The Role of Genetic and Phenotypic Variation in Prey Survival Under Novel Predation: A Test of the APES Theory

Abstract

The APES (Aging, Predation, Extinction, and Sex) theory posits that genetic and phenotypic diversity, facilitated by sexual reproduction and aging, enables prey species to survive evolving predation pressures. This study examines cases of invasive predator introductions to assess whether surviving prey species exhibit greater adaptive variation compared to extinct competitors. Evidence from invasive predator systems, such as the California kingsnake in Gran Canaria and curly-tailed lizards in Caribbean islands, supports the theory: surviving species demonstrated phenotypic shifts linked to predator avoidance, while less adaptable competitors faced extinction. These findings underscore the critical role of diversity in buffering ecosystems against novel predation.

Introduction

Novel predation events, such as invasive species introductions, provide natural experiments to test evolutionary theories. The APES theory argues that aging and sex evolved as mechanisms to maintain genetic and phenotypic diversity, allowing prey populations to adapt to evolving predators. Key predictions include:

1. Phenotypic plasticity: Surviving species will exhibit morphological or behavioral shifts to evade novel predators.

2. Extinction risk: Competitors lacking adaptive variation face higher extinction risk.

3. Sexual reproduction: Genetic diversity from sexual recombination enhances resilience.

This report evaluates these predictions using case studies of invasive predators and their impacts on native prey communities.

Case Studies and Analysis

1. California Kingsnake Invasion in Gran Canaria

Context: The invasive Lampropeltis californiae caused local extinctions of the Gran Canaria giant lizard (Gallotia stehlini) but not the skink (Chalcides sexlineatus) or gecko (Tarentola boettgeri)57.
Findings:

• Extinct species: G. stehlini showed no morphological changes despite predation pressure.

• Surviving species:

  • C. sexlineatus developed elongated limbs and bodies for burrowing.

  • T. boettgeri exhibited enhanced clinging ability via toe-pad modifications.
    APES alignment: Phenotypic shifts in surviving species directly correlate with predator-avoidance traits (e.g., burrowing, climbing), while the extinct species’ lack of adaptability led to demographic collapse7.

2. Curly-Tailed Lizards and Anole Extinctions

Context: The introduction of curly-tailed lizards (Leiocephalus carinatus) to experimental islands disrupted coexistence between green (Anolis smaragdinus) and brown (Anolis sagrei) anoles26.
Findings:

• Behavioral competition: Both anole species were forced into shared arboreal refuges, intensifying competition.

• Outcome: Local extinctions of brown anoles occurred in high-predation zones.
  APES alignment: While not explicitly tied to genetic diversity, the surviving green anoles’ arboreal specialization (a pre-existing phenotypic trait) highlights how functional variation mitigates extinction risk under novel predation6.

3. Brown Treesnake and Avian Extinctions in Guam

Context: The brown treesnake (Boiga irregularis) extirpated 10 of 12 native forest bird species on Guam3.
Findings:

• Indirect cascades: Bird loss disrupted seed dispersal, reducing plant recruitment by 61–92%.

• Survivors: Small, generalist bird species persisted.
  APES alignment: Surviving birds’ generalized diets and nesting behaviors (phenotypic plasticity) contrast with specialists’ reliance on mutualisms, illustrating how niche breadth buffers against predation-driven extinction3.

Discussion

Phenotypic Adaptation as a Survival Mechanism

The APES theory is strongly supported by the Gran Canaria case, where surviving prey developed predator-specific traits (e.g., burrowing, clinging). These shifts align with the theory’s emphasis on phenotypic diversity as a response to novel predation. Conversely, the extinct giant lizard’s static morphology highlights the vulnerability of low-variation populations57.

The Role of Pre-Existing Variation

In Guam and Caribbean systems, surviving species leveraged pre-existing traits (arboreality, dietary flexibility) to exploit predator-free niches. This aligns with APES’s argument that sex-generated diversity provides a “toolkit” for rapid adaptation36.

Limitations of the Modern Synthesis

Traditional models attribute extinction to competition or predation efficiency alone. However, APES provides a unifying framework by linking extinction risk to prey adaptability-a factor absent in non-evolving mortality sources (e.g., starvation)4.

Conclusion

The APES theory gains empirical support from invasive predator systems, where phenotypic and genetic diversity determine survival outcomes. Extinct species often exhibit limited adaptive capacity, while survivors leverage variation to evade novel threats. These findings reinforce the theory’s central tenet: aging and sex evolved not merely as life-history strategies but as critical defenses against evolving predation. Future studies should quantify genetic diversity in extinct versus surviving populations to further validate this framework.

Keywords: APES theory, invasive predators, phenotypic plasticity, extinction risk, evolutionary rescue