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Sexual versus asexual dispersal in clonal animals: examples from cheilostome bryozoans

Published online by Cambridge University Press:  08 February 2016

Erik Thomsen  and
Eckart Håkansson
Erik Thomsen
Affiliation:
Department of Geology, University of Aarhus, C. F. M⊘llers Allé, DK 8000 Aarhus C, Denmark
Eckart Håkansson
Affiliation:
Geological Institute, University of Copenhagen, ⊘ster Voldgade 10, DK 1350 Copenhagen K, Denmark
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Abstract

The relative numbers of sexually and asexually recruited colonies and the proportion of brooding zooids were determined in 26 species of cheilostome bryozoans of Late Cretaceous and Early Tertiary ages. Asexual reproduction seems to be much more widespread than previously realized, although its relative importance is related to growth habit. Arborescent species of these fossil assemblages reproduce mainly asexually via fragmentation; encrusting species reproduce sexually via motile larvae. Free-living species use both methods; some reproduce sexually, whereas other species have enhanced the ability to break and reproduce predominantly asexually. Mode of reproduction was stable over a period of 3 m.y. in all species except the vinelike Columnotheca cribrosa. In this species both the proportion of asexual recruits and brooding zooids varied in accord with environmental parameters. In all cases populations dominated by asexual propagation had a significantly lower proportion of brooding zooids than populations dominated by sexual propagation.

Type
Articles
Information
Paleobiology , Volume 21 , Issue 4 , Fall 1995 , pp. 496 - 508
Copyright
Copyright © The Paleontological Society 

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