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A new study by researchers at The University of Queensland has revealed that the impressive claws (chelae) of freshwater crayfish come with certain costs: The size slows their swimming and saps energy.

The findings, published in the article "Honesty is costly in a deceptive system: locomotor costs of producing large and strong weapons for the crayfish, Cherax destructor," shed light on the evolutionary trade-offs of animal signaling, particularly how "unreliable signals" of strength can persist in nature. The article in Ecological and Evolutionary ÌÇÐÄÊÓƵiology.

"Our study is the first to demonstrate the independent costs of both signal size and their reliability," write the authors. "While individuals must bear the costs of signaling large weapons, the costs of their reliability may also incentivize the use of unreliable weapons."

Animals often use physical traits to signal fighting ability and deter costly battles. In crustaceans, large claws serve as both weapons and displays of strength. However, some individuals display large but relatively weak claws—creating a mismatch between signal size and actual strength.

The research team studied 145 male and female Cherax destructor Australian freshwater crayfish, measuring their claw size, claw strength, and swimming performance. Crayfish were tested intact, after removal of one or both claws, and again after complete removal of all claws.

The study provides evidence that both the magnitude and reliability of animal signals are independently costly. Both sexes with larger chelae swam more slowly, suggesting an energetic trade-off between claw muscle investment and locomotion. Removal of one claw boosted speed by 11.6%, while removal of both claws improved speed by 14.6%. Crayfish with disproportionately large claws gained the greatest boost in speed once claws were removed—highlighting the physical burden of carrying oversized weapons.

"While crayfish will benefit from producing larger chelae as they can intimidate opponents during disputes with conspecifics, large chelae can have costly consequences," the authors write. "Therefore, the display of these weapons provides information to a receiver on both the probability of their strength—albeit with variance—and their ability to survive with the additional locomotor burden of their larger weapons."

The paper highlights the trade-offs animals face when allocating resources to growth, strength, and survival.

"Male C. destructor more frequently escalate to fights, which should directly limit the benefits accrued to males who signal unreliably," the authors write. However, the findings suggest that males who were weaker for their size, and thus possess unreliable signals of strength, were faster when both chelae were intact.

"Therefore, this benefit could also provide an important incentive for unreliability in male C. destructor, despite the higher likelihood of combat," the authors conclude.