Ms. DeSimoni’s evolution of species Journal Journal #1 Biogeoraphy




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Ms. DeSimoni’s evolution of species Journal
Journal #1 Biogeoraphy:
Broadclub cuttlefishes, Sepia latimanus

They are large fascinating cephalopods with oval mantles and crescent-shaped clubs . This species can reach up to 50 cm in mantle length and weigh up to 10 kg. Like many cephalopods, broadclub cuttlefishes can be seen displaying a range of colors and textures. Commonly they are light brown or yellowish with white mottled markings. Males are sometimes dark brown, particularly during courtship and mating. Their arms have longitudinal white bands that appear as broad white blotches when extended. Some of their arms have longitudinal brown bands that extend to their heads. Their dorsal (upper) mantle can sometimes be seen with a saddle mark with small white and brown spots. Their dorsal mantle also has narrow brown transverse bands, and bold, white, transverse stripes and spots. Their eyes are yellow around the ventral (lower) margins and their fins are pale with white, transverse stripes extending onto their mantle and narrow, white bands along their outer margins.


The broadclub has a variety of different sucker sizes, some that are significantly larger than others. Their cuttlebone is bluntly rounded on either end, with a convex dorsal (curved upper) surface that flattens at the anterior (front) end. Their dorsal mantle is also covered with numerous large papillae and elongate papillae along the sides adjacent to base of each fin.
Sepia latimanus mates in shallow water between January and May. Their eggs hatch in 38 to 40 days. During the breeding season, males establish a territory, defending a coral head where females lay eggs after mating. Courtship is highly ritualized and involves striking visual displays. Males often guard females to ward off other males. This species mates head-to-head and the male places spermatophores on the female's buccal membrane near her mouth. The eggs harden after they are laid, which makes them difficult for predators to extract from the coral. When they hatch, juveniles hide among the coral and coral rubble, and often mimic mangrove leaves.
They are found all over in Indonesia south to northwestern and northeastern Australia and across northern Australian waters to southern Great Barrier Reef. I will focus on a population in the Great Barrier Reef. Broadclub cuttlefishes, Sepia latimanus, hunt during the day and appears to mesmerize prey with its rhythmic colored bands. They feed on small fishes and crustaceans.
Journal #2 Natural Selection:
Variation currently present:

  • Sucker size

  • Body size

  • Coloration

Important facts



  • Hunt during the day

  • Live in coral reefs

  • Feed on small fish and crustaceans

Changes possible due to natural selection



  • change in color due to coral reef degradation- Reef bleaching and dying off of corals are changing the color landscape. Could cause the change in coloration over time to adapt to the more muted landscape. Muted colors increase over time and elaborate coloration minimizes




  • Change in food sources due to over fishing outside Sydney. If prey are changing how might that lead to changes in morphology? Change in tentacles or club to reaching into spaces in the reef where fish hide is possible




  • Changes in food, geographic location or hunting times due to increased competition for food?: For the last two decades, Indo-Pacific reefs have shrunk by 1 percent each year—a loss equivalent to nearly 600 square miles (1,553 square kilometers). That makes the rate of reef loss about twice the rate of tropical rain forest loss. How would this affect the species?

Journal #3 Sexual Selection:


Sepia latimanus mates in shallow water between January and May. Their eggs hatch in 38 to 40 days. During the breeding season, males establish a territory, defending a coral head where females lay eggs after mating. Courtship is highly ritualized and involves striking visual displays. Males often guard females to ward off other males. This species mates head-to-head and the male places spermatophores on the female's buccal membrane near her mouth. The eggs harden after they are laid, which makes them difficult for predators to extract from the coral. When they hatch, juveniles hide among the coral and coral rubble, and often mimic mangrove leaves.
There is sexual dimorphism males display elaborate mating displays to win females and to scare off or deter other males. Males are generally smaller than females.
See a divergent selection: in areas where reefs are still intact and competition is lower less elaborate males. In areas where populations are stressed due to reef degradation male coloration and rituals will become more elaborate to promote their fitness. Competition between males can lead to changes in size of body and club size to compete and establish territory
Journal #4 Genetic Drift:
Multiple possibilities: Founder effect small populations move due to changes in ocean temperatures or acidity, or habitat destruction
Bottleneck due to loss of variety from natural disasters like tsunami, loss in population from overfishing or loss of habitat.
Since it is random I would have to decide which traits might be lost due to these mechanisms.
Fossil Record
The fossil record of most cephalopods in the clade Coloidea (squid, cuttlefish, octopuses, and their relatives) is poor, especially when compared to their shelled relatives. Their hard parts, if any, are internal, can be greatly reduced in size, and often lack calcification. The extinct belemnites, however, are the exception. These squid-like animals swam with ammonoids and nautiloids in oceans of the Triassic,Jurassic, and Cretaceous Periods and are considered by paleontologists to be the ancestors of the Coleoidea. Like orthocones, belemnites had a straight shell, but it was internal, not external. It was made of three parts, a proostracum and phragmocone followed by a rostrum. Being highly resistant, the posterior bullet-shaped rostrum is most often preserved and can be found in great quantity and concentration inMesozoic marine sediments. Before these bullet-shaped fossils were understood as fossils, early Europeans explained them as the products of lightning hitting the ground and named them "thunderbolts" or "thunderstones."

My Evolution paper


In this paper I will focus on the evolution of the Broadclub cuttlefishes, Sepia latimanus, which lives in the waters to southern Great Barrier Reef. It is classified as Animalia (Kingdom) > Mollusca (Phylum) > Cephalopoda (Class) > Coleoidea (Subclass) > Decapodiformes (Infraclass) > Sepiida (Order) > Sepiidae (Family) > Sepia (Genus) > latimanus (species) They are large fascinating cephalopods with oval mantles and crescent-shaped clubs . This species can reach up to 50 cm in mantle length and weigh up to 10 kg. Commonly they are light brown or yellowish with white mottled markings. Males are sometimes dark brown, particularly during courtship and mating. Their arms have longitudinal white bands that appear as broad white blotches when extended. Some of their arms have longitudinal brown bands that extend to their heads. Their dorsal (upper) mantle can sometimes be seen with a saddle mark with small white and brown spots. Their dorsal mantle also has narrow brown transverse bands, and bold, white, transverse stripes and spots. Their eyes are yellow around the ventral (lower) margins and their fins are pale with white, transverse stripes extending onto their mantle and narrow, white bands along their outer margins.
The broadclub has a variety of different sucker sizes, some that are significantly larger than others. Their cuttlebone is bluntly rounded on either end, with a convex dorsal (curved upper) surface that flattens at the anterior (front) end. During the breeding season, males establish a territory, defending a coral head where females lay eggs after mating. Courtship is highly ritualized and involves striking visual displays. Males often guard females to ward off other males. This species mates head-to-head and the male places spermatophores on the female's buccal membrane near her mouth. The eggs harden after they are laid, which makes them difficult for predators to extract from the coral. When they hatch, juveniles hide among the coral and coral rubble, and often mimic mangrove leaves.
The environment in which the cuttle fish live 50 million years from now is very different from current conditions along the Great Barrier Reef. Over fishing and climate changes have caused the extinction of hundreds of pacific species. Reefs which are very fragile and cannot tolerate changes in pH or increased temperature have begun to die off due to pollution and climate change. Many of the larger open water animals (sharks, seals, whales) which were dependent on the schools of fish that lived in the reef have seen a large decrease in population size and some have migrated to other coastal areas where fish populations are still large enough to support these predators.
Natural Selection and mutation

Due to the degradation of their environment the cuttlefish has undergone many evolutionary changes. Cuttlefish are known for their ability to change color due to chromatophores in their skin. This is an advantage for the cuttlefish to avoid predation by being able to blend into the colorful background of the coral reef. Over time as the coral begins to die all that is left behind are the white skeletons of the coral. The landscape of the reef will become much less colorful. Cuttlefish with more muted colors to blend in with the ocean floor and rocky terrain will be selected for over brightly colored fish. The more plain looking cuttlefish will be able to blend into the background more effectively and survive to reproduce. This will cause a shift over time toward a population of plain colored cuttlefish.


Overfishing causes many of the fish species living in the reef to migrate or go extinct. This forces the cuttlefish to change its diet from primarily fish to organisms that live in the reef or on the seafloor such as eels, clams, crab, shrimp, and other mollusks. Cuttlefish with longer clubs and stronger beaks will be able to reach these organisms that are hiding within the reef and crush the shells of bivalves. Over time this benefit will cause a shift in the population to longer slender cuttlefish with longer clubs. The thinner longer cuttlefish are also selected for because they can avoid being caught in fishing nets. Some cuttlefish develop mutation that causes their chromatophores to produce toxic mucus allowing them to poison any predator that tries to eat them. This is a large advantage for the cuttlefish since they are the prey of many marine species. Over time this trait will increase in the population.
Genetic Drift

There are sections of the reef have been so degraded that no animals can survive there any longer. This has created a geographic barrier between sections of the population. Some of the population that is slightly larger and contain the toxic skin cells begin to hunt for food out in the open ocean. This small population continues to breed among themselves and only females return to the coast to lay their eggs. The open ocean population becomes larger overtime because the larger cuttlefish are faster and better at catching prey. The population of cuttlefish that remain along the coastal reef migrate to find better sources of food and shelter. These smaller muted cuttlefish begin to change over time as well. The flatter cuttlefish begin to camouflage along the ocean floor helping them sneak up on prey and avoid predators. This causes the population to become flatter and wider over time instead of long and narrow. The long and narrow coastal cuttlefish continue to hunt within the reef.


Sexual selection

Males use wildly colored displays to impress the females and for communication to other males during courtship. The males use their changing colors to stake claim on territory and to warn other males that they are willing to fight over a female. The selection of mates based on coloration will decrease as the overall coloration of the species changes over time in response to the environmental degradation. Instead females show preference based on arm length and this causes a sexual dimorphism between the males and females based on arm length instead of color.


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