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The 1996 Annual Award Winner is:
Dr Bernadette Holthuis


Summary of thesis

Background

Work in progress


Bernadette Holthuis has been awarded the Society's 1996 Annual Award for her thesis on " Evolution between marine and freshwater habitats: a case study of the gastropod suborder Neritopsina" (The University of Washington, Ph.D., 1995).

The adjudicators (Alan Bebbington, Stuart Bailey and David Reid) considered that each of the three candidates had produced interesting and high quality work, but were unanimous in their ranking and, with great pleasure, recommended Dr Holthuis for the Award. The adjudicators found her work well researched and presented. The results were stimulating and of wide relevance to malacology and freshwater biology. The work demonstrates that anatomical studies continue to be a relevant and competitive force in biology.

Summary

Why have organisms moved between marine and freshwater habitats repeatedly in evolutionary history? Benthic development is much more prevalent among freshwater invertebrates than among their marine ancestors, and Dr Holthuis concludes that downstream loss of larvae in running waters is primary in selecting for benthic development. In the Neritopsina, Bernadette had first to evaluate the 113 genus group names, concluding that 53 are potentially valid, and that the pallial reproductive duct is derived not from the kidney, as had been previously supposed, but from mantle tissues. A phylogenetic tree was constructed from the anatomical survey, for genera and sub-genera in the Neritidae, Septariidae and Phenacolepadidae, based on the single most parsimonious tree for 57 morphological characters. The most parsimonious reconstructions indicate at least 12 shifts between marine, brackish and freshwaters: the origin of an osmoregulatory kidney in brackish waters is followed by 5 to 6 evolutionary shifts into freshwater. She proposes that the greater intensity of biotic interactions is the primary constraint limiting evolution toward greater salinities. Free-swimming veligers, ancestral for the group, were lost at least four times (twice in freshwater), and food eggs evolved in two different lineages with benthic development.

On being informed of the Award by the President, Dr Holthuis thanked the Society and described how the work was carried out, and how it is continuing.

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Background

"Although I enrolled as a graduate student at the University of Washington, I spent relatively little time in Seattle. Research was done primarily 'in the field' - i.e. on tropical Pacific Islands, where non-marine neritids abound. I collected and dissected specimens in French Polynesia, the Cook Islands, Fiji, Hawaii, Guam and elsewhere. I was also lucky enough to make a trip to the Caribbean to obtain specimens of Fluvinerita (a genus endemic to Jamaica). I am very grateful to a number of malacologists (Philippe Bouchet, Gerhard Haszprunar, Anders Waren, John Wise) who collected, preserved and sent specimens of species that I did not have the opportunities to collect myself. The taxonomic aspects of my research were done in the library and collections of the Division of Mollusks at the USNM, where I spent 1 1/2 years under the tutelage of the late Joe Houbrick.

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Work in progress

"I am currently a research associate at the Marine Laboratory of the University of Guam. I am continuing my anatomical studies of neritids, with the addition of a number of genera: e.g. Shinkailepas and Olgasolaris from hydrothermal vents, and Pisulina from marine caves (living Pisulina had not been known until this year; Tomoki Kase kindly sent me specimens). Another branch of research that I am currently pursuing is a study of the coevolution of male and female reproductive systems among aquatic Neritoidea. The triaulic female systems of some genera are the most complex known among dioecious invertebrates, and have evolved in conjunction with elaborations of the male system (penis and spermatophores). These animals provide a model for testing hypotheses about the nature of selective forces driving the evolution of reproductive systems."

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