Browsing by Author "Cárdenas, L"

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    Diels-Alder reactions of 1-dimethylamino-1-aza-1,3-dienes with benzo[b]thiophene-4,7-quinones
    (2003) Valderrama, JA; Cárdenas, L
    The cycloaddition reactions of 1-dimethylamino-1-azabuta-1,3-dienes with benzo[b]thiophene-4,7-quinones substituted at 2- and 2,3-positions have been investigated. The reactions afforded thienoquinolinequinones or mixture of regioisomeric thienoquinolinequinones depending upon the substituents of the partners. The regiochemistry of the cycloadditions are in accord with the HOMOdiene/LUMOdienophile interactions.
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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.
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    Recovery and genetic diversity of the intertidal kelp Lessonia nigrescens (Phaeophyceae) 20 years after El Nino 1982/83
    (2003) Martínez, EA; Cárdenas, L; Pinto, R
    Massive mortality in kelp beds of the Pacific coasts of North and South America was caused by the rise in surface seawater temperature during the El Nino Southern Oscillation (ENSO) event of 1982/83, the strongest in the four and half previous centuries. In northern Chile a stretch of 600 km of coastline showed massive mortality of the intertidal kelp species Lessonia nigrescens Bory, of which only a few individuals managed to survive. Kelps and their associated biodiversity recovered but kelp beds re-colonization in general was variable in time and space seemingly very slow along northern Chilean coasts. Here we show, effectively, that northward re-colonization advanced less than 60 km in 20 years. Conversely, kelp beds of the Northern Hemisphere recovered 300 km in only six months after the same ENSO event. Genetic diversity in the two most affected populations of L. nigrescens shows half of the heterozygosity and polymorphism with respect to that observed in six non affected populations. In addition, geographically separated populations seem highly isolated as evidenced by high and significant fixation indices (all F-ST values over 0.4).