Insectes Sociaux最新文献

One factor that can affect infection susceptibility is host age, the effects of which vary in a range of ways. For example, susceptibility may increase with age, due to senescence or decrease with age as a result of maturation of the immune system. If certain ages are more susceptible to infection, populations with contrasting demographics, such as same-age cohorts versus a mixture of ages, will exhibit differing disease prevalence. We use the bumblebee, Bombus terrestris, and its interaction with the gut trypanosome Crithidia sp. as a model system to investigate age-related susceptibility in a social insect. Crithidia sp. are widespread and prevalent parasites of bumblebees that are spread between colonies via faeces on flowers when foraging, and within colonies via contact with infected bees and contaminated surfaces and resources. In the field, Bombus spp. live for approximately three weeks. Here, we inoculated bumblebees at 0, 7, 14 and 21 days of age and measured their infection after one week. We also measured the level of gene expression of two antimicrobial peptides important in the defence against Crithidia bombi in bumblebees. We found that younger bumblebees are more susceptible to infection by Crithidia sp. than their older siblings. Specifically, individuals inoculated on their first day of emergence had infection intensities seven days later that were four-fold higher than bees inoculated at 21 days of age. In contrast, the gene expression of two AMPs known to protect against the trypanosome, abaecin and defensin, did not significantly vary with age. These results suggest that age does affect susceptibility to Crithidia sp. infection in B. terrestris. The higher susceptibility of callows may have implications for the susceptibility of colonies at different stages of their lifecycle, due to the contrasting age demography of workers in the colony.

Major evolutionary transitions (METs) across Earth’s biological history describe fusions of lower-level entities into higher-level individuals (evolutionary transitions in individuality: ETIs) as well as novel forms of information storage and transmission (Information Leaps). Obligate eusociality is frequently listed as a MET—most often in the context of being an ETI and with an extrapolation that the ETI requires inclusive fitness maximization for all parties. However, obligate eusociality neither fundamentally alters how information is stored and transmitted nor meets the various criteria proposed for an ETI. We argue that rather than representing a higher-level individual, the evolution of non-reproductive worker castes is more analogous to a novel ‘organ’ that maintains homeostasis and nurtures the gonadal tissue of mated queens. Worker castes benefit queens by performing dangerous but necessary functions such as foraging, while enabling the gamete-producing functions to be kept relatively safe. This is an ecologically successful and significant evolutionary innovation, which can be thought of as a major competitive transition (MCT). In this context, we hypothesize that worker castes are most likely to evolve through parental manipulation. Employing such a MCT perspective generates a broad series of predictions about eusocial life histories.

Flower-visiting social insects use a variety of cues to help them learn and recall which flowers are high-quality resources, including the flower odour. In addition, some species may learn to respond to the odours left at flowers by other insects, either to avoid flowers that have likely been depleted by recent visitors, or to identify profitable floral patches being used by competitors. For example, Australian stingless bees were observed to be more attracted to food sources recently visited, and thus odour-marked, by other stingless bees or honey bees than food sources with no prior visits. Here, we use a proboscis extension response (PER) protocol to investigate the capacity for olfactory associative learning in the Australian stingless bee, Tetragonula carbonaria. We test the ability of T. carbonaria to learn to associate a food reward with each odour in two paired sets of odours: (1) vanilla vs. lavender, and (2) linalool vs. a synthetic version of the honey bee pheromone Nasonov. After conditioning, T. carbonaria foragers demonstrated successful discrimination between the two different odours in a set, learnt to associate all four test odours with a food reward, and maintained this association for 15 min after training. In all, our results, therefore, show that PER can be used to investigate associative learning in T. carbonaria and support olfactory associative learning as a mechanism by which the odours of both flowers and other bees affect foraging decisions in this species.