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Abstract THE LIFE CYCLE, PHYLOGEOGRAPHY, AND COMPARATIVE MITOCHONDRIAL GENOMICS OF PLACOZOANS FROM TWIN CAYS, BELIZE Ana Y. Signorovitch Placozoans are microscopic marine invertebrates that are distributed
along tropic and subtropic latitudes. They possess only four somatic
cell types, a dorsal-ventral polarity, no definite shape, and are
the simplest known free-living animals. Here I describe findings
of three separate studies that utilized placozoans collected from
the mangrove island of Twin Cays, Belize. In the first study, the
margins of Twin Cays were surveyed for placozoans during the summers
of 2003 and 2004. Sampled isolates were haplotyped at the mitochondrial
16S rDNA and mapped to their collection sites along the
island’s margins to form the basis of the first high-resolution
phylogeographic study of placozoans. Twin Cays was found to be home
to an unprecedented diversity of placozoans, including sympatric
highly diverged species. The second study aimed at detecting molecular
signatures of sexual reproduction through a molecular population
genetics approach. Although never observed, it is now known that
placozoans do indeed reproduce sexually as demonstrated by patterns
of allele sharing between individual placozoans. Lastly, a select
group of highly divergent Twin Cays placozoans was used in a comparative
study of whole mitochondrial genomes (mtDNA). While the majority
of animal mtDNAs are ca. 15-20 kb, all placozoans so far examined
possess genomes well above this range, from 32-43 kb. Based on these
data and other complete mtDNAs, phylogenetic analyses of the Lower
Metazoa revealed that all members of the Phylum Placozoa belong
to the earliest diverging animal group.
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