SREL Reprint #3598

Relative size underlies alternative morph development in a salamander

Michael P. Moore1,2,5, Joseph H. K. Pechmann3,4, and Howard H. Whiteman1,4

1Watershed Studies Institute and Department of Biological Sciences,
Murray State University, Murray, KY 42071, USA
2Department of Biology, Case Western Reserve University, Cleveland, OH 44106, USA
3Department of Biology, Western Carolina University, Cullowhee, NC 28723, USA
4Savannah River Ecology Laboratory, University of Georgia, Aiken, SC 29802, USA
5Living Earth Collaborative, Washington University, St. Louis, MO 63105, USA

Abstract: Size thresholds commonly underlie the induction of alternative morphological states. However, the respective importance of absolute and relative size to such thresholds remains uncertain. If absolute size governs expression, morph frequency should differ among environments that infuence absolute sizes (e.g. resources, competition), and individuals of the same morph should have similar average sizes across environments. If relative size determines expression, the frequency of each morph may not differ among environments, but morphs within each environment should differ in size relative to one another. We tested these predictions in a salamander (Ambystoma talpoideum) that develops into either a terrestrial metamorph or an aquatic paedomorph. To generate size variation within and among environments, we reared individuals in mesocosm ponds across three conspecific densities. We found that morph frequency did not differ among density treatments, and the morphs were not similarly sized within each density treatment. Instead, within each environment, relatively larger individuals became metamorphs and relatively smaller individuals became paedomorphs. Relative size therefore determined morph development, highlighting the importance of an individual’s social context to size-dependent morph induction.

Keywords: Facultative paedomorphosis; Intraspecifc competition; Life-history variation; Polyphenism; Resource polymorphism

SREL Reprint #3598

Moore, M. P., J. H. K. Pechmann, and H. H. Whiteman. 2020. Relative size underlies alternative morph development in a salamander. Oecologia 193(4): 879-888.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).