JACOBS, Molly W.; University of Washington, Friday Harbor Labs: Metamorphosis in solitary ascidians: not as constrained as we thought

Solitary ascidians are typically free-spawners and produce small, short-lived, non-feeding larvae. Attachment normally initiates a radical metamorphosis in which larval features are sloughed or resorbed and juvenile features begin to differentiate. Colonial ascidians brood their larvae, and differentiation of most juvenile structures takes place before larval release. I compare differentiation of juvenile structures prior to settlement for a diverse array of solitary and colonial species. Preliminary data suggest that state of differentiation at hatching varies widely for solitary ascidians. Differentiation of juvenile structures also may occur during the pelagic competent period of some larvae, a developmental period previously thought to be static. This precocious differentiation may allay some of the energetic costs of delaying metamorphosis. Evidence from this and other studies suggests that the different components of ascidian metamorphosis- loss of larval features, morphological rearrangements, attachment, tissue differentiation- are independent and can happen in different orders if environmental conditions demand it. This modularity is obvious on an evolutionary scale when one considers the diversity of reproductive strategies employed by solitary and colonial ascidians, and here I present evidence of it within and between species of solitary ascidians.