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Marine Ecology Progress Series

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MEPS 378:113-124 (2009)  -  DOI:

Independent evolution of matrotrophy in the major classes of Bryozoa: transitions among reproductive patterns and their ecological background

Andrew N. Ostrovsky1,4,*, Dennis P. Gordon2, Scott Lidgard3

1Department of Invertebrate Zoology, Faculty of Biology & Soil Science, St. Petersburg State University, Universitetskaja nab. 7/9, 199034, St. Petersburg, Russia
2National Institute of Water & Atmospheric Research, Private Bag 14901, Kilbirnie, Wellington, New Zealand
3Department of Geology, Field Museum of Natural History, 1400 S. Lake Shore Dr., Chicago, Illinois 60605, USA
4Present address: Department of Palaeontology, Faculty of Earth Sciences, Geography and Astronomy, Geozentrum, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria

ABSTRACT: Bryozoa are unique among invertebrates in possessing placenta-like analogues and exhibiting extraembryonic nutrition in all high-level (class) taxa. Extant representatives of the classes Stenolaemata and Phylactolaemata are evidently all placental. Within the Gymnolaemata, placenta-like systems have been known since the 1910s in a few species, but are herein reported to be widespread within this class. Placental forms include both viviparous species, in which embryonic development occurs within the maternal body cavity, and brooding species, in which development proceeds outside the body cavity. We have also identified an unknown reproductive pattern involving macrolecithal oogenesis and placental nutrition from a new, taxonomically extensive anatomical study of 120 species in 92 genera and 48 families of the gymnolaemate order Cheilostomata. Results support the hypothesis of evolution of oogenesis and placentation among Cheilostomata from oligolecithal to macrolecithal oogenesis, followed by brooding, through incipient matrotrophy combining macrolecithal oogenesis and placentation, to oligolecithal oogenesis with subsequent placental brooding. The distribution of reproductive patterns within the phylum suggests that variations of placentation evolved in all 3 bryozoan classes, and possibly several times within both gymnolaemate orders. We infer that extraembryonic nutrition may be advantageous to species through enhanced developmental plasticity, and, in fast-growing ephemeral colonies, simultaneous volumetric growth and embryonic development may facilitate earlier larval release and occupation of vacant space.

KEY WORDS: Matrotrophy · Placenta · Reproductive patterns · Evolution · Bryozoa

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Cite this article as: Ostrovsky AN, Gordon DP, Lidgard S (2009) Independent evolution of matrotrophy in the major classes of Bryozoa: transitions among reproductive patterns and their ecological background. Mar Ecol Prog Ser 378:113-124.

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