Abrothrix Longipilis Research Articles

Quantitative Habitat Associations of Small Mammals in a Temperate Rainforest in Southern Chile: Empirical Patterns and the Importance of Ecological Scale

Multivariate analyses of distributions of small mammals identified important habitat associations in a precordilleran temperate rainforest in southern Chile. Significant differences in vegetation were found between summer (January–March) and winter (July–August) periods, indicating that multiple-season studies may be necessary to fully assess habitat preferences of small mammals. Three species of sigmodontines ( Akodon olivaceus, Abrothrix longipilis, Abrothrix sanborni ), and a putative A. longipilis × A. sanborni hybrid, showed moderate habitat preferences with considerable interspecific overlap. Habitat associations of Oligoryzomys longicaudatus , a sporadic resident, were significantly different from those of the akodonts, perhaps reflecting transient status in the community; other species generally had insufficient captures for quantitative comparisons. These patterns of habitat association differ from those of previous studies and suggest the consequences of methodological, spatiotemporal, and demographic factors in the interpretation and detection of multivariate ecological relationships.

Reproduction in a South American mouse, Abrothrix longipilis.

Approximately 700 Abrothrix longipilis were trapped in Argentina, and their reproductive organs were studied. Some were kept briefly in captivity. Males have the same body length as females but are 8% heavier. Sexually immature males are shorter and lighter than breeding males of the same age. Few individuals in the wild live as long as two years. All overwintering males come into breeding condition in the spring and become infertile in the autumn. All overwintering females have open vaginas in the spring, and most undergo several infertile ovulatory cycles, probably without copulating, before they become pregnant. Corpora lutea of the sterile cycles accumulate; there may be as many as 28 in a pair of ovaries. The average number of ova shed per cycle is 4.66; average litter size is 3.85. Ovulation is spontaneous. There is postpartum ovulation and fertilization without intervening sterile cycles but with maintenance of old corpora lutea. Unusual architecture of the penis and vagina may result from unusual timing of hormone production during development, and the disjunction of ovulation and fertilization may similarly result from hormonal heterochrony at the beginning of the breeding season. The apparently nonadaptive wastage of ova in sterile cycles may be a novel example of kin selection.

Parallel Evolution and Ontogeny of Simple Penis among New World Cricetid Rodents

Two penile types, simple and complex, seem to distinguish North and South American cricetids; their origins were investigated by study of dissected and stained glans of 101 adult and young specimens. A simple penis with only a proximal baculum was found in Abrothrix longipilis and A. sanborni from Chile. In the North American Peromyscus eremicus , juvenile males displayed three small and transient pieces of cartilaginous tissues exactly where those of the complex penis are located. It is suggested that simplification of the baculum was produced independently in the two New World groups. A. longipilis also showed elongation of the glans, probably inducing the formation of a ventral cleft, os bending, and regression of the distal baculum and lateral sacs; strikingly, its proximal baculum ossified late, when third molars erupted. Since ossification and distal bacular differentiation in muroids usually are induced by testosterone much earlier, and testosterone-dependent glands also have been modified in simple-penis species, such delay might be a mechanism inducing elongation, with simplification a secondary heterochronic effect.

Spatiotemporal Patterns of an Irruption and Decline of Small Mammals in Northcentral Chile

During the austral winter of 1987 (June–August) at a semi-arid site in northcentral Chile, an outbreak of small mammals apparently was triggered by one episode of unusually high rainfall. From October 1987 to November 1990, we monitored the outbreak on a monthly basis on two equatorial- and two polar-facing slopes. Overall density on equatorial-facing slopes was 239 individuals/ha in spring 1987, increasing to a peak of 404/ha by summer 1988, and then steadily declining to a crash of 20/ha (5% of peak density) by spring 1990, with no signs of recovery. On polar-facing slopes, mammalian abundances were about one-half those of equatorial-facing slopes. There were 112 individuals/ha in spring 1987, increasing to a peak of 199/ha by summer 1988, and then steadily declining to a crash of 8/ha (4% of peak density) by spring 1989. Since then, mammal populations on polar-facing slopes have been slowly recovering, reaching 11% of their peak density by November 1990. Of the eight species monitored, only three irrupted: the granivorous cricetid Phyllotis darwini , the omnivorous cricetid Akodon olivaceus , and the insectivorous didelphid Marmosa elegans . These three irrupted and declined in phase, simultaneously on the two opposite-facing slopes, such that their relative frequencies did not shift markedly. Two of the three folivores ( Abrocoma bennettii, Octodon degus , but not Chinchilla lanigera ), one granivore ( Oryzomys longicaudatus ), and one insectivore ( Akodon longipilis ) disappeared from the site, persisting longer on equatorial-facing slopes.

Distribution and Abundance of Small Mammals along an Elevational Transect in Temperate Rainforests of Chile

Assemblages of small mammals in temperate Andean rainforests of southern South America are diverse but poorly known. Herein, we describe an elevational transect through temperate rainforests in Valle de La Picada, Chile, during February and March, 1984. The transect consisted of standardized removal trapping (165 traps set in lines at ca. 7-m intervals and operated for 6 consecutive days) at each of seven elevations: 425 m, 505 m, 620 m, 715 m, 820 m, 920 m, and 1,135 m. A total of 514 small mammals representing two species of marsupials and seven species of sigmodontine rodents was collected. Trap success averaged 7.4% across traps, days, and elevations. Number of captures by individual traps during the sample period was indistinguishable from a Poisson distribution, both throughout the transect and at individual levels, suggesting independence of captures among traps. Captures were biased significantly by trap type, with museum specials securing significantly more Dromiciops australis and all forms of Akodon than Sherman live traps; the same biases were suggested by captures of Irenomys tarsalis and Auliscomys micropus . As expected, total number of individuals taken at each elevation declined throughout the sampling period while the cumulative number of species rose. Number of species, number of individuals, and species diversity varied inversely with elevation. Number of species and species diversity taken each day reached a maximum after 2–4 days of sampling. Captures of Rhyncholestes raphanurus, Akodon sanborni , putative hybrids of A. sanborni and Akodon longipilis , and I. tarsalis were correlated inversely with elevation. Conversely, D. australis, A. longipilis , and A. micropus were taken more commonly at higher elevations, whereas captures of Oryzomys longicaudatus, Akodon olivaceus , and Geoxus valdivianus appeared unrelated to elevation. Systematic sampling procedures are viewed as essential for describing fundamental patterns of abundance and distribution that can be compared with other studies.

A Long-Term Study of a Small-Mammal Assemblage in the Central Chilean Matorral

We livetrapped small mammals for 18 months with Sherman traps, and for 13 (simultaneous) months with Tomahawk traps, in a central Chilean matorral (chaparral-like shrub-land) locality near Santiago. Eight species (the marsupial Marmosa elegans , the lagomorph Oryctolagus cuniculus , the cricetids Akodon longipilis, Akodon olivaceus, Oryzomys longicaudatus , and Phyllotis darwini , and the caviomorphs Octodon degus and Abrocoma bennetti ) were captured, with total mean densities of 57.9 and 12.4 individuals per ha in the Sherman and Tomahawk grids, respectively. Tomahawk traps provided the same estimates of density for the two largest rodents, but did not capture small species or adult rabbits. Weights of adult individuals of four species were 20–30% smaller than those reported previously. Octodon and Oryctolagus used shrub cover as available; Abrocoma avoided dense patches, whereas the remaining five species avoided sparse patches. Six mammal species were associated with the six principal shrub species in proportion to their availability, but A. longipilis and Octodon both associated with Colliguaya odorifera more frequently than expected, while apparently avoiding two other shrubs. Stopwatch-timed captures allowed categorization of one small mammal as diurnal and diurnal-crepuscular, two as nocturnal, four as nocturnal and nocturnal-crepuscular; one species was active all day, except at dawn. Comparisons with similar assemblage studies conducted in neighboring matorral areas demonstrate marked differences in population densities of particular mammal species, apparently related to levels of habitat disturbance and associated reductions of shrub cover.

A new genus and species of trombiculid mite (Acari) from a chilean rodent (Mammalia: Cricetidae)

ABSTRACT Chilacarus martini n. gen., n. sp. is described from larvae collected from Akodon longipilis (Waterhouse), wooly mice, obtained in Parque Nahuelbuta, Malleco Province, Chile.

Ecological Relationships of Two Species of Akodon in Central Chile

Analyses of habitat selection and diet showed significant ecological separation between Akodon longipilis and A. olivaceus (Cricetidae) in Mediterranean-climate areas of Chile. Comparing five sites with different climates and vegetation, A. longipilis was more common than A. olivaceus at those localities with higher rainfall and shrub cover. At two coastal scrub sites A. longipilis was strongly associated with trap stations having greater shrub cover, greater litter cover, taller shrubs, less herbaceous cover, and lower herb heights than stations selected by A. olivaceous. A discriminant analysis found measures of herbaceous and litter cover to be the strongest variables differentiating microhabitats of the two species. Analyses of stomach contents showed both species to be omnivorous, but A. longipilis consumed higher proportions of arthropods than A. olivaceus at most sites. Habitat use and diet may be correlated with adaptations in skull morphology and body size in these two species.

Cytogenetic Analysis of some Chilean Species of the GenusAkodonMeyen (Rodentia, Cricetidae)

SUMMARYA comparative chromosome analysis of Akodon longipilis, A. olivaceus and A. xanthorhinus (Rodentia, Cricetidae) was made. A similarity in diploid number (2n = 52), size, morphology, and G- and C-banding patterns was found.