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Abstract Predators must contend with numerous challenges to successfully find and subjugate prey. Complex traits related to hunting are partially controlled by a large number of co‐evolved genes, which may be disrupted in hybrids. Accordingly, research on the feeding ecology of animals in hybrid zones has shown that hybrids sometimes exhibit transgressive or novel behaviors, yet for many taxa, empirical studies of predation and diet across hybrid zones are lacking. We undertook the first such field study for a hybrid zone between two snake species, the Mojave rattlesnake (Crotalus scutulatus) and the prairie rattlesnake (Crotalus viridis). Specifically, we leveraged established field methods to quantify the hunting behaviors of animals, their prey communities, and the diet of individuals across the hybrid zone in southwestern New Mexico, USA. We found that, even though hybrids had significantly lower body condition indices than snakes from either parental group, hybrids were generally similar to non‐hybrids in hunting behavior, prey encounter rates, and predatory attack and success. We also found that, compared toC. scutulatus,C. viridiswas significantly more active while hunting at night and abandoned ambush sites earlier in the morning, and hybrids tended to be moreviridis‐like in this respect. Prey availability was similar across the study sites, including within the hybrid zone, with kangaroo rats (Dipodomysspp.) as the most common small mammal, both in habitat surveys and the frequency of encounters with hunting rattlesnakes. Analysis of prey remains in stomachs and feces also showed broad similarity in diets, with all snakes preying primarily on small mammals and secondarily on lizards. Taken together, our results suggest that the significantly lower body condition of hybrids does not appear to be driven by differences in their hunting behavior or diet and may instead relate to metabolic efficiency or other physiological traits we have not yet identified.
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The spatial ecology of Mojave rattlesnakes ( Crotalus scutulatus ), prairie rattlesnakes ( Crotalus viridis ), and their hybrids in southwestern New Mexico
Abstract Hybridization between species provides unique opportunities to understand evolutionary processes that are linked to reproductive isolation and, ultimately, speciation. However, the extrinsic factors that limit hybridization are poorly understood for most animal systems. Although the spatial ecology of individuals in natural habitats is fundamental to shaping reproductive success and survival, analyses of the spatial ecology of hybrids and their parental groups are rarely reported. Here, we used radiotelemetry to monitor wild rattlesnakes across an interspecific hybrid zone (Crotalus scutulatus and Crotalus viridis) and measured movement parameters and space use (utilization distributions) of individuals to evaluate the hypothesis that hybridization resulted in transgressive or atypical movement patterns. Unexpectedly, of the spatial metrics we investigated, we found that hybrids were very similar to parental individuals. Nonetheless, hybrids did show increased patchiness of core utilization distributions, but this result is likely to be driven by increased habitat patchiness in the hybrid zone. Overall, we did not find evidence for overt extrinsic barriers to hybridization associated with spatial ecology; thus, we suggest that the close evolutionary history between the two parental species and their ecological and behavioural similarities are likely to increase the probability of hybridization events in this unique region of New Mexico.
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- Award ID(s):
- 1856404
- PAR ID:
- 10542821
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Biological Journal of the Linnean Society
- ISSN:
- 0024-4066
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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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. viridiswas more significantly more prone to rattle thanC. scutulatusduring handling tests. Similarly, hybrid individuals that had a greater proportion of their genome derived fromC. viridiswere 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.more » « less
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Abstract Hybridization is a common process that has broadly impacted the evolution of multicellular eukaryotes; however, how ecological factors influence this process remains poorly understood. Here, we report the findings of a 3-year recapture study of the Bryant’s woodrat (Neotoma bryanti) and desert woodrat (Neotoma lepida), two species that hybridize within a creosote bush (Larrea tridentata) shrubland in Whitewater, CA, USA. We used a genotype-by-sequencing approach to characterize the ancestry distribution of individuals across this hybrid zone coupled with Cormack–Jolly–Seber modeling to describe demography. We identified a high frequency of hybridization at this site with ~40% of individuals possessing admixed ancestry, which is the result of multigenerational backcrossing and advanced hybrid-hybrid crossing. F1, F2, and advanced generation hybrids had apparent survival rates similar to parental N. bryanti, while parental and backcross N. lepida had lower apparent survival rates and were far less abundant. Compared to bimodal hybrid zones where hybrids are often rare and selected against, we find that hybrids at Whitewater are common and have comparable survival to the dominant parental species, N. bryanti. The frequency of hybridization at Whitewater is therefore likely limited by the abundance of the less common parental species, N. lepida, rather than selection against hybrids.more » « less
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Abstract We studied hybridization between the Black-crested and Tufted titmouse across two geographically distinct transects that differ in the timing of secondary contact by hundreds to thousands of years. We found that hybridization patterns correspond to localized hybrid swarms and that the titmouse hybrid zone is likely slowly expanding over time, a product of short post-natal dispersal distances coupled with weak or absent selection against admixture. We show the southern part of the hybrid zone located in Texas is four times wider than the northern region of hybridization in Oklahoma, which is likely due to geographic differences in hybrid zone age. Despite differences in width, most individuals in both transects are advanced-generation hybrids and backcrosses, suggesting geographically consistent hybridization dynamics. We documented a strong correlation between genotypes and plumage index, suggesting that hybridization has not yet resulted in the decoupling of plumage and genome-wide ancestry as observed in some other avian hybrid zones. Although our results suggest the ongoing expansion of the hybrid zone, the rate of expansion appears to be slow, on the scale of tens of meters a year, and it will likely take hundreds of thousands to millions of years before homogenization of the parental populations. While we did not find support for partial reproductive isolation in the hybrid zone itself, there is the possibility that ecological or sexual selection limits introgression into allopatric regions. Broadly, the results of our study highlight the value of multiple, geographically distant, transects across a hybrid zone for assessing the evolutionary dynamics of hybridizing lineages.more » « less
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Abstract Genetic introgression, allele exchange across species boundaries, is a commonly recognized feature of animal evolution. Under such a paradigm, contemporary contact zones provide first-hand insight into the geographic, phenotypic, and genetic details of introgression. Also, when mate choice phenotypes are conspicuous and variable in hybrids, contact zones provide potential insight into how sexual selection interacts with species boundary maintenance, particularly when postzygotic reproductive isolation is weak. The Habronattus americanus subgroup includes several recently evolved jumping spider species, with an estimated age of about 200,000 yr, and substantial evidence for hybridization and introgression. We explored a contact zone involving H. americanus (Keyserling, 1885) and H. kubai (Griswold, 1979) on Mount Shasta, CA, in alpine habitats that would have been unavailable (under ice) at the Last Glacial Maximum. We characterized morphological diversity within the contact zone, including the fine-scale geographic distribution of hybrid and parental individuals, and assessed genetic variation using ddRADseq data. Combined results indicate a lack of measured genomic differentiation between specimens with distinct morphologies, including individuals with phenotypes of the parental species. We identified a diverse array of hybrid morphologies, with phenotypic evidence for backcrossing, essentially forming a phenotypic bridge between parental taxa. The study area is characterized by more hybrid than parental individuals, with a significantly larger number of red-palped morphologies than white- and/or yellow-palped morphologies; the novel, white-palped phenotype is perhaps transgressive. Overall, these results contribute to a better understanding of the expected ebb and flow of lineage interactions during the early stages of speciation.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/biolinnean/blae037
