The evolution of trypanosomatid taxonomy

Abstract

Trypanosomatids are protozoan parasites of the class Kinetoplastida predominately restricted to invertebrate hosts (i.e. possess a monoxenous life-cycle). However, several genera are pathogenic to humans, animals and plants, and have an invertebrate vector that facilitates their transmission (i.e. possess a dixenous life-cycle). Phytomonas is one dixenous genus that includes several plant pathogens transmitted by phytophagous insects. Trypanosoma and Leishmania are dixenous genera that infect vertebrates, including humans, and are transmitted by hematophagous invertebrates. Traditionally, monoxenous trypanosomatids such as Leptomonas were distinguished from morphologically similar dixenous species based on their restriction to an invertebrate host. Nonetheless, this criterion is somewhat flawed as exemplified by Leptomonas seymouri which reportedly infects vertebrates opportunistically. Similarly, Novymonas and Zelonia are presumably monoxenous genera yet sit comfortably in the dixenous clade occupied by Leishmania. The isolation of Leishmania macropodum from a biting midge (Forcipomyia spp.) rather than a phlebotomine sand fly calls into question the exclusivity of the Leishmania-sand fly relationship, and its suitability for defining the Leishmania genus. It is now accepted that classic genus-defining characteristics based on parasite morphology and host range are insufficient to form the sole basis of trypanosomatid taxonomy as this has led to several instances of paraphyly. While improvements have been made, resolution of evolutionary relationships within the Trypanosomatidae is confounded by our incomplete knowledge of its true diversity. The known trypanosomatids probably represent a fraction of those that exist and isolation of new species will help resolve relationships in this group with greater accuracy. This review incites a dialogue on how our understanding of the relationships between certain trypanosomatids has shifted, and discusses new knowledge that informs the present taxonomy of these important parasites.

The Role of Cytoplasmic mRNA Cap-Binding Protein Complexes in Trypanosoma brucei and Other Trypanosomatids

“…These organisms evolved from free-living phagotrophic protozoa (similar to their current sister group, the Bodonids) into well-adapted parasitic organisms, having undergone major changes that include serial loss of genes involved in macromolecular digestion and the assimilation and multiplication of membrane transporters for scavenging metabolites from the host [ 2 , 3 , 4 ]. The family Trypanosomatidae is composed, to date, of 19 genera of Monoxenous (one host, insect) and Dixenous (two hosts, insect and vertebrate or plant) parasites [ 5 ]. Two of those, Trypanosoma and Leishmania , are medically relevant, and have elicited substantial interest from the scientific community, due to their role in diseases that affect millions of people.…”

The cotton stainer's gut microbiota suppresses infection of a cotransmitted trypanosomatid parasite

“…Such interactions coupled with the experimental and/or genetic tractability of some insect–microbe associations provide a prospective application of symbionts in disease control strategies (Beard et al., ). Despite the huge number of insect taxa associated with monoxenous trypanosomatids and gut microbiota (Engel & Moran, ; Kaufer et al., ; Maslov et al., ; Schaub, ), the dynamics and outcomes of host–symbiont–parasite interactions have only been reported in a few taxa such as bumblebees (Koch & Schmid‐Hempel, ; Mockler, Kwong, Moran, & Koch, ) and honeybees (Schwarz, Moran, & Evans, ). The study of monoxenous parasites, which has enhanced our understanding of the biology and evolution of their dixenous counterparts (Flegontov et al., ), and the ability of these parasites to complete their life cycle in a single host makes them attractive for use in experimental manipulations.…”

Message in a vesicle – trans-kingdom intercommunication at the vector–host interface

“…Trypanosomes are unicellular flagellate protozoa divided into two major classes: salivarian and stercorarian (Kaufer et al, 2017). T. cruzi is a stercorarian trypanosome that is transmitted by triatomine bugs and causes Chagas disease.…”