Effect of fasting on resting metabolic rate and postprandial metabolic response in Silurus meridionalis

Resting metabolic rate in southern catfish of 2 and 5 day fasting groups were significantly higher than that of the 15 day fasting group ( P  < 0·05). After feeding, peak metabolic rate of specific dynamic action (SDA) of the 15 day fasting group was significantly lower than that of the 2 and 5 day fasting groups ( P  < 0·05). The duration of the SDA of the 15 day fasting group was significantly longer than that of the 2 day fasting group ( P  < 0·05) and the SDA coefficient of the 15 day fasting group was significantly lower than that of the 2 day fasting group ( P  < 0·05).     

Octopamine influences honey bee foraging preference

Colony condition and differences in individual preferences influence forage type collected by bees. Physiological bases for the changing preferences of individual foragers are just beginning to be examined. Recently, for honey bees octopamine is shown to influence age at onset of foraging and probability of dance for rewards. However, octopamine has not been causally linked with foraging preference in the field. We tested the hypothesis that changes in octopamine may alter forage type (preference hypothesis). We treated identified foragers orally with octopamine or its immediate precursor, tyramine, or sucrose syrup (control). Octopamine-treated foragers switched type of material collected; control bees did not. Tyramine group results were not different from the control group. In addition, sugar concentrations of nectar collected by foragers after octopamine treatment were lower than before treatment, indicating change in preference. In contrast, before and after nectar concentrations for bees in the control group were similar. These results, taken together, support the preference hypothesis.     

Dispersal, Infectivity and Sex Ratio of Early- or Late-Emerging Infective Juveniles of the Entomopathogenic Nematode Steinernema carpocapsae

Differences in activity between infective juveniles (IJ) of the entomopathogenic nematode Steinernema carpocapsae that emerged directly from cadavers onto either a sand or agar substrate compared with those emerging from a cadaver into water and then being placed on the same substrate are known to occur. Differences between S. carpocapsae IJ that emerged directly from a cadaver vs. those that emerged from a cadaver and held in water were further elucidated. Dispersed and non-dispersed IJ from a cadaver were compared with those held in water between two time periods designated as early- (first two days) or late-emerging IJ (seventh day). A significantly greater proportion of early-emerging IJ from the cadaver treatment dispersed, compared with late-emerging IJ from a cadaver or either group of emerging IJ held in aqueous suspension. Moreover, IJ from cadavers were more infectious than those from the aqueous suspensions, and IJ that dispersed were less infectious than those that did not disperse. IJ that emerged early were mostly males, whereas those that emerged late were mostly females. For the non-dispersed IJ, most that emerged early were males, and those that emerged later were females, but among dispersing IJ, there was no difference in sex ratio between early- and late-emerging nematodes.     

Evolutionary consequences of a search image

Many predators are able to become better at spotting cryptic prey by recognising specific clues, but by concentrating on one prey type they will become worse at spotting other prey types. This phenomenon is known as the formation of a search image for a certain prey by a predator and is related to apostatic selection. Here, we study the evolution of a search image in the predator by formulating and analysing a mathematical model. The predator forages for two prey types and is able to form an independent search image for both prey. The results show that the evolutionary dynamics can be divided into two parts: a fast and a slow part. At first selection pressure will be strong towards a stable ratio of prey, which is the same as the ratio found for the unbeatable prey choice for predators with a Holling type II functional response. Following this, the slow dynamics will keep this ratio constant independent of the trait values, but the predator will slowly evolve towards a stronger search image and ultimately become a specialist predator or slowly evolve towards generalist with a weak search image. In conclusion, the formation of a search image causes the predator to control the prey densities such that the ratio of available prey is kept constant by the predator.     

Individual differences in foraging site fidelity are not related to time-activity budgets in Herring Gulls

Many populations consist of individuals that differ consistently in their foraging behaviour through resource or foraging site selection. Foraging site fidelity has been reported in several seabird species as a common phenomenon. It is considered especially beneficial in spatially and/or temporally predictable environments in which fidelity is thought to increase energy intake, thereby affecting time-energy budgets. However, the consequences for activity and energy budget have not been adequately tested. In this paper, we studied the consequences of fine-scale foraging site fidelity in adult Herring Gulls Larus argentatus in a highly predictable foraging environment with distinct foraging patches. We measured their time-activity budgets using GPS tracking and tri-axial acceleration measurements, which also made it possible to estimate energy expenditure. Individual variation in foraging site fidelity was high, some individuals spending most of their time on a single foraging patch and others spending the same amount of time in up to 21 patches. While time and activity budgets differed between individuals, we found no clear relationship with foraging site fidelity. We did find a relationship between the size of the birds and the level of site fidelity; faithful birds tend to have a larger body size. Although differences in foraging time and habitat use between individuals could play a role in the results of the current study, short-term consequences of variation in foraging site fidelity within a population remain elusive, even when focusing on individuals with a similar foraging specialization (Blue Mussels Mytilus edulis). Studying individuals over multiple years and under varying environmental conditions may provide better insight into the consequences and plasticity of foraging site fidelity.     

Quality versus quantity: Foraging decisions in the honeybee (Apis mellifera scutellata) feeding on wildflower nectar and fruit juice

Foraging animals must often decide among resources which vary in quality and quantity. Nectar is a resource that exists along a continuum of quality in terms of sugar concentration and is the primary energy source for bees. Alternative sugar sources exist, including fruit juice, which generally has lower energetic value than nectar. We observed many honeybees (Apis mellifera scutellata) foraging on juice from fallen guava (Psidium guajava) fruit near others foraging on nectar. To investigate whether fruit and nectar offered contrasting benefits of quality and quantity, we compared honeybee foraging performance on P. guajava fruit versus two wildflowers growing within 50 m, Richardia brasiliensis and Tridax procumbens. Bees gained weight significantly faster on fruit, 2.72 mg/min, than on either flower (0.17 and 0.12 mg/min, respectively). However, the crop sugar concentration of fruit foragers was significantly lower than for either flower (12.4% vs. 37.0% and 22.7%, respectively). Fruit foragers also spent the most time handling and the least time flying, suggesting that fruit juice was energetically inexpensive to collect. We interpret honeybee foraging decisions in the context of existing foraging models and consider how nest‐patch distance may be a key factor for central place foragers choosing between resources of contrasting quality and quantity. We also discuss how dilute solutions, such as fruit juice, can help maintain colony sugar–water balance. These results show the benefits of feeding on resources with contrasting quality and quantity and that even low‐quality resources have value.     

The Old Ladies of the Seed Harvester ant Pogonomyrmex Rugosus: Foraging Performed by Two Groups of Workers

We examined temporal polyethism in Pogonomyrmex rugosus, predicting a pattern of decreasing age from foragers to nest maintenance workers to individuals that were recruited to harvest a temporary food source. Nest maintenance workers were younger than foragers, as indicated by their heavier mass and lower mandibular wear. In contrast, recruited foragers were similar in mass to foragers but they displayed higher mandibular wear, suggesting that they were at least as old as foragers. Longevity estimates for marked individuals of these two latter task groups showed mixed results. Higher mandibular wear of recruited foragers suggests that they did not follow the normal sequence for temporal polyethism, but rather that they functioned as seed-millers, which should more quickly abrade their dentition. This would be the first demonstration of specialist milling individuals in a monomorphic seed-harvester ant.     

基于RFID技术的西方蜜蜂采集行为研究

蜜蜂能够灵活调整出巢觅食行为,从而有效保证蜂群的正常发育与繁衍.为了探索采集蜂的行为特性,本文利用由江西农业大学蜜蜂研究所与广州市远望谷信息技术股份有限公司合作研发的蜜蜂无线射频识别(RFID)系统,对西方蜜蜂进行为期38 d的全天候监控记录.结果表明: 两蜂群中分别有63.4%和64.5%的采集蜂存在轮休现象,轮休时间比例为22.5%~26.4%;轮休与非轮休蜜蜂的采集工作总量差异不显著,但轮休蜜蜂寿命显著高于非轮休蜜蜂;提前发育的采集蜂的寿命显著低于正常采集蜂.本研究丰富了蜜蜂社会行为学内容,为进一步探索蜜蜂采集行为的形成机制奠定了基础.