Abstract
Plasmodial slime molds (Myxogastria or Myxomycetes) are common and widespread unicellular organisms that are commonly assumed to have a sexual life cycle culminating with the formation of often macroscopic fruiting bodies that efficiently disseminate spores. However, laboratory studies based on mating compatibility revealed the coexistence of asexual as well as sexual strains. To test this hypothesis in natural populations, we investigated the genetic variability of two species of the genus Lamproderma. Detailed ecological relevés were carried out in 2007 and 2009 in several deep ravines in the Elbsandsteingebirge (Saxony, south-eastern Germany). Morphological characters of 93 specimens of Lamproderma were recorded and genetic analyses, based on the small subunit ribosomal gene, the internal transcribed spacer 1 and partial elongation factor 1α sequences were carried out for 52 specimens. Genetic analyses showed the existence of two major clades, each composed of several discrete lineages. Most of these lineages were composed of several identical sequences (SSU, ITS 1 and EF-1α) which is explained best by an asexual mode of reproduction. Detrended Correspondence Analysis of morphological characters revealed two morphospecies that corresponded to the two major clades, except for one genotype (Lc6), thus challenging the morphospecies concept. Genetic patterns were not related to the geographical distribution: specimens belonging to the same genotype were found in distinct ravines, suggesting effective long-distance dispersal via spores, except for the Lc6 genotype which was found only in one ravine. Implications for the morphological and biological species concept are discussed.
Highlights
IntroductionThe paradox of the maintenance of sex arises from the fact that it has many immediate costs, compared to the advantages given by asexual reproduction [1,2]
Why is sex predominant in higher eukaryotes? The paradox of the maintenance of sex arises from the fact that it has many immediate costs, compared to the advantages given by asexual reproduction [1,2]
To shed some light on this question, we investigated the genetic structure of a group of protists, the plasmodial slime molds (Myxogastria, called Myxomycetes)
Summary
The paradox of the maintenance of sex arises from the fact that it has many immediate costs, compared to the advantages given by asexual reproduction [1,2]. Current models on evolution of sexuality are based largely on multicellular organisms such as plants, fungi and metazoans, which represent only a very small fraction of the genetic diversity of eukaryotes – most to be found in various high-ranking clades of protists [6,7,8]. Myxogastria present unique advantages for studying factors shaping the proportion of sexual/asexual strains in nature. If sex (and meiosis) occurs, the spores should represent the offspring of two parents and the genes found in the sporocarps originating from a single plasmodium will show a mixture of the original alleles from both parental amoebae as well as their recombination products. If the sporocarps are produced asexually, no major variation is expected
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