Biology subjects

Bierbach, D.

Publications and source records attributed to Bierbach, D..

18 recordsLinked to original sources

bioRxiv2026

Non-genetic inheritance of stochastically induced behavioral individuality in a naturally clonal fish

The study of among-individual phenotypic variation arising in the apparent absence of genetic and environmental differences has recently emerged as a rapidly growing research area. Despite growing recognition of its existence and fitness relevance, it remains unknown whether signatures of such presumably stochastically induced variation can be transmitted across generations. To address this knowledge gap, we performed a two-generation behavioral screening with a naturally clonal fish: 34 genetically identical mothers and their 232 offspring were separated after birth into near-identical environments, with early-life behavior being tracked continuously at high resolution, constituting a total of ~19,000 observation hours. We find consistent among-individual differences in behavior (i.e., activity and feeding patterns) in both mothers and offspring. Mother behavior correlates with offspring activity (but not offspring feeding): mothers that spend more time feeding produce more active offspring. We find no evidence of body size (maternal or offspring) mediating mother-offspring behavioral associations. Our study provides first evidence for the non-genetic transmission of among-individual phenotypic differences that arise in the apparent absence of genetic or environmental differences, highlighting the potential importance of this variation for evolutionary processes and the adaptive potential of populations.

animal behavior and cognition↗

bioRxiv2026

Activity during the first days of life predicts lifespan in a naturally clonal vertebrate

Lifespan varies widely among individuals, yet the extent to which such variation persists when genetic and environmental differences are minimized remains unclear. Here we quantify such stochastic lifespan variation in a naturally clonal vertebrate and test whether and how this variation is linked to early-life behavioral individuality. We followed N = 33 genetically identical Amazon mollies (Poecilia formosa), separated on day 1 of their life into highly standardized environments, from birth to death. Despite genetic uniformity and environmental standardization, lifespan varies markedly, spanning 502 - 826 days. Continuous high-resolution behavioral tracking during the first four weeks of life reveals that seemingly stochastic early-life activity differences explain 32.5% of this variation. Higher activity predicts shorter lifespan during the first two weeks, but as activity levels and among-individual variation in activity decline over early development, a U-shaped relationship emerges, with both low- and high-activity individuals outliving those with intermediate activity. These findings show that signatures of lifespan emerge within days of birth, even among genetically identical individuals, highlighting developmental stochasticity and early-life contingencies as major contributors to variation in life-history outcomes.

animal behavior and cognition↗

bioRxiv2026

Group-level phenotypes are idiosyncratic yet unpredictable over development in a clonal fish

Behavioral differences among groups can have profound impacts on individual fitness, yet how group-level phenotypes arise and change during development is poorly understood. Group-level differences may originate from genetic differences or subtle variation among individuals, but they can also emerge over time through social feedback mechanisms within and between groups, potentially producing dramatically different group-level behavior. Disentangling these drivers of group phenotypes is challenging because groups are typically studied after they are already well established. Using the naturally clonal Amazon molly, we establish replicate groups of genetically identical individuals and continuously track group-level behavior from birth throughout the first 55 days of life. This design allows us to control for genetic and environmental sources of variance, thereby establishing a null baseline for group-level differences. Furthermore, by recording over an extended period beginning from day 1 of life, we test whether group phenotypes follow predictable trajectories driven by individual differences or instead diverge due to social feedback during development. We find that average behavioral changes across groups follow predictable patterns during this early developmental phase. In contrast, differences among groups are highly unstable over longer timescales: although groups differ from very early in life, it appears that the rank-order of group-level phenotypes undergoes a shuffling mid-development, around 4-5 weeks of age. These results suggest that distinct processes generate group-level variation across ontogeny, with early differences largely reflecting consistent individual variation; then as individuals mature and become more socially responsive, social feedbacks push groups along divergent, less predictable behavioral trajectories.

animal behavior and cognition↗

bioRxiv2025

No paternal effects in a sperm-dependent, naturally clonal fish

Paternal effects, i.e., effects of males on the phenotypes of their offspring that are not caused by the integration of male genetic material, are increasingly recognized as a potentially significant source of phenotypic variation across taxa - even in the absence of paternal care. Gynogenetic systems, which rely on sperm to trigger embryogenesis without incorporating male genetic material, provide a powerful way to experimentally isolate potential paternal effects from effects caused by the integration of male genetic material; up to now, however, paternal effects remain largely unexplored in these systems. Here, we test for paternal effects in the gynogenetic Amazon molly (Poecilia formosa): a naturally clonal, all-female species with no parental care. Using a highly controlled breeding experiment involving 59 Atlantic molly males (P. mexicana) and 57 Amazon molly females, we generated 169 broods and 2,966 offspring. While males were drawn from a naturally variable stock population, females - next to being genetically identical - were highly standardized for age, size, descent, and developmental experience. We asked whether male identity or body size predicted offspring size - a key offspring phenotypic trait. We also asked whether male identity or body size predicted brood size. While we found substantial variation in both offspring size and brood size, we found no evidence for paternal effects on either trait. Next to providing an experimental test for paternal effects in a gynogenetic system, our results also strengthen the Amazon mollys status as a model species for studying - in a highly controlled fashion - the developmental emergence of phenotypic variation.

animal behavior and cognition↗

bioRxiv2025

Synchronization of the collective air-breathing behavior in juvenile Arapaima gigas

Animal collectives are capable of performing behaviors with high degrees of synchrony though their members might differ consistently and substantially in the focal behavior when alone. It is thus not entirely understood how these consistent differences in behavior at the individual level can be (socially) integrated into synchronized behaviors at the collective level. Here we show an unprecedented synchronized behavior in fish - the collective air-breathing of juvenile Arapaima gigas. Individuals of this obligate air-breathing fish from South America differed in their time between consecutive breaths when recorded alone in an aquaculture facility. However, when together in a shoal of about 200 same aged individuals, breathing is executed by a substantial portion of the shoal - within the same second. Our analysis of the individual and collective breathing patterns supported by stochastic individual-based simulations of inherently non-periodic coupled oscillators revealed that this degree of collective synchronization could be achieved by having some kind of assortative interaction rules where individuals respond towards one cluster/subgroup members stronger than to other cluster/subgroup members. By integrating this cluster synchrony rule we could successfully simulate highly synchronized collective behavior with varying proportions of otherwise diverse individuals taking part, matching our experimental observations and providing a mechanism to synchronize agents that differ consistently in the behavior in focus when in isolation.

animal behavior and cognition↗

bioRxiv2024

Better and faster collective decisions by larger fish shoals in the wild

Studies on collective cognition have provided many examples of decision-making benefits in terms of animals sharing information about predators, prey or resources in their environment. It has been shown how the efficient spread of adaptive information within groups can provide benefits which increase with group size. Little is known, however, to which extent groups also amplify maladaptive information such as false alarms and whether such costs reduce or even nullify the above benefits. Here, we investigated fish shoals in the wild that responded collec-tively with escape dives when attacked by birds. We analysed the response of shoals in reac-tion to hard-to-detect bird attacks and similar but harmless flybys as a function of shoal size. With increasing shoal size fish increasingly detected predator attacks (true positives) while their false alarms remained constant. Therefore, larger shoals became better at correctly clas-sifying potentially dangerous stimuli rather than becoming more sensitive to all stimuli poten-tially related to attacks. In addition, decision time decreased with increasing shoal size. Larger shoals were thus able to mitigate two major trade-offs inherent in solitary decision making: the trade-off between true and false positives and the trade-off between speed and accuracy. We report performance increases at shoal sizes of tens of thousands of fish and pose chal-lenges for the modelling of the underlying mechanisms.

animal behavior and cognition↗

bioRxiv2023

Developmental arcs of plasticity in whole movement repertoires of a clonal fish

Developmental plasticity at the behavioral repertoire level allows animals to incrementally adjust their behavioral phenotypes to match their environments through ontogeny, serving as a lynchpin between ecological factors that cue phenotypic adjustments and evolutionary forces that select upon emergent phenotypic variation. Quantifying the continuous arcs of plasticity throughout animals development, however, has often been prohibitively challenging. Here, we leverage recent advancements in high-resolution behavioral tracking and analysis to (i) track the behavior of 45 genetically identical fish clones (Poecilia formosa) reared in near-identical environments during their first four weeks of life at 0.2 s resolution and (ii) quantify the continuous arcs of plasticity across entire behavioral repertoires through development. Doing so, we are able to test one of the most fundamental theoretical predictions from Bayesian models of development that in stable (but initially unknown) environments, behavioral plasticity should gradually decrease from a maximum at the beginning of life. Using two approaches to measure plasticity across ontogeny, we first quantify plasticity in individual behavioral metrics before also developing a novel whole-repertoire approach that calculates plasticity as the degree of behavioral entropy across a multi-dimensional behavioral phenotype space. We robustly find - despite experimentally matching as best as possible the assumptions of models that predict decreasing plasticity - a [~]two-week initial increase in plasticity in movement behaviors before plasticity subsequently decreased. Our results challenge a common intuition about the optimal developmental course of plasticity through early ontogeny, thereby also demonstrating the value of long-term behavioral tracking approaches for testing fundamental predictions on phenotypic development. Significance statementBehavioral plasticity across development may help animals adjust to uncertainty in moderately unpredictable environments. In stable environments, developing animals should gradually decrease this uncertainty through ontogeny, becoming less sensitive to incoming information (and thus less behaviorally plastic) as they age. This intuitive expectation of old dog inflexibility to new tricks, however, has not been adequately tested with the long-term, highresolution datasets that would be ideal. Here, we achieve such a test and emphasize the significance of this study in (1) providing a novel method for quantifying multi-dimensional behavioral plasticity continuously across long-term, high-resolution behavioral timeseries and in (2) testing fundamental theory that links the temporal patterning of environmental conditions to evolved patterns of behavioral plasticity across development.

animal behavior and cognition↗

bioRxiv2023

Increased thermal tolerance under anoxic conditions in an extremophile fish from hot sulfur springs in Mexico

The thermal ecology of ectotherm animals has gained considerable attention in the face of human induced climate change. Particularly in aquatic species the experimental assessment of critical thermal limits (CTmin and CTmax) may help to predict possible effects of global warming on habitat suitability and ultimately species survival. Here we present data on the thermal limits of two endemic and endangered extremophile fish species, inhabiting a geothermally-heated and sulfur-rich spring system in Southern Mexico: The sulfur molly (Poecilia sulphuraria) and the widemouth gambusia (Gambusia eurystoma). Besides physiological challenges induced by toxic hydrogen sulfide and related severe hypoxia during the day, water temperatures have been previously reported to exceed those of nearby clearwater streams. We now present temperature data for various locations and years in the sulphur spring complex and conducted laboratory thermal tolerance tests (CTmin and CTmax) both under normoxic as well as sever hypoxic conditions in both species. Average CTmax limits did not differ between species under normoxic conditions. Surprisingly P. sulphuraria was found to reach a higher critical temperature (CTmax = 43.2{degrees}C) when tested under hypoxic conditions, while G. eurystoma on average had a lower CTmax when oxygen was absent. Based on this data we calculated both species thermal safety margins and used a TDT (thermal death time) model framework to relate our experimental data to observed temperatures in the natural habitat. Our findings suggest, that both species live near their thermal limits during the annual dry season and are locally already exposed to temperatures above their critical thermal limits. We discuss these findings in the light of possible physiological adaptions of the sulfur-adapted fish species and the anthropogenic threats for this unique system.

ecology↗

bioRxiv2023

Reproductive individuality of clonal fish raised in identical environments and its link to early-life behavioural individuality

Recent studies have documented among-individual variation that is unexplained by genetic or apparent environmental differences, but it remains an open question whether such seemingly stochastic variation has fitness consequences. We perform a life-history experiment with naturally clonal fish (Poecilia formosa), separated directly after birth into near-identical (i.e., highly standardized) environments, quantifying 2522 offspring from 152 broods over 280 days. We find that (i) individuals differ consistently in the size of offspring and broods produced over consecutive broods, (ii) these differences are observed even when controlling for trade-offs between brood size, offspring size and reproductive onset, indicating individual differences in life-history productivity and (iii) early-life behavioral individuality in activity and feeding patterns, with among-individual differences in feeding being predictive of growth, and consequently offspring size. In this work, we provide experimental evidence that processes unexplained by genetic and apparent environmental differences translate into predictable differences in life-history measures and ultimately fitness.

animal behavior and cognition↗

bioRxiv2022

Experienced social partners hinder learning performance in naive clonal fish

Social learning is widely assumed to enhance individual learning efficiency, particularly when naive observers have access to skilled demonstrators, yet the conditions under which this assumption holds remain poorly understood. Here, we investigated how individual learning is influenced by the skill level of social partners. We predicted that naive individuals would benefit from observing experienced conspecifics, yet found the opposite: trained partners significantly impaired naive individuals learning performance, while trained individuals remained unaffected by their partners skill level. We conducted experiments in near-identical individuals, using the all-female clonal Amazon molly (Poecilia formosa) to test whether these fish can learn an operant foraging task, whether individuals differ consistently in learning ability, and whether partner skill level influences learning performance. Using an operant conditioning paradigm over five days, half of the fish were trained to locate food inside a cylinder, whereas the remaining individuals received food randomly dispersed within their tank. Trained individuals subsequently visited the cylinder more frequently than randomly fed individuals and exhibited consistent individual differences in learning performance. In a second phase, fish were allowed to observe a conspecific while individual training was either continued (for trained individuals) or initiated (for naive individuals). We found that trained individuals did not benefit from the presence of a partner, regardless of the partners proficiency, but consistently outperformed naive individuals. In contrast, naive individuals showed reduced learning performance when paired with experienced partners, but not with naive partners. Together, our results indicate that Amazon mollies achieve this foraging task through individual learning and exhibit stable differences in learning ability. Moreover, social learning depends on both the learners own skill level and that of the social partner, such that observing an experienced conspecific may, in some cases, impede rather than enhance learning.

animal behavior and cognition↗

bioRxiv2022

Discovery of a new but established population of the guppy in Germany

Feral populations of tropical fish species in temperate climates like Central Europe are a rare but repeatedly observed phenomenon. Due to the influence of industrial or geothermal heated water, released tropical fish may be able to survive harsh winter conditions. Here we characterize a newly discovered thermally polluted river, with an established population of the guppy (Poecilia reticulata) co-occurring with native species. Through a mark-recapture approach, we estimated the population size of the guppies close to the warm water inflow to be around 2000 individuals during summer and we further provide descriptive demographics of this population which allow us to assume it is well established in that river. Further, we found some of the sampled specimen being parasitized by Camallanus roundworms, thus showing the guppies host potential for this genus of internal parasites. The popularity and widespread distribution of guppies as ornamental fish often leads to their intentional or unintentional release into the wild where they are often pioneer species in anthropogenically heavily modified habitats. Guppies threaten native species through niche competition and transmission of diseases. Accordingly, early awareness and knowledge on the status of non-native populations is crucial for effective management strategies.

ecology↗

bioRxiv2021

Cascading indirect genetic effects in a clonal vertebrate

Understanding how individual differences among organisms arise and how their effects propagate through groups of interacting individuals are fundamental questions in biology.Individual differences can arise from genetically-based variation in the conspecifics with which an individual interacts, and these effects might then be propagated to other individuals. Using a clonal species, the Amazon molly (Poecilia formosa), we test the hypothesis that such indirect genetic effects (IGE) propagate beyond individuals that experience them firsthand. We tested this hypothesis by exposing genetically identical Amazon mollies to social partners of different genotypes, and then moving these individuals to new social groups in which they were the only member to have experienced the IGE. We found that genetically different social environments induced different levels of aggression experienced by the focal animals, and that these genetically-based social effects carried over into new social groups to influence the behavior of individuals that did not directly experience the previous social environments. Our data reveal that IGE can cascade beyond the individuals that directly experience them to influence phenotypes even when there is no genetically-based variation present within interacting groups. Theoretical and empirical expansion of the quantitative genetic framework developed for IGE to include cascading and other types of carry-over effects will improve understanding of social behavior and its evolution.

animal behavior and cognition↗

bioRxiv2020

Group-level patterns emerge from individual speed as revealed by an extremely social robotic fish

Understanding the emergence of collective behaviour has long been a key research focus in the natural sciences. Besides the fundamental role of social interaction rules, a combination of theoretical and empirical work indicates individual speed may be a key process that drives the collective behaviour of animal groups. Socially-induced changes in speed by interacting animals make it difficult to isolate the effects of individual speed on group-level behaviours. Here we tackled this issue by pairing guppies with a biomimetic robot. We used a closed-loop tracking and feedback system to let a robotic fish naturally interact with a live partner in real time, and programmed it to strongly copy and follow its partner’s movements while lacking any preferred movement speed or directionality of its own. We show that individual differences in guppies’ movement speed were highly repeatable and shaped key collective patterns: higher individual speeds resulted in stronger leadership, lower cohesion, higher alignment, and better temporal coordination in the pairs. By combining the strengths of individual-based models and observational work with state-of-the-art robotics, we provide novel evidence that individual speed is a key, fundamental process in the emergence of collective behaviour.Competing Interest StatementThe authors have declared no competing interest.View Full Text

animal behavior and cognition↗

bioRxiv2020

Consistent behavioural syndromes across seasons in an invasive freshwater fish

Understanding the linkage between behavioral types and dispersal tendency has become a pressing issue in light of global change and biological invasions. Here, we explore whether dispersing individuals exhibit behavioral types that differ from those remaining in the source population. We investigated a feral population of guppies (Poecilia reticulata) that undergoes a yearly range shift cycle. Guppies are among the most widespread invasive species in the world, but in temperate regions these tropical fish can only survive in winter-warm freshwaters. Established in a thermally-altered stream in Germany, guppies are confined to a warm-water influx in winter, but can spread to peripheral parts as these become thermally accessible. We sampled fish from the source population and a winter-abandoned site in March, June and August. Fish were tested for boldness, sociability and activity involving open-field tests including interactions with a robotic social partner. Guppies differed consistently among each other in all three traits. Behavioral trait expression in the source population differed across seasons, however, we could not detect differences between source and downstream populations. Instead, all sampled populations exhibited a remarkably stable behavioral syndrome between boldness and activity despite strong seasonal changes in water temperature and associated environmental factors. We conclude that random drift (opposed to personality-biased dispersal) is a more likely dispersal mode for guppies, at least in the investigated stream. In the face of fluctuating environments, guppies seem to be extremely effective in keeping behavioral expressions constant, which could help explain their successful invasion and adaptation to disturbed habitats.Competing Interest StatementThe authors have declared no competing interest.View Full Text

animal behavior and cognition↗

bioRxiv2018

Social networks in the presence and absence of visual cues

We compared the social dynamics of two populations of the live-bearing Atlantic molly (Poecilia mexicana) that live in adjacent habitats with very different predator regimes: cave mollies that inhabit a low-predation environment inside a sulfidic cave with a low density of predatory water bugs (Belostoma sp.), and mollies that live directly outside the cave (henceforth called \"surface\" mollies) in a high-predation environment with a high density of fish-eating birds. We filmed the social interactions of marked fish in both environments and analysed their social network dynamics using a Markov model under two different fish densities of 12 and 6 fish per 0.36 m2. As expected, surface mollies spent overall much more time social than cave mollies. This difference in overall social time was a result of surface mollies being less likely to discontinue social contact (once they had a social partner) and being more likely to resume social contact (once alone) than cave mollies. Interestingly surface mollies were also less likely to leave a current social partner than cave mollies. At low density, mollies (in both environments) were expected to show reduced social encounters which should dramatically change their social dynamics. Surface mollies, however, displayed an ability to maintain their social dynamics at low density (primarily by reducing the convex polygon spanned by the group) which was not observed in cave mollies. Despite the fact that we only compared two populations, our data provide a mechanistic explanation for density compensations of social dynamics that have also been observed in other fish species and give an example of how comparisons between the social dynamics of different populations can be made that go beyond conventional network analyses.

animal behavior and cognition↗

bioRxiv2018

Familiarity increases aggressiveness among clonal fish.

Understanding how animal groups form and function is a major goal in behavioural ecology. Both genetic relatedness and familiarity among group mates have been shown to be key mediators of group composition. However, disentangling the two in most species is challenging as the most familiar individuals are often the most related, and vice versa. In order to gain a complete understanding of how individual interactions shape group behaviour it is crucial to understand the role each of this social relationship factors plays individually. To this end, we manipulated the level of familiarity among groups of the naturally clonal, and genetically identical fish, the Amazon molly (Poecilia formosa) and monitored group behaviour in an open-field and when given the opportunity to forage. Contrary to our predictions, fish that were the most familiar with each other showed the highest levels of aggression. Additionally, fish that were less familiar with each other exhibited the highest group cohesion and took the longest to begin feeding, compared to the more familiar fish. These results suggest that familiarity may socially buffer individuals from the perception of risk in novel environments, such as is common in most behavioural tests designed to test group behaviour. Increases in aggression that are associated with increasing familiarity as shown here might be a mechanism by which fish maintain a fission-fusion society with important consequences for the patterns of associations in group living animals.

animal behavior and cognition↗

bioRxiv2018

Guppies prefer to follow large (robot) leaders irrespective of own size

Body size is often assumed to determine how successful an individual can lead others with larger individuals being more likely to lead than smaller ones. However, direct evidence for such a relation is scarce. Furthermore, even if larger individuals are more likely to lead, body size correlates often with specific behavioral patterns (e.g., swimming capacity) and it is thus unclear whether larger individuals are more often followed than smaller ones because they are larger or because they behave in a certain way. To control for behavioral differences among differentially-sized leaders, we used biomimetic robotic fish - Robofish - of different sizes. Robofish is accepted as a conspecific by live guppies (Poecilia reticulata) and provides standardized behaviors irrespective of its size. We specifically asked whether larger leaders are preferentially followed when behavior is controlled for and whether the preferences of followers depend on their own body size or their risk taking behavior ( boldness). We found that live guppies followed larger Robofish leaders closer than smaller ones and this pattern was independent of the followers own body size as well as risk-taking behavior. This is the first study that shows a bigger is better pattern in leadership in shoaling fish that is fully independent of behavioral differences between differentially-sized leaders and followers own size and personality.

animal behavior and cognition↗

bioRxiv2018

Using a robotic fish to investigate individual differences in social responsiveness in the guppy

Responding towards the actions of others is one of the most important behavioral traits whenever animals of the same species interact. Mutual influences among interacting individuals may modulate the social responsiveness seen and thus makes it often difficult to study the level and variation of individuality in responsiveness. Here, biomimetic robots (BRs) that are accepted as conspecifics but controlled by the experimenter can be a useful tool. Studying the interactions of live animals with BRs allows pinpointing the live animals level of responsiveness by removing confounding mutuality. In this paper, we show that live guppies (Poecilia reticulata) exhibit consistent differences among each other in their responsiveness when interacting with a biomimetic fish robot - Robofish - and a live companion. It has been repeatedly suggested that social responsiveness correlates with other individual behavioral traits like risk-taking behavior ( boldness) or activity level. We tested this assumption in a second experiment. Interestingly, our detailed analysis of individual differences in social responsiveness using the Robofish, suggests that responsiveness is an independent trait, not part of a larger behavioral syndrome formed by boldness and activity.

animal behavior and cognition↗