Clouds, shadows, or twilight? Mayfly nymphs recognise the difference

1. We examined the relative changes in light intensity that initiate night-time locomotor activity changes in nymphs of the mayfly, Stenonema modestum (Heptageniidae). Tests were carried out in a laboratory stream to examine the hypothesis that nymphs increase their locomotion in response to the large and sustained reductions in relative light intensity that take place during twilight but not to short-term daytime light fluctuations or a minimum light intensity threshold. Ambient light intensity was reduced over a range of values representative of evening twilight. Light was reduced over the same range of intensities either continuously or in discrete intervals while at the same time nymph activity on unglazed tile substrata was video recorded. 2. Nymphs increased their locomotor activity during darkness in response to large, sustained relative light decreases, but not in response to short-term, interrupted periods of light decrease. Nymphs did not recognise darkness unless an adequate light stimulus, such as large and sustained relative decrease in light intensity, had taken place. 3. We show that nymphs perceive light change over time and respond only after a lengthy period of accumulation of light stimulus. The response is much lengthier than reported for other aquatic organisms and is highly adaptive to heterogeneous stream environments

Colour pattern component phenotypic divergence can be predicted by the light environment

The sensory drive hypothesis predicts that across different light environments sexually selected colour patterns will change to increase an animal's visual communication efficiency within different habitats. This is because individuals with more efficient signal components are likely to have more successful matings and hence produce more offspring. However, how colour pattern signals change over multiple generations under different light environmental conditions has not been tested experimentally. Here, we manipulated colour pattern signal efficiency by providing different ambient light environments over multiple generations to examine whether male colour pattern components change within large replicated populations of guppies (Poecilia reticulata). We report that colour patches change within populations over time and are phenotypically different among our three different light environments. Visual modelling suggests that the majority of these changes can be understood by considering the chroma, hue and luminance of each colour patch as seen by female guppies under each light environment. Taken together, our results support the hypothesis that different environmental conditions during signal reception can directly or indirectly drive the phenotypic diversification of visual signals within species

Fronto-striatal glutamate in children with Tourette's disorder and attention-deficit/hyperactivity disorder

OBJECTIVE: Both Tourette's disorder (TD) and attention-deficit/hyperactivity disorder (ADHD) have been related to abnormalities in glutamatergic neurochemistry in the fronto-striatal circuitry. TD and ADHD often co-occur and the neural underpinnings of this co-occurrence have been insufficiently investigated in prior studies. METHOD: We used proton magnetic resonance spectroscopy (1H-MRS) in children between 8 and 12 years of age (TD n = 15, ADHD n = 39, TD + ADHD n = 29, and healthy controls n = 53) as an in vivo method of evaluating glutamate concentrations in the fronto-striatal circuit. Spectra were collected on a 3 Tesla Siemens scanner from two voxels in each participant: the anterior cingulate cortex (ACC) and the left dorsal striatum. LC-model was used to process spectra and generate glutamate concentrations in institutional units. A one-way analysis of variance was performed to determine significant effects of diagnostic group on glutamate concentrations. RESULTS: We did not find any group differences in glutamate concentrations in either the ACC (F(3132) = 0.97, p = 0.41) or striatum (F(3121) = 0.59, p = 0.62). Furthermore, variation in glutamate concentration in these regions was unrelated to age, sex, medication use, IQ, tic, or ADHD severity. Obsessive-compulsive (OC) symptoms were positively correlated with ACC glutamate concentration within the participants with TD (rho = 0.35, puncorrected = 0.02). CONCLUSION: We found no evidence for glutamatergic neuropathology in TD or ADHD within the fronto-striatal circuits. However, the correlation of OC-symptoms with ACC glutamate concentrations suggests that altered glutamatergic transmission is involved in OC-symptoms within TD, but this needs further investigation