Are microbes fundamentally different than macroorganisms? Convergence and a possible case for neutral phenotypic evolution in testate amoeba (Amoebozoa: Arcellinida).

Angela M. Oliverio,Daniel J. G. Lahr,Jessica Grant,Laura A. Katz

doi:10.1098/rsos.150414

Angela M. Oliverio, Daniel J. G. Lahr + Show 2 more

Open Access

https://doi.org/10.1098/rsos.150414

Copy DOI

Abstract

This study reveals extensive phenotypic convergence based on the non-monophyly of genera and morphospecies of testate (shelled) amoebae. Using two independent markers, small subunit ribosomal DNA (ssu-rDNA) and mitochondrial cytochrome oxidase I (COI), we demonstrate discordance between morphology and molecules for ‘core Nebela’ species (Arcellinida; Amoebozoa). Prior work using just a single locus, ssu-rDNA, also supported the non-monophyly of the genera Hyalosphenia and Nebela as well as for several morphospecies within these genera. Here, we obtained COI gene sequences of 59 specimens from seven morphospecies and ssu-rDNA gene sequences of 50 specimens from six morphospecies of hyalosphenids. Our analyses corroborate the prior ssu-rDNA findings of morphological convergence in test (shell) morphologies, as COI and ssu-rDNA phylogenies are concordant. Further, the monophyly of morphospecies is rejected using approximately unbiased tests. Given that testate amoebae are used as bioindicators in both palaeoecological and contemporary studies of threatened ecosystems such as bogs and fens, understanding the discordance between morphology and genetics in the hyalosphenids is essential for interpretation of indicator species. Further, while convergence is normally considered the result of natural selection, it is possible that neutrality underlies phenotypic evolution in these microorganisms.

Highlights

The majority of eukaryotic diversity is microbial, and eukaryotic microbes are well recognized as major players in various ecosystem processes (e.g. [1,2,3])
2 Further, while convergence is normally considered the result of natural selection, it is possible that neutrality underlies phenotypic evolution in these microorganisms
Our goals are: (i) to refine our understanding of the diversity that exists within the hyalosphenids by comparing ssu-rDNA, a well-conserved marker, with COI, a fast-evolving marker across specimens, and (ii) to elucidate the evolutionary patterns in changing test morphology by exploring multiple hypotheses, including assessing the possibility of convergence or parallelism among neutral phenotypes

Summary

Introduction

The majority of eukaryotic diversity is microbial, and eukaryotic microbes (i.e. protists) are well recognized as major players in various ecosystem processes (e.g. [1,2,3]). Many microbes exhibit considerable discordance between morphological assessments of biodiversity as compared to molecular estimates. This has presented considerable challenges in untangling the diversification and evolutionary patterns among protists [4]. The relationship between molecular and morphological diversity in microbes remains a major question in evolutionary biology [5,6]. This is in part owing to uncertainty regarding the relative importance of natural selection and genetic drift in driving phenotypic evolution at the microbial level

Objectives

Methods

Results

Conclusion