Intra- and interspecific variations in genome sizes ofAgariciacorals from Curaçao

Abstract

Genome size is a fundamental biological trait that is known to exhibit high diversity among eukaryotic species, but its intraspecific diversity has only scarcely been studied to date. In scleractinian corals, genome size data are only available for a few species. In this study, intra- and interspecific variations in genome size of the coral genusAgariciacollected from Curaçao were investigated. Morphology was congruent with genetic analyses of the nuclear markers internal transcribed spacer 2 (ITS2) and L-threonine 3-dehydrogenase (TDH) in delimiting threeAgariciaspecies among our samples. A refined Feulgen Image Analysis Densitometry (FIAD) protocol yielded genome sizes that ranged from 0.359 pg to 0.593 pg within this genus (a 1.7-fold range). The highest intraspecific variation in genome size was recorded in the depth-generalistA. lamarcki(1.5-fold range), followed by the depth specialistA. humilis(1.4-fold range) andA. agaricites(1.3-fold range), the species with an intermediate depth distribution. The mean genome size ofA. agaricites(0.495 pg) was significantly larger than that ofA. lamarcki(0.448 pg) andA. humilis(0.434 pg). No correlation between average genome size and nucleotide polymorphismπwas detected, but we found an almost linear correlation between intraspecific variance of genome size andπof ITS2 (Pearson’s r = 0.984, p = 0.113). Genome size and collection depths of bothA. lamarcki(Pearson’s r = 0.328, p = 0.058) andA. agaricites(Pearson’s r = -0.270, p = 0.221) were also not significantly associated. To our knowledge, this study provides the first account of intraspecific variation in corals; the apparent correlation detected between the nucleotide polymorphism of a species and the variance of its genome size will have to be tested using a larger taxonomic spectrum of scleractinian corals as well as in other groups of animals.