World Congress of Malacology Antwerp ... - Unitas Malacologica

Extinction and immigration in the wake of climatic deterioration: Marine molluscan diversity
in the Pliocene-Quaternary in the southern North Sea Basin
Wesselingh, Frank P.; Janse, Anton; Meijer, Tom
Naturalis, P.O. Box 9517, 2300 RA, Leiden, The Netherlands,
Email: wesselingh@naturalis.nnm.nl
During the Pliocene and early Quaternary, a strong marine molluscan faunal turnover occurred in the
North Sea Basin. In this poster we document the extinction of warm-temperate/subtropical taxa as
well as species endemic to the North Sea Basin during the Zanclean-Gelasian and their replacement
by Pacific and Arctic immigrant species. During the Zanclean (ca. 4 million years ago) the mollusc
fauna was rich in species, several of which persist nowadays in more southerly areas such as the
Mediterranean. Also, a considerable number of supposed North Sea endemics occurred. Diversity
deteriorated drastically during the Piacenzian and Gelasian (c. 1.8-3.5 million years ago). This is in
part explained due to cooler climate regimes and a general shallowing of the North Sea, but mostly
caused by the disappearance of oligotrophic habitats as a result of increased glacial cyclicity and
associated hinterland erosion. Immigrants expanded to become major faunal elements in the North
Sea Basin at the same time. At the end of the Gelasian, an impoverished boreal fauna inhabited the
North Sea.
The genesis of Tyrian purple precursors in the gonoduct and egg masses of Dicathais orbita
(Neogastropoda: Muricidae)
Westley, Chantel; Benkendorff, Kirsten
School of Biological Sciences, Flinders University, GPO Box 2100, Adelaide, South Australia, 5001,
Email: chantel.westley@flinders.edu.au; kirsten.benkendorff@flinders.edu.au
Muricid molluscs, such as Dicathais orbita, are renowned for production of the ancient dye, Tyrian
purple. Within the hypobranchial gland is the prochromogen, tyrindoxyl sulphate. By action of
arylsulphatase, cytotoxic intermediates are generated, and in the presence of sunlight, Tyrian purple
evolves. Tyrian purple genesis also occurs in muricid egg masses; however, the origin of precursors
is presently unknown. As the hypobranchial gland lies adjacent to the capsule gland, it is
hypothesized that precursors are introduced into the intracapsular fluid as a form of maternal
investment. Alternatively, encapsulated embryos may possess the capacity to synthesize precursors
de novo. To determine precursor distribution in the female reproductive system, a method was
developed for the quantification of dye precursors using liquid chromatography-mass spectrometry
(LC-MS). Tyrindoxyl sulphate dominated capsule, albumen and ingesting gland extracts and the
intermediates, tyrindoxyl, tyrindoleninone and tyriverdin were detected in capsule gland extracts.
This provides preliminary evidence for the involvement of Tyrian purple genesis in muricid
reproduction. To investigate the potential incorporation of precursors into egg capsules, novel
histochemical techniques for the localization of compounds and enzymes essential for prochromogen
and intermediate synthesis were applied to the female pallial gonoduct and encapsulated juveniles.
Albumen and capsule glands were found to incorporate tryptophan, bromoperoxidase and
arylsulphatase into the intracapsular fluid and lamina of egg capsules, and the vitellus of embryos. In
regions where bromoperoxidase and tryptophan were found to coincide, tyrindoxyl sulphate was also
histochemically detected, indicating the potential for prochromogen synthesis. LC-MS analysis of
egg capsule fractions revealed that tyrindoxyl sulphate concentration was 1000-fold higher in embryo
than intracapsular fluid extracts, but declined from embryo to veliger in conjunction with vegetal pole
absorption. This and the absence of a true hypobranchial gland in embryos, suggest that precursors
arise in the egg masses of D. orbita from a maternal source.
240