Pregnancy termination by prostaglandin F2α stimulates maternal behavior in the rat

Treatment with PGF_2α resulted in the termination of pregnancy in 16- and 19-day pregnant rats, but not in 10- or 13-day pregnant rats. Rats that aborted displayed a rapid onset of maternal behavior when tested with foster pups. Aborted rats also displayed sexual receptivity and ovulation: these phenomena resemble the sequence of events following hysterectomy on the same days of pregnancy. Both can be related to the events surrounding normal parturition in the rat. The results are interpreted as due to a pregnancy-induced deactivation of the factor in the uterus that prevents estrogen from stimulating maternal behavior in nonpregnant females. In the absence of this factor, the PGF_2α-induced rise in estrogen secretion facilitates maternal behavior and sexual behavior and induces ovulation.     

The North American «Hipparion Datum and implications for the Neogene of the Old World

A large sample of skulls and associated dentitions of Cormohipparion sphenodus (Cope, 1889). new combination, is described from Miocene deposits of Nebraska, Colorado, New Mexico, and California. This species is morphologically more advanced than the most primitive species of the genus, C. goorisiMacFadden & Skinner, 1981, and more primitive than a third and more advanced species of this genus. C. occidentale (Leidy, 1856). In several characters such as configuration of the preobrital fossa, size, hypsodonty, shape of protocone, and complexity of enamel plication, C. sphenodus is morphologically similar, and potentially related to, some Old World Vallesian «Hipparion. In addition, based on radiometric calibration of stratigraphic sequences in Nebraska and California, C. sphenodus spans an interval of time from about 13.6 to 11 Ma. Inasmuch as the Old World «Hipparion Datum is calibrated at about 12 Ma, we conclude that C. sphenodus exhibits the morphological and chronological prerequisites to have been directly ancestral to some of these Old World forms.The hipparion horses apparently were a polyphyletic assemblage of several genera, and their biogeographic and biochronologic history is more complex than classically thought. Several dispersal events involving these horses may have occurred between the New and Old Worlds during the late Miocene.     

Late Albian Dinosaur Tracks from the Cratonic (Eastern) Margin of the Western Interior Seaway,Nebraska, USA

At least 22 tridactyl dinosaur tracks, poorly preserved in various degrees of expression, have recently been found at an exposure in the Dakota Formation (Lower Cretaceous, Albian) in Jefferson County, Nebraska. These tracks generally have broad, blunt digits and a broad posterior margin. The largest of the tracks measures 57 cm in length and 58 cm in width. All of the tracks lie within a stratigraphic horizon of 40 cm or less, but they do not form a single trackway. We interpret the trackmakers to have been ornithopods.

The Jefferson County tracks are in a well-cemented sandstone with oscillation ripples, at a stratigraphic level between two well-established sequence boundaries. Channel forms and lateral accretion units are common in the stratigraphic interval enclosing the tracks, and the site is interpreted as a bar or sand flat in a tidally influenced river.

The Jefferson County tracks are only the second known occurrence of large Mesozoic tetrapod tracks east of the Rocky Mountain Front-High Plains Margin, including the Black Hills of South Dakota, west of the Atlantic Coastal Plain, and north of the Gulf Coastal Plain. Further, this paper is the first documentation of in situdinosaur fossils from the Nebraska-Iowa area.     

Community Structure of Wetland Birds During Spring Migration Through the Rainwater Basin

Abstract: Staging areas and migratory stopovers of wetland birds have the potential to function as geographic bottlenecks; entire populations within a flyway may be affected by the quality and quantity of available wetland habitat at stopover sites. Although approximately 90% of playa wetlands in the Rainwater Basin (RWB) region of south-central Nebraska, USA, have been destroyed, the area still provides essential stopover habitat for >10 million waterfowl each spring. We evaluated community patterns and species associations to assess importance of assembly rules in structuring wetland bird communities during migration and to better facilitate multispecies conservation and management strategies. We surveyed 36–40 playas twice weekly in the RWB and observed approximately 2.6 million individual migratory wetland birds representing 72 species during 3 spring migrations 2002–2004. We evaluated spatial and temporal species co-occurrence patterns of geese, dabbling ducks, diving ducks, and shorebirds using null model analysis. Goose species co-occurrence scores did not differ from random in any year of the study, suggesting that goose species frequently use the same habitats during migration. Co-occurrence patterns among dabbling ducks were not different than expected by chance in any year; however, when we evaluated co-occurrence at a weekly scale, dabbling ducks co-occurred less often than expected during weeks of peak migration (high abundance), indicating that dabbling duck species spatially segregated at high densities. Diving duck co-occurrence patterns did not differ from random in any year, suggesting that diving duck species used the same habitats during migration. Shorebird species co-occurred less often than expected in 2002 and 2004, and during weeks of high shorebird abundance, indicating that shorebird communities were distinctly structured during those times. Most association values among lesser snow geese (Chen caerulescens) and dabbling duck species were positive, indicating dabbling ducks did not avoid wetlands with snow geese, a concern for waterfowl managers. However, we frequently observed snow geese and dabbling ducks using different microhabitats within a wetland, which indicate species associations and co-occurrence patterns may have occurred at a finer spatial scale than we measured. This approach of co-occurrence analysis will allow wildlife managers charged with multispecies management at migration stopover sites to make informed conservation and management decisions based on community structure rather than historic single-species approaches.     

Effect of great-horned owl trapping on chick survival in piping plovers

We studied the effect of great-horned owl (Bubo virginianus) removal on piping plover (Charadrius melodus) hatchling survival on Missouri River sandbars (2008–2009). Owl removal increased daily survival of piping plover chicks in 2008 (β = 2.03, 95% CI: 0.04–4.02), but this effect decreased with increasing age of the chick (β = −0.42, 95% CI: −0.81 to −0.03). Results for 2009 were similar in direction but not significant. Survival was higher in 2008 than in 2009, regardless of owl capture, indicating that even if owl capture consistently were effective at increasing survival, overall survival resulting from trapping may vary annually. Owl trapping was a successful means to raise chick survival on the Missouri River in ≥1 year and could be used at other sites experiencing depressed chick survival due to avian predators. © 2011 The Wildlife Society.     

Spatial ecology of female bighorn sheep in a prairie landscape in Nebraska

Understanding the spatial ecology of small populations at the periphery of their range is important for identifying factors limiting population growth and developing sound management strategies. Bighorn sheep were reintroduced to Nebraska in 1981 and persist in a small population at the easternmost extent of the distribution of the species, where 1 of the 2 subpopulations is declining. Bighorn sheep space use and movement has been studied extensively in mountain and desert populations, but information is sparse from prairie populations in the Northern Great Plains. We investigated the spatial ecology of female bighorn sheep in Nebraska, USA, with global positioning system (GPS) telemetry. We tested the hypothesis that space use and movements would vary across seasons, years, and individuals but predicted that migration would involve relatively short distances in this translocated population (relative to native populations) occupying a fragmented landscape. Overall, females used smaller seasonal home ranges (3.3–7.8 km²) than most of those reported previously for the species and exhibited a high degree of variability in space use and movements across seasons, subpopulations, and individuals. Most females (92–100%) exhibited fidelity to their home ranges across seasons and years. Six females migrated between spatially distinct core lambing and winter ranges, although the distances (range = 7.9–8.7 km) and mean elevations (range = 31–41 m) between these core seasonal ranges were less than those reported for most native, migratory bighorn sheep populations. After accounting for variation in season, subpopulation, and years, home range size was positively associated with road density in both subpopulations (P < 0.001), suggesting that females incur greater energetic costs associated with greater space use in areas of higher fragmentation. Our results establish the basic spatial ecology of female bighorn sheep in Nebraska where their behavior appears to reflect the isolated nature of suitable habitat in this fragmented prairie landscape.     

Regional and local variation in tallgrass prairie remnants of Iowa and eastern Nebraska

Tallgrass prairie vegetation, persisting as numerous small relics scattered across central North America, exhibits a complex pattern of community structure and composition. We sampled vegetation from 11 prairie preserves in Iowa and eastern Nebraska spanning three physiographic regions and a wide variety of upland habitats. Numerical classification and partitioned ordination revealed a complex pattern of both local and geographical variation in the vegetation. The primary coenocline is a complex topographic-moisture gradient. Secondary factors influencing the vegetation include subsoil permeability, chorological differences, and local peculiarities of stand history and dynamics. Local patterns of interaction between the primary and secondary environmental factors vary among Quaternary landscapes resulting in regional vegetation complexity.Nomenclature follows Gleason (1952) except for the grasses which follow Pohl (1966).Supported by the National Science Foundation (No. GU 2795 and GU 3373), The Nature Conservancy, and the Iowa State Advisory Board for Preserves. We thank T. L. Roberts, S. Taylor, and S. Lundquist for help with field work, and R. K. Peet, A. T. Harrison, and J. K. White for advice, comments, and criticisms.     

Acetaldehyde adducts with proteins: Binding of [14C]acetaldehyde to serum albumin

Acetaldehyde, the immediate oxidation product of ethanol metabolism, was assessed for its ability to bind covalently to a purified protein in solution. Bovine serum albumin (BSA)² was used as the model protein incubated in the presence of 0.2 mm [¹⁴C]acetaldehyde at pH 7.4 and at 37 °C. Acetaldehyde formed both stable and unstable adducts with serum albumin. Unstable adducts were identified following stabilization with the reducing agent sodium borohydride. We examined both types of binding using trichloroacetic acid precipitation, gel filtration, and dialysis as means to separate bound from free acetaldehyde. All three methods of analysis gave comparable results except that the number of stable acetaldehyde adducts with albumin were significantly lower following separation by dialysis. The effects of l-cysteine, l-lysine, and reduced glutathione were assessed for their abilities as competitive reagents to decrease binding of [¹⁴C]acetaldehyde to BSA. Addition of cysteine caused a rather dramatic concentration-dependent reduction in [¹⁴C]acetaldehyde binding to BSA when compared to that caused by lysine which displayed a relatively mild effect on covalent binding. The presence of glutathione caused a concentration-dependent decrease in protein-bound radioactivity that was stronger than that by lysine but not as effective as cysteine. The ability of each reagent to reverse the formation of preformed acetaldehyde adducts with BSA was also examined. Only l-cysteine effectively decreased the number of unstable acetaldehyde adducts with BSA while stable binding of acetaldehyde remained essentially unaffected by any of the three reagents. These results indicate that acetaldehyde can covalently bind to protein and form unstable as well as stable adducts.