Does the temperature signal determining a turtle’s sex pass through a tiny cellular ‘antenna’? July 29, 2026 PLOS ONE A study published on [this date] compared the gene regulatory networks of two turtle species with different sex-determination systems, proposing a new hypothesis that primary cilia on the cell surface may be involved in temperature-dependent sex determination.
The key point is not experimental proof that “cilia directly sense temperature.” The research team reconstructed network data on embryonic gonad development in the painted turtle (Painted Turtle) and the spiny softshell turtle (Apalone spinifera) reconstructed data on embryonic gonad development into a network and discovered a recurring pattern linking known sex-determination signals—such as temperature, calcium, redox status, and Wnt—with functions related to primary cilia. Thus, while these findings suggest a sophisticated candidate mechanism, they represent a starting point that still requires functional experiments.
30-Second Summary
- The original paper was published on July 29, 2026, and the DOI is 10.1371/journal.pone.0353280.
- A comparison was made between the painted turtle, which exhibits temperature-dependent sex determination (TSD), and the spiny softshell turtle, which utilizes ZZ/ZW genetic sex determination (GSD).
- Analysis of 89 comparable transcription factor hubs did not support the model suggesting a complete replacement of the sex-determination network.
- Functions related to primary cilia were notably prominent, leading to the proposal of the ‘primary cilia integration hypothesis.’
- Direct temperature-sensing capability has not yet been proven; larger sample sizes and functional validation are required.
What happened?
A research team led by Thea Gessler, Dean Adams, and Nicole Valenzuela at Iowa State University constructed gene regulatory networks governing urogenital system development in two turtle species with distinct sex-determination mechanisms. The painted turtle is a representative TSD species, where sex is determined by the temperature during embryonic development, whereas the spiny softshell turtle is a GSD species utilizing ZZ/ZW sex chromosomes. The researchers compared the connections between transcription factors and target genes by integrating protein-protein and protein-DNA interaction data with previously published time-series embryonic transcriptome data.
| Category | Painted turtle | Spiny softshell turtle |
|---|---|---|
| English name | Painted turtle | Spiny softshell turtle |
| Scientific name | Painted Turtle | Apalone spinifera |
| Classification | Order Testudines; Family Emydidae | Order Testudines; Family Trionychidae |
| Distribution | From southern Canada through the United States to Mexico Northern | Rivers and lakes of North America |
| Sex Determination | Temperature-dependent sex determination (TSD) | ZZ/ZW genetic sex determination (GSD) |
| Global conservation status | IUCN Least Concern (LC) | IUCN Least Concern (LC); regional populations may be at risk |
Insights from the 89 hubs
Researchers analyzed 89 transcription factor hubs that were sufficiently expressed in the transcriptomes of both species to allow for comparison. The results did not support the ‘complete overhaul’ hypothesis—which suggests that the existing sex-determination network was entirely replaced by a new one during the evolution of GSD. Instead, the findings indicated a combination of rewiring mechanisms, such as existing hubs acquiring new targets or other hubs taking over the regulation of certain targets.
Notably, among the 37 transcription factors with altered targets between the two species, five—EMX2, LHX9, LIN54, ARID3B, and MEOX2—showed an overrepresentation of terms related to primary cilia (these were the five factors for which functional annotation and statistical testing could be robustly applied). The researchers cited the link between primary cilia and pathways previously associated with temperature-dependent sex determination—such as calcium-redox, pSTAT3, Wnt/Rspo1/β-catenin, and Dhh—as supporting evidence.
Why are primary cilia important?
Primary cilia are sensory organelles that receive signals at the cell surface and coordinate various developmental pathways. While their critical role in mammalian urogenital development and disease is already established, this study breaks new ground by directly linking them to the evolution of temperature-dependent sex determination in turtles. Pinpointing the structure that acts as an ‘integration point’ between external temperature conditions and intracellular sex-differentiation pathways allows us to investigate how different sex-determination mechanisms have rewired the same fundamental developmental toolkit.
While interesting in the context of climate change, this finding does not immediately serve as a tool for predicting population sex ratios. Ecological variables—such as nest temperature, maternal nesting choices, embryonic developmental stages, and species-specific pivotal temperatures—must still be measured independently. This study merely proposes candidates to be investigated at the molecular level.
Points to avoid overinterpreting
First, the analysis relies on an integrated model of previously published transcriptome and interaction data rather than newly generated large-scale experimental data. Second, because some analyses involved pooled samples, it is difficult to assess individual variations in detail. Third, the study did not directly test whether sex-determination responses change when primary cilia are removed or their function is blocked. The researchers themselves acknowledged the need to validate the hypothesis through experiments involving turtle gonad organoids, proteomic analysis, and functional genomics across developmental stages.
This does not mean that keepers are free to arbitrarily alter incubation temperatures or manipulate sex ratios. In particular, as safe incubation ranges and developmental responses vary by species, the findings of this study should not be applied as a general guideline for artificial incubation.
Key takeaways for readers
- A significant portion of the common developmental network remains despite differing sex-determination mechanisms.
- Primary cilia are a candidate integration point linking temperature signals to sex-differentiation pathways.
- A comparison of 89 transcription factor hubs supports gradual rewiring rather than ‘complete replacement.’
- The current stage involves a network-based hypothesis; functional validation remains to be done.
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Original source, DOI, and references
- Gessler TB, Adams DC, Valenzuela N. (2026). Original PLOS ONE paper. DOI: 10.1371/journal.pone.0353280
- PubMed bibliographic record
- Iowa State research summary (EurekAlert)
- Reptile Database: Painted Turtle
- Reptile Database: Apalone spinifera
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