A model of visual detection of angular speed for bees

A fly or bee's responses to widefield image motion depend on two basic parameters: temporal frequency and angular speed. Rotational optic flow is monitored using temporal frequency analysers, whereas translational optic flow seems to be monitored in terms of angular speed. Here we present a possible model of an angular speed detector which processes input signals through two parallel channels. The output of the detector is taken as the ratio of the two channels’ outputs. This operation amplifies angular speed sensitivity and depresses temporal frequency tuning. We analyse the behaviour of two versions of this model with different filtering properties in response to a variety of input signals. We then embody the detector in a simulated agent's visual system and explore its behaviour in experiments on speed control and odometry. The latter leads us to suggest a new algorithm for optic flow driven odometry.     

Symmetric faces are a sign of successful cognitive aging

It has been proposed that a common cause underlies individual differences in bodily and cognitive decline in old age. No good marker for this common cause has been identified to date. Here, fluctuating asymmetry (FA), an indicator of developmental stability that relates to intelligence differences in young adults, was measured from facial photographs of 216 surviving members of the Lothian Birth Cohort 1921 at age 83 and related to their intelligence at ages 11, 79 and 83 years. FA at age 83 was unrelated to intelligence at ages 11 and 79 and to cognitive change between 11 and 79 years. It was, however, associated with intelligence and information processing efficiency at age 83 and with cognitive change between 79 and 83 years. Significant results were limited to men, a result predicted by sex differences in life history tradeoffs and life expectancy. Results were stronger when directional asymmetries were corrected in facial FA measures. Thus, FA is a candidate marker for the common cause of differential senescence.     

Age of arboreous Tamarix austromongolica and its growth response to environment in Tongde County of Qinghai,China

Aims The objectives were to identify the age of the arboreous Tamarix austromongolica in the flood plain area of the Qinghai Plateau and clarify the response patterns of T. austromongolica’s growth to the environmental factors. We focused on social issues about whether the T. austromongolica should be protected and how to protect in the reservoir area of a hydropower station. Methods In this study, arboreous T. austromongolica in both reservoir submerged and non-submerged areas were sampled and measured based on the dendrochronology method. The ages were estimated based on the geometrical characteristics of the pith and the identified age of the inner ring. The correlation and response analysis showed the relationship between T. austromongolica’s growth and environmental factors. Important findings We accurately determined the age and historical growth dynamics of the T. austromongolica with large diameter at breast height (DBH). The results showed a special accretion phenomenon in arboreous T. austromongolica, which accelerated the DBH increasing, i.e. no direct relationship existed between the plants’ DBH and ages of the individuals. Radial growth of T. austromongolica, increased rapidly in the 1970s and 1980s and began to stabilize in the late 1980s, and mainly responded to the runoff in July and August of the Yellow River. Increasing runoff would promote the radial growth of T. austromongolica. The growth of the immaturate plant showed significant negative correlation with the wind speed in the growing season. The results will be of theoretical significance to the formation of the special morphology of the T. austromongolica, and will provide scientific practical guidance in designing the protection schemes.     

Climate change and nesting behaviour in vertebrates: a review of the ecological threats and potential for adaptive responses

Nest building is a taxonomically widespread and diverse trait that allows animals to alter local environments to create optimal conditions for offspring development. However, there is growing evidence that climate change is adversely affecting nest‐building in animals directly, for example via sea‐level rises that flood nests, reduced availability of building materials, and suboptimal sex allocation in species exhibiting temperature‐dependent sex determination. Climate change is also affecting nesting species indirectly, via range shifts into suboptimal nesting areas, reduced quality of nest‐building environments, and changes in interactions with nest predators and parasites. The ability of animals to adapt to sustained and rapid environmental change is crucial for the long‐term persistence of many species. Many animals are known to be capable of adjusting nesting behaviour adaptively across environmental gradients and in line with seasonal changes, and this existing plasticity potentially facilitates adaptation to anthropogenic climate change. However, whilst alterations in nesting phenology, site selection and design may facilitate short‐term adaptations, the ability of nest‐building animals to adapt over longer timescales is likely to be influenced by the heritable basis of such behaviour. We urgently need to understand how the behaviour and ecology of nest‐building in animals is affected by climate change, and particularly how altered patterns of nesting behaviour affect individual fitness and population persistence. We begin our review by summarising how predictable variation in environmental conditions influences nest‐building animals, before highlighting the ecological threats facing nest‐building animals experiencing anthropogenic climate change and examining the potential for changes in nest location and/or design to provide adaptive short‐ and long‐term responses to changing environmental conditions. We end by identifying areas that we believe warrant the most urgent attention for further research.     

不同游泳速度条件下瓦氏黄颡幼鱼的有氧和无氧代谢反应

在(25±1)℃的条件下,测定瓦氏黄颡(Pelteobagrus vachelli Richardson)幼鱼体重(4.34±0.13)g的临界游泳速度(Ucrit),然后分别以临界游泳速度的不同百分比(20、40、60、80、100%Ucrit)将实验鱼分为5个速度处理组,另外设置静止对照组和高速力竭对照组。处理组实验鱼在不同游泳速度下分别游泳20min,在此过程中测定并计算运动代谢率(Activity metabolic rate,AMR),随后测定肌肉、血液和肝脏中的乳酸、糖原和葡萄糖含量。结果显示:实验鱼的绝对临界游泳速度为(48.28±1.02)cm/s,相对临界游泳速度为(6.78±0.16)BL/s;随着游泳速度的提高AMR显著增加(Pcrit时肌乳酸和血乳酸含量显著高于80%Ucrit的水平(P0.05);100%Ucrit时肝糖原含量显著低于40%Ucrit的水平(P0.05)。经计算瓦氏黄颡幼鱼到达临界游泳速度时的无氧代谢功率比例仅为11.0%,表明其游泳运动主要以有氧代谢供能;实验鱼的无氧代谢大约在80%Ucrit才开始启动,与其他鱼类比较启动时间较晚,说明其游泳运动对无氧代谢的依赖程度较低。研究提示瓦氏黄颡幼鱼是一种有氧运动能力较强的鱼类,这一能量代谢特征可能与提高其生存适合度有关。       

Invasion dynamics of epidemic with the Allee effect

Investigating the likely success of epidemic invasion is important in the epidemic management and control. In the present study, the invasion of epidemic is initially introduced to a predator-prey system, both species of which are considered to be subject to the Allee effect. Mathematically, the invasion dynamics is described by three nonlinear diffusion-reaction equations and the spatial implicit and explicit models are designed. By means of extensive numerical simulations, the results of spatial implicit model show that the Allee effect has an opposite impact on the invasion criteria and local dynamics when that on the different species. As the intensity of the Allee effect increases, the domain of epidemic invasion reduces and the system dynamics is changed from the stable state to the limit cycle and finally becomes the chaotic state when the susceptible prey with the Allee effect, but the domain expands and the system dynamics is changed from limit cycle to a table point when the predator is subject to the Allee effect. Results from the spatial explicit model show that the strong intensity of the Allee effect can lead to the catastrophic global extinction of all species in the case of that on the susceptible prey. While the predator with the Allee effect, the increased intensity of which makes spatial species reach a stable state. Furthermore, numerical simulations reveal a certain relationship between the invasion speed and spatial patterns.     

Early marine migration of European silver eel Anguilla anguilla in northern Norway

To study the migratory behaviour in wild northern European silver eel Anguilla anguilla during sea entry and early marine migration, 32 individuals were tagged with acoustic transmitters and registered at four automatic listening station arrays from the mouth of the north Norwegian River Alta and throughout the Alta Fjord. The A. anguilla entered the fjord during all parts of the tidal cycle and did not seem to utilize the outgoing tidal currents. They migrated mainly during the night, in both the river mouth and the fjord. On average, they spent 2·7 days travelling from the river mouth to the outermost array, 31 km from the river mouth, corresponding to an average migratory speed of 0·5 km h(-1) . The A. anguilla generally migrated in the central part of the fjord and in the uppermost 10-25% of the water column, but with frequent dives to greater depths. Already 4 km after sea entry, A. anguilla were observed diving deeper than 130 m within 20-30 min periods. Hence, this study demonstrated that A. anguilla may perform an active diving behaviour during the early marine migration. The study took place in a pristine area with a minimum of anthropogenic interventions and by individuals from a population still uninfected by the introduced parasite Anguillicoloides crassus. The results may therefore be used as a baseline for future studies of the A. anguilla early marine migration.