Evolutionary Arms Race!

This week the topic of predator-prey coevolution is continued. The relationship that I will be talking about has resulted in an evolutionary arms race where the predator has developed incredible tolerance to its highly toxic prey!

The rough-skinned newt has over time concentrated an extremely potent neurotoxin within its skin; and through a series of genetic mutations and natural selection for increased resistance, the common garter snake has developed a resistance to the newts neurotoxin (Williams et al., 2003). The relationship is an evolutionary arms race because as the garter snakes’ resistance is continuing to increase, so is the levels of toxin that the rough-skinned newt can produce.

The studies show that the garter snake assesses the newt toxicity and its own resistance, rejecting newts that are too toxic to devour. The really interesting thing is that all of the newts that were rejected by the snakes survived attempted ingestion and attack, even if they had already been ingested for over 50 minutes!!

If the predator doesn’t survive the encounter with the toxic prey, natural selection for increased resistance cannot occur.

References:

Williams, B. L., Brodie Jr, E. D. & Brodie III, E. D. 2003. Coevolution of Deadly Toxins and Predator Resistance: Self-Assessment of Resistance by Garter Snakes Leads to Behavioral Rejection of Toxic Newt Prey. Herpetologica, 59(2), 155-163.

Credits for image located bottom right of image.

Predator-Prey Coevolution

Predator-prey coevolution is based on how a predatory organism may gain an advantage over its prey, which then triggers an evolutionary response from the prey to better avoid the predator; or vice versa.

My example of predator-prey coevolution this week is between broadheaded snakes and velvet geckos.

Broadheaded snakes are nocturnal and venomous, primarily feeding on nocturnal rock-dwelling velvet geckos. Geckos within the same geographical area of these snakes showed strong tendencies to avoid them by using chemosensory cues; detecting the specific scent of the broadheaded snake. It was found that if the snake’s scent was distributed all over the rock surface, the geckos were unlikely to enter the crevice. However, if the scent was only localised to a central part of the rock, the gecko would feel safe enough to enter the rock crevice as a retreat-site.

To attempt to hide its scent from the gecko, the broadheaded snake will hide in a rock crevice and remain sedentary for weeks so that it can minimise the spread of its scent over the rocks forming the crevice and therefore no longer being considered a threat by the gecko.

An interesting thing about this relationship is that it only occurs within sympatric populations. The geckos from sympatric populations could also detect the different scent of a small-eyed snake that does not eat geckos; however, in response to this chemical cue the geckos did not change its behaviour or its retreat-site choice. Additionally, geckos from allopatric populations did not show the same avoidance of the rock crevices containing a broadheaded snake, nor did they show any apparent detection of scent made by small-eyed snakes (Downes & Shine, 1998).

References:

Downes, S. & Shine, R. 1998. Sedentary snakes and gullible geckos: predator-prey coevolution in nocturnal rock-dwelling reptiles. Animal Behaviour, 55(5), 1373-1385.

Image 1: http://animal.memozee.com/view.php?tid=3&did=19871 sourced 7/4/14

Image 2: http://www.pittwater.nsw.gov.au/environment/animals_and_plants/native_fauna_management_plan/threatened_fauna_species_list/broad-headed_snake sourced 7/4/14

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/