Journal of Experimental Biology - Latest Issue

• Influence of water temperature, body size, condition and gull-inflicted lesions on heat loss in southern right whales in Península Valdés, Argentina

  ABSTRACT

  Southern right whales (Eubalaena australis; SRWs) are well adapted to cold waters because of their large body size and thick blubber. Each year, they migrate from high-latitude feeding grounds to warmer breeding grounds where they give birth. To assess thermal benefits of this migration, we modelled the effects of body size, condition and water temperature on heat loss. Using unmanned aerial vehicle photogrammetry at the Península Valdés calving ground in Argentina, we measured body length, volume, condition and surface area of living SRWs. Blubber thickness was predicted from a blubber-mass model and validated using necropsy/catch data. Sensible heat loss was estimated using a model incorporating blubber thermal conductivity and body temperature, whereas respiratory heat loss was based on respiration rate and tidal volume models. We compared heat loss in Península Valdés with that in South Georgia/Georgia del Sur (SG/GS), a key feeding ground. Body size had a strong positive effect on both heat loss values, but mass-specific loss decreased as surface-area-to-volume ratio declined. Increased body condition reduced sensible heat loss. Migration from SG/GS to Península Valdés reduced calf heat loss by 26% during early lactation. However, total heat loss remained low relative to field metabolic rate (FMR), indicating limited thermoenergetic benefit from migration. Only at poor body condition (<−0.35) did heat loss exceed FMR, threatening survival. Notably, gull-inflicted lesions significantly increased heat loss in small and poorly conditioned calves, but had no effect on larger or better-conditioned calves. These findings highlight body condition as a key regulator of heat loss in baleen whales.

• Light wavelength and intensity modulate phototaxis in the nocturnal bee Megalopta aegis

  ABSTRACT

  Positive phototaxis in diurnal bees is modulated by the wavelength and intensity of light. Unlike diurnal bees, nocturnal bees such as Megalopta aegis forage exclusively during twilight, when light intensity drops rapidly and irradiance peaks in the blue spectrum. How light parameters influence phototaxis in these nocturnal bees remains unclear. We evaluated the phototactic responses of M. aegis in a dark circular arena using UV, blue and green monochromatic lights presented at six absolute intensities. In contrast to diurnal bees, M. aegis was not always attracted to light. When attracted, they showed stronger attraction to UV than to blue or green. Paths toward UV were shorter, faster and straighter, suggesting a greater involvement of UV photoreceptors in this phototactic behaviour. Compared with honeybees tested in similar experimental setups, M. aegis exhibited slower but more directed paths. These results align with their highly light-sensitive eyes, which trade off temporal resolution for improved reliability in dim light.

• Evolution, accessibility and community: JEB's journey into 2026

• Digestion is unaffected by surgical elimination of the right-to-left cardiac shunt in American alligators ( Alligator mississippiensis )

  ABSTRACT

  Crocodilian cardiac anatomy is characterized by a four-chambered heart with complete septal division of ventricles, with the pulmonary artery and systemic left aorta (LAo) originating from the right ventricle (RV). This morphology allows for right-to-left (R–L) cardiac shunting, in which a fraction of oxygen-poor blood can be recirculated from the RV to the systemic circulation through the LAo, bypassing the pulmonary circulation. The R–L shunt can be eliminated through surgical occlusion of the LAo, which permits investigation into its physiological and adaptive significance. As the LAo delivers blood to the gut, it has been suggested that desaturated blood supplied by R–L shunting delivers higher levels of CO₂ and H⁺, ultimately increasing gastric acid secretion and facilitating digestion. Consequently, we hypothesized that chronic surgical occlusion would negatively impact digestive performance of lab-raised American alligators (Alligator mississippiensis). In this study, two groups of alligators (9 years old; 7 years post-operation) with and without the capacity for R–L shunting (recipients of sham surgery or surgery to occlude LAo, respectively) were fed rodent meals of known mass and energy content to investigate digestive performance. There were no differences in apparent digestive efficiency or transit time between groups. We demonstrated that there were no underlying compensatory changes in mass or length of digestive or accessory digestive organs and no change in relative surface area or digestive enzyme activity in any intestinal region. Surgical elimination of the R–L cardiac shunt did not affect digestion in alligators, refuting the hypothesis that the R–L shunt is advantageous for crocodilian digestion.

• Cadences of the collective: conspecific stimulation patterns interact with endogenous rhythms to cue socially mediated response shifts

  ABSTRACT

  Many animals form behavioral collectives, and optimal interaction strategies often differ across social contexts. Sensory scenes generated by many interacting conspecifics are complex. Thus, maintaining socially calibrated responses requires individuals to distill key features from conspecific scenes to guide continued adjustments to social fluctuations. Túngara frogs produce mating calls in choruses varying in size, and interaction patterns differ across social environments; rivals alternate their calls in smaller choruses, but increasingly overlap one another's calls in a stereotyped fashion as chorus size increases. We used automated playback to investigate the cues guiding this socially mediated shift in interaction modes. We played conspecific stimulus calls to males at various delays relative to their own calls, preceded by various acoustic motifs that mimicked conspecific stimulation patterns males will hear in different social environments. Males almost never overlapped isolated stimulus calls at any delays. However, their probabilities of overlapping stimulus calls increased markedly when stimulus calls were preceded by motifs characteristic of larger choruses, i.e. those exhibiting intense conspecific stimulation patterns. Furthermore, the escalatory effects of motifs became increasingly pronounced as motif/stimulus combinations were played at later delays. Thus, interaction strategies are calibrated to current social dynamics each call cycle in response to a multifaceted cue that incorporates both the nature of conspecific stimulation experienced and how the timing of this stimulation interacts with endogenous responsiveness rhythms. Our results highlight that inactive phases within behavioral rhythms provide repeated opportunities to sample current social dynamics, allowing response patterns to be continually calibrated to social fluctuations in behavioral collectives.