Mutualistic Coevolution Continued...

As promised, the topic of mutualism in coevolution continues!! Yay!! This week is about the extraordinary lengths that plants go to ensure their flowers are pollinated.

Flowers produce a store of nectar (corolla) within them as a reward for pollinating organisms transferring their pollen from one flower to another. What happens when pollinating insects evolve their proboscis so that they can reach the nectar store within the flower without having to land?

To reduce the risk of being disadvantaged, flowers began to increase the depth at which they store their nectar; forcing the insects to get close enough to acquire pollen. This process is constant as the insects continually increase their proboscis length and the flowers continually deepening their corolla to accommodate (Anders Nilsson, 1988).

A prime example of this coevolution is seen in the photo below of a Morgan’s Sphinx moth extending its phenomenal proboscis into a Comet Orchid, which has an equally phenomenal corolla depth.

References:

http://news.discovery.com/earth/plants/top-10-evolutionary-tricks-for-pollinators-1310112.htm - date sourced 31/03/14

Anders Nilsson, L. 1988. The evolution of flowers with deep corolla tubes. Nature, 334, 147-149.

Mutualistic Coevolution

Mutualistic coevolution is something that I am going to focus on over the next couple of weeks. It is where species coevolve into a mutualistic symbiotic relationship.

I am choosing to discuss the mutualistic relationship between clownfish and anemones because although it is common knowledge that clownfish can live unharmed in an anemone, it is not common knowledge what the reason for this is.

Does the protection come from the mucous of the anemone itself? Or, does the clownfish alter its own mucous coating to allow it to occupy the anemone unharmed?

Brooks and Mariscal (1984) tested these questions by exposing a clownfish to a constructed surrogate anemone for a period of time before exposing to a real anemone, observing how long it takes for the clownfish to acclimate. They concluded, due to the rapid acclimation rate, that it was the clownfish altering its own mucous during acclimation to form protection from the anemone.

Different subspecies of clownfish along with different subspecies of anemones can show preference to each other, and each subspecies of clownfish can share its own mutualistic bond with its particular subspecies of anemone. For example, ocellaris clownfish will only occupy the magnifica anemone. The reason for this is unknown, possibly due to convenience of not having to alter its mucous to a new anemone.

 

References:

Photo: http://www.colormaniacs.com/blog/?m=201003 - date cited 26/03/2014

Brooks, W. R. & Mariscal, R. N. 1984. The acclimation of anemone fishes to sea anemones: Protection by changes in the fish’s mucous coat. Journal of Experimental Marine Biology and Ecology, 80(3), 277-285.

Types of Coevolution

This week, rather than focus on a specific coevolutionary interaction, I am going to go through the five different modes of coevolution that have been suggested by various scientists so far.

I know, I know... not quite as interesting as my previous blog! However, I think it’s necessary to chat about it so that we all know what types of species interactions are likely to occur in each particular mode.

The five different modes of coevolution are as follows: Gene-for-gene, Specific, Guild, Diversifying and Escape-and-radiation (Thompson, 1989).

Gene-for-gene coevolution is most likely seen in species interactions of plants and pathogens with the perception that each gene affecting resistance in the host population is matched by a specific gene affecting virulence in the parasite population.

Specific coevolution is most likely seen in all interactions with selection pressures that are reciprocal, however uncommon in competitive interactions. This type of coevolution has an assortment of possible outcomes; divergence, convergence and ‘evolutionary arms races’ being the main three.

Guild coevolution, or diffuse coevolution, is seen in all species interactions and is a helpful experimental tool for discerning how groups of species within communities link and change together; Showing that evolutionary interactions could be more extensive than a pair of species.

Diversifying coevolution is most likely seen in seed-parasitic pollinators & plants, hosts & symbionts that regulate movement of host gametes, and maternally inherited symbionts & hosts. In some cases this form of coevolution may result in reciprocal speciation.

Escape-and-radiation coevolution is most commonly seen in species interactions involving hosts and parasites and is a more explicit form of how guild coevolution could involve both speciation and adaptation.

As I mentioned earlier, not quite as interesting but hopefully informative :)

Reference:

Thompson, J. N. 1989. Concepts of coevolution. Trends in ecology & evolution, 4, 179-183.

Summary: Heiling and Herberstein (2004)

Hi fellow science lovers!

My weekly blog is going to be based on all things involving COEVOLUTION; A topic that never ceases to interest me with eye-opening discoveries.

For people who don’t know—coevolution is defined as “…the evolution of two or more interdependent species, each adapting to changes in the other…” – basically meaning that one species evolves and the other follows to ‘even up the playing field’ so to speak.

This week whilst researching I came across this little gem: Thomisus spectabilis (Australian crab spiders) evolved to mimic flower colour signals in order to lure pollinating insects. The really interesting part to this story is the Australian native bee (Austroplebia australis) has coevolved to avoid landing on flowers occupied by the predator! When offered the choice between two white daisies, one occupied by a crab spider; the native bees would land on the vacant flower more often, displaying an anti-predatory response to avoid the flower occupied by the predator (Heiling and Herberstein, 2004)

References:

Definition: http://www.thefreedictionary.com/_/dict.aspx?rd=1&word=coevolution

Journal Article: Heiling, A. & Herberstein, M. 2004. Predator–prey coevolution: Australian native bees avoid their spider predators. Proceedings of the Royal Society of London. Series B: Biological Sciences, 271, S196-S198.

Photo: http://mq.edu.au/newsroom/2013/12/17/australia-a-hot-spot-for-flora-and-fauna-deception/