Variation in the genetic composition of coral (Pocillopora damicornis and Acropora palifera) populations from different reef habitats

120

ABSTRACT. The widespread and morphologically variable coral Pocillopora damjcornis has been reported to exhlbit huge variation in Me-history traits (e.g. inode of reproduction, growth rate, longevity and dispersal) both locally and regionally throughout the Indo-Pacific Ocean. Dispersal may b e achieved by the settlement of sexually or asexually generated brooded planula larvae, by broadcast spawning or more locally through asexual fragmentation of large colonies. In the present study, we conducted a hierarchical survey of allozyme variation within and among reef-crest sites on 3 mid-shelf reefs separated by up to 1200 km on the Great Barrier Reef (GBR), Australia. Our objective was to use allozyme data ( 1 ) to quantify local and reglonal patterns of varlatlon in P, damicornis (along the northeastern coast of Australia), (2) to determine the relative contr~bution of sexual versus asexual production of planulae in P damicornis, and (3) to estimate levels of gene flow among adlacent sites (>5 km apart) and among reefs separated by 500 to 1200 km. High levels of genotypic dlvers~ty in our samples of P. darn~cornis imply that dispersive propagules in this species are produced sexually rather than asexually along the length of the GBR. Corals a t all sites displayed the same level of multi-locus genotypic diversity expected for randomly mating, sexually derived populations, and the majority of individual colonies possessed unique 7-locus genotypes. We also detected consistent deficits of heterozygotes within each collection (from 3 local sites on each of the 3 widely spaced reefs). This pattern is consistent with the predicted effects of sexual reproduction associated with some localised dispersal of gametes or larvae (although other explanations cannot be excluded). Furthermore, each reef was genetically subdivided, suggesting that larval recruitment was localised and that these populations are slightly inbred: hierarchical analysis of the standardised genetic variances (FsT) (estimated as Weir & Cockerham's 0) revealed that, although there was only moderate variation among all 9 sites (FST = 0.055 t 0.029), more variation was found among sites within reefs (F,, = 0.035 * 0.04 to 0.088 2 0.033) than among distant reefs = 0.008 * 0.014) This homogeneity of gene frequencies across widely separated reefs lmplles that reefs are connected by high levels of gene flow (.V,~m = 31) and that local populat~ons of P. damlcornls separated by >l000 km can interbreed sufficiently to maintain a consistent sulte of life-history characters.

Section: Discussionmentioning

confidence: 52%

“…Nonetheless, high levels of genotypic diversity and histological data imply that sexual spawning also occurs (Stoddart & Black 1985, Stoddart 1988, Ward 1992. In contrast, Benzie et al (1995) found no evidence of asexual replication of genotypes in P. damicornis on One Tree Island reef, at the southern tip of the GBR.…”

Section: Introductionmentioning

confidence: 77%

Genetic differentiation, reproductive mode, and gene flow in the brooding coral Pocillopora damicornis along the Great Barrier Reef, Australia

Ayre¹,

Hughes²,

Standish³

1997

120

“…Such habitat variation may affect the population genetic structure and distribution of species. For example, genetic differentiation in the coral Pocillopora damicornis between lagoonal and reef slope sites has previously been attributed to habitatspecific selection (Benzie et al 1995). Also, Acropora papillare, which is restricted to shallow, exposed reef environments is only rarely encountered at the most exposed edges of NE Fantome reef, further emphasizing the different nature of this site.…”

Section: Spatial Population Genetic Structurementioning

confidence: 94%

Location and disturbance affect population genetic structure in four coral species of the genus Acropora on the Great Barrier Reef

Souter¹,

Willis²,

Bay³

et al. 2010

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.

“…More research will be required to determine if a single action spectrum can be used for corals under different spectral irradiances and composition; however, there is already some evidence to suggest that deeper corals exhibit greater sensitivity than their shallow-water conspecifics (Shick et al 1995). Additionally, the genetic composition of the host (Benzie et al 1995) and the symbionts (Rowan & Knowlton 1995) will also contribute to the variability of action spectra within and between species.…”

Section: Discussionmentioning

confidence: 99%

Action spectrum for the effects of UV radiation on photosynthesis in the hermatypic coral Pocillopora damicornis

Lesser¹,

Lewis²

1996

Colonies of the hermatypic coral Pocillopora damcornis were collected from the shallow reefs of Kaneohe Bay, Hawaii, to assess the wavelength-dependent effects of ultraviolet (UV) radiation on photosynthesis. Measurements of photosynthesis and respiration were made while corals were exposed to different UV irradiances, keeping visible radiation constant, using long-band pass filters. A differential action spectrum (biological weighting function) for the inhibition of photosynthesis by UV radiation was then determined for P darnicornis The action spectrum revealed an increase in the wavelength-dependent effects of UV radiation on photosynthesis between 290 and 310 nm that is greater than those increases reported for action spectra on natural assemblages and unialgal cultures of marine microalgae. The greater effect at these wavelengths is a result of the high biologically effective doses of UV radiation experienced by these corals on shallow reefs, and the decrease in the absorbance of UV radiation by UV absorbing compounds found in the host tissues and algal symbionts between 290 and 310 nm. The irradiances of wavelengths in the region between 290 and 310 nm are those which will increase in the event of any decrease in stratosphenc ozone over equatonal regions. If the observed sensitivity of P. damicorn~s in this spectral region is common in other species, it may have important consequences for growth, reproduction, and occurrence of the bleaching phenomenon for shallow water corals.