Aim The partition of the geographical variation in Argentinian terrestrial mammal species richness (SR) into environmentally, human and spatially induced variation.Location Argentina, using the twenty-three administrative provinces as the geographical units. MethodsWe recorded the number of terrestrial mammal species in each Argentinian province, and the number of species belonging to particular groups (Marsupialia, Placentaria, and among the latter, Xenarthra, Carnivora, Ungulates and Rodentia). We performed multiple regressions of each group's SR on environmental, human and spatial variables, to determine the amounts of variation explained by these factors. We then used a variance partitioning procedure to specify which proportion of the variation in SR is explained by each of the three factors exclusively and which proportions are attributable to interactions between factors.Results For marsupials, human activity explains the greatest part of the variation in SR. The purely environmental and purely human influences on all mammal SR explain a similarly high proportion of the variation in SR, whereas the purely spatial influence accounts for a smaller proportion of it. The exclusive interaction between human activity and space is negative in carnivores and rodents. For rodents, the interaction between environment and spatial situation is also negative. In the remaining placental groups, pure spatial autocorrelation explains a small proportion of the variation in SR.Main conclusions Environmental factors explain most of the variation in placental SR, while Marsupials seem to be mainly affected by human activity. However, for edentates, carnivores, and ungulates the pure human influence is more important than the pure spatial and environmental influences. Besides, human activity disrupts the spatial structure caused by the history and population dynamics of rodents and, to a lesser extent, of carnivores. The historical events and population dynamics on the one hand, and the environment on the other, cause rodent SR to vary in divergent directions. In the remaining placental groups the autocorrelation in SR is mainly the result of autocorrelation in the environmental and human variables.

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The central region of Argentina is occupied by a karyotypically stable group of Ctenomys species that form the "mendocinus" complex (C. australis, C. azarae, C. mendoci-nus, C. porteousi and C. chasiquensis), which contacts with populations of C. talarum, C. pundti and intermediate karyomorphs between both species called the "pundti" complex. In this paper, eight populations of the region of reference from La Pampa province were chromosomally studied, to help resolve the systematic and evolutionary problems posed by these entities. In one population (El Guanaco) a 2n=48, FN=81-82 karyotype was found, which comprised 18 pairs of biarmed and 5 pairs of telocenctric autosomes. The NOR was carried by a small metacentric and the sperm was of the symmetric type. In the rest of the populations, 2n=47 and 2n=48 karyotypes were observed with FNs varying between 71-74. The 2n=48 karyotypes include 14 pairs of biarmed (A complement) and 9 pairs of telocentric (B complement) autosomes. One exceptional individual had 15 A pairs and 8 B pairs respectively. The NOR is carried by B5. The 2n=47 karyotype was originated by a complex rearrangement that involved the standard Al and B2 autosomes, producing a novel large metacentric. This hypothesis was based on G banding comparisons and in this paper was corroborated by observation on male meiosis of heterozygotes. Additionally a series of polymorphisms involving heterochromatic short arm variation of several autosomal pairs was observed in most populations. The sperm was of the asymmetric type. From the observed karyotypes and sperm morphology the studied populations may be divided into two groups: a) the El Guanaco population, which can be assigned to the subspecies C. talarum talarum, and b) the rest of the populations, which clearly belong to the "mendocinus" complex, being closely related to C. azarae and C. porteousi. Nevertheless, the geographic boundaries of the putative species of the "mendocinus" group are poorly defined and reproductive studies between these populations are needed to assess their specific status. The high frequency of 2n=47 heterozygotes for the complex rearrangement (ca. 50%) coupled to the extreme rarity of the homozygous 2n=46 karyotype, suggests the existence of positive chromosomal heterosis. Athough it is clear that the homozygous karyotype is not le-tal, it is possible that fitness differences are involved in the maintenance of the polymorphism perhaps through heterozygote superiority.

We analysed the main geographical trends of terrestrial mammal species richness (SR) in Argentina, assessing how broad-scale environmental variation (defined by climatic and topographic variables) and the spatial form of the country (defined by spatial filters based on spatial eigenvector mapping (SEVM)) influence the kinds and the numbers of mammal species along these geographical trends. We also evaluated if there are pure geographical trends not accounted for by the environmental or spatial factors. The environmental variables and spatial filters that simultaneously correlated with the geographical variables and SR were considered potential causes of the geographic trends. We performed partial correlations between SR and the geographical variables, maintaining the selected explanatory variables statistically constant, to determine if SR was fully explained by them or if a significant residual geographic pattern remained. All groups and subgroups presented a latitudinal gradient not attributable to the spatial form of the country. Most of these trends were not explained by climate. We used a variation partitioning procedure to quantify the pure geographic trend (PGT) that remained unaccounted for. The PGT was larger for latitudinal than for longitudinal gradients. This suggests that historical or purely geographical causes may also be relevant drivers of these geographical gradients in mammal diversity.