Résumé
Individual variation in growth is high in cooperative breeders and may
reflect plastic divergence in developmental trajectories leading to
breeding vs. helping phenotypes. However, the relative importance of
additive genetic variance and developmental plasticity in shaping growth
trajectories is largely unknown in cooperative vertebrates. This study
exploits weekly sequences of body mass from birth to adulthood to
investigate sources of variance in, and covariance between, early and
later growth in wild meerkats (Suricata suricatta), a cooperative
mongoose. Our results indicate that (i) the correlation between early
growth (prior to nutritional independence) and adult mass is positive but
weak, and there are frequent changes (compensatory growth) in
post-independence growth trajectories; (ii) among parameters describing
growth trajectories, those describing growth rate (prior to and at
nutritional independence) show undetectable heritability while associated
size parameters (mass at nutritional independence and asymptotic mass) are
moderately heritable (0.09 ≤ h2 < 0.3); and (iii) additive genetic
effects, rather than early environmental effects, mediate the covariance
between early growth and adult mass. These results reveal that meerkat
growth trajectories remain plastic throughout development, rather than
showing early and irreversible divergence, and that the weak effects of
early growth on adult mass, an important determinant of breeding success,
are partly genetic. In contrast to most cooperative invertebrates, the
acquisition of breeding status is often determined after sexual maturity
and strongly impacted by chance in many cooperative vertebrates, who may
therefore retain the ability to adjust their morphology to environmental
changes and social opportunities arising throughout their development,
rather than specializing early.