Worker caste determination in the army ant
            Eciton burchellii

Elaborate division of labour has contributed significantly to the ecological success of social insects. Division of labour is achieved either by behavioural task specialization or by morphological specialization of colony members. In physical caste systems, the diet and rearing environment of developing larvae is known to determine the phenotype of adult individuals, but recent studies have shown that genetic components also contribute to the determination of worker caste. One of the most extreme cases of worker caste differentiation occurs in the army ant genus Eciton , where queens mate with many males and colonies are therefore composed of numerous full-sister subfamilies. This high intracolonial genetic diversity, in combination with the extreme caste polymorphism, provides an excellent test system for studying the extent to which caste determination is genetically controlled. Here we show that genetic effects contribute significantly to worker caste fate in Eciton burchellii . We conclude that the combination of polyandry and genetic variation for caste determination may have facilitated the evolution of worker caste diversity in some lineages of social insects.

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Epigenetics in Social Insects: A New Direction for Understanding the Evolution of Castes

Genetics Research International ◽

10.1155/2012/609810 ◽

2012 ◽

Vol 2012 ◽

pp. 1-11 ◽

Cited By ~ 28

Author(s):

Susan A. Weiner ◽

Amy L. Toth

Keyword(s):

Dna Methylation ◽

Social Insects ◽

Differential Methylation ◽

Caste Determination ◽

The Social ◽

Worker Castes ◽

Regulatory Flexibility ◽

Worker Caste ◽

Caste Differences ◽

Epigenetic Research

Epigenetic modifications to DNA, such as DNA methylation, can expand a genome’s regulatory flexibility, and thus may contribute to the evolution of phenotypic plasticity. Recent work has demonstrated the importance of DNA methylation in alternative queen and worker “castes” in social insects, particularly honeybees. Social insects are an excellent system for addressing questions about epigenetics and evolution because: (1) they have dramatic caste polyphenisms that appear to be tied to differential methylation, (2) DNA methylation is widespread in various groups of social insects, and (3) there are intriguing connections between the social environment and DNA methylation in many species, from insects to mammals. In this article, we review research on honeybees, and, when available, other social insects, on DNA methylation and queen and worker caste differences. We outline a conceptual framework for the effects of methylation on caste determination in honeybees that may help guide studies of epigenetic regulation in other polyphenic taxa. Finally, we suggest future paths of study for social insect epigenetic research, including the importance of comparative studies of DNA methylation on a broader range of species, and highlight some key unanswered mechanistic questions about how DNA methylation affects gene regulation.

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Genetic polymorphism in leaf-cutting ants is phenotypically plastic

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2007.0347 ◽

2007 ◽

Vol 274 (1618) ◽

pp. 1625-1630 ◽

Cited By ~ 31

Author(s):

William O.H Hughes ◽

Jacobus J Boomsma

Keyword(s):

Division Of Labour ◽

Genetic Influence ◽

Caste Determination ◽

Adaptive Property ◽

The Social ◽

Before And After ◽

Large Worker ◽

Leaf Cutting ◽

Response Thresholds ◽

Worker Caste

Advanced societies owe their success to an efficient division of labour that, in some social insects, is based on specialized worker phenotypes. The system of caste determination in such species is therefore critical. Here, we examine in a leaf-cutting ant ( Acromyrmex echinatior ) how a recently discovered genetic influence on caste determination interacts with the social environment. By removing most of one phenotype (large workers; LW) from test colonies, we increased the stimulus for larvae to develop into this caste, while for control colonies we removed a representative sample of all workers so that the stimulus was unchanged. We established the relative tendencies of genotypes to develop into LW by genotyping workers before and after the manipulation. In the control colonies, genotypes were similarly represented in the large worker caste before and after worker removal. In the test colonies, however, this relationship was significantly weaker, demonstrating that the change in environmental stimuli had altered the caste propensity of at least some genotypes. The results indicate that the genetic influence on worker caste determination acts via genotypes differing in their response thresholds to environmental cues and can be conceptualized as a set of overlapping reaction norms. A plastic genetic influence on division of labour has thus evolved convergently in two distantly related polyandrous taxa, the leaf-cutting ants and the honeybees, suggesting that it may be a common, potentially adaptive, property of complex, genetically diverse societies.

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Among the shapeshifters: parasite-induced morphologies in ants (Hymenoptera, Formicidae) and their relevance within the EcoEvoDevo framework

EvoDevo ◽

10.1186/s13227-021-00173-2 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Alice Laciny

Keyword(s):

Social Insects ◽

Morphological Changes ◽

Evolutionary Developmental Biology ◽

Caste Differentiation ◽

Natural Experiments ◽

Evolutionary Mechanisms ◽

Open Questions ◽

Caste Evolution ◽

High Level ◽

Host Development

AbstractAs social insects, ants represent extremely interaction-rich biological systems shaped by tightly integrated social structures and constant mutual exchange with a multitude of internal and external environmental factors. Due to this high level of ecological interconnection, ant colonies can harbour a diverse array of parasites and pathogens, many of which are known to interfere with the delicate processes of ontogeny and caste differentiation and induce phenotypic changes in their hosts. Despite their often striking nature, parasite-induced changes to host development and morphology have hitherto been largely overlooked in the context of ecological evolutionary developmental biology (EcoEvoDevo). Parasitogenic morphologies in ants can, however, serve as “natural experiments” that may shed light on mechanisms and pathways relevant to host development, plasticity or robustness under environmental perturbations, colony-level effects and caste evolution. By assessing case studies of parasites causing morphological changes in their ant hosts, from the eighteenth century to current research, this review article presents a first overview of relevant host and parasite taxa. Hypotheses about the underlying developmental and evolutionary mechanisms, and open questions for further research are discussed. This will contribute towards highlighting the importance of parasites of social insects for both biological theory and empirical research and facilitate future interdisciplinary work at the interface of myrmecology, parasitology, and the EcoEvoDevo framework.

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Caste in Social Insects: Genetic Influences Over Caste Determination

Encyclopedia of Animal Behavior ◽

10.1016/b978-0-12-809633-8.20759-0 ◽

2019 ◽

pp. 274-281

Author(s):

Nathan Lo ◽

Madeleine Beekman ◽

Benjamin P. Oldroyd

Keyword(s):

Social Insects ◽

Genetic Influences ◽

Caste Determination

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Polymorphism and division of labour in a socially complex ant: neuromodulation of aggression in the Australian weaver ant, Oecophylla smaragdina

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2015.0704 ◽

2015 ◽

Vol 282 (1811) ◽

pp. 20150704 ◽

Cited By ~ 27

Author(s):

J. Frances Kamhi ◽

Kelley Nunn ◽

Simon K. A. Robson ◽

James F. A. Traniello

Keyword(s):

Social Systems ◽

Division Of Labour ◽

Oecophylla Smaragdina ◽

Minor Worker ◽

Task Specialization ◽

Territorial Defence ◽

Weaver Ant ◽

Eusocial Insects ◽

Worker Size ◽

Pharmacological Manipulations

Complex social structure in eusocial insects can involve worker morphological and behavioural differentiation. Neuroanatomical variation may underscore worker division of labour, but the regulatory mechanisms of size-based task specialization in polymorphic species are unknown. The Australian weaver ant, Oecophylla smaragdina , exhibits worker polyphenism: larger major workers aggressively defend arboreal territories, whereas smaller minors nurse brood. Here, we demonstrate that octopamine (OA) modulates worker size-related aggression in O. smaragdina . We found that the brains of majors had significantly higher titres of OA than those of minors and that OA was positively and specifically correlated with the frequency of aggressive responses to non-nestmates, a key component of territorial defence. Pharmacological manipulations that effectively switched OA action in major and minor worker brains reversed levels of aggression characteristic of each worker size class. Results suggest that altering OA action is sufficient to produce differences in aggression characteristic of size-related social roles. Neuromodulators therefore may generate variation in responsiveness to task-related stimuli associated with worker size differentiation and collateral behavioural specializations, a significant component of division of labour in complex social systems.

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Honeybee (Apis mellifera) Maternal Effect Causes Alternation of DNA Methylation Regulating Queen Development

Sociobiology ◽

10.13102/sociobiology.v68i1.5935 ◽

2021 ◽

Vol 68 (1) ◽

pp. 5935

Author(s):

Xu Jiang He ◽

Hao Wei ◽

Wu Jun Jiang ◽

Yi Bo Liu ◽

Xiao Bo Wu ◽

...

Keyword(s):

Dna Methylation ◽

Apis Mellifera ◽

Signaling Pathways ◽

Maternal Effect ◽

Caste Differentiation ◽

Hippo Signaling ◽

Thorax Length ◽

Queen Cell ◽

Epigenetic Analysis ◽

Worker Caste

Queen-worker caste dimorphism is a typical trait for honeybees (Apis mellifera). We previously showed a maternal effect on caste differentiation and queen development, where queens emerged from queen-cell eggs (QE) had higher quality than queens developed from worker cell eggs (WE). In this study, newly-emerged queens were reared from QE, WE, and 2-day worker larvae (2L). The thorax size and DNA methylation levels of queens were measured. We found that queens emerging from QE had significantly larger thorax length and width than WE and 2L. Epigenetic analysis showed that QE/2L comparison had the most different methylated genes (DMGs, 612) followed by WE/2L (473), and QE/WE (371). Interestingly, a great number of DMGs (42) were in genes belonging to mTOR, MAPK, Wnt, Notch, Hedgehog, FoxO, and Hippo signaling pathways that are involved in regulating caste differentiation, reproduction and longevity. This study proved that honeybee maternal effect causes epigenetic alteration regulating caste differentiation and queen development.

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Major Evolutionary Transitions in Social Insects, the Importance of Worker Sterility and Life History Trade-Offs

Frontiers in Ecology and Evolution ◽

10.3389/fevo.2021.732907 ◽

2021 ◽

Vol 9 ◽

Author(s):

Abel Bernadou ◽

Boris H. Kramer ◽

Judith Korb

Keyword(s):

Life History ◽

Social Insects ◽

Division Of Labour ◽

Evolutionary Transitions ◽

Individual Level ◽

Individual Fitness ◽

Trade Offs ◽

Group Members ◽

The Individual ◽

Worker Sterility

The evolution of eusociality in social insects, such as termites, ants, and some bees and wasps, has been regarded as a major evolutionary transition (MET). Yet, there is some debate whether all species qualify. Here, we argue that worker sterility is a decisive criterion to determine whether species have passed a MET (= superorganisms), or not. When workers are sterile, reproductive interests align among group members as individual fitness is transferred to the colony level. Division of labour among cooperating units is a major driver that favours the evolution of METs across all biological scales. Many METs are characterised by a differentiation into reproductive versus maintenance functions. In social insects, the queen specialises on reproduction while workers take over maintenance functions such as food provisioning. Such division of labour allows specialisation and it reshapes life history trade-offs among cooperating units. For instance, individuals within colonies of social insects can overcome the omnipresent fecundity/longevity trade-off, which limits reproductive success in organisms, when increased fecundity shortens lifespan. Social insect queens (particularly in superorganismal species) can reach adult lifespans of several decades and are among the most fecund terrestrial animals. The resulting enormous reproductive output may contribute to explain why some genera of social insects became so successful. Indeed, superorganismal ant lineages have more species than those that have not passed a MET. We conclude that the release from life history constraints at the individual level is a important, yet understudied, factor across METs to explain their evolutionary success.

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Three new species of Leptanilloides Mann from Andean Ecuador (Formicidae: Leptanilloidinae)

Zootaxa ◽

10.11646/zootaxa.1201.1.2 ◽

2006 ◽

Vol 1201 (1) ◽

pp. 47 ◽

Cited By ~ 8

Author(s):

DAVID A. DONOSO ◽

JUAN M. VIEIRA ◽

ALEXANDER L. WILD

Keyword(s):

New Species ◽

Phenotypic Variation ◽

Morphological Characters ◽

Generic Diagnosis ◽

Army Ant ◽

First Case ◽

Three New Species ◽

Worker Caste

We report three new species of the ant genus Leptanilloides from Andean Ecuador. Leptanilloides nomada sp. n. and L. caracola sp. n. are described from the worker caste, the latter from a unique specimen; L. nubecula sp. n. is described from workers, males, and two gyne subcastes previously unknown for the entire subfamily. Phenotypic variation in morphological characters in the new species L. nomada and L. nubecula is more plastic than suggested by the traditional generic diagnosis. These records represent the first case of three Leptanilloides species occurring in sympatry. We discuss aspects of the army ant syndrome and its relevance to the genus Leptanilloides.Tres nuevas especies del género de hormigas Leptanilloides son descritas a partir de especimenes encontrados en Los Andes ecuatorianos. Leptanilloides nomada sp. n. y L. caracola sp. n. son descritas en base a obreras, ésta última es descrita a partir de un sólo espécimen. L. nubecula sp. n. es descrita en base a obreras, machos y dos subcastas de ginas previamente desconocidas para toda la subfamilia. La variación fenotípica encontrada en algunos caracteres morfológicos de las nuevas especies L. nomada y L. nubecula es más plástica de lo que sugiere la diagnosis genérica tradicional. Estos registros constituyen el primer ejemplo de tres especies de Leptanilloides viviendo en simpatría. Discutimos aspectos del síndrome de las hormigas legionarias y su aplicación al género Leptanilloides.

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