Biology subjects

Schultner, E.

Publications and source records attributed to Schultner, E..

7 recordsLinked to original sources

bioRxiv2025

Metabolic plasticity supports a flexible nutritional symbiosis in Cardiocondyla ants

Nutritional symbioses have repeatedly evolved in insects, yet how hosts regulate these partnerships to balance benefits across development and environments remains unclear. Ants provide an exceptional system to address this question, as several lineages maintain ancient symbionts that can be naturally lost without harming the host. Using Cardiocondyla obscurior, which carries and occasionally loses the vertically transmitted symbiont Cand. Westeberhardia cardiocondylae, we reveal the regulatory dynamics and function of this labile association. Symbionts provide shikimate-derived nutrients that enhance colony resilience under protein limitation, while hosts actively regulate symbiont abundance during protein scarcity and cuticle formation to optimise resource allocation. In the symbionts absence, ants compensate by upregulating genes enabling tyrosine acquisition from external sources. This metabolic flexibility allows colonies to exploit symbiont-derived and environmental nutrients, sustaining both growth and survival across nutritional contexts. Our findings reveal dynamic host regulation as a mechanism sustaining the persistence and adaptability of ancient symbioses.

ecology↗

bioRxiv2024

Variability of immune gene expression among different groups within ant colonies shows a multifaceted response to infection by a non-lethal ectoparasitic fungus

Social insect colonies are known to be targeted by a wide variety of different parasites and pathogens because of their high host abundance. However, within a colony, the level of risk to exposure could vary among individuals depending on their role. Unlike many known parasites, which mostly target specific groups of individuals, e.g. foragers, the myrmecoparasitic fungus Rickia wasmannii infects entire ant colonies, being linked to subtle changes in physiology, morphology and behaviour. We investigated how different groups within the colonies respond to being exposed to the fungus by measuring the expression of the genes defensin 1 and prophenoloxidase, both vital components of ant immunity. We found that workers, queens and broods varied in their immune response. Workers displayed diverse profiles, with variable responses to infection: in same-age workers, both prophenoloxidase and defensin 1 levels exhibited increases in correlation with pathogen loads. Queens exhibited a more pronounced immune response. Highly infected queens had a heightened immune response. Larvae did not show a discernible response. Morphological and physiological characteristics had limited effects on gene expression, except in the case of queens, where larger individuals displayed higher defensin 1 expression. Our study shows that these divergent responses likely stem from the differing physiological needs and priorities of various groups within the colony. HighlightsO_LIIn same-age workers, prophenoloxidase and defensin 1 levels increased with pathogen loads. C_LIO_LIBody size affected defensin 1 expression in a caste-specific manner: larger queens displayed higher expression. C_LIO_LIInfection did not elicit any specific response in larvae. C_LIO_LIThe diverse response to infection likely arise from distinct physiological needs and priorities within colony groups. C_LI

zoology↗

bioRxiv2023

Darwin's "neuters" and the evolution of the sex continuum in a superorganism

Ant castes are an amazing example of phenotypic plasticity. In worker-destined embryos of the ant Cardiocondyla obscurior, the default female developmental trajectory is interrupted even before the gonadal precursor cells acquire a sexual identity. miRNA and mRNA expression in embryos reveal three distinct phenotypic entities: males, females, and "neuters", as Darwin coined the worker caste in "On the Origin of Species". Based on these results we propose that haplodiploidy, in conjunction with insect sex determination, allows for the expression of a third dimension on the sex continuum, thus facilitating the evolution of individuals which develop traits their parents do not have. One sentence summarySex and caste differentiation begin during the same embryonic developmental window in the ant Cardiocondyla obscurior.

evolutionary biology↗

bioRxiv2023

Sex- and caste-specific developmental responses to juvenile hormone in an ant with maternal caste determination

Queen-worker caste polyphenism in social insects is a prime example for developmental plasticity. Most of what we know about caste development comes from studies of the honeybee, in which female caste is determined during larval development and workers retain functional ovaries. The ant genus Cardiocondyla is one of only few genera in which complete worker sterility has evolved, so that adult workers completely lack reproductive organs. In C. obscurior, queen- and worker-destined individuals are distinct in their development by late-embryogenesis, and castes can be distinguished in a non-invasive manner from this stage onwards. This provides the opportunity to investigate the degree of flexibility in caste development in a species with early caste determination. Using topical juvenile hormone treatment, a method known to influence caste determination and differentiation in some species, we investigated whether hormone manipulation affects the development and growth of queen and worker-destined late-stage embryos and larvae, as well as of early-stage embryos which cannot yet be distinguished by caste. We found no effect of hormone treatment on female caste ratios or body sizes in any of the treated stages, even though individuals reacted to heightened hormone availability with increases in the expression of kruppel-homolog 1, a conserved JH first-response gene. In contrast, hormone treatment resulted in the emergence of significantly larger males. These results show that in C. obscurior, early, presumably maternal caste determination leads to irreversible and highly-canalized caste-specific development and growth.

zoology↗

bioRxiv2022

The indispensable soma of Cardiocondyla obscurior ants

The evolutionary mechanisms that shape aging in social insects are not well understood. It is commonly assumed that queens live long and prosperous, while workers are regarded as a short-lived disposable caste because of their low reproductive potential. Queens of the ant Cardiocondyla obscurior gain high fitness late in life by increasing investment into sexual offspring as they age. This results in strong selection against senescence until shortly before death. Here, we show that workers have the same lifespan and shape of aging as queens, even though workers lack reproductive organs and cannot gain direct fitness. Under consideration of the prevailing aging theories and the biology of the species, we hypothesize that programmed aging has possibly evolved under kin selection. Impact statementMorphologically distinct fertile queen and sterile worker castes in the model ant Cardiocondyla obscurior show the same pace and shape of aging, contradicting the paradigm of queen/worker lifespan divergence in social insects.

evolutionary biology↗

bioRxiv2021

Crystalline deposits reveal caste identity of late embryos and larvae of the ant Cardiocondyla obscurior

Ant queens and workers commonly engage in conflict over reproductive allocation because they have different fitness optima. How such conflicts are resolved depends on the power that each party of interest holds. Here, we show that queens have control over caste allocation in the ant Cardiocondyla obscurior. With the discovery of crystalline deposits that allow the identification of queens and workers across the entire course of development, we demonstrate that caste fate is irreversibly determined in the egg stage. Comparison of queen and worker-destined eggs and larvae revealed size and weight differences in late development, but no discernible differences in traits that may be used in social interactions, including hair morphology and cuticular odors. In line with this lack of caste-specific traits, adult workers treated developing queens and workers indiscriminately, even in the presence of a fertile queen. Together with previous studies showing queen control over sex allocation, these results provide evidence that conflict over reproductive allocation is absent in this ant.

evolutionary biology↗

bioRxiv2020

Cytoplasmic incompatibility between Old and New World populations of a tramp ant

As we enter the Anthropocene, the evolutionary dynamics of species will change drastically, and as yet unpredictably, due to human activity. Already today, increases in global human traffic have resulted in the rapid spread of species to new areas, leading to the formation of geographically isolated populations. These go on to evolve in allopatry, which can lead to reproductive isolation, and potentially, the formation of new species. Surprisingly, little is known about such eco-evolutionary processes in ants, even though numerous invasive ant species are globally distributed in geographically isolated populations. Here, we describe the first case of cytoplasmic incompatibility (CI) between populations of a cosmotropic distributed tramp ant with Asian roots, Cardiocondyla obscurior, which has acquired a novel Wolbachia strain in the New World. Our study uncovers the first symbiont-induced mechanism of reproductive isolation in ants, providing a novel perspective on the biology of globally distributed ants.

evolutionary biology↗