Dispersal is the central mechanism that determines connectivity between populations yet few studies connect the mechanisms of movement with realized dispersal in natural populations. To make such a link, we assessed how physiological variation among individuals predicted dispersal in natural populations of unisexual (all-female) and sexual Ambystoma salamanders on the same fragmented landscape in Ohio. Specifically, we assessed variation in a trait that influences long-distance animal movement (locomotor endurance) and determined whether variation in endurance matched patterns of realized dispersal assessed using genetic assignment tests. A possible mechanism for why unisexuals would have lower locomotor endurance than a sympatric sexual species (Ambystoma texanum) is the potential energetic cost of evolutionarily mismatched mitochondrial and nuclear genomes within polyploid unisexuals. We found that sexuals walked four times farther than unisexuals during treadmill endurance trials that mimic the locomotor endurance required for dispersal. We then applied landscape genetic methods to identify dispersed adults and quantify realized dispersal. We show that the differences in locomotor endurance between unisexual and sexual salamanders scale to realized dispersal: dispersing sexual individuals travelled approximately twice the distance between presumed natal wetlands and the site of capture compared to dispersing unisexuals. This study links variation in individual performance in terms of endurance with realized dispersal in the field and suggests a potential mechanism (physiological limitation due to mitonuclear mismatch) for the reduced endurance of unisexual individuals relative to sexual individuals although we discuss other possible explanations. The differences in dispersal between these two types of salamanders also informs our understanding of sexual/unisexual coexistence by suggesting that unisexuals are at a competitive disadvantage in terms of colonization ability under a extinction-colonization model of coexistence. A lay summary is available for this article.
Bibliographical noteFunding Information:
We thank the Crawford County landowners who granted us access to their properties. We thank B. Johnson and M. Gray for providing the treadmill used in this study. We thank J. Dyer, S. Hedge, M. Holding, M. Saccucci, M. Parsley, P. Hudson, K. Costello, C. Ries, J. Lorenz, B. Arnold and J. Diaz for assistance with both field and laboratory work. We thank G. Gerald for helpful discussions and preliminary work. Finally, we thank B. Carstens, S. Matthews, J. Williams and the members of the Gibbs lab for comments on this manuscript. This work was supported by the State Wildlife Grants Program, administered jointly by the U.S. Fish and Wildlife Service and the Ohio Division of Wildlife, with funds provided by the Ohio Biodiversity Conservation Partnership between Ohio State University and the Ohio Division of Wildlife. Funds were also provided by the American Society of Ichthyologists and Herpetologists, the Ohio State University Graduate School, and those who contributed to a SciFund crowdfunding campaign by R.D.D. This work was conducted under Ohio State Institutional Animal Care and Use Protocol #2012A00000039.
© 2016 The Authors. Functional Ecology © 2016 British Ecological Society
- Ambystoma salamanders
- genetic assignment
- mitonuclear mismatch