Range-wide validation of reduced locomotor endurance in unisexual Ambystoma salamanders

Locomotor endurance is a critical physiological trait dictating terrestrial dispersal and metapopulation connectivity, especially in amphibians. The unisexual Ambystoma complex is an ancient, all-female polyploid lineage that reproduces via kleptogenesis. This unique reproductive mode creates an evolutionary mismatch between a conserved mitochondrial genome and divergent nuclear subgenomes that are taken from sympatric, sexual species. This provides a compelling system for testing the physiological limits of polyploidy and how subgenome composition influences phenotypes. Previous locomotor assessments of this lineage demonstrate that polyploid salamanders display reduced locomotor endurance compared to sexual species. To overcome previous limitations in geographic sampling and sample size, we conducted standardized treadmill endurance trials on a broad geographic sampling of 110 salamanders, comparing the performance of triploid unisexual biotypes (LJJ and LLJ) directly to their sexually reproducing parental species (A. jeffersonianum and A. laterale). We found that biotype significantly dictates endurance performance. Both sexual species demonstrated significantly greater total distance traveled prior to exhaustion compared to the unisexual hybrids. But within the unisexual cohort, subgenome dosage influenced performance: LJJ individuals outperformed LLJ individuals, aligning with A. jeffersonianum demonstrating greater endurance than A. laterale. We propose that the aerobic capacity of unisexual salamanders is limited, potentially due to mitonuclear mismatch or the biophysical constraints of increased cellular volume. This endurance deficit is likely to restrict unisexual salamanders’ dispersal capabilities, leaving populations uniquely vulnerable to ongoing habitat fragmentation compared to more mobile, sexual species