Variation in defensive and exploratory behaviors across a rattlesnake (Crotalus scutulatus × viridis) hybrid zone in Southwestern new Mexico

Abstract

Studies on animal temperaments (consistent differences in behaviors across contexts) and behavioral syndromes (suites of correlated behaviors across contexts) have surged in recent decades. Accordingly, behavioral ecologists have gained greater appreciation for their evolutionary role and significance. Yet, despite their importance as potential evolutionary drivers, research focused on temperament and syndromes in shaping hybridization events is vastly understudied. Case studies have shown that hybridization has multiple effects on these phenomena, such as eliminating syndromes present in parental lineages and generating novel syndromes within hybrids. Here, we assessed temperament and syndromes in a naturally occurring rattlesnake hybrid zone (Crotalus scutulatus × viridis). We used laboratory behavioral assays to quantify defensive and explorative behaviors, and tested whether these traits were correlated with spatial and hunting behaviors of free-ranging individuals. C. viridis was more significantly more prone to rattle than C. scutulatus during handling tests. Similarly, hybrid individuals that had a greater proportion of their genome derived from C. viridis were also more prone to rattle. Parental and hybrid snakes exhibited varying syndromes in defensiveness and exploratory behaviors, yet further research is necessary to determine whether they impact hybrid fitness by creating mismatches between temperaments and predation pressures under natural conditions.

Fig. 1

Bar graph of the proportions of snakes that rattled during the handling assay. Propensity to rattle was significantly different across groups (X² = 20.8; df = 2; p < 0.001). More Crotalus viridis rattled than either C. scutulatus or C. scutulatus × viridis (post-hoc Tukey: z-ratio = −3.52, 3.98; p = 0.001, < 0.001; respectively), whereas there was no difference between C. scutulatus and C. scutulatus × viridis (post-hoc Tukey: z-ratio = −0.247, p = 0.967). Letters above the bars indicate statistically significant groupings of the genetic groups. Sample sizes: C. scutulatus = 41, C. viridis = 59, C. scutulatus × viridis = 85.

Fig. 2

Bar graph of the proportions of adult versus juvenile snakes that rattled during the handling assay (X² = 9.38; df = 1; p = 0.002). Letters above the bars indicate statistically significant groupings of the genetic groups. Sample sizes: adults = 135, juveniles = 50.

Fig. 3

Scatter plot of propensity to rattle versus hybrid index (proportion of genome derived from C. viridis) for hybrid snakes. The dotted line is the binomial regression line (X² = 5.45, df = 1, p = 0.020) and the shaded region flanking either side of the line is ± 1 SE. Sample size = 85.

Fig. 4

Scatter plot showing the negative correlation (behavioral syndrome) between the number of days per movement for individuals when they were free-ranging and the number of quadrant transitions those individuals performed during the exploratory assay. (Spearman correlation, Holm’s adjustment: r = 0.−386, n = 43, p = 0.032).