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. 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. Egg 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. We 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.

The Kinmen Islands on the coastline of China represent a recent case of the protection of endangered wildlife in a demilitarized zone. These islands represent the last remaining habitat in southeastern China that supports a healthy natural population of Reeves’ turtle Mauremys reevesii. However, human‐mediated dispersal appears to have aided the establishment of an introduced population of the Chinese stripe‐necked turtle M. sinensis since the late 1990s, resulting in population mixture of the two congeners. To evaluate the potential impacts of hybridization, we evaluated the magnitude of genetic introgression in ponds on Kinmen using mitochondrial cytochrome b sequences and 13 microsatellite loci. We further used eight environmental and biological factors of the ponds to conduct general linear regression model analysis between environmental factors and the magnitude of genetic introgression. Among the 41 sampled ponds, M. reevesii was recorded in 21, of which 12 ponds (57.1%) contained genetic hybrids or backcrosses, corresponding to 11.3–12.7% of the total individuals on the islands. The magnitude of genetic introgression was positively correlated with the amount of introduced M. sinensis occurring in a pond, and marginally negatively associated with the shortest distance from the pond to secondary roads. We conclude that this considerable genetic introgression is attributable to human‐mediated dispersal of M. sinensis; roads and habitat modification may increase the likelihood of unexpected encounters between these two congeners.

Clonal reproduction can provide an advantage for invasive species to establish as it can circumvent inbreeding depression which often plagues introduced populations. The world's most widespread invasive ant,Paratrechina longicornis, was previously found to display a double‐clonal reproduction system, whereby both males and queens are produced clonally, resulting in separate male and queen lineages, while workers are produced sexually. Under this unusual reproduction mode, inbreeding is avoided in workers as they carry hybrid interlineage genomes. Despite the ubiquitous distribution ofP. longicornis, the significance of this reproductive system for the ant's remarkable success remains unclear, as its prevalence is still unknown. Further investigation into the controversial native origin ofP. longicornisis also required to reconstruct the evolutionary histories of double‐clonal lineages. Here, we examine genetic variation and characterize the reproduction mode ofP. longicornispopulations sampled worldwide using microsatellites and mitochondrial DNA sequences to infer the ant's putative native range and the distribution of the double‐clonal reproductive system. Analyses of global genetic variations indicate that the Indian subcontinent is a genetic diversity hotspot of this species, suggesting thatP. longicornisprobably originates from this geographical area. Our analyses revealed that both the inferred native and introduced populations exhibit double‐clonal reproduction, with queens and males around the globe belonging to two separate, nonrecombining clonal lineages. By contrast, workers are highly heterozygous because they are first‐generation interlineage hybrids. Overall, these data indicate a worldwide prevalence of double clonality inP. longicornisand support the prediction that the unusual genetic system may have pre‐adapted this ant for global colonization by maintaining heterozygosity in the worker force and alleviating genetic bottlenecks.

While Wolbachia, an intracellular bacterial symbiont, is primarily transmitted maternally in arthropods, horizontal transmission between species has been commonly documented. We examined kleptoparasitism as a potential mechanism for Wolbachia horizontal transmission, using ant crickets and their host ants as the model system. We compared prevalence and diversity of Wolbachia across multiple ant cricket species with different degrees of host specificity/integration level. Our analyses revealed at least three cases of inter-ordinal Wolbachia transfer among ant and ant crickets, and also showed that ant cricket species with high host-integration and host-specificity tend to harbor a higher Wolbachia prevalence and diversity than other types of ant crickets. This study provides empirical evidence that distribution of Wolbachia across ant crickets is largely attributable to horizontal transmission, but also elucidates the role of intimate ecological association in successful Wolbachia horizontal transmission.