The evolution and origin of the Bombardier Beetle is a hot topic among scientists and creationists because of the incredible uniqueness and complexity of the insects defense mechanism. Chemical defenses are found in many living organisms of all shapes and sizes to deter predators, from plants and corals to reptiles and mammals. Many other insects use quinones as their defense mechanism, however Bombardier Beetles are different because they don't just store them in glands but produce and fire them at enemies with powerful chemical reactions as explained in the defense mechanism chapter.
Since this species of insects has such a unique mechanism, creationists have argued that evolution could not have occurred in the development of this beetle and its actions. Irreducible complexity, a theory that a biological process is too complex to have evolved from a simpler process, is often related to the Bombardier Beetle. However, research has identified evolutionary pathways that explain the development of the defenses from other beetle species through natural selection and evolutionary methods over time.
At this time a specific evolutionary path is still unknown, however biological and evolutionary steps have been explained to show the evolution of the beetle.
The defensive measures of this beetle comes from predation pressure and a need for more defenses against evolving predators (Isaak, 1997).
The evolutionary steps include:
These steps can be seen by diagrams and an explanation in the following video:
Since this species of insects has such a unique mechanism, creationists have argued that evolution could not have occurred in the development of this beetle and its actions. Irreducible complexity, a theory that a biological process is too complex to have evolved from a simpler process, is often related to the Bombardier Beetle. However, research has identified evolutionary pathways that explain the development of the defenses from other beetle species through natural selection and evolutionary methods over time.
At this time a specific evolutionary path is still unknown, however biological and evolutionary steps have been explained to show the evolution of the beetle.
The defensive measures of this beetle comes from predation pressure and a need for more defenses against evolving predators (Isaak, 1997).
The evolutionary steps include:
- Quinones sit on the epidermis (outer layer cells) of many insects and beetles, making them distateful to predators (Dettner, 1987).
- Small invaginations (infoldings) are created in the epidermis to store and secrete more quinones (Eisner, Chemical defense against predation in arthropods, 1970).
- Some invaginations become increasingly deep, resulting in separate reservoirs (Holldobler & Wilson, 1990).
- Cells that produce and release chemical toxins develop in multiple layers and become ducts to transport chemicals to secretary cells from the reservoir (common in many beetles of this suborder) (Eisner, Chemical defense against predation in arthropods, 1970).
- Muscles adapt to control release and movement of chemicals .
- Cells releasing catalases for the reaction of hydrogen peroxide and hydroquinones develop along the release pathway from the resevoir to produce chemical reactions to deter enemies even greater.
- The concentrations become greater over time to have a larger effect (Eisner, et al., 2000).
- The cell walls of the release point become firmer and tougher to expel the reaction at greater pressure as the concentrations of the chemicals and catalyst continues to increase.
- The abdomen becomes longer and flexible to allow for movement and aiming as seen in today's Bombardier Beetles (Forsyth, 1970).
These steps can be seen by diagrams and an explanation in the following video:
There is more evidence of the origin of the Bombardier Beetle when referring to the most primitive of the species, Metrius contractus. This beetle has only undergone the evolutionary steps up to number 7, as indicated above. This specific species releases the reaction as a froth that clings to the body of the insect. It is yet to develop higher concentrations and explosive firing capabilities of the more developed Bombardier Beetle.
Natural selection entails that traits passed on through generations will be positive to the species and this is why we see better defenses occurring over time to result in the incredible mechanism in Bombardier Beetles (Eisner, et al., 2000).
Image and Video Credits:
Natural selection entails that traits passed on through generations will be positive to the species and this is why we see better defenses occurring over time to result in the incredible mechanism in Bombardier Beetles (Eisner, et al., 2000).
Image and Video Credits:
- Cross section model of beetle: http://www.dkimages.com/discover/Home/Animals/Invertebrates/Arthropods/Insects/Beetles/Families/Ground-Beetles/Bombardier-Beetle/Bombardier-Beetle-3.html
- Evolution Video: https://www.youtube.com/watch?v=SUvLR2yyWuE
Alexander Kloppers
The University of Queensland, BIOL2205
The University of Queensland, BIOL2205