Underlying mechanisms and ecological context of variation in exploratory behavior of the Argentine ant, Linepithema humile

Colonies of ants allocate exploratory individuals to where they are ecologically needed

Individual differences in behavior have large consequences for the way in which ecology impacts fitness. Individuals differ in how they explore their environment and how exploratory behavior benefits them. In group-living animals, behavioral heterogeneity can be beneficial because different individuals perform different tasks. For example, exploratory individuals may discover new food sources and recruit group members to exploit the food, while less exploratory individuals forgo the risks of exploration. Here we ask how individual variation in exploratory behavior affects the ability of Argentine ant Linepithema humile colonies to (1) locate novel food sources, (2) exploit known food resources, and (3) respond to disruptions while foraging. To address these questions, we conducted field experiments on L. humile foraging trails in which we manipulated food availability near and at the foraging trails and disrupted the foraging trails. We sampled individuals based on their response to the perturbations in the field and tested their exploratory behavior in the lab. We found that exploratory individuals benefit the colony by locating novel foods and increasing resource exploitation, but they do not play an important role in the recovery of a foraging trail after disruption. Thus, the benefits of behavioral heterogeneity to the group, specifically in exploratory behavior, differ across ecological contexts.

Disparate behavioral types in wild and reared juveniles of gilthead seabream

Fish differ consistently in behavior within the same species and population, reflecting distinct behavioral types (BTs). Comparing the behavior of wild and reared individuals provides an excellent opportunity to delve into the ecological and evolutionary consequences of BTs. In this work, we evaluated the behavioral variation of wild and reared juvenile gilthead seabreams, Sparus aurata, a highly relevant species for aquaculture and fisheries. We quantified behavioral variation along the five major axes of fish behavioral traits (exploration-avoidance, aggressiveness, sociability, shyness-boldness, and activity) using standardized behavioral tests and a deep learning tracking algorithm for behavioral annotation. Results revealed significant repeatability in all five behavior traits, suggesting high consistency of individual behavioral variation across the different axes in this species. We found reared fish to be more aggressive, social and active compared to their wild conspecifics. Reared individuals also presented less variance in their aggressiveness, lacking very aggressive and very tame individuals. Phenotypic correlation decomposition between behavioral types revealed two different behavioral syndromes: exploration-sociability and exploration-activity. Our work establishes the first baseline of repeatability scores in wild and reared gilthead seabreams, providing novel insight into the behavior of this important commercial species with implications for fisheries and aquaculture.

The effect of resource availability on interspecific competition between a native and an invasive ant

Interspecific competition influences the composition of ecological communities. Species may differ in their needs for different resources, therefore resource availability may determine the outcome of interspecific interactions. Species often compete over food, shelter or both. When more than one resource is limited, different species may prioritize different resources. To determine the impact of resource availability on the competitive relationship between an invasive and a native species, we examined interactions between groups of the invasive Argentine ant (Linepithema humile) and the native odorous ant (Tapinoma sessile) over (1) food, (2) shelter or (3) both simultaneously. We further examined the mechanisms underlying the competitive relationship, asking whether aggressive interactions, exploratory behaviour or the order of arrival at a resource explained resource use. Shelter was preferred by both species when no competitors were present. In a competitive setting, L. humile groups controlled shelter through aggressive displacement but lost control over food due to investment of workers in the control of shelter. Thus, there are tradeoffs when competing over multiple resources and aggressive interactions allow invasive species to displace native species from a preferred resource.

This article is part of the theme issue ‘Intergroup conflict across taxa’.

Constitutive gene expression differs in three brain regions important for cognition in neophobic and non-neophobic house sparrows (Passer domesticus)

Neophobia (aversion to new objects, food, and environments) is a personality trait that affects the ability of wildlife to adapt to new challenges and opportunities. Despite the ubiquity and importance of this trait, the molecular mechanisms underlying repeatable individual differences in neophobia in wild animals are poorly understood. We evaluated wild-caught house sparrows (Passer domesticus) for neophobia in the lab using novel object tests. We then selected a subset of neophobic and non-neophobic individuals (n = 3 of each, all females) and extracted RNA from four brain regions involved in learning, memory, threat perception, and executive function: striatum, caudal dorsomedial hippocampus, medial ventral arcopallium, and caudolateral nidopallium (NCL). Our analysis of differentially expressed genes (DEGs) used 11,889 gene regions annotated in the house sparrow reference genome for which we had an average of 25.7 million mapped reads/sample. PERMANOVA identified significant effects of brain region, phenotype (neophobic vs. non-neophobic), and a brain region by phenotype interaction. Comparing neophobic and non-neophobic birds revealed constitutive differences in DEGs in three of the four brain regions examined: hippocampus (12% of the transcriptome significantly differentially expressed), striatum (4%) and NCL (3%). DEGs included important known neuroendocrine mediators of learning, memory, executive function, and anxiety behavior, including serotonin receptor 5A, dopamine receptors 1, 2 and 5 (downregulated in neophobic birds), and estrogen receptor beta (upregulated in neophobic birds). These results suggest that some of the behavioral differences between phenotypes may be due to underlying gene expression differences in the brain. The large number of DEGs in neophobic and non-neophobic birds also implies that there are major differences in neural function between the two phenotypes that could affect a wide variety of behavioral traits beyond neophobia.

Understanding Drivers of Variation and Predicting Variability Across Levels of Biological Organization

Differences within a biological system are ubiquitous, creating variation in nature. Variation underlies all evolutionary processes and allows persistence and resilience in changing environments; thus, uncovering the drivers of variation is critical. The growing recognition that variation is central to biology presents a timely opportunity for determining unifying principles that drive variation across biological levels of organization. Currently, most studies that consider variation are focused at a single biological level and not integrated into a broader perspective. Here we explain what variation is and how it can be measured. We then discuss the importance of variation in natural systems, and briefly describe the biological research that has focused on variation. We outline some of the barriers and solutions to studying variation and its drivers in biological systems. Finally, we detail the challenges and opportunities that may arise when studying the drivers of variation due to the multi-level nature of biological systems. Examining the drivers of variation will lead to a reintegration of biology. It will further forge interdisciplinary collaborations and open opportunities for training diverse quantitative biologists. We anticipate that these insights will inspire new questions and new analytic tools to study the fundamental questions of what drives variation in biological systems and how variation has shaped life.

The Drosophila melanogaster foraging gene affects social networks

Drosophila melanogaster displays social behaviors including courtship, mating, aggression, and group foraging. Recent studies employed social network analyses (SNAs) to show that D. melanogaster strains differ in their group behavior, suggesting that genes influence social network phenotypes. Aside from genes associated with sensory function, few studies address the genetic underpinnings of these networks. The foraging gene (for) is a well-established example of a pleiotropic gene that regulates multiple behavioral phenotypes and their plasticity. In D. melanogaster, there are two naturally occurring alleles of for called rover and sitter that differ in their larval and adult food-search behavior as well as other behavioral phenotypes. Here, we hypothesize that for affects behavioral elements required to form social networks and the social networks themselves. These effects are evident when we manipulate gene dosage. We found that flies of the rover and sitter strains exhibit differences in duration, frequency, and reciprocity of pairwise interactions, and they form social networks with differences in assortativity and global efficiency. Consistent with other adult phenotypes influenced by for, rover-sitter heterozygotes show intermediate patterns of dominance in many of these characteristics. Multiple generations of backcrossing a rover allele into a sitter strain showed that many but not all of these rover-sitter differences may be attributed to allelic variation at for. Our findings reveal the significant role that for plays in affecting social network properties and their behavioral elements in Drosophila melanogaster.

Ant Collective Behavior Is Heritable and Shaped by Selection

AbstractCollective behaviors are widespread in nature and usually assumed to be strongly shaped by natural selection. However, the degree to which variation in collective behavior is heritable and has fitness consequences-the two prerequisites for evolution by natural selection-is largely unknown. We used a new pharaoh ant (Monomorium pharaonis) mapping population to estimate the heritability, genetic correlations, and fitness consequences of three collective behaviors (foraging, aggression, and exploration), as well as of body size, sex ratio, and caste ratio. Heritability estimates for the collective behaviors were moderate, ranging from 0.17 to 0.32, but lower than our estimates for the heritability of caste ratio, sex ratio, and body size of new workers, queens, and males. Moreover, variation in collective behaviors among colonies was phenotypically correlated, suggesting that selection may shape multiple colony collective behaviors simultaneously. Finally, we found evidence for directional selection that was similar in strength to estimates of selection in natural populations. Altogether, our study begins to elucidate the genetic architecture of collective behavior and is one of the first studies to demonstrate that it is shaped by selection.

Exploratory behaviour, memory and neurogenesis in the social Damaraland mole-rat (Fukomys damarensis)

Both exploratory behaviour and spatial memory are important for survival in dispersing animals. Exploratory behaviour is triggered by novel environments and having a better spatial memory of the surroundings provides an adaptive advantage to the animals. Spatial challenges can also affect neurogenesis in the hippocampus by increasing cell proliferation and enhancing survival of young neurons. In social Damaraland mole-rat colonies, the social hierarchy is largely based on body size. Individuals with different social statuses in these colonies display different dispersal behaviours and as behavioural differences have been linked to dispersal behaviour, I investigated exploratory behaviour, memory and hippocampal neurogenesis in wild-captured Damaraland mole-rats. Dispersal behaviour gives rise to differential exploratory behaviour in Damaraland mole-rats; they readily explored in a novel environment but resident, worker mole-rats explored more slowly. In the Y-maze, animals entered the escape hole significantly faster by the second day; however, they did not make fewer wrong turns with successive days of the experiment. Female dispersers did not show any improvement in time to reach the escape hole or the number of wrong turns over the 4 day experimental period. Damaraland male and female dispersers employ different dispersal strategies, and this is evident in their approach to the learning task. Females are less motivated to complete the task, leading to a difference in behaviour, and this has important survival implications for the different sexes. Finally, in the context of memory, adult neurogenesis does not seem to be a good marker in mole-rats as it is generally low and has not been investigated thoroughly enough to determine which and how other factors can influence it in these animals.

Construction, comparison and evolution of networks in life sciences and other disciplines

Network approaches have become pervasive in many research fields. They allow for a more comprehensive understanding of complex relationships between entities as well as their group-level properties and dynamics. Many networks change over time, be it within seconds or millions of years, depending on the nature of the network. Our focus will be on comparative network analyses in life sciences, where deciphering temporal network changes is a core interest of molecular, ecological, neuropsychological and evolutionary biologists. Further, we will take a journey through different disciplines, such as social sciences, finance and computational gastronomy, to present commonalities and differences in how networks change and can be analysed. Finally, we envision how borrowing ideas from these disciplines could enrich the future of life science research.

Underlying mechanisms and ecological context of variation in exploratory behavior of the Argentine ant, Linepithema humile

Uncovering how and why animals explore their environment is fundamental for understanding population dynamics, the spread of invasive species, species interactions, etc. In social animals, individuals within a group can vary in their exploratory behavior, and the behavioral composition of the group can determine its collective success. Workers of the invasive Argentine ant (Linepithema humile) exhibit individual variation in exploratory behavior, which affects the colony's collective nest selection behavior. Here, we examine the mechanisms underlying this behavioral variation in exploratory behavior and determine its implications for the ecology of this species. We first establish that individual variation in exploratory behavior is repeatable and consistent across situations. We then show a relationship between exploratory behavior and the expression of genes that have been previously linked with other behaviors in social insects. Specifically, we found a negative relationship between exploratory behavior and the expression of the foraging (Lhfor) gene. Finally, we determine how colonies allocate exploratory individuals in natural conditions. We found that ants from inside the nest are the least exploratory individuals, whereas workers on newly formed foraging trails are the most exploratory individuals. Furthermore, we found temporal differences throughout the year: in early-mid spring, when new resources emerge, workers are more exploratory than at the end of winter, potentially allowing the colony to find and exploit new resources. These findings reveal the importance of individual variation in behavior for the ecology of social animals.