Angel E. Spotorno

Radiation of Extant Marsupials After the K/T Boundary: Evidence from Complete Mitochondrial Genomes

The complete mitochondrial (mt) genomes of five marsupial species have been sequenced. The species represent all three South American orders (Didelphimorphia, Paucituberculata, and Microbiotheria). Phylogenetic analysis of this data set indicates that Didelphimorphia is a basal marsupial lineage followed by Paucituberculata. The South American microbiotherid Dromiciops gliroides (monito del monte) groups with Australian marsupials, suggesting a marsupial colonization of Australia on two occasions or, alternatively, a migration of an Australian marsupial lineage to South America. Molecular estimates suggest that the deepest marsupial divergences took place 64–62 million years before present (MYBP), implying that the radiation of recent marsupials took place after the K/T (Cretaceous/Tertiary) boundary. The South American marsupial lineages are all characterized by a putatively nonfunctional tRNA for lysine, a potential RNA editing of the tRNA for asparagine, and a rearrangement of tRNA genes at the origin of light strand replication.

PHYLOGEOGRAPHY OF OLIGORYZOMYS LONGICAUDATUS (RODENTIA: SIGMODONTINAE) IN TEMPERATE SOUTH AMERICA

Abstract Phylogeographic relationships were evaluated at the intraspecific level using nucleotide sequence data from the mitochondrial cytochrome b gene of representative specimens of “colilargo” (Oligoryzomys longicaudatus) from 31 localities, along its distributional range over a large part of the western Andes and southern Argentina. Based on approximately 1,000 base pairs (bp), we recognized a single species on both the Chilean and the Argentinean side as far as at least latitude 51°S, rejecting the subspecific distinctiveness of longicaudatus and philippi. We thus placed the latter in full synonymy with O. longicaudatus as earlier studies proposed, and enlarged its range as far as Torres del Paine, about 51°S. The occurrence of subspecies in this range is doubtful given the low sequence divergence values and the absence of significant associations between haplotypes and their geography. Additionally, we hypothesized that the entrance of this species into the Chilean side of the Andes mountains occurred through the Patagonian forests of southern Argentina, with further dispersal to the north from the south.

The largest known chromosome number for a mammal, in a South American desert rodent.

Tympanoctomys barrerae, a desert specialist member of the family Octodontidae, until now thought to be conservative, and ancestral to South American hystricognath rodents, presents the highest diploid chromosome number (2n=102) known in a mammal. Unexpectedly, its karyotype was found to be composed mainly of metacentric to sub-metacentric chromosomes. Mechanisms by which such a karyotype may have been derived are discussed.

MOLECULAR DIVERGENCE AND PHYLOGENETIC RELATIONSHIPS OF CHINCHILLIDS (RODENTIA: CHINCHILLIDAE)

Abstract Molecular phylogenetic relationships were investigated in 6 species of Chinchillidae (Chinchilla lanigera, C. brevicaudata, Lagidium peruanum, L. viscacia, L. wolffsohni, and Lagostomus maximus), 1 species of Dinomyidae (Dinomys branickii), 1 of Abrocomidae (Abrocoma cinerea), and 1 of Octodontidae (Octodon degus) using the first 548 base pairs of the mitochondrial cytochrome-b gene. Maximum-parsimony and maximum-likelihood analyses consistently showed Chinchillidae as a robust clade and confirmed a close relationship with Dinomyidae. Both Chinchilla species differed at 22 sites, and 3 were nonsilent; average genetic distances were approximately 6%. Sequences from domestic C. lanigera and wild C. brevicaudata showed low levels of variation. Although all topologies obtained were congruent with current taxonomy, Lagidium exhibited large genetic distances (range 5.9–8.9%), suggesting the existence of more than the 3 species currently recognized.

Mitochondrial phylogeography and demographic history of the Vicuña: implications for conservation

The vicuña (Vicugna vicugna; Miller, 1924) is a conservation success story, having recovered from near extinction in the 1960s to current population levels estimated at 275 000. However, lack of information about its demographic history and genetic diversity has limited both our understanding of its recovery and the development of science-based conservation measures. To examine the evolution and recent demographic history of the vicuña across its current range and to assess its genetic variation and population structure, we sequenced mitochondrial DNA from the control region (CR) for 261 individuals from 29 populations across Peru, Chile and Argentina. Our results suggest that populations currently designated as Vicugna vicugna vicugna and Vicugna vicugna mensalis comprise separate mitochondrial lineages. The current population distribution appears to be the result of a recent demographic expansion associated with the last major glacial event of the Pleistocene in the northern (18 to 22°S) dry Andes 14–12 000 years ago and the establishment of an extremely arid belt known as the ‘Dry Diagonal’ to 29°S. Within the Dry Diagonal, small populations of V. v. vicugna appear to have survived showing the genetic signature of demographic isolation, whereas to the north V. v. mensalis populations underwent a rapid demographic expansion before recent anthropogenic impacts.

Evolución de los filotinos (Rodentia, Muridae) en los Andes del Sur

La tribu Phyllotini es un grupo avanzado de 46 especies endemicas entre los Muridae de America del Sur que, estando adaptado a sus ambientes xericos, parece haber tenido el Altiplano Sur como area de diferenciacion original (Reig 1986). Esta hipotesis es puesta a prueba examinando la distribucion geografica y los datos citogeneticos de 35 especies, incluyendo la descripcion de bandas G de Andinomys edax y Euneomys chinchilloides y su comparacion con Phyllotis, bandas AgNOR y FISH para ADNr en siete especies, asi como datos de electroforesis de proteinas (118 electroalelos en 12 especies) y de secuencias del gen para citocromo b en el ADNmt (407 pb en 14 especies). Todos los cariotipos resultaron cromosomicamente distintos, excepto dos en los que no se conto con bandas G. Se encontro una asociacion general entre distribucion altiplanica de las especies con estados de caracteres ancestrales (cromosomas telocentricos, 2n altos, posiciones basales en las filogenias basadas en proteinas y secuencias de citocromo b), asi como entre distribucion no altiplanica y estados derivados. Se documentan aqui distintas combinaciones de brazos cromosomicos tipo Andinomys que se fusionarian para formar cromosomas metacentricos en Euneomys y Phyllotis, y tambien una disminucion del numero de NORes estructurales en Auliscomys respecto de Loxodontomys, rasgos derivados que demuestran una diversificacion hacia el sur y otra hacia el norte respectivamente, desde un centro en el Altiplano Sur

Sistemática, taxonomía y domesticación de alpacas y llamas: nueva evidencia cromosómica y molecular

Four camelid species exist in South America: two wild, the guanaco (Lama guanicoe) and the vicuna (Vicugna vicugna), and two domestic, the alpaca (Lama pacos) and the llama (Lama glama). However, the origin of the domestic species has been a matter of debate. In the present study, variations in chromosome G banding patterns and in two mitochondrial gene sequences have been used to study the origin and classification of the llama and alpaca. Similar patterns in chromosome G band structure were observed in all four Lamini species, and these in turn were similar to the bands described for camels, Camelus bactrianus. However, fine and consistent differences were found in the short arms of chromosome 1, separating camels, guanacos and llamas from vicunas and alpacas. This pattern was consistent even in a hybrid guanaco x alpaca. Equivalent relationship

Mitochondrial DNA variation and systematics of the Guanaco (Lama Guanicoe, Artiodactyla: Camelidae)

Abstract Guanacos (Lama guanicoe) are the most important native herbivorous species in the South American steppes and the dominant ungulate in a fauna rich in rodents but poor in large mammal species. Between 2 and 4 subspecies are usually recognized within Lama guanicoe, based on subtle morphological differences and geographic distribution. To evaluate whether molecular variation is consistent with the latter hypotheses, we analyzed the complete cytochrome-b and partial control region mitochondrial DNA sequences of L. guanicoe from 22 localities in Peru, Bolivia, Argentina, and Chile. Sequence analyses of both genes support the monophyly of the species but failed to distinguish the occurrence of subspecies along the geographic range. Despite that, the northernmost populations (Peru and northern Chile) showed some degree of genetic differentiation with respect to southern representatives from Argentina, Bolivia, and rest of Chile. Analysis of genetic diversity also showed a strong signal of past low population size and a recent population expansion.

Morphological Variation of the Glans Penis of South American Octodontid and Abrocomid Rodents

Morphological variation in the glans penis of the six genera and most species of octodontid rodents was studied and compared to members of the Abrocomidae and Ctenomyidae. Most specimens of Octodon degus, O. lunatus, O. bridgesi, Octodontomys gliroides, Aconaemys fuscus , and A. sagei presented two spikes on each side at the bottom of the intromitent sac (2–2 pattern), although the number of spikes varies from 1–2 to 4–5. The largest variability in number of spikes was shown by Spalacopus cyanus , ranging from 1–1 to 4–5; although they were rather short. The 1–1 pattern characterized Tympanoctomys barrerae and Octomys mimax . This pattern was found in the species of the genera Abrocoma and Ctenomys , which belong to the related families Abrocomidae and Ctenomyidae. Our results support the view that the 1–1 pattern is ancestral and that other patterns are derived states. Within the octodontids, only Tympanoctomys barrerae and Octomys mimax showed the ancestral condition shared with Ctenomyidae and Abrocomidae. All other octodontid genera share the derived state 2–2 or modifications of it.

Cytogenetic and reproductive studies of two nominal subspecies of Phyllotis darwini and their experimental hybrids

Phyllotis darwini vaccarum and Phyllotis darwini darwini live contiguously in Central Chile, the former in the high Andes and the latter in the Central Valley and on the coast. All individuals examined of both kinds had 38 chromosomes of similar shape, but P. d. vaccarum always showed large paracentromeric C-bands on all chromosomes, whereas P. d. darwini showed none or only small ones. Fifty-six pairings between the two forms were made in the laboratory. They resulted in 23 hybrids produced by four P. d. vaccarum females and four P. d. darwini females. A higher incidence of aggression and mortality was observed in the cross-pairings, as well as a lower incidence of birth (14.3%), and a lower mean litter size (2.9), in comparison with 117 pairings within forms (65.0% and 4.2%, respectively). C-banded hybrid metaphases showed 19 chromosomes with large paracentromeric C-bands and 19 with none or only small ones. In the G-banded hybrid karyotypes, it was possible to identify eight chromosome pairs with total correspondence of band patterns, five pairs with correspondence only at their long arms, and 10 autosomes and the X chromosomes with no correspondence at all. Hybrids were completely sterile; adults had incomplete germinal lines and a lack of differentiated gametes in their gonads. These results, and the presence of individuals of both chromosomal forms in the same trap line with no traces of mixing, provide strong evidence of complete genetic isolation of the two forms; that is, they should be considered as separate species. Further considerations suggest the existence of gene flow between vaccarum and the other Andean forms living in northern Chile, and probably with those from southern Chile; the oldest species-group name available for all of these is xanthopygus .