Like many jelly species, members of the group Hydra have a polyp stage that reproduces asexually by budding off little clones, and people have speculated this could last for thousands of years. So Daniel E. Martínez closely watched members of one species, Hydra vulgaris, for 4 years, and in that time very few animals died [3]. Dr. Martínez suggests that since animals that start reproducing only a few days after birth, such as Hydra, tend to kick the bucket earlier than animals that wait, 4 years is a pretty long time. But does that really mean they’re immortal?

More information is needed about Hydra, but it’s not the only species people keep for decades, nor the only species that could help us understand if some jellies may last forever. So, to get to the bottom of this I polled the experts.  I sent emails to some of the top jelly aquarists asking: do polyp clone populations change over time?

Most public aquaria display jellyfish, and to do this they take advantage of the peculiar jelly life cycle.  The life of jellies is broken into two parts: the polyp-type stage, which looks like Hydra and divides asexually, and the jelly stage, which grows from polyps and gets on with the busy act of sexual reproduction. To keep the number of exhibit jellies constant, aquarists use polyps as a literal clone bank, cueing them to produce more jellies as needed.

And do these clone banks ever change or grow old? The answer was a unanimous “yeah, kinda.” According to aquarists at both the Monterey Bay Aquarium and the New England Aquarium, over about six years clonal populations do get “tired.” They become more fragile, don’t produce healthy jellies, and stop responding to environmental signals. Many aquarists replace their polyp stocks with new baby polyps quite regularly, so that none of this fickleness gets in the way of jelly production. The whole colony may continue to kick, but it gets more and more fragile over time. To me, this sounds a lot like aging.

When humans die it’s not because a special gene turns on that shouts: “YOUR TIME IS UP!” Rather, little things start breaking all over, cells stop dividing and those that do accumulate mutations, this is why getting older is often accompanied by all sorts of biological issues. The truth is, accumulating mutations and cell gunk isn’t something special about aging people, even clone lines of E. coli bacteria accumulate harmful cellular products over time [4]. This is just the cost of being alive. So does the “immortal jellyfish” Turritopsis dohrnii really last forever, even with all this gunk slowly working its way into its cells and genomes?

I’m not convinced. Just because you can reverse your life cycle or clone yourself doesn’t mean you’ve got a get out of jail free card for all the consequences that come with being a living thing in the first place. You are still subject to that nasty gunk build up.  Some species like Hydra vulvaris may have evolved ways to clean this gunk and beat the system, but the jury is still out on how, and for how long. While the “immortal” jellyfish Turritopsis dohrnii may be able to turn back its life cycle, it may not escape the inevitable slowing down that comes with age. In other words, while reversing your fate and escaping death for a short while may be a neat trick, it doesn’t guarantee immortality.

Work Cited

[1] Stefano Piraino, Ferdinando Boero, Brigitte Aeschbach and Volker Schmid (1996). Reversing the Life Cycle: Medusae Transforming into Polyps and Cell Transdifferentiation in Turritopsis nutricula (Cnidaria, Hydrozoa). Biological Bulletin , Vol. 190, No. 3 (Jun., 1996), pp. 302-312

[2] Stefano Piraino, Ferdinando Boero, Brigitte Aeschbach and Volker Schmid (1996). Reversing the Life Cycle: Medusae Transforming into Polyps and Cell Transdifferentiation in Turritopsis nutricula (Cnidaria, Hydrozoa). Biological Bulletin vol. 190, no. 3  pp 302-312

[3] Martínez DE (1998). Mortality patterns suggest lack of senescence in hydra. Exp Gerontol. vol 33 no 3 pp 217-25.

[4] Ariel B. Lindner, Richard Madden, Alice Demarez, Eric J. Stewart and François Taddei (2008). Asymmetric segregation of protein aggregates is associated with cellular aging and rejuvenation. PNAS vol. 105 no. 8 pp 3076-3081 doi: 10.1073/pnas.0708931105

The post Are Jellyfish Immortal? first appeared on Deep Sea News.

The post TGIF: Portuguese Man-O-War Feeding first appeared on Deep Sea News.

Intonjutsu: Cheating Death

In true ninja fashion the marine hydroid Turritopsis dohrnii disappears when the going gets tough. Instead of dying with honor, they “de-differentiate” into a cyst, settle to the seafloor and reform into a benthic polyp (see figure above). The polyps then asexually bud off medusae, the jelly stage of the life cycle, thus granting this inconspicuous hydroid virtual immortality. The implications for this process, called transdifferentiation, are enormous. If T. dohrnii can withstand extreme conditions, transdifferentiation allows for unlimited travel throughout the ocean via ship’s hulls and ballast, currents or hitching a ride of some marine debris.

Hensõjutsu: Phenotypic Plasticity, The Art of Concealment

A ninja hydroid has but one weakness – its genetic code. Miglietta and Lessios used the power of the mitochondrial 16S genetic marker to disarm the stealthy intruder. Surprisingly, little genetic structure was found among the unidentified samples from as far apart as Italy, Mallorca, Japan, Panama and Florida. Less than one half of a percent genetic difference was detected, concealed in a clade with Turritopsis dohrnii.

Turritopsis dohrnii from most of the world has between 12 and 24 tentacles (see above). But after measuring over 250 adults, Miglietta and Lessios found that the renegade hydrozoans living in tropical Panama always have exactly 8 tentacles (see right). The authors suggest that tropical T. dohrnii may retain a juvenile state in a process called heterochrony, defined by Stephen J. Gould as a “change in the timing of gonad development versus somatic development”. Despite this one morphological difference, the panama specimens are still genetically identical to all other T. dohrnii.

Shinobi-iri: Stealth Through Ballast

The high degree of genetic similarity suggests rapid transport throughout the marine realm between the Mediterranean and Japan, through the Panama Canal. The planktonic medusa phase of hydrozoans could explain the wide dispersal range. But with 15 identical sequences from geographically widespread localities, life history traits do not explain this extreme similarity. Miglietta and Lessios suggest that medusae may sneak into a ship’s ballast water where they can de-differentiate back into a polyp, settling on the bottom of the ballast tank. Hitchhiking along the shipping route, they asexually bud off more medusae which settle into new territory. So take heed of their warning: a true ninja species finds a way and will rapidly evolve to new situations.

See also:
Science News: Nearly Immortal Sea Creature Spreads
How to Be a Ninja
—————————————————————————
Miglietta, M.P., Lessios, H.A. (2008). A silent invasion. Biological Invasions DOI: 10.1007/s10530-008-9296-0

The post Hydromedusa Mounts Ninja Style Invasion first appeared on Deep Sea News.