LSM 3261 Assignment - Blog Action Day Surprise!

15 October is Blog Action Day and everyone is encouraged to blog about the environment on this day. So our dear environmental-friendly lecturer, with the intention of training us for the 'ability to write concisely, with sufficient enthusiasm, absorb information and deliver it with accuracy, to be able to avoid unsubstantiated speculation and craft a logical storyline'

He decided to award us 5% of our module marks for writing a reflection as if we are submitting a piece for inclusion to a science blog portal and hope to increase awareness about the research, methods or other elements he expounded on during his talk. Hence, I decided to post up my "submission" here as well, for the fun of it. ....

European shore crab (Carcinus maenas). Peter Barfield /Sea-nature Studies (published on the MarLIN Web site)

Natural selection comprises of two components, ecological selection and sexual selection. Though essential, they tend to contradict each other in terms of how the mechanisms function. As camouflage is associated to the aspect of ecological selection while communication is associated to sexual selection, it is thus inevitable that camouflaging and communication colorations of crabs in Rocky Shore and Mangrove will contradict. Therefore, how does these conflicting colorations of the life forms mentioned by today’s guest lecturer, Dr Peter Todd, function for their respective survivability and reproduction?

To understand this better, we shall explore them separately first before concluding the functions of both different types of colorations to exist in the environment.

First, the camouflaging ability of crabs makes them harder to be spotted by their natural predator, thus increasing their survivability. During the lecture, the European shore crab (Carcinus maenas) was mentioned as an example to illustrate such mechanism. Crabs found in three different locations have different color patterns. Coincidently, the three places have different percentage of constituents, thus indicating a possibility of different visual backdrop. This may suggest that the crabs have evolved their colorations to prevent predation. Hence, study was done where human volunteers were asked to spot the crab shapes with color patterns over a stimulated background. Results showed that there was a correlation between the color patterns and the ease of spotting them. Thus, indicating that their color patterns serve as camouflage from predation, giving the camouflage crabs greater advantage in ecological selection, allowing them to pass on their genes to the next generations, thus ensuring the survival of their species.

In conflict to the camouflaging coloration of European shore crab, two local species of mangrove crab (Perisesarma eumolpe and Perisesarma indiarum) have bright colorations which make them easily spotted by predators. However, these colorations are important for intra species communications to attract the opposing sexes for reproduction. Experiments in the laboratory have shown that the females of such crabs have preference mates with such colorations. Thus, showing that these communication colorations function to increase their lifetime reproductive success by improving their ability to attract mates and fertilize them (Stephen C. Stearns, Rolf F. Hoekstra. 2005), which offset the tradeoff of being easily spotted for predation. Hence, enabling the species to continue their existence through the sexual selection mechanism.

Therefore in conclusion, despite the differences in the types of colorations on crabs, whether to camouflage or to communicate, they still function to ensure the continual existence of their species through various different beneficial mechanisms as illustrated by Dr Peter Todd. However, research is still on-going for the final conclusion of these mechanisms on the particular species of crabs studied.

Reference:

Stephen C. Stearns, Rolf F. Hoekstra. 2005. Evolution, an Introduction, 2nd edition. Oxford University Press. 249.