Is Natural Population of Candida tropicalis Sexual, Parasexual, and/or Asexual?

Jianping Xu

doi:10.3389/fcimb.2021.751676

Abstract

Candida tropicalis is one of the most common opportunistic yeast pathogens of humans, especially prevalent in tropical and subtropical regions. This yeast has broad ecological distributions, can be found in both terrestrial and aquatic ecosystems, including being associated with a diversity of trees, animals, and humans. Evolutionary theory predicts that organisms thriving in diverse ecological niches likely have efficient mechanisms to generate genetic diversity in nature. Indeed, abundant genetic variations have been reported in natural populations (both environmental and clinical) of C. tropicalis. However, at present, our understanding on how genetic diversity is generated in natural C. tropicalis population remains controversial. In this paper, I review the current understanding on the potential modes of reproduction in C. tropicalis. I describe expectations of the three modes of reproduction (sexual, parasexual, and asexual) and compare them with the observed genotypic variations in natural populations. Though sexual and parasexual reproduction cannot be excluded, the analyses suggest asexual reproduction alone could explain all the observations reported so far. The results here have implications for understanding the evolution and epidemiology of C. tropicalis and other related human fungal pathogens.

Highlights

Candida tropicalis is a common opportunistic yeast pathogen, capable of causing both superficial and systemic infections in humans (Zuza-Alves et al, 2017)
I briefly reviewed our current understanding of the C. tropicalis genome and its population genetic variation, summarized the major expectations of the three different modes of reproduction, and compared the expectations of the different modes of reproduction with observed genetic variations
The comparisons showed that the traditional tests used to identify signatures of recombination (Hardy-Weinberg equilibrium, haplotype number > single nucleotide polymorphisms (SNPs) number +1, phylogenetic incompatibility or the four-gamete test, and linkage equilibrium) are difficult to distinguish the three modes of reproduction

Summary

Introduction

Candida tropicalis is a common opportunistic yeast pathogen, capable of causing both superficial and systemic infections in humans (Zuza-Alves et al, 2017). C. tropicalis was first isolated from a patient with fungal bronchitis in 1910 and was initially named Oidium tropicale (Castellani, 1912) Since this yeast has been found in diverse ecological niches such as in the soil, aquatic environments (both fresh water and marine ecosystems), a diversity of trees and plant debris, as well as from humans and other animals (e.g., Odds, 1988; Carvalho et al, 2014; Brilhante et al, 2015; Zuza-Alves et al, 2017; Aljohani et al, 2018). Bloodstream infections by C. tropicalis are associated with high mortality rates, ranging from 41–61% (e.g., Muñoz et al, 2011)

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