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1990 A predator-prey arms race
CHAPTER FIFTY SIX
1990 A predator-prey arms race The concept Anti-predator defenses of the newt Taricha granulosa are countered by a garter snake that feeds on them. These predator responses appear to be proportional to the level of defense mounted by the newt, consistent with an evolutionary arms race.
The explanation The skin of the newt Taricha granulosa contains the neurotoxin tetrodotoxin (TTX) which is highly toxic to most animals. The garter snake Thamnophis sirtalis specializes on amphibians and will eat T. granulosa where the two species are sympatric. This suggests that the garter snakes had evolved some tolerance for this toxin. Brodie and Brodie (1990) attempted to study the geographic patterns of TTX resistance. Brodie and Brodie (1990) developed an assay for TTX tolerance that involves injecting snakes with know amounts of TTX and then measuring the snakes sprint speed. They tested two populations of T. sirtalis: one from Oregon that was sympatric with toxic newts and a population in Idaho where newts are not found. In addition, Brodie and Brodie tested a related species of snake, T. ordinoides from the same Oregon location, which is not known to feed on toxic newts. Brodie and Brodie found that allopatric populations of T. sirtalis and the congeneric species T. ordinoides showed similar levels of sensitivity to TTX. However, the sympatric populations of T. sirtalis showed substantially elevated resistance to TTX. Brodie and Brodie (1990) conclude that “These facts suggest that TTX resistance is not a property of the genus Thamnophis or even of the species T. sirtalis at large, but rather has arisen only in populations of T. sirtalis that feed on T. granulosa”. In a later study Brodie and Brodie (1991) found a population of T. sirtalis on Vancouver Island, British Columbia, with TTX resistance between the previously studied Oregon population of T. sirtalis and T. ordinoides. Such an observation seems to contradict the coevolutionary nature of this TTX resistance. However, a closer examination of Vancouver population of Conceptual Breakthroughs in Evolutionary Ecology ISBN: 978-0-12-816013-8 https://doi.org/10.1016/B978-0-12-816013-8.00056-9
© 2020 Elsevier Inc. All rights reserved.
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Conceptual Breakthroughs in Evolutionary Ecology
newts showed that the toxicity of their skin was at least 1000 times less than the toxicity of the previously studied Oregon population of newts. These observations suggest that the garter snakes evolve a level of tolerance needed to tolerate the TTX but not more. A third study by Brodie and Brodie (1999) showed that there is a cost to TTX resistance. Brodie and Brodie found that snakes with the greatest resistance to TTX tended to be slower than snakes with lower resistance. Since snakes themselves can be prey, sprint speed is an important phenotype for predator avoidance.
Impact: 7 The work by Brodie and Brodie provide an excellent example of predator-prey coevolution. It also demonstrates the geographic variability of coevolution (Thompson, 1994).
References Brodie III, E.D., Brodie Jr., E.D., 1990. Tetrodotoxin resistance in garter snakes: an evolutionary response of predators to dangerous prey. Evolution 44, 651e659. Brodie III, E.D., Brodie Jr., E.D., 1991. Evolutionary response of predators to dangerous prey: reduction of toxicity of newts and resistance of garter snakes in island populations. Evolution 45, 221e224. Brodie III, E.D., Brodie Jr., E.D., 1999. Costs of exploiting poisonous prey: evolutionary trade-offs in a predator-prey arms race. Evolution 53, 626e631. Thompson, J.N., 1994. The Coevolutionary Process. University of Chicago Press, Chicago.
1990 A predator-prey arms race The concept Anti-predator defenses of the newt Taricha granulosa are countered by a garter snake that feeds on them. These predator responses appear to be proportional to the level of defense mounted by the newt, consistent with an evolutionary arms race.
The explanation The skin of the newt Taricha granulosa contains the neurotoxin tetrodotoxin (TTX) which is highly toxic to most animals. The garter snake Thamnophis sirtalis specializes on amphibians and will eat T. granulosa where the two species are sympatric. This suggests that the garter snakes had evolved some tolerance for this toxin. Brodie and Brodie (1990) attempted to study the geographic patterns of TTX resistance. Brodie and Brodie (1990) developed an assay for TTX tolerance that involves injecting snakes with know amounts of TTX and then measuring the snakes sprint speed. They tested two populations of T. sirtalis: one from Oregon that was sympatric with toxic newts and a population in Idaho where newts are not found. In addition, Brodie and Brodie tested a related species of snake, T. ordinoides from the same Oregon location, which is not known to feed on toxic newts. Brodie and Brodie found that allopatric populations of T. sirtalis and the congeneric species T. ordinoides showed similar levels of sensitivity to TTX. However, the sympatric populations of T. sirtalis showed substantially elevated resistance to TTX. Brodie and Brodie (1990) conclude that “These facts suggest that TTX resistance is not a property of the genus Thamnophis or even of the species T. sirtalis at large, but rather has arisen only in populations of T. sirtalis that feed on T. granulosa”. In a later study Brodie and Brodie (1991) found a population of T. sirtalis on Vancouver Island, British Columbia, with TTX resistance between the previously studied Oregon population of T. sirtalis and T. ordinoides. Such an observation seems to contradict the coevolutionary nature of this TTX resistance. However, a closer examination of Vancouver population of Conceptual Breakthroughs in Evolutionary Ecology ISBN: 978-0-12-816013-8 https://doi.org/10.1016/B978-0-12-816013-8.00056-9
© 2020 Elsevier Inc. All rights reserved.
131
j
132
Conceptual Breakthroughs in Evolutionary Ecology
newts showed that the toxicity of their skin was at least 1000 times less than the toxicity of the previously studied Oregon population of newts. These observations suggest that the garter snakes evolve a level of tolerance needed to tolerate the TTX but not more. A third study by Brodie and Brodie (1999) showed that there is a cost to TTX resistance. Brodie and Brodie found that snakes with the greatest resistance to TTX tended to be slower than snakes with lower resistance. Since snakes themselves can be prey, sprint speed is an important phenotype for predator avoidance.
Impact: 7 The work by Brodie and Brodie provide an excellent example of predator-prey coevolution. It also demonstrates the geographic variability of coevolution (Thompson, 1994).
References Brodie III, E.D., Brodie Jr., E.D., 1990. Tetrodotoxin resistance in garter snakes: an evolutionary response of predators to dangerous prey. Evolution 44, 651e659. Brodie III, E.D., Brodie Jr., E.D., 1991. Evolutionary response of predators to dangerous prey: reduction of toxicity of newts and resistance of garter snakes in island populations. Evolution 45, 221e224. Brodie III, E.D., Brodie Jr., E.D., 1999. Costs of exploiting poisonous prey: evolutionary trade-offs in a predator-prey arms race. Evolution 53, 626e631. Thompson, J.N., 1994. The Coevolutionary Process. University of Chicago Press, Chicago.