Green mutant frequency in natural populations ofGracilaria domingensis(Gracilariales, Rhodophyta) from Brazil

Green, brown and red phenotypes of Gracilaria domingensis have been observed growing side by side in natural populations in the north-east of Brazil. The phycoerythrin phycocyanin ratio of the three colour types increased from green to brown to red phenotypes. The frequency of green mutant individuals was studied during three consecutive years in two natural populations 110 km apart in Ceara State. Brazil. Green variants were found at frequencies of 7% to 19% in both populations showing that the deficiency in phycoerythrin did not strongly affect the fitness of individuals in these sunny intertidal populations. Moreover, the relative stability of the green allele frequency in space and time suggested that the selective pressures are equivalent in the two sites and/or that the two populations are not genetically isolated.