Highly plastic resource allocation to growth and reproduction in females of an African annual fish

Abstract

Phenotypic plasticity is an important mechanism to maximise fitness in unpredictable environments by fine‐tuning phenotypes to a specific environmental setting. We used Nothobranchius furzeri, an African annual fish from temporary pools with erratic changes in habitat condition, to study changes in the allocation to growth and reproduction and to test the key trade‐off between egg size and number. In an experimental setting, we quantitatively varied ration at two levels and over two time periods, including temporal switches in ration level. As predicted, female N. furzeri possessed the capacity for compensatory growth, which surprisingly came with no longer‐term cost to fecundity. Females responded strongly to ration manipulation, with a pronounced decrease in fecundity associated with a low ration, even after accounting for body mass. Due to the unpredictability of offspring environment, we expected no adaptive change in oocyte size. However, females responded to the quality of their environment in accordance with an adaptive maternal effect, with females receiving a low ration producing larger eggs. Further, a switch in ration size in either direction was associated with a decrease in egg size. There was a trade‐off between egg size and number in half of the treatments, but high variability in egg size among females made the relationship complex. Overall, N. furzeri females demonstrated high plasticity in both growth rate and fecundity parameters. Females appear able to track and respond adaptively to unpredictable changes in food availability in their environment.

Life-history plasticity in female threespine stickleback

“…Reproductive effort in fish tends to remain fairly consistent throughout a reproductive season (examples in Vrtilek and Reichard, 2014), and therefore within-season plasticity of reproductive effort may be mediated primarily via the number of clutches in many cases. Studies by Ali and Wootton (1999a) and Wootton and Fletcher (2009) show that once stickleback females begin reproducing, they maintain their initial strategy of making a size-appropriate clutch mass regardless of subsequent changes in ration levels.…”

“…Even the most rapid plastic responses in female life-history traits cannot be considered activational (sensu Snell-Rood, 2013), a common characteristic of behavioral traits. Nevertheless, life-history plasticity may be expressed at several very different timescales-from clutch-to-clutch adjustments (Kolm, 2001;Vrtilek and Reichard, 2014), to a gradual adjustment in reproductive traits as the breeding season approaches (Kennedy et al, 2008), to year-to-year shifts (Lee et al, 2012) and across generations via maternal effects (Bashey, 2006;Galloway and Etterson, 2009).…”

Rapid growth and large body size in annual fish populations are compromised by density‐dependent regulation

“…Nothobranchius spp. are income breeders with an immediate conversion of resources into current reproductive effort (Vrtílek & Reichard, ). They feed on a wide range of planktonic and benthic invertebrates whose availability severely decreases at high killifish density (Polačik et al, ; Polačik & Reichard, ).…”

“…Sexual dimorphism in colouration, morphology and body size is pronounced, with males being the larger sex. The growth of annual killifishes is particularly plastic and continues after sexual maturity when resources are available (Vrtílek & Reichard, ). Cross‐sectional sampling of natural populations usually shows large body size differences among populations and relatively low intra‐population variation (Vrtílek & Reichard, ), indirectly suggesting the effect of local conditions.…”

“…Fish must reproduce before their habitat desiccates, resulting in sexual maturation in as few as 14 days (Vrtílek et al, ). Female fecundity is strongly correlated to body mass (Blažek et al, ; Vrtílek & Reichard, ) while male hierarchy is contingent upon variation in body size (Polačik & Reichard, ). Here, we demonstrate that the selection for rapid growth and large body size imposed by habitat seasonality and reproductive strategy is severely compromised by density‐dependent regulation at the population level.…”