title: Exceptional running and turning performance in a mite.
abstract: The Southern California endemic mite Paratarsotomus macropalpis was filmed in the field on a concrete substrate and in the lab to analyze stride frequency, gait and running speed under different temperature conditions and during turning. At ground temperatures ranging from 45 to 60 °C, mites ran at a mean relative speed of 192.4 ± 2.1 body lengths (BL) s(-1), exceeding the highest previously documented value for a land animal by 12.5%. Stride frequencies were also exceptionally high (up to 135 Hz), and increased with substrate temperature. Juveniles exhibited higher relative speeds than adults and possess proportionally longer legs, which allow for greater relative stride lengths. Although mites accelerated and decelerated rapidly during straight running (7.2 ± 1.2 and -10.1 ± 2.1 m s(-2), respectively), the forces involved were comparable to those found in other animals. Paratarsotomus macropalpis employs an alternating tetrapod gait during steady running. Shallow turns were accomplished by a simple asymmetry in stride length. During tight turns, mites pivoted around the tarsus of the inside third leg (L3), which thus behaved like a grappling hook. Pivot turns were characterized by a 42% decrease in turning radius and a 40% increase in angular velocity compared with non-pivot turns. The joint angle amplitudes of the inner L2 and L3 were negligible during a pivot turn. While exceptional, running speeds in P. macropalpis approximate values predicted from inter-specific scaling relationships.
authors.affiliation: Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: Samuel
authors.initials: S
authors.lastname: Rubin
authors.affiliation: Department of Biology, Pomona College, Claremont, CA 91711, USA.
authors.forename: Maria Ho-Yan
authors.initials: MH
authors.lastname: Young
authors.affiliation: Department of Biology, Pomona College, Claremont, CA 91711, USA jcw04747@pomona.edu.
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Wright
authors.affiliation: Department of Physics, Pomona College, Claremont, CA 91711, USA.
authors.forename: Dwight L
authors.initials: DL
authors.lastname: Whitaker
authors.affiliation: Department of Biology, Harvey Mudd College, Claremont, CA 91711, USA.
authors.forename: Anna N
authors.initials: AN
authors.lastname: Ahn
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D005121:Extremities / Q000033:anatomy & histology / Q000502:physiology; D005684:Gait; D008925:Mites / Q000254:growth & development / Q000502:physiology*; D012420:Running; D013696:Temperature
keywords: Gait; Paratarsotomus; Relative speed; Stride frequency; Turning