My dissertation research explored the phylogeography of Oculina corals, particularly the invasive Oculina patagonica, and their algal symbionts.
Corals of the genus Oculina were originally described from the southeastern coast of North America, but Oculina patagonica is thought to have recently been introduced to the Mediterranean coast of Spain via shipping. From Spain, it supposedly spread east to Italy and eventually the Levant. For the first part of my dissertation, I investigated whether the alleged introduced and invasive O. patagonica, is in fact new to the Mediterranean Sea. Using five genetic markers, I found no genetic or historical demographic evidence to support a recent human-mediated introduction of O. patagonica from the western North Atlantic. Instead, it seems more likely that O. patagonica has always existed somewhere in the eastern Atlantic, either in undetectable numbers or overlooked sites and habitats, and has recently become invasive in the Mediterranean due to environmental changes.
My dissertation research also explored the algal symbiont communities harbored by Oculina corals, and their role in explaining the success of this genus across the western Atlantic and Mediterranean Sea. Corals form a crucial relationship with algal endosymbionts called zooxanthellae of the genus Symbiodinium. Bleaching is the result of a disruption of this relationship and is associated with nutritionally depleted coral with impaired reproduction and increased susceptibility to disease and mortality. Many studies link different Symbiodinium types to varying levels of thermal tolerance for the coral host. I examined whether Oculina corals harbor geographically different Symbiodinium communities across their range and, if so, whether the host’s genetics or habitat differences are correlated with this geographical variation. Using genetic and environmental data, I found that Oculina corals harbor different Symbiodinium communities across their range, and that habitat differences in sea surface temperature are better correlated with this variation than the host’s genetics, chlorophyll a concentration or depth, particularly in the Mediterranean. The results suggest that the Symbiodinium communities harbored by Oculina corals may reflect acclimatization to local environmental conditions.
Having established that O. patagonica is most likely a native invasive, my dissertation finally aimed to identify mechanisms that facilitate this coral's recent invasive characteristics. O. patagonica's expansion along the Mediterranean coast of Spain over the last 2 decades has been well documented. The invasive nature of this coral species is likely due in part to increased sea temperatures and coastal habitat modifications. Using a modified RAD-Seq to target host DNA, I found that populations from the recent northern expansion are genetically distinct from the westward expansion and core populations, and also harbor greater genetic diversity. I also found that temperature may have driven adaptation along the northern expansion, as genome scans for selection found three candidate loci associated with temperature in the north but none in the west. These results suggest that unique genetic variation, possibly due to limited dispersal across the Ibiza Channel, an influx of individuals from different depths, and/or adaptation to cooler temperatures along the northern expansion front may have facilitated the northward range expansion of O. patagonica in the western Mediterranean.
Altogether, my dissertation suggests that O. patagonica has been able to successfully respond to changing environmental conditions and expand in its native range by both symbiont switching and host adaptation. PDF
My dissertation research also explored the algal symbiont communities harbored by Oculina corals, and their role in explaining the success of this genus across the western Atlantic and Mediterranean Sea. Corals form a crucial relationship with algal endosymbionts called zooxanthellae of the genus Symbiodinium. Bleaching is the result of a disruption of this relationship and is associated with nutritionally depleted coral with impaired reproduction and increased susceptibility to disease and mortality. Many studies link different Symbiodinium types to varying levels of thermal tolerance for the coral host. I examined whether Oculina corals harbor geographically different Symbiodinium communities across their range and, if so, whether the host’s genetics or habitat differences are correlated with this geographical variation. Using genetic and environmental data, I found that Oculina corals harbor different Symbiodinium communities across their range, and that habitat differences in sea surface temperature are better correlated with this variation than the host’s genetics, chlorophyll a concentration or depth, particularly in the Mediterranean. The results suggest that the Symbiodinium communities harbored by Oculina corals may reflect acclimatization to local environmental conditions.
Having established that O. patagonica is most likely a native invasive, my dissertation finally aimed to identify mechanisms that facilitate this coral's recent invasive characteristics. O. patagonica's expansion along the Mediterranean coast of Spain over the last 2 decades has been well documented. The invasive nature of this coral species is likely due in part to increased sea temperatures and coastal habitat modifications. Using a modified RAD-Seq to target host DNA, I found that populations from the recent northern expansion are genetically distinct from the westward expansion and core populations, and also harbor greater genetic diversity. I also found that temperature may have driven adaptation along the northern expansion, as genome scans for selection found three candidate loci associated with temperature in the north but none in the west. These results suggest that unique genetic variation, possibly due to limited dispersal across the Ibiza Channel, an influx of individuals from different depths, and/or adaptation to cooler temperatures along the northern expansion front may have facilitated the northward range expansion of O. patagonica in the western Mediterranean.
Altogether, my dissertation suggests that O. patagonica has been able to successfully respond to changing environmental conditions and expand in its native range by both symbiont switching and host adaptation. PDF
Oculina patagonica colonies