A species of spiny orb-weaver spider has a 19-hour circadian clock. Photo: ojogabonitoo / iStock

Three species of orb-weaving spiders may have the fastest biological clocks known in nature. Their circadian cycles range between 17.4 and 19.0 hours on average, instead of synchronizing with a 24-hour solar light cycle. The research, conducted at East Tennessee State University, was presented Sunday at the annual meeting of the Society for Neuroscience.

Why it matters: Their clock is so fast, it's unclear how the spiders survive. Studying extreme sleep-wake cycles and circadian clocks can help scientists understand the role these neurological timekeepers play in species survival and what causes our own rhythms to go awry due to disease.

Most research on fast circadian clocks has been done in deliberately-created mutant hamsters and fruit flies.

How they did it: Animals tend to maintain their natural circadian rhythm in the absence of light so the researchers exposed the spiders to constant dark. The spiders alternated between moving and resting in 17-19 hour loops, depending on the species.

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The three species are

Allocyclosea bifurca

and

Cyclosa turbinata

, both types of trashline orb-weavers, and the spiny orb-weaver (

Gasteracanthea cancriformis).

Researchers note that the spiders are most active late at night, in contrast with most nocturnal spiders, which are active early at night. It's unclear if this is related to their abnormally short circadian rhythm.

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