Phylogenetic tree by Josh Gong

Common Ancestor(Photorhachis chromatica)

gongj2 — 2025-02-25 19:20:04 UTC

marine reptile
possess photosynthetic spines
lives in reefs
can change color

mating ritual
fed on by sharks

Choral bleaching

gongj2 — 2025-02-25 19:21:16 UTC

Choral bleaching causes a part of the reef to turn white, causing one part of the population to sympatrically speciate. Due to selective pressures, a portion of the population adapts to change 'white' instead. This effects sexual selection as colorful females prefer colorful males and vice versa, introducing a barrier to reproduction.

1: White (Photorhachis albavita)

gongj2 — 2025-02-25 19:25:32 UTC

2: colorful (Photorhachis chromatica)

gongj2 — 2025-02-25 19:25:46 UTC

Disruptive Selection

yuey57185 — 2025-02-25 19:30:00 UTC

The partially bleached choral favours individuals at the two extremes: completely white or very colorful.

Less predation

gongj2 — 2025-02-25 19:33:17 UTC

predators don't like the white choral as it is less attractive and have less prey. This reduced predation causes their population to dramatically increase, to a point where their current habitat can no longer support them.

migrating to deeper waters

gongj2 — 2025-02-25 19:36:38 UTC

deeper waters have minimal access to sunlight but more oxygen. This selective pressure causes them to lose their photosynthetic ability and develop a carnivorous diet, eating whatever fish is available.

3: white carnivor (Abyssal Fang Lizard)

gongj2 — 2025-02-25 19:37:20 UTC

Because their camouflage ability is no longer useful, their mating ritual has changed to offering food. This shows how sexual selection is often synonymous to natural selection.

drought (bottleneck)

gongj2 — 2025-02-25 19:39:01 UTC

A drought kills a majority of the population due to the depletion of water level as they live in the shallow water area. The few that are left happen to have extra long fins. As the remaining population begins to grow, the allele for having long fins remains at a high frequency, causing most individuals to have long fins.

4: land (Photorhachis terrasol)

gongj2 — 2025-02-25 19:42:20 UTC

over time, as resources in the choral reef diminish, they begin to crawl onto land in search of food.

5: swamp (Photorhachis amphibicolor palustris)

gongj2 — 2025-02-25 19:44:00 UTC

2n = 8

6: forest (Photorhachis amphibicolor sylvaticus)

gongj2 — 2025-02-25 19:44:53 UTC

2n = 6

7: desert (Photorhachis amphibicolor aridus)

gongj2 — 2025-02-25 19:45:03 UTC

8: swamp-forest hybrid (Photorhachis amphibicolor nemoropalustris)

gongj2 — 2025-02-25 19:46:08 UTC

the resulting hybrid is a viable polyploid, with 2n = 14. A polyploid is an individuals with more than 2 complete sets of chromosomes. They are reproductively isolated from swamp and forest but can reproduce with other polyploids.

9: crustacean eating (Abyssorhachis crustavorax)

gongj2 — 2025-02-25 19:48:46 UTC

Crustaceans like crabs and lobsters are shell-fortified. Therefore, our creature have developed sharp teeth to prey on them effectively.

10: swordfish eating (Abyssorhachis xiphicida)

gongj2 — 2025-02-25 19:49:23 UTC

Swordfishes are fast swimmers. In order to hunt them effectively, our creatures' previously photosynthetic spines have turned into fins that allow them to swim faster.

11: sand crab eating (Arenarhachis carcinovorax)

gongj2 — 2025-02-25 19:51:04 UTC

They begin to feed on sand crab, which only becomes active at night.

12: cactus eating (Photorhachis amphibicolor cactovorax)

gongj2 — 2025-02-25 19:51:26 UTC

As water is scarce, they begin eating cactus.

temporal isolation

gongj2 — 2025-02-25 19:52:19 UTC

Sand crabs are nocturnal. This means the two groups will be active at different times of day. The resulting temporal isolation creates two distinct species sympatrically.

mutation

gongj2 — 2025-02-25 19:57:33 UTC

A mutation arises that causes individuals to not have the ability to do photosynthesis

Convergence Evolution

yuey57185 — 2025-02-26 19:00:15 UTC

Both sand crab eating and crustacean eating species feed on shell fortified creatures. This led to both species have evolving convergently and developing similar teeth despite not sharing a common ancestor.

Adaptive radiation

gongj2 — 2025-02-26 19:07:15 UTC

on land, there are many more niches for them to fill. Therefore, they quickly diverge into three distinct species living in different habitats.

Gene flow

gongj2 — 2025-02-26 19:12:47 UTC

During the winter, the large lake in between the swamp and forest freeze, allowing individuals from the two populations to reproduce.

gongj2 — 2025-02-26 19:38:41 UTC

Mating ritual evolves as well; those that feed on swordfish use swordfish as offering. This is a barrier to reproduction, contributing to sympatric speciation.

Analogous vs. Homologous Structures

gongj2 — 2025-02-27 16:40:13 UTC

Fossil evidence shows similarities between the spine of Abyssorhachis xiphicida and the photosynthetic spine of the photorhachis species: they are homologous structures as they have different functions but share evolutionary origins. The similar teeth mentioned prior are analogous structures as they hare the same function but differ in evolutionary origin.