ENVIRONMENTAL AND EVOLUTIONARY DETERMINANTS OF THERMAL TOLERANCE VARIATION IN DIVERGENT PRISTIONCHUS PACIFICUS CLADES
Abstract
Thermal tolerance is an important adaptive trait that influences ecological distribution and evolutionary divergence in free-living nematodes. Environmental gradients such as altitude may shape thermal exposure and contribute to phenotype differentiation among Pristionchus pacificus clades. The present study evaluated the environmental and evolutionary determinants of thermal tolerance variation among divergent P. pacificus clades. A quantitative retrospective analysis was conducted using secondary data from 310 P. pacificus strains. Thermal tolerance phenotypes, consensus clades,
altitude, and environmental temperature were analyzed using descriptive statistics, chi-square test, binary logistic regression, Pearson correlation, and Kruskal–Wallis test. Medium-temperature tolerance was the dominant phenotype representing 78.39% of strains, followed by high-temperature tolerance at 19.68% and low-temperature tolerance at 1.94%. Consensus clade was significantly associated with thermal tolerance phenotype (χ² = 135.998, df = 8, p < 0.001). Altitude was a significant negative predictor of high-temperature tolerance (OR = 0.9965, p < 0.001). Environmental temperature showed a strong negative correlation with altitude (r = −0.966, p < 0.001), and altitude differed significantly
among phenotype groups (H = 70.056, p < 0.001). These findings indicate that thermal tolerance variation in P. pacificus is shaped by both environmental gradients and evolutionary clade structure, supporting the role of altitude-linked thermal conditions in adaptive phenotype distribution.
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