Abstract
BackgroundReproductive division of labor is one of the key features of social insects. Queens are adapted for reproduction while workers are adapted for foraging and colony maintenance. In many species, however, workers retain functional ovaries and can lay unfertilized male eggs or trophic eggs. Here we report for the first time on the occurrence of physogastric workers and apparent worker reproduction in the invasive yellow crazy ant Anoplolepis gracilipes (Fr. Smith). We further examined the reproductive potential and nutritional role of physogastric workers through multidisciplinary approaches including morphological characterization, laboratory manipulation, genetic analysis and behavioral observation.ResultsEgg production with two types of eggs, namely reproductive and trophic eggs, by physogastric workers was found. The reproductive egg was confirmed to be haploid and male-destined, suggesting that the workers produced males via arrhenotokous parthenogenesis as no spermatheca was discovered. Detailed observations suggested that larvae were mainly fed with trophic eggs. Along with consumption of trophic eggs by queens and other castes as part of their diet, the vital role of physogastric workers as “trophic specialist” is confirmed.ConclusionWe propose that adaptive advantages derived from worker reproduction for A. gracilipes may include 1) trophic eggs provisioned by physogastric workers likely assist colonies of A. gracilipes in overcoming unfavorable conditions such as paucity of food during critical founding stage; 2) worker-produced males are fertile and thus might offer an inclusive fitness advantage for the doomed orphaned colony.
Highlights
Reproductive division of labor is one of the key features of social insects
While this study found little support for worker reproduction of A. gracilipes, our preliminary observation, in contrast, suggested that egg production often occurred in queenless A. gracilipes laboratory colonies, and that artificiallyorphaned colonies are invariably found with the presence of “corpulent” workers, whose gaster sizes were conspicuously greater than those of “normal” foraging workers and appeared brown-whitish in color
Our study demonstrates for the first time that A. gracilipes workers possess functional ovaries and are able to produce both reproductive and trophic eggs
Summary
Reproductive division of labor is one of the key features of social insects. Queens are adapted for reproduction while workers are adapted for foraging and colony maintenance. Workers retain functional ovaries and can lay unfertilized male eggs or trophic eggs. A haplodiploid sex determination system is common to all hymenopterans, in which males arise parthenogenetically from unfertilized eggs (arrhenotoky) and are haploid, whereas females arise from fertilized eggs and are diploid [2, 3]. Such unique system results in an asymmetrical genetic relatedness among the colony members where workers. The workers in most ant species retain functional ovaries, and are capable of producing viable male eggs and/or non-viable trophic eggs [6]. Trophic eggs are nutritional packets, and act as an important mechanism
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