Proximity to an edge affects search strategy in adults and children

When searching for a hidden goal, search patterns are often defined according to one of two main search strategies: an absolute strategy, which usually involves searching at a fixed learned distance and direction from a particular reference point, or a relational strategy, which involves searching at a point that maintains the relationship between two or more other points. Past research has shown that humans tend to prefer a relational strategy whereas most non-humans prefer an absolute strategy. However, recent research (Hartley et al., 2004) used a simulated 3D environment to demonstrate that proximity to a boundary affects strategy. In particular, when searching close to an edge, human participants were more likely to use an absolute strategy whereas when searching at a central location, participants were more likely to use a relational strategy. The current studies extend the findings of Hartley et al. Experiment 1 showed that adult humans use different strategies based on the goal's proximity to the edge of a search space, and that strategies differed between males and females. Experiment 2 suggested that children also use different strategies based on the goal's proximity to a boundary, and that some goal locations may be harder to learn than others. Taken together, our results show that search strategies are flexible and context-specific.     

Neural correlates of individual differences in circadian behaviour

Daily rhythms in mammals are controlled by the circadian system, which is a collection of biological clocks regulated by a central pacemaker within the suprachiasmatic nucleus (SCN) of the anterior hypothalamus. Changes in SCN function have pronounced consequences for behaviour and physiology; however, few studies have examined whether individual differences in circadian behaviour reflect changes in SCN function. Here, PERIOD2::LUCIFERASE mice were exposed to a behavioural assay to characterize individual differences in baseline entrainment, rate of re-entrainment and free-running rhythms. SCN slices were then collected for ex vivo bioluminescence imaging to gain insight into how the properties of the SCN clock influence individual differences in behavioural rhythms. First, individual differences in the timing of locomotor activity rhythms were positively correlated with the timing of SCN rhythms. Second, slower adjustment during simulated jetlag was associated with a larger degree of phase heterogeneity among SCN neurons. Collectively, these findings highlight the role of the SCN network in determining individual differences in circadian behaviour. Furthermore, these results reveal novel ways that the network organization of the SCN influences plasticity at the behavioural level, and lend insight into potential interventions designed to modulate the rate of resynchronization during transmeridian travel and shift work.     

Effects of acculturation and age on the exercise capacities of Solomon Islanders

Submaximal exercise tests were carried out on 197 females and 290 males from five populations in the Solomon Islands to determine how acculturation affects the fitness of different age and sex groups. Males and females in the least acculturated group show the highest fitness levels, reflecting strenuous work patterns. Subjects from the most acculturated groups exhibit the lowest levels of fitness, a consequence of their more sedentary life-styles. Unexpectedly, older females in these groups show exercise capacities that are equal to those of younger women. This may be a consequence of generational differences in the practice of traditional activities, such as those associated with gardening. Groups ranked intermediate in acculturation show variable patterns. For some age and sex groups, modernization has reinforced and even intensified strenuous activity patterns, resulting in high levels of fitness. For others, modernization has promoted inactivity and/or altered dietary patterns, resulting in increased body fat and low levels of fitness.     

Ovine mitochondrial DNA: restriction enzyme analysis, mapping and sequencing data

Restriction endonuclease fragment patterns of mitochondrial DNA (mtDNA) in sheep were analysed with 11 enzymes. Four breeds (Merinolandschaf, Rhoenschaf, Schwarzkoepfiges Fleischschaf and Skudde) of domestic sheep and European Mouflon were examined. A restriction map with 28 cleavage sites of seven enzymes was established. KpnI and PstI do not cut ovine mtDNA. Two EcoRI fragments of Merinolandschaf, Rhoenschaf and Mouflon each were cloned and partially sequenced. Intraspecific nucleotide sequence differences within 1.101 kb ranged from 0.09 to 0.27%. Hybridization analysis with a fragment of porcine mtDNA along with sequencing data from cloned fragments was used for orientation of the restriction map along the bovine sequence. Ovine mtDNA sequences encompassing parts of the Cyt.b-, ND5-, CoIII- and ATPase6 genes were compared with the corresponding sequences of the bovine mtDNA.     

Diploids v . triploids of Rutilus alburnoides: spatial segregation and morphological differences

Rutilus alburnoides complex is a common and widely distributed Iberian cyprinid, whose natural populations include mainly diploid and triploid forms. The Guadiana populations of R. alburnoides were studied to determine whether habitat segregation and morphological differences exist between these forms. The ploidy level of each specimen was determined by measuring erythrocyte DNA content using flow cytometry. Evidence of spatial segregation between diploid males and the two female forms was found. Diploid males were best represented in the River Degebe, which was shallow, with higher temperatures (especially during the spring and summer), and silt and sandy substrate. Diploid females were found in deeper water, on steeper gradients and coarse substrata, while triploid females preferred higher current velocity and a high proportion of instream cover, especially during the spring. The ecological differences may reduce competitive interactions, and should promote a stable coexistence of the different forms. Morphological distinction between fish of different ploidy levels was not established, but differences were found between the males and females. Discriminant analysis allowed, with a 10% error, the separation of both sexes through six morphological characteristics that could be recorded in the field.     

Weight-Loss Strategies of Young Adults: Exercise Versus Dieting

This cross-sectional survey study examined weight control practices of 2,092 male and 1,748 female freshman students aged 18 years. For women, the desire for weight loss was observed at all levels of body weight. Most women (79%) wished to weigh less than their current weight, and 23% were following a restricted-calorie diet. In contrast, more men wished to gain (46%) rather than lose weight (32%), and only 3% were dieting at the time of the study. A comparison of weight control practices of men and women who wished to lose weight showed that women restricted calories far more frequently than did men. In contrast, although men were more likely to use exercise for weight control than were women, the differences between the sexes were small. A combined analysis of dieting and exercise behaviors showed that while men relied almost exclusively on intensive exercise as opposed to dieting, women employed exercise as well as dieting for the purpose of weight control.     

Sex and the Developing Brain: Suppression of Neuronal Estrogen Sensitivity by Developmental Androgen Exposure

The developmental effects of androgen play a central role in sexual differentiation of the mammalian central nervous system. The cellular mechanisms responsible for mediating these effects remain incompletely understood. A considerable amount of evidence has accumulated indicating that one of the earliest detectable events in the mechanism of sexual differentiation is a selective and permanent reduction in estrogen receptor concentrations in specific regions of the brain. Using quantitative autoradiographic methods, it has been possible to precisely map the regional distribution of estrogen receptors in the brains of male and female rats, as well as to study the development of sexual dimorphisms in receptor distribution. Despite previous data suggesting that the left and right sides of the brain may be differentially responsive to early androgen exposure, there is no significant right-left asymmetry in estrogen receptor distribution, in either sex. Significant sex differences in receptor density are, however, observed in several regions of the preoptic area, the bed nucleus of the stria terminalis and the ventromedial nucleus of the hypothalamus, particularly in its most rostral and caudal aspects. In the periventricular preoptic area of the female, highest estrogen receptor density occurs in the anteroventral periventricular region: binding in this region is reduced by approximately 50% in the male, as compared to the female. These data are consistent with the hypothesis that androgen-induced defeminization of feminine behavioral and neuroendocrine responses to estrogen may involve selective reductions in the estrogen sensitivity of critical components of the neural circuitry regulating these responses, mediated in part through a reduction in estrogen receptor biosynthesis.     

Sex differences in residency patterns of Risso's dolphins (Grampus griseus) in the Azores: Causes and management implications

Knowledge of the residency patterns of marine mammals is an important element for management and conservation strategies. Here we investigate a population of Grampus griseus off Pico Island, Azores. Our data set covers the period 2004–2007, based on at‐sea observations of 1,250 individually identified animals, 303 of known or assumed sex. Using photo identification and GPS locations we calculated mean monthly sighting rates and lagged identification rates to analyze temporal patterns, and estimated kernel density to study the home range. Our results show site fidelity and relatively restricted home ranges, which corroborate the existence of a resident population on the study site. We further document sex differences, including a higher number of males present in the area at any given time but females staying for longer consecutive periods, and male home ranges with significantly less overlap than those of females. These observations are consistent with a mating system based on multimale pods defending areas where females periodically return. We hypothesize that squid distribution is a major factor in structuring these patterns. These findings reinforce the need for a precautionary management approach that would include limiting pressure from commercial activities.