The quantum needle of the avian magnetic compass.

Migratory birds have a light-dependent magnetic compass, the mechanism of which is thought to involve radical pairs formed photochemically in cryptochrome proteins in the retina. Theoretical descriptions of this compass have thus far been unable to account for the high precision with which birds are able to detect the direction of the Earth's magnetic field. Here we use coherent spin dynamics simulations to explore the behavior of realistic models of cryptochrome-based radical pairs. We show that when the spin coherence persists for longer than a few microseconds, the output of the sensor contains a sharp feature, referred to as a spike. The spike arises from avoided crossings of the quantum mechanical spin energy-levels of radicals formed in cryptochromes. Such a feature could deliver a heading precision sufficient to explain the navigational behavior of migratory birds in the wild. Our results (i) afford new insights into radical pair magnetoreception, (ii) suggest ways in which the performance of the compass could have been optimized by evolution, (iii) may provide the beginnings of an explanation for the magnetic disorientation of migratory birds exposed to anthropogenic electromagnetic noise, and (iv) suggest that radical pair magnetoreception may be more of a quantum biology phenomenon than previously realized.

etnografía, territorio y conflicto armado. metodológia de una investigación sobre la construcción regional de los llanos del yarí (Caquetá, Colombia) / Ethnography, territory and armed conflict. una's methodology investigation on the regional construction of the plains of the yarí (Caquetá Colombia)

El siguiente artículo es un informe de investigación que da cuenta del planteamiento de unaEtnografía realizada en la región colombiana de los llanos del Yarí. El eje central de la investigación giró en torno al proceso de construcción territorial que han desplegado las comunidades campesinas de la zona.

The following article is a research report that realizes of the exposition of an ethnography realized in the plains of the Yari - Colombia. The backbone of the investigation turned concerning the process of territorial construction that the communities have opened compesinas of the zone.

Legalización e inclusión social: barrio 20 de Julio del municipio de Urrao / Legalization and social inclusion: 2oth of july neighborhood in the municipality of Urrao, southwest of Antioquia

El presente texto es producto de la segunda fase de la investigación Caracterización Psicosocial Barrio 20 de Julio Municipio de Urrao – Suroeste Antioqueño, dentro del área de legalización, titulación y normalización del Barrio 20 de Julio y con el fin de hacer recomendaciones para el Plan Básico de Ordenamiento Territorial. Para realizar dicho trabajo se toma en primera instancia los antecedentes de la primera fase, segundo se presentan los objetivos y preguntas, en tercer lugar se presentan los resultados de investigación y finalmente se presentan las conclusiones aunadas a las recomendaciones.

The present text is the result of a second phase of the research called psychosocial characterization of the 20th of july neighborhood in the municipality of Urrão, in the Southwest of Antioquia, within the area of legalization, certification, and standardization of the aforementioned neighborhood. Its purpose is to make some suggestions for the basic land-use plan. In order to carry out such a work, the antecedents are taken into account in th first place; in the second place, the objectives and the questions are introduced; in the third place, the research results are introduced; and in the fourth place, the conclusions, along with the recommendations, are presented.

Photoperiodic influences on ultradian rhythms of male Siberian hamsters.

Seasonal changes in mammalian physiology and behavior are proximately controlled by the annual variation in day length. Long summer and short winter day lengths markedly alter the amplitude of endogenous circadian rhythms and may affect ultradian oscillations, but the threshold photoperiods for inducing these changes are not known. We assessed the effects of short and intermediate day lengths and changes in reproductive physiology on circadian and ultradian rhythms of locomotor activity in Siberian hamsters. Males were maintained in a long photoperiod from birth (15 h light/day; 15 L) and transferred in adulthood to 1 of 7 experimental photoperiods ranging from 14 L to 9 L. Decreases in circadian rhythm (CR) robustness, mesor and amplitude were evident in photoperiods ≤14 L, as were delays in the timing of CR acrophase and expansion of nocturnal activity duration. Nocturnal ultradian rhythms (URs) were comparably prevalent in all day lengths, but 15 L markedly inhibited the expression of light-phase URs. The period (τ'), amplitude and complexity of URs increased in day lengths ≤13 L. Among hamsters that failed to undergo gonadal regression in short day lengths (nonresponders), τ' of the dark-phase UR was longer than in photoresponsive hamsters; in 13 L the incidence and amplitude of light-phase URs were greater in hamsters that did not undergo testicular regression. Day lengths as long as 14 L were sufficient to trigger changes in the waveform of CRs without affecting UR waveform. The transition from a long- to a short-day ultradian phenotype occurred for most UR components at day lengths of 12 L-13 L, thereby establishing different thresholds for CR and UR responses to day length. At the UR-threshold photoperiod of 13 L, differences in gonadal status were largely without effect on most UR parameters.

'Looping'-an exploration mechanism in a dark open field.

The behavior of Tristram's jird (a species of gerbil) in an illuminated open field resembled that of other rodents, comprising round trips to a home base and alternating between periods of progression (locomoting) and of stopping. In this study, we compared the characteristics of exploration in a dark arena with exploration by the same individuals in a lit arena. In the dark arena, stopping episodes were brief and fewer, suggesting almost continuous locomotion by the rodents. The clear distinction between progression and stopping that had characterized locomotion in an illuminated arena, thus diminished in the dark. There was also no apparent home base in the dark and traveling consisted in moving in a circular path, closing a loop to a recently traveled place that varied from one loop to the next. Locomotion in the dark may thus be regarded as a set of loops (round trips) to a continuously shifting home base, whereas with lights on the round trips converge to a home base using visible environmental landmarks. We suggest that a similar looping mechanism may be applicable to the behavior of hippocampal rats displaying hyperactivity and diversified locomotion, reminiscent of that seen in jirds in a dark arena.

Specializations for aerial hawking in the echolocation system of Molossus molossus (Molossidae, Chiroptera).

While searching for prey, Molossus molossus broadcasts narrow-band calls of 11.42 ms organized in pairs of pulses that alternate in frequency. The first signal of the pair is at 34.5 kHz, the second at 39.6 kHz. Pairs of calls with changing frequencies were only emitted when the interpulse intervals were below 200 ms. Maximum duty cycles during search phase are close to 20%. Frequency alternation of search calls is interpreted as a mechanism for increasing duty cycle and thus the temporal continuity of scanning, as well as increasing the detection range. A neurophysiological correlate for the processing of search calls was found in the inferior colliculus. 64% of neurons respond to frequencies in the 30- to 40-kHz range and only in this frequency range were closed tuning curves found for levels below 40 dB SPL. In addition, 15% of the neurons have double-tuned frequency-threshold curves with best thresholds at 34 and 39 kHz. Differing from observations in other bats, approach calls of M. molossus are longer and of higher frequencies than search calls. Close to the roost, the call frequency is increased to 45.0-49.8 kHz and, in addition, extremely broadband signals are emitted. This demonstrates high plasticity of call design.

The directional homing behaviour of the subsocial shield bug, Parastrachia japonensis (Heteroptera: Cydnidae), under different photic conditions.

The female subsocial shield bug, Parastrachia japonensis, provisions its nymphs by foraging on the ground in the forest during the Japanese rainy season, and the bug uses homing navigation to drag a drupe back to its burrow by the shortest route during the day. To study whether or not this bug performs this provisioning behaviour under different photic conditions, we observed the homing behaviour and homing direction of bugs in the field around the clock and/or under various weather conditions. The bugs foraged the whole day during the busiest provisioning period, and the number of walking bugs was not affected by the different weather conditions. Such navigational behaviour, regardless of the time of the day and the weather conditions, is rare in insect navigation. To test whether the bug uses visual cues, we covered the compound eyes and ocelli with opaque or clear paint just before homing began. During the day and at night, and in all weather conditions, the homing direction of blind bugs, but not those with clear-painted eyes was disoriented, indicating that this species uses visual cues dominantly under all photic conditions.