Deciphering a Century-Old Genetic Enigma: Bee Gender Dictated by Molecular Chance Mechanisms

Deciphering a Century-Old Genetic Enigma: Bee Gender Dictated by Molecular Chance Mechanisms

The Complementary sex determiner (Csd) gene, which can have over 100 different forms, is pivotal in deciding a bee’s gender. This gene amalgamates during sexual fertilization: If the resultant genome contains two disparate versions of the Csd gene, a female bee emerges and is nurtured. Conversely, if identical variants are combined, a male bee is generated but is not reared by the worker bees. Rather, male bees—known as drones—are produced through asexual reproduction. Source: HHU/Paul Schwaderer/stock.adobe.com – Alekss, Tran-Photography

Up until now, the precise method of bee gender determination has been nebulous. Scientists comprising biologists and chemists from Heinrich Heine University Düsseldorf (HHU) have pinpointed a key gene and its associated molecular workings. In the latest edition of the scientific journal Science Advances, they liken this procedure to a game of chance involving two dice.

The gender of an organism has far-reaching implications for its physical structure, function, and behavior. Normally, biological sex is determined at the inception of life. In the human species, for example, the existence of the “Y chromosome” delineates the birth of a male individual.

Johann Dzierzon, a Silesian priest, had already scrutinized the gender determination processes of honeybees (Apis mellifera) as early as 1845. Among his findings was the asexual reproduction method of male bees, or “drones.”

Bee Gender Determination

Unlike humans, bees lack a singular chromosome for determining sex. A research collective led by Professor Dr. Martin Beye from the Institute of Evolutionary Genetics at HHU has verified that a unique gene, named “Csd,” operates through a specialized mechanism to decide gender.

This particular gene exhibits over 100 potential variants, termed alleles. In other contexts, such as in flowers, varying alleles of a gene may dictate characteristics like petal hue.

In sexual reproduction, the singular chromosome sets from both the egg and sperm merge to establish a diploid chromosome set. Hence, two variants of the Csd gene exist in each sexually reproduced bee.

Subsequent findings from the Düsseldorf-based bee researchers reveal that when the two alleles of the Csd gene differ, a female bee is created. On the other hand, identical alleles result in a male bee, which worker bees do not nurture to avoid the risks associated with inbreeding.

Molecular Underpinnings of Gender Determination

Outstanding questions remained regarding the molecular mechanisms underlying this gender determination. Lead author Dr. Marianne Otte elucidates that each distinct allele of the Csd gene gives rise to a unique version of the corresponding Csd protein. Their research demonstrated that only varying Csd proteins can combine with each other to activate a molecular switch, which then instigates the development of a female bee. Conversely, identical proteins interact differently, thus failing to activate this molecular switch, resulting in a male bee that is not nurtured.

Professor Beye, the study’s concluding author in Science Advances, notes that the process resembles a game of molecular chance involving two dice. In this analogy, a roll that yields identical numbers is not the favorable outcome. Instead, divergent numbers must be rolled for a new female bee to be reared.

In contrast, drones arise from unfertilized eggs and thus have a single set of chromosomes with matching Csd proteins. The choice not to fertilize the egg during the laying stage lies with the queen bee.

Conclusion and Prospects for Future Research

Dr. Otte states, “We have successfully demystified a genetic puzzle that has confounded scientists for over a century by tracing it to the switching function of the Csd protein.” Professor Beye adds that future research must explore how worker bees discern whether a fertilized egg possesses two dissimilar Csd proteins, thus shifting to ‘female’, as this recognition method remains uncertain. He suggests that an olfactory signal could be involved, given the hive’s lack of light.

The insights garnered will inform future strategies for bee breeding.

Reference: “Recognition of polymorphic Csd proteins determines sex in the honeybee” by Marianne Otte, Oksana Netschitailo, Stefanie Weidtkamp-Peters, Claus A. M. Seidel and Martin Beye, published on 4 October 2023 in Science Advances.
DOI: 10.1126/sciadv.adg4239

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More about Bee Gender Determination

• Heinrich Heine University Düsseldorf
• Institute of Evolutionary Genetics at HHU
• Science Advances Journal
• Historical Overview of Johann Dzierzon’s Research
• Genetic Mechanisms in Bees
• DOI for the Original Study
• Bee Breeding Practices
• Overview of Gender Determination Mechanisms
• Olfactory Signals in Bees