Homing by path integration when a locomotion trajectory crosses itself

Path integration is a process with which navigators derive their current position and orientation by integrating self-motion signals along a locomotion trajectory. It has been suggested that path integration becomes disproportionately erroneous when the trajectory crosses itself. However, there is a possibility that this previous finding was confounded by effects of the length of a traveled path and the amount of turns experienced along the path, two factors that are known to affect path integration performance. The present study was designed to investigate whether the crossover of a locomotion trajectory truly increases errors of path integration. In an experiment, blindfolded human navigators were guided along four paths that varied in their lengths and turns, and attempted to walk directly back to the beginning of the paths. Only one of the four paths contained a crossover. Results showed that errors yielded from the path containing the crossover were not always larger than those observed in other paths, and the errors were attributed solely to the effects of longer path lengths or greater degrees of turns. These results demonstrated that path crossover does not always cause significant disruption in path integration processes. Implications of the present findings for models of path integration are discussed.

Productivity and health effects of anaplasmosis and babesiosis on Bos indicus cattle and their crosses, and the effects of differing intensity of tick control in Australia

Tick fever is an important disease of cattle where Rhipicephalus (Boophilus) microplus acts as a vector for the three causal organisms Babesia bovis, Babesia bigemina and Anaplasma marginale. Bos indicus cattle and their crosses are more resistant to the clinical effects of infection with B. bovis and B. bigemina than are Bos taurus cattle. Resistance is not complete, however, and herds of B. indicus-cross cattle are still at risk of babesiosis in environments where exposure to B. bovis is light in most years but occasionally high. The susceptibility of B. indicus cattle and their crosses to infection with A. marginale is similar to that of B. taurus cattle. In herds of B. indicus cattle and their crosses the infection rate of Babesia spp. and A. marginale is lowered because fewer ticks are likely to attach per day due to reduced numbers of ticks in the field (long-term effect on population, arising from high host resistance) and because a smaller proportion of ticks that do develop to feed on infected cattle will in turn be infected (due to lower parasitaemia). As a consequence, herds of B. indicus cattle are less likely than herds of B. taurus cattle to have high levels of population immunity to babesiosis or anaplasmosis. The effects of acaricide application on the probability of clinical disease due to anaplasmosis and babesiosis are unpredictable and dependent on the prevalence of infection in ticks and in cattle at the time of application. Attempting to manipulate population immunity through the toleration of specific threshold numbers of ticks with the aim of controlling tick fever is not reliable and the justification for acaricide application should be for the control of ticks rather than for tick fever. Vaccination of B. indicus cattle and their crosses is advisable in all areas where ticks exist, although vaccination against B. bigemina is probably not essential in pure B. indicus animals.

Studies on hybridization effects of different geographic populations of Chlamys farreri - II. The medium-term growth and development of Chlamys farreri populations from China and Russia and their reciprocal crosses

Based on the research of juvenile (2, 3, 4 months) growth and survival of three populations of two different geographic areas in Chlamys farreri from Russian and China and their F, hybrids derived from Chinese cultural population (CC) female x Russian population (RW) male, Chinese wild population (CW) female x Russian population (RW) male, Russian population (RW) female x Chinese wild population (CW) the study of the medium-term (6, 8, 10, 12 months) growth and development of Chlamys farreri was carried out. The four determined results indicated that there existed different extent heterosis (3% similar to 52 %) for the growth in three types of F-1 hybrids, and the offspring derived from CC female X Rmale had a stronger heterosis among the crosses at the medium-term; the uptrend among traits are wet weight > shell width > shell length > shell height, Chinese cultural population could be recognized as excellent parent, and seasonal variations influence very much on the daily increment and growth rate of each trait of Chlamys farreri and it is only able to survive and could barely grow in winter (6 similar to 8 months), but grows fast in temperate season (10similar to12 months).

Growth and survival of reciprocal crosses between two bay scallops, Argopecten irradians concentricus Say and A-irradians irradians Lamarck

A complete diallel cross between two bay scallop populations, Argopecten irradians concentricus Say (M) and A. irradians irradians Lamarck (C), was carried out. Growth and survival were compared among hybrids and pure populations. No significant difference in the shell length was found among the four groups on the first day of D-larvae. On day 10, shell lengths of the two reciprocal crosses (CM, MC)(female x male ) were significantly greater than those of the CC (141.97 mu m) and MM (146.20 mu m) groups, with the growth rate of the MC (156.14 mu m) cross greater than that of the CM (155.35 mu m) cross. Also, heterosis for survival was significantly larger than that for growth. Both maternal origin and mating strategy had significant effects on growth and survival throughout the whole larval stage. Heterosis was also observed in later spat and adult stages. On day 170, the mean shell length, shell height and total weight of the CM cross were significantly larger than those of the other crosses (P<0.05). The results from this study indicate that hybridization between A. irradians concentricus and A. irradians irradians may be a promising way for genetic improvement of existing bay scallop brood stocks in China. (c) 2007 Elsevier B.V. All rights reserved.

MAPfastR : quantitative trait loci mapping in outbred line crosses

MAPfastR is a software package developed to analyze QTL data from inbred and outbred line-crosses. The package includes a number of modules for fast and accurate QTL analyses. It has been developed in the R language for fast and comprehensive analyses of large datasets. MAPfastR is freely available at: http://www.computationalgenetics.se/?page_id=7.

Noughts and crosses on a draughts board

Some of the various mathematical ways in which the popular board game noughts and crosses can be played are discussed. Details of different types of variants of noughts and crosses along with instructions on the same are highlighted.

Simple noughts and crosses.

The development of a good winning strategy for Noughts and Crosses is a good exercise to give children in a mathematics class in schools to solve. The main challenge in the game lies is discovering the optimum way of playing or a perfect strategy for forcing a draw.

Heritability estimation in early generations of two-way crosses in soybean

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Suckling behaviour of Nelore, Gir and Caracu calves and their crosses

It is reasonable to assume that the knowledge of suckling behaviour contributes to optimal management and selection of beef cattle. However, there is little information about suckling behaviour of some beef cattle breeds. The aim of this study was to describe the suckling behaviour of two zebu (Bos indicus) and one criollo (Bos taurus) breeds, analysing the potential effects of breed and some environmental factors on suckling frequency and duration. Forty cows, 17 Nelore, 14 Gir (both zebu) and 9 Caracu (criollo) were bred in a diallelic crossing design. The cows and resulting calves were kept on pasture from birth to weaning. Their behaviour was recorded weekly during daylight. Three behavioural traits were considered: number of suckling meals (NSM), duration of each suckling meal (DSM) and total suckling duration (TSD). Allosuckling was not observed. The calves suckled at any time during the daylight and the overall means were: NSM = 2.57 +/- 0.05 meals/12 h (from back transformed data), DSM = 9.25 +/- 0.11 min/suckling meal and TSD = 23.76 +/- 0.47 min/12 h. There was an effect of dam's breed on NSM and DSM; the calf's genetic group within breed of cow influenced NSM and TSD when the dams were from the Nelore breed. The age of calf had significant effects on all traits. Males averaged higher NSM and TSD (2.60 +/- 0.03 meals and 25.05 +/- 1.37 min/12 h, respectively) than females (2.12 +/- 0.04 meals and 21.51 +/- 1.55 min/12 h, respectively). The differences in suckling behaviour seem to be produced by a complex combination of genetic and environmental factors, which result in a particular behavioural relationship within mother-offspring pairs. (c) 2006 Elsevier B.V. All rights reserved.

Candidate SNPs for carcass and meat traits in Nelore animals and in their crosses with Bos taurus

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)