World Congress of Malacology Antwerp ... - Unitas Malacologica

mixtures of pollutants. Moreover, as the development of biomarkers is based on the mechanistic
understanding of the biological responses to pollutants, biomarkers provide early warning signals that
precede changes in feeding activity and growth (which are endpoints of ecological relevance) and, on
the other hand, also may provide indication of chronic pollution after long-term exposure. A battery
of biomarkers (MT induction, intralysosomal metal accumulation, enlargement/shrinkage of digestive
cell lysosomes, lysosomal membrane stability; induction of AOX activity, accumulation of
lipofuscins, and (quantitative) histopathological alterations in the digestive gland) is currently
available. This battery was applied separately to male, female and immature slugs exposed to diverse
pollutants (metals –Cd, Cu, Zn, Pb, Hg-, organic chemicals –Kerosene-, and mixtures of metals and
metals+organic chemical compounds). It was observed that sensitivity and responsiveness to
pollution insult changes throughout slug life cycle (females are more susceptible than males and
immature juveniles). Likewise, slugs subjected to chronic pollution (i.e., inhabiting ancient miles)
and their descendents were less responsive to chemical insult but, interestingly, they were also less
affected by additional pollutant exposures. These are crucial issues in order to determine critical
values of biomarkers (baselines, toxicity thresholds –NOEC-) suitable for soil health assessment.
Overall, although biomarkers, pollutant tissue burdens and parameters indicative of general stress are
rarely correlated between them, biomarkers are valuable tools to link exposure to pollutants to
ecologically relevant effects in soils.
This research has been funded by Basque Government (BERRILUR I & II-Etortek), Spanish MEC
(PACARI – PNCYT) and Univ Basque Country (Consolidated Res Grp)
Cell and tissue biology of the mussel (Mytilus galloprovincialis) digestive gland: a novel view of its form
and function
Marigómez, Ionan
Cell Biol & Histol Lab, Zool & Cell Biol Dept, School of Sci & Technol, Univ of the Basque
Country, POBOX 644, E-48080, Bilbo, Basque Country,
Email: ionan.marigomez@ehu.es
A novel view of form and function of the mussel, Mytilus galloprovincialis, digestive gland is proposed
based on recent data concerning its cell and tissue biology. The digestive gland is comprised of complex
alveoli that include a central chamber from which finger-like tubular projections are projected. Each
digestive alveolus is connected by a single opening into a secondary duct in a non-terminal position, and is
packed by a layer of fibrous connective tissue. In small juvenile mussels, dozens of tubules arise from one
single chamber whereas in mature individuals each alveolus is comprised by 6-10 tubules connected to
one flattened chamber. The form of the alveolus may change throughout digestion, due to environmental
stress (finger-like tubules reduced in length), and with intertidal position (tubules are shorter and thicker in
subtidal than in intertidal mussels). Two differentiated mature cell types (digestive and basophilic cells)
comprise its epithelium. Since both cell types may undergo division by separate (autologous cell division
of mature cells) they must be considered two distinct cell types. Cell proliferation is neither eventual nor
continuous but governed by environmental factors. It follows a circatidal pattern modulated by tide (food)
and light in both intertidal and subtidal mussels and presents marked seasonal variability (whereas the
epithelium is entirely renovated every month in summer only vestigial cell proliferation occurs in winter).
As a result, it seems unconceivable that breakdown and reconstituting phases take place every digestion
cycle, as proposed in conventional models of feeding and digestion in bivalves. Accordingly, digestion
phases have been reinterpreted based on enzyme and lectin histochemistry, 3D-reconstruction and image
analysis, and a new model (digestions waves) is presented to explain cyclic intracellular digestion
processes and trafficking of food and debris in digestive diverticula., which includes close collaboration
between digestive and basophilic cells to produce lysosomal hydrolases.
This investigation was funded by Consolidated Res Grp (Univ Basque Country).
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