Browsing by Author "Kornfield, I"

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    Divergence and zoogeography of mole crabs, Emerita spp (Decapoda: Hippidae), in the Americas
    (1996) Tam, YK; Kornfield, I; Ojeda, FP
    Six of the nine described species of the mole crab genus Emerita are distributed in the Americas, two [E. analoga (Stimpson, 1857) and E. rathbunae Schmitt, 1935] on the west coast, and four [E. benedicti Schmitt, 1935, E. brasiliensis Schmitt, 1935, E. portoricensis Schmitt, 1935 and E. talpoida (Say, 1817)] on the east. The presence of an extended planktonic larval stage in all Emerita species suggests high dispersal potential and the possibility of extensive gene flow among conspecific populations. Two taxa were sampled to study the extent of gene flow between widely separated conspecific populations: E. analoga (California and Chile) and E. talpoida (Massachusetts, South Carolina, and the west coast of Florida), while all other taxa were characterized from a single location. Portions of two mitochondrial genes, cytochrome oxidase I(COI) and 16S ribosomal RNA (16S rRNA) were sequenced. For data analysis, approximately 500 bp (COI) and 400 bp (16S rRNA) were examined. Estimated genetic divergence of 5.41% in COI between E. talpoida populations sampled from the Gulf of Mexico and the Atlantic coast, and 3.47% between E. analoga sampled in Chile and California, indicates that in both cases there has been no recent gene flow between disjunct populations. Additional molecular and morphological studies are necessary to decide whether disjunct populations should be accorded specific status. We predict that many marine invertebrates with antitropical distributions similar to E. analoga may consist of sibling species. In contrast to relationships inferred earlier from distribution patterns, parsimony analyses of both COI and 16S rRNA data yield similar phylogenetic trees in which E. analoga is separated from a clade composed of other species in the Americas; a bootstrap value (67%) in the COI inferred tree marginally supports the separation, but the same tree topology with a higher bootstrap value (84%) is obtained with 16S rRNA sequence data. Genetic divergence among the taxa indicates that the Emei ita species constitute an old group and that distribution of species has been modified by past climatic and geological events.
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    Origin, diversification, and historical biogeography of the genus Trachurus (Perciformes: Carangidae)
    (2005) Cárdenas, L; Hernández, CE; Poulin, E; Magoulas, A; Kornfield, I; Ojeda, FP
    We addressed phylogenetic relationships in the genus Trachurus using cytochrome b gene and D-loop sequences. The trees showed five groups: (1) the Southwest Pacific species (T. japonicus, T. novaezelandiae, and T. declivis); (2) The Mediterranean Sea and Eastern Atlantic species (T. mediterraneus); (3) The Atlantic Ocean species (T. lathami and T trecae); (4) Eastern Atlantic species (T. trachurus and T. capensis); and (5) a group of highly mobile pelagic species, two from the Eastern Pacific (T. symmetricus and T. murphyi) and one from the Eastern Atlantic (T. picturatus). The phylogeny based on Cyt b, supports the molecular clock hypothesis and our results agree with the reported fossil indicating that the origin of this genus occur when the Thetys Sea closed (around 18.4 MYA). In addition, a very slow neutral substitution rate is reported identified only two periods of maximum diversification: the first occurring between 18.4 and 15.0 MYA and the second between 8.4 MYA and present day. (c) 2005 Elsevier Inc. All rights reserved.