A new look at extreme parasitism

The Natural History Museum is offering one joint PhD studentship with the University of Southampton, starting on 1 November 2014 or as soon as possible thereafter.

Applications are invited from suitably qualified graduates (first degree results at least 2:1) and the studentship is only open to those who qualify for ‘Home’ tuition fees (UK/EU residence).

Deadline for applications: 19 September 2014. See below for project details and application instructions.
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Studentship details:

Parasitism is one of the most common modes of life on Earth and it is estimated that all metazoan species serve as hosts to at least one unique parasite species. Extreme parasites such as Sacculina, are of special interest to evolutionary biologists because they represent the peak of morphological adaptation achieved against a positively hostile microhabitat (i.e. being embedded within the host tissues and exposed to the host’s defence mechanisms). Parasitism has evolved independently numerous times within the Crustacea, in taxa such as copepods, isopods, cirripedes and tantulocarids. Highly transformed and secondarily reduced forms have become meso- or endoparasitic, living partially embedded in, or entirely within, their hosts. This process of reduction typically involves loss of body segmentation, swimming appendages, feeding apparatus and sensory structures, in tandem with the development of novel attachment and feeding systems, and enhanced sexual dimorphism. The diversity of body forms makes the Crustacea an ideal group to model and explore the impact of these conflicting processes.
In this project we aim to use a comparative approach and an innovative suite of methods to explore the impact of such extreme parasitism on the trophic and reproductive biology of different crustacean lineages that utilise fish, polychaetes and other crustaceans as hosts. The use of innovative methods including X-ray computed tomography (micro-CT, nano-CT, and synchrotron radiation micro-CT, SR-CT), and confocal laser scanning microscopy (CLSM), will allow us to characterise, in detail, the interface between parasite and host, and improve our understanding of the drivers of morphological change in parasitic lineages. The objectives are:
(i) To develop innovative techniques for visualising the physical interface between the embedded part (the endosoma) of the parasite and the surrounding host tissues.
(ii) To investigate how the properties of this interface relate to its twin function of securing attachment to the host and absorbing nutrients from the host.
(iii) To compare endosomal morphology in four families of copepods (Herpyllobiidae, Bradophilidae, Saccopsidae and Phyllodicolidae) from polychaete hosts, those taxa that parasitise crustaceans (Nicothoidae, Tantulocarida, Rhizocephala), and fish (Pennellidae). Trace fossils (cysts etc.) attributed to fossil parasitic crustaceans will also be investigated.
(iv) To explore the biology of males in extreme parasites i.e. some taxa have dwarf males which are dependent on the female for nutrients, others are virtually unknown.

The outcomes will include an improved understanding of key drivers of morphological change in extreme parasitic lineages – which will manifest as a major comparative paper in a high impact journal, supported by additional papers in good parasitological journals. An important additional outcome will be improved staining techniques for CT, in order to reveal more of the internal anatomy of highly modified parasites.
The key innovation will be in the use of cutting edge techniques: the most effective method currently available to accurately characterise and compare such internal structures is X-ray micro-CT. Features can be visualised in isolation, within the context of surrounding tissues and compared against those of other taxa using morphometrics. Using these non- destructive, non-invasive methods to create 3-D models has numerous advantages over

traditional techniques. However, the range of density differences in biological tissues is limited and must be enhanced before X-rays can be applied. Experimentation with staining agents, such as iodine and PTA, that increase X-ray opacity differentially within organisms, is still an active area of research and will be an important focus for this project. There are relatively few published methods, and none has been tested on closely coupled, host- parasite systems. Systematic comparison and correlation of data between a variety of imaging techniques (CT, scanning electron microscopy, CSLM and classic histology) and methodologies will allow us to evaluate this novel approach.

Full details can be found here: http://www.nhm.ac.uk/resources-rx/files/boxshall_hawkins-project-132561.pdf