The marbled crayfish reproduces asexually, with the all-female species making clones of itself. The species is thought to have come from the mating of two slough crayfish 25 years ago. The offspring were able to clone themselves because of a mutation that led to an entire additional set of chromosomes. 

Since their discovery in Germany, the crayfish have invaded and disturbed ecosystems all over Europe. The crayfish spread because people bought the species to have them in their aquariums and often released them when they suddenly had too many. The marbled crayfish doesn’t need to mate and reproduces six times as much as most sexually reproducing crayfish.

Because of their high reproductive rate and ability to force out native species

 the marbled crayfish were labeled as an invasive species

 and banned from the aquarium trade in Europe. Since their discovery, they have spread to other places around the globe including Japan, Romania, and Africa.

A population of asexually reproducing marbled crayfish arrived on the island of Madagascar in 2003 through the aquarium trade. Native crayfish in Madagascar reproduce sexually. People are worried that the marbled crayfish may drive out native crayfish populations and change ecosystems in Madagascar.

Would you expect the sexually-reproducing native crayfish or the asexually reproducing marbled crayfish to survive and reproduce in higher numbers? Give evidence and reasoning for your claim.

(you can use evidence from the introduction, the “why sex” video, or the pond fish activity)

The data was collected every 2 years in Madagascar in the same stream in Ambohimangakely from 2000 - 2018 (pictures in Section 1). The data shows the number of individuals of each species found in surveying expeditions each year. Researchers went into a 10m

area in the stream and collected data by physically counting number of individuals seen inside the area during 1 hour. 

Plot the data (on the last page of this lab report) as a line graph using equal intervals. 

Include a title, axis labels, units, and a key. (Look to your pond fish activity for an example)

What do you notice from looking at the graph? Explain.

Does the data for marbled crayfish and native crayfish match your hypothesis? Explain using specific evidence from your graph. 

Using what you know about asexual and sexual reproduction, how might you explain the data? Use specific evidence from your graph.

Fisheries are a large part of the economy in rural Madagascar. There is concern among fisherman that the rise in marbled crayfish is causing the decline of fish. Does the data in this study support that claim? Explain using specific evidence.

Another important part of the economy in Madagascar is rice production. Some farmers are worried that the rise in marbled crayfish will mean less rice plants. Does the data in this study support that claim? Explain using specific evidence.

What are some limitations of the study? What would you do differently if you took the data yourself? Explain. (use the information provided in Section 2)

In Europe, the marbled crayfish was banned from the aquarium trade because it threatened the survival of native species and changed ecosystems. Do you think a similar ban should be enforced in Madagascar? Support your claim using specific evidence.

Genetic variation may result from new genetic combinations through meiosis and / or viable errors occurring during reproduction. 

Marbled Crayfish Takeover