The cavity-nest ant Temnothorax crassispinus prefers larger nests

Sexual Offspring Production by Acorn Ant Temnothorax crassispinus Colonies Is Associated with the Colony Size but Not with the Volume of the Nest Cavity

Nest sites are important for ants, as the nests provide refuge against enemies and ensure optimal conditions for the brood development. As the construction of a nest is a time and energy consuming activity, many ant species dwell in ready-for-use cavities. For them, choosing a good nest site is important, as the quality of nest site could affect factors such as the energy allocation and production of sexual individuals. Ants of genus Temnothorax inhabit cavities in, e.g., acorns and twigs, and these ant colonies prefer larger cavities as nest sites. It was previously shown that colonies inhabiting more durable nest sites invested more resources in sexual production. The aim of this study was to find out whether the volume of a nest cavity influences the sexual offspring production of acorn ant Temnothorax crassispinus colonies. For this purpose, a three-month long laboratory experiment was performed. Colonies of the Temnothorax ant were kept in artificial nest cavities differing in volume. It was found that there was no correlation between the productivity per capita and the colony size. More populous colonies produced more sexual individuals; however, we found no statistical difference in the production of sexual individuals between the colonies that inhabited cavities of different volumes.

Emergent collective behavior evolves more rapidly than individual behavior among acorn ant species

Emergence is a fundamental concept in biology and other disciplines, but whether emergent phenotypes evolve similarly to nonemergent phenotypes is unclear. The hypothesized process of emergent evolution posits that evolutionary change in at least some collective behaviors will differ from evolutionary change in the corresponding intrinsic behaviors of isolated individuals. As a result, collective behavior might evolve more rapidly and diversify more between populations compared to individual behavior. To test whether collective behavior evolves emergently, we conducted a large comparative study using 22 ant species and gathered over 1,500 behavioral rhythm time series from hundreds of colonies and isolated individuals, totaling over 1.5 y of behavioral data. We show that analogous traits measured at individual and collective levels exhibit distinct evolutionary patterns. The estimated rates of phenotypic evolution for the rhythmicity of activity in ant colonies were faster than the evolutionary rates of the same behavior measured in isolated individual ants, and total variation across species in collective behavior was higher than variation in individual behavior. We hypothesize that more rapid evolution and higher variation is a widespread feature of emergent phenotypes relative to lower-level phenotypes across complex biological systems.

Distribution of brood of the acorn ant Temnothorax crassispinus in artificial nests after forced migration

Nest sites are important for social insects, as they provide refuge against enemies and ensure optimal conditions for the brood development. In large nests, the different chambers can be used for different reasons; for example, for food storage or as a brood chamber. Acorn ants from the genus Temnothorax dwell in small cavities in acorns and wood; however, even such small chambers can have a high degree of spatial heterogeneity. During this study, the distribution of brood items of the acorn ant Temnothorax crassispinus inside artificial nest cavities composed of three chambers in a linear system was analysed. 29 ant colonies were photographed 13 times during a period of approximately one month: during three consecutive days, and after forced migrations. I found that the distribution of the brood inside the nest cavity was similar during the consecutive days; however, after the forced migration, the distribution typically changed. Almost all the brood items were kept farther from the entrance. Keeping the brood farther from the entrance could be explained as a safer option.

Acorn Ants May Create and Use Two Entrances to the Nest Cavity

Simple Summary

Large nests of ants, or ant hills, which are inhabited by numerous workers, are universally known. However, many ant species live in small colonies and do not construct nests, but instead dwell in ready-for-use cavities. In Central Europe, acorn ants are among the most widely distributed and common species but are also frequently overlooked as the workers are small and colonies of the species typically range from only a few dozen to about two hundred individuals. Often, a whole colony lives in just one empty acorn or a cavity inside a small twig. Such a cavity, such as an empty acorn, typically has one hole resulting from the activity of wood-boring beetles, and that hole is used by the ant colony as the entrance to the nest. Acorn ants have been the subject of numerous experiments, including those focused on the choice of nest sites. For example, it was previously found that ants prefer sites with a narrow vs. a wider entrance. However, cavities with good-sized hole are rare; thus, the possibility to modify a potential nest site, including a reduction in the size of the hole, should be a favorable matter for the ants. The results of this study showed that the ant colonies could inhabit imperfect cavities that need a modification, e.g., a reduction of the available holes, and that such small colonies may even create two entrances to the nest cavity. However, the effect of the presence of more than one entrance to the nest on the behavior of the ants is unknown.

Abstract

Many ant species construct large nests that are inhabited by numerous workers, but other species dwell in ready-for-use cavities and live in small colonies. Ants of the genus Temnothorax inhabit small cavities, e.g., in acorns, twigs, and under rocks. Although a preference for nest sites with a narrower entrance is known, recent studies have shown that they also use cavities with wider entrances and may modify the size of such entrances. As good cavities for nest sites are a limited resource, the possibility to modify a potential nest site, including a reduction in the size of the hole, should be a favorable matter for the ants. Through field and laboratory experiments, I studied the acorn ant Temnothorax crassispinus. Observations showed that they readily inhabited imperfect cavities and, if necessary, modified the holes to such cavities. If they had to repair a nest site, they sometimes created a second entrance; there was no difference in the sizes of the entrances. In the field, for entrance modification or blocking an unnecessary hole, the acorn ants used soil, grains of sand, and parts of plants. In the laboratory, the ant colonies showed no preference for nest sites with one entrance vs. a nest cavity with two entrances. The results of this study showed that even such small ant colonies could use nest sites with multiple entrances; however, the effect of the presence of more than one entrance on the behavior of the ants is unknown.

Queen execution in a monogynous ant

Workers in many species of social insects are capable of laying unfertilized eggs, which can develop into haploid males. This causes a conflict about male parentage between queens and workers. In a few species, this may result in matricide, that is, workers kill the colony's queen. Queen killing has so far been observed mainly in multi-queen colonies or in annual species, when the queen's fecundity declines at the end of the reproductive period. Here, we report queen expulsion and matricide in a monogynous, monandrous ant with perennial societies. Workers were seen to aggressively expel both related and unrelated queens from their nest shortly after the end of hibernation. Queen expulsion and matricide led to a significant decrease in the number of workers and brood, but eventually increased the direct fitness of workers through significant male production. Long-term observations revealed a short lifespan of queens, while workers in orphaned colonies survived and produced male offspring over several years.

Nest Site Selection during Colony Relocation in Yucatan Peninsula Populations of the Ponerine Ants Neoponera villosa (Hymenoptera: Formicidae)

In the Yucatan Peninsula, the ponerine ant Neoponera villosa nests almost exclusively in tank bromeliads, Aechmea bracteata. In this study, we aimed to determine the factors influencing nest site selection during nest relocation which is regularly promoted by hurricanes in this area. Using ants with and without previous experience of Ae. bracteata, we tested their preference for refuges consisting of Ae. bracteata leaves over two other bromeliads, Ae. bromeliifolia and Ananas comosus. We further evaluated bromeliad-associated traits that could influence nest site selection (form and size). Workers with and without previous contact with Ae. bracteata significantly preferred this species over others, suggesting the existence of an innate attraction to this bromeliad. However, preference was not influenced by previous contact with Ae. bracteata. Workers easily discriminated between shelters of Ae. bracteata and A. comosus, but not those of the closely related Ae. bromeliifolia. In marked contrast, ants discriminated between similar sized Ae. bracteata and Ae. bromeliifolia plants, suggesting that chemical cues and plant structure play an important role. Size was also significant as they selected the largest plant when provided two dissimilar Ae. bracteata plants. Nest site selection by N. villosa workers seems to depend on innate preferences but familiarization with plant stimuli is not excluded.

Sources of intraspecific variation in the collective tempo and synchrony of ant societies

Populations of independently oscillating agents can sometimes synchronize. In the context of animal societies, conspicuous synchronization of activity is known in some social insects. However, the causes of variation in synchrony within and between species have received little attention. We repeatedly assessed the short-term activity cycle of ant colonies (Temnothorax rugatulus) and monitored the movements of individual workers and queens within nests. We detected persistent differences between colonies in the waveform properties of their collective activity oscillations, with some colonies consistently oscillating much more erratically than others. We further demonstrate that colony crowding reduces the rhythmicity (i.e., the consistent timing) of oscillations. Workers in both erratic and rhythmic colonies spend less time active than completely isolated workers, but workers in erratic colonies oscillate out of phase with one another. We further show that the queen's absence can impair the ability of colonies to synchronize worker activity and that behavioral differences between queens are linked with the waveform properties of their societies.

Exploring nest structures of acorn dwelling ants with X-ray microtomography and surface-based three-dimensional visibility graph analysis

The physical spaces within which organisms live affect their biology and in many cases can be considered part of their extended phenotype. The nests of social insect societies have a fundamental impact on their ability to function as complex superorganisms. Ants in many species excavate elaborate subterranean nests, but others inhabit relatively small pre-formed cavities within rock crevices and hollow seeds. Temnothorax ants, which often nest within acorns, have become a model system for studying collective decision making. While these ants have demonstrated remarkable degrees of rationality and consistent precision with regard to their nest choices, never before has the fine scale internal architecture and spatial organization of their nests been investigated. We used X-ray microtomography to record high-resolution three-dimensional (3D) scans of Temnothorax colonies within their acorns. These data were then quantified using image segmentation and surface-based 3D visibility graph analysis, a new computational methodology for analysing spatial structures. The visibility graph analysis method integrates knowledge from the field of architecture with the empirical study of animal-built structures, thus providing the first methodological cross-disciplinary synergy of these two research areas. We found a surprisingly high surface area and degree of spatial heterogeneity within the acorn nests. Specific regions, such as those associated with the locations of queens and brood, were significantly more conducive to connectivity than others. From an architect's point of view, spatial analysis research has never focused on all-surface 3D movement, as we describe within ant nests. Therefore, we believe our approach will provide new methods for understanding both human design and the comparative biology of habitat spaces.This article is part of the theme issue 'Interdisciplinary approaches for uncovering the impacts of architecture on collective behaviour'.

Emigration speed and the production of sexuals in colonies of the ant Temnothorax crassispinus under high and low levels of disturbance

A nest relocation is costly for social insects, and involves hazards. Emigrations were studied in Temnothorax crassispinus ant colonies, which inhabit ephemeral nest sites, and which frequently change their nests. In a laboratory experiment, ant colonies from one group were forced to change their nest sites 10 times over a ca. 3-month period, whilst colonies from the second group were forced to adopt this practice twice (on the beginning of May, and in the second half of July). Colonies of the ant from both the groups reduced their total emigration duration. However, the duration of the transport phase remained unchanged. In the case of colonies with higher level of disturbance, there was no relation between colony growth rate and energy allocation in sexual individuals, whilst a negative correlation between these parameters was present in group with lower level of disturbance. In colonies with lower level of disturbance, the investment in sexuals was not correlated with the number of workers at the end of the experiment, whereas such a correlation was demonstrated for colonies with higher level of disturbance. The disturbance, and thus necessity of frequent nest relocations, may be perceived by ants as a signal that nest sites are of a lower quality and may contribute to a change in energy allocation.