Rising temperatures are reshaping life in ways that go far beyond melting ice or shifting habitats. They are reaching into the most intimate biological process of all – how genes are shuffled and passed to the next generation.

New research shows that heat and cold can alter the genetic machinery that produces sperm and eggs in reptiles, even tilting the odds of embryos developing as one sex or the other. These subtle shifts strike at the foundation of fertility and evolutionary change.

Temperature tests reptile fertility

A team from the Universitat Autònoma de Barcelona (UAB) tested the effect in a small Madagascan lizard, the Guibé’s ground gecko. The experts tracked recombination – the exchange of DNA between paired chromosomes that fuels genetic diversity.

To measure this, the researchers analyzed 1,169 sperm cells from 12 male geckos kept at six different temperatures for a week. The results revealed a U-shaped response: recombination events rose at both cooler (68°F) and warmer (86°F) conditions compared to a mid-range 82°F.

“Our findings show the presence of hyper-CO spermatocytes in individuals exposed to both high and low temperatures,” said Laura González Rodelas, lead author of the study.

The study also noted shorter chromosome axes and more lingering double-strand breaks at the extremes.

Why recombination matters

Crossover events are needed for chromosomes to separate cleanly during meiosis. Too few, or too many in the wrong places, can reduce fertility or alter which gene combinations survive.

The gecko study found that long chromosomes soaked up most of the extra crossovers at hot and cold settings.

It also detected weaker crossover interference, the spacing rule that normally keeps events apart along the synaptonemal complex.

Heat flips reptile chromosomes

Some reptiles go a step further, pairing sex chromosomes with heat and cold cues, which can cause temperature-induced sex reversal under hot incubation.

“This is the first report of reptile sex reversal in the wild,” said geneticist Clare Holleley. Her fieldwork on the Australian central bearded dragon reported male to female sex reversal in the wild at high egg temperatures. 

Understanding that switch needs high quality genomes that resolve both Z and W sex chromosomes. One study delivered a near telomere to telomere assembly from a female ZW bearded dragon.

Researchers created a complete, high-quality map of the bearded dragon’s genome, covering both of its sex chromosomes.

The team found that the genome contains about 1.75 billion DNA bases, and they were able to piece together the Z and W chromosomes in full, giving scientists a clearer view of how sex is determined in this species.

Mapping reptile sex genes

Having a full genome map lets researchers track genes linked to reproduction, growth, and disease. It also provides a baseline for comparing different reptiles and understanding how sex chromosomes evolve over time.

These insights can help identify which genes respond to environmental stress and which ones remain stable. For conservation, this kind of data can guide breeding programs and population management.

By knowing the genetic makeup of males and females, scientists can predict how changes in temperature might affect sex ratios in the wild, an issue that becomes more urgent as global warming accelerates.

Geckos echo plant findings

A plant genetics study showed the same U-shaped recombination response in Arabidopsis, from a low point near 64°F to higher rates at cooler and warmer settings.

The pattern suggests organisms often keep recombination low in comfortable conditions, then shift upward under stress.

Mechanisms are still being worked out. A yeast paper connects temperature, DNA supercoiling, and weaker interference, offering one plausible route for how heat can ripple through meiotic structure.

Genetics under climate strain

These changes land where evolution does its work. When environments move quickly, extra recombination can speed the shuffle of gene combinations that selection can test.

There is a tradeoff. If crossover placement and interference are distorted for long periods, fertility and chromosome stability could suffer in some lineages.

For reptiles that already face habitat loss and pollution, this genetic sensitivity adds a quiet risk. Protecting reptile nesting sites from extreme heat, shading exposed sand, and buffering water temperatures can safeguard early development.

Captive breeding programs can monitor incubation ranges that avoid persistent sex bias. They can also track genetic health when recombination patterns drift from physiological norms.

Genes, maps, and temperature

The gecko result is not a vague climate story. It rests on direct cell counts, such as the increase in crossover markers at 68°F and 86°F relative to 82°F.

The bearded dragon work is not only about embryos. It gives a map of the Z and W regions, including candidate sex genes, which anchors future tests of how temperature interacts with sequence.

The study is published in the journal PLOS Genetics.

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