MODES OF REPRODUCTION IN RECENT AND FOSSIL CUPULADRIID BRYOZOANS

:  Cupuladriid cheilostome bryozoans can make new colonies both sexually and asexually. Sexual (aclonal) colonies are derived from larvae while asexual (clonal) colonies result from the fragmentation or division of larger colonies. A number of specialised morphologies exist which either enhance or d...

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Bibliographic Details
Published in:Palaeontology 2008-07, Vol.51 (4), p.847-864
Main Authors: O’DEA, AARON, JACKSON, JEREMY B. C., TAYLOR, PAUL D., RODRÍGUEZ, FELIX
Format: Article
Language:English
Subjects:
aclonal
Animal behavior
Animal reproduction
bryozoa
clonal
Cupuladriidae
evolution
Evolutionary biology
Fossils
fragmentation
life history
Paleontology
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Summary::  Cupuladriid cheilostome bryozoans can make new colonies both sexually and asexually. Sexual (aclonal) colonies are derived from larvae while asexual (clonal) colonies result from the fragmentation or division of larger colonies. A number of specialised morphologies exist which either enhance or discourage clonality, and cupuladriids preserve these in their skeletons, meaning that it is possible to count the abundances of individual modes of reproduction in fossil assemblages, and thus measure the mode and tempo of evolution of life histories using fossil colonies. In this paper we categorise, illustrate and describe the various clonal and aclonal methods of propagation in cupuladriids through the Cenozoic. Sexual reproduction is the only aclonal method of propagation, while four clonal methods are described comprising: (1) mechanical fragmentation, (2) autofragmentation, (3) colonial budding and (4) peripheral fragmentation. The processes involved in each are discussed and we explain how their prevalence can be measured in the fossil record using preservable morphologies. Compiling a record of the occurrence and distribution of the various modes of propagation through time and space we discover a general trend of evolution towards more complex modes in all three cupuladriid genera, but a geologically recent extinction of some modes of propagation that has left the present‐day assemblage relatively depauperate. We see striking similarities in the general timing of expansion of modes of reproduction between the two most important genera, Cupuladria and Discoporella, although it is clear that Discoporella evolved a much wider range of special morphologies either to enhance or to discourage clonality than did Cupuladria.
ISSN:0031-0239
1475-4983
DOI:10.1111/j.1475-4983.2008.00790.x