Life cycle polyphenism as a factor affecting ecological divergence within <Emphasis Type="Italic">Notophthalmus viridescens</Emphasis> |
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Authors: | Mizuki K Takahashi Matthew J Parris |
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Institution: | (1) Department of Biology, University of Memphis, Memphis, TN 38152, USA |
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Abstract: | Polyphenism, which allows a single genotype to express multiple discrete phenotypes in response to environmental cues, is
an adaptive trait in heterogeneous environments. Pond hydroperiod is an important ecological parameter affecting amphibian
life history, and variation in local pond hydrology has been hypothesized to play a role in species divergence via changes
in polyphenism. The eastern newt (Notophthalmus viridescens) expresses life cycle polyphenism. Larvae develop along three possible pathways: metamorphosis to aquatic lunged adult via
a terrestrial juvenile (eft) stage, metamorphosis directly to an aquatic lunged adult, or maturation directly to an aquatic
gilled adult without metamorphosis (i.e., paedomorphosis). Subspecies of N. viridescens vary in their polyphenic patterns, suggesting possible adaptation to different environments. However, no studies have experimentally
tested how genetic and environmental components contribute to the observed differences among subspecies and whether such differences
may facilitate divergence. We tested whether adaptation to local pond hydrology via polyphenic changes existed among subspecies
by rearing larvae of three subspecies (N. v. dorsalis, N. v. louisianensis, and N. v. viridescens) along three hydroperiod regimes (short, long, and constant) in outdoor artificial ponds. We found that larval N. v. viridescens obligately metamorphosed to efts under all hydroperiods, whereas N. v. dorsalis and N. v. louisianensis exhibited plasticity: larvae metamorphosed to efts under drying conditions but metamorphosed directly to aquatic adults or
became paedomorphic in constant water. Also, N. v. viridescens metamorphosed to efts faster and at a smaller body size than the other two subspecies. These data suggest that subspecies
of N. viridescens are adapted to different pond hydroperiods, supporting the potential for polyphenism to facilitate divergence. Canalizing
selection for certain alternative phenotypes within a single species in which other populations remain plastic may play an
important role in the initiation of ecological divergence. |
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Keywords: | Adaptation Ecological divergence Life cycle polyphenism Pond hydroperiods Salamanders |
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