Development time mediates the effect of larval diet on ageing and mating success of male antler flies in the wild

Abstract

High-quality developmental environments often improve individual performance into adulthood, but allocating toward early life traits, such as growth, development rate and reproduction, may lead to trade-offs with late-life performance. It is, therefore, uncertain how a rich developmental environment will affect the ageing process (senescence), particularly in wild insects. To investigate the effects of early life environmental quality on insect life-history traits, including senescence, we reared larval antler flies (Protopiophila litigata) on four diets of varying nutrient concentration, then recorded survival and mating success of adult males released in the wild. Declining diet quality was associated with slower development, but had no effect on other life-history traits once development time was accounted for. Fast-developing males were larger and lived longer, but experienced more rapid senescence in survival and lower average mating rate compared to slow developers. Ultimately, larval diet, development time and body size did not predict lifetime mating success. Thus, a rich environment led to a mixture of apparent benefits and costs, mediated by development time. Our results indicate that 'silver spoon' effects can be complex and that development time mediates the response of adult life-history traits to early life environmental quality.

Keywords: Protopiophila litigata; longevity; mark-recapture; senescence; silver spoon; trade-off.

Figure 1.

Variation in egg-to-adult development time and wing length within and among larval diet treatments. (a) Boxplot of development time in each diet. Thick horizontal lines denote the median, boxes demarcate the first and third quartiles and whiskers indicate the minimum and maximum values. (b) Wing size as a function of developmental time across all larval diet treatments. The regression was fitted on the pooled dataset (F_1,159 = 9.39, p = 0.003 for this simplified regression), as there was no significant difference in intercept or slope among diets. Diet treatments: A (100% ground beef); B (9 : 1 ratio of ground beef : fibre); C (8 : 1 ratio of ground beef : fibre); D (7 : 1 ratio of ground beef : fibre). (Online version in colour.)

Figure 2.

The effect of (a), egg-to-adult development time and (b), wing length (body size) on actuarial senescence (daily mortality rate) in male P. litigata. The effect of development time and wing length on the scale parameter were analysed as continuous variables, but are plotted as mortality curves for males above or below the median trait value. Symbols are observed daily mortality rates for the two groups, while the lines represent fitted mortality curves based on the best supported Weibull survival model (weighted means across blocks). Owing to the shape effect of development time, (b) shows mortality rates for fast developers only.

Figure 3.

Relationship between egg-to-adult development time and average mating rate in male antler flies. Points represent the lifetime average mating rate for each male and the line represents predicted values from the minimal adequate GLMM (weighted mean across antlers and blocks).