The origin of the pelagobenthic metazoan life cycle: what's sex got to do with it?

Degnan, S. M. and Degnan, B. M. (2006) The origin of the pelagobenthic metazoan life cycle: what's sex got to do with it?. Integrative And Comparative Biology, 46 6: 683-690. doi:10.1093/icb/icl028

Author Degnan, S. M.
Degnan, B. M.
Title The origin of the pelagobenthic metazoan life cycle: what's sex got to do with it?
Journal name Integrative And Comparative Biology   Check publisher's open access policy
ISSN 1540-7063
Publication date 2006-01-01
Sub-type Article (original research)
DOI 10.1093/icb/icl028
Open Access Status Not Open Access
Volume 46
Issue 6
Start page 683
End page 690
Total pages 8
Place of publication Cary
Publisher Oxford University Press Inc
Language eng
Subject C1
270205 Genetic Development (incl. Sex Determination)
780105 Biological sciences
Abstract The biphasic (pelagobenthic) life cycle is found throughout the animal kingdom, and includes gametogenesis, embryogenesis, and metamorphosis. From a tangled web of hypotheses on the origin and evolution of the metazoan pelagobenthic life cycle, current opinion appears to favor a simple, larval-like holopelagic ancestor that independently settled multiple times to incorporate a benthic phase into the life cycle. This hypothesis derives originally from Haeckel's (1874) Gastraea theory of ontogeny recapitulating phylogeny, in which the gastrula is viewed as the recapitulation of a gastracan ancestor that evolved via selection on a simple, planktonic hollow ball of cells to develop the capacity to feed. Here, we propose an equally plausible hypothesis that the origin of the metazoan pelagobenthic life cycle was a direct consequence of sexual reproduction in a likely holobenthic ancestor. In doing so, we take into account new insights from poriferan development and from molecular phylogenies. In this scenario, the gastrula does not represent a recapitulation, but simply an embryological stage that is an outcome of sexual reproduction. The embryo can itself be considered as the precursor to a biphasic lifestyle, with the embryo representing one phase and the adult another phase. This hypothesis is more parsimonious because it precludes the need for multiple, independent origins of the benthic form. It is then reasonable to consider that multilayered, ciliated embryos ultimately released into the water column are subject to natural selection for dispersal/longevity/feeding that sets them on the evolutionary trajectory towards the crown metazoan planktonic larvae. These new insights from poriferan development thus clearly support the intercalation hypothesis of bilaterian larval evolution, which we now believe should be extended to discussions of the origin of biphasy in the metazoan last common ancestor.
Keyword Zoology
Animal Phylogeny
Defining Phyla
Sponge Larva
Body Plans
Q-Index Code C1

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Created: Wed, 15 Aug 2007, 19:48:16 EST