Year

2022

Degree Name

Bachelor of Marine Science (Honours) (Dean’s Scholar)

Department

School of Earth, Atmospheric and Life Sciences

Advisor(s)

Natalie Rosser

Abstract

Symbiodiniaceae is family of unicellular photosynthetic microalgae which commonly form endosymbiotic relationships with reef-building corals, providing up to 95% of their photosynthetic products to their coral host, contributing a significant portion of the coral’s energy needs. Within the family Symbiodiniaceae there are several named genera, with many genetically distinct ‘types’ or ‘strains’ within each genus. There is a high level of physiological and ecological variation between types, which in many cases allows corals to adapt to local environmental conditions by associating with better suited symbionts. On multiple reefs off the coast of Western Australia there are several coral species in which conspecific colonies spawn in different seasons, and genetic analysis has shown that colonies which reproduce in different seasons represent genetically distinct cohorts. The aim of this thesis was to determine whether genetic variation in Symbiodiniaceae hosted by Acropora species in Western Australia is greatest between (a) different geographical locations, (b) different Acropora species (Acropora millepora and Acropora samoensis), or (c) conspecific individuals which reproduce in different seasons. Low-coverage whole genome sequencing of 49 coral colonies from Ashmore Reef, Barrow Island and Ningaloo Reef in Western Australia was used to investigate patterns in variation of symbionts. Population structure was examined using principal component analysis (PCA) and permutational analysis of variance (PERMANOVA) to find patterns in genetic variation among colonies and statistically test which factors (spawning time, host species identity, and geographic location) were significant influences on this variation. The proportion of different symbiont genera in each sample was also calculated, along with phylogenetic analysis to identify which symbiont types were present. Population structure analysis revealed that the most influential factor on Symbiodiniaceae variation was latitude, with significant differences in genetic composition between northern (Ashmore Reef), and southern (Barrow Island and Ningaloo Reef) sites. There was no detected effect of either coral host species identity or reproductive timing on Symbiodiniaceae composition. >99% of symbiont DNA sequences in each sample were identified as belonging to genus Cladocopium, which is the most widespread genus of symbiont, dominating most Acropora vi communities. Further phylogenetic analysis suggested that the dominant symbiont type in the northern site (Ashmore Reef) was Cladocopium type C40, while the dominant type in both southern sites (Ningaloo Reef and Barrow Island) was Cladocopium type C123. This is the first study to find differences in the dominant symbiont type in conspecific Acropora corals between locations of varying latitude in Western Australia. The most probable cause of this difference is the variation in environmental conditions between sites, with temperature and light availability being the most common predictors of Symbiodiniaceae distribution. Future studies could include investigation into how these environmental conditions vary between these locations, and whether there are other Symbiodiniaceae types present in smaller densities which were unable to be detected using the methods in this study.

FoR codes (2020)

310204 Genomics and transcriptomics, 310305 Marine and estuarine ecology (incl. marine ichthyology)

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.