PhD Student
Advisor: Andreas Wanninger

Unit for Integrative Zoology, Department of Evolutionary Biology
University of Vienna

Abstract

Despite its curious adult appearance, early development of the caenogastropod worm snail Thylaeodus cf. rugulosus (Vermetidae) follows a conserved, gastropod-typical indirect development including trochophore and veliger larval stages. However, what appears common on a morphogenetic level, seems to be controlled by a complex mechanism of brood regulation that putatively covers two distinct events of developmental arrest which prevent progeny from entering subsequent developmental stages. 
In more detail, the whole embryonic as well as larval development takes place inside of maternal brooding capsules, each capsule containing a multitude of embryos. But only a small number of embryos within one capsule develops until the larval phase. Most embryos remain in a multicellular pre-blastula stage and serve as nutritive resource for their viable siblings which enter the larval stage. However, out of about 10 viable larvae per brooding capsule it is again only a maximum of three animals that complete their development until hatching. Remaining siblings appear to get arrested in a stage that morphologically corresponds to the early veliger larva. In-situ labelling of candidate genes indicate that veliger larvae of different developmental fates show notable differences in their gene expression despite sharing the same morphology.

Although, some form of brood regulation frequently occurs in diverse marine gastropods, the particular combination of embryonic and larval arrest appears to be unique for Thylaeodus rugulosus and could allow for additional opportunities to regulate offspring. The exact molecular mechanisms controlling these complex and multilayered developmental mode, however, remain unexplored to date. The current project aims at unravelling transcriptomic differences that shape the distinction between viable and arrested animals in Thylaeodus rugulosus. We apply differential gene expression analysis on stage-specific transcriptomes and investigate expression patterns in situ. This will allow for insights into the genetic toolkit that determines developmental arrest versus regular embryonic and larval development in these elusive gastropod mollusks.