Aposematic theory has historically predicted that predators should select for warning signals to converge on a single form, as a result of frequency‐dependent learning. However, widespread variation in warning signals is observed across closely related species, populations and, most problematically for evolutionary biologists, among individuals in the same population. Recent research has yielded an increased awareness of this diversity, challenging the paradigm of signal monomorphy in aposematic animals. Here we provide a comprehensive synthesis of these disparate lines of investigation, identifying within them three broad classes of explanation for variation in aposematic warning signals: genetic mechanisms, differences among predators and predator behaviour, and alternative selection pressures upon the signal. The mechanisms producing warning coloration are also important. Detailed studies of the genetic basis of warning signals in some species, most notably Heliconius butterflies, are beginning to shed light on the genetic architecture facilitating or limiting key processes such as the evolution and maintenance of polymorphisms, hybridisation, and speciation. Work on predator behaviour is changing our perception of the predator community as a single homogenous selective agent, emphasising the dynamic nature of predator–prey interactions. Predator variability in a range of factors (e.g. perceptual abilities, tolerance to chemical defences, and individual motivation), suggests that the role of predators is more complicated than previously appreciated. With complex selection regimes at work, polytypisms and polymorphisms may even occur in Müllerian mimicry systems. Meanwhile, phenotypes are often multifunctional, and thus subject to additional biotic and abiotic selection pressures. Some of these selective pressures, primarily sexual selection and thermoregulation, have received considerable attention, while others, such as disease risk and parental effects, offer promising avenues to explore. As well as reviewing the existing evidence from both empirical studies and theoretical modelling, we highlight hypotheses that could benefit from further investigation in aposematic species. Finally by collating known instances of variation in warning signals, we provide a valuable resource for understanding the taxonomic spread of diversity in aposematic signalling and with which to direct future research. A greater appreciation of the extent of variation in aposematic species, and of the selective pressures and constraints which contribute to this once‐paradoxical phenomenon, yields a new perspective for the field of aposematic signalling.

BackgroundToxoplasma gondii is found on all continents and can infect all endothermic vertebrates. Toxoplasmosis is a globally important zoonosis with potentially devastating health impacts both for humans and a range of domestic and wild species. The World Health Organisation have repeatedly recommended the collection of accurate epidemiological data for T. gondii, yet despite recognised links between infection of wildlife, domestic animals and humans, seroprevalence in wild species is rarely monitored. Here, serological investigation using the Gold Standard Sabin-Feldman Dye Test was used to test for T. gondii in Eurasian otters (Lutra lutra) found dead, mainly as road-kill, in England and Wales. This is the first spatially widespread study of T. gondii in UK wildlife, and the first extensive survey of T. gondii in Eurasian otters, a sentinel species of fresh waters.FindingsInfection was both common (39.5% prevalence, n = 271) and widespread, with significantly more infection in the east than the west of the UK. There was an increase in seroprevalence with age, but no sex bias.ConclusionsThe relatively high prevalence of T. gondii in a predominantly piscivorous freshwater mammal suggests widespread faecal contamination of freshwater ecosystems with oocysts. Continued surveillance of the Eurasian otter for T. gondii is valuable because of conservation concerns due to the otter’s ‘near threatened’ status on the IUCN Red List and because of the host’s role as a sentinel for freshwater health.

Pharmacophagy involves the sequestration of specialised plant metabolites for non-nutritive purposes and commonly occurs in insects. Here we investigate pharmacophagy in the turnip sawfly, Athalia rosae, where adults not only collect specialised metabolites (clerodanoids) from a plant (Ajuga reptans), but also from the exterior of conspecifics via fighting. Using behavioural assays, chemical analytics, and RNAseq we show that when individuals nibble on conspecifics that have already acquired clerodanoids from A. reptans leaves, this nibbling results in the transfer of compounds between individuals. Furthermore, unlike other pharmacophagous insects, the acquisition of clerodanoids by A. rosae from the leaves of A. reptans does not induce the upregulation of known detoxification or sequestration genes and pathways. In contrast, pharmacophagous nibbling on conspecifics results in the upregulation of metabolic pathways associated with elevated metabolic rates and increased energy consumption. It therefore seems that individuals attack conspecifics to acquire clerodanoids despite the apparent metabolic costs of this form of pharmacophagy compared to clerodanoid uptake from a plant. Changes in the metabolic phenotype of A.rosae individuals consequently has profound consequences for social interactions with possible ramifications for their social niche.

Individuals of the same species, population and generation frequently exhibit sub maximal and significant genetic and phenotypic variation in their rate of development, showing slow and fast developers. Fast developers commonly have higher foraging and predation rates than slow developers.The consequence of such differences and foraging for the efficacy of biocontrol species remains underexplored.Slow and fast developers from a population of the ladybird, Propylea dissecta were separated and selected experimentally for F15 generations, and the predatory response of fourth instar larvae of control and experimentally selected slow and fast developers was then assessed at differing levels of prey (pea aphid, Acyrthosiphon pisum) and conspecific predator abundance. All individuals, whether slow or fast developers, showed a Type-II functional response, decrease in proportion of prey consumed with increasing prey biomass, and an increase in proportion of prey consumed with increasing predator density.The proportion of prey consumed was highest in experimental fast developers and lowest in experimental slow developers. Attack rate was highest and handling time longest in slow developers of control/experimental groups. Mutual interference was least while area of discovery was highest in experimental fast developers. Thus, selection of fast developers for F15 generations led to higher functional responses, slower attackrates, and faster prey consumption. Thislower mutual interference and high searching efficiency indicates that they can be experimentally selected and used for better control of the pea aphids. This study is the first attempt to evaluate predatory responses of selected lines of an aphidophagous ladybird.