NEW MURID RODENTS FROM THE LATE CENOZOIC OF YUSHE BASIN, SHANXI

<正> As scientific collaborators of the Chinese-American joint project "Neogene Rocks and Faunas, Yushe Basin, Shanxi, PRC", the present authors, with William R. Downs, Northern Arizona University, sampled the Yushe microfauna in the fall of 1987 and 1988. The fossil temains were retrieved by surface collection and by wet-sieving bulk quantities of sediment.     

Thymus-independent immunogenicity in vitro of the divalent antigen DNP-polyethylene oxide

Chemically simple and physically well-defined dinitrophenyl derivatives of polyethylene oxide (DNP-PEO) can be prepared in a wide range of forms and sizes. These materials were used to investigate the molecular basis of immunogenicity and the binding of the antigens to membrane-bound receptors. Both di- and multivalent DNP-PEO activate normal murine B lymphocytes to yield primary anti-DNP antibody response in vitro. The immunogenicity is dependent on the carrier chain length but independent of T cells. Responses comparable to those induced by DNP-conjugated polymerized flagellin are induced by divalent linear materials of medium molecular weights of about 60,000. A highly multivalent material is moderately immunogenic, but at much lower antigen doses than divalent materials. The carrier PEO does not affect B-cell responses to DNP-PEO or T-cell response to succinyl concanavalin A. Moreover, it shows no polyclonal mitogenicity at concentrations as high as 1 mg/ml. Studies of antigen binding to cell surface DNP receptors show that the strongly immunogenic materials of medium molecular weights have an appreciable tendency to bind bivalently and thus potentially to crosslink receptors. The binding of smaller, less immunogenic antigen appears predominantly monovalent.     

Thermodynamics of antibody-antigen reactions. 2. The binding of bivalent synthetic random coil antigens to antibodies having different antigen precipitating properties

The objects of this study were the equine IgG and IgG(T) classes of antibodies with immunologic specificity for the dinitrophenyl group and bivalent antigens consisting of linear poly(ethylene glycol) polymers which terminated at both ends in dinitrophenyl groups. Complex formation between antibodies of both classes and one of several sharp fractions of antigen having number average molecular weights in the range 25 000 to 75 000 were studied by measuring the light scattered from solutions containing equimolar amounts (approximately 5 x 10(-6) mol/L) of one of the antibodies and one size fraction of antigen, and variable amounts of monovalent hapten. The data were analyzed in the context of a model that accounted for the formation of linear and cyclic complexes of all extents of aggregation. Two parameters in addition to the intrinsic antibody-dinitrophenyl group association constant were found to be necessary in the assumed equilibrium model to account for the behavior of the system. One of these accounted for the looses in configuration entropy that resulted when a random-coil polymer became bound at one end to a space-occupying antibody. The other was a ring closure factor for the formation of cyclic complexes. Ring closure factors for the formation of larger cyclic complexes (present in only small amounts under the conditions studied) were related to the ring closure factor for the formation of the smallest, which was found to increase as antigen size decreased, and for each antigen size to be consistently higher for IgG(T) antibody than for IgG antibody. Comparison of the theoretically estimated values of the two parameters within their measured values indicated that the average conformation of IgG antibodies in solution is open ("T" shaped) but the average inter-Fab are angle in IgG(T) antibodies is approximately 60 degrees or less.     

Photobleaching recovery studies of membrane events accompanying lectin stimulation of rabbit lymphocytes.

Fluorescence photobleaching recovery methods reveal marked changes in lateral mobilities of rabbit lymphocyte membrane components during the course of stimulation with succinyl concanavalin A (S Con A). The diffusion constant of S Con A receptors on T lymphocytes falls from 1.6×10^?10 cm²/sec to 6.5×10^?11 cm²/sec within 4 hr after stimulation, remains constant for 14 hr, and returns to its former value. The mobility of B cell receptors similarly falls from 1.4×10^?10 cm²/sec to 5.5×10^?11 cm²/sec but regains its unstimulated value much more slowly. In contrast, a fluorescent phospholipid analog shows constant mobilities of 1.9×10^?8 cm²/sec and 1.5×10^?8 cm²/sec in T and B cells, respectively, throughout the experiment.     

The evolution of virus-induced apoptosis.

Viruses from several different families are able to exploit their host''s cell death programmes so as to maximize viral fitness. Consideration of the evolution of such strategies has lead to the suggestion that the virus should inhibit apoptosis, in order to prolong the life of the cell and thereby maximize the number of progeny virions. The host, on the other hand, should stimulate apoptosis thereby inhibiting viral growth and blocking viral spread. For example, the function of the latent membrane protein I (LMPI) of the Epstein-Barr virus and the bcl-2 homologue gene A179L of African swine fever virus is to inhibit apoptosis. However, in other cases it is the virus that stimulates cell death or the host that benefits from inhibiting apoptosis, such as in fatal alphavirus encephalitis. This has been explained by assuming that virus-induced apoptosis in non-regenerating cells would be detrimental to the host. We present a mathematical framework for understanding virus-induced apoptosis which accounts for these two opposite solutions to virus infection with respect to the mode of virus replication and the life cycle of the target cell.     

Removal of adult males from the rearing environment increases preference for same-sex partners in the zebra finch

The developmental processes producing preferences for opposite-sex mating partners are not well understood. Zebra finches, Taeniopygia guttata, are colonial and socially monogamous with biparental care. To determine whether the early social environment contributes to sexual partner preference, we removed adult males from breeding colonies when the oldest chicks were less than 1 week old (male-removal rearing) or left them in the breeding cage (control rearing). At independence, male-removal and control offspring were moved to unisex cages. As adults they were given two-choice tests with male versus female stimuli followed by group aviary tests. Male-removal subjects, unlike controls, did not prefer opposite-sex stimuli in the two-choice tests. Male-removal subjects were less likely than controls to successfully pair with opposite-sex birds in the group aviary tests; 38% of them paired with a same-sex bird. Thus early social experience may contribute to a critical component of mate choice, choosing the opposite sex, in this pair-bonding species. Copyright 2000 The Association for the Study of Animal Behaviour.     

Rethinking motor learning and savings in adaptation paradigms: model-free memory for successful actions combines with internal models

Although motor learning is likely to involve multiple processes, phenomena observed in error-based motor learning paradigms tend to be conceptualized in terms of only a single process: adaptation, which occurs through updating an internal model. Here we argue that fundamental phenomena like movement direction biases, savings (faster relearning), and interference do not relate to adaptation but instead are attributable to two additional learning processes that can be characterized as model-free: use-dependent plasticity and operant reinforcement. Although usually "hidden" behind adaptation, we demonstrate, with modified visuomotor rotation paradigms, that these distinct model-based and model-free processes combine to learn an error-based motor task. (1) Adaptation of an internal model channels movements toward successful error reduction in visual space. (2) Repetition of the newly adapted movement induces directional biases toward the?repeated movement. (3) Operant reinforcement through association of the adapted movement with successful error reduction is responsible for savings.     

Ecological distribution and niche segregation of sibling species: the case of bean beetles, Acanthoscelides obtectus Say and A. obvelatus Bridwell

Abstract.  1. Molecular techniques have greatly added to the number of known sympatric cryptic species in insects. Ecological differences between these newly distinguished species are little explored, but niches often appear to overlap strongly. These cases are good models for exploring new ideas about species coexistence and community structure.
2.  Acanthoscelides obtectus and A. obvelatus are two sister species of bean bruchids, which have been confused until the last decade. One important ecological difference between them has emerged, however: A. obtectus is multivoltine and now distributed worldwide, whereas A. obvelatus is univoltine and restricted to Mesoamerica. Where their ranges overlap, the two species share the same host plants and larvae can sometimes complete development in the same seed.
3. The analysis of 27 622 Mexican individuals of the two species in 2001-2002 and 2002-2003 indicates that their niches overlap, but are differentiated with respect to altitude and the kind of beans (wild vs. domesticated). The principal patterns in their relative abundance in different habitats, and at different seasons, were constant from one year to the next.
4. As sympatry of these species seems to be of recent origin, the observed niche differentiation may not have evolved in response to competition, but could instead be the consequence of physiological differences, evolved independently in each species in allopatry, that pre-adapted them for different altitudes and kinds of resources.
5. The combination of biological and historical factors thus appears to allow these two sibling species to coexist in sympatry, despite their broadly overlapping ecological niches.     

Social structure, robustness, and policing cost in a cognitively sophisticated species

Conflict management is one of the primary requirements for social complexity. Of the many forms of conflict management, one of the rarest and most interesting is third-party policing, or intervening impartially to control conflict. Third-party policing should be hard to evolve because policers personally pay a cost for intervening, while the benefits are diffused over the whole group. In this study we investigate the incidence and costs of policing in a primate society. We report quantitative evidence of non-kin policing in the nonhuman primate, the pigtailed macaque. We find that policing is effective at reducing the intensity of or terminating conflict when performed by the most powerful individuals. We define a measure, social power consensus, that predicts effective low-cost interventions by powerful individuals and ineffective, relatively costly interventions by low-power individuals. Finally, we develop a simple probabilistic model to explore whether the degree to which policing can effectively reduce the societal cost of conflict is dependent on variance in the distribution of power. Our data and simple model suggest that third-party policing effectiveness and cost are dependent on power structure and might emerge only in societies with high variance in power.