Addendum/Corrigendum

Coral biodiversity and evolution: recent molecular contributions

Tropical reefs are among the most diverse ecosystems. Corals, as the most prominent members and framework builders of these communities, deserve special attention, especially in light of the recent decline of coral reefs worldwide. The diversity of corals at various levels has been the subject of many studies, and has traditionally been investigated using morphological characters. This approach has proved insufficient, owing to several ecological and life-history traits of corals. The use of molecular/biochemical approaches has been propelling this discipline forward at an ever-increasing rate for the past decade or so. Reticulate evolution in corals, which has challenged traditional views on the ecology, evolution, and biodiversity of these organisms, is only one example of the results of molecular studies supporting the development of new concepts. We review recent literature reporting studies of the biodiversity, ecology, and evolution of corals in which molecular methods have been employed. We anticipate that in the coming years, an increasing number of studies in molecular biology will generate new and exciting ideas regarding the biology of corals.

Host-Associated Speciation in a Coral-Inhabiting Barnacle

Host specificity of symbionts is considered an important factor associated with sympatric speciation. Here, we examine host specificity and the degree of host-associated speciation in the barnacle Savignium milleporum, an obligate symbiont of the hydrocoral Millepora (the "fire coral"). Little morphological variability was revealed between barnacles collected from two morphs of the hydrocoral Millepora dichotoma (encrusting or branching) or from its congener Millepora platyphylla, but a molecular analysis revealed an unexpected pattern of DNA sequence divergence. The sequences of the 12S mitochondrial rDNA were nearly identical within each of the three barnacle populations (average sequence divergence <1%), and the sequences obtained for barnacles collected from the two different morphs of M. dichotoma differed considerably (ca. 9% average sequence divergence). However, S. milleporum collected from M. platyphylla were nearly identical to the barnacles from the branching M. dichotoma (<0.5% average sequence divergence). The pattern of speciation demonstrated by Savignium barnacles indicates the gradual colonization of similar hosts (i.e., sequential evolution), rather then "casual" colonization, as indicated for other systems. If this is indeed so, then symbiont phylogeny should roughly correlate with host phylogeny. Additionally, the data support the "rendezvous host" hypothesis, which invokes the opportunity of both sexes to meet as a major component for which selection favors the costly habit of host specificity.