Pollinator cognition and the function of complex rewards.

The cognitive ecology of pollination is most often studied using simple rewards, yet flowers often contain multiple types of chemically complex rewards, each varying along multiple dimensions of quality. In this review we highlight ways in which reward complexity can impact pollinator cognition, demonstrating the need to consider ecologically realistic rewards to fully understand plant-pollinator interactions. We show that pollinators' reward preferences can be modulated by reward chemistry and the collection of multiple reward types. We also discuss how reward complexity can mediate pollinator learning through a variety of mechanisms, both with and without reward preference being altered. Finally, we show how an understanding of decision-making strategies is necessary to predict how pollinators' evaluation of reward options depends on the other options available.

Ripple effects in a communication network: anti-eavesdropper defence elicits elaborated sexual signals in rival males.

Emitting conspicuous signals into the environment to attract mates comes with the increased risk of interception by eavesdropping enemies. As a defence, a commonly described strategy is for signallers to group together in leks, diluting each individual's risk. Lekking systems are often highly social settings in which competing males dynamically alter their signalling behaviour to attract mates. Thus, signalling at the lek requires navigating fluctuations in risk, competition and reproductive opportunities. Here, we investigate how behavioural defence strategies directed at an eavesdropping enemy have cascading effects across the communication network. We investigated these behaviours in the túngara frog (Engystomops pustulosus), examining how a calling male's swatting defence directed at frog-biting midges indirectly affects the calling behaviour of his rival. We found that the rival responds to swat-induced water ripples by increasing his call rate and complexity. Then, performing phonotaxis experiments, we found that eavesdropping fringe-lipped bats (Trachops cirrhosus) do not exhibit a preference for a swatting male compared to his rival, but females strongly prefer the rival male. Defences to minimize attacks from eavesdroppers thus shift the mate competition landscape in favour of rival males. By modulating the attractiveness of signalling prey to female receivers, we posit that eavesdropping micropredators likely have an unappreciated impact on the ecology and evolution of sexual communication systems.

Label-based expectations affect incentive contrast effects in bumblebees.

While classic models of animal decision-making assume that individuals assess the absolute value of options, decades of research have shown that rewards are often evaluated relative to recent experience, creating incentive contrast effects. Contrast effects are often assumed to be purely sensory, yet consumer and experimental psychology tell us that label-based expectations can affect value perception in humans and rodents. However, this has rarely been tested in non-model systems. Bumblebees forage on a variety of flowers that vary in their signals and rewards and show contrast when rewards are lowered. We manipulated bees' expectations of stimulus quality, before downshifting the reward to induce incentive contrast. We found that contrast effects were not solely driven by experience with a better reward, but also influenced by experience with associated stimuli. While bees' initial response did not differ between treatments, individuals were faster to accept the lower-quality reward when it was paired with a novel stimulus. We explored the boundaries of these label-based expectations by testing bees along a stimulus gradient and found that expectations generalized to similar stimuli. Such reference-dependent evaluations may play an important role in bees' foraging choices, with the potential to impact floral evolution and plant community dynamics.

Prey Exploits the Auditory Illusions of Eavesdropping Predators.

Mating signals have evolved to attract target receivers, even to the point of exploiting receivers through perceptual manipulation. Signals, however, can also expose signalers to nontarget receivers, including predators and parasites, and thus have also evolved to decrease enemy attraction. Here we show that male tree frogs (Smilisca sila) reduce their attractiveness to eavesdropping enemies (bats and midges) by overlapping their calls at near-perfect synchrony with the calls of neighboring conspecifics. By producing calls that closely follow those of other males, synchronizing S. sila take advantage of an auditory illusion where enemies are more attracted to the leading call. Female S. sila, however, are less susceptible to this illusion. Thus, synchronization among signaling males can result in acoustic crypsis from predators without affecting female attraction. Given the widespread use of conspicuous mating signals and eavesdropping enemies, perceptual exploitation of eavesdroppers is likely a common driver of signal evolution.