Genetic composition of zooxanthellae between and within colonies of the octocoral Plexaura kuna, based on small subunit rDNA and multilocus DNA fingerprinting

Abstract

In intracellular symbiosis, the host is both the symbiotic partner and the habitat for the symbiont. Physical conditions may vary within a host individual, leading to niche partitioning within a host according to symbiont genotype. In this study, the algal symbionts (zooxanthellae) inhabiting the octocoral Plexaura kuna (Lasker, Kim, Coffroth) were characterized. Zooxanthellae are currently divided into clades based on sequence variation of the small and large subunit ribosomal gene and internal transcribed spacer regions. Zooxanthellae isolated from the top and bottom of a P. kuna colony, from colonies sampled at various depths and geographic locations (Bahamas, Florida Keys, Panama and St. Croix, USVI), from 1988 to 1998, all belonged to clade B. Since symbiont variability within a host is an individual-level question, in the second part of the study, multilocus DNA fingerprinting was used. Each genetically distinct P. kuna colony (i.e. nonclonemate) hosted a unique prominent zooxanthella genotype. This zooxanthella genotype was found at both the top and the bottom of the host colony, although physical conditions differed between these areas. The existence of one prominent zooxanthella genotype throughout a colony may indicate a fixed symbiontacquisition period or the active maintenance of a hostsymbiont genotypic association.

Bleaching susceptibility and mortality of corals are determined by fine-scale differences in symbiont type

“…Although the adaptive bleaching hypothesis (ABH) has found support in a number of studies (19,21,44), increasing evidence now points toward a highly specific and persistent nature of established host-symbiont associations (24,(45)(46)(47). This is supported by our data whereby symbiont communities in S. pistillata were stable over two years despite minor fluctuations observed during bleaching.…”

“…However, because these symbionts mainly belonged to those naturally present within the host populations, we believe that the rapid changes in symbiont communities proposed by the ABH may be restricted to symbiont types native to the host. Even within this framework it appears that changes in symbiont communities are not sustained postbleaching, and permanent changes are more likely to occur over generations rather than within the life cycle of individual hosts (24,(45)(46)(47)(48).…”

Real-time PCR reveals a high incidence of Symbiodinium clade D at low levels in four scleractinian corals across the Great Barrier Reef: implications for symbiont shuffling

“…While their conclusion is consistent with current data, absence of evidence is not necessarily evidence of absence. This study investigated whether the low value is an artifact caused by the low sensitivity of the most commonly used survey techniques for symbiont detection: denaturing gradient gel electrophoresis (LaJeunesse 2002), single strand conformational polymorphism (Fabricius et al 2004), restriction fragment length polymorphism (Diekmann et al 2002), and DNA fingerprinting (Goulet and Coffroth 2003a). None of these methods can detect clades, which are present at levels below 5-10% of the total symbiont population, and direct sequencing of PCR products will also only detect the dominant symbiont.…”

Stability of an octocoral-algal symbiosis over time and space

“…Rowan & Powers (Rowan 1991, Rowan & Powers 1991, 1992, using sequence comparisons and restriction fragment length polymorphisms (RFLP) of DNA coding for small subunit ribosomal RNA (SSuRNA), provided a relatively easy and attainable division of zooxanthellae into genetically discernable groups termed clades. Since then, researchers have assigned zooxanthella cladal identity to symbionts in a wide variety of hosts such as stony corals (Darius et al 1998, Baker 1999, Rodriguez-Lanetty et al 2001, van Oppen et al 2001, Diekmann et al 2002, LaJeunesse 2002, octocorals (Carlos et al 1999, Goulet 1999, LaJeunesse 2002, Santos et al 2002, Goulet & Coffroth 2003, sponges (Hill & Wilcox 1998) and giant clams (Baillie et al 2000b).…”

“…As an adult, P. kuna hosts only zooxanthellae belonging to Clade B (Rowan & Powers 1991, Goulet & Coffroth 2003. Using multilocus DNA fingerprinting, we determined the zooxanthella genotypic identity in individual P. kuna colonies temporally for up to a decade.…”