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Abstract With the accelerating pace of climate change, we urgently need to understand how physiological traits shape behavioural plasticity in response to environmental stress. In social insects, collective behaviour operates without central control but through interactions among individual participants. In the aggregate, this produces a collective response to environmental conditions.Here we consider how variation among desert ant colonies in the cuticular hydrocarbons (CHCs) that prevent water loss is associated with variation among colonies in the collective behaviour that manages water stress. Colonies of the desert ant,Pogonomyrmex barbatus, differ in the collective regulation of foraging activity to manage water loss to evaporation while foraging. Foraging is regulated through olfactory interactions between outgoing and returning foragers, which determine a forager's decision whether to leave the nest on the next trip. Some colonies are risk‐averse, with foragers less likely to make foraging trips in dry conditions, while others are risk‐tolerant, with foragers who do not reduce foraging trips in dry conditions.We found that behavioural differences among colonies are associated with the capacity of their foragers' CHCs to prevent water loss. In risk‐averse colonies whose foragers make fewer trips in dry conditions, the abundance of alkenes was significantly higher. High abundance of alkenes, with a low melting point, makes the CHC layer more permeable, increasing susceptibility to water loss. In one of 2 years of this study, we found that workers in risk‐averse colonies also had significantly shortern‐alkanes, which further enhance water permeability of the CHC layer and thus desiccation risk.To our knowledge, this is the first report of variation among conspecific colonies in CHC profile that is linked to colony differences in collective behaviour. Read the freePlain Language Summaryfor this article on the Journal blog.
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Nest Entrance Architecture and the Regulation of Foraging Activity in Desert Harvester Ants
ABSTRACT The architecture of an ant colony's nest entrance modulates the regulation of activity in and out of the nest. This study considers how the architecture of nests of the desert harvester antPogonomyrex barbatusfacilitates the regulation of foraging activity in an arid environment. Colonies must spend water, in water lost to evaporation when outside the nest, to obtain food and water. Previous work shows that encounters in the chamber just inside the entrance function as the valve to manage this tradeoff by regulating whether foragers decide to leave the nest on another trip. Here both complete and partial excavations, and observations inside active nests, were made in a long‐term study population in New Mexico, US. Both the overall nest architecture and the set of chambers around the nest entrance are structured as a minimum spanning tree with the entrance chamber as hub. The entrance chamber is surrounded by 1–6 adjacent chambers not linked to each other, with 2–3 tunnels that lead to strings of widely spaced chambers descending 1–2 m. Observations with a videoscope inside active nests show that exterior workers of different tasks move up to the entrance chamber each day during foraging activity and descend below it afterwards, and that interior workers quickly carry food down from the entrance chamber to the deeper nest. Larger, older colonies have more nest entrances with tunnels leading to a single entrance chamber than younger, smaller colonies; this may reduce variability in encounter rates. The nest entrance architecture facilitates rapid adjustment of activity outside the nest. However, in current, deepening drought conditions, it is susceptible to damage when the upper clay layer of the calichi soil dries out, disrupting encounters in the entrance chamber and inhibiting the colony's capacity to manage water loss.
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- Award ID(s):
- 1940647
- PAR ID:
- 10675488
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Ecology and Evolution
- Volume:
- 15
- Issue:
- 9
- ISSN:
- 2045-7758
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Collective behavioural plasticity allows ant colonies to adjust to changing conditions. The red harvester ant (Pogonomyrmex barbatus), a desert seed-eating species, regulates foraging activity in response to water stress. Foraging ants lose water to evaporation. Reducing foraging activity in dry conditions sacrifices food intake but conserves water. Within a year, some colonies tend to reduce foraging on dry days while others do not. We examined whether these differences among colonies in collective behavioural plasticity persist from year to year. Colonies live 20–30 years with a single queen who produces successive cohorts of workers which live only a year. The humidity level at which all colonies tend to reduce foraging varies from year to year. Longitudinal observations of 95 colonies over 5 years between 2016 and 2021 showed that differences among colonies, in how they regulate foraging activity in response to day-to-day changes in humidity, persist across years. Approximately 40% of colonies consistently reduced foraging activity, year after year, on days with low daily maximum relative humidity; approximately 20% of colonies never did, foraging as much or more on dry days as on humid days. This variation among colonies may allow evolutionary rescue from drought due to climate change.more » « less
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In the course of conducting honey bee experiments on the Greek Island of Lesbos we took the opportunity to observe the reactions of ants, Messor oertzeni Forel (Hymenoptera Formicidae Myrmicinae), to a baited ant trap placed in its main foraging path (active ingredient: sodium cacodylate). Each trap had three entrances and we tested five nests. For 14 days we observed the nests and photographs were taken daily to document our observations. Following a baseline condition in which none of the three entrances were open, one entrance was open. Several days later the entrance we opened was turned 90 degrees away from the main foraging trail and a second entrance was opened and placed in the same orientation as the first entrance (i.e., in the main foraging path). Our observations revealed that for four of the five ant colonies, the ants built a barrier around the opened entrance preventing other ants from entering the trap. The materials they used to bar the entrance was composed of twigs, pebbles and soil. We believe that the apparent ability of ants to avoid the effects of an insecticide by baring the entrance to a bait trap is a novel finding and should be replicated under more controlled conditions.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/ece3.72122
