Johanna Seegel, M.Sc.
Zoological Institute and Museum
Cytology and Evolutionary Biology
Phone: +49 (0)3834 420 4108
Fax: +49 (0)3834 420 4067
In my PhD Project, I am working on developmental aspects of the olfactory system (both central and peripheral) of three malacostracan crustacean species in a comparative approach.
Distant chemoreception, or olfaction, is of central importance for a crustacean’s perception of its environment. The first antennae of Malacostraca are equipped with a number of unimodal olfactory sensilla, the aesthetascs. Each has hundreds of olfactory sensory neurons (OSNs) that project into the chemosensory lobes of the deutocerebrum, which are structured into globular to cone-shaped synaptic regions called glomeruli.
The central olfactory pathway has already been well-studied in insects, and despite there being considerable similarities of the general architecture between insect and crustacean olfactory processing, there are also some fundamental differences. It seems that in most insects, the olfactory receptor neurons expressing the same odorant receptor converge onto one respective glomerulus, whereas in crustaceans, a different wiring logic applies. Interestingly, while in the insect olfactory system the glomeruli are individually identifiable, no such individually different glomeruli are known in crustaceans. Futhermore, glomerular numbers are generally higher in malacostracan crustaceans than in insects, and the number of interneurons in the central olfactory pathway remarkably is two to three orders of magnitude higher in the former.
So far, the embryonic and larval development of the malacostracan olfactory pathway have mainly been studied on crayfish and never in a comparative approach for different malacostracan groups with different lifestyles, even though the olfactory systems of the adults are known to differ distinctly. Few data on the development of the peripheral olfactory pathway in Brachyuran crabs exist and indicate differences of aesthetasc development within Malacostraca. It seems likely that species with different life histories such as direct development versus metamorphosis and free-living lifestyle versus larval dependency on the mother would reflect on the function of olfaction in different live stages and thus on the development of both the peripheral and the central olfactory pathway.
Another interesting aspect of the development of a Malacostracan’s olfaction over time is turnover of antennae parts in crayfish. Crayfish add considerable numbers of annuli with aesthetascs and OSN clusters to their first antennae during their postembryonic phase, and also grow new ones and shed the old throughout adult life. This poses the question how each OSN cluster contributes to the odour spectrum an animal receives, and how newly emerging OSNs are integrated into an existing olfactory pathway.
In my project, I am studying the formation, morphology and immunoreactivity of the deutocerebral chemosensory lobes and their neurons, as well as the emergence and morphology of aesthetascs, on embryos and larvae of three Malacostraca with different life histories: Paryhale hawaiensis (Gammaridea, Amphipoda) with a direct development of the benthic larvae, Procambarus virginalis (Astacidea, Decapoda) with early larvae staying attached to the mother, and Hemigrapsus sanguineus (Brachyura, Decapoda) with a metamorphosis from planctic larvae to benthic adults. I am using confocal laser-scanning microscopy and immunohistochemistry against synapsin and different neurotransmitters such as orcokinin, and I am also planning to do 3D-reconstruction of parts of the central nervous system.
In my studies, I mainly worked in the field of Evolutionary Morphology of arthropods, mostly malacostracan crustaceans.
I did my Master’s Thesis at the University of Rostock, working on the comparative morphology of the female reproductive apparatus of several species the Anaspidesidae or “Tasmanian Mountain Shrimps” (Anaspidacea, Malacostraca, Crustacea). This research is yet to be published.
As part of my studies at the James Cook University, Queensland, Australia, I did fieldwork both in a rural tropical area and in the tropical mountain rainforest.
As part of my studies at the University of Rostock, I participated in a field trip to Russia, where I gained experience in species identification of amphipods of the White Sea.
In my Bachelor’s Thesis, I was concerned with the biology and ecology of non-indigenous species in the Baltic Sea, focusing on a newly introduced gastropod.