Mikat, M. | bioRxiv Science

bioRxiv2022

Genetic evidence for parthenogenesis in small carpenter bee, Ceratina dallatoreana in its native distribution area

Arrhenotoky is typical mode of reproduction for Hymenoptera - females originate from fertilized eggs, males from unfertilized eggs. However, some lineages of Hymenoptera have switched to thelytoky, where diploid females originate instead from unfertilized diploid eggs. In the contras with some other hymenopteran lineages, thelytoky is generally very rare in bees. Here, we examined reproduction in the small carpenter bee Ceratina dallatoreana, which is assumed to be thelytokous. We compared genotype of microsatellite loci between mothers and their offspring. Offspring were genetically identical with mother in all cases. We did not detect any male offspring. Therefore, we conclude that parthenogeny is the prevailing, and perhaps obligate, mode of reproduction in C. dallatoreana. Offspring were clones of their mother with no observed decrease of heterozygosity. Thus the cytological mode of parthenogenesis is apomixis, or automimic with central fusion and extremely reduced or non-existing recombination. Ceratina bees are originally facultatively eusocial, therefore thelytoky may influence social evolution by causing extremely high within-colony relatedness. However, to date no multifemale nests have been recorded in C. dallatoreana.

genetics↗

bioRxiv2021

Individual-level specialisation and interspecific resource partitioning in bees revealed by pollen DNA metabarcoding

It is increasingly recognised that intraspecific variation in traits, such as morphology, behaviour, or diet is both ubiquitous and ecologically important. While many species of predators and herbivores are known to display high levels of between-individual diet variation, there is a lack of studies on pollinators. It is important to fill in this gap because individual-level specialisation of flower-visiting insects is expected to affect their efficiency as pollinators with consequences for plant reproduction. Accordingly, the aim of our study was to quantify the level of individual-level specialisation and foraging preferences, as well as interspecific resource partitioning, across different temporal scales in three co-occurring species of bees of the genus Ceratina (Hymenoptera: Apidae: Xylocopinae), C. chalybea, C. nigrolabiata, and C. cucurbitina. We conducted a field experiment where we provided artificial nesting opportunities for the bees and combined a short-term mark-recapture study with the dissection of the bees nests to obtain repeated samples from individual foraging females and complete pollen provisions from their nests. Hence, we could study variation of the composition of pollen collected by the bees at different temporal scales. We used DNA metabarcoding based on the ITS2 locus to identify the composition of the pollen samples. We found that the composition of pollen carried on the bodies of female bees and stored in the brood provisions in their nests significantly differed among the three co-occurring species. At the intraspecific level, individual females consistently differed in their level of specialisation and in the composition of pollen carried on their bodies and stored in their nests. Our study thus provides evidence of consistent individual-level specialisation in pollinators across multiple temporal scales. We also demonstrate that higher generalisation at the species level stemmed from larger among-individual variation in diets as observed in other types of consumers, such as predators. Our study thus reveals how specialisation and foraging preferences of bees change from the scale of individual foraging bouts to complete pollen provisions accumulated in their nests over their lifetime. Such multi-scale view of foraging behaviour is necessary to improve our understanding of the functioning of plant-flower visitor communities.

ecology↗

bioRxiv2020

Unrelated males in colonies of facultatively social bee

Colonies of social Hymenoptera are usually groups of closely related females, in which the dominant female(s) is specialized for reproduction and subordinate females care for immature offspring. Kin selection is thought to be the main factor that supports social cohesion. We have discovered a simple society of the bee Ceratina chalybea with an average of 4.68 colony members that cannot be maintained by kin selection alone. These colonies consisted of old reproductive female, young adults and provisioned brood cells. About half of young adults are unrelated to the old female, and almost all of the young adults are male. The old female provisions new brood cells, while continuing to feed young adult offspring. As young adults do not perform demanding or risky activities, they incur little or no cost, but they do benefit from the food they obtain from the old female.

evolutionary biology↗