Natalia O. Leiner

SEASONAL VARIATION IN THE DIET OF THE BRAZILIAN SLENDER OPOSSUM (MARMOSOPS PAULENSIS) IN A MONTANE ATLANTIC FOREST AREA, SOUTHEASTERN BRAZIL

Abstract The diet of the Brazilian slender opossum (Marmosops paulensis) was determined through analysis of fecal samples collected in an area of montane Atlantic forest in southeastern Brazil. M. paulensis consumed insects, arachnids, gastropods, fruits, flower parts, and small vertebrates. The observed preference for Piper fruits could be related to the spatiotemporal predictability of this item, whereas the observed preference for the Coleoptera, the Blattodea, and the Opiliones could be due to overestimation of hard-bodied prey. Diet composition varied seasonally, with invertebrates and flower parts being consumed more during the dry season, probably because of their higher relative abundance when compared to fruits in this season. Diet was more diverse during the dry season, because of the inclusion of new fruit species and the reduced contribution of Piper fruits in the diet. We suggest that M. paulensis is more frugivorous than previously thought and that this species can be an important seed disperser of pioneer plants, especially of Piper species.

Semelparity and Factors Affecting the Reproductive Activity of the Brazilian Slender Opossum (Marmosops paulensis) in Southeastern Brazil

Abstract Data on the reproductive patterns of the Brazilian slender opossum (Marmosops paulensis) were collected in an area of Montane Atlantic forest, southeastern Brazil, from August 2002 to July 2004. Reproduction occurred from September to March in both years, a period of high food supply, probably as a way to maximize survival of juveniles. There was nearly zero postmating survival, thus, no individual took part in more than 1 breeding event. This pattern characterizes a semelparous life history, which has been described in other small didelphids and dasyurids. Females were reproductively active during months with longer day lengths and abundant fruit supply. Breeding seems to be initiated by a 12L:12D photoperiod and a rapid rate of change in day length, as demonstrated in semelparous dasyurids. Hence, the effect of photoperiodic cues on the onset of reproduction also may stand for other semelparous didelphids. We suggest that fruit availability controlled the length of breeding activity in M. paulensis, and it could play a role in the occurrence of semelparity in this species. However, semelparity may occur only due to phylogenetic constraints, whereas food supply works as a selective force maintaining this trait.

On the sticky cobwebs of two theridiid spiders (Araneae: Theridiidae)

In this study we describe and illustrate a new species, Chrysso intervales n. sp., based on males and females collected in Parque Estadual Intervales, an area of Atlantic Forest in the State of São Paulo, Brazil. We present data on habitat selection, web architecture, thread adhesiveness, diet, and mortality due to fungi for both Chrysso intervales and the sympatric species, Helvibis longicauda. Both species build webs on vegetation close to river margins, but they were not found in forest sites away from these shaded and extremely humid corridors. The webs of both species are entirely composed of viscid silk lines, occupying the space between two or more large leaves. The construction of this web type by Helvibis and Chrysso, and the large amount of viscid droplets in their threads, indicate that the investment in adhesive components in theridiids may be dependent on the ambient conditions. We suggest that the costs of maintaining viscid silk lines in humid areas may be relatively low, explaining the habitat restriction observed in the species studied. By selecting humid habitats, however, these spiders are susceptible to attacks by fungi. The webs constructed by both species intercepted mostly Diptera, especially tipulids, but H. longicauda was also observed consuming a wide variety of prey types.

Tooth Eruption Sequence and Replacement Pattern in Woolly Opossums, Genus Caluromys (Didelphimorphia: Didelphidae)

Abstract The sequence of molar eruption, along with the timing of replacement of the 3rd deciduous premolar by a permanent premolar, has been documented in several species in the family Didelphidae, and routinely used to establish age classes. We documented the dental eruption and replacement patterns in the 3 species of the neotropical marsupial genus Caluromys, which constitute one of the most basal groups within the Didelphidae. We examined 258 specimens of Caluromys derbianus, 54 specimens of C. lanatus, and 386 specimens of C. philander. These species have a dental eruption pattern that is similar to that of Marmosops, with replacement of the 3rd deciduous premolar after eruption of the 4th molar. However, we sometimes found incompletely erupted P3 and M4 occurring simultaneously as part of a M4–P3 eruption sequence. We suggest that the occurrence of this intermediate pattern in other taxa should be verified by examination of large series of specimens. Because teeth erupting in sequence can be erroneously considered as fitting an intermediate pattern, eruption sequence and time of completion of development should be used separately when using dental eruption in phylogenetic analyses. Because of the high degree of intraspecific variation observed in several taxa in Didelphidae, a system of age classes based solely on eruption of upper molars may be more useful than those that combine information on molar eruption sequence and timing of premolar replacement.

Multiscale habitat selection by slender opossums (Marmosops spp.) in the Atlantic forest of Brazil

Abstract The relative importance of factors that influence the habitats that animals select often varies with spatial scale. We evaluated the hypotheses that habitat selection by 2 sympatric slender opossums (Marmosops) is scale-dependent, and that coexistence in the gray slender opossum (Marmosops incanus) and the Brazilian slender opossum (M. paulensis) is enabled through differential use of habitat components or segregation in the use of vertical strata, or both. At a mesohabitat scale both species selected areas with dense understory, especially vertical obstruction 0–0.5 m above the ground. At a finer, microhabitat scale M. incanus preferred places with higher plant cover and vertical obstruction 0.5–1.0 m above the ground, and M. paulensis showed no evident pattern of selection. This result supports the hypothesis that habitat selection is scale-dependent. Although both species selected similar habitats at the mesoscale, we found segregation in the use of vertical strata, with M. paulensis being more terrestrial than M. incanus. Habitat segregation could reflect the intrinsic habitat preferences of each species or potential competition for space between the 2 congeners.

Effects of resource availability on the use of space by the mouse opossumMarmosops paulensis (Didelphidae) in a montane Atlantic forest area in southeastern Brazil

Food supply is an important determinant of animal movements. In the present study we tested the occurrence of an inverse relationship between daily movements ofMarmosops paulensis (Tate, 1931) and their food supply. This species is a member of the family Didelphidae, occurring in areas of high elevation in the Brazilian Atlantic Forest.M. paulensis moved mostly over the ground, although the understory was also used. Mean daily range ofM. paulensis estimated through spool-and-line device was about 0.40 ha; no differences were noted between body sizes and sexes. As expected, there was an inverse relationship between daily movements and food supply. This relationship resulted from the clumped distribution of fruits, particularlyPiper rather than the sparser distribution of arthropods.

Territoriality in females of the slender opossum (Marmosops paulensis) in the Atlantic forest of Brazil

Spatial organization within animal populations is often thought to reflect the outcome of strategies implemented by each individual to enhance its reproductive success and survival (Clutton-Brock 1989). Thus, while females usually focus on the acquisition of food and breeding sites, male dispersion is more often determined by the distribution and availability of females (Clutton-Brock 1989). Due to these factors, intraspecific competition for space could lead to the adoption of a territorial strategy, whenever the benefits of territorial defence are higher than the costs (Brown & Orians 1970). Among small mammals, two main hypotheses have been proposed to explain the occurrence of territoriality in females. Ostfeld (1990) proposed that females should defend food resources, so the distribution and availability of food items should determine the cost-benefit relationship of adopting a territorial strategy. However, Wolff (1993) developed a hypothesis, based on small rodents, that females should defend nest sites in order to avoid infanticide, the so-called pup-defence hypothesis. Territoriality has been studied in many species of mammal; however, little is known about its occurrence in didelphid opossums (Didelphimorphia: Didelphidae). In the present study, our main objective was to evaluate patterns of home-range overlap between and within sexes in Marmosopspaulensis (T?te 1931), a semelparous didelphid, with a diet composed mainly of fruits and invertebrates (Leiner & Silva 2007b) and a breeding