NEW YORK (GenomeWeb) – A gene expression and sequencing study of pigment-associated proteins in one species of coral has provided new evidence of how these organisms can exhibit such broad ranges in color even within a single species, and also how they might use this ability to survive in stressful environments.
The results, published yesterday in Molecular Ecology, used the staghorn coral, Acropora millepora, to demonstrate that the color of corals is dependant on the expression of multiple copies of the same gene. Depending on how many copies of a gene are active, a coral can show completely different pigmentation.
Moreover, the presence of multiple numbers of the same gene appears to allow these corals to change the levels of protein transcripts in response to their environment, the study authors reported.
Jörg Wiedenmann, head of the University of Southampton's Coral Reef Laboratory and the senior author of the study, said in a statement that the wide range of color among corals of the same species in the exact same environment, even existing right next to each other, has been "one of the longstanding mysteries of coral reef biology."
According to the study authors, the group's most important finding is that so-called 'colour morph' corals, like the staghorn, rely on multiple copies of the same gene to control their pigment, either investing in more pigment under unfavorable light conditions, or less pigment to conserve their resources when light is less of an issue.
In the study, the team replicated and grew experimental colonies of corals with different levels of color, specifically redness. Analysis of gene expression and copy number variation in these samples revealed that expression of one color-associated transcript, amilFP579, differed between corals with greater or lesser redness. Looking further, the team found that differences in transcript levels of this marker appeared to be due to gene dosage effects produced by variations in copy number.
Because differences in the intensity of pigment in corals can be a response to environmental stressors, such as too-bright light, which threaten a coral's symbiotic relationship with other reef wildlife, the researchers also investigated how the expression of amilFP579 would contribute directly to light stress tolerance.
Comparing two coral organisms, the group measured their ability to absorb light and linked this clearly to the concentration of the transcript.
From an environmental standpoint, the results suggest that multiple copies of the same gene controlling pigment allow corals to be selective and adaptive in environment of less or more light; either spending more energy and producing more pigment to maintain and protect symbiotic communities under harsh light, or expending less resources toward pigment and more toward reproduction and growth in a lower-light environment.
"The resulting color polymorphism increases the potential of the coral species to extend their distribution range along the steep light gradients of coral reefs and to inhabit more ecological niches," Weidenmann said.