Brinedew

Unpublished draft

Research Gaps

Gap — How long is the continuous medusa-phase maintained in Turritopsis dohrnii (no reversions)?

What this gap is: We lack a documented upper bound (or even a proper survival curve) for continuous maintenance of the medusa body plan in T. dohrnii when reversions to polyp are disallowed.

What’s known (relevant facts):

  • T. dohrnii medusae reach sexual maturity after ~25–30 days at 20 °C and ~18–22 days at 22 °C (16L:8D photoperiod), based on lab culture work that focused on development and ontogeny, not longevity per se. [Martell et al., 2016]
  • Medusae of hydrozoans typically die after releasing gametes; in T. dohrnii they may instead revert to a cyst → polyp, restarting the cycle. Recent experimental work emphasizes that basic biology is still poorly characterized, including responses to stress and reversal rates. [Invertebrate Biology, 2024/2025]
  • Reversal (medusa → cyst → polyp) is well established from classic through modern studies. [Piraino et al., 1996; Pascual-Torner et al., 2022; Matsumoto et al., 2019/2021]
  • For scale-setting across small hydromedusae, lab medusae lifespans rarely exceed ~3 months (e.g., Phialidium spp.) under culture. This is not Turritopsis, but it sets a plausible order-of-magnitude for small hydromedusae kept as medusae. [Roosen-Runge, 1970]

What’s missing: No peer-reviewed report that tracks medusa-only husbandry of T. dohrnii into the multi-month range with explicit censoring of any reversion events and with a published survival curve (median, variance, tails). The field largely measures time-to-maturity and reversal dynamics, not medusa-phase longevity.

Why this matters: If medusae routinely senesce (or die for ecological reasons) within weeks to a few months unless they revert, then the “immortality” is fundamentally a body-plan switching strategy rather than unusually durable medusae. Quantifying the medusa-only limit makes that trade-off legible.

Minimal closure test (publishable protocol):

  • Design: Start N ≥ 100 ephyrae; maintain at 20–22 °C, 16L:8D, gently aerated kreisel or equivalent; ad lib Artemia nauplii with daily water quality checks.
  • Rule:Any detectable reversal (cyst formation, attached tissue) = failure event; exclude from “medusa-continuous” survival.
  • Tracking: Daily imaging; weekly morphometrics; Kaplan–Meier survival with right-censoring only for accidental loss unrelated to biology.
  • Reporting: Median and 95% CI for medusa-phase longevity; temperature/feeding covariates; raw logs and videos in a repository.

Decision rule for closing the gap: At least one dataset (N ≥ 100) showing a survival curve with median and 95% CI for medusa-only longevity, under clearly stated conditions and with reversal-censoring.

References

  1. Martell, L., Piraino, S., Boero, F., Gravili, C., & Kubota, S. (2016). Life cycle, morphology and medusa ontogenesis ofTurritopsis dohrnii. https://doi.org/10.1080/11250003.2016.1203034
  2. Piraino, S., Boero, F., Aeschbach, B., & Schmid, V. (1996). Reversing the life cycle: Medusae transforming into polyps and cell transdifferentiation inTurritopsis nutricula. https://doi.org/10.2307/1543022
  3. Pascual-Torner, M., et al. (2022). Comparative genomics of mortal and immortal cnidarians unveils novel keys behind rejuvenation. https://doi.org/10.1073/pnas.2118763119
  4. Matsumoto, Y., Piraino, S., & Miglietta, M. P. (2019). Transcriptome characterization of reverse development inTurritopsis dohrnii. https://doi.org/10.1534/g3.119.400487
  5. Juliana Giraldo-Meneses and Maria Pia Miglietta (2025). TestingTurritopsis dohrnii’s life-cycle reversal in response to multiple stressors. https://doi.org/10.71161/ivb.144.1.2024.00023
  6. Roosen-Runge, E. C. (1970). Life cycle of the hydromedusaPhialidium. https://doi.org/10.2307/1540137