Forest-dwelling Rodents Research Articles

Seasonal Changes in Nycthemeral Availability of Sympatric Temperate Mixed Forest Rodents: The Predators' Perspective.

(1) Background: Bank voles (Clethrionomys glareolus) and Apodemus mice are of exceptional importance as prey for predators in temperate mixed forests. We hypothesized that overall prey availability would increase linearly with prey frequency, and that the daylight hours, which are considered particularly dangerous, would be used only during seasonal rodent population peaks and only in the twilight hours. (2) Methods: We conducted a two-year camera-trapping study in an inner alpine mixed forest and collected 19,138 1 min videos in 215 camera-trap nights. Prey availability was defined as the pseudo-replication-limited maximum number of the respective rodent taxon per 30 min period, summed per season. (3) Results: Overall prey availability increased with frequency, i.e., the maximum number of rodent individuals per camera-trap night. Seasonally, Apodemus mice were particularly available to predators in the summer and bank voles in the autumn after a tree mast year. In both cases, this was accompanied by a significant increase in diurnal availability. During the population peak of Apodemus mice, the nocturnal availability of bank voles decreased without a concurrent increase in absolute diurnal availability, even though the significant relative shift to diurnal activity superficially suggested this. Bank voles were active throughout the day, while Apodemus mice were nocturnal and (rarely) crepuscular. (4) Conclusions: Availability of rodents to predators, especially during daylight hours, was mainly dependent on their tree mast-induced increased frequencies. Bank voles likewise responded strongly to interspecific competition with the larger and aggressive Apodemus mice, which negatively affected availability to predators. At our seasonal level of evaluation, we conclude that nycthemeral availability of forest-dwelling rodents to generalist predators of temperate mixed forests is predominantly driven by bottom-up mechanisms.

Population genomic structure of a widespread, urban-dwelling mammal: The eastern grey squirrel (Sciurus carolinensis).

Urbanization is a persistent and widespread driver of global environmental change, potentially shaping evolutionary processes due to genetic drift and reduced gene flow in cities induced by habitat fragmentation and small population sizes. We tested this prediction for the eastern grey squirrel (Sciurus carolinensis), a common and conspicuous forest-dwelling rodent, by obtaining 44K SNPs using reduced representation sequencing (ddRAD) for 403 individuals sampled across the species' native range in eastern North America. We observed moderate levels of genetic diversity, low levels of inbreeding, and only a modest signal of isolation-by-distance. Clustering and migration analyses show that estimated levels of migration and genetic connectivity were higher than expected across cities and forested areas, specifically within the eastern portion of the species' range dominated by urbanization, and genetic connectivity was less than expected within the western range where the landscape is fragmented by agriculture. Landscape genetic methods revealed greater gene flow among individual squirrels in forested regions, which likely provide abundant food and shelter for squirrels. Although gene flow appears to be higher in areas with more tree cover, only slight discontinuities in gene flow suggest eastern grey squirrels have maintained connected populations across urban areas in all but the most heavily fragmented agricultural landscapes. Our results suggest urbanization shapes biological evolution in wildlife species depending strongly on the composition and habitability of the landscape matrix surrounding urban areas.

Методи обліку чисельності гризунів

This is a republication of the methodological review originally published in 1957, which has been important for the organization of local and regional studies of the mammal fauna, particularly in the identification of species composition and estimates of the relative abundance of small (mouse-like) rodents. The present publication is accompanied by an editorial foreword and contains seven chapters. The first three are titled ‘Rodents as objects of census and monitoring,’ ‘Census of rodents and its components,’ and ‘Census of rodents in the field with attention to relative and absolute census.’ The section on relative census includes such topics as ‘Census by biological indicators,’ ‘Census by analysis of pellets and excrements of predators of mice,’ ‘Census by counting burrows (holes),’ and ‘Cenus on trap lines.’ The section on absolute census includes parts such as ‘Census by complete excavation of burrows and complete capture of their population’ and ‘Census of rodents in various kinds of haystack.’ The other sections are ‘Census of forest-dwelling rodents,’ ‘Census of rats and mice in human settlements’ (includes three parts: the method of dusty areas, the method of trial bait, and the method of almost complete capture), ‘Methods of combating certain species of harmful rodents’ (abridged), ‘Controlling methods of some species of harmful rodents’ (abridged), and ‘Collection and transfer to specialists of rodent materials for scientific purposes.’

Influence of tree thinning on abundance and survival probability of small rodents in a natural deciduous forest

This study was conducted to investigate the influence of tree thinning on habitat variables and small rodents in a natural deciduous forest in South Korea. We focused on the populations of the small forest-dwelling rodents, striped field mouse Apodemus agrarius and Korean field mouse A. peninsulae. Populations were monitored for 2 years in a natural deciduous forest subject to tree thinning. The coverage of ground vegetation and number and volume of downed trees were significantly increased after thinning. However, the coverage of overstory and understory vegetation and number of standing trees were decreased in postthinning session. The abundance and survival probability of captured A. agrarius and the total small rodents were significantly influenced by tree thinning. We hypothesize that the major factors determining the greater abundance and survival of small rodents after thinning may be the increased coverage of ground vegetation and number of downed trees, and the decreased number of standing trees. This study suggests that tree thinning could be a tool to both encourage tree productivity and create suitable habitats for small rodents.

A small mammal’s map: identifying and improving the large-scale and cross-border habitat connectivity for the hazel dormouse Muscardinus avellanarius in a fragmented agricultural landscape

Fragmentation and habitat loss pose major threats to global biodiversity. Especially forest dwelling species with small ranges and high habitat specialisation are affected by ongoing land use change. Building projects for infrastructural purposes, expanding settlements, and extensive agricultural areas are assumed to have a high impact on these species. The European Habitat’s Directive aims to conserve and restore habitat networks to lower these impacts. We propose that the idea of securing habitat networks for protected species should be incorporated within large scale landscape planning e.g. by modelling and improving corridors for umbrella species. Within a Danish-German project we developed a model demonstrating potential connecting corridors for Muscardinus avellanarius, a specialised forest dwelling rodent species with low dispersal ability. We used presence data and eco-geographical variables to find a data based time-efficient procedure which may be applied also in other species for future landscape planning. The habitat suitability model shows that the hazel dormouse occupies a narrow niche with highly suitable habitats comprising edge habitats. It indicates the preference of forest patches, linear structures and networks of the mentioned habitats. Along with connectivity the diversity of suitable habitats diversity is the major factor predicting hazel dormouse presence. For conservation management, we calculated habitat corridors and highlight sections with missing connections. This allowed us to accentuate regions of high management interest. The results represent the foundation not only for this cross-border conservation project, but also for long-term dormouse conservation on a federal-state level.

Habitat and nest use during natal dispersal of the urban red squirrel (Sciurus vulgaris)

As urban environments differ from the natural environment, the ability of a species to move in and use variable land composition types determines its fate in the urban environment. In many mammalian species, the selection of home ranges mainly occurs during natal dispersal. Thus, habitat selection of juvenile individuals greatly determines where animals are found in the city. Here, our goal is to understand how an originally forest-dwelling rodent selects components of an urban habitat. We used radio telemetry to record the habitat and nest use of Eurasian red squirrels (Sciurus vulgaris) in the city of Turku in southwestern Finland, with the main focus on habitat use during natal dispersal. We found that although the red squirrels preferred areas with more trees available than in the surrounding urban landscape they nevertheless often used sites with only a few trees. This result was highlighted by the analysis of the home range scale, as the area used did not differ greatly from the habitat composition of the available landscape. Juvenile red squirrels used the deciduous land cover type more often during movements in the natal area than during dispersal and explorative movements; however, they also settled in areas with less deciduous land cover type than in the natal area. Our results show that in urban areas movements of red squirrels are not restricted to their natural habitat type, which is a coniferous forest, but that they seem to be well adapted to urban areas, being able to utilize urban structures.

Seasonal Foraging by Forest Mice Enhances Loss of Weed Seeds from Crop—Field Edges

Abstract Native seed predators, such as mice (Peromyscus spp.) and ground beetles (Carabidae), consume weed seeds and waste grain within agricultural fields and thus provide a potentially important service to farmers. Most previous investigations of agricultural seed predation services have focused on within-field factors that affect rates of seed removal and consumption by field-resident seed predators. However, seasonal migrants from adjacent non-crop habitats may also contribute to removal of weed seed, particularly along field edges. We investigated whether rates of weed seed removal within fields increased during summer crop growth when Peromyscus leucopus noveboracensis (White-Footed Mouse), a ubiquitous forest-dwelling rodent in the eastern US, seasonally migrates into crop fields from adjacent forested woodlots. We used exclosure experiments to quantify the relative number of Setaria faberi (Giant Foxtail) seeds removed from seed trays by vertebrate and invertebrate seed predators within 4 corn fi...

Impact of Anthropogenic Disturbance on Native and Invasive Trypanosomes of Rodents in Forested Uganda.

Habitat disturbance and anthropogenic change are globally associated with extinctions and invasive species introductions. Less understood is the impact of environmental change on the parasites harbored by endangered, extinct, and introduced species. To improve our understanding of the impacts of anthropogenic disturbance on such host-parasite interactions, we investigated an invasive trypanosome (Trypanosoma lewisi). We screened 348 individual small mammals, representing 26 species, from both forested and non-forested habitats in rural Uganda. Using microscopy and PCR, we identified 18% of individuals (order Rodentia) as positive for trypanosomes. Further phylogenetic analyses revealed two trypanosomes circulating-T. lewisi and T. varani. T. lewisi was found in seven species both native and invasive, while T. varani was identified in only three native forest species. The lack of T. varani in non-forested habitats suggests that it is a natural parasite of forest-dwelling rodents. Our findings suggest that anthropogenic disturbance may lead to spillover of an invasive parasite (T. lewisi) from non-native to native species, and lead to local co-extinction of a native parasite (T. varani) and native forest-dwelling hosts.

소백산국립공원 내 환경특성에 따른 설치류의 분포 특징

This study was conducted to differences in distribution of rodents in relation to enviroment type in Sobaeksan National Park. 123 individuals of three species, such as Apodemus agrarius, Apodemus peninsulae, Myodes regulus were captured in this study. A. agrarius, A. peninsulae, M. regulus showed statistically significant differences according to altitude of rodents distribution in study area((One-way ANOVA, F=21.815, p<0.05). A. agrarius is prefer to lower the average altitude than A. peninsulae and M. regulus. However, A. peninsulae and M. regulus has been shown to prefer the a similar altitude. Distinction in distribution of rodents in relation to vegetation type showed that a significant difference(Chi-square test, χ2=43.797, p=0.00). A. agrarius were shown higher number of captured in open-space, A. peninsulae were in Japanese larch plantation forest, and M. regulus were in Deciduous forest. At the same altitude, the distribution of the rodents were differences relation to habitat type in study area(Chi-square test, χ2=32.429, p=0.00). A. agrarius is a generalist species, prefer Heliport(open-space). A. peninsulae and M. regulus is a forest-dwelling rodents, prefers deciduous forest.

Will an ancient refuge become a modern one? a critical review on the conservation and research priorities for the red squirrel ( Sciurus vulgaris ) in the Iberian peninsula

Mediterranean peninsulas are well-known glacial refugia for several mammal species. For Eurasian red squirrel ( Sciurus vulgaris ), a forest-dwelling rodent, there is some evidence that population diversification was influenced by these refugia. Here, we review the poorly known history of the red squirrel in the Iberian Peninsula, and discuss current threats to this species, suggesting conservation guidelines and exploring several research lines for forthcoming studies. Red squirrel populations suffered several bottlenecks in Iberia, but recently, after four centuries of absence, this species is expanding throughout the Portuguese territory. Although S. vulgaris taxonomic and genetic status needs further investigation, molecular data support the occurrence of a possible distinct cluster in the Iberian Peninsula. Additionally, a distinct and endemic population was recorded to the Sierra de Espuna, in Spain, which was probably the result of Quaternary climatic and vegetation fluctuations. Two major threats for red squirrels in Europe were identified: (i) habitat deterioration; and (ii) competition with the invasive Eastern grey squirrel ( S. carolinensis ). Conservation actions should focus on the conservation, restoration and appropriate management of suitable forested habitats. Although to date no grey squirrels occur in the wild in the Iberia, the trade and release of this invasive sciurid species is already forbidden by national conservation agencies in both Iberian countries and awareness campaigns are suggested. An integrated research approach using both molecular and ecological data, and a large dataset containing samples from the entire Iberian Peninsula, should be followed to better understand historical, contemporary and future factors that may affect squirrel distribution. Download the complete issue.

Interspecific Differences in Tannin Intakes of Forest-Dwelling Rodents in the Wild Revealed by a new Method Using Fecal Proline Content

Mammalian herbivores adopt various countermeasures against dietary tannins, which are among the most widespread plant secondary metabolites. The large Japanese wood mouse Apodemus speciosus produces proline-rich salivary tannin-binding proteins in response to tannins. Proline-rich proteins (PRPs) react with tannins to form stable complexes that are excreted in the feces. Here, we developed a new method for estimating the tannin intake of free-living small rodents, by measuring fecal proline content, and applied the method to a field investigation. A feeding experiment with artificial diets containing various levels of tannic acid revealed that fecal proline content was clearly related to dietary tannin content in three species (A. speciosus, Apodemus argenteus, and Myodes rufocanus). We then used fecal proline content to estimate the tannin intakes of these three forest-dwelling species in a forest in Hokkaido. In the autumn, estimated tannin intakes increased significantly in the Apodemus species, but not in M. rufocanus. We speculated that an increase in tannin intake during autumn may result from consumption of tannin-rich acorns. This hypothesis was consistent with population fluctuation patterns of the three species, which were well-synchronized with acorn abundance for the Apodemus species but not for M. rufocanus.

The roles of rivers and Pleistocene refugia in shaping genetic diversity in Praomys misonnei in tropical Africa

Aim This study aims to elucidate the phylogeography of the murid rodent Praomys misonnei and to document whether or not rain forest refugia and rivers structure patterns of diversity within this species. Location Tropical Africa, from Ghana to Kenya. Methods Patterns of genetic structure and signatures of population history (cytochrome b gene) were assessed in a survey of 229 individuals from 54 localities. Using maximum likelihood, Bayesian, network and genetic structure analyses, we inferred intra-specific relationships and tested hypotheses for historical patterns of gene flow within P. misonnei. Results Our phylogenetic analyses reveal a strong phylogeographical structure. We identified four major geographical clades within P. misonnei: one clade in Ghana and Benin, a Nigerian clade, a West Central African clade and a Central and East African clade. Several subclades were identified within these four major clades. A signal of population expansion was detected in most clades or subclades. Coalescence within all of the major clades of P. misonnei occurred during the Middle Pleistocene and/or the beginning of Late Pleistocene. Main conclusions Our results suggest a role for both Pleistocene refugia and rivers in structuring genetic diversity in P. misonnei. This forest-dwelling rodent may have been isolated in a number of forest fragments during arid periods and expanded its range during wetter periods. Potential forest refugia may have been localized in Benin-Ghana, south-western Cameroon, southern Gabon, northern Gabon and eastern Democratic Republic of Congo-western Uganda. The Niger and/or the Cross Rivers, the Oubangui-Congo, Sanaga, Ogooue and/or Ivindo Rivers probably stopped the re-expansion of the species from relict areas.

A Silent Enzootic of an Orthopoxvirus in Ghana, West Africa: Evidence for Multi-Species Involvement in the Absence of Widespread Human Disease

Human monkeypox has never been reported in Ghana, but rodents captured in forested areas of southern Ghana were the source of the monkeypox virus introduced into the United States in 2003. Subsequent to the outbreak in the United States, 204 animals were collected from two commercial trapping sites in Ghana. Animal tissues were examined for the presence of orthopoxvirus (OPXV) DNA using a real-time polymerase chain reaction, and sera were assayed for antibodies against OPXV. Animals from five genera (Cricetomys, Graphiurus, Funiscirus, and Heliosciurus) had antibodies against OPXV, and three genera (Cricetomys, Graphiurus, and Xerus) had evidence of OPXV DNA in tissues. Additionally, 172 persons living near the trapping sites were interviewed regarding risk factors for OPXV exposure, and their sera were analyzed. Fifty-three percent had IgG against OPXV; none had IgM. Our findings suggest that several species of forest-dwelling rodents from Ghana are susceptible to naturally occurring OPXV infection, and that persons living near forests may have low-level or indirect exposure to OPXV-infected animals, possibly resulting in sub-clinical infections.

Effect of Woody Debris Abundance on Daytime Refuge Use by Cotton Mice

Daytime refuges are important to nocturnal rodents for protection from predators and environmental extremes. Because refuges of forest-dwelling rodents are often associated with woody debris, we examined refuge use by 37 radio-collared Peromyscus gossypinus (cotton mice) in experimental plots with different levels of woody debris. Treatment plots had six times (≈ 60 m3/ha) the volume of woody debris as control plots (≈ 10 m3/ha). Of 247 refuges, 159 were in rotting stumps (64%), 32 were in root boles (13%), 19 were in brush piles (8%), and 16 were in logs (6%); 10 refuges could not be identified. Stumps were the most common refuge type in both treatments, but the distribution of refuge types was significantly different between treatment and control plots. Root boles and brush piles were used more on treatment plots than on control plots, and logs were used more on control plots than on treatment plots. Refuge type and vegetation cover were the best predictors of refuge use by cotton mice; root bole refuges and refuges with less vegetation cover received greater-than-expected use by mice. Abundant refuges, particularly root boles, may improve habitat quality for cotton mice in southeastern pine forests.

Digestive responses of two omnivorous rodents (Peromyscus maniculatus and P. alstoni) feeding on epigeous fungus (Russula occidentalis)

The sporocarps of hypogeous and epigeous fungi are important dietary items for forest dwelling rodents in temperate and tropical forests throughout the world. However, results of some pioneering works have demonstrated that fungi cannot be considered as nutritionally high-quality food items for some mycophagous small rodents. According to these studies, when mycophagous rodents feed on fungus, they showed a minimal digestibility, but whether this applies to most rodent species that include fungi in their diets is unknown. In this study, we experimentally evaluated body mass changes and feed preferences in captive deer (Peromyscus maniculatus) and volcano (P. alstoni) mice when fed on epigeous fungus (Russula occidentalis). In experiment 1, the animals were fed with fungus as the only feedstuff in comparison to regular rodent chow and oat. In experiment 2, the animals were fed with fungus in a free-choice arrangement together with equal amounts of rodent chow and oat. Both species lost approximately 15% of their body mass within 4 days when fed on fungus alone, but gained 5-10% body mass during the same time period when ingesting oat and rodent chow, respectively, as the only feedstuff. However, in contrast, in the free-choice arrangement with all three feedstuffs, both species gained 20-30% body mass, and showed the highest feed preference for fungus followed by oat and rodent chow. In addition, apparent digestibility of energy and nitrogen were analyzed in both rodent species, which were 50-60% for fungus, whereas approximately 90-94% for rodent chow and oat. According to our results, animals need to supplement their diets with alternative high-quality food items in order to maintain and increase their body mass, suggesting that epigeous fungi are only of moderate nutritional value for small rodents. Futures studies should focus on exploring the importance of a mixture of fungal species in the diet of small mycophagous rodents.

Multi-species fruit and seed removal in a tropical deciduous forest in Mexico

We determined patterns of post-dispersal fruit and seed removal for 11 common native plants, as well as sunflower seeds ( Helianthus annuus L.), within a tropical deciduous forest in Jalisco, Mexico. Removal values were high in Delonyx regia (Bojer) Raf. (90%), Crescentia alata Kunth. (87%), H. annus (81%), Pithecellobium dulces (Roxb.) Benth (81%), Albizia occidentalis Brandegee (80%), Coccoloba barbadensis Jacq. (80%), Recchia mexicana DC. (80%), Caesalpinia pulcherrima (L.) Sw. (79%), Enterolobium cyclocarpum (Jacq.) Griseb. (73%), moderate in Guazuma ulmifolia Lam. (42%) and Celtis iguanaeus Sarg. (44%), and low in Amphipterygium adstringens (Schlechtend.) Schiede ex Standl. (17%). Low removal rates (29%) in experimental patches open only to arthropods suggest that arthropods have a minor role in removing fruits and seeds of these species. Removal values were high in experimental patches open to all potential agents (77%) and semipermeable patches open to forest-dwelling rodents (76%), suggesting that the latter group, the most abundant terrestrial mammal in this forest, was an important agent for removing the fruits and seeds of study plants. Removal values were higher in experimental patches located in tropical deciduous forest than in tropical semideciduous forest, as well as higher in high density (patches of 30 fruits or seeds) than in low density (patches of five fruits or seeds) experimental patches for most study plants. Mice appear to selectively remove and hoard fruits and seeds according to their energy and nutritional content and the presence of secondary metabolites, and from from high-density food patches and preferred habitats. Nonindependent effects of species, habitat, and density suggest that a complex interplay of factors determines fruit and seed removal for the plants examined from the Chamela tropical forest.

Effect of Plant Species, Fruit Density and Habitat on Post-Dispersal Fruit and Seed Removal by Spiny Pocket Mice (Liomys pictus, Heteromyidae) in a Tropical Dry Forest in Mexico

We tested whether quality, habitat, and food patch density affected post-dispersal fruit and seed removal of common plants in a tropical deciduous forest in western Mexico (Chamela, Jalisco). To identify the quality of seed or fruit, caged spiny pocket mice (Liomys pictus) were fed mono-specific diets of sunflower seeds (Helianthus annuus), seeds of Delonix regia, Lonchocarpus eriocarinalis, Caesalpinia coriaria, or fruits of Spondias purpurea. Caged mice gained weight with sunflower seeds, marginally lost weight with D. regia seeds, and significantly lost weight with S. purpurea fruits and L. eriocarinalis and C. coriaria seeds. Fruit and seed removal values in experimental patches were high in sunflower (80%) and D. regia (70%) seeds, and moderate in S. purpurea fruits (50%); L. eriocarinalis (0.1%) and C. coriaria (0%) seeds were not removed. More fruits and seeds were removed from experimental patches in tropical deciduous forest (57%) than from semi-deciduous forest (23%), and from high (43%) and medium density (46%) than from low density (31%) food patches. Similar fruit and seed removal values from experimental patches open either to all removal agents or open only to forest-dwelling rodents, suggest that spiny pocket mice were important removal agents of tested plants. Spiny pocket mice food choices can influence observed non-random patterns in seedling recruitment.

Postdispersal fruit and seed removal by forest-dwelling rodents in a lowland rainforest in Mexico

This study examined whether postdispersal fruit and seed removal by terrestrial mammals of common plant species was affected by the type of item, item density (low, medium, high), and habitat (gap, mid-succession, mature). Fruits of Brosimum alicastrum and Ficus yoponensi (Moraceae), Astrocaryum mexicanum (Palmae), and Nectandra ambigens (Lauraceae), and seeds of Omphalea oleifera (Euphorbiaceae) and Cymbopetalum baillonii (Annonaceae) were tested at the Los Tuxtlas rainforest in Mexico. Item removal from 108 experimental patches (N = 2340 fruits or seeds for each plant species tested) after 5 d was lower for F. yoponensis (6.6%) than for N. ambigens (68.8%), B. alicastrum (67.8%), C. baillonii (64.0%) and A. mexicanum (60.0%). No seeds of O. oleifera were removed. A higher fruit or seed removal was observed from high density than low density food patches in A. mexicanum, C. baillonii and N. ambigens, but not in B. alicastrum and F. yoponensis. A higher fruit or seed removal was observed from food patches in mature forest than in gaps in all plant species tested. Similar removal values between open (open to all terrestrial mammals) and caged (open to small rodents) fruit and seed patches, abundant rodent live-trapping, and a scarcity of large terrestrial mammals, indicated that forest-dwelling small rodents were the main postdispersal removal agents. Differences in plant species seedling recruitment resulting from small rodent food choices can partially determine long-term forest floristic composition at the Los Tuxtlas rainforest.

Rates of Gut Passage and Retention of Hypogeous Fungal Spores in Two Forest-Dwelling Rodents

Alimentary retention of hypogeous fungal spores by small mammals influences the spatial and temporal dynamics of spore dispersal. We investigated, in laboratory experiments, retention of spores of Elaphomyces granulatus by two mycophagous small mammals, the golden-mantled ground squirrel, Spermophilus saturatus , and the deer mouse, Peromyscus maniculatus . The concentration of spores in feces peaked at 20 h and < 12 h after feeding in S. saturatus and P. maniculatus , respectively, but the time for it to fall to half its maximum was similar (approximately 12 h) in both species. Mean retention times of spores were 24 h for S. saturatus and 12 h for P. maniculatus . Alimentary mechanisms that selectively retain small particles such as fungal spores may be common among small mammals, but spores were not retained for longer than the much larger particles of stained alfalfa ( Medicago sativa ) leaf in either S. saturatus or P. maniculatus . Despite the rapid excretion of most spores, the inoculating potential of feces may remain high for many days after cessation of feeding on fungus if large numbers of spores are ingested initially. Fungal spores ingested by S. saturatus immediately before onset of hibernation are excreted slowly, and a significant proportion may remain in the gut throughout hibernation. These could be dispersed in spring when little dispersal might occur otherwise.

Biochemical genetics of chromosome forms of Venezuelan spiny rats of the proechimys guairae and proechimys trinitatis superspecies

Spiny rats from Venezuela show an extensive karyotypic diversification (2n=24 to 2n=62) and little morphological differentiation. This study reports genetic distance, heterozygosity and polymorphism based upon 22 loci in semispecies and allospecies of the Proechimys guairae superspecies from N Central Venezuela, as compared with Proechimys urichi, a member of the Proechimys trinitatis superspecies from eastern Venezuela. Four chromosome forms of the P. guairae complex are included, each characterized by karyotypes of 2n=46 (Fundamental Number=72), 2n=48 (FN=72), 2n=50 (FN=72) and 2n=62 (FN=74). Proechimys urichi has a distinetive karyotype of 2n=62 (FN=88). The overall mean value of Nei's genetic identity index for all pair-wise comparisons is I=0.942±0.011. Mean identity within the P. guairae complex is Ī=0.969±0.033. Mean identity between P. urichi and members of that complex is Ī=0.889±0.011. Within the P. guairae complex, increased genetic divergence is correlated with higher karyotypic divergence. Heterozygosity varies from H=0.059 to H=0.153, with a mean value of H0.059. The mean percent of polymorphic loci is P=18.2±3.9 after the ‘0,95%’ polymorphism criterion, and P=20,5±5.2 after the ‘0.99%’ criterion. These results are compared with similar data from fossorial and non-fossorial rodents. Spiny rats are non-fossorial, forest-dwelling rodents which have undergone a speciation process with little genetic divergence and extensive chromosome rearrangements.