The evolutionary history of parasitic gastropods and their coral hostsin the Indo-Pacific = De evolutionaire geschiedenis van parasitaire slakken en hun gastheer koralen in de Indo-Pacific
Gittenberger, A. (2006). The evolutionary history of parasitic gastropods and their coral hostsin the Indo-Pacific = De evolutionaire geschiedenis van parasitaire slakken en hun gastheer koralen in de Indo-Pacific. PhD Thesis. Universiteit Leiden: Leiden. ISBN 90-9021100-4. 249 pp.
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Document type: Dissertation
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| Keywords |
Animal products > Coral
Biological phenomena > Evolution
Hosts
Interspecific relationships
Parasites
Gastropoda [WoRMS]
I, Indo-Pacific [Marine Regions]
Marine/Coastal |
| Abstract |
The central Indo-Pacific hosts the world’s richest marine fauna. For this extraordinarily high level of biodiversity two main explanations can be given. (1) Most Indo-West Pacifi c species are widespread, with most distributions overlapping in the Indo-Malayan centre of maximum diversity. (2) Many species have complex symbiotic and parasitic relationships that may accelerate speciation and promote diversity. Various questions still wait for answers, like for example: (1) Has speciation usually occurred in allopatry, so that the areas of overlap between sister taxa should be seen as a result of secondary range-shifts (related to the complex geological history of the area, with varying currents and water/land distributions related to plate tectonics and sea-level changes)? (2) How can gene fl ow be maintained over very long distances in putatively widespread species, whose pelagic larvae are supposed to be relatively shortlived? (3) Do complex symbiotic relationships among marine organisms lead to co-evolution, co-speciation, and hence elevated biodiversity? These questions can only be answered when the species themselves are clearly diagnosed and when their phylogenetic relationships have been unraveled. In the present study, mushroom corals (Fungiidae) and their gastropod parasites (Epitoniidae and Coralliophilidae) were studied as model organisms to contribute to answering the more general research questions. Morphological, ecological, molecular and distributional data were collected and analysed to be able to reach this goal. The primary results of this approach form the largest part of this thesis. For my research on the evolutionary and ecological relationships between scleractinian corals (Fungiidae, Dendrophylliidae, Euphylliidae) and their gastropod symbionts (Coralliophilidae, Epitoniidae), about 800 hours were spent underwater with the help of SCUBA. Approximately 60,000 stony coral specimens were searched for endoparasitic and ectoparasitic snails in various parts of the Indo-West Pacifi c, i.e. coastal areas of Egypt (Red Sea), Maldives, Thailand, Malaysia, Japan, Palau, Philippines, Indonesia and Australia. At most localities the fi eldwork lasted one week to a month. Additional periods of three and nine months (in 1997 and 2001, respectively) were spent in the Spermonde Archipelago, off Makassar, SW Sulawesi, Indonesia, which is situated in the centre of maximum diversity. The coral diversity here is among the highest in the world (fi g. 1). The family of the mushroom corals (Fungiidae) was used as a model taxon for the study on host specifi city in associated gastropods. A special effort was made to search all species within this family, in particular also the less commonly observed ones, which live in environments that are usually avoided by divers, such as sandy reef bases, shallow reef fl ats, areas with strong currents, or murky water. During the study, in total about 1000 individual coralliophilid and 3000 epitoniid snails were found in association with the corals examined. For most of these coral infestations the locality, depth, microhabitat, parasite species and host species were noted. Subsequently, the DNA of about 600 parasitic gastropods and mushroom corals was sequenced and used for phylogeny reconstructions. The genetic analyses made clear that both families of associated gastropods showed a surprisingly speciose, cryptic, adaptive radiation. There appeared to be many more endo- and ectoparasitic gastropod species associated with fungiid corals than previously thought on the basis of shell characters only. Furthermore, the associations between parasites and their host species are far more exclusive than hitherto perceived. In associations where parasitic species cannot unequivocally be identifi ed on the basis of their shell morphology, molecular data (DNA sequences), host species preferences, and the structure of radulae and jaws, turned out to be much more useful in species distinctions. The phylogeny reconstruction of the mushroom corals, based on molecular data, in general resembles the one based on morphological data (Hoeksema, 1989). The most conspicuous deviation is caused by a misleading case of convergent evolution, associated with a reversal to an ancestral character state (the loss of the ability to detach from the substrate). A comparison between the phylogeny reconstructions of the fungiid corals, the epitoniids and the Leptoconchus species, respectively, indicates that the phylogenetic histories of these three species groups are clearly interlinked. For outgroup comparisons also epitoniids not associated with corals were collected in the fi eld. The phylogenetic analyses indicate that the ancestors of the recent coral-associated wentletraps were parasites of sea-anemones and that a host shift from sea-anemones (Actiniaria) to hard corals (Scleractinia) has occurred only once in their evolutionary history, since the coral-associated epitoniids form a monophyletic group. |
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