Which came first, bee venom or bee stingers?

Venoms, remarkable for their complexity and potency, have independently evolved in numerous animal groups, including bees. Within the diverse insect order Hymenoptera, which encompasses over 6,000 bee species alone, venomous species are notably abundant.

Despite their ecological and economic significance, the evolutionary development of hymenopteran venoms has remained largely unexplored. A recent study led by Dr. Björn von Reumont, a visiting scientist at Goethe University Frankfurt, has made significant strides in understanding this mysterious evolutionary path.

Studying bee venom evolution

The research, grounded in comparative genomics, marks the first systematic exploration of the evolution of bee and other hymenopteran venoms.

The team identified prevalent peptides and proteins in hymenopteran venom using protein databases. They then analyzed venoms from two wild bee species — the violet carpenter bee (Xylocopa violacea) and the great-banded furrow-bee (Halictus scabiosae) — as well as of the honeybee (Apis mellifera).

Twelve peptide and protein families were found to be common across the hymenopteran venoms studied, suggesting these are fundamental “common ingredient” of their venom cocktails.

Surprising genetic discoveries

In collaboration with institutions like the Leibniz Institute, TUM, and LOEWE TBG, the researchers examined the genes of these 12 families in 32 hymenopteran taxa.

This group included sweat bees and stingless bees, and also wasps and ants such as the notorious fire ant (Solenopsis invicta). The genetic differences were sometimes as minute as a single letter change in the genetic code. Nonetheless, this enabled the team to trace relationships and compile a lineage of venom genes using artificial intelligence and machine learning.

A key revelation was the presence of many venom genes across all hymenopterans, indicating a common ancestral origin. Bees, it seems, have been venomous from their beginnings.

This finding challenges current debates in other groups, such as Toxicofera, about the independent evolution of venoms. “This makes it highly probable that hymenopterans are venomous as an entire group,” concludes von Reumont. “For other groups, such as Toxicofera, which includes snakes, anguids (lizards) and iguania, science is still debating whether the venoms can be traced back to a common ancestor or whether they evolved separately.”

Hymenoptera specialization

In the Hymenoptera order, it’s specifically the stinging insects like bees, wasps, and ants that are equipped with a stinger for venom delivery. In contrast, the ancient parasitic sawflies, such as the sirex wood wasp (Sirex noctilio), employ a different method. They use their ovipositor, in conjunction with laying eggs, to introduce substances that modify the physiology of their host plants.

A notable example is the sirex wood wasp, which not only injects a fungus aiding its larvae in colonizing the wood but also delivers its unique blend of venomous proteins, as highlighted in the study.

These proteins are crucial in preparing the plant environment to be conducive for the larvae’s growth. Dr. von Reumont points out, “Based on this, we can categorize the sirex wood wasp as venomous too.”

Novel venom components in bees

Particularly intriguing was the discovery related to the peptide melittin in bees. Contrary to previous beliefs that multiple gene copies were responsible for its diversity and abundance in bee venom, the study revealed it is encoded by a single gene.

This discovery refutes the hypothesis of melittin belonging to the postulated aculeatoxins group, emphasizing the importance of genome data in understanding venom evolution.

Additionally, the study identified anthophilin-1 as a new protein family in bee venom, further enriching our understanding of venom composition and evolution.

Dr. von Reumont explains, “Not only are there many different variants of melittin, but the peptide also accounts for up to 60 percent of the dry weight of bee venom. That is why science previously assumed that there must be many gene copies. We were able to disprove this quite clearly.”

Future venom evolution research

This important study by Dr. von Reumont and his team offers unprecedented insights into the origin and evolution of venom genes in Hymenoptera. It sets the stage for future research in tracing venom gene evolution in the ancestors of Hymenoptera and understanding specializations within the group.

However, large-scale comparative genomics will require the automation of analysis methods for the expansive protein families involved.

This research illuminates the evolutionary paths of venoms, while also opening new avenues for understanding the intricate relationships between genetics and ecology in one of the most diverse and ecologically significant insect orders.

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