Nemertean, copepod, and amphipod symbionts of the dimorphic ascidian Pyura stolonifera near Melbourne, Australia: specificities to host morphs, and factors affecting prevalences

Abstract

On the central coast of Victoria, Australia, the dimorphic ascidian Pyura stolonifera (Heller, 1878) harbors three endosymbionts: the nemertean Gononemertes australiensis Gibson, 1974, the copepod Doropygus pulex (Thorell, 1859), and the amphipod ParaIeucothoe novaehollandiae (Haswell, 1880). The specificities of these symbionts to two host colour morphs were studied during 1989 to 1991 as part of a multidisciplinary investigation aimed at determining whether the two morphs are genetically distinct. Distributional surveys revealed that nemerteans and copepods occur only in yellow and brown ascidians, respectively, and that amphipods live in both forms. These specificities held true not only when the two morphs were in allopatry, but also in sympatry. These observations, especially the sympatric data, suggest that the two host morphs might be genetically distinct. For example, the two morphs might have different genetically encoded internal milieus that favour the survival of nemerteans in yellow ascidians, and copepods in brown hosts. In transplant experiments, which involved moving ascidian morphs within and between habitats, the "wrong" symbionts never colonised the "wrong hosts". These results, although consistent with the hypothesis of genetic maintenance of specificity, were deemed inconclusive because of the difficulty of establishing reliable controls (i.e. vacant hosts). The relationships between symbiont prevalences and several factors (season, year, site within host, host individual, host habitat, host size/age, host breeding condition, and co-occurrence of other symbiont Department of Biology, Carnegie Science Hall, Bates College, 44 Campus Avenue, Lewiston, Maine 04240-6084, USA species) were also analysed. Both simple (e.g. greater prevalences for large hosts) and complex (e.g. prevalence x season x gonad state of host) interactions were detected for all three symbiont species. These are among the very few quantitative analyses of factors affecting prevalences of ascidicolous nemerteans and amphipods. The present report identifies one of very few definite nemertean-ascidian symbioses. Since no differences in gross condition were ever noticed between occupied and vacant hosts, it is suggested that all three symbionts are commensals rather than parasites or mutuals.

Characterization of macrofaunal assemblages associated with sponges and tunicates collected off the southeastern United States

“…The current study presents the first in‐depth look at sponges and their associated fauna inhabiting the continental shelf and slope off the southeastern United States. The current study is also one of a few studies that have examined fauna associated with tunicates (e.g., Svavarsson 1990; Dalby 1996; Theil 2000) and hexactinellid glass sponges (e.g., Kunzmann 1996; Beaulieu 2001a,b).…”

Environmental factors affecting reproduction and development in ascidians and other protochordates

“…The most familiar endobionts are parasitic copepods (Ooishi and Illg 1977;Illg and Dudley 1980;Gotto 1993;Dalby 1996), which are usually specialized to live in one or more of the host's internal organs. Amphipods live in the branchial sac of most solitary species (Dalby 1996;Thiel 1999Thiel , 2000 and feed on the mucous sheet produced by the host.…”

“…The most familiar endobionts are parasitic copepods (Ooishi and Illg 1977;Illg and Dudley 1980;Gotto 1993;Dalby 1996), which are usually specialized to live in one or more of the host's internal organs. Amphipods live in the branchial sac of most solitary species (Dalby 1996;Thiel 1999Thiel , 2000 and feed on the mucous sheet produced by the host. The amphipod Polycheria osborni Calman, 1898 makes a shallow burrow in the surface tunic of various colonial ascidians and orients itself ventral side up; it creates a feeding current by rhythmic beat-ing of the pleopods (Skogsberg and Vansell 1928;Lambert 1979).…”

“…The bivalve Mytilimeria nuttalli Conrad, 1837 is also found embedded in a variety of colonial ascidian species, apparently its exclusive habitat (Yonge 1952;Lambert 1979). Other symbionts recorded from ascidians include nemerteans (for review see Dalby 1996), pinnotherid crabs (Kozloff 1987), the cnidarian Bythotiara huntsmani (Fraser, 1911) in the oral siphon of Ascidia paratropa (Huntsman, 1912) and Ascidia columbiana (Huntsman, 1912) (Mills and Miller 1987;O'Clair and O'Clair 1998), and microfilamentous algae in the tunic matrix of several New Zealand species (Lambert et al 1996). The exact relationship between host and symbiont for many of these species has not been determined.…”

The solitary ascidian Herdmania momus: native (Red Sea) versus non-indigenous (Mediterranean) populations

“…For instance, higher winter temperatures may result in higher recruitment rates and faster growth rates of non-indigenous species (Stachowicz et al 2002b). In addition, since it is common to find in the branchial cavities of many solitary ascidians different crustaceans (Millar 1971;Monniot et al 1991;Dalby 1996) the study of these ''hitchhikers'' in their new environment may provide unique information on the mode of invasion and the origin of the non-indigenous host.…”