diversification, because they are both species-rich and comparatively morphologically complex[9, 10] These eukaryotic microbes are diverse functionally, acting in a variety of roles such as fine to coarse filter feeders, hunters, scrapers or sucking feeders[11, 12]. We investigated the impact of key quantitative and qualitative morphological features on speciation, extinction, and net-diversification rates of rhynchostomatian lineages. This complex approach enabled us to recognise which intrinsic traits increase diversification directly through elevating speciation rate, which indirectly via decreasing extinction rate, and which intrinsic traits do not cause asymmetries in cladogenesis

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