Ascidians exhibit a rich array of body plans and life history strategies. Colonial species typically consist of zooids embedded in a common test and brood large, fully developed larvae, while solitary species live singly and usually free-spawn eggs that develop into small, undifferentiated larvae. Ascidians in the order Stolidobranchia include both colonial and solitary species, as well as several species with intermediate morphologies. These include social species, which are colonial but do not live completely embedded in a common test, and a few solitary species that brood embryos and larvae until they are competent to metamorphose. We examined how many times coloniality has evolved within the Stolidobranchia, with phylogenetic analyses using full-length 18S rDNA and partial cytochrome oxidase B sequences for taxa in the families Molgulidae, Styelidae, and Pyuridae. Tunicata orders Phlebobranchia and Stolidobranchia are sister groups, and the family Molgulidae is a monophyletic group and should be raised to the subordinal level, as shown previously by analyses from this lab with partial 18S sequences. In contrast to previous studies, styelids and pyurids are separated into monophyletic groups by ML and Bayesian analyses. We show a single clade within the family Styelidae that contains two colonial (compound) botryllid species, a Symplegma (colonial compound), a colonial (social) species Metandrocarpa taylori, as well as four solitary species, thus confirming that the botryllids are a subfamily of the Styelidae. These results suggest that the ancestor of the Stolidobranchia was solitary and that coloniality has evolved only once within this clade of ascidians. Further phylogenetic analyses of aplousobranch and phlebobranch ascidians will be necessary to understand the number of times that coloniality has evolved within the class Ascidiacea.

Arenas, F., Bishop, J.D.D., Carlton, J.T., Dyrynda, P.J., Farnham, W.F., Gonzalez, D.J., Jacobs, M.W., Lambert, C., Lambert, G., Nielsen, S.E., Pederson, J.A., Porter, J.S., Ward, S., Wood, C.A. (2006). Alien species and other notable records from a rapid assessment survey of marinas on the south coast of England. Journal of the Marine Biological Association of the United Kingdom, 86, (6), 1329-1337. Sponsorship: National Science Foundation grant IOB 0407527; Esme Fairbairn Foundation ALIENS projectIn September 2004, a rapid assessment survey for non-native species was conducted at 12 harbours along the south coast of England from East Sussex to Cornwall, focusing on communities of algae and invertebrates colonizing floating pontoons in marinas. Over 80 taxa each of algae and invertebrates were recorded, including 20 recognized non-native species. The southern hemisphere solitary ascidian Corella eumyota was recorded in the UK for the first time and was present at three sites. The colonial ascidian Botrylloides violaceus was also recorded as new to the UK, but was very widespread and has probably been present for a number of years but misidentified as the native congener B. leachi, which was infrequent. Other ascidians included Styela clava, introduced at Plymouth in the early 1950s, which was recorded at all locations visited, and Perophora japonica, which was found only at the Plymouth locality where it first occurred in the UK in 1999. The diverse algal flora included nine alien species previously recorded in the British Isles. Range extensions and population increases were noted for the kelp Undaria pinnatifida and the bryozoan Tricellaria inopinata, both first recorded in UK waters during the 1990s. The widespread occurrence of another non-native bryozoan, Bugula neritina, appears significant, since in earlier times this was known in UK waters predominantly from artificially heated docks. The results of this survey indicate that dock pontoon systems in southern England are significant reservoirs of non-native species dispersed by vessels and other means. The proliferation of these structures is therefore of conservation importance. The new UK records highlight the need for periodic monitoring of ports for non-native species.Peer reviewe

Metamorphosis (Gr. meta- "change" + morphe "form") as a biological process is generally attributed to a subset of animals: most famously insects and amphibians, but some fish and many marine invertebrates as well. We held a symposium at the 2006 Society for Integrative and Comparative Biology (SICB) annual meeting in Orlando, FL (USA) to discuss metamorphosis in a comparative context. Specifically, we considered the possibility that the term "metamorphosis" could be rightly applied to non-animals as well, including fungi, flowering plants, and some marine algae. Clearly, the answer depends upon how metamorphosis is defined. As we participants differed (sometimes quite substantially) in how we defined the term, we decided to present each of our conceptions of metamorphosis in 1 place, rather than attempting to agree on a single consensus definition. Herein we have gathered together our various definitions of metamorphosis, and offer an analysis that highlights some of the main similarities and differences among them. We present this article not only as an introduction to this symposium volume, but also as a reference tool that can be used by others interested in metamorphosis. Ultimately, we hope that this article-and the volume as a whole-will represent a springboard for further investigations into the surprisingly deep mechanistic similarities among independently evolved life cycle transitions across kingdoms.

Metamorphosis is both an ecological and a developmental genetic transition that an organism undergoes as a normal part of ontogeny. Many organisms have the ability to delay metamorphosis when conditions are unsuitable. This strategy carries obvious benefits, but may also result in severe consequences for older larvae that run low on energy. In the marine environment, some lecithotrophic larvae that have prolonged periods in the plankton may begin forming postlarval and juvenile structures that normally do not appear until after settlement and the initiation of metamorphosis. This precocious activation of the postlarval developmental program may reflect an adaptation to increase the survival of older, energy-depleted larvae by allowing them to metamorphose more quickly. In the present study, we investigate morphological and genetic consequences of delay of metamorphosis in larvae of Herdmania momus (a solitary stolidobranch ascidian). We observe significant morphological and genetic changes during prolonged larval life, with older larvae displaying significant changes in RNA levels, precocious migration of mesenchyme cells, and changes in larval shape including shortening of the tail. While these observations suggest that the older H. momus larvae are functionally different from younger larvae and possibly becoming more predisposed to undergo metamorphosis, we did not find any significant differences in gene expression levels between postlarvae arising from larvae that metamorphosed as soon as they were competent and postlarvae developing from larvae that postponed metamorphosis. This recalibration, or convergence, of transcript levels in the early postlarva suggests that changes that occur during prolonged larval life of H. momus are not necessarily associated with early activation of adult organ differentiation. Instead, it suggests that an autonomous developmental program is activated in H. momus upon the induction of metamorphosis regardless of the history of the larva.