Shaking a leg and hot to trot: the effects of body size and temperature on running speed in ants

We studied in the field the load transport behavior of workers of the polymorphic Mediterranean seed harvester ant Messor barbarus. Individual ants used two different methods to transport food items: carrying and dragging. The probability of dragging instead of carrying varied significantly with both the mass of the item transported and its linear dimension. Moreover, the values of item mass and length at which dragging began to occur increased with increasing size of the workers. However, larger ants began dragging at decreasing values of the relative mass represented by the items transported, which reflects different biomechanical constraints resulting from allometric relationships between the different parts of their body. Transport rate was significantly higher in large ants but varied in the same way for workers of different sizes with the relative mass of the item transported. Nevertheless, although large ants were individually more efficient than small ants in transporting food items, the relative transport rate, defined as the ratio of transport rate to the mass of the ant, was higher for small ants than for large ants. Colonies should thus have a greater benefit in investing in small ants than in large ants for the transport of food items. This may explain why the proportion of large ants is so small on the foraging columns of M. barbarus and why large ants are most often employed in colonies for tasks other than transporting food items.

Section: Discussionmentioning

confidence: 99%

Ergonomics of load transport in the seed harvesting ant Messor barbarus Linnæus, 1767: morphology influences transportation method and efficiency

Bernadou

Felden

Moreau

et al. 2016

“…If we replace the spring constant with muscle stiffness, we would expect the frequency of oscillatory movements in animals to increase with increasing muscle stiffness and decrease with increasing body mass. Much work on oscillatory movement has shown that body size is often correlated with frequency (Heglund and Taylor, 1988;Young et al, 1992;Lindstedt and Schaeffer, 2002 and references therein; Hurlbert et al, 2008;Sato et al, 2010;Dickerson et al, 2012). The frequency of muscle activation during shivering thermogenesis also seems to be correlated with body mass (Spaan and Klussmann, 1970).…”

Section: Introductionmentioning

confidence: 99%

Shiver me titin! Elucidating titin's role in shivering thermogenesis

Taylor-Burt

Monroy

Pace

et al. 2015

Shivering frequency scales predictably with body mass and is 10 times higher in a mouse than a moose. The link between shivering frequency and body mass may lie in the tuning of muscle elastic properties. Titin functions as a muscle 'spring', so shivering frequency may be linked to titin's structure. The muscular dystrophy with myositis (mdm) mouse is characterized by a deletion in titin's N2A region. Mice that are homozygous for the mdm mutation have a lower body mass, stiffer gait and reduced lifespan compared with their wild-type and heterozygous siblings. We characterized thermoregulation in these mice by measuring metabolic rate and tremor frequency during shivering. Mutants were heterothermic at ambient temperatures of 20-37°C while wild-type and heterozygous mice were homeothermic. Metabolic rate increased at smaller temperature differentials (i.e. the difference between body and ambient temperatures) in mutants than in nonmutants. The difference between observed tremor frequencies and shivering frequencies predicted by body mass was significantly larger for mutant mice than for wild-type or heterozygous mice, even after accounting for differences in body temperature. Together, the heterothermy in mutants, the increase in metabolic rate at low temperature differentials and the decreased tremor frequency demonstrate the thermoregulatory challenges faced by mice with the mdm mutation. Oscillatory frequency is proportional to the square root of stiffness, and we observed that mutants had lower active muscle stiffness in vitro. The lower tremor frequencies in mutants are consistent with reduced active muscle stiffness and suggest that titin affects the tuning of shivering frequency.

“…Both relative speed (v r ) and stride frequency ( f ) scale negatively with body mass (M b ) (Alexander, 1982;Weyand et al, 2000;IriarteDíaz, 2002;Biewener, 2003;Wu et al, 2010). Dynamic similarity and the length-resonance relationship predict that f∝l −0.5 , where l is leg length, as for a pendulum (Alexander and Jayes, 1983;Biewener, 2003;Hurlbert et al, 2008). Early work showed that this predicted scaling for v r holds true for East African mammals (Pennycuick, 1975), and this was subsequently corroborated for other mammals (Garland, 1983).…”

Section: Introductionmentioning

confidence: 92%

“…More recently, however, Iriarte-Díaz (2002) showed that mammals can be subdivided into smaller species (<30 kg) with a lower v r :M b exponent of −0.09, and larger species with a considerably larger exponent (−0.46). Several factors may account for different exponent values and size-dependent changes in the exponent, including non-isometric scaling of limb length, metabolic power (Schmidt-Nielsen, 1984;Jones and Lindstedt, 1993), and the interaction of metabolic power and dynamic similarity constraints (Hurlbert et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

Exceptional running and turning performance in a mite

Rubin

Young

Wright

et al. 2016

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 , 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.