After a neat video on Tardigrades, we discuss them

Check this video by Neil DeGrasse Tyson on these cute little buggers

https://www.youtube.com/shorts/qcje-Y63PpU?feature=share

Conversation with Perplexity

Tell me about the DNA and genetic relationships with tardigrades.

 Tardigrades have several interesting genetic and DNA-related characteristics:

 Genome Size and Structure

Tardigrade genomes vary considerably in size, ranging from about 75 to 800 megabase pairs of DNA. For example, Hypsibius exemplaris (formerly Hypsibius dujardini) has a compact genome of about 100 megabase pairs. This is relatively small compared to many other animals.

 Evolutionary Relationships

Although tardigrades superficially resemble arthropods like insects and spiders, genetic evidence suggests they are more closely related to nematodes (roundworms). Molecular analyses have confirmed tardigrades as a sister group to arthropods.

 Unique Genes

Tardigrades possess several unique gene families associated with their extreme tolerance abilities:

1. Cytosolic, mitochondrial, and secretory abundant heat soluble proteins (CAHS, MAHS, and SAHS)
2. Damage suppressor protein (Dsup), which helps protect DNA from radiation and oxidative stress
3. Tardigrade-specific proteins (TDPs) involved in desiccation tolerance

 

Gene Expansion

Some stress-related gene families have expanded in tardigrades, including:

1. Superoxide dismutases (SODs) - 16 found in some tardigrades compared to less than 10 in most animals
2. Meiotic recombination 11 (MRE11) genes

Horizontal Gene Transfer

There was initially controversy over the extent of horizontal gene transfer (HGT) in tardigrades. An early study suggested up to one-sixth of tardigrade genes came from HGT, but later research found much lower levels (1-2%) more consistent with other animals.

 DNA Protection Mechanisms

Tardigrades have evolved mechanisms to protect their DNA during extreme stress:

1. The Dsup protein can bind to DNA and help prevent damage from radiation and oxidative stress
2. They can efficiently repair DNA damage upon rehydration after desiccation

Evolutionary History

Molecular clock estimates suggest crown-group tardigrades diversified in the early Paleozoic era, around the late Cambrian period. The split between the two main tardigrade groups (Eutardigrada and Heterotardigrada) is estimated to have occurred around the middle Cambrian, about 499 million years ago. In summary, tardigrades have compact genomes with several unique genes and expanded gene families related to stress tolerance. Their genetic makeup confirms their position as close relatives of arthropods and nematodes, with a long evolutionary history dating back to the Cambrian period.

The fact that they can survive naked in the vacuum of space leads me to wonder -- maybe tardigrades didn't evolve 500 million years ago. Maybe they rained down from space as the earth cooled down enough for liquid water about 4 billion years ago. Maybe they evolved ONCE in this universe, and have spread throughout the cosmos, driven by solar winds and quasar jets. Maybe they took root on many planets in many galaxies, and are the ancestors of all terrestrial and extraterrestrial life -- all with spiral helix DNA constructed of the same atoms and molecules like ours. Many others must have thought of this. Please comment.

 

While the idea of tardigrades as cosmic travelers is intriguing, current scientific evidence does not support the hypothesis that tardigrades originated in space or are the ancestors of all terrestrial life. Here are some key points to consider:

1. Evolutionary history: Molecular clock analyses suggest that tardigrades diverged from other panarthropods during the Cambrian period, around 540-500 million years ago. This places their origin firmly on Earth, long after the planet had cooled and life had already evolved.
2. Genetic relationships: Tardigrades are part of the superphylum Ecdysozoa, which includes arthropods and nematodes. Their genetic makeup and evolutionary relationships tie them closely to other terrestrial life forms.
3. Adaptations to Earth environments: Many of tardigrades' extreme survival abilities are adaptations to terrestrial environments on Earth, such as desiccation tolerance for surviving in mosses and lichens.
4. Limits of space survival: While tardigrades can survive short-term exposure to space conditions, they cannot actively live and reproduce in space without protectionpair mechanisms: Tardigrades have evolved specific DNA repair mechanisms and protective proteins (like Dsup) that allow them to withstand radiation and other stressors. These mechanisms are adaptations to Earth conditions, not necessarily cosmic travel.
5. Fossil record: Although sparse, the tardigrade fossil record, including specimens found in Cretaceous amber, supports their terrestrial evolution.
6. Independent terrestrialization: Research suggests that eutardigrades and heterotardigrades independently adapted to land environments, further supporting their Earth-based evolution

While tardigrades' extreme resilience is remarkable, it's more likely a result of terrestrial evolutionary processes rather than extraterrestrial origin. The idea of panspermia (life spreading through the cosmos) remains a hypothesis, but there's currently no strong evidence supporting tardigrades as the origin of all life.

 

 

How high is the chance, that the Mars Rover was contaminated with Tardigrades when we send it to Mars? So practically there is now life on Mars, because Tardigrades can survive in space.

 

While the idea of tardigrades contaminating Mars is intriguing, the actual likelihood of this scenario is extremely low for several reasons:

1.     Rigorous decontamination: NASA and other space agencies employ extremely thorough cleaning and sterilization procedures for all spacecraft components destined for Mars. The Mars 2020 mission (which includes the Perseverance rover) underwent extensive biological cleanliness protocols.

2.     Planetary protection measures: Strict planetary protection policies are in place to prevent contamination of Mars with Earth organisms. This includes trajectory biasing to ensure even the launch vehicle has a very low chance of impacting Mars

3.     Harsh conditions: Even if tardigrades somehow made it to Mars, the planet's surface conditions are extremely hostile. While tardigrades can survive brief exposure to space, long-term survival on Mars is unlikely due to intense radiation, extreme temperature fluctuations, and lack of liquid water.

4.     Limited survivability: Studies show that even highly resistant organisms like Deinococcus radiodurans would only potentially survive for long periods if buried deep below the Martian surface. Tardigrades on a rover's surface would be fully exposed.

5.     No active metabolism: Tardigrades enter a dormant state to survive extreme conditions. They cannot actively grow or reproduce in this state, limiting their potential impact.

6.     Ongoing monitoring: Spacecraft are carefully monitored for biological contamination before and after launch. Any significant contamination would likely be detected.

While tardigrades are remarkably resilient, it's important to note that their ability to survive brief exposure to space conditions does not equate to thriving on Mars long-term. The planetary protection measures in place are designed to prevent even the hardiest Earth organisms from contaminating Mars. In conclusion, while not impossible, the chance of viable tardigrades contaminating Mars via a rover is extremely low due to the multiple, stringent safeguards in place and the harsh Martian environment.