Taphonomy of modern communal burrow systems of the Plains vizcacha (Lagostomus maximus,Chinchillidae) in the Pampas region of Argentina: implications for the fossil record

The Plains vizcacha (Lagostomus maximus) is one of the largest rodents in South America. They live in communal burrow systems (vizcacheras) shaped by complex subterranean galleries which produce a strong impact on the local landscape. This paper presents the results of an actualistic study conducted with abandoned vizcacheras from the Pampas region of Argentina. The main objective is to evaluate the role of this rodent in the formation of the fossil record. Results indicate that the Plains vizcacha is responsible for the mixing, accumulation, and transport of materials; such as sticks, caliche, dung, feces, and abundant bone remains. Their burrowing activity and the accumulating habits, modifies the landscape, creating environments conducive to the buildup of objects and the reuse by different animals. These characteristics result in very complex associations of materials of different origins; making this rodent an important taphonomic agent with the potential to significantly impact the fossil record.     

Role of exotic tree stands on the current distribution and social behaviour of Swainson's hawk, Buteo swainsoni in the Argentine Pampas

Aim The Argentine Pampas was extensively and abruptly altered by European colonization. Between 1880 and 1885 the indigenous human inhabitants were completely displaced, and native grasslands were replaced by exotic pasture plants and crops. One of the most important ecological changes in the Pampas landscape, the introduction of tall exotic tree species, has received little attention, and its effect on wildlife has never been assessed. We have made an intensive survey of habitat use of Swainson's hawk, Buteo swainsoni in its most important non‐breeding quarters, the Pampas of Argentina, aiming to characterize the sites used by hawks for communal roosting. Location Pampas grasslands, Argentina. Methods We surveyed 30,000 km of roads by car during the austral summer from 2001 to 2004, covering the main non‐breeding area occupied by Swainson's hawks. Their roost sites were located by direct observation of birds roosting in tree stands close to the roads, by surveying potential roost sites around places where groups of pre‐ and post‐roosting hawks were recorded, and by gathering information from local farmers. Results Swainson's hawks exclusively used stands of exotic tree species for roosting. Eucalyptus viminalis was present in all 34 roosts surveyed, and in 59% of them it was the only species present. The remaining exotic tree species were the Siberian elm, Ulmus pumila, pines (Pinus spp.) and cypress (Cupressus spp.). Flock sizes at roost sites were unusually high for a raptor, with an average of 658 individuals (range 8–5000 hawks, n = 27 flocks). Main conclusions The introduction of exotic trees may have resulted in the expansion of the suitable habitat for Swainson's hawks, permitting a recent colonization of the Argentine Pampas. Tree stands may have also changed the communal roosting behaviour of this raptor, by virtue of their providing new structural elements in a region that almost completely lacked trees prior to European occupation.     

Comparative histology of the digestive tract in three new world marsupials

We compare the main histological features of the digestive tract of three selected New World didelphid marsupials (Mammalia, Metatheria, Didelphimorphia, Didelphidae): the White-eared Opossum Didelphis albiventris Lund, 1840, the Short-tailed Opossum Monodelphis dimidiata Wagner, 1847, and the Patagonian Opossum Lestodelphys halli Thomas, 1921. The three species have a geographic distribution restricted to south-eastern and southern South America, and have quite distinct body masses, adaptations and life histories. Our observations include the following: (i) submucosal glands are present throughout the oesophagus of D. albiventris, only in its first third in M. dimidiata, and are lacking in L. halli; (ii) in the stomach and duodenum, the serus coat coat in D. albiventris is cuboidal (simple, squamous mesothelial layer in the other two species); (iii) the duodenum in L. halli has large folds, short crypts and Brunner's glands (the other species lack folds and Brunner's glands); (iv) the colon's mucous membrane has short, scarce villi in D. albiventris (villi absent in the remaining species). Some of the observed differences can be due to ecological adaptations, especially in the relatively large-sized, extremely omnivorous D. albiventris (e.g., colon villi).     

Avian remains from the Upper Pleistocene (MIS3) site of Aguilón P-7, south of the Ebro River,Spain

Aves are represented by abundant fossil remains in Quaternary sites. Birds are well adapted to the environment they inhabit, so they make very good paleoenvironmental indicators for Quaternary sites. Here we analyse the avian remains from the Late Pleistocene (probably MIS3) site of Aguilón P-7 (AGP-7). The Pleistocene sediments fill up a shallow cave, which is located in the Zaragozan part of the Iberian Range, 55 km south of the city of Zaragoza. We have for the first time provided a taxonomic and taphonomic study of the avian assemblage of AGP-7, as well as a preliminary paleoenvironmental analysis based on these data. Nine avian taxa have been identified: Galliformes indet., Lagopus sp., Aquila chrysaetos, Gyps fulvus, Passeridae indet., Anthus sp., Prunella modularis,Sturnus cf. unicolor and Corvus monedula. The taphonomic analysis did not provide conclusive information. However, it suggests an accumulation of uneaten food remains by diurnal birds of prey. The identified taxa currently inhabit the Iberian Peninsula, populating woodland environments with rocky areas. They are found in areas with an oceanic climate, in contrast to the Mediterranean climate that now prevails in Aguilón.     

Histological and histochemical study of the duodenum of the plains viscacha (Lagostomus maximus) at different stages of its ontogenetic development

The general objective of this study focused on the duodenal histological and histochemical analysis of fetuses and adults of plains viscacha (Lagostomus maximus) from the Buenos Aires province (Argentina). Histological techniques, histochemical procedures for localizing and characterizing glycoproteins (GPs) and lectin histochemical techniques for the identification of specific sugar residues were used. The duodenal structure of all age groups here considered was typical of mammals. We identified a proliferation phase and an epithelial morphogenesis in mid‐gestational fetuses, an intermediate period of cell differentiation in at‐term fetuses and a posterior stage of physiological maturation in adults. According to histochemistry, the diverse GPs elaborated and secreted into the duodenum show a high degree of histochemical complexity related to the multiple functions of mucus in the digestive tract. The GPs in the duodenum of L. maximus and their glycosylation patterns varied according to the animal's age and the developmental state of the organ.     

Morphology of the carpal region in some rodents with special emphasis on hystricognaths

We examined the morphology of the wrist (carpal region) skeleton using histological serial sections and cleared and stained forelimbs of representatives of three rodent clades: ‘Hystricomorpha’ (Caviomorpha: Ctenomys opimus, C. talarum, Cuniculus taczanowskii, Erethizon dorsatum, Galea sp., Lagostomus maximus, Spalacopus cyanus; Phiomorpha: Fukomys mechowii, Heliophobius argenteocinereus, Hystrix cristata, H. africaeaustralis; Ctenodactylids (Ctenodactylus gundi)), ‘Myomorpha’ (Arvicola amphibius, Ondatra zibethicus, Meriones unguiculatus, Myodes glareolus, Spalax sp.) and ‘Sciuromorpha’ (Eliomys quercinus, Glis glis, Marmota marmota). We describe the arrangement of the carpal bones and identify several variable traits, some of which represent convergent evolution. One element, the Os posthamatum, lies in the carpal region and has not been recorded before. We interpret this bone as a putative autapomorphy of Hystricognathi but not of ‘Hystricomorpha’.     

May captive populations of Greater Rhea (Rhea americana) act as genetic reservoirs in Argentina?

The Greater Rhea (Rhea americana) is a characteristic bird of the Argentine Pampas. Despite the increasing farming interest of this ratite, their natural populations are progressively decreasing in size and range. The object of this study was to evaluate the status of captive populations as potential genetic reservoirs. Using Inter‐Simple Sequence Repeats as molecular markers, levels of genetic variability of F1 individuals from two captive populations were estimated and compared with those of wild populations in the same region. The captive populations were polymorphic for 12.22 and 13.33% of the loci, with a genetic diversity of 0.050. Differences with wild populations were not significant (z=1.79; P>0.05). Therefore, captive populations of rheas in Argentina should not be overlooked as genetic reservoir and source of individuals for reinforcement of natural populations, through reintroduction and translocation. Zoo Biol 30:65–70, 2011. © 2010 Wiley‐Liss, Inc.     

Effect of the Argentine ant on the specialist myrmecophilous cricket Myrmecophilus kubotai in western Japan

Effects of the Argentine ant on myrmecophilous animals living inside ant nests have been rarely studied to date. We investigated whether the “specialist” myrmecophilous cricket Myrmecophilus kubotai Maruyama that lives only in colonies of a Japanese native ant, Tetramorium tsushimae Emery, could live with the Argentine ant. In the field, the cricket was never found in nests of the Argentine ant. Our experiments showed that the cricket could not survive in artifical nests of the Argentine ant under laboratory conditions.     

Effects of local extinction of the plains vizcacha (Lagostomus maximus) on vegetation patterns in semi-arid scrub

We studied spatial and temporal effects of local extinction of the plains vizcacha (Lagostomus maximus) on plant communities following widespread, natural extinctions of vizcachas in semi-arid scrub of Argentina. Spatial patterns in vegetation were examined along transects extending outward from active and extinct vizcacha burrow systems. Responses of vegetation to removal of vizcachas were assessed experimentally with exclosures and by documenting vegetation dynamics for 6 years following extinctions. Transect data demonstrated clear spatial patterns in plant cover, particularly an increase in perennial grasses, outward from active vizcacha burrows. These patterns were consistent with predictions based on foraging theory and studies that document grasses as the preferred food of vizcachas. Removal of vizcachas, experimentally and with extinctions, resulted in an immediate increase in perennial and annual forbs indicating that intense herbivory can depress forb cover, as well as grasses. After a 1-year lag following cessation of herbivory, cover of grasses increased. Forbs declined as grasses increased. The long-term effect of extinction of vizcachas was a conversion of colony sites from open patches dominated by forbs to dense bunch grass characteristic of the matrix. Major changes in vegetation occurred within 2–3 years after extinction, resulting in a large pulse of landscape change. However, some species of grasses were uncommon until 5–6 years after the vizcacha extinction. With extinction and colonization, vizcachas generate a dynamic mosaic of patches on the landscape and create temporal, as well as spatial, heterogeneity in semi-arid scrub.     

Status of the alien pathogen Paranosema locustae (Microsporidia) in grasshoppers (Orthoptera: Acridoidea) of the Argentine Pampas

After experimental introductions from North America in 1978–1982, the biocontrol agent Paranosema locustae became established in grasshopper communities of the western Pampas region of Argentina. The use and establishment of P. locustae in Argentina constitute both a case of neoclassical or new association biological control (use of an alien species against native pests) and a case of pathogen pollution (anthropogenic introduction–establishment of an infectious disease in populations of native species). Since P. locustae is a multihost pathogen among grasshoppers, its presence in the western Pampas represents an additional factor disrupting grasshopper communities according to the differential susceptibility of each species and possibly threatening some species. Microscopic examination of 504 grasshopper samples (the mean number of individuals per sample = 185) belonging to 43 species from 93 localities throughout the Pampas revealed an establishment area of approximate 90,000 km² from about 35° North to 38° South and from 61° East to 65° West. Field infections by P. locustae have now been detected in 21 grasshopper species in the western Pampas. Susceptible species with geographic distributions mostly restricted to the establishment area and with numerically small populations, like the melanopline Scotussa daguerrei, are predicted to be the ones facing higher risks of negative impacts.     

AMPHIBIANS FROM THE MIDDLE JURASSIC BALABANSAI SVITA IN THE FERGANA DEPRESSION, KYRGYZSTAN (CENTRAL ASIA)

Abstract: Larval and metamorphosed Ferganobatrachus riabinini (Temnospondyli, Brachyopoidea), metamorphosed Kokartus honorarius (Caudata, Karauridae), an indeterminated karaurid (Karauridae indet.) and, presumably, anurans (?Anura indet.) are represented by isolated cranial and postcranial skeletal elements in the Middle Jurassic (Bathonian–Callovian) Balabansai Svita of the Fergana Depression, Kyrgyzstan. The Balabansai vertebrate assemblage is one of the few faunas in which non‐lissamphibian temnospondyls, stem caudates and anurans occur together. The presence of a supraglenoid foramen and a complex strap‐like glenoid on the scapulocoracoid in Kokartus supports its basal phylogenetic position within the Caudata.     

Pampas fox (Lycalopex gymnocercus) of the Argentine Pampas as intermediate host for Neospora caninum

The Pampas fox (Lycalopex gymnocercus) is the most abundant wild canid from South America. This wild canid inhabits grasslands, open woodlands, and areas highly modified by extensive ranching and agricultural activities. We aimed to evaluate Neospora caninum infection in tissues from the Pampas fox from Argentina. A total of 41 free-living Pampas foxes were sampled in rural areas located in the Humid Pampas region, Argentina. Brain tissue and different muscles were assessed by histologic and molecular methods. No N. caninum cysts were observed in brain and muscle tissue samples analyzed by histology and immunohistochemistry. Molecular N. caninum identification from brain tissue was based on amplification by PCR of Nc-5 gene and ITS1 rRNA fragments and subsequent sequencing. The presence of N. caninum DNA was 74% (23/31) for the Nc-5 gene and was confirmed by a second ITS1 PCR in 55% (17/31) of the brain tested. Thirteen ITS1 consensus sequences were obtained, and all have a 99.58–100% similarity with N. caninum reference sequences. Only 4% (1/23) of muscles samples analyzed were positive for the Nc-5 gene of N. caninum. This study demonstrated a high prevalence of N. caninum DNA in brain from free-ranging Pampas fox of the Pampa Argentine, thus confirming that this wild canid is a wide distributed intermediate host.     

Intertidal burrows of the air-breathing eel goby, <Emphasis Type="Italic">Odontamblyopus lacepedii</Emphasis> (Gobiidae: Amblyopinae)

Odontamblyopus lacepedii inhabits burrows in mudflats and breathes air at the surface opening. Investigations of the intertidal burrows using resin casting demonstrated a highly branched burrow system. The burrows are composed primarily of branching patterns of interconnected tunnels and shafts that communicate into two to seven surface openings. Bulbous chambers (i.e., dilated portions of the burrow) at branching sections of the tunnels or shafts are common features of the burrow. The presence of these chambers accords the fish adequate space to maneuver inside the burrow, and thus constant access to the surface. The combination of all burrow characteristics and previously reported variability in air breathing patterns are ostensibly of selective value for aerial predator avoidance during air breathing in O. lacepedii.     

The radula of the Late Cretaceous scaphitid ammonite Rhaeboceras halli (Meek and Hayden, 1856)

Abstract: Radular teeth occur between the jaws in two specimens of the Late Cretaceous scaphitid ammonite Rhaeboceras halli (Meek and Hayden, 1856) from the Western Interior of the United States. The detailed morphology of the teeth has been revealed by propagation phase contrast X‐ray synchrotron microtomography. Each row of the radula of R. halli consists of a total of seven teeth (a central rachidian, two pairs of lateral and one pair of marginal teeth), as in other known ammonoid radulae, although the central tooth could not be confirmed in the specimens examined. The lateral teeth are multicuspid and robust, and the marginal teeth are long (4.6 mm) and slender. In overall morphology, the heterodont and ctenoglossan radula of R. halli is similar that of Jurassic and Cretaceous ammonites with the same aptychus‐type lower jaw, that is, the Aptychophora. This discovery reveals the range of variation in radular morphology, which could be related to ecological or phylogenetic factors. It also invalidates the hypothesis that the hook‐like structures in R. halli previously described are radular elements.     

Diet of the killifish Rivulus marmoratus collected from land crab burrows,with further ecological notes

Synopsis One-hundred eleven specimens of the cyprinodont fish Rivulus marmoratus were trapped from burrows of the great land crab Cardisoma guanhumi in east central Florida and the entire alimentary tract removed for analysis of food items. Three categories of burrows (inactive, active and sealed) were sampled to examine possible relationships between burrow type and presence of R. marmoratus. Forty percent of the guts examined contained no food items, while the remaining 60% contained items of both terrestrial and aquatic origin. Capture rates among burrow categories did not vary significantly, and most collections consisted of 1 or 2 individuals per burrow. Mean standard length of fish within a burrow declined when more than 3 specimens were captured from a burrow. Supplemental observations on reproductive status and burrow water temperature are noted.     

Utilization of food resources by small and medium‐sized mammals in the Monte Desert biome,Argentina

Theoretical models of species coexistence between desert mammals have generally been based on a combination of food and microhabitat selection by granivorous rodents. Although these models are applicable in various deserts of the world, they cannot explain resource use by mammals in Neotropical deserts. The present study examines diet composition in a mammal assemblage in the Monte desert, Argentina. The results show that two main strategies are used by these mammals: medium‐sized species (hystricognath rodents: Dolichotis patagonum, Lagostomus maximus, Microcavia australis and Galea musteloides; and an exotic lagomorph: Lepus europaeus) are herbivores, whereas small‐sized species (a marsupial: Thylamys pusillus; and sigmodontine rodents: Graomys griseoflavus, Akodon molinae, Calomys musculinus, Eligmodontia typus) are omnivorous. Small mammals also show a tendency towards granivory (C. musculinus), insectivory (A. molinae and T. pusillus) and folivory (G. griseoflavus).     

Fishery and Ontogenetic Driven Changes in the Diet of the Spiny Dogfish, Squalus acanthias, in Patagonian Waters, Argentina

The diet of the spiny dogfish in northern and central Patagonian waters was studied from the by-catch of the bottom trawling fisheries directed to Argentine hake Merluccius hubbsi and Argentine red shrimp Pleoticus muelleri between 1996 and 1998. Food habits were analyzed in relation to sex and maturity of sharks. Also, the relationship between diet and abundance of the main prey was explored. Intraspecific diet comparisons were performed. Differences in diet were found between immature individuals, mature males, and mature females. The Argentine shortfin squid Illex argentinus, the Argentine hake and ctenophores Pleurobrachia pileus were the most important prey for the spiny dogfish. Immature and small individuals were pelagic predators. After sexual maturity, the spiny dogfish shifted its diet. Mature and large individuals tended to reduce the consumption of ctenophores, and increase the consumption of demersal and benthic species. Previous diet studies on the spiny dogfish in 1984–1985 and 1994 indicated that the Argentine hake was the most important prey. In the present study, carried out in 1998, squid was the most important prey, followed by the hake. This diet change was related to the major decrease of hake due to overfishing and the increase of squid abundance between 1994 and 1999.     

Firmground crustacean burrow systems (Glossifungites ichnofacies) in marine shelf deposits,Paleocene Clayton Formation,Alabama, USA

The Paleocene (Danian) Clayton Formation of western Alabama, USA, includes multiple marine shelf parasequences, each comprising a relatively thick marl, capped by a thin limestone, the latter variably reflecting marine flooding episodes. The marls host relatively large firmground burrow systems that penetrate 50–60 cm beneath, and are cast by, superjacent limestones. Excavation of two partially exposed burrow systems – one beneath a highstand parasequence-bounding flooding surface and the other beneath an overlying coplanar sequence boundary/transgressive surface (SB/TS) – reveals complex, primarily horizontal, irregularly branching networks. The former, allied with Thalassinoides paradoxicus, lacks wall bioglyphs, whereas the latter, allied with Spongeliomorpha iberica, is characterized by pervasive, mainly rhombohedral wall bioglyphs that reflect a relatively more firm substrate. Contrasts between these burrow systems are consistent with sequence stratigraphical context and inferred differences in the mechanism and magnitude of depositional hiatuses responsible for firmground development. Both excavated burrow systems likely represent cumulative structures produced by multiple organisms over extended periods of time. The cumulative nature and potential taphonomic biases associated with these and comparable burrow systems in the stratigraphical record preclude confident interpretation of tracemakers and their behaviours. The Clayton burrow systems likely were produced by one or more species of decapod crustacean that engaged in suspension-feeding, surface detritus feeding, gardening or some combination thereof.     

Early and natural embryonic death in Lagostomus maximus: Association with the uterine glands,vasculature, and musculature

The uterus is an organ with great plasticity due to the morphological and physiological changes it experiences during the estrous cycle and pregnancy. In mammals, pregnancy requires diverse sex hormones, growth factors and cytokines, among others, for promoting uterine remodeling to favor implantation, placentation, and embryo/fetus survival and growth. The hystricognathi rodent Lagostomus maximus (plains viscacha) has a high rate of embryonic resorption. The cranial and middle implants are reabsorbed 25–35 days after intercourse while the caudal embryos continue with their development until two precocial offspring are born. So far, no uterine studies of non-pregnant L. maximus females were performed to determine the possible existence of variations in the organ that could be related to the differential survival of the implants. We used ultrasonography, as well as morphological, morphometric, histochemical, lectinhistochemical, and immunohistochemical methods to study differences in the uterine glands (area), vasculature (area), and musculature (thickness) along the uterine horns in non-pregnant females. Along the uterus, all these structures were in more advanced developmental condition in the caudal region as compared to more anterior positions. These regional variations could be decisive in explaining the reason why only caudal implantations come to term. In contrast, no differences in the in the luminal and glandular epithelial cells, nor in the degree of cell proliferation and apoptosis, and hormonal receptor staining were found. These parameters could be related to implantation along the uterine horns, but not to the differential survival of the implants.     

Native herbivore exerts contrasting effects on fire regime and vegetation structure

Although native herbivores can alter fire regimes by consuming herbaceous vegetation that serves as fine fuel and, less commonly, accumulating fuel as nest material and other structures, simultaneous considerations of contrasting effects of herbivores on fire have scarcely been addressed. We proposed that a colonial rodent, vizcacha (Lagostomus maximus), reduces and increases fire intensity at different stages in its population cycle in the semiarid scrub of Argentina. Specifically, we hypothesized that, when colonies are active, vizcachas create natural fire-breaks through intense grazing, generating over time patches of large unburned shrubs in grazed zones. In contrast, when colonies are abandoned, recovery of fine fuels and previous accumulation of coarse wood on colonies during territorial displays increases fire intensity, creating patches of high shrub mortality. To test these hypotheses, we estimated stem age of the dominant shrub (Larrea divaricata) and measured aboveground biomass in zones actively grazed by vizcachas and in ungrazed zones, and compared densities of live and dead shrubs on abandoned colonies and adjacent zones following fire. In active colonies, age and biomass of shrubs were much greater in grazed than ungrazed zones. In abandoned colonies that had been burnt, density of dead, burned shrubs was higher and density of live shrubs was lower than in adjacent zones. These results support our hypotheses and reveal a new interaction between native herbivores and fire, in which herbivores augment fire intensity by gathering fuel. Our findings indicate that, through opposing effects on fire, native herbivores enhance the heterogeneity of vegetation in woody-dominated ecosystems.