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Causes and consequences of spatial genetic variation in two species of scleractinian coral in East Africa: Levels of genetic differentiation and intraspecific diversity of Pocillopora damicornis and Platygyra daedalea
Södertörn University, School of Life Sciences. Stockholms universitet, Zoologiska institutionen.
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The work presented in this thesis is a study of the spatial genetic structure of two species of scleractinian corals, Pocillopora damicornis and Platygyra daedalea. The overall objective was to investigate the current capacity of MPAs to preserve and restore coral reefs and to contribute information to improve management decisions. Samples were taken from 11 sites along the coast of Kenya. In addition P. daedalea was sampled from one site on each of the islands of Unguja (Zanzibar archipelago) and Mafia in Tanzania.

Populations of P. daedalea were largely panmictic within two lagoonal clusters. Samples obtained from two off-shore sites were more similar to the samples from the island samples in Tanzania than they were to proximal lagoonal samples. Off-shore and island samples were also significantly more genetically diverse in both the level of heterozygosity and allelic richness. Migration predominantly occurs from off-shore and island reefs toward the lagoonal reefs. The investigated populations of P. damicornis exhibited limited genetic neighbourhoods and highly localised recruitment and a significant pair-wise differentiation was found between a majority of the sampling sites. These results are probably a cause of the genetic bottleneck caused by the high mortality of this species during the 1998 coral bleaching event and reflects subsequent founder events and variable recruitment patterns, causing genetically distinct populations.

P. damicornis also displayed plastic reproduction, with some sites being dominated by large numbers of identical multilocus genotypes. The clonal colonies showed signs of being genotypcially distinct as they were all found to be homozygotes for a specific allele at one of the microsatellite loci. Due to the decreased genotypic diversity, associated with the high rate of clonal reproduction, the level of genetic diversity and allelic richness tended to be lower at unmanaged reefs. Also, the probability of encountering clonally produced individuals was significantly greater on unprotected reefs compared with protected reefs.

Canonical discriminant analysis of measurements of ten skeletal characters identified two distinct morphological types of P. daedalea. Analysis of molecular variance showed that morphotype explained a larger proportion of the genetic divergence than did the geographic distribution of sites sampled within MMP. However, phylogenetic analysis of rRNA sequences showed no evidence of sequence divergence, neither between morphotypes nor between samples of P. daedalea from MMP and samples of Platygyra sinensis from Hong Kong.

In summary, these data demonstrate the importance of incorporating multiple species and aspects when addressing the issue of connectivity and its implications for management. P. damicornis would benefit from localised management efforts to preserve its genotypic diversity, whereas P. daedalea would benefit from larger reserves to minimise the risk of loosing rare alleles through genetic drift which would further reduce its genetic diversity on lagoonal reefs. It also brings the subject of morphological characteristics and local adaptation into focus by revealing possible genetic divergence between two morphotypes of P. daedalea and two reproductive modes in P. damicornis.

Place, publisher, year, edition, pages
Stockholm: Stockholm University, 2007. , 190 p.
Keyword [en]
population genetics, corals, Kenya, Tanzania
National Category
Zoology
Identifiers
URN: urn:nbn:se:sh:diva-25142ISBN: 978-91-7155-398-0OAI: oai:DiVA.org:sh-25142DiVA: diva2:758403
Public defence
2007-05-25, sal G, Arrheniuslaboratorierna, Svante Arrhenius väg 14-18, 13:00
Opponent
Supervisors
Available from: 2014-10-27 Created: 2014-10-27 Last updated: 2014-10-27Bibliographically approved
List of papers
1. Spatial genetic patterns in lagoonal, reef-slope and island populations of the coral Platygyra daedalea in Kenya and Tanzania
Open this publication in new window or tab >>Spatial genetic patterns in lagoonal, reef-slope and island populations of the coral Platygyra daedalea in Kenya and Tanzania
2008 (English)In: Coral reefs (Print), ISSN 0722-4028, E-ISSN 1432-0975, Vol. 27, no 2, 433-439 p.Article in journal (Refereed) Published
Abstract [en]

Considering the rapid degradation of coral reefs, it is becoming increasingly important to assess factors such as levels of intraspecific genetic diversity and degree of connectivity between populations and reefs. In this study, five DNA microsatellite markers were used to infer migration patterns and levels of genetic diversity in ten populations of the faviid coral Platygyra daedalea along the coast of East Africa. Populations from reef-slopes and offshore islands had significantly greater genetic diversity, measured as expected heterozygosity and allelic richness than those of inshore lagoonal reefs. A combination of F-statistics and individual assignment tests indicated moderate to high levels of gene flow among lagoonal populations, and less migration between lagoonal sites and the reef-slope and island sites. These results suggest that reef-slope and island reefs could be important reservoirs of genetic diversity for this coral species.

National Category
Biological Sciences
Identifiers
urn:nbn:se:sh:diva-5564 (URN)10.1007/s00338-007-0342-7 (DOI)000255191100027 ()2-s2.0-42549099151 (ScopusID)
Note

Som manuskript i avhandling. As manuscript in dissertation.

Variable migration patterns and differences in levels of genetic diversity between lagoonal, off-shore and island populations of the coral Platygyra daedalea in Kenya and Tanzania

Available from: 2011-01-18 Created: 2011-01-18 Last updated: 2014-10-27Bibliographically approved
2. Limited migration and significant population sub-division in the coral Pocillopora damicornis on reefs along the coast of Kenya
Open this publication in new window or tab >>Limited migration and significant population sub-division in the coral Pocillopora damicornis on reefs along the coast of Kenya
(English)Manuscript (preprint) (Other academic)
National Category
Biological Sciences
Identifiers
urn:nbn:se:sh:diva-25143 (URN)
Note

Som manuskript i avhandling. As manuscript in dissertation.

Available from: 2014-10-27 Created: 2014-10-27 Last updated: 2015-07-17Bibliographically approved
3. Higher prevalence of clonal reproduction in teh coral Pocillopora damicornis on reefs outside marine protected areas in Kenya
Open this publication in new window or tab >>Higher prevalence of clonal reproduction in teh coral Pocillopora damicornis on reefs outside marine protected areas in Kenya
(English)Manuscript (preprint) (Other academic)
National Category
Biological Sciences
Identifiers
urn:nbn:se:sh:diva-25144 (URN)
Note

Som manuskript i avhandling. As manuscript in dissertation.

Available from: 2014-10-27 Created: 2014-10-27 Last updated: 2015-07-17Bibliographically approved
4. Phenotypic variation in the coral Platygyra daedalea in Kenya: morphometry and genetics
Open this publication in new window or tab >>Phenotypic variation in the coral Platygyra daedalea in Kenya: morphometry and genetics
2007 (English)In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 345, 105-115 p.Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Biological Sciences
Identifiers
urn:nbn:se:sh:diva-5566 (URN)10.3354/meps07013 (DOI)000250195800010 ()2-s2.0-35348898931 (ScopusID)
Note

In dissertation In press: Understanding phenotypic variation in the scleractinian coral Platygyra daedalea (Ellis & Solander 1786) in Kenyan lagoonal reefs through morphometric and genetic studies

Available from: 2011-01-18 Created: 2011-01-18 Last updated: 2014-10-27Bibliographically approved

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