Halictinae
Encyclopedia
Within the insect
order Hymenoptera
, Halictinae is the largest, most diverse, and most recently diverged of the four unique Halictidae
subfamilies. It comprises over 2400 bee
species
belonging to the five taxonomic tribes
Augochlorini, Thrinchostomini, Caenohalictini, Sphecodini, and Halictini, which some entomologists
alternatively organize into the two tribes Augochlorini and Halictini.
The subfamily Halictinae also belongs to the Hymenopteran monophyletic clade Aculeata
, whose members are characterized by the possession of a modified ovipositor
in the form of a poisonous sting for predator and prey defense. Including all eusocial
and cleptoparasitic
Halictidae taxa, these small bees are pollen
feeders who mass provision
their young and exhibit a broad spectrum of behavioral social
polymorphies
, ranging from solitary
nest
ing to obligate
eusociality
. Estimated from the fossil record
, eusociality in this subfamily evolved about 20 to 22 million years ago, which is relatively recent in comparison with other inferred eusociality origins. Thus, Halictinae are believed to model the primitive eusociality of advanced eusocial Hymenopterans. Because of their polymorphic sociality and recently evolved eusociality, Halictinae are valuable to the study of social evolution
.
, mainly inhabiting the Neotropics and some areas of North America
. Augochlorini sociality, though not well-understood, is significantly polymorphic across its range as well as between and within species
and genera
. Facultative
eusociality has been observed in genera such as Augochloropsis and Megalopta, and cleptoparasitism has recently developed separately in the three augochlorine genera and subgenera Temnosoma, Megalopta [Noctoraptor], and Megammation [Cleptommation].
and the Africa
n and Asia
tropics
. Twelve of the 56 Thrinchostoma species are native to Madgascar and exhibit some host
-plant specificity. Parathincrostoma species, two of which are native to Madagascar, are likely cleptoparasites, indicated by a lack of pollen
collecting structures in their female morphology
. Though evidence of Thrinchostomini sociality and nesting biology is limited, observed population
s in southern Africa are believed to be solitary.
their eggs onto or near the pollen stores of their hosts’ nests. These cleptoparasitic bees are host generalists and belong to an ancient lineage of parasites
that uniquely shares no specificity with any non-parasitic Halictinae taxa. Bees belonging to the largest Sphecodini genus Sphecodes exhibit especially aggressive
parasitism, attacking and sometimes killing solitary or social nest host female(s) before ovipositing eggs
into pollen-provisioned host cells. Such parasites inhabit every continent with the exception of Australia
.
, Mexalictus, and Patellapis sensu lato are notable Halictini genera. Most Halictini species belong to the genus Lasioglossum, which encompasses a variety of nocturnal and diurnal, socially parasitic, solitary, eusocial, and communal
bees. Lasioglossum are distinguished by a weakened outer wing venation, while species of Mexalictus resemble Lasioglossum in body shape but possess strong wing venation. Mexalictus includes six described species of rare bees observed in humid areas of high elevation
ranging from southeast Arizona
to northern Guatemala
. The social behavior of Mexalictus species is unknown. Recent observational data of Patellapis s. l. suggests that the genus practices communal nesting, with as many as eight females sharing a nest. Most Patellapis s. l. species inhabit southern Africa and Madagascar though species are also found in tropical Asia and northern Australia.
occur both locally and across geographic locations. The variety of colony organizations expressed by Halictinae species is represented along a gradient ranging from solitary nesting to obligate eusociality.
nesting and brood
care, an overlap in adult generation
s, and a division of social roles, marked by intracolony reproductive hierarchies
. The social roles of a eusocial colony are distributed into caste
s that include the reproductive queen(s)
, female workers
who forage
for pollen and care for the brood and nest, and brood composed of potential workers and reproductive males and gyne
. In Halictinae, one or more females found a colony site, and initiate its development, first producing brood of workers to forage for resources and care for future offspring followed by brood of males and gynes to mate and propagate the nest’s gene
s. A mated
gyne is a potential queen who will either disperse to a new nest, succeed
to the position of the former nest queen, or suffer subordination or harm by the current queen.
In a mating season
, a eusocial Halictinae queen will usually lay multiple broods, with earlier broods composed of dominantly female workers and later broods of reproductive males and gynes. A eusocial queen monopolizes the reproductive capacity within a nest, preventing reproduction of colony workers. Overlapping of adult generations importantly enables worker daughters to contribute to the rearing of later broods. However, eusociality also exists within generations with no adult overlap. As a result of the heavy work load requirement of nest building and repeated food provisioning in eusocial colonies, nest sharing also saves time, energy, and natural resources.
When multiple females found a colony, a dominant queen can subordinate another foundress. However, such foundresses may remain in the colony, likely because of the potential to succeed to the queen caste if the current queen dies or loses her position. Also, subordinate females may find an opportunity to lay their own eggs in the nest.
The large colony size of eusocial insects elicits both costs and benefits. Increased group size is often correlated with increased predator
attraction. However, in appropriate situations, aggregations of individuals can provide more effective predator defense. Under situations of low parasite and predator threat as well as plentiful territory and resource availability, the risk of attracting a predator from aggregating is greater than the possible benefits of collaborative nesting and reproductive rearing. When parasite and predator threats are high and territory and resources are limited, a greater number of individual workers may improve parental care of offspring. For example, increased numbers of workers in a colony increase the effectiveness of nest defenses such as stinging enemies and blocking nest entrances. Possession of poisonous stinger
in Halictinae were likely beneficial in the subfamily’s evolution of eusociality by providing a thwart to the increased predator attention caused by group living. Also a benefit of cooperative nesting, the requirement for foraging away from the nest does not necessitate temporary nest abandonment when a surplus of females are available to stay behind in the nest, reducing risks of brood predation.
(Halictus), Halictus (Seladonia), Lasioglossum
(Evylaeus), Lasioglossum (Dialictus), Augochlora, Augochlorella, Augochloropsis. Though eusociality is always expressed, obligately eusocial species still exhibit social diversity in degrees of eusociality.
eusociality. This species’ colonies produce a single brood of workers for three to four years and then produce a brood of males and gynes in its final breeding season. Before the end of the breeding season, males disperse to gyne-producing nests to mate. Males introduced into non-final-year nests mate with workers, and workers disperse to found new nests. Queens are the same size as workers but experience a life span of four to five years, while workers live one year.
of social taxa are critical. Phylogenies constructed from fossil evidence dating demonstrate numerous reversions within the Halictidae family to solitary nesting. Morphological
data was employed in the 1960s to create a phylogeny suggesting the behavioral reversion from eusociality to solitary nesting in the genera Augochlora and Augochlorella. In mapping other taxonomic relationships, however, morphological data has been troublesome. DNA sequence-based phylogenies have been the most enlightening of Halictinae relationships. The most recent molecular evidence suggest three to four independent origins of eusociality and frequent reversions from eusociality to solitary nesting.
and maintenance of nonreproductive castes of offspring through parental manipulation with the use of pheromone
s or assertion of behavioral dominance. Queens can establish dominance by striking workers with her head, blocking workers’ travel through nest passageways, and coaxing workers more deeply into the nest. A queen’s successful reproduction monopolization is contingent on her ability to control the colony’s workers and on the size of the worker population. An excess of workers may be unmanageable for a queen and lead to worker reproduction.
When a queen is responsible for the majority of the offspring her nest produces, her nest exhibits a high reproductive skew between the queen and worker castes. A low reproductive skew occurs when a nest possesses little deviation between queen and worker reproductive success. Strong eusociality is measured by a high reproductive skew, and the influence of various factors on this skew determines a colony’s expressed sociality.
, altitudinal
, and local variation have been partially ascribed to environmental
influences such as flowering season length, temperature, nesting substrate availability, and risk of predation or parasitism. In order for eusociality to be expressed, the summer breeding season must provide time for consecutive production of both worker and reproductive broods. Thus, obligately eusocial species are restricted to environments characterized by long breeding seasons. Communal and solitary species are usually limited to short breeding seasons, and facultative eusocial species are represented in more various environments.
In warmer climates with longer breeding seasons, colonies have longer cycles and are larger in size, requiring the queen(s) to interact with more worker members. This result explains latitudinal gradients of obligate eusociality in Halictus ligatus and Lasioglossum malachurum. Both species exhibit to some extent that as the colony size increases, queens’ ability to control their workers and monopolize colony reproduction decreases, reducing the reproductive skew and degree of eusociality. However, in L. malachrum this trend is only observed in northern populations.
In Europe
, northern colonies of L. malachurum produce a single worker brood, followed by a gyne brood. However, southern European colonies produce more broods as a result of longer breeding season
s. Queens in these colonies rarely survive to the final, gyne-producing broods, increasing worker mating potential and decreasing queen monopolization of a reproduction in a mating season. A study of L. malachurum in southern Greece
demonstrated that local populations’ degree of eusociality varied among colonies and years, a possible result of queen survival differences during breeding seasons. Additionally, the study revealed the colony social organization of L. malachurum to vary geographically. In comparison to those in northern Greece, southern Greek populations exhibited larger colony sizes, increased ovarian development, decreased worker mating, and a smaller number of worker-sized queens.
Megalopta genalis, a facultative eusocial Halictinae, has been observed to primarily exhibit solitary nesting while possessing the capacity for cohabitation and social dominance. These eusocial behaviors are expressed in response to changes in local environments.
Reversions to solitary behavior in some facultative eusocial Halictinae species are associated with environmental conditions that cause removal of worker broods from eusocial colonies. Within some local populations, eusocial nests and reversions to solitary nests coexist, possibly reflecting an individual queen’s control of colony adaptation to environmental conditions through her decision of brood types produced.
make-up influences its expressed sociality. An individual Halictinae bee’s repertoire of accessible social behaviors is determined by its specific genetic make-up.
The phylogeographic
distribution of Halictus rubicundus
, a socially polymorphic Halictinae, supports the importance of genetics in expressed sociality. Within its range, H. rubicundus eusocial populations exist in areas with typically longer growing seasons, while solitary populations inhabit areas with shorter growing seasons. This geographical distribution suggests social determination by environmental factors. However, DNA sequence-based phylogenetic analysis revealed genetic structure across H. rubicundus populations. Social and solitary H. rubicundus populations in North America belong to distinct evolutionary lineages, and some populations are more closely related to populations with which they share social behavior than to geographically nearer populations.
Ultimately, a Halictinae colony’s social organization is influenced by the interaction between its members’ genotype, social plasticity, intracolony relationships, and environmental conditions. The mechanisms by which these factors interact in Halictinae are not currently well-understood. However, the vastness of Halictinae social diversity, within and between species, provides ample opportunities for study.
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
order Hymenoptera
Hymenoptera
Hymenoptera is one of the largest orders of insects, comprising the sawflies, wasps, bees and ants. There are over 130,000 recognized species, with many more remaining to be described. The name refers to the heavy wings of the insects, and is derived from the Ancient Greek ὑμήν : membrane and...
, Halictinae is the largest, most diverse, and most recently diverged of the four unique Halictidae
Halictidae
Halictidae is a cosmopolitan family of the order Hymenoptera consisting of small to midsize bees which are usually dark-colored and often metallic in appearance...
subfamilies. It comprises over 2400 bee
Bee
Bees are flying insects closely related to wasps and ants, and are known for their role in pollination and for producing honey and beeswax. Bees are a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila...
species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
belonging to the five taxonomic tribes
Tribe (biology)
In biology, a tribe is a taxonomic rank between family and genus. It is sometimes subdivided into subtribes.Some examples include the tribes: Canini, Acalypheae, Hominini, Bombini, and Antidesmeae.-See also:* Biological classification* Rank...
Augochlorini, Thrinchostomini, Caenohalictini, Sphecodini, and Halictini, which some entomologists
Entomology
Entomology is the scientific study of insects, a branch of arthropodology...
alternatively organize into the two tribes Augochlorini and Halictini.
The subfamily Halictinae also belongs to the Hymenopteran monophyletic clade Aculeata
Aculeata
The name Aculeata is used to refer to a monophyletic lineage of Hymenoptera. The word "Aculeata" is a reference to the defining feature of the group, which is the modification of the ovipositor into a stinger . In other words, the structure that was originally used to lay eggs is modified instead...
, whose members are characterized by the possession of a modified ovipositor
Ovipositor
The ovipositor is an organ used by some animals for oviposition, i.e., the laying of eggs. It consists of a maximum of three pairs of appendages formed to transmit the egg, to prepare a place for it, and to place it properly...
in the form of a poisonous sting for predator and prey defense. Including all eusocial
Eusociality
Eusociality is a term used for the highest level of social organization in a hierarchical classification....
and cleptoparasitic
Kleptoparasitism
Kleptoparasitism or cleptoparasitism is a form of feeding in which one animal takes prey or other food from another that has caught, collected, or otherwise prepared the food, including stored food...
Halictidae taxa, these small bees are pollen
Pollen
Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...
feeders who mass provision
Mass provisioning
Mass provisioning is a term used in entomology to refer to a form of parental behavior in which an adult stocks all of the food for each offspring in a small chamber prior to laying the egg...
their young and exhibit a broad spectrum of behavioral social
Social
The term social refers to a characteristic of living organisms...
polymorphies
Polymorphism (biology)
Polymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...
, ranging from solitary
Solitary
Solitary is the state of being alone. The term may refer to:* shortened form of solitary confinement in jail* Solitary but social, a type of social organization in biology where individuals forage alone but share sleeping space...
nest
Nest
A nest is a place of refuge to hold an animal's eggs or provide a place to live or raise offspring. They are usually made of some organic material such as twigs, grass, and leaves; or may simply be a depression in the ground, or a hole in a tree, rock or building...
ing to obligate
Obligate
Obligate means "by necessity" and is used mainly in biology in phrases such as:* Obligate aerobe, an organism that cannot survive without oxygen* Obligate anaerobe, an organism that cannot survive in the presence of oxygen...
eusociality
Eusociality
Eusociality is a term used for the highest level of social organization in a hierarchical classification....
. Estimated from the fossil record
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
, eusociality in this subfamily evolved about 20 to 22 million years ago, which is relatively recent in comparison with other inferred eusociality origins. Thus, Halictinae are believed to model the primitive eusociality of advanced eusocial Hymenopterans. Because of their polymorphic sociality and recently evolved eusociality, Halictinae are valuable to the study of social evolution
Social evolution
Social evolution is a subdiscipline of evolutionary biology that is concerned with social behaviors that have fitness consequences for individuals other than the actor...
.
Augochlorini
The roughly 250 species belonging to the tribe Augochlorini exist only in the New WorldNew World
The New World is one of the names used for the Western Hemisphere, specifically America and sometimes Oceania . The term originated in the late 15th century, when America had been recently discovered by European explorers, expanding the geographical horizon of the people of the European middle...
, mainly inhabiting the Neotropics and some areas of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. Augochlorini sociality, though not well-understood, is significantly polymorphic across its range as well as between and within species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
and genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
. Facultative
Facultative
Facultative means "optional" or "discretionary" , used mainly in biology in phrases such as:* Facultative anaerobe, an organism that can use oxygen but also has anaerobic methods of energy production...
eusociality has been observed in genera such as Augochloropsis and Megalopta, and cleptoparasitism has recently developed separately in the three augochlorine genera and subgenera Temnosoma, Megalopta [Noctoraptor], and Megammation [Cleptommation].
Thrinchostomini
The two genera Thrinchostoma and Parathincrostoma comprise the tribe Thrinchostomini. These insects are large, non-metallic bees residing in MadagascarMadagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
and the Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
n and Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
tropics
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
. Twelve of the 56 Thrinchostoma species are native to Madgascar and exhibit some host
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
-plant specificity. Parathincrostoma species, two of which are native to Madagascar, are likely cleptoparasites, indicated by a lack of pollen
Pollen
Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...
collecting structures in their female morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
. Though evidence of Thrinchostomini sociality and nesting biology is limited, observed population
Population
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...
s in southern Africa are believed to be solitary.
Caenohalictini
Species of the tribe Caenohalictini inhabit areas in only the New World and are similar in physical appearance to Augochlorini. Caenohalictini species practice either solitary or communal nesting. Some Caenohalictini genera are nocturnal.Sphecodini
The tribe Sphecodini contains four cleptoparasitic genera of bees that ovipositOviposition
Oviposition is the process of laying eggs by oviparous animals.Some arthropods, for example, lay their eggs with an organ called the ovipositor.Fish , amphibians, reptiles, birds and monetremata also lay eggs....
their eggs onto or near the pollen stores of their hosts’ nests. These cleptoparasitic bees are host generalists and belong to an ancient lineage of parasites
Parasitism
Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...
that uniquely shares no specificity with any non-parasitic Halictinae taxa. Bees belonging to the largest Sphecodini genus Sphecodes exhibit especially aggressive
Aggression
In psychology, as well as other social and behavioral sciences, aggression refers to behavior between members of the same species that is intended to cause humiliation, pain, or harm. Ferguson and Beaver defined aggressive behavior as "Behavior which is intended to increase the social dominance of...
parasitism, attacking and sometimes killing solitary or social nest host female(s) before ovipositing eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
into pollen-provisioned host cells. Such parasites inhabit every continent with the exception of Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
.
Halictini
Assigned more than 2000 described species, Halictini is the largest tribe of halictid bees, including considerable behavioral diversity. LasioglossumLasioglossum
The sweat bee genus Lasioglossum is the largest of all bee genera, containing over seventeen hundred species in numerous subgenera worldwide. They are highly variable in size, coloration, and sculpture; among the more unusual variants, some are cleptoparasites, some are nocturnal, and some are...
, Mexalictus, and Patellapis sensu lato are notable Halictini genera. Most Halictini species belong to the genus Lasioglossum, which encompasses a variety of nocturnal and diurnal, socially parasitic, solitary, eusocial, and communal
Community
The term community has two distinct meanings:*a group of interacting people, possibly living in close proximity, and often refers to a group that shares some common values, and is attributed with social cohesion within a shared geographical location, generally in social units larger than a household...
bees. Lasioglossum are distinguished by a weakened outer wing venation, while species of Mexalictus resemble Lasioglossum in body shape but possess strong wing venation. Mexalictus includes six described species of rare bees observed in humid areas of high elevation
Elevation
The elevation of a geographic location is its height above a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface ....
ranging from southeast Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
to northern Guatemala
Guatemala
Guatemala is a country in Central America bordered by Mexico to the north and west, the Pacific Ocean to the southwest, Belize to the northeast, the Caribbean to the east, and Honduras and El Salvador to the southeast...
. The social behavior of Mexalictus species is unknown. Recent observational data of Patellapis s. l. suggests that the genus practices communal nesting, with as many as eight females sharing a nest. Most Patellapis s. l. species inhabit southern Africa and Madagascar though species are also found in tropical Asia and northern Australia.
Social diversity
A great diversity of social systems exists between and within Halictinae species. These discrepancies in social phenologiesPhenology
Phenology is the study of periodic plant and animal life cycle events and how these are influenced by seasonal and interannual variations in climate...
occur both locally and across geographic locations. The variety of colony organizations expressed by Halictinae species is represented along a gradient ranging from solitary nesting to obligate eusociality.
Eusociality
Eusocial behavior is associated with cooperativeCo-operation (evolution)
Co-operation or co-operative behaviours are terms used to describe behaviours by organisms which are beneficial to other organisms, and are selected for on that basis. Under this definition, altruism is a form of co-operation in which there is no direct benefit to the actor...
nesting and brood
Offspring
In biology, offspring is the product of reproduction, of a new organism produced by one or more parents.Collective offspring may be known as a brood or progeny in a more general way...
care, an overlap in adult generation
Generation
Generation , also known as procreation in biological sciences, is the act of producing offspring....
s, and a division of social roles, marked by intracolony reproductive hierarchies
Hierarchy
A hierarchy is an arrangement of items in which the items are represented as being "above," "below," or "at the same level as" one another...
. The social roles of a eusocial colony are distributed into caste
Caste
Caste is an elaborate and complex social system that combines elements of endogamy, occupation, culture, social class, tribal affiliation and political power. It should not be confused with race or social class, e.g. members of different castes in one society may belong to the same race, as in India...
s that include the reproductive queen(s)
Queen bee
The term queen bee is typically used to refer to an adult, mated female that lives in a honey bee colony or hive; she is usually the mother of most, if not all, the bees in the hive. The queens are developed from larvae selected by worker bees and specially fed in order to become sexually mature...
, female workers
Worker bee
A Worker bee is any female eusocial bee that lacks the full reproductive capacity of the colony's queen bee; under most circumstances, this is correlated to an increase in certain non-reproductive activities relative to a queen, as well...
who forage
Foraging
- Definitions and significance of foraging behavior :Foraging is the act of searching for and exploiting food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce...
for pollen and care for the brood and nest, and brood composed of potential workers and reproductive males and gyne
Gyne
Gyne is the primary reproductive female caste of social insects . Gynes are those destined to become queens, whereas female workers are typically sterile and cannot become queens...
. In Halictinae, one or more females found a colony site, and initiate its development, first producing brood of workers to forage for resources and care for future offspring followed by brood of males and gynes to mate and propagate the nest’s gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s. A mated
Mating
In biology, mating is the pairing of opposite-sex or hermaphroditic organisms for copulation. In social animals, it also includes the raising of their offspring. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization...
gyne is a potential queen who will either disperse to a new nest, succeed
Succession
Succession is the act or process of following in order or sequence. It may further refer to:*Order of succession, in politics, the ascension to power by one ruler, official, or monarch after the death, resignation, or removal from office of another, usually in a clearly defined order*Succession...
to the position of the former nest queen, or suffer subordination or harm by the current queen.
In a mating season
Estrous cycle
The estrous cycle comprises the recurring physiologic changes that are induced by reproductive hormones in most mammalian placental females. Estrous cycles start after puberty in sexually mature females and are interrupted by anestrous phases or pregnancies...
, a eusocial Halictinae queen will usually lay multiple broods, with earlier broods composed of dominantly female workers and later broods of reproductive males and gynes. A eusocial queen monopolizes the reproductive capacity within a nest, preventing reproduction of colony workers. Overlapping of adult generations importantly enables worker daughters to contribute to the rearing of later broods. However, eusociality also exists within generations with no adult overlap. As a result of the heavy work load requirement of nest building and repeated food provisioning in eusocial colonies, nest sharing also saves time, energy, and natural resources.
When multiple females found a colony, a dominant queen can subordinate another foundress. However, such foundresses may remain in the colony, likely because of the potential to succeed to the queen caste if the current queen dies or loses her position. Also, subordinate females may find an opportunity to lay their own eggs in the nest.
The large colony size of eusocial insects elicits both costs and benefits. Increased group size is often correlated with increased predator
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
attraction. However, in appropriate situations, aggregations of individuals can provide more effective predator defense. Under situations of low parasite and predator threat as well as plentiful territory and resource availability, the risk of attracting a predator from aggregating is greater than the possible benefits of collaborative nesting and reproductive rearing. When parasite and predator threats are high and territory and resources are limited, a greater number of individual workers may improve parental care of offspring. For example, increased numbers of workers in a colony increase the effectiveness of nest defenses such as stinging enemies and blocking nest entrances. Possession of poisonous stinger
Stinger
-Biology:* Stinger, an organ or body part found in various animals that usually delivers some kind of venom.* Stinger , a minor neurological injury suffered by athletes.-Sports and entertainment:...
in Halictinae were likely beneficial in the subfamily’s evolution of eusociality by providing a thwart to the increased predator attention caused by group living. Also a benefit of cooperative nesting, the requirement for foraging away from the nest does not necessitate temporary nest abandonment when a surplus of females are available to stay behind in the nest, reducing risks of brood predation.
Solitary nesting
In solitary nesting, a single reproductive female mates, lays and independently cares for her personal brood of reproductive males and females. Young females mature and then disperse away from the colony to establish their own nest and mate. In a solitary nest, Halictinae less easily attract predator and parasite attention. However, they must independently forage for pollen provisions and protect their nest and brood.Obligate eusociality
Obligate eusociality describes species that exhibit eusociality across all local, geographic, and temporal populations. Such species are known to exist within seven Halictinae genera: HalictusHalictus
The genus Halictus is a large assemblage of bee species in the family Halictidae. The genus is divided into 15 subgenera, containing well over 300 species, primarily in the Northern Hemisphere...
(Halictus), Halictus (Seladonia), Lasioglossum
Lasioglossum
The sweat bee genus Lasioglossum is the largest of all bee genera, containing over seventeen hundred species in numerous subgenera worldwide. They are highly variable in size, coloration, and sculpture; among the more unusual variants, some are cleptoparasites, some are nocturnal, and some are...
(Evylaeus), Lasioglossum (Dialictus), Augochlora, Augochlorella, Augochloropsis. Though eusociality is always expressed, obligately eusocial species still exhibit social diversity in degrees of eusociality.
Facultative eusociality
Facultative eusociality, also known as facultative solitary, describes species or populations in which both solitary and eusocial behavior is expressed. Eusociality evolved independently from multiple lineages of solitary Hymenoptera. However, some facultative eusocial species demonstrate a reversion from eusociality back to solitary nesting.Communal nesting
In communal nesting, also known as egalitarian eusociality, is less common than eusocial nesting. Bees exhibiting communal nesting share a common nest or nest component, as in eusocial nest. However, each female in a communal nest cares for and raises her brood independently. Communal nesting may demonstrate an intermediate behavior in reversions from eusocial to solitary societies, suggested by the species Halictus sexcinctus, whose various colonies assume eusocial, communal, and/or solitary nesting.Perennial eusociality
Lasioglossum marginatum is the only species known to exhibit perennialPerennial (disambiguation)
Perennial is a word with several meanings relating to yearly or ongoing activity. Perennial may refer to:* Perennial plant, a plant which lives for more than two growing seasons, including all trees and shrubs. See also Perennial vegetable...
eusociality. This species’ colonies produce a single brood of workers for three to four years and then produce a brood of males and gynes in its final breeding season. Before the end of the breeding season, males disperse to gyne-producing nests to mate. Males introduced into non-final-year nests mate with workers, and workers disperse to found new nests. Queens are the same size as workers but experience a life span of four to five years, while workers live one year.
Evolution of eusociality
In order to hypothesize origins and losses of social behavior in Halictinae species, phylogeniesPhylogenetics
In biology, phylogenetics is the study of evolutionary relatedness among groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...
of social taxa are critical. Phylogenies constructed from fossil evidence dating demonstrate numerous reversions within the Halictidae family to solitary nesting. Morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
data was employed in the 1960s to create a phylogeny suggesting the behavioral reversion from eusociality to solitary nesting in the genera Augochlora and Augochlorella. In mapping other taxonomic relationships, however, morphological data has been troublesome. DNA sequence-based phylogenies have been the most enlightening of Halictinae relationships. The most recent molecular evidence suggest three to four independent origins of eusociality and frequent reversions from eusociality to solitary nesting.
Queen-worker roles and reproductive skew
Eusocial queens have large bodies, are nest foundresses, monopolize nest oviposition, and raise brood with the help of less or non-reproductive female workers. These workers are daughters of the queen, have small bodies, help raise younger nest brood primarily produced by the queen. Workers are capable of laying gyne or male eggs and occasionally do so, limited by the queen’s physical control. A queen can direct the evolutionEvolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
and maintenance of nonreproductive castes of offspring through parental manipulation with the use of pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
s or assertion of behavioral dominance. Queens can establish dominance by striking workers with her head, blocking workers’ travel through nest passageways, and coaxing workers more deeply into the nest. A queen’s successful reproduction monopolization is contingent on her ability to control the colony’s workers and on the size of the worker population. An excess of workers may be unmanageable for a queen and lead to worker reproduction.
When a queen is responsible for the majority of the offspring her nest produces, her nest exhibits a high reproductive skew between the queen and worker castes. A low reproductive skew occurs when a nest possesses little deviation between queen and worker reproductive success. Strong eusociality is measured by a high reproductive skew, and the influence of various factors on this skew determines a colony’s expressed sociality.
Environmental factors
LatitudinalLatitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
, altitudinal
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
, and local variation have been partially ascribed to environmental
Natural environment
The natural environment encompasses all living and non-living things occurring naturally on Earth or some region thereof. It is an environment that encompasses the interaction of all living species....
influences such as flowering season length, temperature, nesting substrate availability, and risk of predation or parasitism. In order for eusociality to be expressed, the summer breeding season must provide time for consecutive production of both worker and reproductive broods. Thus, obligately eusocial species are restricted to environments characterized by long breeding seasons. Communal and solitary species are usually limited to short breeding seasons, and facultative eusocial species are represented in more various environments.
In warmer climates with longer breeding seasons, colonies have longer cycles and are larger in size, requiring the queen(s) to interact with more worker members. This result explains latitudinal gradients of obligate eusociality in Halictus ligatus and Lasioglossum malachurum. Both species exhibit to some extent that as the colony size increases, queens’ ability to control their workers and monopolize colony reproduction decreases, reducing the reproductive skew and degree of eusociality. However, in L. malachrum this trend is only observed in northern populations.
In Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, northern colonies of L. malachurum produce a single worker brood, followed by a gyne brood. However, southern European colonies produce more broods as a result of longer breeding season
Breeding season
The breeding season is the most suitable season, usually with favourable conditions and abundant food and water, for breeding among some wild animals and birds . Species with a breeding season have naturally evolved to have sexual intercourse during a certain time of year in order to achieve the...
s. Queens in these colonies rarely survive to the final, gyne-producing broods, increasing worker mating potential and decreasing queen monopolization of a reproduction in a mating season. A study of L. malachurum in southern Greece
Greece
Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....
demonstrated that local populations’ degree of eusociality varied among colonies and years, a possible result of queen survival differences during breeding seasons. Additionally, the study revealed the colony social organization of L. malachurum to vary geographically. In comparison to those in northern Greece, southern Greek populations exhibited larger colony sizes, increased ovarian development, decreased worker mating, and a smaller number of worker-sized queens.
Behavioral plasticity
Contributing to the vast Halictinae social diversity, adult female Halictinae possess the capacity to express any reproductive role their species exhibits and can adjust their social behavior in response to behavioral interactions within their nest and environmental conditions. The degree of this social plasticity differs among Halictinae species and populations, further contributing to the subfamily’s great inter- and intraspecific variation.Megalopta genalis, a facultative eusocial Halictinae, has been observed to primarily exhibit solitary nesting while possessing the capacity for cohabitation and social dominance. These eusocial behaviors are expressed in response to changes in local environments.
Reversions to solitary behavior in some facultative eusocial Halictinae species are associated with environmental conditions that cause removal of worker broods from eusocial colonies. Within some local populations, eusocial nests and reversions to solitary nests coexist, possibly reflecting an individual queen’s control of colony adaptation to environmental conditions through her decision of brood types produced.
Genetics
In combination with environmental conditions, a Halictinae population’s geneticGenetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
make-up influences its expressed sociality. An individual Halictinae bee’s repertoire of accessible social behaviors is determined by its specific genetic make-up.
The phylogeographic
Phylogeography
Phylogeography is the study of the historical processes that may be responsible for the contemporary geographic distributions of individuals. This is accomplished by considering the geographic distribution of individuals in light of the patterns associated with a gene genealogy.This term was...
distribution of Halictus rubicundus
Halictus rubicundus
Halictus rubicundus is a species of sweat bee found throughout the Northern Hemisphere. It is small , dark brown, with fine white bands across the apices of the abdominal segments. The legs are often somewhat reddish...
, a socially polymorphic Halictinae, supports the importance of genetics in expressed sociality. Within its range, H. rubicundus eusocial populations exist in areas with typically longer growing seasons, while solitary populations inhabit areas with shorter growing seasons. This geographical distribution suggests social determination by environmental factors. However, DNA sequence-based phylogenetic analysis revealed genetic structure across H. rubicundus populations. Social and solitary H. rubicundus populations in North America belong to distinct evolutionary lineages, and some populations are more closely related to populations with which they share social behavior than to geographically nearer populations.
Ultimately, a Halictinae colony’s social organization is influenced by the interaction between its members’ genotype, social plasticity, intracolony relationships, and environmental conditions. The mechanisms by which these factors interact in Halictinae are not currently well-understood. However, the vastness of Halictinae social diversity, within and between species, provides ample opportunities for study.