Osvaldo A. Reig

Spatial distribution and attributes of a population of Ctenomys talarum (Rodentia: Octodontidae)

ROBERTSHAW, J. D., AND R. H. HARDEN. 1986. The ecology of the dingo in northeastern New South Wales. IV. Prey selection and its effect on the major prey species, the swamp wallaby Wallabia bicolor (Desmarest). Australian Wildl. Res., 13:141-164. RUSSELL, E. M. 1982. Patterns of parental care and parental investment in marsupials. Biol. Rev., 57: 423-486. SCHLAGER, F. 1981. The distribution, status and ecology of the rufous rat-kangaroo, Aepyprymnus rufescens, in northern New South Wales. Unpubl. M. Nat. Res. thesis, Univ. New England, Armidale, New South Wales, 190 pp.

The evolutionary history of Drosophila buzzatti. XXVI. Macrogeographic patterns of inversion polymorphism in New World populations

Inversion polymorphisms in the second and fourth chromosomes of the cactophilic Drosophila buzzatti in the native distribution range of the species are described. Over 5,000 flies from 26 localities were scored revealing interesting geographic structuring of arrangement frequencies. Multiple regression and partial correlation approaches showed that the frequencies of second and fourth chromosome arrangements vary clinically along latitudinal and altitudinal gradients and to a lesser extent with longitude. Although many non selective explanations can account for this pattern, its resemblance to the clinal pattern described in recently established Australian populations of Drosophila buzzatii, strongly suggests a selective explanation. Additionally, the correlated variation observed between the frequencies of arrangements 2St on the second chromosome and 4St on the fourth suggests a pattern of interchromosomal association, which, when considering the vast area surveyed, might be explained as the result of epistatic interactions. The analysis of population structure revealed a significant regional pattern, concordant with previously described phytogeographic regions. F‐statistics showed that the patterns of variation were different not only between the second and fourth chromosomes, but also between second chromosome arrangements, suggesting that selective differentiation might have contributed to population structure.

The evolutionary history of Drosophila buzzatii . XXIV. Second chromosome inversions have different average effects on thorax length

We demonstrate a genetic correlation between rearrangements of the second chromosome of D. buzzatii and thorax length, as a measure of body size. The results indicate that 2j and 2jz3 arrangements are correlated with large size, whereas 2st arrangement is correlated with small size. Some inversions (2st and 2jz3) show dominant effects and others (2j/jz3) exhibit overdominance. These results show that at least 25 per cent of body size variation may be accounted for by the studied karyotypes. The possible integration of the genotypic, phenotypic and fitness levels, and also the possible implications to life-history evolution theories, are discussed. These results suggest that, under moderate to high heritability values, some kinds of chromosomal endocyclic and/or balancing selection may be valuable mechanisms for maintenance of body size variation.

Cytogenetics of south American akodont rodents (Cricetidae): new karyotypes and chromosomal banding patterns of Argentinian and Uruguayan forms

Cytogenetic analysis was performed in Akodon (Akodon) puer (= Akodon coenosus ) , Akodon azarae bibianae, Akodon ( Hypsimys ) budini, Bolomys temchuki elioi, Bolomys temchuki liciae, Oxymycterus rufus rufus, Oxymycterus ruf us platensis , and Oxymycterus paramensis . Diploid numbers, chromosomal morphology, and lengths and banding patterns (G and C) were determined for each taxon. Chromosomal number and gross morphology are also described in topotypical specimens of Akodon ( Akodon ) arenicola (= Akodon ( Akodon ) azarae azarae ) and Oxymycterus nasutus . A 2n = 34 karyotype, similar to one previously reported as Akodon coenosus , was confirmed in Akodon puer. A. budini showed a 2n = 38 karyotype peculiar within the genus as regards chromosomal morphology and C bands. A. a. bibianae has a 2n = 38 karyotype closely related with that of A. a. azarae . The two subspecies of B. temchuki , which differ strikingly in fur color, showed an identical 2n = 34 karyotype, which was quite similar in diploid number, chromosomal morphology, and banding patterns to that reported for B. lasiurus , but was different in the morphology of the Y and in G and C bands when compared with B. obscurus from the south of Buenos Aires Province. The three species of Oxymycterus , which markedly differ in morphometric character states, showed an identical 2n = 54 karyotype, and no banding differences were observed between O. rufus and O. paramensis .

The evolutionary history of Drosophila buzzatii. XVI. Fitness component analysis in an original natural population from Argentina

The adaptive significance of the chromosomal polymorphism of Drosophila buzzati has been studied by means of fitness component analysis in an original population from Argentina. The results show evidence of selection acting through pupal viability, longevity (adult viability) and fecundity on the second chromosome polymorphism, and through pupal viability and virility on the fourth chromosome polymorphism.

The evolutionary history of Drosophila buzzatii XXVII

The correlation between body size and longevity was tested in an Argentinian natural population of Drosophila buzzatii. Mean thorax length of flies newly emerging from rotting cladodes of Opuntia vulgaris was significantly smaller than that of two samples of flies caught at baits. The present results which might be interpreted as directional selection for longevity favoring larger flies are in agreement with previous results achieved in a Spanish natural population of D. buzzatii. Flies emerging from different substrates showed significant differences in thorax length, suggesting that an important fraction of phenotypic variance can be attributed to environmental variability. However, laboratory and field work in different populations of D. buzzatii showed a significant genetic component for thorax length variation.

Genetic variability in the subterranean rodents Ctenomys australis and Ctenomys porteousi (Rodentia:Octodontidae)

Abstract Genetic variation encoded by 31–35 loci was estimated in four populations of subterranean rodent Ctenomys australis and in one population of C. porteousi . Estimates of observed heterozygosity per population ranged from 0.00 to 11.18%, and polymorphism from 0.00 to 45.00%. These results were compared with data from other subterranean and non-subterranean rodents in their bearing on different models for interpretation of genetic variability in subterranean rodents. The high variation in H and P values found in different species and populations of tuco-tucos suggest that in them, population structure is probably more important that environmental homogeneity in triggering genetic variation. In contrast to C. porteousi, F is values suggested that there is no strong evidence for inbreeding within populations of C. australis. F st values indicated a considerable genetic divergence among population samples in C. autralis . Estimates of genetic distance [ D ] values among the four populations of C. australis showed an average value of D = 0.0158, similar to those found between local populations of the same species in other organisms.