Journal of Experimental Biology - Latest Issue

• Biosynthesis of long-chain omega-3 fatty acids by the nestlings of a generalist seabird

  ABSTRACT

  Docosahexaenoic acid (DHA), a long-chain omega-3 fatty acid (n3-LCPUFA), is an integral component of vertebrate brains. Vertebrates maintain their DHA levels through biosynthesis using alpha-linolenic acid (ALA; omega-3 precursor) or by consuming preformed DHA and other n3-LCPUFAs which abound in the natural diets of marine predators. Yet, numerous marine predators, including generalist seabirds, now exploit anthropogenic resources potentially deficient in n3-LCPUFAs. Whether they can offset such deficiency by bioconverting ALA into DHA remains unknown. Here, we tested whether chicks of the ring-billed gull (Larus delawarensis), a generalist seabird thriving in cities, can biosynthesize n3-LCPUFAs, including DHA, from ALA. We brought into captivity 12 hatchlings from an urban colony and 12 from a natural colony. Nine hatchlings per colony were gavaged 490 μl of ALA-rich flaxseed oil daily for 3 days. The control groups (N=3 urban hatchlings, 3 natural hatchlings) received an omega-3-free caloric equivalent in place of the ALA supplement. All chicks received an omega-3-free diet throughout captivity (72 h). We also attempted to follow ALA's potential bioconversion into n3-LCPUFAs using an oral ¹³C₁-enriched ALA tracer. Unfortunately, compound-specific isotope analyses of brain and liver tissue failed to detect any ¹³C enrichment. Nevertheless, the flaxseed oil supplementation study provided evidence of some ALA bioconversion. Compared with controls, supplemented chicks from both colonies accumulated more of all ALA derivates in their tissues except for DHA. We demonstrate for the first time that a seabird shows incomplete omega-3 bioconversion abilities, leaving them potentially vulnerable to deficiencies associated with urban foraging and shifting marine ecosystems.

• Addressing issues of experimental design, ecological realism and local adaptation for applications of ectotherm upper thermal limits

  ABSTRACT

  Upper thermal limits of ectotherms are widely used to understand and predict species' thermal responses and sensitivity to warming. These limits are often defined for species using experiments with rapid ramping temperatures that test critical thermal maxima (CT_max). However, there are issues that arise with relying on these experimental results including (1) the influence of experimental design on thermal maxima, (2) the lack of ecological realism and (3) the potential for population-level local adaptation of upper thermal limits. We addressed these issues by comparing the CT_max approach with an ecologically realistic design using slower incremental temperature ramping with diel fluctuations (ITD_max) and by applying both to evaluate local adaptation of juvenile coho salmon (Oncorhynchus kisutch). We compared populations from thermal regimes spanning 7° latitude and coastal to inland systems by testing three populations, combining results with a fourth population from a prior ITD_max study, and comparing with other studies that used CT_max experiments to test thermal maxima of juvenile coho salmon. Most notably, we found that unlike CT_max experiments, ITD_max results were not influenced by acclimation temperature. This stemmed from acclimation during the ITD_max trials, likely representing more ecologically relevant responses to longer term warming. Furthermore, local adaptation of thermal maxima, as measured by both CT_max and ITD_max, was not evident for juvenile coho salmon, with no influence of population across the nine included in the cross-study examination. The results suggest the ability to use ITD_max-based upper thermal limits across species' extents and with differing prior environmental exposure, providing a more accurate representation of responses and sensitivity to long-term warming.

• New method for ramping up the heat could help scientists save salmon

• Behavior choices amongst grooming, feeding and courting in Drosophila show contextual flexibility, not an absolute hierarchy of needs

  ABSTRACT

  To determine the algorithmic rules and neural circuits controlling selection amongst competing behaviors, we established assays where adult Drosophila melanogaster choose between grooming and feeding, grooming and courting, or feeding and courting. We found that there is not an absolute hierarchy: while flies typically perform grooming first, they can choose to feed if sufficiently starved, or court if an appropriate female is available. Flies alternate between competing behaviors, performing short bouts of each action rather than completely satisfying one drive before transitioning to another. While we did not do an exhaustive screen, from the candidates we examined, we did not find evidence for a specific genetic or neuronal locus that affects all decisions. We did identify genetic background effects, suggesting that multiple genes may contribute to decision-making priorities. Our results add to a growing body of work on decision making in Drosophila and provide a foundation for future investigation of the exact neural circuits required to achieve appropriate choices.

• ECR Spotlight – Carla Ladd

  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. Carla Ladd is an author on ‘ Behavior choices amongst grooming, feeding and courting in Drosophila show contextual flexibility, not an absolute hierarchy of needs’, published in JEB. Carla is a postdoc in the lab of Kenneth Kosik at the Neuroscience Research Institute, University of California, Santa Barbara, USA, investigating the effects of Alzheimer's Disease on habituation.