Biological Diversity:

Biological diversity always amazes me. From the sheer numbers of species we find around us, to just how incredibly complex these can be--from a life history perspective and from a morphological perspective. I have learned a lot this year about marine creatures and their life histories, from whale barnacles (e.g. gray whale barnacle, a species of barnacle that lives only on gray whales) to Pacific Giant Octopus (which can sometimes be found tucked under boulders during low tide). Then there is the lion's mane jellyfish, which can die off in the thousands in the fall and cover our beaches. One that I recently learned about is the great morphological variation present in juvenile red crabs (Cancer productus). During a recent trip to the Vancouver Aquarium, I noticed this poster illustration of the array of colour types present in juveniles. Adults are usually brick red in colour, but look at just how variable the juveniles are.

Researchers think colour variation in these juveniles is a way to escape detection by predators, thus increasing survival rates. Researchers Nehring et al. (2010) say: "Most probably, the large variety of different juvenile morphs is a result of frequency-dependent selection in which abundant variants are attacked disproportionately often and rarer forms are favoured. Juvenile colour polymorphism in C. productus may reduce the vulnerability to visual predators, impede the formation of a search image, and consequently decrease the risk of predation during the juvenile stages." Search image is something predators use to find their prey, and it's not a lot different than the search image photographers use to spot species in a tidal pool or botanists use to find one tiny plant species in the midst of a big green(ish) tangle or visually diverse landscape. It's all about pattern recognition. That is much more of a challenge if the object of your search varies dramatically from one individual to the next.

Reference:

Krause-Nehring J., Matthias Starck J, Palmer A.R. 2010. Juvenile colour polymorphism in the red rock crab, Cancer productus: patterns, causes, and possible adaptive significance. Zoology (Jena). 2010 May;113(3):131-9.