Morphological and molecular evolution are not linked in Lamellodiscus (Plathyhelminthes, Monogenea).

Timothée Poisot,Yves Desdevises,Olivier Verneau,Dirk Steinke

doi:10.1371/journal.pone.0026252

Abstract

Lamellodiscus Johnston & Tiegs 1922 (Monogenea, Diplectanidae) is a genus of common parasites on the gills of sparid fishes. Here we show that this genus is probably undergoing a fast molecular diversification, as reflected by the important genetic variability observed within three molecular markers (partial nuclear 18S rDNA, Internal Transcribed Spacer 1, and mitonchondrial Cytochrome Oxidase I). Using an updated phylogeny of this genus, we show that molecular and morphological evolution are weakly correlated, and that most of the morphologically defined taxonomical units are not consistent with the molecular data. We suggest that Lamellodiscus morphology is probably constrained by strong environmental (host-induced) pressure, and discuss why this result can apply to other taxa. Genetic variability within nuclear 18S and mitochondrial COI genes are compared for several monogenean genera, as this measure may reflect the level of diversification within a genus. Overall our results suggest that cryptic speciation events may occur within Lamellodiscus, and discuss the links between morphological and molecular evolution.

Highlights

Describing new species solely on the basis of their morphology is often not straightforward, and especially so for small-bodied organisms that display few morphological features on which to rely
Lamellodiscus Johnston & Tiegs 1922 (Monogenea, Diplectanidae) is a genus of common parasites on the gills of sparid fishes. We show that this genus is probably undergoing a fast molecular diversification, as reflected by the important genetic variability observed within three molecular markers
In the specific case of monogeneans, the haptoral parts, because they are used by the parasite to attach to its host, are likely to be more strongly affected by phenotypic plasticity in generalist species, even if this process appears to be limited [9]

Summary

Introduction

Describing new species solely on the basis of their morphology is often not straightforward, and especially so for small-bodied organisms that display few morphological features on which to rely. A good illustration is highlighted in monogenean parasitic flatworms, where the main morphological structures used for species identification, namely the hard parts of the host attachment apparatus (haptor) and male copulatory organ, often require expert advice to discriminate closely related species, and displaying phylogenetic conservatism in some genera [1], may display variations with environmental conditions [2,3,4] and host species [5,6], eventually leading to speciation [7]. Our goals were (i) to assess the taxonomic status of these recently described Lamellodiscus species: L. neifari, L. falcus, L. confusus, L. diplodi; (ii) to check whether or not these species are closely related to L. ignoratus (sensu stricto, referred to as L. ignoratus s.s.), comparing the relative merits of morphological and molecular investigation of species status in this genus; and (iii) to evaluate the level of molecular diversity in Lamellodiscus, within and between species and discuss how it can assist in species assignment problems

Materials and Methods

Results

Discussion

Genetic diversity in Lamellodiscus and other monogeneans