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Different spore structures in sympatric Isoetes histrix populations and their relationship with gross morphology, chromosome number, and ribosomal nuclear ITS sequences

Bagella, Simonetta and Caria, Maria Carmela and Molins, Arántzau and Rosselló, Josep Antoni (2011) Different spore structures in sympatric Isoetes histrix populations and their relationship with gross morphology, chromosome number, and ribosomal nuclear ITS sequences. Flora, Vol. 206 (5), 451-457 . ISSN 0367-2530. Article.

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DOI: 10.1016/j.flora.2011.01.003

Abstract

Traditionally, megaspores have supplied the most relevant character for the taxonomy of Isoetes at several systematic levels, including discriminant features usually used in species identification and diagnosis. Isoetes histrix Bory is a terrestrial circum-Mediterranean quillwort characterized by dark, shiny, and persistent phyllopodia with megaspore sporangia completely covered by a velum and tuberculate megaspores. Specimens of this species from Sardinian temporary wetlands showed the sympatric presence of two kinds of individuals with correlated variation in size, ornamentation, and radial ridges of megaspores, and in ornamentation of microspores. However, they showed the same diploid chromosome number (2n = 20), ITS ribotype, and macromorphological feature. No intermediate individuals, showing mixed characters of each spore types as well as malformed or aborted spores have been detected. These results suggest that the gene flow between both kinds of I. histrix plants is heavily restricted, if not limited at all. On the basis of the cytogenetic and molecular uniformity detected in I. histrix in this study, genomic incompatibilities do not seem to be the main reasons involved in the maintenance of the two kinds of I. histrix individuals. Prezygotic barriers involving changes in phenology (e.g. spore maturation) or differential gamete dispersal should be further assessed to gain insights in this topic. The presence of two kinds of individuals in I. histrix differing in significant spore features used in quillwort taxonomy, whatsoever the causes involved in its origin, could be the basis of an incipient differentiation process upon which selective pressures could ultimately lead to speciation.

Item Type:Article
ID Code:5760
Status:Published
Refereed:Yes
Uncontrolled Keywords:Cytogenetics, mediterranean flora, Sardinia, spore polymorphism, temporary wetlands, terrestrial quillworts
Subjects:Area 05 - Scienze biologiche > BIO/03 Botanica ambientale e applicata
Divisions:001 Università di Sassari > 01 Dipartimenti > Scienze botaniche, ecologiche e geologiche
Publisher:Urban und Fischer / Elsevier
ISSN:0367-2530
Deposited On:11 May 2011 10:07

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