Social context affects camouflage in a cryptic fish species

Crypsis, or the ability to avoid detection and/or recognition, is an important and widespread anti-predator strategy across the animal kingdom. Many animals are able to camouflage themselves by adapting their body colour to the local environment. In particular, rapid changes in body colour are often critical to the survival of cryptic prey which rely on evading detection by predators. This is especially pertinent for animals subject to spatio-temporal variability in their environment, as they must adapt to acute changes in their visual surroundings. However, which features of the local environment are most relevant is not well understood. In particular, little is known about how social context interacts with other environmental stimuli to influence crypsis. Here, we use a common cryptic prey animal, the goby ( Pseudogobius species 2) to examine how the presence and body colour of conspecifics influence the rate and extent to which gobies change colour. We find that solitary gobies change colour to match their background faster and to a greater extent than gobies in pairs. Further, we find that this relationship holds irrespective of the colour of nearby conspecifics. This study demonstrates the importance of social context in mediating colour change in cryptic animals.

Large contribution of pulsed subsidies to a predatory fish inhabiting large stream channels

Resource subsidies exert critical influences on recipient habitats with relatively higher perimeter-to-area ratios, such as headwaters in watersheds. However, little is known about how those subsidies contribute to the energy sources in recipient habitats where the perimeter-to-area ratio is low, such as large stream channels. Here, we show that the diet of small Japanese eels (Anguilla japonica) <500 mm in total length inhabiting natural shoreline areas in large stream channels consists largely of terrestrial earthworms (Metaphire spp.). Stable isotopic analyses showed that the earthworms were the prey animal that contributed most to the eels’ diet (45%–47%). Earthworms constituted the largest portion of the eels’ stomach contents (7%–93%). Eels ingested earthworms within 2 days after rainfall during spring, summer, and autumn, and their consumption increased as the precipitation increased. These findings indicate that the pulsed earthworm subsidy that is driven by rainfall could temporarily bias the eels’ diet toward this allochthonous resource, which may explain the large contribution of the subsidy for consumers inhabiting large stream channels. Furthermore, diverse earthworm species could drive multiple pulsed subsidies across seasons and provide the predators with a prolonged subsidy, enhancing the long-term contribution of the subsidy to the predators’ diet.

Modeling escape success in terrestrial predator–prey interactions

Synopsis Prey species often modify their foraging and reproductive behaviors to avoid encounters with predators; yet once they are detected, survival depends on out-running, out-maneuvering, or fighting off the predator. Though predation attempts involve at least two individuals—namely, a predator and its prey—studies of escape performance typically measure a single trait (e.g., sprint speed) in the prey species only. Here, we develop a theoretical model in which the likelihood of escape is determined by the prey animal’s tactics (i.e., path trajectory) and its acceleration, top speed, agility, and deceleration relative to the performance capabilities of a predator. The model shows that acceleration, top speed, and agility are all important determinants of escape performance, and because speed and agility are biomechanically related to size, smaller prey with higher agility should force larger predators to run along curved paths that do not allow them to use their superior speeds. Our simulations provide clear predictions for the path and speed a prey animal should choose when escaping from predators of different sizes (thus, biomechanical constraints) and could be used to explore the dynamics between predators and prey.

How molecular tools can help understanding species interactions to improve restoration outcomes

Preserving species interactions should be a key desired outcome in restoration ecology. With progress in environmental DNA techniques and the dramatic reduction in the cost of high-throughput DNA sequencing, large amounts of information can be gathered on how species interact with little to no disturbance to ecosystems. Here, we argue that the use of molecular tools to study ecological interactions will become increasingly important in restoration projects. We describe specific examples where recent advances in genetics allow for a better understanding of predator-prey, animal-plant, plant-microbe and trophic cascade interactions, which can inform restoration practice and substantially improve our capacity to restore functioning ecosystems.

How molecular tools can help understanding species interactions to improve restoration outcomes

Preserving species interactions should be a key desired outcome in restoration ecology. With progress in environmental DNA techniques and the dramatic reduction in the cost of high-throughput DNA sequencing, large amounts of information can be gathered on how species interact with little to no disturbance to ecosystems. Here, we argue that the use of molecular tools to study ecological interactions will become increasingly important in restoration projects. We describe specific examples where recent advances in genetics allow for a better understanding of predator-prey, animal-plant, plant-microbe and trophic cascade interactions, which can inform restoration practice and substantially improve our capacity to restore functioning ecosystems.

Prey should hide more randomly when a predator attacks more persistently

When being searched for and then (if found) pursued by a predator, a prey animal has a choice between choosing very randomly among hiding locations so as to be hard to find or alternatively choosing a location from which it is more likely to successfully flee if found. That is, the prey can choose to be hard to find or hard to catch, if found. In our model, capture of prey requires both finding it and successfully pursuing it. We model this dilemma as a zero-sum repeated game between predator and prey, with the eventual capture probability as the pay-off to the predator. We find that the more random hiding strategy is better when the chances of repeated pursuit, which are known to be related to area topography, are high. Our results extend earlier results of Gal and Casas, where there was at most only a single pursuit. In that model, hiding randomly was preferred by the prey when the predator has only a few looks. Thus, our new multistage model shows that the effect of more potential looks is opposite. Our results can be viewed as a generalization of search games to the repeated game context and are in accordance with observed escape behaviour of different animals.

Large variation among photoreceptors as the basis of visual flexibility in the common backswimmer

The common backswimmer, Notonecta glauca , uses vision by day and night for functions such as underwater prey animal capture and flight in search of new habitats. Although previous studies have identified some of the physiological mechanisms facilitating such flexibility in the animal's vision, neither the biophysics of Notonecta photoreceptors nor possible cellular adaptations are known. Here, we studied Notonecta photoreceptors using patch-clamp and intracellular recording methods. Photoreceptor size (approximated by capacitance) was positively correlated with absolute sensitivity and acceptance angles. Information rate measurements indicated that large and more sensitive photoreceptors performed better than small ones. Our results suggest that backswimmers are adapted for vision in both dim and well-illuminated environments by having open-rhabdom eyes with large intrinsic variation in absolute sensitivity among photoreceptors, exceeding those found in purely diurnal or nocturnal species. Both electrophysiology and microscopic analysis of retinal structure suggest two retinal subsystems: the largest peripheral photoreceptors provide vision in dim light and the smaller peripheral and central photoreceptors function primarily in sunlight, with light-dependent pigment screening further contributing to adaptation in this system by dynamically recruiting photoreceptors with varying sensitivity into the operational pool.

The Coevolution of Tyrannosaurus & Its Prey

Students will analyze the coevolution of the predator–prey relationships between Tyrannosaurus rex and its prey species using analyses of animal speeds from fossilized trackways, prey-animal armaments, adaptive behaviors, bite marks on prey-animal fossils, predator–prey ratios, and scavenger competition. The students will be asked to decide whether T. rex was a predator, an opportunistic scavenger, or an obligate scavenger.