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Male frogs court females from within crowded choruses, selecting for mechanisms allowing them to call at favourable times relative to the calls of rivals and background chorus noise. To accomplish this, males must continuously evaluate the fluctuating acoustic scene generated by their competitors for opportune times to call. Túngara frogs produce highly frequency- and amplitude-modulated calls from within dense choruses. We used similarly frequency- and amplitude-modulated playback tones to investigate the sensory basis of their call-timing decisions. Results revealed that different frequencies present throughout this species’ call differed in their degree of call inhibition, and that lower-amplitude tones were less inhibitory. Call-timing decisions were then driven by fluctuations in inhibition arising from underlying frequency- and amplitude-modulation patterns, with tone transitions that produced steeper decreases in inhibition having higher probabilities of triggering calls. Interactions between the varied behavioural sensitivities to different conspecific call frequencies revealed here, and the stereotyped amplitude- and frequency-modulation patterns present in this species’ calls, can explain previously surprising patterns observed in túngara frog choruses. This highlights the importance of understanding the specific sensory drivers underpinning conspecific signalling interactions, and reveals how sensory systems can mediate the interplay between signal perception and production to facilitate adaptive communication strategies. 

Abstract Species worldwide are disappearing in the most devastating mass extinction in human history and one of the six most profound extinctions in the history of life. Amphibians are greatly affected, approximately one third of living species are threatened, and many others are extinct. One of the main causes of amphibian species extinctions and population declines is the emerging infectious disease chytridiomycosis, caused by the fungusBatrachochytrium dendrobatidis(Bd). Although some species are somewhat tolerant of the disease, the non-lethal effects of the infection with Bd and their short or long term consequences are poorly understood. In these species there is the potential for behavioral responses to mitigate the spread of the fungus. Here we show that in túngara frogs, infection status influences the males’ mating calls. These infection-induced changes in the quality of males’ mating calls ultimately reduce the calls’ attractiveness to females making females less likely to respond to and thus mate with infected males. More broadly, our results imply that females might avoid mating with disease-infected males by assessing the acoustic signal only, and that such recruitment of behavioral responses might potentially ameliorate some of the effects of this sixth mass extinction. Lay summaryChytridiomycosis is an amphibian disease well known for its lethal effects. Túngara frogs are infected in nature, but seem to be resistant to the disease. Here we show that chytridiomycosis has non-lethal behavioral effects on túngara frogs. Females discriminate against infected males by assessing only their acoustic signal. The mating call of a male that is not infected with the disease is more attractive to females than the call of that same male when he is infected. 

Abstract Sexual selection can result in the evolution of extreme armaments and ornaments, and the development and maintenance of these traits can come at a considerable cost. These costs have been implicated in enforcing an upper limit on trait divergence and promoting condition-dependent traits, such that only individuals in sufficiently high condition can effectively wield these armaments and advertise these ornaments. Numerous studies demonstrate the condition-dependence of sexually selected traits, especially those used by males to advertise to females. In this study, we investigated condition-dependent mating calls in the túngara frogPhysalaemus(= Engystomops)pustulosus. We manipulated male condition in the laboratory over a nine-day period by restricting food availability. We then documented: the relationship between male condition (the relative change in body mass from night 1 to night 9) and acoustic parameters of his mating call; how male condition influenced the male’s responses to call playbacks; and finally, how male condition influenced the attractiveness of the male’s calls to females. Males who were not fed during this period showed significant changes in call frequency, duration, and amplitude. In response to playbacks, unfed males called less, and made fewer complex calls. Finally, in phonotaxis experiments, females were more attracted to the calls of unfed males on night 1 to the calls of the same males on night 9. Fed males, on the other hand, showed no significant differences between nights 1 and 9 in call parameters, calling effort, and call attractiveness. This study shows the pervasive effects of condition on three aspects of sexual communication: signal parameters, behavioral response to vocal competition, and mating call attractiveness. 

Abstract Plant survival depends on a balance between carbon supply and demand. When carbon supply becomes limited, plants buffer demand by using stored carbohydrates (sugar and starch). During drought, NSCs (non-structural carbohydrates) may accumulate if growth stops before photosynthesis. This expectation is pervasive, yet few studies have combined simultaneous measurements of drought, photosynthesis, growth, and carbon storage to test this. Using a field experiment with mature trees in a semi-arid woodland, we show that growth and photosynthesis slow in parallel as$${\psi }_{{pd}}$$ ${\psi }_{pd}$declines, preventing carbon storage in two species of conifer (J. monospermaandP. edulis). During experimental drought, growth and photosynthesis were frequently co-limited. Our results point to an alternative perspective on how plants use carbon that views growth and photosynthesis as independent processes both regulated by water availability.