Odourant dominance in olfactory mixture processing: what makes a strong odourant?

The question of how animals process stimulus mixtures remains controversial as opposing views propose that mixtures are processed analytically, as the sum of their elements, or holistically, as unique entities different from their elements. Overshadowing is a widespread phenomenon that can help decide between these alternatives. In overshadowing, an individual trained with a binary mixture learns one element better at the expense of the other. Although element salience (learning success) has been suggested as a main explanation for overshadowing, the mechanisms underlying this phenomenon remain unclear. We studied olfactory overshadowing in honeybees to uncover the mechanisms underlying olfactory-mixture processing. We provide, to our knowledge, the most comprehensive dataset on overshadowing to date based on 90 experimental groups involving more than 2700 bees trained either with six odourants or with their resulting 15 binary mixtures. We found that bees process olfactory mixtures analytically and that salience alone cannot predict overshadowing. After normalizing learning success, we found that an unexpected feature, the generalization profile of an odourant, was determinant for overshadowing. Odourants that induced less generalization enhanced their distinctiveness and became dominant in the mixture. Our study thus uncovers features that determine odourant dominance within olfactory mixtures and allows the referring of this phenomenon to differences in neural activity both at the receptor and the central level in the insect nervous system.     

Acute injections of brain‐derived neurotrophic factor in a vocal premotor nucleus reversibly disrupt adult birdsong stability and trigger syllable deletion

Behavioral variability serves an essential role in motor learning by enabling sensory feedback to select those motor patterns that minimize error. Birds use auditory feedback to learn how to sing, and their songs lose variability and become highly stereotyped, or crystallized, at the end of a sensitive period for sensorimotor learning. The molecular cues that regulate song variability are not well understood. In other systems, neurotrophins, and brain‐derived neurotrophic factor (BDNF) in particular, can mediate various forms of neural plasticity, including sensitive period neural circuit plasticity and activity‐dependent synapse formation, and may also influence learning and memory. Here, we have tested the hypothesis that neurotrophin expression in the robust nucleus of the arcopallium (RA), the telencephalic output controlling song, regulates song variability. BDNF and its receptor trkB are expressed in RA, and BDNF expression in RA appears to be highest in juveniles, when song is most variable and plastic, and synapse density highest. Thus, song variability and synaptic connectivity could be enhanced by augmented expression of BDNF in RA. In support of this idea, we found that BDNF injections into the adult RA induced the re‐expression of juvenile‐like phenotypes, including song variability and an increased synaptic density in RA. Furthermore, BDNF treatment also induced vocal plasticity, characterized by syllable deletions and persistent changes to the song patterns. These results suggest that endogenous BDNF could be a molecular regulator of the song variability essential to vocal plasticity and, ultimately, to song learning. © 2004 Wiley Periodicals, Inc. J Neurobiol, 2005     

Proteome plasticity in response to persistent environmental change

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Innovative problem solving by wild spotted hyenas

Innovative animals are those able to solve novel problems or invent novel solutions to existing problems. Despite the important ecological and evolutionary consequences of innovation, we still know very little about the traits that vary among individuals within a species to make them more or less innovative. Here we examine innovative problem solving by spotted hyenas (Crocuta crocuta) in their natural habitat, and demonstrate for the first time in a non-human animal that those individuals exhibiting a greater diversity of initial exploratory behaviours are more successful problem solvers. Additionally, as in earlier work, we found that neophobia was a critical inhibitor of problem-solving success. Interestingly, although juveniles and adults were equally successful in solving the problem, juveniles were significantly more diverse in their initial exploratory behaviours, more persistent and less neophobic than were adults. We found no significant effects of social rank or sex on success, the diversity of initial exploratory behaviours, behavioural persistence or neophobia. Our results suggest that the diversity of initial exploratory behaviours, akin to some measures of human creativity, is an important, but largely overlooked, determinant of problem-solving success in non-human animals.     

A phenotypic and molecular characterization of the fmr1-tm1Cgr fragile X mouse

Fragile X Syndrome is the most common form of inherited mental retardation. It is also known for having a substantial behavioral morbidity, including autistic features. In humans, Fragile X Syndrome is almost always caused by inactivation of the X-linked FMR1 gene. A single knockout mouse model, fmr1-tm1Cgr, exists. In this report we further characterize the cognitive and behavioral phenotype of the fmr1-tm1Cgr Fragile X mouse through the use of F1 hybrid mice derived from two inbred strains (FVB/NJ and C57BL/6J). Use of F1 hybrids allows focus on the effects of the fmr1-tm1Cgr allele with reduced influence from recessive alleles present in the parental inbred strains. We find that the cognitive phenotype of fmr1-tm1Cgr mice, including measures of working memory and learning set formation that are known to be seriously impacted in humans with Fragile X Syndrome, are essentially normal. Further testing of inbred strains supports this conclusion. Thus, any fmr1-tm1Cgr cognitive deficit is surprisingly mild or absent. There is, however, clear support presented for a robust audiogenic seizure phenotype in all strains tested, as well as increased entries into the center of an open field. Finally, a molecular examination of the fmr1-tm1Cgr mouse shows that, contrary to common belief, it is not a molecular null. Implications of this finding for interpretation of the phenotype are discussed.     

Social effects on fruit fly courtship song

Courtship behavior in Drosophila has often been described as a classic innate behavioral repertoire, but more recently extensive plasticity has been described. In particular, prior exposure to acoustic signals of con‐ or heterspecific males can change courtship traits in both sexes that are liable to be important in reproductive isolation. However, it is unknown whether male courtship song itself is socially plastic. We examined courtship song plasticity of two species in the Drosophila melanogaster subgroup. Sexual isolation between the species is influenced by two male song traits, the interpulse interval (IPI) and sinesong frequency (SSF). Neither of these showed plasticity when males had prior experience of con‐ and heterospecific social partners. However, males of both species produced longer bursts of song during courtship when they were exposed to social partners (either con‐ or heterospecific) than when they were reared in isolation. D. melanogaster carrying mutations affecting short‐ or medium‐term memory showed a similar response to the social environment, not supporting a role for learning. Our results demonstrate that the amount of song a male produces during courtship is plastic depending on the social environment, which might reflect the advantage of being able to respond to variation in intrasexual competition, but that song structure itself is relatively inflexible, perhaps due to strong selection against hybridization.     

A-Level ‘Questions’ in Biology—The Nature of the Influence

The purpose of keeping animals in schools and the main problems encountered in their maintenance are summarised. Many teachers prefer animals which are kept typically in research laboratories over animals which can be collected from the student's environment. However, small animals of economic importance can combine some of the advantages of both of these groups of animals. Chickens, bees, plant pests and their natural enemies have been tried out in the Agriculture as Environmental Science Curriculum Project and can be used for observation and measurement as well as to stress the aspect of relevance to real life problems. In their maintenance, standard equipment and methods can often be used and help the teacher to solve some of the main problems of keeping animals.

Two curriculum units, on a fruit fly and on honey bees, are described. Reasons for a widespread negative image of rural studies are discussed, and positive, effective outcomes, reported in the evaluation of an environmental science course, are used to substantiate the advantages of keeping animals of economic importance in schools.     

The Time Factor in Understanding the Ecology of Wildlife

This study examined the effectiveness of worksheets while learning about biodiversity in a natural history museum. Despite the frequent use of worksheets by school classes during out-of-school activities, their effectiveness in enhancing knowledge acquisition has been addressed by relatively few empirical studies. 148 Austrian grammar school students aged eleven to fifteen took part in the pre- and post-test questionnaire study which included a one-hour learning phase with worksheets in the museum. Results indicate a high learning effect from pre- to post-test. Further analyses show that worksheets contributed to knowledge gain, but this contribution is similar to that afforded by prior knowledge. The design of the worksheet tasks was also important. A closed task setting required the students to look for clearly defined solutions. This led to greater knowledge gains than open worksheet tasks, where the spectrum of possible answers was wider. We concluded that worksheets can be used effectively for acquiring basic knowledge about biodiversity and suggest how to integrate the findings into the design of worksheets for out-of-school learning.