Ontogenies in Mice Selected for High Voluntary Wheel-Running Activity. I. Mean Ontogenies

Abstract

Abstract. The evolutionary importance of postnatal ontogenies has long been recognized, but most studies of ontogenetic trajectories have focused exclusively on morphological traits. For animals, this represents a major omission because behavioral traits and their ontogenies often have relatively direct relationships to fitness. Here four replicate lines of house mice artificially selected for high early-age wheel running and their four replicate control lines were used to evaluate the effects of early-age directional selection, genetic drift, and activity environment (presence or absence of a running wheel) on variation in the ontogenies of three traits known to be genetically correlated: voluntary wheel running, body mass, and food consumption. Early-age selection significantly changed both the shape and position of the wheel-running and food-consumption ontogenies while influencing the position, but not the shape, of the body mass ontogeny. Genetic drift (as indicated by variation among replicate lines) produced significant changes in both the position and shape of all three ontogenies; however, its effect differed between the selection and control groups. For wheel running and food consumption, genetic drift only influenced the control ontogenies, whereas for body mass, genetic drift had a significant effect in both selection groups. Both body-mass and food-consumption ontogenies were significantly altered by activity environment, with the environment causing significant changes in the shape and position of both ontogenies. Overall the results demonstrate strong effects of early-age selection, genetic drift, and environmental variation on the evolution and expression of behavioral and morphological ontogenies, with selection changing only the position of the morphological ontogeny but both the position and shape of the behavioral ontogenies.

Age-Related Changes in Locomotor Performance Reveal a Similar Pattern forCaenorhabditis elegans,Mus domesticus,Canis familiaris,Equus caballus, andHomo sapiens

“…Based on these results, we hypothesize that these age-related patterns are common features of the relationship between age and locomotor performance in a wide range of organisms. The shape of the patterns seems to match descriptions of other age-related locomotor performances in different species, such as flight performances in Drosophila (31), honeybees (32), and codling moths (33), maximal sprint speed in dogs and horses (34)(35)(36), physical activity in different rodents and monkeys (16,27,28), grip strength in mouse lemurs (15), hunting rates and success in wolves (37), swimming speed in zebrafish (38), and voluntary activity and electrotactic behavior in C. elegans (29,39). Likewise, other performance traits might follow a similar pattern, such as biting force in mouse lemur (40), cognitive performances in Rhesus monkey (41), attentiveness in domestic dogs (42), pharynx pumping rate in C. elegans (43), and perhaps even photosynthetic yield in cotton leaves (44).…”

“…We used respectively 33 (27,28) who conducted studies of life-long voluntary activity in two groups of mice: A control population composed of 79 mice and a population of 80 mice from the 16th generation of selection for high wheel-running activity. All the details of the population selection and living conditions are available in Morgan et al (27).…”

“…All the details of the population selection and living conditions are available in Morgan et al (27).…”

Day-to-day variability in voluntary wheel running among genetically differentiated lines of mice that vary in activity level

“…As expected for mice of this age, some increase in physical activity level occurs as they are still undergoing physical maturation (Swallow et al 1999;Morgan et al 2003). This age-related trend makes it diYcult to interpret the daily variability in raw wheel revolutions with respect to normal maturation versus inherent control (regulation) of physical activity level.…”

“…Previous studies of these lines of mice from earlier generations have demonstrated that daily wheel-running distances increase for approximately 5 weeks following Wrst exposure to wheels at weaning (3 weeks of age) or shortly thereafter (Swallow et al 1999;Morgan et al 2003). In the present study, we analyzed data from a later generation and considered weeks 3-5 of wheel access (6-8 weeks of age), in order to parallel our previous studies of human adolescents and young adults Eisenmann 2006, 2007a, b;Wickel et al 2007).…”