University of Liverpool
Institute of Integrative Biology
Dept. of Evolution, Ecology and Behaviour
Biosciences Building, Crown Street, L69 7ZB
Liverpool, L69 7ZB
Abstracts (first author)
Maternal-age effects on rates of senescence differ between clones of the water flea, Daphnia pulex: causes and consequences
Senescence is widely believed to be the evolved consequence of life-history strategies that are themselves shaped by extrinsic mortality. Consequently, evolutionary explanations of senescence are static. But recent studies investigating lifespan extension, genetic intervention and dietary restriction suggest that rates of senescence are plastic and may be regulated by the same mechanisms that underpin life-history plasticity. The Lansing effect refers specifically to plasticity in lifespan that are derived from maternal age effects: offspring from older mothers often senesce at faster rates. Lansing demonstrated this effect in rotifers over 60 years ago, and Lansing effects have now been observed in a broad range of taxa. However, there is still no evolutionary framework for the Lansing effect, or a mechanism explaining how maternal age effects are transmitted and alter offspring life-histories. We repeated Lansing's experiments in D. pulex. Using offspring from the first clutch to set up young maternal lines, and offspring from the fifth clutch to set up old maternal lines, we reared three clones for three generations. Offspring development, life-history and rates of senescence were then compared in the fourth generation. Lansing Effects were observed irrespective of the measure of senescence used, and varied in strength between clones. Offspring from old maternal lines were born larger, grew more, initiated maturation at larger sizes, and had increased early lifetime reproductive effort. However, differences in the growth and maturation decisions of offspring from young and old maternal lines were size-independent, supporting Lansing's assertion that older mothers transmit a non-genetic "ageing factor" to their offspring that alters their life-histories. We propose a novel adaptive explanation for the Lansing effect, and discuss the implications that an interaction between genetic and non-genetic inheritance have life-history evolution and population demography.