Computer animations of color markings reveal the function of visual threat signals in Neolamprologus pulcher

© The Author (2016). Visual signals, including changes in coloration and color patterns, are frequently used by animals to convey information. During contests, body coloration and its changes can be used to assess an opponent's state or motivation. Communication of aggressive propensity is particularly important in group-living animals with a stable dominance hierarchy, as the outcome of aggressive interactions determines the social rank of group members. Neolamprologus pulcher is a cooperatively breeding cichlid showing frequent within-group aggression. Both sexes exhibit two vertical black stripes on the operculum that vary naturally in shape and darkness. During frontal threat displays these patterns are actively exposed to the opponent, suggesting a signaling function. To investigate the role of operculum stripes during contests we manipulated their darkness in computer animated pictures of the fish. We recorded the responses in behavior and stripe darkness of test subjects to which these animated pictures were presented. Individuals with initially darker stripes were more aggressive against the animations and showed more operculum threat displays. Operculum stripes of test subjects became darker after exposure to an animation exhibiting a pale operculum than after exposure to a dark operculum animation, highlighting the role of the darkness of this color pattern in opponent assessment. We conclude that (i) the black stripes on the operculum of N. pulcher are a reliable signal of aggression and dominance, (ii) these markings play an important role in opponent assessment, and (iii) 2D computer animations are well suited to elicit biologically meaningful short-term aggressive responses in this widely used model system of social evolution

Individual behavioural responses of an intermediate host to a manipulative acanthocephalan parasite and the effects of intra-specific parasite competition

© 2018 Timo Thünken. Background: Parasites with complex life cycles depend on the ingestion of their intermediate host by the final host. To complete their life cycle successfully, parasites frequently manipulate the behaviour and appearance of the intermediate host. Within host–parasite systems, there is considerable variation in the intermediate host’s behavioural response to infection. Aim: Identify sources of parasite-induced variation in intermediate hosts’ traits by focusing on intra- and inter-individual variation in behavioural responses to parasitic manipulation, taking infection intensity – and thus parasitic competition – into account. Organism: The acanthocephalan parasite Polymorphus minutus, which alters the phototactic behaviour and activity of its intermediate host, Gammarus pulex, thereby increasing the probability of being eaten by the final host. Methods: We repeatedly examined the behaviour of individual G. pulex varying in intensity of infection with P. minutus from uninfected to multiple-infected. We analysed phototactic responses and activity. Results and conclusions: Individual gammarids differed in phototactic behaviour and in activity patterns, with repeatability ranging from 20% to 50%. Infected gammarids showed greater between-individual variation in phototaxis but not activity than uninfected gammarids. All uninfected gammarids were photophobic, whereas the phototactic behaviour of infected gammarids ranged from photophobia to photophilia. On average, multiple-infected gammarids were similarly photophobic as uninfected ones. Single-infected gammarids were less photophobic than uninfected and multiple-infected conspecifics. This suggests that intra-specific parasitic competition affects the manipulative abilities of parasites. Both groups of infected gammarids were on average less active than uninfected ones, and this effect was mainly driven by some infected individuals. In conclusion, behavioural variation of gammarids was caused both by individual differences in responses to manipulation/infection, and by the reduced manipulative capacities of parasites facing intra-specific competition

Four’s a crowd: social preferences for larger groups in golden mantella (Mantella aurantiaca) tadpoles

Group living results in various benefits and costs, which often depend on group size and ontogenetic state of the individual. Therefore, certain group sizes are favourable over others, often depending on individual age or intrinsic state. Under natural conditions many amphibians can be found in aggregations, especially during the larval stage. Yet, whether these aggregations are the result of active social preferences or are driven by environmental factors has only been tested in a limited number of taxa. This study explores social preferences and group size discrimination in golden mantella (Mantella aurantiaca) tadpoles. We gave tadpoles the choice between different numbers of conspecifics using a two-choice design. To test for general social tendency, tadpoles could either join a group of three or remain solitary (3 vs. 0). To test for group size preferences, we tested tadpoles in two different ratios: 2 vs. 1 and 4 vs. 2 conspecifics. We repeated the trials weekly until metamorphosis to determine potential shifts in preference through ontogeny. Tadpoles preferred being with a group over being alone, and the strength of this preference declined with increasing age. Furthermore, tadpoles preferred to be close to the larger of two groups. This preference was stronger in the 2 vs. 1 treatment. Mantella aurantiaca tadpoles, therefore, show clear social tendencies and possess the ability to spontaneously discriminate between group sizes. The lower preference at higher group sizes might indicate cognitive limitations or lower benefits of choosing the larger of two groups when overall group size is high. These findings are one of the few showing social preferences depending on group size in tadpoles and contribute to our understanding of social behaviour in amphibians in general

Task-dependent workload adjustment of female breeders in a cooperatively breeding fish

©The Author(s) 2017. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved. Parental investment affects the future survival and reproductive success of breeders. Therefore, breeders should optimize the amount of care they invest into the current offspring. In cooperative breeding systems, the amount of breeders' parental care is influenced by the behavior of brood-care helpers. Such workload adjustment is expected to depend on the task that needs to be fulfilled. While investment rules of breeders in respect to single tasks are well investigated in many bird and mammal species, little is known about behavioral adjustment of breeders when dealing with multiple tasks. Here, we examined the workload adjustment in multiple tasks of female breeders in the cooperatively breeding fish Neolamprologus obscurus. By combining behavioral observations with helper removal experiments in a wild population, we show that female territory defense and offspring care significantly decreased with increasing helper number. Furthermore, the workload invested in these tasks significantly increased after the removal of a helper, suggesting load-lightening effects in territory defense and offspring care. On the other hand, female territory maintenance behavior (i.e., excavating sand from the breeding shelter) did not correlate with helper number. While sand excavation significantly increased after the helper removal experiment, the size of the excavated stone area decreased after the helper removal in the recent study, suggesting that sand excavation may have additive effects for the breeders. These results demonstrate and underline the importance of task-dependent workload adjustment in cooperative breeders

Parasite-induced colour alteration of intermediate hosts increases ingestion by suitable final host species

© 2019 by The authors. Parasites with complex life cycles often alter the phenotypic appearance of their intermediate hosts in order to facilitate ingestion by the final host. However, such manipulation can be costly as it might increase ingestion by less suitable or dead-end hosts as well. Species-specific parasitic manipulation is a way to enhance the transmission to suitable final hosts. Here, we experimentally show that the altered body colouration of the intermediate host Gammarus pulex caused by its acanthocephalan parasite Pomphorhynchus laevis differently affects predation by different fish species (barbel, perch, ruffe, brown trout and two populations of three-spined stickleback) depending on their suitability to act as final host. Species that were responsive to colour manipulation in a predation experiment were more susceptible to infection with P. laevis than unresponsive species. Furthermore, three-spined stickleback from different populations responded to parasite manipulation in opposite directions. Such increased ingestion of the intermediate host by preferred and suitable hosts suggests fine-tuned adaptive parasitic manipulation and sheds light on the ongoing evolutionary arms race between hosts and manipulative parasites

Heritable Differences in Schooling Behavior among Threespine Stickleback Populations Revealed by a Novel Assay

Identifying the proximate and ultimate mechanisms of social behavior remains a major goal of behavioral biology. In particular, the complex social interactions mediating schooling behavior have long fascinated biologists, leading to theoretical and empirical investigations that have focused on schooling as a group-level phenomenon. However, methods to examine the behavior of individual fish within a school are needed in order to investigate the mechanisms that underlie both the performance and the evolution of schooling behavior. We have developed a technique to quantify the schooling behavior of an individual in standardized but easily manipulated social circumstances. Using our model school assay, we show that threespine sticklebacks (Gasterosteus aculeatus) from alternative habitats differ in behavior when tested in identical social circumstances. Not only do marine sticklebacks show increased association with the model school relative to freshwater benthic sticklebacks, they also display a greater degree of parallel swimming with the models. Taken together, these data indicate that marine sticklebacks exhibit a stronger tendency to school than benthic sticklebacks. We demonstrate that these population-level differences in schooling tendency are heritable and are shared by individuals within a population even when they have experienced mixed-population housing conditions. Finally, we begin to explore the stimuli that elicit schooling behavior in these populations. Our data suggest that the difference in schooling tendency between marine and benthic sticklebacks is accompanied by differential preferences for social vs. non-social and moving vs. stationary shelter options. Our study thus provides novel insights into the evolution of schooling behavior, as well as a new experimental approach to investigate the genetic and neural mechanisms that underlie this complex social behavior

Balancing the dilution and oddity effects: Decisions depend on body size

Background Grouping behaviour, common across the animal kingdom, is known to reduce an individual's risk of predation; particularly through dilution of individual risk and predator confusion (predator inability to single out an individual for attack). Theory predicts greater risk of predation to individuals more conspicuous to predators by difference in appearance from the group (the ‘oddity’ effect). Thus, animals should choose group mates close in appearance to themselves (eg. similar size), whilst also choosing a large group. Methodology and Principal Findings We used the Trinidadian guppy (Poecilia reticulata), a well known model species of group-living freshwater fish, in a series of binary choice trials investigating the outcome of conflict between preferences for large and phenotypically matched groups along a predation risk gradient. We found body-size dependent differences in the resultant social decisions. Large fish preferred shoaling with size-matched individuals, while small fish demonstrated no preference. There was a trend towards reduced preferences for the matched shoal under increased predation risk. Small fish were more active than large fish, moving between shoals more frequently. Activity levels increased as predation risk decreased. We found no effect of unmatched shoal size on preferences or activity. Conclusions and Significance Our results suggest that predation risk and individual body size act together to influence shoaling decisions. Oddity was more important for large than small fish, reducing in importance at higher predation risks. Dilution was potentially of limited importance at these shoal sizes. Activity levels may relate to how much sampling of each shoal was needed by the test fish during decision making. Predation pressure may select for better decision makers to survive to larger size, or that older, larger fish have learned to make shoaling decisions more efficiently, and this, combined with their size relative to shoal-mates, and attractiveness as prey items influences shoaling decisions

Evidence of adaptive evolutionary divergence during biological invasion

Rapid phenotypic diversification during biological invasions can either arise by adaptation to alternative environments or by adaptive phenotypic plasticity. Where experimental evidence for adaptive plasticity is common, support for evolutionary diversification is rare. Here, we performed a controlled laboratory experiment using full-sib crosses between ecologically divergent threespine stickleback populations to test for a genetic basis of adaptation. Our populations are from two very different habitats, lake and stream, of a recently invaded range in Switzerland and differ in ecologically relevant morphological traits. We found that in a lake-like food treatment lake fish grow faster than stream fish, resembling the difference among wild type individuals. In contrast, in a stream-like food treatment individuals from both populations grow similarly. Our experimental data suggest that genetically determined diversification has occurred within less than 140 years after the arrival of stickleback in our studied region