A new species of Archaebranchinecta (Anostraca: Branchinectidae) from the South American Altiplano.

A detailed morphological comparison was carried out among specimens of several samples of Archaebranchinecta Rogers Coronel, 2011 from the Altiplano of Peru, Bolivia, and Argentina. Surprisingly, striking differences were found between Peruvian samples collected near the western shore of Lake Titicaca, and those from Bolivia taken southwardly, near the east coasts of River Desaguadero and Lake Poopó. Accordingly, the new species Archaebranchinecta aimara sp. nov. is described, representing the second specific entity of a genus that so far included only A. pollicifera (Harding, 1940). The main differential features between both species include: (a) size and shape of the three processes of basal segment of the male second antenna; (b) shape and protrusion degree of the pair of medioventral bulges in the male genital segments; (c) presence or absence of strong ventrolateral spine on the second genital segment of female; and (d) presence or absence of a pair of ventrolateral outgrowths in the brood pouch. This research contributes to our understanding of the biodiversity and endemism of the unique Altiplano region of South America.

The Hyalella (Crustacea: Amphipoda) species cloud of the ancient Lake Titicaca originated from multiple colonizations.

Ancient lakes are renowned for their exceptional diversity of endemic species. As model systems for the study of sympatric speciation, it is necessary to understand whether a given hypothesized species flock is of monophyletic or polyphyletic origin. Here, we present the first molecular characterization of the Hyalella (Crustacea: Amphipoda) species complex of Lake Titicaca, using COI and 28S DNA sequences, including samples from the connected Small and Large Lakes that comprise Lake Titicaca as well as from a broader survey of southern South American sites. At least five evolutionarily distant lineages are present within Lake Titicaca, which were estimated to have diverged from one another 12-20 MYA. These major lineages are dispersed throughout the broader South American Hyalella phylogeny, with each lineage representing at least one independent colonization of the lake. Moreover, complex genetic relationships are revealed between Lake Titicaca individuals and those from surrounding water bodies, which may be explained by repeated dispersal into and out of the lake, combined with parallel intralacustrine diversification within two separate clades. Although further work in deeper waters will be required to determine the number of species present and modes of diversification, our results strongly indicate that this amphipod species cloud is polyphyletic with a complex geographic history.

Review of the Eulimnadia (Branchiopoda: Spinicaudata: Limnadiidae) from Argentina with the description of a new species.

A new spinicaudatan species, Eulimnadia pampa sp. nov., is described from Argentina mostly based on the differential egg morphology. This species was collected from rainwater pools from Buenos Aires City and the provinces of Buenos Aires and Entre Ríos, and compared to other Neotropical species. Previous Argentine record of E. brasiliensis is shown to belong to our new species, which represents the southernmost Neotropical Eulimnadia. We also present new records of the Paraguayan Eulimnadia ovisimilis Martin and Belk, 1989 from northeastern Argentina. Eulimnadia santiaguensis is treated as a species inquirenda, thus we recognize only three Eulimnadia species in Argentina: E. pampa sp. nov., E. ovilunata and E. ovisimilis, and we provide a brief indentification key. We present the first description and SEM images of the putative Eulimnadia spermatophore, which we found in the new species.

UV radiation as a potential driving force for zooplankton community structure in Patagonian lakes.

This article explores the potential role of UV radiation (UVR) as an influence on zooplankton communities. In the first section we provide a general overview of UVR effects on freshwater zooplankton, with an emphasis on Argentine and Chilean environments. In the second section we present the results of a survey involving 53 temperate lakes across a gradient of UVR exposure to determine patterns of species richness and specific diversity. These community characteristics decreased at high potential UVR exposure (i.e. high mean water column irradiance or low lake optical density). A threshold value of mean water column irradiance of approximately 10% of the surface level seems to limit both richness and diversity to minimum values. On the basis of the collected evidence it is not possible to definitely conclude that UVR rather than another covarying factor is responsible for the decrease in specific diversity observed at the lowest end of lake optical depth. However, lakes with values above the previous threshold are likely to exhibit highly depauperate zooplankton communities regardless of the mechanism. As a cautionary note we suggest that changes in the optical characteristics (i.e. changes due to atmospheric conditions, precipitation patterns or vertical displacement of the tree line) may result in sudden shifts in zooplankton community structure.

New insights into the distribution of polyploid Daphnia: the Holarctic revisited and Argentina explored.

It has long been known that polyploid organisms are more prevalent in arctic than in temperate environments. Past explanations for this geographical trend have focused on the role of glacial cycles in generating polyploids and the influence of abiotic factors in favouring polyploidy in the north. In combination, these mechanisms probably suffice to explain the observed geographical cline in ploidy levels in members of the Daphnia pulex complex in the Holarctic. While only diploid members of the D. pulex complex are found in the temperate regions of North America and Europe, allozyme and DNA quantification analyses indicate that the southern Argentine pulex-complex fauna is dominated by polyploids. Indeed, the present study is the first to document the presence of polyploid members of the D. pulex complex in any temperate climate. The results of phylogeographic analyses suggest that this difference in polyploid distribution between the northern and southern hemispheres is based more on ecological and historical contingencies than direct selection for polyploidy. Specifically, competition with diploid relatives probably limits the lower latitudinal range of polyploids in the north, but appears not to have occurred in Argentina. Because of these differences, the present study provides important insights into the diverse factors that determine the distributions and evolutionary fates of polyploid organisms.