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Abstract Circadian rhythms are ubiquitous in nature and endogenous circadian clocks drive the daily expression of many fitness-related behaviors. However, little is known about whether such traits are targets of selection imposed by natural enemies. In Hawaiian populations of the nocturnally active Pacific field cricket (Teleogryllus oceanicus), males sing to attract mates, yet sexually selected singing rhythms are also subject to natural selection from the acoustically orienting and deadly parasitoid fly, Ormia ochracea. Here, we use T. oceanicus to test whether singing rhythms are endogenous and scheduled by circadian clocks, making them possible targets of selection imposed by flies. We also develop a novel audio-to-circadian analysis pipeline, capable of extracting useful parameters from which to train machine learning algorithms and process large quantities of audio data. Singing rhythms fulfilled all criteria for endogenous circadian clock control, including being driven by photoschedule, self-sustained periodicity of approximately 24 h, and being robust to variation in temperature. Furthermore, singing rhythms varied across individuals, which might suggest genetic variation on which natural and sexual selection pressures can act. Sexual signals and ornaments are well-known targets of selection by natural enemies, but our findings indicate that the circadian timing of those traits’ expression may also determine fitness. 

1. Primary succession after a volcanic eruption is a major ecological process, but relatively little is known about insects that colonise barren lava before plants become established. 2. On Hawai'i Island, the endemic cricket,Caconemobius foriGurney & Rentz, 1978, is known as the first multicellular life form to colonise lava after an eruption from Kīlauea Volcano. In the Kona region, a congener,Caconemobius anahuluOtte, 1994 inhabits unvegetated lava flows from Hualālai Volcano, but little has been documented about its distribution. 3. Our aim was to characterise the presence/absence ofCaconemobiusspp.across lava flows that are largely unvegetated, but differ in age since eruption and connectivity to older flows. We used baited live traps to survey 9 month–50 year‐old Kīlauea lava flows forC. fori, and ∼220 year‐old Hualālai lava flows forC. anahulu. 4. We found no evidence thatC. forihas colonised the Kīlauea flows from the 2018 eruption. However, we did discover thatC. foriwas persistent and widespread on Kīlauea lava up to 50 years old within Hawai'i Volcanos National Park. We also capturedC. anahuluacross much of the Hualālai lava flows we surveyed in Kona. 5. We demonstrated thatC. forido not always arrive on new lava within months after an eruption, in contrast to previous reports, and that bothC. foriandC. anahulucan remain on lava longer than previously appreciated. Vegetation successional state may be more important than true age for the persistence of these endemic crickets. 

Abstract Migration can allow individuals to escape parasite infection, which can lead to a lower infection probability (prevalence) in a population and/or fewer parasites per individual (intensity). Because individuals with more parasites often have lower survival and/or fecundity, infection intensity shapes the life‐history trade‐offs determining when migration is favored as a strategy to escape infection. Yet, most theory relies on susceptible‐infected (SI) modeling frameworks, defining individuals as either healthy or infected, ignoring details of infection intensity. Here, we develop a novel modeling approach that captures infection intensity as a spectrum, and ask under what conditions migration evolves as function of how infection intensity changes over time. We show that relative timescales of migration and infection accumulation determine when migration is favored. We also find that population‐level heterogeneity in infection intensity can lead to partial migration, where less‐infected individuals migrate while more infected individuals remain resident. Our model is one of the first to consider how infection intensity can lead to migration. Our results frame migratory escape in light of infection intensity rather than prevalence, thus demonstrating that decreased infection intensity should be considered a benefit of migration, alongside other typical drivers of migration. 

Abstract Most studies on the evolution of migration focus on food, mates and/or climate as factors influencing these movements, whereas negative species interactions such as predators, parasites and pathogens are often ignored. Although infection and its associated costs clearly have the potential to influence migration, thoroughly studying these interactions is challenging without a solid theoretical framework from which to develop testable predictions in natural systems.Here, we aim to understand when parasites favour the evolution of migration.We develop a general model which enables us to explore a broad range of biological conditions and to capture population and infection dynamics over both ecological and evolutionary time‐scales.We show that when migration evolves depends on whether the costs of migration and infection are paid in reduced fecundity or survival. Also important are the parasite transmission mode and spatiotemporal dynamics of infection and recovery (if it occurs). Finally, we find that partial migration (where only a fraction of the population migrates) can evolve but only when parasite transmission is density‐dependent.Our results highlight the critical, if overlooked, role of parasites in shaping long‐distance movement patterns, and suggest that infection should be considered alongside more traditional drivers of migration in both empirical and theoretical studies.