Biology subjects

Helanterä, H.

Publications and source records attributed to Helanterä, H..

10 recordsLinked to original sources

bioRxiv2026

Viral infection patterns in ants are affected by colony structure and phylogenetic lineage

Across ant species, there are differences in how their societies are structured. Single-queened (monogynous) societies only have one reproducing queen in the colony, and new queens disperse and start colonies independently. In multiple-queened (polygynous) societies, the colony instead can contain several reproductive queens, and newborn queens often remain and reproduce within their natal colony. As a result, polygynous societies are comparatively larger, more genetically diverse, and can span large areas through several interconnected nests, whereas monogynous societies are typically smaller in scale. In this study, we investigated how these different social structures, as well as their phylogenetic lineage, affect the diversity (number of virus species per ant sample) and abundance (number of viral sequences per sample) of viruses in ants. We produced pooled RNA sequence libraries from 15 ant species, representing both monogynous and polygynous social structures, and the two largest ant subfamilies: Formicinae and Myrmicinae, with each library containing the RNA of up to 400 individual worker ants from a single population. We identified 168 virus species in total, of which 152 species were new to science. Out of these 168 viruses, 59 were active viruses based on the host immune response. We observed that polygynous ant species harbor a higher diversity of viruses and also tend to have higher virus abundance compared to monogynous species. Also, the ant subfamily Myrmicinae had a higher virus diversity than Formicinae. These findings highlight how social structure and evolutionary history shape viral diversity in ants.

genomics↗

bioRxiv2025

Group size dependent selection for cooperation versus freeloading in collective chemical defence

Individuals can cooperate in groups to achieve greater fitness, but the contribution of each individual to the collective good may depend on group size and on strategies employed by other members. How environmental contexts influence selection for cooperation is currently poorly understood and lacks experimental evidence from systems exhibiting behavioural plasticity in collective acts. This study investigates group size dependent selection on collective chemical defence in a gregarious pine sawfly (Neodiprion sertifer). Larvae perform chemical defence by secreting a costly deterrent fluid while adopting a U-posture. By manipulating group size and the individuals ability to deploy the defensive fluid for the collective good, we show that survival against predation is higher in cooperative groups and that the benefits gained via collective defence are more pronounced in smaller groups. As predicted by theory, individuals participate less in collective defence in larger groups than in smaller ones. This lower contribution is not attributed to higher life-history costs from increased resource competition. Altogether, these results suggest that selection for cooperation in public goods is group size dependent, promoting cooperation in smaller groups whereas the relative fitness of freeloaders is higher in larger groups.

evolutionary biology↗

bioRxiv2025

Direct and indirect benefits of cooperation in collective defense against predation

The evolution and maintenance of public goods cooperation, despite cheating, remains a key interest in social biology. Identifying how ecological factors determine the direct and indirect benefits that maintain cooperation has proven challenging, as these can vary significantly across species and environments. Here, we study this problem using the social pine sawfly Neodiprion sertifer (Hymenoptera) as a model system. During their larval stage, N. sertifer live in groups and collectively secrete a defensive fluid against predators. This behavior comprises a public good as it is costly to exhibit and beneficial to others, and individuals vary in their contribution to group defense. We experimentally manipulated individual contributions to defense to assess how these influence survival under natural insect predation. Our results indicate that defense has a group-level benefit as individuals were more likely to survive in cooperative groups with a higher proportion of defending larvae. Moreover, being able to deploy defensive fluid confers direct survival benefits. Genetic and phenotypic analyses of natural populations further show that kin selection promotes collective defense, as groups of larvae are often composed of full siblings. We also find that the contribution to defense is female-biased and diminishes in larger, more male-biased groups, and to some extent with decreased kinship, indicating that individuals adjust their contributions based on social context. Overall, we find that contribution to the collective defense provides both direct and indirect benefits and that individuals regulate their contributions mainly based on the social environment, resulting in variation within and among natural populations. Significance statementIndividuals in groups can cooperate to achieve shared goals, but they face an evolutionary challenge: if the benefits of cooperation are shared equally, freeloaders receive the same benefits as others while contributing less. Although theoretical solutions to this problem are abundant, we still lack empirical evidence on how those mechanisms function in natural systems. We study this with pine sawfly larvae, which defend collectively against predators. We show that while cooperation increases the survival of individuals and their relatives, they adjust their contributions based on who and how many they are surrounded by, relying more on freeloading in larger and male-biased groups. This results in variation in cooperativeness but prevents freeloaders from taking over.

evolutionary biology↗

bioRxiv2025

A novel supergene controls queen size and colony social organization in the ant Myrmica ruginodis

In some ant species, the size of queens is dimorphic, with larger queens dispersing to form single-queen colonies and smaller queens remaining in natal colonies as part of multiple-queen societies. These alternative reproductive strategies influence colony kin structure and worker behavior, and their many independent origins make them ideal systems to study parallel evolution of genome organization and adaptability. We investigate the genetic basis of alternative reproductive strategies in the queen-size dimorphic ant Myrmica ruginodis by sampling 95 queens from 31 colonies in southern Finland. Whole-genome sequencing revealed a novel 9 Mb supergene associated with both queen size and social organization. Queens homozygous for the AA haplotype were larger and found only in single-queen colonies, while queens in multiple-queen colonies were smaller and contained only AB and BB genotypes. This supergene is not homologous to previously identified supergenes in ants, suggesting it was formed by a unique evolutionary pathway.

evolutionary biology↗

bioRxiv2024

Population Genomics of the Invasive Argentine Ant (Linepithema humile) - Adaptive Evolution in the Introduced Supercolonies Despite Low Genetic Diversity

The Argentine ant (Linepithema humile), native to South America, has spread globally over the past 150 years, forming extremely large supercolonies in its introduced range. Despite the recent demographic history, including founder effects, Argentine ants thrive in the introduced range and displace native ant species. We adopted a comprehensive approach to investigate selection signals across the whole genome of this highly invasive species, with a specific focus on introduced supercolonies. We also investigated genome-wide diversity and divergence patterns and compared the results with earlier microsatellite marker data studies. We used pooled whole-genome sequence data from 100 workers from the species' native range and each of the three invasive supercolonies -- European Main, Catalonia, and Chile. Invasive supercolonies harboured low genetic diversity and were genetically highly differentiated. Despite this, we could detect signs of positive selection in their genomes. Some of the selected genes showed parallel adaptive evolution in invasive supercolonies. Furthermore, there were no signs that a social organisation based on unrelated workers had led to impaired adaptability (genetic meltdown). We conclude that introduced Argentine ant supercolonies evolve adaptively, indicating that founder effects, low genetic diversity and supercolony social organisation do not always hamper species adaptability.

genomics↗

bioRxiv2024

The loss of a supergene in obligately polygynous Formica wood ant species

Some of the most striking examples of phenotypic variation within species are controlled by supergenes. However, most research on supergenes has focused on their emergence and long-term maintenance, leaving the later stages of their life cycle largely unexplored. Specifically, what happens to a derived supergene haplotype when the trait it controls reaches fixation? Here we answer this question using the ancient supergene system of Formica ants, where (monogynous) single-queen colonies carry only the ancestral haplotype M while the derived haplotype P is exclusive to (polygynous) colonies with multiple queens. Through comparative genomics of all seven European wood ant species, we found that the P haplotype was present in only one of the three obligate polygynous species (F. polyctena). In the two others (F. aquilonia and F. paralugubris) the P haplotype was completely missing except for duplicated P-specific paralogs of two genes, Zasp52 and TTLL2, with Zasp52 being directly involved in wing muscle development. We hypothesize that these genes play a direct role in polygyny and contribute to differences in body size and/or dispersal behaviour between monogynous and polygynous queens. A complete lack of P/P genotypes among the 136 workers suggest strong selection against such genotypes. While our analyses did not reveal evidence of increased mutation load on the P, it is possible that this skew in genotype distributions is driven by a few loci with strong fitness effects. We propose that selection to escape P-associated fitness costs underlies the loss of this haplotype in obligate polygynous wood ants.

genomics↗

bioRxiv2022

Lack of self-medication by fungus infected Lasius platythorax ants in a multitrophic experiment

Ants live in dense colonies with low genetic diversity between nestmates, creating favourable conditions for the spread of diseases. Due to the constant pressure by infectious disease, ants have evolved different mechanisms to cope with it. One way to combat pathogens is via consumption of biologically active compounds, which can inhibit the growth of the microbes or eliminate them. Although ants are known to respond to pathogen infections by altering their foraging to incorporate reactive oxygen species (ROS) into their diet to successfully combat disease under laboratory conditions, it is still unknown how ants would self-medicate in the wild. By designing a multitrophic environment, we try for the first time to identify potential sources of medicinal compounds for ants to use against fungal infections under natural conditions to better understand how the behaviour is expressed in nature. We investigated whether a bean plant suffering from an infestation of Megoura viciae aphids would be a source of ROS which the ant could use for self-medication, and whether the ant Lasius platythorax changes its foraging behaviour on bean plants if exposed to infectious spores of the entomopathogenic fungus Beauveria bassiana. We found no clear evidence that the ants significantly change their foraging behaviour on extrafloral nectaries in response to the pathogen or that the nectar produced by aphid stressed plants contains ROS. The aphids contained ROS in levels which ants could potentially use, however Megoura viciae is considered unpalatable to ants and we saw no evidence of predation on the aphids. Our results mean that the combination of species of the ant - plant - aphid interactions which we studied does result in a detectable self-medication response in ants. Therefore, we suggest that alternative species of aphids as well as other natural sources of ROS should be studied for self-medication.

animal behavior and cognition↗

bioRxiv2022

Pathogen prevalence modulates medication behavior in ant Formica fusca

Ants face unique challenges regarding pathogens, as the sociality which has allowed them to form large and complex colonies also raises the potential for transmission of disease within these colonies. To cope with the threat of pathogens, ants have developed a variety of behavioral and physiological strategies. One of these strategies is self-medication, in which animals use biologically active compounds to combat pathogens in a way which would be harmful in the absence of them. Formica fusca ants are to date the only species of ants proven to successfully self-medicate against an active infection caused by a fungal pathogen by supplementing their diet with food containing hydrogen peroxide. Here, we build on that research by investigating how the prevalence of disease in colonies of F. fusca affects the strength of the self-medication response. We exposed either half of the workers of each colony or all of them to a fungal pathogen and offered them different combinations of diets. We see that workers of F. fusca engage in self-medication behavior even if exposed to a low lethal dose of a pathogen, and that the strength of that response is affected by the prevalence of the disease in the colonies. We also saw that the infection status of the individual foragers did not significantly affect their decision to forage on either control food or medicinal food as uninfected workers were also foraging on hydrogen peroxide food, which opens up the possibility of kin medication in partially infected colonies. Our results further affirm the ability of ants to self-medicate against fungal pathogens, shed new light on plasticity of self-medication and raise new questions to be investigated on the role self-medication has in social immunity.

animal behavior and cognition↗

bioRxiv2021

Relatedness modulates reproductive competition among queens in ant societies with multiple queens

Reproductive sharing in animal groups with multiple breeders, insects and vertebrates alike, contains elements of both conflict and cooperation, and depends on both relatedness between co-breeders, as well as their internal and external conditions. We studied how queens of the ant Formica fusca adjust their reproductive efforts in response to experimental manipulations of the kin competition regime in their nest, as well as their own reproductive status. Queens respond to the presence of competitors by increasing their egg laying efforts, but only if the competitors are highly fecund and distantly related. Furthermore, queens only engage in cannibalism of eggs when the risk of erroneously destroying own offspring is absent. We demonstrate that queens of Formica fusca fine-tune their behaviours in response to kinship and fecundity of others as well as their own physiological state in an unusually precise manner.

evolutionary biology↗

bioRxiv2021

Whole-genome analysis of multiple wood ant population pairs supports similar speciation histories, but different degrees of gene flow, across their European range

The application of demographic history modeling and inference to the study of divergence between species is becoming a cornerstone of speciation genomics. The demographic history is usually reconstructed by analysing a single population from each species, assuming that the divergence history inferred between these populations represents the actual speciation history. However, this assumption is rarely explicitly tested, and it may not be met when species diverge with gene flow. For instance, secondary contact between two species after a range expansion may be confined into a specific geographic region. In this study, we tested to what extent the divergence history inferred from two heterospecific populations would vary depending on their geographic locations, using mound-building red wood ants. The wood ant species Formica polyctena and F. aquilonia have contrasting distributions in Europe and naturally hybridize in Finland. We first performed whole-genome resequencing of 20 individuals sampled in multiple populations across both species ranges. We then reconstructed the divergence histories of distinct heterospecific population pairs using a coalescent-based approach. We found that the analysis of these different population pairs always supported a scenario of divergence with gene flow, suggesting that species divergence started in the Pleistocene (ca. 500 kya) and occurred with continuous asymmetrical gene flow from F. aquilonia to F. polyctena until a recent time, when migration stopped (2-19 kya, depending on the population pair considered). However, we found support for contemporary gene flow in the sympatric population pair from Finland, where hybrids have been described. Overall, our results suggest that divergence histories reconstructed from a few individuals may be reliable and applicable at the species level. Nonetheless, the geographical context of populations chosen to represent their species should be taken into account, as it may affect estimates of migration rates between species when gene flow is heterogeneous across their geographical ranges.

evolutionary biology↗