Biology subjects

Linksvayer, T. A.

Publications and source records attributed to Linksvayer, T. A..

3 recordsLinked to original sources

bioRxiv2018

The convergent evolution of caste in ants and honey bees is based on a shared core of ancient reproductive genes and many plastic genes

Eusociality has convergently evolved multiple times, but the genomic basis of caste-based division of labor and degree to which independent origins of eusociality have utilized common genes remain largely unknown. Here we characterize caste-specific transcriptomic profiles across development and adult body segments from pharaoh ants (Monomorium pharaonis) and honey bees (Apis mellifera), representing two independent origins of eusociality. We identify a substantial shared core of genes upregulated in the abdomens of queen ants and honey bees that also tends to be upregulated in mated female flies, suggesting that these genes are part of a conserved insect reproductive groundplan. Outside of this shared groundplan, few genes are differentially expressed in common. Instead, the majority of the thousands of caste-associated genes are plastically-expressed, rapidly evolving, and relatively evolutionarily young. These results emphasize that the recruitment of both highly conserved and lineage-specific genes underlie the convergent evolution of novel traits such as eusociality.

evolutionary biology↗

bioRxiv2017

Ant nurse workers exhibit behavioral and transcriptomic specialization on larval stage but not caste

Division of labor within and between the worker and queen castes is thought to underlie the tremendous success of social insects. Colonies might benefit if subsets of nurse workers specialize further in caring for larvae of a certain stage or caste, given that larval nutritional requirements depend on stage and caste. We used short- (<1 hr) and long-term (ten days) behavioral observations to determine whether nurses of the pharaoh ant (Monomorium pharaonis) exhibit such specialization. We found that nurses were behaviorally specialized based on larval instar but not on larval caste. This specialization was widespread, with 56% of nurses in the short-term and between 22-27% in the long-term showing significant specialization. Additionally, we identified [~]200 genes that were differentially expressed in nurse head and abdominal tissues between nurses feeding young versus old larvae. These included 18 genes predicted to code for secreted proteins, which may be passed from nurses to larvae via trophallaxis, as well as vitellogenin and major royal jelly protein-1, which have previously been implicated in the transfer of nutrition from nurse to larvae and the regulation of larval development and caste in social insects. Altogether, our results provide the first evidence in any social insect for a division of labor among nurse workers based on larval stage, and our study begins to elucidate the molecular mechanisms underlying this specialization.

evolutionary biology↗

bioRxiv2017

Pharaoh ant colonies dynamically regulate colony demography by culling young queen and male-destined larvae

The success of social insect colonies is dependent upon efficient and dynamic allocation of resources to alternate queen and worker castes. The developmental and molecular mechanisms regulating the caste fate of individual larvae in response to environmental cues have been the focus of intense study. However, the mechanisms regulating colony-level resource allocation into alternate castes (i.e. caste allocation ratios) are less well studied. Here, we systematically manipulate colony demography to elucidate the social regulatory mechanisms of caste allocation in the ant Monomorium pharaonis. We find that differences in caste allocation result from differences in timing and efficiency of culling of very young reproductive-destined larvae, which are always present in colonies. Based on our results, we develop a conceptual model depicting how colonies integrate numerous individual-level caste determination decisions to regulate colony-level caste allocation. We propose that adult workers make decisions about culling larvae based on the ratio of the number of workers to the number of eggs contained in colonies, likely signalled by pheromone present on eggs. This strategy is a bet-hedging strategy which enables the dynamic alteration of colony demography in response to internal and external conditions. The strategy is likely key to the ability of M. pharaonis and similar ants to thrive in disturbed habitats and to become widespread invasive species.\n\nSignificance StatementThe defining feature of social insect societies is the presence of alternate queen (reproductive) and worker (non-reproductive) castes of individuals. The fitness of social insect colonies is dependent upon efficient allocation of resources to alternate castes, particularly in the case of highly polygynous (multi-queen) societies. However, the mechanisms by which such societies regulate caste allocation are largely unknown. In this study, we show that colonies manipulate their production of queens (and also males) versus workers according to the present density of eggs in the colony, which serves as a reliable indicator of queens fertility. Provided egg density is high, colonies kill queen-and male-destined larvae; when egg density falls, colonies begin to rear queens and males. This flexible resource allocation strategy is key to the ability of highly polygynous species to thrive in marginal (often human-associated) habitats.

ecology↗