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" Morphological and Reproductive Plasticity in Pocillopora Corals "
Johnston, Erika Caitlin
Toonen, Robert
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Latin Dissertation
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English
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| Record Number
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1052479
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| Doc. No
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TL51596
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| Main Entry
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Johnston, Erika Caitlin
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| Title & Author
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Morphological and Reproductive Plasticity in Pocillopora Corals\ Johnston, Erika CaitlinToonen, Robert
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| College
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University of Hawai'i at Manoa
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| Date
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2019
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| Degree
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Ph.D.
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| student score
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2019
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| Note
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92 p.
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| Abstract
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Corals in the genus Pocillopora are found throughout the Indo-Pacific, Red Sea, and Arabian Gulf, and are notoriously phenotypically plastic. Historical morphological classification of this genus has resulted in over 60 species described, of which only about 16 are generally accepted today. Such morphological plasticity has obscured species boundaries, distributions, ecology, reproductive biology, and stress response for more than a century, leading many to hypothesize that hybridization in this genus is rampant. Several recent studies that defined species boundaries used both morphological and genetic data and typically focused on the mitochondrial open reading frame marker (mtORF). Such efforts have produced conflicting results such that genetic lineages agree with morphological taxonomy for some studies but not others. In this dissertation, I investigated species boundaries and described their evolutionary history using ezRAD-seq data from 15 Pocilloporidae individuals. This approach allowed me to resolve clear monophyletic groups that are in concordance with mtORF data. I found no evidence of introgressive hybridization, with the possible exception of the most recently derived sister species. The rooted mitochondrial phylogeny agreed with fossil evidence and indicates that the genus Pocillopora evolved during the Eocene, however, extant species are young (<3 MYA). These data suggest that Pocillopora experienced a strong bottleneck and subsequent radiation around the same time as the closure of the Isthmus of Panama, which resulted in Northern Hemisphere glaciation and a reduction in the El Niño effect. The concordance between the mtORF marker and this phylogenomic approach indicates that the mtORF marker can be used to assign species identity for nearly all species of Pocillopora. The exception is P. meandrina and P. eydouxi, which can usually be distinguished using gross colony morphology, but cannot be differentiated using the mtORF marker. However, using ezRAD-seq data, these species could be distinguished with nuclear DNA. By developing a simple restriction fragment length polymorphism (RFLP) assay that quickly and cheaply distinguishes the six Pocillopora species found in Hawai‘i, I document frequent misidentification of species in the field and unexpected patterns of species distribution across the state that were masked by morphological plasticity. The final research chapter of this dissertation investigated reproductive plasticity in P. meandrina as a result of the bleaching severity that individual colonies experienced in situ across four sites around O‘ahu, Hawai‘i, during the 2015 mass coral bleaching event that occurred across the state. Colonies of P. meandrina showed no overall loss of reproductive effort as a result of the bleaching event, but individual impacts were size dependent. Colony size mediates the effect of bleaching on reproductive output such that fecundity was significantly reduced in small colonies that bleached severely, while it had no apparent effect in medium colonies, and actually increased fecundity in large colonies. Pocillopora corals today are currently found throughout ~98% of the Indo-Pacific ecoregions and are abundant in suitable habitats from high to low latitudes. Such morphological and reproductive plasticity may have allowed this genus to rapidly adapt to and diversify throughout its range.
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Biology
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Ecology
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Zoology
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Toonen, Robert
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University of Hawai'i at Manoa
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