Displaying in the dark: light-dependent alternative mating tactics in the Alpine newt

Cross-Latitude Behavioural Axis in an Adult Damselfly Calopteryx splendens (Harris, 1780)

Simple Summary

Animals adapt to the environment they live in. If the environment changes, animals usually adapt behaviourally as a first response. By studying behavioural profiles across long distances, we can detect environmental change reflected in shifts in behavioural profiles. This study examined variation in three behavioural axes: activity, courtship and boldness, and the association between these behaviours, i.e., behavioural syndromes, across three damselfly populations along a latitudinal gradient (i.e., climatic gradient). Our study organism was the temperate damselfly Calopteryx splendens. We predicted that behavioural expressions would gradually increase from southern to northern regions. This is because northern animals should compensate behaviourally for a brief and cold breeding season (i.e., time constraint). Activity was the only behaviour feature positively associated with latitudinal gradient. Courtship effort was highest in the central region, whereas boldness values were highest in the north but did not differ between central and south. In the southern region, an activity–boldness and a courtship—boldness syndrome were present, and in the northern region, only an activity–boldness syndrome was found. Our results confirm that environmental variability in biotic and abiotic factors across studied latitudes generates regional differences in behavioural profiles, which do not always follow latitudinal gradient.

Abstract

Behavioural variation is important for evolutionary and ecological processes, but can also be useful when predicting consequences of climate change and effects on species ranges. Latitudinal differences in behaviour have received relatively limited research interest when compared to morphological, life history and physiological traits. This study examined differences in expression of three behavioural axes: activity, courtship and boldness, and their correlations, along a European latitudinal gradient spanning ca. 1500 km. The study organism was the temperate damselfly Calopteryx splendens (Harris). We predicted that the expression of both behavioural traits and behavioural syndromes would be positively correlated to latitude, with the lowest values in the southern populations, followed by central and the highest in the north, because animals usually compensate behaviourally for increasing time constraints and declining environmental conditions. We found that behavioural expression varied along the latitudinal cline, although not always in the predicted direction. Activity was the only behaviour that followed our prediction and gradually increased northward. Whereas no south-to-north gradient was seen in any of the behavioural syndromes. The results, particularly for activity, suggest that climatic differences across latitudes change behavioural profiles. However, for other traits such as courtship and boldness, local factors might invoke stronger selection pressures, disrupting the predicted latitudinal pattern.

Ecology and extent of freshwater browning - What we know and what should be studied next in the context of global change

Water browning or brownification refers to increasing water color, often related to increasing dissolved organic matter (DOM) and carbon (DOC) content in freshwaters. Browning has been recognized as a significant physicochemical phenomenon altering boreal lakes, but our understanding of its ecological consequences in different freshwater habitats and regions is limited. Here, we review the consequences of browning on different freshwater habitats, food webs and aquatic-terrestrial habitat coupling. We examine global trends of browning and DOM/DOC, and the use of remote sensing as a tool to investigate browning from local to global scales. Studies have focused on lakes and rivers while seldom addressing effects at the catchment scale. Other freshwater habitats such as small and temporary waterbodies have been overlooked, making the study of the entire network of the catchment incomplete. While past research investigated the response of primary producers, aquatic invertebrates and fishes, the effects of browning on macrophytes, invasive species, and food webs have been understudied. Research has focused on freshwater habitats without considering the fluxes between aquatic and terrestrial habitats. We highlight the importance of understanding how the changes in one habitat may cascade to another. Browning is a broader phenomenon than the heretofore concentration on the boreal region. Overall, we propose that future studies improve the ecological understanding of browning through the following research actions: 1) increasing our knowledge of ecological processes of browning in other wetland types than lakes and rivers, 2) assessing the impact of browning on aquatic food webs at multiple scales, 3) examining the effects of browning on aquatic-terrestrial habitat coupling, 4) expanding our knowledge of browning from the local to global scale, and 5) using remote sensing to examine browning and its ecological consequences.

Alpine Newts (Ichthyosaura alpestris) Avoid Habitats Previously Used by Parasite-Exposed Conspecifics

Many organisms avoid habitats posing risks of parasitism. Parasites are not generally conspicuous, however, which raises the question of what cues individuals use to detect parasitism risk. Here, we provide evidence in alpine newts (Ichthyosaura alpestris) that non-visual cues from parasite-exposed conspecifics inform habitat avoidance. Alpine newts breed in aquatic habitats and occasionally move among adjacent terrestrial habitat during breeding seasons. We completed experiments with newts whereby individuals had access to both habitats, and the aquatic habitats varied in prior occupancy by conspecifics with different histories of exposure to the parasitic skin fungus, Batrachochytrium dendrobatidis (Bd). Continuous filming of newt activity for 2 days provided little evidence that prior use of aquatic habitats by conspecifics, regardless of their Bd exposure history, immediately influenced newt habitat use. However, newts that encountered aquatic habitats used specifically by Bd-exposed conspecifics on day 1 spent less time aquatic on day 2, whereas other newts did not alter habitat use. Responses could have been elicited by cues generated by Bd stages on the conspecifics or, perhaps more likely, cues emitted by the conspecifics themselves. In either case, these observations suggest that newts use non-visual cues sourced from exposed conspecifics to detect Bd risk and that those cues cause newts to avoid aquatic habitats. Bd may therefore influence host behavior in early phases of interactions, and possibly before any contact with infectious stages is made, creating potential for non-consumptive effects.

Brain size affects responsiveness in mating behaviour to variation in predation pressure and sex ratio

Despite ongoing advances in sexual selection theory, the evolution of mating decisions remains enigmatic. Cognitive processes often require simultaneous processing of multiple sources of information from environmental and social cues. However, little experimental data exist on how cognitive ability affects such fitness-associated aspects of behaviour. Using advanced tracking techniques, we studied mating behaviours of guppies artificially selected for divergence in relative brain size, with known differences in cognitive ability, when predation threat and sex ratio was varied. In females, we found a general increase in copulation behaviour in when the sex ratio was female biased, but only large-brained females responded with greater willingness to copulate under a low predation threat. In males, we found that small-brained individuals courted more intensively and displayed more aggressive behaviours than large-brained individuals. However, there were no differences in female response to males with different brain size. These results provide further evidence of a role for female brain size in optimal decision-making in a mating context. In addition, our results indicate that brain size may affect mating display skill in male guppies. We suggest that it is important to consider the association between brain size, cognitive ability and sexual behaviour when studying how morphological and behavioural traits evolve in wild populations.

Living in the dark does not mean a blind life: bird and mammal visual communication in dim light

For many years, it was believed that bird and mammal communication 'in the dark of the night' relied exclusively on vocal and chemical signalling. However, in recent decades, several case studies have conveyed the idea that the nocturnal world is rich in visual information. Clearly, a visual signal needs a source of light to work, but diurnal light (twilight included, i.e. any light directly dependent on the sun) is not the only source of luminosity on this planet. Actually, moonlight represents a powerful source of illumination that cannot be neglected from the perspective of visual communication. White patches of feathers and fur on a dark background have the potential to be used to communicate with conspecifics and heterospecifics in dim light across different contexts and for a variety of reasons. Here: (i) we review current knowledge on visual signalling in crepuscular and nocturnal birds and mammals; and (ii) we also present some possible cases of birds and mammals that, due to the characteristics of their feather and fur coloration pattern, might use visual signals in dim light. Visual signalling in nocturnal animals is still an emerging field and, to date, it has received less attention than many other means of communication, including visual communication under daylight. For this reason, many questions remain unanswered and, sometimes, even unasked.This article is part of the themed issue 'Vision in dim light'.

Sexual selection on wing interference patterns in Drosophila melanogaster

Animals with color vision use color information in intra- and interspecific communication, which in turn may drive the evolution of conspicuous colored body traits via natural and sexual selection. A recent study found that the transparent wings of small flies and wasps in lower-reflectance light environments display vivid and stable structural color patterns, called "wing interference patterns" (WIPs). Such WIPs were hypothesized to function in sexual selection among small insects with wing displays, but this has not been experimentally verified. Here, to our knowledge we present the first experimental evidence that WIPs in males of Drosophila melanogaster are targets of mate choice from females, and that two different color traits--saturation and hue--experience directional and stabilizing sexual selection, respectively. Using isogenic lines from the D. melanogaster Genetic Reference Panel, we compare attractiveness of different male WIPs against black and white visual backgrounds. We show that males with more vivid wings are more attractive to females than are males with dull wings. Wings with a large magenta area (i.e., intermediate trait values) were also preferred over those with a large blue or yellow area. These experimental results add a visual element to the Drosophila mating array, integrating sexual selection with elements of genetics and evo-devo, potentially applicable to a wide array of small insects with hyaline wings. Our results further underscore that the mode of sexual selection on such visual signals can differ profoundly between different color components, in this case hue and saturation.

Sex differences in ventral side colouration of Alpine newts

Sexual selection based on visual stimuli was recently studied in several amphibian species with permanent or temporary dichromatism. The Alpine newt (Ichthyosaura alpestris) is a Caudate species with prominent sexual dichromatism during the breeding period. We focused on the intersexual differences in the orange, carotenoid-base ventral colouration of this widespread European species. We used an image analysis approach to compare the content of the red colour and saturation of the belly in 80 male and 62 female aquatic adult newts captured during spring migration in two localities in the Czech Republic. Both studied colour parameters of the ventral side of the Alpine newt are connected with sex. Males have significantly higher values of saturation on both localities, but the relationship with red content was not so clear. Individual characteristics (body condition, body length) affect colour variables of males and females similarly. Effect of body condition on colour variables was not demonstrated. Therefore we presume that the pronounced colouration of males is a cue facilitating detection, localisation or interspecies identification, rather than a direct component of male quality as assessed by females.

Introduced goldfish affect amphibians through inhibition of sexual behaviour in risky habitats: an experimental approach

The introduction of alien species is one of the major causes of current and global biodiversity loss. The introduction of fish can be a particular threat to native amphibian populations, which are declining worldwide. One way for amphibians to persist in such altered environments is to adopt anti-predator strategies especially at the behavioural level. However, although it has been shown that avoidance behaviour may decrease the probability of being detected by a potential predator, little is known on the consequences on sexual behaviour. In this study, we tested the hypothesis that adult Alpine newts (Ichthyosaura alpestris) use shelters more often and exhibit less sexual activity in the presence of goldfish (Carassius auratus) and that they reduce sexual activity more in risky micro-habitats than in safe environments. To this end, we assessed behavioural patterns of adult newts in a replicated laboratory design. Goldfish were present in direct contact with newts in half of the tanks. Consistently throughout the study period, significantly more newts used shelter in the presence of fish than in their absence. Newts also significantly decreased their sexual activity level overall, but specially outside the shelter when they were in direct contact with fish. These results show that fish presence can affect newts in complex ways, such as through inhibition of their reproduction. Our work highlights that integrating behaviour in conservation studies is essential to understanding the patterns of coexistence and exclusion between introduced fish and amphibians.

Love is blind: indiscriminate female mating responses to male courtship pheromones in newts (Salamandridae)

Internal fertilization without copulation or prolonged physical contact is a rare reproductive mode among vertebrates. In many newts (Salamandridae), the male deposits a spermatophore on the substrate in the water, which the female subsequently takes up with her cloaca. Because such an insemination requires intense coordination of both sexes, male newts have evolved a courtship display, essentially consisting of sending pheromones under water by tail-fanning towards their potential partner. Behavioral experiments until now mostly focused on an attractant function, i.e. showing that olfactory cues are able to bring both sexes together. However, since males start their display only after an initial contact phase, courtship pheromones are expected to have an alternative function. Here we developed a series of intraspecific and interspecific two-female experiments with alpine newt (Ichthyosaura alpestris) and palmate newt (Lissotriton helveticus) females, comparing behavior in male courtship water and control water. We show that male olfactory cues emitted during tail-fanning are pheromones that can induce all typical features of natural female mating behavior. Interestingly, females exposed to male pheromones of their own species show indiscriminate mating responses to conspecific and heterospecific females, indicating that visual cues are subordinate to olfactory cues during courtship.

Asymmetric female preferences for courtship pheromones in two closely-related newt species, the smooth newt (Lissotriton vulgaris) and the Carpathian newt (L. montandoni) (Salamandridae)

The smooth (Lissotriton vulgaris) and Carpathian (L. montandoni) newts are sister species. These are separated by a moderate genetic distance, but exhibit striking morphological differences, especially in male epigamic traits. In the areas where they co-occur, they readily mate with each other and produce viable hybrids. However, a high level of pre-zygotic isolation with an unknown behavioral basis has been reported. The complex courtship of newts consists of at least three types of modality: chemical, visual, and tactile. The relative significance of these in mate choice is unclear, but it is commonly accepted that pheromones are an important communication channel. The goal of this study was to determine whether the females of L. vulgaris and L. montandoni exhibit preferences for conspecific extracts from the pheromone-producing abdominal (dorsal) glands. Females of both species spent more time in proximity to the source of the abdominal gland extracts of their own species when a liver extract was presented as an alternative. In a second trial, females were simultaneously confronted with conspecific and heterospecific abdominal gland extracts. Asymmetric preferences were found. Lissotriton vulgaris females were not selective, whereas L. montandoni females preferred the conspecific abdominal gland extract. This finding is consistent with the results of earlier experiments on mate choice in these species. The results strongly indicate that pheromones play a crucial role in courtship and species recognition in this pair of closely related, hybridizing species.