CHADRON – As often happens in research, a study doesn’t necessarily provide answers, but may instead trigger additional questions.
That's exactly what happened when Dr. Mathew Brust, associate professor in Chadron State College’s Physical and Life Sciences, began to notice almost all of the thousands of tiger beetles he collected and preserved exhibited a chirality, or dominance, of the left mandible.
“Chirality refers to something like handedness, such as left-handedness. In this case it is refers to which of the two mandibles, the large chewing mouthparts of beetles, crosses over the other,” Brust said. “When I stumbled upon the pattern and searched the literature, it amazed me that such an obvious pattern in the most diverse group of animals in the world had previously gone virtually unnoticed.”
In an article published this month in “The Coleopterists Bulletin” and on the BioOne website, Brust and W. Wyatt Hoback shared their findings from examination of 10,575 specimens in the Chadron State College collection and Brust’s personal collection.
The study encompassed 58 species of beetles, 46 of which were tiger beetles. Groups such as the longhorned beetles displayed a lower rate of the left dominant chirality, 71 percent, compared to the tiger beetles’ 99 percent.
In addition to being used to eat, the male mandibles are also used to grasp females during mating, which suggests multiple factors may be influencing the trait, according to Brust.
Until Brust’s and Hoback’s research, only one other study in 2010 recorded patterns of mandible chirality, and it only examined less than 300 specimens from two species.
Brust and Hoback conclude their publication with observations that mandible chirality is not random, but probably a fixed genetic characteristic. They suggest further study, including the evolution and genetics involved in the left-superior trait, what physical modifications, such as curvature and position on the head, are influenced by the left-superior trait, mandible shape for feeding by both genders, and mate grasping by males.
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