Carry-over effect of artificial light at night on daytime mating activity in an ecologically important detritivore, the amphipod Gammarus pulex.

Artificial light at night (ALAN) is a growing environmental problem influencing the fitness of individuals through effects on their physiology and behaviour. Research on animals has primarily focused on effects on behaviour during the night, whereas less is known about effects transferred to daytime. Here, we investigated in the lab the impact of ALAN on the mating behaviour of an ecologically important freshwater amphipod, Gammarus pulex, during both daytime and nighttime. We manipulated the presence of ALAN and the intensity of male-male competition for access to females, and found the impact of ALAN on mating activity to be stronger during daytime than during nighttime, independent of male-male competition. At night, ALAN only reduced the probability of precopula pair formation, while during the daytime, it both decreased general activity and increased the probability of pair separation after pair formation. Thus, ALAN reduced mating success in G. pulex not only directly, through effects on mating behaviour at night, but also indirectly through a carry-over effect on daytime activity and the ability to remain in precopula. These results emphasise the importance of considering delayed effects of ALAN on organisms, including daytime activities that can be more important fitness determinants than nighttime activities.

Behavioural responses of fishes to anthropogenic disturbances: Adaptive value and ecological consequences.

Aquatic ecosystems are changing at an accelerating rate because of human activities. The changes alter the abundance and distribution of fishes, with potential consequences for ecosystem structure and function. Behavioural responses often underlie these changes in population dynamics, such as altered habitat choice or foraging activity. Here, we present a framework for understanding how and why behaviour is affected by human activities and how the behavioural responses in turn influence higher ecological levels. We further review the literature to assess the present state of the field and identify gaps in our knowledge. We begin with discussing the factors that determine how an individual responds to a change in the environment and whether the response is adaptive or not. In particular, we explain the importance of the evolutionary history of the species. We then search the literature to assess our current knowledge of the impact of human disturbances on the behaviour of fishes and the consequences for ecosystems. The search reveals that much attention has been directed to the impact of human activities on the behaviour of fishes, but that worryingly little is known about the consequences of these responses for populations, communities and ecosystems. Yet, behavioural responses can have profound ecological consequences given that behaviour underly many, if not most, species interactions. Thus, more attention should be paid to the mechanisms and pathways through which behavioural responses influence higher ecological levels. Such information is needed if we are to determine the ultimate effects of human activities on biodiversity and the function and stability of aquatic ecosystems.

Delayed early life effects in the threespine stickleback.

Early life conditions can have a decisive influence on viability later in life. However, the influence of embryo density within a nest or body cavity on subsequent viability has received little attention within an ecological setting. This is surprising given that embryos often compete for limited resources, such as nutrients and oxygen, and this could influence their viability later in life through carry-over and compensatory effects. We show that the density of fertilized eggs within the nests of threespine stickleback males (Gasterosteus aculeatus) influences their viability after hatching. Embryos from larger broods hatch earlier and at a smaller size than those from smaller broods, which reduces their survival until the age of four weeks. This indicates a trade-off between the number and viability of offspring that males can raise to the hatching stage, which could explain the high incidence of partial egg cannibalism in nest-brooding fishes-as a strategy to improve the survival of remaining offspring. These results highlight the importance of considering conditions at the embryonic stage when evaluating the impact of early life conditions on viability and the adaptive value of reproductive decisions.

The importance of considering the duration of extreme temperatures when investigating responses to climate change.

The frequency and duration of heatwaves are increasing because of human activities. To cope with the changes, species with longer generation times may have to rely on plastic responses. The probability that their responses are adaptive is higher if the species have experienced temperature fluctuations also in their evolutionary past. However, experimental studies investigating responses to heatwaves often use exposure times that are significantly shorter than recent heatwaves. We show that this can lead to faulty conclusions and that the duration of higher temperature has to be considered in experimental designs. We recorded the response of threespine stickleback to prolonged duration of higher temperature during the breeding season, using a population that has experienced large fluctuations in temperature in its past and, hence, is expected to endure temperature changes well. We found males to adaptively adjust their reproductive behaviours to short periods of higher temperature, but not to longer periods that extended across two breeding cycles. Males initially increased their reproductive activities-nest building, courtship and parental care-which ensured high reproductive success during the first breeding cycle, but decreased their reproductive activities during the second breeding cycle when exposed to sustained high temperature. This reduced their courtship success and resulted in fewer offspring. Thus, a species expected to cope well with higher temperature suffers fitness reductions when the duration of high temperature is prolonged. The results stress the importance of considering the duration of extreme environmental conditions when investigating the impact that human activities have on species. Responses to short-term exposures cannot be extrapolated to assess responses to longer periods of extreme conditions.

No strong associations between temperature and the host-parasite interaction in wild stickleback.

As climate change progresses, thermal stress is expected to alter the way that host organisms respond to infections by pathogens and parasites, with consequences for the fitness and therefore population processes of both host and parasite. The authors used a correlational natural experiment to examine how temperature differences shape the impact of the cestode parasite Schistocephalus solidus on its host, the three-spined stickleback (Gasterosteus aculeatus). Previous laboratory work has found that high temperatures benefit S. solidus while being detrimental to the stickleback. The present study sought to emulate this design in the wild, repeatedly sampling naturally infected and uninfected fish at matched warmer and cooler locations in the Baltic Sea. In this wild study, the authors found little evidence that temperature was associated with the host-parasite interaction. Although infection reduced host condition and reproductive status overall, these effects did not vary with temperature. Host fitness indicators correlated to some extent with temperature, with cooler capture sites associated with larger size but warmer sites with improved reproductive potential. Parasite fitness (prevalence or size) was not correlated with temperature at the capture site. These mismatches between laboratory and field outcomes illustrate how findings from well-controlled laboratory experiments may not fully reflect processes in more variable natural settings. Nonetheless, the findings of this study indicate that temperature can influence host fitness regardless of infection, with potential consequences for both host demography and parasite transmission dynamics in this complex system.

Reproduction under light pollution: maladaptive response to spatial variation in artificial light in a glow-worm.

The amount of artificial light at night is growing worldwide, impacting the behaviour of nocturnal organisms. Yet, we know little about the consequences of these behavioural responses for individual fitness and population viability. We investigated if females of the common glow-worm Lampyris noctiluca-which glow in the night to attract males-mitigate negative effects of artificial light on mate attraction by adjusting the timing and location of glowing to spatial variation in light conditions. We found females do not move away from light when exposed to a gradient of artificial light, but delay or even refrain from glowing. Further, we demonstrate that this response is maladaptive, as our field study showed that staying still when exposed to artificial light from a simulated streetlight decreases mate attraction success, while moving only a short distance from the light source can markedly improve mate attraction. These results indicate that glow-worms are unable to respond to spatial variation in artificial light, which may be a factor in their global decline. Consequently, our results support the hypothesis that animals often lack adaptive behavioural responses to anthropogenic environmental changes and underlines the importance of considering behavioural responses when investigating the effects of human activities on wildlife.

Environmental change disrupts communication and sexual selection in a stickleback population.

Environmental change that disrupts communication during mate choice and alters sexual selection could influence population dynamics. Yet little is known about such long-term effects. We investigated experimentally the consequences that disrupted visual communication during mate choice has for the quantity and viability of offspring produced in a threespine stickleback population (Gasterosteus aculeatus). We further related the results to long-term monitoring of population dynamics in the field to determine if changes are apparent under natural conditions. The results show that impaired visual communication because of algal blooms reduces reliability of male visual signals as indicators of offspring survival during their first weeks of life. This relaxes sexual selection but has no effect on the number of offspring hatching, as most males have a high hatching success in turbid water. Despite eutrophication and high turbidity levels that interfere with communication during mate choice, the population has grown during recent decades. Large numbers of offspring hatching, combined with high variation in juvenile fitness, has probably shifted selection to later life history stages and maintained a viable population. Together with reduced cost of sexual selection and ongoing ecosystem changes caused by human activities, this could have promoted population growth. These results point to the complexity of ecosystems and the necessity to consider all influencing factors when attempting to understand impacts of human activities on populations.

The sexual selection paradigm: have we overlooked other mechanisms in the evolution of male ornaments?

Extravagant male ornaments expressed during reproduction are almost invariably assumed to be sexually selected and evolve through competition for mating opportunities. Yet in species where male reproductive success depends on the defence of offspring, male ornaments could also evolve through social competition for offspring survival. However, in contrast to female ornaments, this possibility has received little attention in males. We show that a male ornament that is traditionally assumed to be sexually selected--the red nuptial coloration of the three-spined stickleback--is under stronger selection for offspring survival than for mating success. Males express most coloration during parenting, when they no longer attract females, and the colour correlates with nest retention and hatching success but not with attractiveness to females. This contradicts earlier assumptions and suggests that social selection for offspring survival rather than for sexual selection for mating success is the main mechanism maintaining the ornament in the population. These results suggest that we should consider other forms of social selection beyond sexual selection when seeking to explain the function and evolution of male ornaments. An incorrect assignment of selection pressures could hamper our understanding of evolution.

I'm sexy and I glow it: female ornamentation in a nocturnal capital breeder.

In many species, males rely on sexual ornaments to attract females. Females, by contrast, rarely produce ornaments. The glow-worm (Lampyris noctiluca) is an exception where wingless females glow to attract males that fly in search of females. However, little is known about the factors that promote the evolution of female ornaments in a sexual selection context. Here, we investigated if the female ornament of the glow-worm is a signal of fecundity used in male mate choice. In support of this, we found brightness to correlate with female fecundity, and males to prefer brighter dummy females. Thus, the glow emitted by females is a reliable sexual signal of female fecundity. It is likely that male preference for the fecundity-indicating ornament has evolved because of large variation among females in fecundity, and because nocturnal males cannot directly assess female size and fecundity. These results indicate that female ornamentation may evolve in capital breeders (i.e. those in which stored resources are invested in reproduction) when females vary significantly in fecundity and this variation cannot be assessed directly by males.

Human-induced eutrophication maintains high parasite prevalence in breeding threespine stickleback populations.

Anthropogenic activities are having profound impacts on species interactions, with further consequences for populations and communities. We investigated the influence that anthropogenic eutrophication has on the prevalence of the parasitic tapeworm Schistocephalus solidus in threespine stickleback Gasterosteus aculeatus populations. We caught stickleback from four areas along the coast of Finland, and within each area from one undisturbed and one eutrophied habitat. We found the prevalence of the parasite to be lower in the eutrophied habitats at the start of the breeding season, probably because of fewer piscivorous birds that transmit the parasite. However, while the prevalence of the parasite declined across the season in the undisturbed habitat, it did less so in eutrophied habitats. We discuss different processes that could be behind the differences, such as lower predation rate on infected fish, higher food availability and less dispersal in eutrophied habitats. We found no effect of eutrophication on the proportion of infected stickleback that entered reproductive condition. Together with earlier findings, this suggests that eutrophication increases the proportion of infected stickleback that reproduce. This could promote the evolution of less parasite resistant populations, with potential consequences for the viability of the interacting parties of the host-parasite system.

Indirect effects of human-induced environmental change on offspring production mediated by behavioural responses.

Human-induced rapid environmental changes often cause behavioural alterations in animals. The consequences that these alterations in turn have for the viability of populations are, however, poorly known. We used a population of threespine sticklebacks Gasterosteus aculeatus in the Baltic Sea to investigate the consequences of behavioural responses to human-induced eutrophication for offspring production. The investigated population has been growing during the last decades, and one cause could be increased offspring production. We combined field-based surveys with laboratory-based experiments, and found that an enhanced growth of macroalgae relaxed agonistic interactions among males. This allowed more males to nest, improved hatching success, and increased the number of reproductive cycles that males completed. Thus, the behavioural responses were adaptive at the individual level and increased offspring production. However, a larger proportion of small males of low competitive ability reproduced in dense vegetation. As male size and dominance are heritable, this could influence the genetic composition of the offspring. Together with a higher number of offspring produced, this could influence natural selection and the rate of adaptation to the changing environment. Thus, behavioural responses to a rapid human-induced environmental change can influence offspring production, with potential consequences for population dynamics and evolutionary processes.

How does human-induced environmental change influence host-parasite interactions?

Host-parasite interactions are an integral part of ecosystems that influence both ecological and evolutionary processes. Humans are currently altering environments the world over, often with drastic consequences for host-parasite interactions and the prevalence of parasites. The mechanisms behind the changes are, however, poorly known. Here, we explain how host-parasite interactions depend on two crucial steps--encounter rate and host-parasite compatibility--and how human activities are altering them and thereby host-parasite interactions. By drawing on examples from the literature, we show that changes in the two steps depend on the influence of human activities on a range of factors, such as the density and diversity of hosts and parasites, the search strategy of the parasite, and the avoidance strategy of the host. Thus, to unravel the mechanisms behind human-induced changes in host-parasite interactions, we have to consider the characteristics of all three parts of the interaction: the host, the parasite and the environment. More attention should now be directed to unfold these mechanisms, focusing on effects of environmental change on the factors that determine encounter rate and compatibility. We end with identifying several areas in urgent need of more investigations.

Coping with light pollution in urban environments: Patterns and challenges.

Artificial light at night is a growing environmental problem that is especially pronounced in urban environments. Yet, impacts on urban wildlife have received scant attention and patterns and consequences are largely unknown. Here, I present a conceptual framework outlining the challenges species encounter when exposed to urban light pollution and how they may respond through plastic adjustments and genetic adaptation. Light pollution interferes with biological rhythms, influences behaviors, fragments habitats, and alters predation risk and resource abundance, which changes the diversity and spatiotemporal distribution of species and, hence, the structure and function of urban ecosystems. Furthermore, light pollution interacts with other urban disturbances, which can exacerbate negative effects on species. Given the rapid growth of urban areas and light pollution and the importance of healthy urban ecosystems for human wellbeing, more research is needed on the impacts of light pollution on species and the consequences for urban ecosystems.

Leveraging AI to improve evidence synthesis in conservation.

Systematic evidence syntheses (systematic reviews and maps) summarize knowledge and are used to support decisions and policies in a variety of applied fields, from medicine and public health to biodiversity conservation. However, conducting these exercises in conservation is often expensive and slow, which can impede their use and hamper progress in addressing the current biodiversity crisis. With the explosive growth of large language models (LLMs) and other forms of artificial intelligence (AI), we discuss here the promise and perils associated with their use. We conclude that, when judiciously used, AI has the potential to speed up and hopefully improve the process of evidence synthesis, which can be particularly useful for underfunded applied fields, such as conservation science.

The color of artificial light affects mate attraction in the common glow-worm.

Artificial light at night, often referred to as 'light pollution', is a global environmental problem that threatens many nocturnal organisms. One such species is the European common glow-worm (Lampyris noctiluca), in which reproduction relies on the ability of sedentary bioluminescent females to attract flying males to mate. Previous studies show that broad-spectrum white artificial light interferes with mate attraction in this beetle. However, much less is known about wavelength-specific effects. In this study, we experimentally investigate how the peak wavelength (color) of artificial light affects glow-worm mate attraction success in the field by using dummy females that trap males landing to mate. Each dummy was illuminated from above by either a blue (peak wavelength: 452 nm), white (449 nm), yellow (575 nm), or red (625 nm) LED lighting, or light switched off in the control. We estimated mate attraction success as both the probability of attracting at least one male and the number of males attracted. In both cases, mate attraction success depended on the peak wavelength of the artificial light, with short wavelengths (blue and white) decreasing it more than long wavelengths (yellow and red). Hence, adjusting the spectrum of artificial light can be an effective measure for mitigating the negative effects of light pollution on glow-worm reproduction.

Habitat change alters the expression and efficiency of a female ornament.

Anthropogenic habitat changes are disrupting the mate choice process in a range of organisms, with consequences for populations and communities. Research has so far focused on male sexually selected traits and female mate choice, given their conspicuousness, whereas effects on female ornaments and male mate choice have been largely overlooked. Yet, females of many species develop ornaments that males use in mate choice. These ornaments can be costly and reduce female fecundity and viability and, hence, influence population growth rate. Thus, attention should be paid to changes in female ornaments and the consequences the changes have for populations. Here, we show that declining visibility in aquatic ecosystems reduces the investment of female three-spined stickleback in a melanin-based ornament in favor of increased mate search activity. The adjustment appears adaptive as males pay less attention to the ornament under poor visibility, and as melanin-based ornaments are generally physiologically costly. It is likely that past fluctuations in visibility have promoted the evolution of environment-dependent plasticity in female ornamentation. More attention should be paid to changes in female ornaments and their adaptive value, across taxa, given the impact that female investment in ornaments can have on fecundity and population growth rate. Environments are changing at an accelerating rate because of human activities and knowledge of the responses of both males and females is needed to evaluate and predict the ultimate impact on populations and biodiversity.

Phenotypic plasticity in courtship exposed to selection in a human-disturbed environment.

When environments change rapidly, evolutionary processes may be too slow to rescue populations from decline. Persistence then hinges on plastic adjustments of critical traits to the altered conditions. However, the degree to which species harbour the necessary plasticity and the degree to which the plasticity is exposed to selection in human-disturbed environments are poorly known. We show that a population of the threespine stickleback (Gasterosteus aculeatus) harbours variation in plasticity in male courtship behaviour, which is exposed to selection when visibility deteriorates because of enhanced algal growth. Females in clear water show no preference for plastic males, while females in algal-rich, turbid water switch their mate preference towards males with adaptive plasticity. Thus, while the plasticity is not selected for in the original clear water environment, it comes under selection in turbid water. However, much maladaptive plasticity is present in the population, probably because larger turbidity fluctuations have been rare in the past. Thus, the probability that the plasticity will improve the ability of the population to cope with human-induced increases in turbidity-and possibly facilitate genetic adaptation-depends on its prevalence and genetic basis. In conclusion, our results show that rapid human-induced environmental change can expose phenotypic plasticity to selection, but that much of the plasticity can be maladaptive, also when the altered conditions represent extremes of earlier encountered conditions. Thus, whether the plasticity will improve population viability remains questionable.

Mechanisms behind bottom-up effects: eutrophication increases fecundity by shortening the interspawning interval in stickleback.

Anthropogenic eutrophication is altering aquatic environments by promoting primary production. This influences the population dynamics of consumers through bottom-up effects, but the underlying mechanisms and pathways are not always clear. To evaluate and mitigate effects of eutrophication on ecological communities, more research is needed on the underlying factors. Here we show that anthropogenic eutrophication increases population fecundity in the threespine stickleback (Gasterosteus aculeatus) by increasing the number of times females reproduce-lifetime fecundity-rather than instantaneous fecundity. When we exposed females to nutrient-enriched waters with enhanced algal growth, their interspawning interval shortened but the size of their egg clutches, or the size of their eggs, did not change. The shortening of the interspawning interval was probably caused by higher food intake, as algae growth promotes the growth of preferred prey populations. Enhanced female lifetime fecundity could increase offspring production and, hence, influence population dynamics. In support of this, earlier studies show that more offspring are emerging in habitats with denser algae growth. Thus, our results stress the importance of considering lifetime fecundity, in addition to instantaneous fecundity, when investigating the impact of human-induced eutrophication on population processes. At a broader level, our results highlight the importance of following individuals over longer time spans when evaluating the pathways and processes through which environmental changes influence individual fitness and population processes.

Does competition allow male mate choosiness in threespine sticklebacks?

The theory of mate choice posits that intensified competition for mates can generate variation in either the strength or the direction of mate preferences within the competing sex. Here, we show that intensified male competition, manipulated through the operational sex ratio, induced differential mate choosiness among threespine stickleback males Gasterosteus aculeatus. In the absence of male competition, males were choosy independent of their condition when presented sequentially with a large and a small female. However, in a male-biased social setting, males in poor condition became indiscriminate, whereas good-condition males continued to be selective. Hence, competition induced condition-dependent mate choosiness. This was probably due to mating opportunities decreasing more for poor-condition than for good-condition males when competition intensified, resulting in condition-dependent cost of choice. Variation in condition and cost of choice could thus allow the persistence of male mate choosiness in populations experiencing intense male competition.

Mate choice in a changing world.

Human activities by altering environmental conditions are influencing the mate choice of animals. This is by impacts on: (i) the production and expression of traits evaluated by mate choosers; (ii) the transmission of information about potential mates to choosers; (iii) the reception and processing of the information by choosers; and (iv) the final mate choice. Here, I first discuss how these four stages of the mate-choice process can be altered by environmental change, and how these alterations, in turn, can influence individuals, populations, and communities. Much evidence exists for human-induced environmental changes influencing mate choice, but the consequences for the fitness of courters and choosers are less well known, and even less is known about the impact on population dynamics, species interactions and community composition. More evidence exists for altered mate-choice systems influencing interspecific matings and thereby community composition and biodiversity. I then consider whether plastic adjustments and evolutionary changes can rescue adaptive mate-choice systems, and reflect on the possibility of non-adaptive mate-choice systems becoming less maladaptive under environmental change. Much evidence exists for plastic adjustments of mate-choice systems, but whether these are adaptive is seldom known, as is the contribution of genetic changes. Finally, I contemplate the possibility of mate-choice systems rescuing populations from decline in changing environments. I explain how this is context dependent with both positive and negative outcomes possible. In summary, while much evidence exists for human-induced environmental changes influencing mate-choice systems, less is known about the consequences for ecological and evolutionary processes. Considering the importance that mate choice plays in determining individual fitness and population viability, the effects of environmental change on mate-choice systems should be considered in studies on the ecological and evolutionary consequences of human disturbances to habitats.