Origin, behaviour, and genetics of reproductive workers in an invasive ant

Lenancker, Pauline, Feldhaar, Heike, Holzinger, Anja, Greenfield, Melinda, Strain, Angela, Yeeles, Peter, Hoffmann, Benjamin D., Tay, Wee Tek, and Lach, Lori (2021) Origin, behaviour, and genetics of reproductive workers in an invasive ant. Frontiers in Zoology, 18. 13.

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Abstract

Background

Worker reproduction has an important influence on the social cohesion and efficiency of social insect colonies, but its role in the success of invasive ants has been neglected. We used observations of 233 captive colonies, laboratory experiments, and genetic analyses to investigate the conditions for worker reproduction in the invasive Anoplolepis gracilipes (yellow crazy ant) and its potential cost on interspecific defence. We determined the prevalence of worker production of males and whether it is triggered by queen absence; whether physogastric workers with enlarged abdomens are more likely to be reproductive, how normal workers and physogastric workers compare in their contributions to foraging and defence; and whether worker-produced males and males that could have been queen- or worker-produced differ in their size and heterozygosity.

Results

Sixty-six of our 233 captive colonies produced males, and in 25 of these, some males could only have been produced by workers. Colonies with more workers were more likely to produce males, especially for queenless colonies. The average number of days between the first appearance of eggs and adult males in our colonies was 54.1 ± 10.2 (mean ± SD, n = 20). In our laboratory experiment, queen removal triggered an increase in the proportion of physogastric workers. Physogastric workers were more likely to have yolky oocytes (37–54.9%) than normal workers (2–25.6%), which is an indicator of fertile or trophic egg production. Physogastric workers were less aggressive during interspecific aggression tests and foraged less than normal workers. The head width and wing length of worker-produced males were on average 4.0 and 4.3% greater respectively than those of males of undetermined source. Our microsatellite DNA analyses indicate that 5.5% of worker-produced males and 14.3% of males of undetermined source were heterozygous, which suggests the presence of diploid males and/or genetic mosaics in A. gracilipes.

Conclusions

Our experimental work provides crucial information on worker reproduction in A. gracilipes and its potential cost to colony defence. The ability of A. gracilipes workers to produce males in the absence of queens may also contribute to its success as an invasive species if intranidal mating can take place between virgin queens and worker-produced males.

Item ID: 68025
Item Type: Article (Research - C1)
ISSN: 1742-9994
Keywords: Anoplolepis gracilipes, Aggression tests, Eusocial insects, Haplodiploid, Hymenoptera,Oecophyllasmaragdina, Oocytes, Ovaries, Worker conflict, Worker reproduction
Copyright Information: This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.
Funders: Universities Australia-German Academic Exchange Service (DAAD), Holsworth Wildlife Research Endowment (HWRE), Ecological Society of Australia (ESA), Skyrail Rainforest Foundation (SRF), Kuranda Envirocare, Wet Tropics Management Authority (WTMA)
Date Deposited: 22 Jun 2021 02:03
FoR Codes: 41 ENVIRONMENTAL SCIENCES > 4102 Ecological applications > 410202 Biosecurity science and invasive species ecology @ 60%
31 BIOLOGICAL SCIENCES > 3109 Zoology > 310913 Invertebrate biology @ 40%
SEO Codes: 18 ENVIRONMENTAL MANAGEMENT > 1806 Terrestrial systems and management > 180602 Control of pests, diseases and exotic species in terrestrial environments @ 50%
28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280102 Expanding knowledge in the biological sciences @ 50%
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