Microevolutionary change in mimicry? Potential erosion of rattling behaviour among nonvenomous snakes on islands lacking rattlesnakes

Allf, Bradley C.; Sparkman, Amanda M.; Pfennig, David W.

doi:10.1080/03949370.2020.1837962

Cited by 4 publications

(1 citation statement)

References 39 publications

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“…We therefore hypothesized that Catalina snakes would exhibit behavioral decrements in rattling, cloacal gland discharge, capture difficulty by a human, biting propensity, and venom expenditure. The findings showing that C. helleri on Isla Coronado Sur appears to be less risk averse and potentially more explorative than mainland counterparts [60], and that non-venomous gopher snakes on two other Channel Islands exhibit a reduced tail vibration defensive response compared to mainland counterparts [61], support our hypothesis. Nevertheless, both natural and introduced snake predators and antagonists exist on Catalina, and these must be taken into consideration when interpreting differences in behavior that might be detected.…”

Section: Introductionsupporting

confidence: 77%

Paradoxical Exception to Island Tameness: Increased Defensiveness in an Insular Population of Rattlesnakes

Hayes,

Person,

Fox

et al. 2024

Toxins

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Island tameness results largely from a lack of natural predators. Because some insular rattlesnake populations lack functional rattles, presumably the consequence of relaxed selection from reduced predation, we hypothesized that on Santa Catalina Island, California, USA, populations of the southern Pacific rattlesnake (Crotalus helleri), which possesses functional rattles, would exhibit a decrement in defensive behavior relative to their mainland counterparts. Contrary to our prediction, rattlesnakes from the island not only lacked tameness compared to mainland snakes, but instead exhibited measurably greater levels of defensiveness. Island snakes attempted to bite 4.7 times more frequently as we endeavored to secure them by hand, and required 2.1-fold more time to be pinned and captured. When induced to bite a beaker after being grasped, the island snakes also delivered 2.1-fold greater quantities of venom when controlling for body size. The additional venom resulted from 2.1-fold larger pulses of venom ejected from the fangs. We found no effects of duration in captivity (2–36 months), which suggests an absence of long-term habituation of antipredator behaviors. Breeding bird surveys and Christmas bird counts indicated reduced population densities of avian predators on Catalina compared to the mainland. However, historical estimates confirmed that populations of foxes and introduced mammalian predators (cats and pigs) and antagonists (herbivorous ungulates) substantially exceeded those on the mainland in recent centuries, and therefore best explain the paradoxically exaggerated defensive behaviors exhibited by Catalina’s rattlesnakes. These findings augment our understanding of anthropogenic effects on the behaviors of island animals and underscore how these effects can negatively affect human safety.

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Section: Introductionsupporting

confidence: 77%

Paradoxical Exception to Island Tameness: Increased Defensiveness in an Insular Population of Rattlesnakes

Hayes,

Person,

Fox

et al. 2024

Toxins

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Snake-like hissing calls made by nestlings of the open nesting zitting cisticola Cisticola juncidis

Barlow¹,

Liu

Xia

et al. 2023

Ethology Ecology & Evolution

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The function of red and banded patterns in snakes: a review of hypotheses and evidence

Mouy

2023

Biological Journal of the Linnean Society

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The functions of bright bands in coral and other snakes have long been a puzzle. The most common opinion is that coral snakes display aposematic marks and that other red and black banded snakes in the Americas are mimics of coral snakes. Although supported by some evidence, the notion comes with unresolved difficulties. Here, I review the proposed functions of the colour of coral snakes and similar-coloured snakes, taking a more comprehensive view than usual, from the plausibility of aposematism in coral snakes to the apparent existence of a selective force for red and black banded patterns across the world. Theoretical models of the maintenance of aposematic signals do not seem applicable, hence aposematism has a low a priori plausibility in coral snakes. Evidence of avoidance is weak, field studies rely on unsettled methods and do not reproduce well, and two laboratory studies reporting strong innate fear are questioned. Coral snakes predict the geography and richness of ‘mimics’ in the Americas, but not in line with expectations. Conversely, polymorphism and evidence of local selection and of a worldwide selective force for patterns similar to coral snakes, including complex banded patterns, contradicts aposematism and mimicry and points to an undefined alternative. In summary, aposematism and mimicry fail on too many fronts to be sustained, existing alternatives also fail to be supported sufficiently, and hypotheses need to be formulated to account for the widespread selection for red and black bands and for complex banded patterns in snakes.

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Microevolutionary change in mimicry? Potential erosion of rattling behaviour among nonvenomous snakes on islands lacking rattlesnakes

Cited by 4 publications

References 39 publications

Paradoxical Exception to Island Tameness: Increased Defensiveness in an Insular Population of Rattlesnakes

Paradoxical Exception to Island Tameness: Increased Defensiveness in an Insular Population of Rattlesnakes

Snake-like hissing calls made by nestlings of the open nesting zitting cisticola Cisticola juncidis

The function of red and banded patterns in snakes: a review of hypotheses and evidence

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