Галиктус рубикундус: география, социальное поведение и адаптация к климату.

Species of bee

Halictus rubicundus, the orange legged furrow bee, is a species of sweat bee found throughout the Northern Hemisphere. H. rubicundus entered North America from the Old World during one of two main invasions of Halictus subgenera. These invasions likely occurred via the Bering land bridge at times of low sea level during the Pleistocene epoch. The species exhibits different social behaviors depending on climate: it is a solitary species in high elevations or latitudes where the season is short, but eusocial in other areas. Often, solitary and eusocial colonies appear simultaneously in the same population. These sweat bees are extensively studied for their variability in social behavior, which has become a model for social plasticity. This variability has contributed to an understanding of evolution of social behavior. but Halictus rubicundus are not metallic. Females are about 1 cm in body length and brown in color, with fine white bands across the apices of the abdominal segments, and rusty orange legs.

H. rubicundus has one of the widest natural distributions of any bee species, occurring throughout the temperate regions of the Holarctic region. It is believed that differences in climate across this vast range actually contribute to variation in their social behavior.

Both solitary and eusocial types of the species typically excavate nest burrows in southward facing slopes in isolated areas, consisting of sand or soil. This slope maximizes the heat absorption from the sun, making the nest warmer. The nests with a favorable slope were thought to increase foraging efficiency of adults and development of larvae with a stable thermal environment. The nests can be up to 120 mm deep, and are constructed in a wide range of soil types.

The nests are typically burrowed into the ground in loam soil. this species prefers less dense aggregations. Foundresses will choose to build their nests in patches of softer ground until they reach the critical nearest neighbor distance of about 50 mm, at which point the close spacing poses a high risk of the nests collapsing. At this point, further foundresses would be forced to build their nests in harder soils where the nests could be built closer together without compromising nest architecture. Foundresses may test the hardness of the soil by biting into the surface or performing a short test dig. After hibernation during the winter, female foundresses who mated the previous cycle emerge in the spring.

Halictus rubicundus is widely studied for their variability in behavior depending on geographic location, and with changes in temperature. Those at low elevations are known to exhibit eusocial behavior, while those at high elevations and latitudes are known to be solitary. In these colonies in New York, the first brood is primarily worker females, which in turn help the foundress rear her second brood, and a number of gynes and males. However, in solitary nests, the offspring do not serve as workers and do not help the mother establish a second brood, but rather go off to try to establish nests of their own the following season. If she is left unmated for two or three days, however, she will likely stay a non gyne, even if she mates later on; no female who began acting as a worker (pollen collecting behavior, typically starting within two or three days after emergence) was ever found to return the following season. In H. rubicundus, the Dufour’s gland produces pheromones that may aid females in recognizing brood cells as well as other individuals in the nest.

Following standard models, it is assumed that worker bees who help their mother raise the following brood are in a position to benefit from the effects of kin selection. Females within the first brood therefore that stays in the colony, and are directly genetically related to their mother by half, are able to help to raise a second brood containing sisters, which are also (due to haplodipoidy) related to them by half.

There is evidence for greater genetic relatedness between two colonies with similar behavioral patterns (either eusocial or solitary), than between those of closer geographic distance but different social behaviors. This does not necessarily mean that social behavior is governed by certain genes, but it could be linked to certain genetic lineages that are more suited for certain environments. Empirical data from within a single population, however, indicates that females who do not remain as workers in their mother's nest are not more likely to have daughters that similarly depart. Although there is only limited research to date on the correlation between genetics, the environment, and social behavior, there is ample evidence that there are links between these three factors. The differences between the populations of H. rubicundus exhibiting solitary behavior, and those exhibiting eusocial behavior could be the result of environmental control of sociality, rather than having a purely genetic explanation.

In environments with short breeding seasons, sociality is not expected because there is no benefit to acting as a worker in the absence of an opportunity to produce another brood that season, and no potential for kinship selection benefits. Populations in environments that allow for multiple broods exhibit eusocial behavior, and there are potential benefits to worker behavior in eusocial colonies, as workers are related to the foundress (their mother) and the brood (their sisters, in particular). Under theories of inclusive fitness, it is potentially beneficial for workers to help their mother produce a second brood if that brood is primarily female. However, H. rubicundus does not show female bias in the second brood, with values only ranging to a maximum of 40% female. Furthermore, the one study providing empirical data for H. rubicundus shows that a typical worker contributes to the production of 0.9 sisters and 0.8 brothers, far below the threshold for inclusive fitness effects to favor helping, but above the threshold at which their mother benefits directly; as such, this species provides evidence that kin selection effects would not apply to this species, and instead suggests that mothers manipulate some of their daughters into acting as workers because of direct gains to maternal fitness, even though these manipulated daughters have lower fitness than they could have had if they had been gynes.