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BR Staff Publications --- lake Tanganyika --- new species --- phytoplankton

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Tropical high Andes lakes represent a group of aquatic ecosystems that exhibit peculiar limnological characteristics related to their geographical location and high altitude. Despite the uniqueness of the high Andes ecosystems they remained understudied. Lakes of the Cordillera del Tunari are oligotrophic and clear water bodies sharing similar environmental characteristics (eg. pH, oxygen, temperature, conductivity, among others) due to the climatic conditions of the ecological region they occupy (Peruvian Puna Province). Because of the homogeneity of the environment and climatic conditions, the zooplankton communities would be expected to be similar among lakes. In addition, most lakes differ sharply in morphometry and while some lakes are fishless, many lakes have been stocked with the exotic fish species rainbow trout. These characteristics make Andes lakes of the Cordillera del Tunari good model systems to study how zooplankton community and population genetics are structured by ecological variables. Chapter I is an introduction on the environmental variables that structure the zooplankton communities and population genetics of Daphnia . We expose briefly the limnological and ecological characteristics of the mountain lakes in general and Bolivian Andes lakes in particular as well as their importance. UV radiation is presented as one of the main drivers of the zooplankton community structure and behavior in Andes lakes. We present some results on a preliminary experiment in which we quantify the effect of natural Ultraviolet Radiation on the mortality of the two dominant species of crustaceans ( Daphnia pulex and Boeckella titicacae ) in two lakes of the Cordillera del Tunari. Daphnia pulex showed higher mortality under natural UV conditions during the wet period (March). Chapter II presents a description of the limnological and ecological characteristics of lakes of the Cordillera del Tunari. Gradients on fish density, chlorophyll a contents, and morphometry grouped three types of lakes: large and depth, small and shallow and very highly productive lakes of medium to small size. Lakes with high values of copepods, rotifers, fish density, and chlorophyll a suggest that both plankton and fish are mainly bottom-up regulated and that their standing stocks are primarily depending on the productivity of the lake Chapter III presents a description of the zooplankton richness and community structure of Andes lakes and their association to physico-chemical, biotic and morphometric variables. Cladoceran community structure showed differences in large and small lakes, while copepods and rotifers were more related to fish density and chlorophyll a contents. Daphnia was absent from small lakes probably due to fish predation in lakes with fish and UV radiation in fishless lakes.   Chapter IV presents a description of the diel vertical migration behavior (DVM) of the dominant species of the zooplankton (cladocerans, copepods, and rotifers) in nine lakes of the Cordillera del Tunari. Our data revealed a strong day-time deficit of Daphnia pulex that can be interpreted as a clear DVM pattern in this species. Ultraviolet radiation is probably one of the factors determining DVM in Daphnia.   In Chapter V In this chapter we present a description on the inter and intra population genetic variability of “ Daphnia pulex complex” of the lakes in Cordillera del Tunari in relation to environmental variables. Genetic analysis on Daphnia populations revealed low clonal diversity and obligate parthenogenetic reproduction. In Chapter VI The phylogeny reveals that the mountain lakes studied harbor two formerly unknown neotropical species of the D. pulex complex. Two of the clades revealed by the mitocondrial DNA analysis corresponded to two species that arose independently in the tropical mountains denoting the endemic character of the zooplankton in the Andean lakes. In additions the species of Daphnia in our study demonstrated being polyploids. Polyploidy in the Bolivian populations seems to have arisen as an adaptation to cold conditions at high altitudes.