Abstract Classic examples of convergent trophic evolution in fishes have focused predominantly on adaptations in craniofacial morphology to piscivorous and durophagous diets. With the physiological demands of nutrient-poor, plant-based diets, adaptation to herbivory also significantly influences digestive physiology and morphology, so convergence onto similar herbivorous phenotypes in elements of postcranial morphology such as body shape and intestinal length might also be expected. Here, we integrate dietary and ecomorphological data, geometric morphometrics and phylogenetic comparative methods to investigate convergence in the body plan of Terapontoidei, an ecomorphologically diverse marine and freshwater fish radiation. We show that while diet has shaped morphology, herbivores have not converged towards distinct morphotypes, instead encompassing much of the broader body shape and size morphospace of Terapontoidei fishes. Significantly longer intestines have, however, remained a constant selective demand for adapting to plant-based diets.
Abstract Heatwaves are becoming longer, more frequent and more intense under climate change. However, we still have a limited understanding of the longer term (multi-generational) impacts of heatwaves, and of the demographic mechanisms that underly these effects. To address these gaps, we conducted an experiment using a model system of flour beetles (Tribolium castaneum) that tested the effects of heatwave duration on population dynamics. We subjected replicate beetle populations to a single 38°C heatwave event of one of four durations (0, 5, 10 or 15 days) and then tracked population sizes, birth rates and mortality rates for 7 months (approx. 7 generations). We found that, initially, heatwaves reduced population growth rates by temporarily lowering birth rates (via reduced fecundity), but that later in the experiment, the impact of heatwaves on population dynamics occurred via increased mortality rates. Together, these demographic effects resulted in a sustained suppression of population sizes throughout the experiment, as populations exposed to longer heatwaves (10-day and 15-day) experienced reduced carrying capacities for the duration of the experiment. Our findings indicate that heatwaves can have persistent negative impacts on population dynamics that could be underestimated by focusing solely on short-term responses.
Abstract Egg-laying decisions are crucial in insect parasitoids because the host constitutes the only resource available for immature development. We estimated the extent to which host sex, size and mating behaviour are involved and interact in shaping host selection in the association between the Japanese beetle, Popillia japonica, and a parasitoid fly, Istocheta aldrichi. Under field conditions, we found that females and larger individuals of the Japanese beetle, both males and females, are associated with the highest levels of parasitism, regardless of seasonal variations in host size and sex ratio. Furthermore, we propose that foraging I. aldrichi females exploit the sexual selection behaviour of the host to their own advantage. The increased vulnerability to parasitism of Japanese beetle females during mating when immobilized by males, the extended duration of mating and the preference of males for larger females contribute to the strong bias towards large females being the most parasitized. This leads to the hypothesis that I. aldrichi females have evolved to ‘merely’ rely on Japanese beetle males to select the most suitable hosts for reproduction. Finally, we discuss the possible impact on both seasonal and long-term demographics of the Japanese beetle populations and biological control.
Abstract Understanding how targeted prey conditions influence foraging decisions is a fundamental issue in animal behaviour. The present study investigated whether cuttlefish use prey liveness to assess overall food quality. Cuttlefish were allowed to choose between different levels of prey freshness and quantity. Experiments 1 and 2 examined cuttlefish choices between one live shrimp alone and one live shrimp paired with either one or four freshly dead shrimps. Experiment 3 evaluated their preferences of one live shrimp paired with either one freshly dead shrimp or one hourly dead shrimp. Experiment 4 assessed their choices between these two types of dead shrimp alone. Results showed that cuttlefish significantly avoided the side containing one live shrimp paired with one freshly dead shrimp, and this avoidance increased proportionally with the quantity of dead shrimp. However, cuttlefish choice did not differ significantly between freshly and hourly dead shrimps. These findings suggest that the presence of dead shrimp decreases a cuttlefish's perceived food value, and that motionless prey, regardless of their condition, serve as a negative indicator of overall food quality. This study demonstrates that cuttlefish assess total prey value based on the negation of dead prey, a mental process of intentionally removing hindrances during evaluation.
Abstract Illumination conditions have a tremendous influence on the appearance of colours in nature. This is especially true for glossy objects, which generate bright highlights in direct sunlight, but the visibility of these highlights is noticeably reduced in shaded or overcast conditions. Despite this dramatic change in appearance with illumination, we know little about how illumination influences the visibility of glossy objects, and no study has directly tested the functional consequences. Here, we investigated whether jewel beetles (family: Buprestidae) use glossiness as a long-distance cue of conspecifics and how weather conditions determine the visibility of glossy beetles. We documented beetle attraction to glossy and matte interception traps in their natural habitat. Male beetles were more attracted to glossy than matte traps, but only on sunny days. To determine whether surface gloss is also used to locate conspecifics at short-range, we documented beetle behaviour towards glossy and matte replica beetle models placed on host trees. Beetles were more likely to approach glossy than matte replica beetles. Our results indicate that jewel beetles use glossiness as both long- and short-range cues of potential conspecifics, but only in sunny conditions. This demonstrates that environmental conditions determine when these brilliant visual cues are functionally relevant.
