The origin of the metazoan biphasic life cycle: New insights from an ancient phylum

Degnan, S. M. and Degnan, B. M. (2006). The origin of the metazoan biphasic life cycle: New insights from an ancient phylum. In: Integrative And Comparative Biology: Symposia and Oral Abstracts. SICB Annual Meeting 2006, Orlando, FL, (986-986). January 4-8, 2006. doi:10.1093/icb/45.6.955

Author Degnan, S. M.
Degnan, B. M.
Title of paper The origin of the metazoan biphasic life cycle: New insights from an ancient phylum
Conference name SICB Annual Meeting 2006
Conference location Orlando, FL
Conference dates January 4-8, 2006
Proceedings title Integrative And Comparative Biology: Symposia and Oral Abstracts   Check publisher's open access policy
Journal name Integrative and Comparative Biology   Check publisher's open access policy
Place of Publication McLean. VA
Publisher Society for Integrative and Comparative Biology
Publication Year 2006
DOI 10.1093/icb/45.6.955
Open Access Status Not Open Access
ISSN 1540-7063
Volume 45
Issue 6
Start page 986
End page 986
Total pages 1
Language eng
Abstract/Summary The biphasic life cycle, characterised by metamorphosis from a pelagic larva to a benthic adult, is found throughout the Metazoa. So is sexual reproduction via eggs and sperm. Amidst a tangled web of hypotheses on the origin of metazoan biphasy, current weight of opinion lies with a simple, larva-like holopelagic ancestor that independently settled multiple times to incorporate a benthic phase into the life cycle. This school of thought derives from Haeckel's interpretation of the gastrula as the recapitulation of a gastrean ancestor that evolved via selection on a simple, planktonic hollow ball-of-cells to develop the capacity to feed. We suggest that a paradigm shift is required to accomodate accumulating evidence of the genomic and developmental complexity of the metazoan last common ancestor, which was likely to have already possessed a biphasic lifecycle. Here we incorporate recent evidence from basal metazoans, in particular poriferans, to argue that a more parsimonious theory of the origin of biphasy is as a direct consequence of sexual reproduction in an ancestral benthic adult form. The metazoan embryo can itself be considered the precursor to a biphasic life cycle, wherein the embryo represents one phase and the adult another. Embryos in the water column are subject to natural selection for longeveity and dispersal, which sets them on the evolutionary trajectory towards the crown metazoan planktonic larvae. This alternate view considers the conserved use of regulatory genes in disparate metazoans as a reflection of both the complexity of the LCA and the antiquity of the biphasic life cycle. It does not require that extant embryogenesis, including gastrulation, recapitulates evolution.
Subjects 0608 Zoology
Keyword Zoology
Q-Index Code EX
Q-Index Status Provisional Code
Institutional Status Unknown

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Created: Tue, 14 Aug 2007, 01:59:00 EST