Tadpoles bulk up to meet the alien invaders

What happens when an invasive, carapaced, and clawed alien predator arrives in your pond? Do you change your daily habits to avoid drawing dangerous attention? Bulk up to make yourself a tougher target? If you are an Iberian water frog, you do both.


Pelophylax perezi is the most widespread and numerous of the native frogs and toads on the Iberian peninsula, known in Spain as rana común, the common frog. In this video abstract, Germán Orizaola of Uppsala University describes experimental confrontations between variously naïve Portuguese populations of the waterfrog and a very successful migrant, the red swamp crayfish (Procambarus clarkii ), conducted by Ana Nunes with himself, Anssi Laurila, and Rui Rebelo. Over generations, the threat of the great red invader has selected physical and behavioral changes in the frogs. Their report was published in the June issue of ESA’s Ecology.

Known to many culinary fans as the Louisiana crawfish, the red swamp crayfish is a menu staple in the southern United States and a popular export. Aquaculturists precipitated the crayfish’s emigration from the North American Gulf Coast to rivers, marshes, and rice paddies in China, Portugal, Spain, and other far-flung parts of the world. It has generally been a strong competitor. The red swamp crayfish is territorial and aggressive, and, unlike many of its crayfish kin, not a vegetarian.

When meeting a red swamp crayfish for the first time, Iberian waterfrog tadpoles from traditional pond communities with no history of invasion quickly learned to hold still. After 30 years of ancestral coexistence with the crayfish, P. perezi tadpoles had bulked up and formed a habit of muted activity at all times.

The arrival of the crayfish is driving rapid evolutionary change in these invaded ponds, wrote the authors, and this frog story may illustrate a more general effect of exotic predators on the new communities they enter.

Read more about this story on Orizaola’s blog.

<strong>Prolific traveler</strong>. The red swamp crayfish <em>(Procambarus clarkii</em>) has journied from it's native lands on the North American Gulf Coast and Florida's panhandle to colonize warm fresh waters around the world -- often at the expense of local crustaceans and amphibians. <em>Credit, <a href="https://flic.kr/p/jdmnf5" target="_blank">National Park Service</a></em>.

Prolific traveler. The red swamp crayfish (Procambarus clarkii) has journied from it’s native lands on the North American Gulf Coast and Florida’s panhandle to colonize warm fresh waters around the world — often at the expense of local crustaceans and amphibians. Credit, National Park Service. Cropped for size.

Ana L. Nunes, Germán Orizaola, Anssi Laurila, and Rui Rebelo 2014. Rapid evolution of constitutive and inducible defenses against an invasive predator. Ecology 95(5):1520–1530. http://dx.doi.org/10.180/13-1380.1

Author: Liza Lester

ESA's Communications Officer came on board in the fall of 2011 after a Mass Media Science and Engineering fellowship with AAAS and a doctorate in Molecular and Cellular Biology at the University of Washington.

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