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Abstract There exists extensive variation in eye size. Much work has provided a connection between light availability and differences in eye size across taxa. Experimental tests of the role of the light environment on the evolution of eye size are lacking. Here, we performed a selection experiment that examined the influence of light availability on shifts in eye size and the connection between eye size and phototactic (anti‐predator) behaviour inDaphnia. We set‐up replicate experimental populations ofDaphnia, repeatedly evaluated phenotypic shifts in eye size during the ~50‐day experiment, and performed a common garden experiment at the end of the experiment to test for evolutionary shifts in eye size and behaviour. Our phenotypic analyses showed that eye size rapidly diverged between the light treatments; relative eye size was consistently larger in the low versus high light treatments. Selection on eye size was also modified by variation in density as increases inDaphniadensity favoured a larger eye. However, we did not observe differences in eye size between the light treatments following two generations of common garden rearing at the end of the experiment. We instead observed strong shifts in anti‐predator behaviour.Daphniafrom the low light treatment exhibited decreased phototactic responses to light. Our results show that decreased light relaxes selection on anti‐predator behaviour. Such trends provide new insights into selection on eye size and behaviour.
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Ancestral genetic variation in phenotypic plasticity underlies rapid evolutionary changes in resurrected populations of waterfleas
The role of phenotypic plasticity in adaptive evolution has been debated for decades. This is because the strength of natural selection is dependent on the direction and magnitude of phenotypic responses to environmental signals. Therefore, the connection between plasticity and adaptation will depend on the patterns of plasticity harbored by ancestral populations before a change in the environment. Yet few studies have directly assessed ancestral variation in plasticity and tracked phenotypic changes over time. Here we resurrected historic propagules ofDaphniaspanning multiple species and lakes in Wisconsin following the invasion and proliferation of a novel predator (spiny waterflea,Bythotrephes longimanus). This approach revealed extensive genetic variation in predator-induced plasticity in ancestral populations ofDaphnia. It is unlikely that the standing patterns of plasticity shieldedDaphniafrom selection to permit long-term coexistence with a novel predator. Instead, this variation in plasticity provided the raw materials forBythotrephes-mediated selection to drive rapid shifts inDaphniabehavior and life history. Surprisingly, there was little evidence for the evolution of trait plasticity as genetic variation in plasticity was maintained in the face of a novel predator. Such results provide insight into the link between plasticity and adaptation and highlight the importance of quantifying genetic variation in plasticity when evaluating the drivers of evolutionary change in the wild.
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- Award ID(s):
- 1651613
- PAR ID:
- 10204804
- Publisher / Repository:
- Proceedings of the National Academy of Sciences
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 117
- Issue:
- 51
- ISSN:
- 0027-8424
- Page Range / eLocation ID:
- p. 32535-32544
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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