Imagine a creature so perfectly crafted by evolution that it was around when the Tyrannosaurus rex walked the Earth and survived a mass extinction that wiped out 75% of all life, due to its immaculate "Frozen" genome. That is the Alligator.

Origin of Life

Deep Time &

History of Life

Prokaryotic Diversity & Origin of Eukaryotes

Evolutionary History of the Alligator

Mesozoic Era

Triassic ~245-201 MYA

The Archosaur split the Pseudosuchia (crocodile linage) divided from the Avemmetatarsalia (dinosuar/bird lineage).
Early ancestors were agile and often bipedal.

Jurassic ~201-145 MYA

crocodylomorphs evolve: ancestors become and adapt to be more semiaquatic, sprawing lifestyle, filling ecological niches living alongside massive dinosuars

Cretaceous ~145-66 MYA

Rise of Alligatoroidea: a subfamily including alligators splits from true crocodiles and gharials. Early ancestoral alligator like the Deinosuchus reached sizes up to 35 feet.

Cenozoic

Paleogene/Neogene ~22-2.6 MYA

A greater survivor, the alligators survive the K-PG extinction event. The genus Alligator emerges in Eurasia and North America.

Quaternary/Pleistocene ~2.6 MYA-Present

Alligator mississippiensis the modern alliagators came and stayed.

Multicelluarity

Vertebrate Diversity

Key Alligator Viruses that Co-evolved

Alligator Poxvirus: Double-stranded DNA virus

Regressive hypothesis: shows massive, gene heavy viruses still retain complex traits reminiscent of ancient parasitic cells

Endogenous Retroviruses: within their geneic code

Progressive hypothesis: trapped in the alligator geneome shows how viral genes and host gene swapped places over deep time.

West Nile Virus: deadly virus that hits Alligators farms hard

Virus-First hypothesis: the alligators super-immune system is a product of 80 Million years of both alligators and virus evolving side-by-side.

Genetics and Evolutionary processes

Variability

The Unique Frozen Genome

Alligators have the slowest rate of genetic molecular evolution among vertebrates and have ultra slow mutation rates.

Alligators have a highly stable genome with it containing highly localized variability.

Temperature-Dependent Sex Determination

TSD is a phenotypic variation. (Epigenetic is when the same DNA is read and expressed differently, which is an example Phenotypic plasticity.)

Alligators lack the normal sex chromosomes, instead it is determined epigenetically by the temperature of the egg during the embryonic thermosensitive period, which usually take place by stages 21-24 of development.

Female: 30°C

Male:33.5°C

Female: 34.5°C or higher

Human selection can be seen when ranchers incubate alligator eggs to regulate the sex for the desired outcome.

Natural Selection

As Alligators have seen two mass extinction events ( the end triassic and end-cretaceous extinction) their genetic outcome comes for superior survival in which natural selection had favored metabolic and phenotypic plasticity. Evolutionary pressures have made Alligators hold on to their ancestral traits.

Natural selection favored:

Metabolic Depressors: an efficient cardiovascular system which helps them dive for hours and lower metabolic rate when needed.
Brumation: alligators to able to survive water freezing over. They stick their snout above the ice to breathe and the rest of their bodies freeze over, kinda like a hibernation until the ice thaws.

The Survival of Temperature-Dependent Sex Determination with Climate changes throughout Time

The survival of Temperature-Dependent Sex Determination seems, against all odds, against natural selections with the dramatic climate shifts thourghout history. However, Alligator are still around because TSD is not a fixed mechanism. It was befectly paired with alligator for there cellaur biology, that include behavioral, ecological, and physiological buffer systems, that help maintain balanced sex ratio.

The FMF (Type 2) "safeguard" curve": Alligator possess a Female-Male-Female TSD curve, extreme cold or extreme heat makes females and intermediate temperature makes male. Because the temperature that makes male is sandwiched, any extreme macro-climate shift, naturally makes females, which can easily keep the species from collapsing.

Maternal Nest-Site Selection: As natural selection favored female alligators, they actively change their nesting behavior to the changes in climate. A mother acts like a buffer between the atmosphere and her embryos.

Examples:

Micro-Habitat Choice: If a decade is hotter than normal, natural selection favors females that bulid nest deeper inside dense, shaded swamp areas. If its cooler the build nest exposed on sunny marsh banks.

Material Engineering: Nest are made out of mud (cools) and vegetation (warms it). Heat isnt just provided ed by sun, its also provided by the heat of decompostion from rotting vegetation. The mother Alligator will alter the ration of mud to vegetation to change the temperature of the alligator.

Nesting phenology or timing: Alligator can change their nesting timeline depending on the weather, if needed to ensure the two week thermosensitive period of development is reached.

Thermal Gradient of a Nest: In a large, crude mound, naturally experiences internal temperature variation.

Lifespan and Overlapping Generations: Alligator usually live up t0 50-70 years in the wild, and dont reach sexual maturity until they are 10 to 15 years old. Their long lifespans act as a temporal buffer. If there were to have a skew ratio of hatchlings for 5 to 10 consecutive years, there is an overvall impact of zero to the population. Since the adults reproducing in the swamp remains unchanged until weather stabilize.

Ecological Cooperation and Ecosystem Engineering

Alligators evolutionary success is deeply woven with its role of a keystone species and an ecosystem engineer (species that change their habitat) in its ecosystem. While they participate in symbiotic relationship, they also change the landscape to help other species thrive.

The Alligator Hole are made by adult alligator using their tail and snouts to clear out mud and vegetation, during the dry season, creating deep pools.

These holes help maintain an aquatic habitat for fish, amphibians, invertebrates, and turtles in the dry season.
Wading birds prefer to nest above these alligator holes. Alligators act as bodygruads, counsuming what would be predator to the birds nest. while the bird will drop fish and chicks, feeding the alligator.

Human Co-Evolution and Mutualism

The relationship of Human and American Alligator has transition from turmoil to a form of symbiosis.

Human selection:

Population bottleneck: hunting in the 1950s and 60s, in an unregulated market for leather, caused for artificial selection pressure in favor to those living in the deep swamp.
Conservation: They went to being saved by being placed in the endangered species act in 1967.

Agricultural symbiosis

Humans are artificial selecting the alligators sex via farming and ranching programs
- Farmers harvest wild eggs, legally in public lands
- Due to harsh weather conditions some eggs don't make it, this way they artificial select sex through incubation making sure 90% of the batch of eggs survive and are legally bound to return a fixed percentage of health juvenile alligators to the wild.

Humans and Alligator have been benefiting from each other. The humans make sure the wetlands are protected, preserving its ecosystem. And Alligator help humans, by maintaining the wetland population in check as a keystone species. Both help keeping the ecotourism and conservation economy up.

References

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