Sirenians comprise manatees and dugongs, which host various parasites that cause little or no pathology. Parasitological studies have recommended using Chiorchis spp. as bio-indicators of population distribution. American manatees (Trichechus manatus) live in varied environments (marine, estuarine, fluvial, and lake). However, their relationship to their environment and feeding habits, and thus how it relates to their internal parasites, has yet to be studied. We sought to identify Chiorchis spp. through molecular analysis in manatees from different areas of the Caribbean. A ribosomal RNA 18S gene (18S rRNA) of trematodes collected from 31 carcasses of manatees from Puerto Rico, Florida, the Dominican Republic, and Colombia was amplified using previously published primers. Seventy-seven samples were sequenced, and a phylogenetic reconstruction was made with 437 bp of the 18S rRNA sequences using representative samples of each geographic location. The phylogenetic analysis revealed strongly supported clades with a posterior probability of 0.98 for Chiorchis groschafti and 1.0 for Chiorchis fabaceus. These findings indicate a divergence between trematode species found in freshwater versus those in marine environments. We found that C. groschafti and Solenorchis travassosi infect only manatees and dugongs, respectively, in marine environments where they feed primarily on seagrasses. In contrast, C. fabaceus infects manatees living in freshwater environments where they feed primarily on freshwater aquatic vegetation. Some manatees in Florida were infected with both species, indicative of their movement from marine to freshwater environments and their combined diet of seagrasses and freshwater vegetation. This study documents how these trematodes serve as ecological bio-indicators of the host's habitat distribution and bio-markers of the sirenian type of herbivorous diet.
Keywords: American manatees; Bio-indicators; Chiorchis fabaceus; Chiorchis groschafti; Intestinal trematodes; Parasites; Trichechus manatus.