Approaching the evolution of parasitism in a historical context

Wal, Serita van der (2024): Approaching the evolution of parasitism in a historical context: isopod crustaceans as an example. Dissertation, LMU München: Fakultät für Biologie

Abstract

Parasites are often depicted as harmful antagonists in an ecosystem, hindering the fitness of those they rely on for survival, reproduction and dispersal. Even though this may be the case for a number of cases, parasites and parasitic associations are, and have been crucial in the evolutionary diversification and survival of species. In fact, parasitism is such a highly successful life strategy, that almost half of all multicellular species exhibit some degree of parasitism throughout its lifecycle. In addition, parasites play an essential evolutionary role in the health and sustainability of an ecosystem. By understanding their effects, ecological roles and development, we are able to better manage and describe parasitic interactions and their evolutionary trends. In this dissertation, isopod crustaceans are used as an example group to study the evolution of parasitism in a historical context. This group serves as the ideal ‘model’ group as they are quite well-known; abundant in almost all habitats on earth; have complex and varying ontogenetic developmental patterns; and exhibit extraordinary parasitic life and feeding strategies. Comparative morphometric analyses of attachment structures of groups exhibiting various parasitic life strategies and ecological roles through development, can provide insight into the evolutionary diversification and specialisation of structures for a specific parasitic lifestyle. Including both extant and fossil specimen material from various ingroups and ontogenetic stages, allows for a more comprehensive analysis of differentiation in these structures over time and through development. As adult and immature stages often have varying ecological functions (usually correlated with feeding behaviour and level of maturity) the inclusion of the often overlooked and highly underrepresented immature stages are essential in this study. This study aimed to provide data that can substantiate if and how attachment structure morphologies and changes in these morphologies, are derived from the specific parasitic strategies and ecological functions among ingroups of Cymothoida. The results present and discuss in particular the morphological variation and differentiation in morphology of the distalmost part of the thoracopod, the dactylus, used to attach to a host. The variation in shape is compared between representatives of non-parasitic- temporary parasitic and permanent parasitic ingroups morphological change resulting from ecological function and feeding habit. The results have shown that parasitic strategy and ontogeny play a role in the shape of attachment structures, with most variation seen in the curvature and thickness of the dactylus. The evolution of dactylus shape through parasitic strategies is proposed as a stepwise process where: 1. the posterior dactyli of representatives of temporary parasitic ingroups retain its resemblance to the plesiomorphic condition as seen in the non-parasitic representatives, while the anterior dactyli shapes become specialised for temporary attachment to a host. Finally, 2. the posterior dactyli of representatives of permanent parasitic groups deviate from the plesiomophic condition and diversify along with the anterior dactyli, specialised for permanent association with a host using all attachment structures. The results additionally suggest that the attachment structures of representatives of the permanent parasitic ingroup, Epicaridea follow a similar pattern to representatives of the temporary parasitic ingroup, Aegidae, rather than that of the remaining permanent parasitic representatives of Cymothoidae.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 570 Biowissenschaften, Biologie
• Fakultäten: Fakultät für Biologie
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 22. Januar 2024
• 1. Bericht­erstatter:in: Haug, Joachim