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