Influence of temperature on daily locomotor activity in the crab Uca pugilator.

Animals living in the intertidal zone are exposed to prominent temperature changes. To cope with the energetic demands of environmental thermal challenges, ectotherms rely mainly on behavioral responses, which may change depending on the time of the day and seasonally. Here, we analyze how temperature shapes crabs' behavior at 2 different times of the year and show that a transition from constant cold (13.5°C) to constant warm (17.5°C) water temperature leads to increased locomotor activity levels throughout the day in fiddler crabs (Uca pugilator) collected during the summer. In contrast, the same transition in environmental temperature leads to a decrease in the amplitude of the daily locomotor activity rhythm in crabs collected during the winter. In other words, colder temperatures during the cold season favor a more prominent diurnal behavior. We interpret this winter-summer difference in the response of daily locomotor activity to temperature changes within the framework of the circadian thermoenergetics hypothesis, which predicts that a less favorable energetic balance would promote a more diurnal activity pattern. During the winter, when the energetic balance is likely less favorable, crabs would save energy by being more active during the expected high-temperature phase of the day-light phase-and less during the expected low-temperature phase of the day-dark phase. Our results suggest that endogenous rhythms in intertidal ectotherms generate adaptive behavioral programs to cope with thermoregulatory demands of the intertidal habitat

Moonstruck sleep: Synchronization of human sleep with the moon cycle under field conditions

Before the availability of artificial light, moonlight was the only source of light sufficient to stimulate nighttime activity; still, evidence for the modulation of sleep timing by lunar phases is controversial. Here, we use wrist actimetry to show a clear synchronization of nocturnal sleep timing with the lunar cycle in participants living in environments that range from a rural setting with and without access to electricity in indigenous Toba/Qom communities in Argentina to a highly urbanized postindustrial setting in the United States. Our results show that sleep starts later and is shorter on the nights before the full moon when moonlight is available during the hours following dusk. Our data suggest that moonlight likely stimulated nocturnal activity and inhibited sleep in preindustrial communities and that access to artificial light may emulate the ancestral effect of early-night moonlight.Fil: Casiraghi, Leandro Pablo. University of Washington; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Spiousas, Ignacio. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnologia. Laboratorio de Dinamica Sensomotora.; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Dunster, Gideon P. University of Washington; Estados UnidosFil: McGlothlen, Kaitlyn. University of Washington; Estados UnidosFil: Fernandez Duque, Eduardo. University of Yale; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Centro de Ecología Aplicada del Litoral. Universidad Nacional del Nordeste. Centro de Ecología Aplicada del Litoral; ArgentinaFil: Valeggia, Claudia Rita. University of Yale; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: de la Iglesia, Horacio Oscar. University of Washington; Estados Unido

Mean waveforms throughout the experiments.

<p>Top panel: comparison of the first consensus waveforms drawn for rhythmic crabs at 13.5°C. Lower panel: comparison of the consensus waveforms drawn for rhythmic crabs at 17.5°C. Data are replotted from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0175403#pone.0175403.g001" target="_blank">Fig 1</a>. Each point represents mean ± SEM.</p

Individual actograms at 17°C and 13°C.

<p>Individual double-plotted actograms at 17°C (A) and 13°C (B) for 3 representative crabs for each experiment, kept first under a 12:12 LD cycle (10 and 8 days respectively) and then transferred to LL conditions (12 days for both). To the right of each actogram, periodograms display the period of the oscillation that significantly (<i>p</i> ≤ 0.05) explains most of the variance in the analysis, indicated in minutes. For each actogram, there are two periodograms corresponding to the activity under LD and LL, respectively. Crabs were collected in summer and tested in free-running either at 13 or 17°C. Crabs depicted under 13°C are not the same individuals depicted under 17°C.</p