Genetic Evidence of an Isolation Barrier between Flea Subspecies of Citellophilus tesquorum (Wagner, 1898) (Siphonaptera: Ceratophyllidae).

Yury Ilinsky,Dmitry Verzhutsky,Vasilina Lapshina,Sergey Medvedev,Yulia Fedorova

doi:10.3390/insects13020126

Abstract

Simple SummaryWe studied field collections of two flea subspecies that are plague vectors on the vast Palearctic territory. Analysing the molecular–genetic, geographical, morphological, and reproductive isolation criteria, we conclude that these subspecies could be considered different species.This study investigated the relationship between two subspecies of the Citellophilus tesquorum flea, C. t. altaicus and C. t. sungaris, which are vectors of the bacterium Yersinia pestis that causes human plague across the vast territories of the Palearctic. Adult fleas were collected from 16 localities and 11 populations in 2019 and 2020. Specimens were morphologically verified for subspecies status and analysed for mitochondrial cytochrome c oxidase subunit I (COI) DNA, nuclear ribosomal cluster internal transcribed spacer 1 (ITS1) and ITS2, and Wolbachia-infection status. Our results demonstrated a genetic difference between C. t. altaicus and C. t. sungaris. According to mitochondrial data, the genetic distance between clades of C. t. altaicus and C. t. sungaris was comparable with the species divergence of the genus Callopsylla, which is closely related to Citellophilus. All studied populations of C. t. altaicus were Wolbachia-infected, whereas all studied populations of C. t. sungaris were symbiont-free. Data for ITS1 and ITS2 had much lower phylogenetic signals than mitochondrial data; however, diagnostic substitutions for C. t. altaicus and C. t. sungaris delimitation were also revealed. Analysis of a hardly accessible report on cross experiments allowed us to conclude the partial postzygotic isolation between these subspecies. Taken together, the molecular-genetic, geographical, morphological, and reproductive isolation findings verified that C. t. altaicus and C. t. sungaris subspecies could be considered as different species.

Highlights

Siphonaptera, commonly known as fleas, comprise a relatively small order of secondarily wingless insects with complete metamorphosis
Yersinia pestis bacteria inhabit the foregut of adult fleas where they form a biofilm that interferes with feeding
Fleas were collected in 16 localities from 11 populations

Summary

Introduction

Siphonaptera, commonly known as fleas, comprise a relatively small order of secondarily wingless insects with complete metamorphosis. According to the latest taxonomic revision, this order includes 2005 species and 828 subspecies belonging to 242 genera and 97 subgenera [1]. (cat-scratch disease) [3], and Yersinia pestis (plague) [4]. Plague is a dangerous disease, and several hundred cases in humans are reported annually worldwide, predominantly in developing countries [4]. Developed countries have extensive systems for monitoring plague hot-spots that allow preventive actions to be taken to avoid outbreaks. Flea species differ in their ability to transfer plague infection. 257 species are known to be reservoirs of Y. pestis [5,6]. Yersinia pestis bacteria inhabit the foregut of adult fleas where they form a biofilm that interferes with feeding. While trying to satisfy their hunger, infected fleas actively attack animal or human hosts, and biofilm conglomerates enter the bloodstream transmitting the infection [7]

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