Genetic Divergence and Reproductive Barriers among Morphologically Heterogeneous Sympatric Clones of Eunotia bilunaris Sensu Lato (Bacillariophyta)

The study of reproductive isolation between populations, combined with estimates of genetic divergence, provides important insights into mechanisms of speciation. In this study, sixteen morphologically heterogeneous sympatric clones of Eunotia bilunaris sensu lato (Bacillariophyta) were brought into...

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Bibliographic Details
Published in:Protist 2008-01, Vol.159 (1), p.73-90
Main Authors: Vanormelingen, Pieter, Chepurnov, Victor A., Mann, David G., Sabbe, Koen, Vyverman, Wim
Format: Article
Language:English
Subjects:
Animals
apomixis
Bacillariophyta
Cell Division - genetics
cryptic diversity
diatoms
Diatoms - classification
Diatoms - cytology
Diatoms - genetics
DNA, Ribosomal - chemistry
DNA, Ribosomal - genetics
Eunotia
Genetic Variation
hybridization
Hybridization, Genetic
Phylogeny
reproductive isolation
Sequence Analysis, DNA
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Summary:The study of reproductive isolation between populations, combined with estimates of genetic divergence, provides important insights into mechanisms of speciation. In this study, sixteen morphologically heterogeneous sympatric clones of Eunotia bilunaris sensu lato (Bacillariophyta) were brought into culture to study their phylogenetic relationships and pre- and postzygotic reproductive barriers. An ITS rDNA phylogeny was congruent with morphology and divided the clones into three groups (‘slender’, ‘robust’ and ‘labile’), pointing to the presence of several species in E. bilunaris. Whereas most strains had a heterothallic mating system, four ‘labile’ clones displayed apomictic behaviour. A further ‘labile’ clone had a heterothallic mating behaviour, however, suggesting a very recent origin for apomixis. Despite high sequence divergence, hybridization occurred between clones belonging to different groups, but was 20–400 times less frequent than in intra-group matings. F1 hybrids had an intermediate morphology and were almost completely sterile; gamete formation was generally arrested in the early stages of meiosis I. The ITS divergence of 11.5–12.3% between the ‘robust’ and ‘slender’ clones seems to represent an upper limit of divergence in which cell pairing, gamete formation and auxosporulation are still possible but heavily reduced, and where hybrid sterility has already evolved.
ISSN:1434-4610
1618-0941
DOI:10.1016/j.protis.2007.08.004