Importance of Exogenous Selection in a Fish Hybrid Zone: Insights from Reciprocal Transplant Experiments
A key element in understanding hybridization in fishes is to determine the relative influences of endogenous and exogenous selection on hybrid zone structure. To date, such studies have been limited. To help fill this gap, we conducted reciprocal transplant experiments with two pupfish species, Cyprinodon atrorus and C. bifasciatus, to assess the importance of environmental factors in their hybridization dynamics. Results from our experiments show that C. atrorus survives well when environmental variability is low or high, whereas C. bifasciatus only survives well when environmental variability is low. This corroborates the hypothesis that C. atrorus is euryplastic and C. bifasciatus stenoplastic, and also provides evidence that differential environmental tolerance may be important in regulating the distribution of genetic variation in hybrid zones between these species. However, these differences do not explain why C. atrorus is absent from C. bifasciatus habitats. This absence is likely determined at least in part by other exogenous selection factors, such as disproportionate predator susceptibility and/or inferior competitive ability of C. atrorus. Although the relative role of endogenous selection in this system remains unknown, this study provides insight into the potential complexity of exogenous selection in fish hybrid zones.Abstract
Photographs of the “high variability” (A) and “low variability” (B) sites, with experimental enclosures immersed. Fig. 1B shows a person (EWC) for size reference.
Variation in specific conductance (uS) in summer and winter in the low (closed circles) and high (open circles) variability sites.
Variation in temperature (°C) in the low and high variability sites in summer and winter. The low and high variability sites are represented by closed and open shapes, respectively. Average temperatures are represented by circles, maximum temperatures by triangles, and minimum temperatures by squares. Bars represent one standard deviation around the mean. For clarity, temperature variation at the high variability site is offset to the right of the measurement date.
Contributor Notes
Associate Editor: E. Schultz.