Lenancker Pauline, Feldhaar Heike, Holzinger Anja, Greenfield Melinda, Strain Angela, Yeeles Peter, Hoffmann Benjamin D, Tay Wee Tek, Lach Lori
College of Science and Engineering, James Cook University, Cairns, QLD, 4870, Australia.
CSIRO, Tropical Ecosystems Research Centre, Darwin, NT, 0822, Australia.
Front Zool. 2021 Mar 22;18(1):13. doi: 10.1186/s12983-021-00392-2.
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.
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.
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.
工蚁生殖对社会性昆虫群落的社会凝聚力和效率有重要影响，但其在入侵蚂蚁成功入侵过程中的作用一直被忽视。我们通过对233个圈养蚁群的观察、实验室实验和基因分析，来研究入侵性长足捷蚁（黄疯蚁）中工蚁生殖的条件及其对种间防御的潜在代价。我们确定了工蚁产雄的发生率以及其是否由蚁后缺失引发；腹部膨大的肥腹工蚁是否更有可能具有生殖能力，正常工蚁和肥腹工蚁在觅食和防御贡献方面的比较情况；以及工蚁产的雄蚁与可能由蚁后或工蚁产出的雄蚁在大小和杂合性方面是否存在差异。
在我们的233个圈养蚁群中，有66个蚁群产出了雄蚁，其中25个蚁群中，部分雄蚁只能由工蚁产出。工蚁数量更多的蚁群更有可能产出雄蚁，尤其是无蚁后的蚁群。在我们的蚁群中，从首次出现卵到成年雄蚁出现的平均天数为54.1±10.2（平均值±标准差，n = 20）。在我们的实验室实验中，移除蚁后引发了肥腹工蚁比例的增加。肥腹工蚁比正常工蚁更有可能拥有含卵黄的卵母细胞（37 - 54.9%），这是可育或营养性产卵的一个指标。在种间攻击测试中，肥腹工蚁的攻击性较弱，且觅食比正常工蚁少。工蚁产出的雄蚁的头宽和翅长平均分别比来源不确定的雄蚁大4.0%和4.3%。我们的微卫星DNA分析表明，5.5%的工蚁产出的雄蚁和14.3%来源不确定的雄蚁是杂合的，这表明长足捷蚁中存在二倍体雄蚁和/或基因嵌合体。
我们的实验工作提供了关于长足捷蚁工蚁生殖及其对蚁群防御潜在代价的关键信息。如果未交配的蚁后与工蚁产出的雄蚁能够在蚁巢内交配，那么长足捷蚁工蚁在无蚁后情况下产雄的能力可能也有助于其作为入侵物种的成功入侵。
