Graduation date: 1974

Thesis (M.S.)--University of Wisconsin -- La Crosse, 1991. / Includes bibliographical references (leaves 43-47).

Thesis (Ph. D.)--University of Michigan, 1937. / "Literature cited": p. 63-68.

Thesis (Ph. D.)--University of Michigan, 1937. / "Literature cited": p. 63-68.

Thesis--Copenhagen. / Includes bibliographical references.

Inaug.-diss. - Berlin. / Vita. "Libri adhibiti": p. 33-34.

Inaug.-Diss.--Berlin. / Vita.

Nudibranchia is the major Order of the gastropod Sub-class Opisthobranchia. Nudibranchs demonstrate a considerable evolutionary departure from the typical shelled gastropod and have achieved wide morphological and ecological diversity. Most species are recorded from nearshore rocky habitats where they are primary macrobenthic predators; most species are stenophagous limited to a single, or a few, prey species. Previous investigations had shown that most nudibranch species have evolved to an annual semelparous life history strategy and adopt a planktotrophic larval development strategy which would appear to be the ancestral conditions. Reviews of published data had drawn attention to some species which demonstrated an evolutionary departure from these ancestral modes and had evolved extended life history strategies combined with more advanced larval development strategies. Archidoris pseudoargus and Cadlina laevis are sponge-grazing dorid nudibranchs, and Tritonia hombergi, which feeds on an alyconarean soft coral, appeared to have extended life cycles. The aim of the present study was to investigate the life history and larval development strategies of these species and, via a study their physiological ecology, attempt to determine the selective forces which may have driven any evolutionary departure away from the ancestral condition. Archidoris pseudoargus was found to have a biennial semelparous life history strategy and a planktotrophic larval development strategy; the planktotrophic lai'vae were found to have some characteristics of the more advanced lecithotrophic laeval form. Cadlina laevis was found to have a perennial iteropalous life history strategy and a direct mode of larval development; this was the first observation of perennial iteroparity in the Order Nudibranchia. Archidoris pseudoargus and Cadlina laevis had markedly seasonal growth patterns with a high growth rate in spring and early summer, followed by a period of reduced growth, or even degrowth in late summer and over the winter. An allometric relationship was determined between body size and feeding rate for A. pseudoargus; the exponent was less than unity. For both species, a significant allometric relationship was determined between body size and respiration rate with an exponent less than unity indicating an increase in metabolic efficiency with body size. Both species displayed an acclimatization of respiration rate with increasing temperature; the acclimatization was more pronounced in C. laevis. Fecundity of both species was shown to have a significant allometric relationship body size with an exponent less than unity. Insufficient numbers of T. hombergi were collected and kept alive in the laboratory to undertake any experiments to generate meaningful data to answer these principal questions for this species. Results of the present study together with data published from previous investigations have been interpreted to suggest that the extension of the life cycle is a consequence of seasonal variations in prey quality and quantity. Rather than being an exception to the rule, it is suggested that extended life cycles could be the ancestral condition and the more common annual/sub annual life cycles would be a more adapted condition. These conclusions are based on the results obtained from laboratory investigations which are discussed in their application to the field situation.

The cosmopolitan distribution of the anascan bryozoan Electra pilosa manifests itself in the phenotypic plasticity of growth morphology expressed. Longterm field observations of the bryozoan on the essentially ephemeral substrata of the marine macroalgae, Fucus serratiis and Laminaria digitata, at two contrasting sites in Scotland, confirm this. Despite its potential for exponential indeterminate growth, Electra pilosa rarely realises this in the field. Observations show that any pattern of growth is complicated and distorted by the influences of physical (colony abrasion and the dynamics of the substratum) and biotic disturbance (predation by the nudibranch Adalaria proxima). Rather than effect a visible induced defensive response after sustaining injury from mechanical damage or Adalaria proxima, Electra pilosa was demonstrated to maintain a high specific growth rate. It is suggested that this would preclude the settlement of potential competitors and ensure the fitness of this competitively weak, opportunistic species. Adoption of a stellate colony morphology was not concomittant with higher predation susceptibility but rather represented a plastic adaptive response to an ephemeral, dynamic environment. The lack of a metamorphic response to anything other than the presence of live Electra pilosa clearly demonstrated that metamorphosis of Adalaria proxima is by some component of the live, intact bryozoan. This component is neither water- soluble or extractable, and the inductive property is eliminated by homogenisation and freezing. Although hypotheses for this are evaluated, the mechanism of induction and the reasons for this relationship remain unclear. Adaptations to this close nudibranch-bryozoan association are therefore evident in the life history strategies of both species.

This study investigated the reproduction, larval growth and metamorphosis of the nudibranchs Onchidoris bilamellata (L.) and Goniodoris nodosa (Montagu) under controlled laboratory conditions. In addition, the rare occurrence of spawning events of O. bilamellata taking place in the field outwith the winter and spring reproductive period was studied. Onchidoris bilamellata and Goniodoris nodosa differ in the size and number of eggs produced per spawning event. In the present study O. bilamellata does not exhibit a clear spawning pattern, whereas G. nodosa lays increasingly smaller eggs and larvae as the season progresses. The diameter of the eggs of O. bilamellata is not correlated with the organic content per egg. The data available for G. nodosa were insufficient to analyse this relationship. The rates of larval growth and development are reported for Onchidoris bilamellata and Goniodoris nodosa. These variables do not differ significantly for O. bilamellata between cultures maintained under various light regimes, ranging from continuous darkness to continuous illumination, and are comparable to those of G. nodosa. The shell growth pattern exhibited by larvae of G. nodosa is sigmoid, similar to that of other opisthobranchs. Spawn masses laid during the winter and spring months were collected fresh from the field and compared to spawn masses collected from the field in July and September, outwith the typical spawning period of Onchidoris bilamellata in the British Isles. The shell size of the July and September hatchlings was significantly smaller than that of the winter and spring hatchlings. Furthermore, the larvae hatched from spawn masses laid in September cultured in the laboratory exhibited high mortality rates and the overwhelming majority did not survive through metamorphosis. The significance of the spawning activity of O. bilamellata past the typical spawning period of this species is discussed. The induction of metamorphosis of Onchidoris bilamellata was investigated using seawater containing elevated concentrations of potassium ion, and the results indicate that the optimal concentration inductive of metamorphosis is 19 mM K+ ASW, Metamorphosis experiments were also performed with the natural prey of O. bilamellata, the acorn barnacle Semibalanus balanoides (L.). The results suggest that pediveligers can be induced to metamorphose at a distance from the inductive substrata. Attempts were made to identify the natural inductive cue of Goniodoris nodosa, but this was not successful.