Finding. Anna's hummingbirds (Calypte anna) drop into torpor without rewriting the genome. Kumar, Shankar and colleagues report the first multi-tissue whole-transcriptome of avian torpor entry, paired with real-time thermal imaging and respirometry across seven tissues. Under 5 percent of the genome changes, versus the 10 to 60 percent often quoted for mammalian hibernation. Most of those genes move before torpor entry is finished. They do not track body temperature like a thermometer.
The tissue split is sharp. Heart and lung stay transcriptionally quiet enough to keep essential function. Liver and gut rewire metabolism. The authors report global suppression of transcription and translation, plus cell-cycle arrest: the three expensive items on a cellular energy budget. They hypothesize an apoptosis arrest, a switch from carbohydrate to lipid, and changes in alternative splicing and circadian control. The mitochondrial sentence runs the wrong way for a shutdown story. Genes of mitochondrial metabolism go up, which they read as staging for a fast arousal.
Why this paper matters
Torpor looks like a dimmer switch. This brief says the dimmer is thrown by a small, early programme, not by temperature-driven collapse. That matters for anyone who treats mitochondria as passive victims of cooling. If mitochondrial transcripts rise while the animal is still falling, the organelle is being prepared for the expensive return to normothermy.
It also sets a magnitude expectation. If your hibernation dataset moves half the genome and a hummingbird dataset moves a twentieth, you are not looking at the same regulatory strategy. Comparative mitochondrial physiology needs that distinction before it borrows gene lists.
What they actually measured
Physiology plus transcriptome: thermal imaging, respirometry, seven tissues. The abstract gives a genome-fraction, a timing claim (before entry completes), a tissue split, three energy-budget processes, and a set of hypotheses. It does not name the mitochondrial genes, give fold-changes, or show a respiration curve aligned to the transcriptional pulse.
Read the last sentence as interpretation. Upregulated mitochondrial-metabolism genes are not the same as increased oxidative phosphorylation during the nadir. They are a prediction about readiness.
How to read the score
Low eighties. First avian multi-tissue torpor transcriptome and a mitochondrial claim that is specific enough to use. Confidence is medium because the teaser is rich in programme language and thin on named genes and numbers.
What to do with it
If you model metabolic suppression, arousal thermogenesis, or avian mitochondrial flexibility, pull the seven-tissue differential table and the thermal/respirometry alignment. Treat apoptosis arrest and splicing/circadian changes as hypotheses. Do not cite this brief as proof that mitochondria stay "on" throughout torpor.