Offspring Size Plasticity in Response to Intraspecific Competition: An Adaptive Maternal Effect across Life‐History Stages

Abstract

When provisioning offspring, mothers balance the benefits of producing a few large, fitter offspring with the costs of decreased fecundity. The optimal balance between offspring size and fecundity depends on the environment. Theory predicts that larger offspring have advantages in adverse conditions, but in favorable conditions size is less important. Thus, if environmental quality varies, selection should favor mothers that adaptively allocate resources in response to local conditions to maximize maternal fitness. In the bryozoan Bugula neritina, we show that the intensity of intraspecific competition dramatically changes the offspring size/performance relationship in the field. In benign or extremely competitive environments, offspring size is less important, but at intermediate levels of competition, colonies from larger larvae have higher performance than colonies from smaller larvae. We predicted mothers should produce larger offspring when intermediate competition is likely and tested these expectations in the field by manipulating the density of brood colonies. Our findings matched expectations: mothers produced larger larvae at high densities and smaller larvae at low densities. In addition, mothers from high-density environments produced larvae that have higher dispersal potential, which may enable offspring to escape crowded environments. It appears mothers can adaptively adjust offspring size to maximize maternal fitness, altering the offspring phenotype across multiple life-history stages.

Seasonal variation in reproductive traits of the oriental shrimp Palaemon macrodactylus (Crustacea: Caridea: Palaemonidae) in a non-native population

“…Egg weight of middle season females could not be estimated, but it may be assumed that their weight was similar to that of late females, since larval dry weight did not differ between these females. In general, the production of large eggs reflects an enhanced maternal energy investment at the cost of reduced fecundity (Allen et al 2008). In this species, by contrast, the increased fecundity of middle season females without a reduction in egg size (and presumably in weight) and without increasing their reproductive output suggests a better body condition.…”

Phenotypic plasticity in growth and fecundity induced by strong population fluctuations affects reproductive traits of female fish

“…1996; Allen et al. 2008) offspring size and survival. Plaistow and Benton (2009) concluded that maternal effects in high competition population (low food ration) impact more on juvenile survival compared with low competition populations (high food ration), where maternal effects have more impact on the population growth rate.…”

Life-history plasticity in female threespine stickleback

“…Adaptive plasticity may be expressible only by reduction in reproductive effort that, as indicated above, is probably mediated in one of (or a combination of) the three ways: (1) via a reduction in the number of follicles recruited into vitellogenesis (that is, reduced clutch size) as body size/energy content declines, (2) via a longer interclutch interval or (3) by earlier cessation of reproduction (produce fewer seasonal clutches). If fluctuations in adult ration are mirrored by reductions in fry ration (via density effects, for example; Allen et al, 2008), this means that fry fitness would also be reduced as the environment now requires a larger fry while, in addition, clutch size is also reduced-a double hit to within-season fitness. Thus, the principal fitness benefit of life-history plasticity must be survival to reproduce in a subsequent Figure 9 Matrix plot showing the relationships between female life-history traits, body mass and somatic condition in Big Beaver Lake, Alaska.…”