Study finds compensatory growth in male guppies carries hidden reproductive costs
A new study on guppies (Poecilia reticulata) found that males who experienced early-life social competition and subsequently underwent compensatory growth produced significantly fewer sperm as adults, despite reaching normal body size. The research isolated social competition from nutritional factors, demonstrating that the social environment alone can reshape life-history trade-offs. The findings suggest that adult body size can mask hidden reproductive costs, with implications for understanding how early social conditions influence fitness in vertebrates.
Researchers studying male guppies found that scramble competition among peers during early development triggers compensatory 'catch-up' growth once those social constraints are removed, but this recovery comes at a reproductive cost. Males that exhibited higher compensatory growth reached comparable adult body sizes to their peers yet produced significantly fewer sperm at maturity — a deficit that persisted even after controlling for adult body size. This indicates a direct physiological trade-off between somatic recovery and ejaculate investment, rather than a simple size-dependent effect. The study also identified a negative association between gonopodium length and sperm count, pointing to competing resource allocations between pre-copulatory and post-copulatory reproductive traits during development. Crucially, the experiment was designed to isolate social competition from resource availability, establishing that the social environment alone — not nutrition — can recalibrate life-history trajectories. The authors describe these lingering effects as the 'ghosts of competition past,' arguing that ontogenetic history must be considered to fully understand the evolution of sexually selected traits. The work highlights how adult morphology can conceal underlying differences in reproductive quality, with broader relevance to sexually reproducing social vertebrates.
What's missing
The study is a preprint posted to bioRxiv and has not yet undergone formal peer review, so findings should be interpreted with caution. Key limitations not detailed in the abstract include the specific sample sizes used, the magnitude of the sperm count reduction, whether sperm quality (motility, morphology) was also affected beyond count, and whether the observed trade-offs translate into measurable differences in actual reproductive success or offspring fitness under natural conditions. It is also unclear whether these effects are reversible or permanent across the lifespan.
What different sources said
- bioRxivCenter
Socially-mediated compensatory growth carries hidden sperm costs in male guppies
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