Adaptation of reef corals to climate change is an issue of much debate, and often viewed as too slow a process to be of relevance over decadal time scales. This notion is based on the long sexual generation times typical for some coral species. However, the importance of somatic mutations during asexual reproduction and growth on evolution and adaptation (i.e., cell lineage selection) is rarely considered. Here we review the existing literature on cell lineage selection and show that the scope for somatic mutations to arise in the coral animal and associated Symbiodinium is large. For example, we estimate that ~100 million somatic mutations can arise within a branching Acropora coral colony of average size. Similarly, the large population sizes and rapid turn-over times of in hospite Symbiodinium likely result in considerable numbers of somatic mutations. While the fate of new mutations depends on many factors, including ploidy level and force and direction of selection, we argue that they likely play a key role in the evolution of reef corals
Background: Studies of population genetic structures provide an indication of direction and magnitude of larval transport and hence are an important component in the assessment of the ability of reefs to recover from severe disturbance. This paper reports data on population genetic structures in the coral Pocillopora damicornis from 26 reefs in Kenya and Tanzania.
Here we report the isolation of 44 microsatellites from the brooding, pocilloporid coral, Seriatopora hystrix, developed from a partial genomic DNA library using a repeat enrichment protocol. A further eight previously published microsatellites were also tested; five of these were developed for S. hystrix, whereas three were isolated from corals of the closely related genus Pocillopora. Out of these, we incorporated nine and 10 primer pairs into two multiplex reactions that reliably amplified polymorphic microsatellites in populations from the west and the east coast of Australia, respectively. Number of alleles ranged from three to 22 per locus.
We report an accurate multiplex reverse transcription quantitative polymerase chain reaction (RT-qPCR) assay, capable of reproducing gene expression profiles from 16 target genes [12 genes of interest (GOIs) and four reference genes (RGs)] in Acropora millepora, a common reef-building model coral species. The 12 GOIs have known or putative roles in the coral bleaching response, yet the method is not restricted to this particular assay and gene set. The procedure is based on the Beckman Coulter (Fullerton, CA, USA) GenomeLab™ GeXP Genetic Analysis System and bridges the gap between quantitative real-time PCR (qPCR) expression analysis of a single or a small number of genes and microarray gene expression surveys of thousands of genes. Despite large variation among biological replicates, the majority of GOIs were up-regulated (up to 4000%) in most colonies during a laboratory-based thermal stress experiment. Two genes, Nf-kβ2 and MnSod, were consistently up-regulated in all colonies tested, and we therefore propose these as candidate markers useful for population-level evaluations of thermal stress. Our assay provides an important new tool for coral bleaching studies; because of the lower cost, labour and amount of cDNA required compared with singleplex qPCR, population-level studies with large biological replication are feasible.
The impact of a mass bleaching event on temporal and spatial population genetic structure in 4 scleractinian coral species in the Acropora aspera group was studied around the Palm Islands in the central Great Barrier Reef. Species status of sympatric populations of 2 of the 4 species, A. millepora and A. spathulata, was confirmed by the population genetic data; these species have recently been separated based on morphological and breeding characters. Spatial analyses of population samples from 2004 detected differences in the level of gene flow among locations. No significant genetic differentiation was inferred between conspecific populations at Orpheus and Pelorus Islands, which are both located in the northern part of the island group and separated by ~1000 m. In contrast, all populations at Fantome Island were genetically differentiated, despite this island being located only 11 km south. Sampling of A. millepora and A. pulchra in the year prior to the 1998 mass bleaching event enabled a temporal comparison across this event. The genetic composition of these populations changed between 1997 and 2004, but patterns of genetic differentiation among locations were similar in 1997 and 2004. Extensive mortality of these species following the 1998 bleaching event did not cause an apparent reduction in genetic diversity and identical multi-locus genotypes were encountered in both temporal samples, suggesting that re-growth of surviving genotypes contributed to the recovery of these populations. Comparisons among the 4 study species revealed lower genetic diversity in A. papillare, consistent with its low abundance throughout its distributional range.
High intraspecific variability and lack of adequate field descriptions or distinguishing skeletal features has made identification of the scleractinian coral Platygyra daedalea challenging. This species displays a number of distinct morphological types that co-occur on lagoonal reefs in Kenya and which often cannot be separated by field observations. To better understand how morphological and genetic variations are related, morphometric and molecular techniques were used to examine phenotypic variation in P. daedalea. A canonical discriminant analysis of measurements of 10 skeletal characters confirmed the existence of 2 morphotypes. No single diagnostic trait could be used to distinguish the 2 morphotypes, though a combination of 4 characters separated them. A mathematical equation is presented to separate colonies into the 2 morphotypes, where field identification is not possible. Genetic differentiation was studied using 5 microsatellite loci and sequence analysis of the internal transcriber spacer (ITS1 and ITS2) and 5.8S region of the nuclear ribosomal RNA gene. AMOVA of the microsatellite and ITS sequence data showed significant genetic differences between the 2 morphotypes. However, phylogenetic analysis of the ITS sequences showed no evidence of sequence divergence between morphotypes, which suggests that they share a gene pool, or that the genetic divergence is recent. We conclude that the occurrence of distinct morphotypes is a characteristic of P. daedalea and that there does appear to be a genetic basis for separating morphotypes. However, genetic differences in P. daedalea could only be detected when combined with morphometric data.
KEY WORDS: Coral reefs · Taxonomy · Morphotypes · Indian Ocean · Platygyra daedaleaResale or republication not permitted without written consent of the publisher
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