The Genus Cerion (Gastropoda: Cerionidae) in the Florida Keys

Abstract

The systematic relationships and phylogeography of Cerion incanum, the only species of Cerion native to the Florida Keys, are reviewed based on partial sequences of the mitochondrial COI and 16S genes derived from 18 populations spanning the range of this species and including the type localities of all four described subspecies. Our samples included specimens of Cerion casablancae, a species introduced to Indian Key in 1912, and a population of C. incanum x C. casablancae hybrids descended from a population of C. casablancae introduced onto Bahia Honda Key in the same year. Molecular data did not support the partition of C. incanum into subspecies, nor could populations be apportioned reliably into subspecies based on morphological features used to define the subspecies. Phylogenetic analyses affirmed the derived relationship of C. incanum relative to other cerionids, and indicated a Bahamian origin for the Cerion fauna of southern Florida. Relationships among the populations throughout the Keys indicate that the northernmost populations, closest to the Tomeu paleoislands that had been inhabited by Cerion petuchi during the Calabrian Pleistocene, are the oldest. The range of Cerion incanum expanded as the archipelago that is the Florida Keys was formed since the lower Tarantian Pleistocene by extension from the northeast to the southwest, with new islands populated as they were formed. The faunas of the High Coral Keys in the northeast and the Oölite Keys in the southwest, both with large islands that host multiple discontinuous populations of Cerion, are each composed of well supported clades that are characterized by distinctive haplotypes. In contrast, the fauna of the intervening Low Coral Keys consist of a heterogeneous series of populations, some with haplotypes derived from the High Coral Keys, others from the Oölite Keys. Individuals from the C. incanum x C. casablancae hybrid population inhabiting the southeastern coast of Bahia Honda Key were readily segregated based on their mitogenome lineage, grouping either with C. incanum or with C. casablancae from Indian Key. Hybrids with C. casablancae mitogenomes had haplotypes that were more divergent from their parent mitogenome than were hybrids with C. incanum mitogenomes.

Island biogeography and ecological modeling of the amblypygid Phrynus marginemaculatus in the Florida Keys archipelago

“…We selected regions a priori based on geologic features: the Key Largo region for its size and proximity to the mainland; the Upper and Lower Keys for their geologic variation in formation, if not timing thereof; and the mainland, as an obvious delineator from island populations. This generally aligns with the population structure of native Cerion land snails, which showed isolation between the Upper and Lower Keys (Shrestha et al., ). Species on the Lower Keys likely have a unique evolutionary history separate from the rest of the Keys.…”

“…This pattern suggests that a mainland–metapopulation model described the landscape genetics of the Keys. As mentioned, genetic analyses of land snails in the Florida Keys also show an Upper–Lower Key division (Shrestha et al., ). But research on marine species like bicolor damselfish ( Eupomacentrus partitus ) and common reef sponge ( Callyspongia vaginalis ) found much lower levels of divergence between regions than we found for P. marginemaculatus (DeBiasse, Richards, & Shivji, ; Lacson et al., ) .…”

“…Shrestha et al. () proposed that the C. incanum spread southwesterly to colonize new Keys as they formed, with Lower Key populations being the youngest. Lastly, ant gut microbiota showed genetic structure between the Upper and Lower Keys (Hu et al., 2013).…”

“…The Keys are made from two geologic formations that both formed during the Tarantian Pleistocene (0.126-0.0117 mya) and raising above sea level during the Wisconsin glaciation (ca. 100,000 before present; Hoffmeister & Multer, 1968;Shrestha et al, 2015). The Lower Keys (Big Pine Key to Key West) formed from cemented sand bars, resulting in oölitic limestone (termed Miami Limestone).…”

“…Our understanding of the genetic structure of Florida Keys organisms largely comes from research of marine species, where ocean currents play a major role in gene flow and migration (Apodaca, Trexler, Jue, Schrader, & Travis, 2013;DeBiasse, 2010;Kirk, Andras, Harvell, Santos, & Coffroth, 2009;Lacson & Morizot, 1991) . Genetic patterns of terrestrial species are expected to differ considerably, as the marine ecosystem acts as an uninhabitable matrix and the formation of terrestrial habitat occurred on different timescales (Hoffmeister & Multer, 1968;Shrestha et al, 2015).…”