Sifaka positional behavior: Ontogenetic and quantitative genetic approaches

Abstract

In many primate species, hands and feet are large relative to neonatal body weight, and they subsequently exhibit negative allometric growth during ontogeny. Here, data are presented showing that this pattern holds for a wild population of lemur, Verreaux's sifaka (Propithecus verreauxi verreauxi). Using morphometric data collected on this population, it is shown that younger animals possess relatively large hands and feet. This ontogenetic pattern suggests a simple behavioral test: do juvenile animals with their larger, almost adult-sized hands and feet locomote on similarly sized substrates as adult animals? Using locomotor bout sampling, this question was tested by collecting positional behavior data on this population. Results from this test find no differences in locomotor behaviors or substrate use between yearlings and adult animals. To place these results in a broader evolutionary context, heritabilities and selection gradients of hands, feet, and other limb elements for animals in this population were estimated. Among limb elements, heritabilities range from 0.16-0.44, with the foot having the lowest value. Positive directional selection acts most strongly on the foot (directional selection gradient = 0.119). The low heritability and positive selection coefficient indicate that selection has acted, and continues to act, on foot size in young animals. These results are interpreted within a functional context with respect to the development of locomotor coordination: larger feet enable young animals to use "adult-sized" substrates when they move through their habitat. It is suggested that the widespread pattern of negative allometry of the extremities in sifaka and other primates is maintained by selection, and does not simply reflect a primitive developmental pathway that has no adaptive basis.

Ontogeny of joint mechanics in squirrel monkeys (Saimiri boliviensis): functional implications for mammalian limb growth and locomotor development

“…Because, by definition, juveniles have yet to reproduce, there should be strong selection for compensatory mechanisms, such as allometric musculoskeletal growth trajectories or developmental changes in behavior, that could enhance locomotor performance despite size-and growth-related limitations on performance (Pennycuick, 1975;Carrier, 1983;Werner and Gillam, 1984;Carrier and Leon, 1990;Irschick, 2000;Trillmich et al, 2003;Main and Biewener, 2004;Irschick et al, 2005;Young, 2005;Herrel and Gibb, 2006;Lawler, 2006). This study tests the hypothesis that allometric changes in joint mechanics allow growing squirrel monkeys to compensate for ontogenetic limits on locomotor performance.…”

Multivariate Selection Theory in Primatology: An Introduction to the Concepts and Literature

“…One of the goals of this study was to examine if foot length, which scales with negative allometry to body size during growth, was associated with survival [82]. In this regard, Lawler [82] sought to test if foot size was adaptive.…”

“…Another study that looked at heritability in a wild primate population was that of Lawler [82]. This study is outlined above with respect to estimating selection pressures that act on limb elements on Verreaux's sifaka.…”

Kinematics of quadrupedal locomotion in sugar gliders (Petaurus breviceps): effects of age and substrate size

“…Carrier, 1983;Carrier and Leon, 1990;Carrier, 1995;Main and Biewener, 2004;Main and Biewener, 2006;Main and Biewener, 2007;Young, 2009a). For example, the relatively large hands and feet of juvenile mammals compared with those of adults provide stability and, in arboreal contexts, permit navigation of adult-sized substrates (Jungers and Fleagle, 1980;Ravosa et al, 1993;Turner et al, 1997;Lammers and German, 2002;Raichlen, 2005b;Lawler, 2006;Schilling and Petrovitch, 2006;Young, 2009a; Heard-Booth and . Juvenile mammals compensate for limited muscle mass with relatively long muscle lever arms compared with those of adults (Carrier, 1983;Peters, 1983;Young, 2005;Fellmann, 2011) and/or behavioral adjustment of joint postures that reduce limb joint loading (Young, 2009a).…”

“…This may be particularly true with regard to arboreal habitats, where substrate navigation is complex, locomotor stability is at a premium, and selection pressures on juveniles might be enhanced (Lawler, 2006;. Previous biomechanical studies of locomotor ontogeny have documented heightened, even adult-like, levels of performance in a host of juvenile animals, including crickets (Dangles et al, 2007), fish (Hale, 1996;Gibb et al, 2006), birds (Dial and Jackson, 2011), salamanders (D'Aout and Aerts, 1999;Landberg and Azizi, 2010), lizards (Irschick, 2000;Toro et al, 2003), frogs (Emerson, 1978), guinea pigs (Trillmich et al, 2003), jackrabbits (Carrier, 1995), horses (Grossi and Canals, 2010), gnu (Pennycuick, 1975) and elephants (Hutchinson et al, 2006).…”