Bird evolution by insulin resistance

Area of Science:

• Evolutionary Biology
• Paleontology
• Physiology

Background:

• Atmospheric oxygen levels have fluctuated throughout Earth's history, significantly impacting vertebrate evolution.
• The Permian-Triassic boundary experienced a severe oxygen drop, posing a major challenge to vertebrate life.
• Later increases in oxygen during the Jurassic, Cretaceous, and Tertiary periods presented new evolutionary pressures.

Purpose of the Study:

• To investigate the evolutionary adaptations of theropods in response to changing atmospheric oxygen concentrations.
• To explore the genetic and physiological mechanisms underlying theropod adaptation to both hypoxic and hyperoxic environments.
• To understand how these adaptations influenced theropod competitiveness and diversification.

Main Methods:

• Comparative genomics to identify gene losses in theropod genomes (e.g., omentin, GLUT4).
• Physiological analysis to understand insulin resistance and hyperathleticism in theropods.
• Examination of genetic pathways related to reactive oxygen species (ROS) defense in Neoaves (e.g., NRF2, KEAP1).

Main Results:

• Theropods lost genes for insulin sensitivity (omentin, GLUT4), leading to insulin resistance and enhanced athletic performance under hypoxia.
• Some theropods increased body size to mitigate ROS leakage during periods of high oxygen.
• Neoaves evolved constitutively active NRF2 due to KEAP1 C-terminal deletion, enabling robust antioxidant defenses against ROS.

Conclusions:

• Theropod adaptations to oxygen fluctuations were crucial for their evolutionary success, including outcompeting mammals in the Triassic.
• Insulin resistance and antioxidant systems represent key evolutionary solutions to environmental oxygen challenges.
• Genetic modifications in theropods, such as NRF2 activation, highlight the power of molecular adaptations in shaping vertebrate evolution.