Abstract: Species are one of the fundamental units of biodiversity. Yet, defining a species remains a challenging task. The current consensus is that an integrative approach, using multiple lines of evidence, such as biology, ecology, morphology and genetics, is most appropriate for species delimitation. In the last two decades, molecular approaches coupled with a re-examination of morphology, have revolutionized our understanding of scleractinian taxonomy and phylogeny. Yet, some of the most abundant and species rich genera, such as Acropora, Montipora and Porites, have proved more challenging. In particular, the genus Porites includes many species that are major contributions to coral reef structure and function. Moreover, species in the genus often serves as models for ecological, physiological and paleoclimate studies. Yet, the taxonomy of the genus Porites is notoriously difficult, which undermines both accurate assessments of biodiversity and the interpretation of experiment results. The aim of this thesis was to use an integrated approach that included reduced genome analyses, quantitative and qualitative morphological data, and breeding trials, to clarify the species richness, taxonomy and historical biogeography of the Porites from 16 localities throughout the Indo-Pacific Ocean. I firstly evaluated the molecular diversity of Porites in the Indo-Pacific using high throughput sequencing data (RADseq), supplying a comprehensive hypothesis of the evolutionary history and historical biogeography of 31 nominal species and 11 morphologies that did not correspond to any of the type material examined. The phylogenetic analyses recovered 16 molecular lineages, 11 of which were composed of only one species, while the remaining five contained a complex of several nominal species plus unknown morphologies. In most of these species complexes, a recent origin between 1.9 and 0.1 Mya, coupled with clear morphological differences, suggests recent or on going speciation. Finally, historical distribution analyses suggest an Indian Ocean or Arabian origin for at least eight molecular lineages in the phylogeny. I next used multivariate morphometric analysis to determine the number of morphological groups based on 8 skeletal characters. Cluster analyses suggested there were 11 groups. PERMANOVA estimated that 63% of the variance was explained by the traditional a priori morphological groupings (based on comparison to type material), while 32% of the variance was explained by the genetic clades. The failure of the morphological analysis to find clear boundaries among the majority of nominal species, the additional unknown morphologies and the molecular clusters, confirms high morphological plasticity or homoplasy in Porites. Lastly, I tested for barriers to gene flow between Porites lutea and P. cylindrica, two nominal species of Porites that were not differentiated by the molecular analyses but have fundamentally distinct morphologies and ecologies. Cross-fertilization did not occur, suggesting that they are good biological species. In conclusion, the taxonomy and evolutionary history of the genus Porites is highly complex and uncertain, with different lines of evidence suggesting different numbers of groups. In addition, there are many groups that do not correspond to any of the type material, suggesting there are a number of undescribed species in the genus. A great deal of work is required to improve our understanding of the taxonomy and systematics of the genus, including the use of alternative molecular techniques, and sampling greater proportion of the nominal species in the group.

Biography: Tullia is originally from Italy, where she completed her Bachelor degree in Biological Sciences in 2013 at the University of Milano-Bicocca. In 2014 she moved to King Abdullah University of Science and Technology (KAUST) in Saudi Arabia, where she joined the Reef Ecology Lab of Prof. Michael Berumen. She completed her Master in Marine Science in December 2015 with the thesis “Species boundaries in the coral genus Goniopora from the Red Sea”. She started her PhD at KAUST in January 2016 under the supervision of Prof. Berumen, Prof. Voolstra and Prof. Tester, and, in the context of a co-tutelle programme, she joined the ARC Centre of Excellence for Coral Reef Studies in January 2017, where she works under the supervision of Prof. Andrew Baird and Prof. David Miller. Her PhD focuses on the use of different lines of evidence, spanning from genomics, morphology, and reproductive biology, towards a better understanding of species boundaries in the hard coral genus Porites.