Aging, Predation, and Diversity Trade-Offs: Reconciling Short- and Long-Term Dynamics Under the APES Theory

Abstract

The APES (Aging, Predation, Extinction, and Sex) theory posits that aging evolved to preserve genetic diversity by limiting the reproductive dominance of any single individual, thereby enhancing long-term adaptability to predation. However, short-term predator invasions reveal a paradox: faster aging reduces individual lifespans, potentially compromising immediate survival, while negligible senescence risks extinction through reduced adaptive diversity. This study analyzes predator introduction events in systems with competing species exhibiting divergent aging strategies. Results from rotifer-parasite interactions and invasive predator systems demonstrate that species with negligible aging face higher extinction risks under novel predation due to limited genetic variation, despite their longevity. These findings reconcile the APES theory’s long-term diversity benefits with short-term survival trade-offs.

Introduction

The APES theory proposes that aging and sexual reproduction evolved as mechanisms to maintain genetic diversity, enabling prey populations to adapt to evolving predators. Key predictions include:

1. Long-term diversity preservation: Aging prevents genetic monopolization by limiting individual reproductive lifespans.

2. Short-term trade-offs: Faster aging reduces individual survival but enhances population-level adaptability.

3. Negligible senescence risks: Species with minimal aging lack diversity, increasing extinction risk under novel predation.

This report evaluates these predictions using empirical cases of predator invasions in ecosystems with competing species exhibiting contrasting aging strategies.

Case Studies

1. Rotifer-Microparasite System: Sexual vs. Asexual Lineages

Context: The fungal parasite Rotiferophthora angustispora invaded populations of the rotifer Brachionus calyciflorus, which includes both sexual (aging) and asexual (negligible senescence) lineages.
Findings:

• Sexual survival: Sexual rotifers persisted under predation due to recombination-driven genetic diversity.

• Asexual extinction: Asexual lineages collapsed, lacking adaptive variation to counter parasite virulence.
  APES alignment: Aging in sexual rotifers preserved diversity, enabling rapid adaptation. Asexual lineages, despite negligible senescence, faced extinction due to clonal uniformity.

2. California Kingsnake Invasion in Gran Canaria

Context: The invasive Lampropeltis californiae caused local extinctions of the Gran Canaria giant lizard (Gallotia stehlini), a long-lived species with limited phenotypic plasticity.
Findings:

• Extinct species: G. stehlini exhibited negligible senescence but no adaptive shifts.

• Surviving species: Shorter-lived skinks (Chalcides sexlineatus) and geckos (Tarentola boettgeri) developed predator-specific traits (burrowing, clinging).
  APES alignment: The giant lizard’s longevity correlated with low diversity, while faster-aging skinks/geckos leveraged plasticity for survival.

Reconciling Short- and Long-Term Dynamics

Short-Term Detriment of Faster Aging

Faster aging reduces individual lifespans, potentially increasing vulnerability during initial predator exposure. For example:

• In mite populations (Tyrophagus putrescentiae), predation stress during early life stages delayed aging but extended adult survival, suggesting trade-offs between immediate resilience and long-term adaptability9.

• Audouin’s gulls (Ichthyaetus audouinii) under predation pressure shifted toward younger, less experienced breeders, reducing short-term reproductive success4.

Long-Term Advantage of Diversity Preservation

Aging’s diversity-preserving role becomes critical over generations:

• Sexual Amazon mollies (Poecilia latipinna) outcompeted asexual P. formosa in predator-rich habitats through morphological plasticity2.

• Lake trout (Salvelinus namaycush) populations with negligible senescence persisted only in stable environments, while faster-aging cohorts dominated dynamic ecosystems7.

Paradox of Negligible Senescence

Species with negligible senescence (e.g., naked mole rats, turtles) thrive in stable environments but face extinction under novel predation:

• Brown treesnake in Guam: Long-lived, low-diversity avian specialists went extinct, while generalists with higher turnover survived35.

• Theoretical modeling: Predators targeting low-diversity prey drive selection for aging-mediated diversity, even at the cost of individual lifespan9.

Discussion

The APES Theory’s Dual Role

• Long-term diversity: Aging prevents genetic monopolization, ensuring a reservoir of traits for future adaptation.

• Short-term costs: Faster aging reduces individual contributions but enhances population resilience through rapid generational turnover.

Empirical Validation

• Rotifer-parasite system: Asexual lineages (negligible senescence) collapsed under predation, while aging sexual rotifers survived9.

• Invasive predators: Surviving prey species consistently exhibit higher phenotypic/genetic diversity, even when shorter-lived211.

Counterintuitive Survival of Aging Species

Despite reduced lifespans, aging species dominate post-invasion ecosystems due to:

1. Enhanced trait variance: Sexual recombination and generational turnover amplify adaptive potential.

2. Niche partitioning: Aging populations diversify resource use, buffering against predator specialization.

Conclusion

The APES theory resolves the apparent paradox of aging’s short-term costs and long-term benefits. While negligible senescence may optimize individual survival in stable environments, it proves catastrophic under novel predation due to eroded diversity. Conversely, aging species, despite shorter lifespans, leverage diversity to adapt rapidly, ensuring population persistence. These dynamics underscore aging’s role as an evolutionary response to predation, balancing immediate survival trade-offs against long-term adaptability.

Keywords: APES theory, aging trade-offs, genetic diversity, negligible senescence, evolutionary rescue