Causes and consequences of parental age effects on offspring quality
How ageing occurs, why it varies across individuals, and what determines its pace, pattern, and form are crucial questions for understanding life-history diversity. Genomic variation accounts for a low proportion of phenotypic variation in ageing trajectories, highlighting the role of environmental and other non-genetic factors , but these factors remain relatively understudied. Albert Lansing discovered that parental age negatively affects the longevity of descendants, indicating the transgenerational transmission of parental state at breeding. Subsequent research suggests this “Lansing effect” is common  and may be ubiquitous in insects . The Lansing effect has important consequences as it means the transitory aspects of the environment affecting parents can also affect their offspring. However, most research focusses on processes occurring within generations; how parental age affects lifespan and fitness of descendants across generations requires urgent attention . Insects provide powerful models for this type of question because of their short generation time and conduciveness to performing both manipulative experiments and field studies. Using the field cricket Gryllus bimaculatus as the ideal model, we will for the first time uncover these aspects of the Lansing effect:
Form: The Lansing effect has mainly been studied in ectotherms and is understood in terms of their age. However, physiological processes are dependent on temperature, so the biological age of an ectothermic individual will also depend on the temperature it has experienced [6–9]. Therefore, it is unclear whether the parents chronological or biological age at breeding causes the Lansing effect. We will establish the independent effects of chronological age (time since birth) and biological age (temperature-dependent deterioration in an individual’s condition, expressed as time until death) on offspring longevity. We will also unravel how, and in what form, offspring longevity is affected. Offspring from older parents may be in poor condition at birth, exhibiting increased baseline mortality risk, or they could age faster, with no differences in condition at birth. These contrasting causes of mortality have important implications. The Lansing effect is assumed to negatively affect offspring fitness, but the negative effect on longevity could covary with increased early-life performance through a switch to a fast life-pace strategy, limiting the net effect on fitness.
Mechanism: It remains unclear how parental age affects offspring quality. The germline is separated from the soma by the Weismann barrier, but this barrier could be leaky, meaning age related damage can accumulate in the germline . We will determine whether parental age at breeding causes oxidative damage in the germline, reducing DNA integrity. We will also determine if DNA-methylation state of the germline could underpin parental age effects on offspring quality.
Function: Experimental field studies of the Lansing effect are lacking, meaning their fitness consequences remain unclear. We will conduct a novel field study, exploiting our extensive experience with a highly suitable field system in Spain (www.wildcrickets.org), to estimate the fitness consequences of the Lansing effect across multiple generations, assessing its importance for adaptation/evolution.
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Fig. 1 High altitude meadow in Asturias, Spain,Fig 2. Tagged Gryllus campestris adults outside burrow