Journal of Experimental Biology - Latest Issue
-
The photoacclimation state of stolen chloroplasts affects the light preferences in the photosynthetic sea slug Elysia crispata
ABSTRACTPhotosynthetic sacoglossan sea slugs sequester the chloroplasts of the algae they feed upon and keep these organelles functional in the cells of their ramified digestive system. Whether the stolen chloroplasts – kleptoplasts – influence animal behavioural responses towards light is uncertain. To address this matter, we: (1) determined the light preferences of the photosynthetic sea slug Elysia crispata when offered different light spectra (450, 517, 520–650 and 665 nm) and intensities (60, 180, 425 and 1400 µmol photons m–2 s–1); and (2) established whether the light intensity preferences of E. crispata were different when fed algae acclimated to low (40 µmol photons m–2 s–1) and high irradiance (425 µmol photons m–2 s–1). Sea slugs were collected from a coral reef in the Gulf of Mexico and transported to the laboratory to perform controlled experiments. During trials, sea slugs exhibited marked exploratory behaviour. However, results show that E. crispata avoids red light (665 nm) and prefers low irradiance (60 µmol photons m–2 s–1), showing that both light spectrum and intensity are relevant to their behaviour. Furthermore, sea slugs increased their selection for high irradiance after being fed algae acclimated to high light. These results support our hypothesis that the acclimation state of the acquired kleptoplasts affects sea slug behaviour towards light. Light perception and photobehaviour in photosynthetic sea slugs seem to depend not only on animal photoreceptors, but also on a communication network between the endosymbiotic chloroplasts and the animal host. -
Control of metabolism by hypoxia and starvation and the consequences for the pattern of ecdysone secretion in Manduca sexta
ABSTRACTWhen larvae of Manduca sexta pass a critical weight, they initiate an endocrine cascade that leads to molting and metamorphosis. The critical weight coincides with a leveling off of the metabolic rate, and we hypothesize that it is the size at which the metabolic needs of a growing body reach the maximum capacity of the tracheal system to deliver oxygen. We examined two simple predictions about the role of oxygen supply in the regulation of growth: first, that restricting access to oxygen by blocking spiracles should affect growth and metabolism, and second, that placing larvae in a hypoxic atmosphere shortly before they reached the critical weight should prematurely trigger cessation of growth and metamorphosis. When sets of spiracles were blocked, growth rate was reduced, as was the metabolic rate and the body size at metamorphosis. The effect of blocking the posterior-most spiracles was greater than that of blocking the anterior-most ones, suggesting the presence of a required abdominal factor. Contrary to expectations, placing larvae in hypoxia a day before they reached the critical weight delayed the molt significantly, suggesting that hypoxia is not a trigger for the initiation of metamorphosis. Nevertheless, an increase in lactate levels in the second half of the final instar, and the leveling off of metabolic rate, indicate that a metabolic shift occurs at the critical weight. Ecdysone secretion in starved and hypoxic larvae was delayed by about 2 days relative to feeding controls, which explains the delayed timing of the metamorphic molt. -
Solar powered sea slugs take cues from chloroplasts
A sea slug making the choice between low or high intensity light. Photo credit: Xochitl Vital. -
ECR Spotlight – Xochitl Vital
ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. Xochitl Vital is an author on ‘ The photoacclimation state of stolen chloroplasts affects the light preferences in the photosynthetic sea slug Elysia crispata’, published in JEB. Xochitl conducted the research described in this article while a PhD student in Nuno Simões's lab at School of Sciences UMDI-Sisal, National Autonomous University of Mexico, Mexico. Xochitl is now a postdoc in the lab of Leopoldina Aguirre at Center for Research and Advanced Studies of the National Polytechnic Institute, Merida, Mexico, investigating diversity, ecology and distribution of aquatic benthic invertebrates, mostly marine mollusks. -
Gas exchange dynamics in bottlenose dolphins around 2 min apneas conform to values for terrestrial mammals
ABSTRACTCetaceans are often assumed to employ very high oxygen extractions of ∼40–60% and high tidal volumes (60–80% of vital capacity) to decrease surface time and increase foraging time at depth. However, such oxygen extractions and tidal volumes are greatly at odds with gas exchange in terrestrial mammals, and may, if incorrect, lead to severe overestimations of field metabolic rate (FMR) in wild animals when modeling oxygen uptake from respiration rates. Here, we tested the hypothesis that bottlenose dolphins have such high average oxygen extractions and tidal volumes. By measuring oxygen extractions and tidal volumes of >2000 breaths before and after a 2 min apnea bout in three trained bottlenose dolphins, we show that average pre-apnea resting oxygen extractions are between 17% and 25%, less than half of what has historically been reported for cetaceans. Following apnea, initial oxygen extractions are high (∼60%) but drop below pre-apnea levels in 11–20 breaths. Tidal volumes in this experimental setting were between 21% and 37% of vital capacity, consistent with recent findings for marine mammals, but less than half the 60–80% often assumed for cetaceans in FMR modeling. We therefore reject the hypothesis that bottlenose dolphins on average employ high oxygen extractions and high tidal volumes at rest and following short apneas. Consequently, using fixed high values for tidal volumes and oxygen extractions when modeling FMR from breathing rates in wild cetaceans may possibly lead to overestimations of their energy expenditure, food requirements and ecological roles.