Environmental effects on growth; consequences for parents and offspring

Why don't animals all grow at their maximum possible rate? It has long been recognised that animals have the potential to grow faster than they normally do, and the reason for this restraint is thought to be the existence of delayed costs of rapid growth. While such costs have been widely documented, there has been little attempt to determine the underlying mechanisms, so we still do not understand how the costs of rapid growth are incurred.
It has been suggested that rapid growth hastens the rate of ageing, but the evidence so far has largely been unconvincing. By using a novel approach to manipulate growth rates, we recently provided the first rigorous experimental test of this relationship, and found dramatic changes in both lifespan and other measures of senescence in the predicted direction in response to both upward and downward manipulations of growth rates. Moreover, the strength of these effects depended on the perceived time available to recover from the growth perturbation prior to the breeding season: for a given rate of growth, animals with less time to spare before the start of the breeding season subsequently suffered a greater reduction in their lifespan.
These results demonstrate that, while growing more slowly can postpone senescence, the best outcome for the animal is influenced by time constraints in a seasonal environment. However the physiological mechanisms underlying these dramatic effects, and how they influence offspring fitness, are unknown. This project aims to uncover those mechanisms, and to quantify their effect on offspring viability, using experiments that manipulate the growth rate of stickleback fish. This is a highly original study that will explore how adverse and favourable environmental conditions encountered early in life can leave an imprint on an organism's cells that influence both the rate at which it starts to senescence later in life, and potentially the fate of its offspring. It aims to explain phenomena long suspected by ecologists, which have increasing relevance in a changing environment.

The main beneficiaries of this research are members of the academic community in many different areas of biology and biomedicine. To understand how and why growth is optimised rather than maximised requires that we understand the costs and benefits across different time scales. We need to elucidate the mechanisms underlying these effects in order to evaluate constraints and predict outcomes.
These results are of interest also in an applied context and will have wider societal benefits. Managing growth and its effects on other life history traits is important for practitioners in many areas of society including human and animal medicine, animal breeding and management of captive breeding programmes for endangered species. The basic mechanisms and trade-offs that we will be investigating apply to a wide range of taxa. It is of great importance that we are able to predict the consequences of erratic, extreme and unseasonal weather patterns in both aquatic and terrestrial systems. The long term effects of changes in growth patterns are poorly understood, and we should expect that groups exposed to particular weather patterns, such as unseasonal cold or warm spells as in our aquatic animals in this study, will show different life history patterns. Our work will also be important in predicting the effects on life history traits and performance of different cohorts and geographical populations.