Intraspecific Phenotypic Variation and Morphological Divergence of Strains of Folsomia candida (Willem) (Collembola: Isotomidae), the "Standard" Test Springtaill.

Thomas Tully,Mikhail Potapov,Peter Shaw

doi:10.1371/journal.pone.0136047

Abstract

We describe and compare the external morphology of eleven clonal strains and one sexual lineage of the globally distributed Folsomia candida, known as “standard” test Collembola. Of the 18 morphological characters studied, we measured 14 to have significant between-strains genetic variations, 9 of these had high heritabilities (>78%). The quantified morphological polymorphism was used to analyse the within-species relationships between strains by using both a parsimony analysis and a distance tree. These two detailed morphological phylogenies have revealed that the parthenogenetic strains grouped themselves into two major clades. However the exact position of the sexual strain remains unclear and further analysis is needed to confirm its exact relationship with the parthenogenetic ones. The two morphologically based clades were found to be the same as the ones previously described using molecular analysis. This shows that despite large within-strain variations, morphological characters can be used to differentiate some strains that have diverged within a single morphospecies. We discuss the potential evolutionary interpretations and consequences of these different levels of phenotypic variability.

Highlights

Springtails belong to a very ancient group (Class Collembola, ~410 Mya) [1] which has colonised most terrestrial habitats [2]
Some phenotypic variation was observed for all 18 characters under study but the level of genetic variation varied a lot between characters
No genetic variation was found for four characters: the number of setae on all subcoxa of second and third legs (n° 6–9, Fig 3) strongly varied depending on the specimen but this variation was not found to be structured between the strains

Summary

Introduction

Springtails belong to a very ancient group (Class Collembola, ~410 Mya) [1] which has colonised most terrestrial habitats [2]. This taxon comprises about 8000 described species and is considered to be moderately diversified [2,3]. The real number of existing species of Collembola on Earth is difficult to predict a ballpark estimation of about 50,000 species has been proposed [5]. It seems reasonable to assume that the current species' diversity is considerably underestimated, especially if one takes into account molecular studies that have recently revealed the existence of extensive cryptic genetic diversity in several widely distributed species or complexes of species [3,6,7,8,9,10,11].

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Conclusion