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Abstract

HYDROZOAN SPECIES ACROSS THE ISTHMUS OF PANAMA: GENERAL TRENDS AND THE SPECIFIC CASES OF THE IMMORTAL MEDUSA TURRITOPSIS AND BOUGAINVILLIA

Maria P. Miglietta
Smithsonian Tropical Research Institute
Bio

Geminate species across the Isthmus of Panama have been identified in many phyla, from sea-urchins to fish. However very little is known on the Hydrozoan Fauna of Panama. A survey of benthic and planktonic stages of Hydrozoa across the Isthmus of Panama was conducted over an 18-month period. Polyps and medusae were identified and sequenced for the 16S mitochondrial gene, which is a useful and adequate marker for species level recognition in Hydrozoa (Miglietta et al. 2007, Schuchert 2005, Govindarajan et al. 2005). A molecular phylogenetic analysis of all the species grouped by genera was constructed. Interestingly only a very small number of putative geminate species were found. While genus composition in the two oceans is very similar, geminate species of Hydrozoa are extremely rare to be found. Here I report data from the two genera Turritopsis and Bougainvillia. In a world-wide phylogeny of Turritopsis one clade formed by samples from Japan, Florida, Atlantic and Pacific Panama and the Mediterranean Sea showed no genetic differentiation. This is consistent with Turritopsis being a recent invasive species that is colonizing the world’s oceans. Despite no genetic variation in 16S, the medusae of this species show morphological differences possibly due to heterochronic events. The implication of this result is twofold: it testifies a rapid process of local adaptation of the medusa stage. It also gives insight on the presence of invasive species that can go largely unnoticed due to their rapid morphological change in a new geographic area. Word-wide “silent invasions” like the one observed in Turritopsis may be more common than previously believed. The medusae of the species Bougainvillia muscus from Panama Bay (Pacific Ocean) were collected weekly during 12 months. The same species showed different morphologies depending on the season (dry VS upwelling). Those two cases hint the possibility that the morphological changes in the planktonic stage of Hydrozoa occur extremely rapidly.