EVOLUTION OF LIFE CYCLE, COLONY MORPHOLOGY, AND HOST SPECIFICITY IN THE FAMILY HYDRACTINIIDAE (HYDROZOA, CNIDARIA)
Version of Record online: 19 JUL 2012
© 2012 The Author(s). Evolution© 2012 The Society for the Study of Evolution.
Volume 66, Issue 12, pages 3876–3901, December 2012
How to Cite
Miglietta, M. P. and Cunningham, C. W. (2012), EVOLUTION OF LIFE CYCLE, COLONY MORPHOLOGY, AND HOST SPECIFICITY IN THE FAMILY HYDRACTINIIDAE (HYDROZOA, CNIDARIA). Evolution, 66: 3876–3901. doi: 10.1111/j.1558-5646.2012.01717.x
- Issue online: 3 DEC 2012
- Version of Record online: 19 JUL 2012
- Accepted manuscript online: 25 JUN 2012 08:54AM EST
- Received September 16, 2011 Accepted May 23, 2012
- complex characters;
- Dollo's Law;
- life cycle
Biased transitions are common throughout the tree of life. The class hydrozoa is no exception, having lost the feeding medusa stage at least 70 times. The family hydractiniidae includes one lineage with pelagic medusae (Podocoryna) and several without (e.g., Hydractinia). The benthic colony stage also varies widely in host specificity and in colony form. The five-gene phylogeny presented here requires multiple transitions between character states for medusae, host specificity, and colony phenotype. Significant phylogenetic correlations exist between medusoid form, colony morphology, and host specificity. Species with nonfeeding medusae are usually specialized on a single host type, and reticulate colonies are correlated with nonmotile hosts. The history of feeding medusae is less certain. Podocoryna is nested within five lineages lacking medusae. This requires either repeated losses of medusae, or the remarkable re-evolution of a feeding medusa after at least 150 million years. Traditional ancestral reconstruction favors medusa regain, but a likelihood framework testing biased transitions cannot distinguish between multiple losses versus regain. A hypothesis of multiple losses of feeding medusae requires transient selection pressure favoring such a loss. Populations of species with feeding medusae are always locally rare and lack of feeding medusae does not result in restricted species distribution around the world.