How does rising atmospheric CO2 affect marine organisms?

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Frogs Facing Double Trouble: Can They Rise to the Challenge?
Egea-Serrano, A., Hangartner, S., Laurila, A. and Rasanen, K. 2014. Multifarious selection through environmental change: acidity and predator-mediated adaptive divergence in the moor frog (Rana arvalis). Proceedings of the Royal Society B 281: 10.1098/rspb.2013.3266.

The authors introduce their study by writing that "while adaptation to a single stressor appears commonplace, simultaneous adaptation to multiple stressors may be prevented by ecological or genetic trade-offs or facilitated by correlated evolution," but they add that "our understanding of adaptation to multiple selective agents in natural populations is still limited (Crain et al., 2008; Rogell et al., 2009; MacColl, 2011)."

What was done
Hoping to expand our understanding of the subject, Egea-Serrano et al. studied adaptation of the moor frog Rana arvalis to co-variation between pH and predation risk in six populations located along an acidification gradient in Sweden, where the populations ranged from those inhabiting acid/predator-rich environments (populations at pH 4) to those inhabiting neutral/predator-poor environments (populations at pH 7).

What was learned
The four researchers report that "R. arvalis tadpoles from relatively acidic/predator-rich populations survived better under predation risk than tadpoles from relatively neutral/predator-poor populations," and that "constitutive morphological defenses increased with decreasing pond pH."

What it means
In light of the above-described findings plus their many previous findings that acidity drives divergence in embryonic acid stress tolerance and larval life-history traits (Rasanen et al., 2003; Hangartner et al., 2011; Hangartner et al., 2012a,b), Egea-Serrano et al. feel confident in concluding that their results "provide strong evidence for simultaneous adaptation to acidic pH and increased invertebrate predator pressure in acidified ponds, whereby changes in the abiotic environment (pH) increase strength of selection via biotic interactions (predation)."

Crain, C.M., Kroeker, K. and Halpern, B.S. 2008. Interactive and cumulative effects of multiple human stressors in marine systems. Ecology Letters 11: 1304-1315.

Hangartner, S., Laurila, A. and Rasanen, K. 2011. Adaptive divergence of the moor frog (Rana arvalis) along an acidification gradient. BMC Evolutionary Biology 11: 10.1186/1471-2148-11-366.

Hangartner, S., Laurila, A. and Rasanen, K. 2012a. Adaptive divergence in moor frog (Rana arvalis) populations along an acidification gradient: Inferences from QST-FST correlations. Evolution 66: 867-881.

Hangartner, S., Laurila, A. and Rasanen, K. 2012b. The quantitative genetic basis of adaptive divergence in the moor frog (Rana arvalis) and its implications for gene flow. Journal of Evolutionary Biology 66: 867-881.

MacColl, A. 2011. The ecological causes of evolution. Trends in Ecology and Evolution 26: 514-522.

Rasanen, K., Laurila, A. and Merila, J. 203. Geographic variation in acid stress tolerance of the moor frog, Rana arvalis. I. Local adaptation. Evolution 57: 352362.

Rogell, B., Hofman, M., Eklund, M., Laurila, A. and Hoglund, J. 2009. The interaction of multiple environmental stressors affects adaptation to a novel habitat in the natterjack toad Bufo calamita. Journal of Evolutionary Biology 22: 2267-2277.

Reviewed 21 May 2014