Study
Evolution of Animal Photoperiodism
Bradshaw, William E.; Holzapfel, Christina M.
Annual Review of Ecology, Evolution, and Systematics, 2007
A review of how animals measure day length, what they use the measurement for, and how photoperiodic thresholds vary geographically and evolve — drawing on laboratory manipulation of day length, latitudinal clines and selection experiments.
- Studied in
- Animalia, Insecta
- Sample size
- review of photoperiodic response across animal taxa
Photoperiod is the dominant seasonal cue across animal groups because it is the only environmental variable that is unaffected by weather and identical from year to year. The threshold day length that triggers a response varies clinally with latitude, is heritable, and can shift measurably within a few decades under selection.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
Photoperiodic response is a genetically variable trait under strong seasonal selection, and the capacity to evolve is a central factor in how populations respond to changing seasons.
How NatureHQ reads it
The important thing here is not that animals use day length — it is why. Temperature is the thing that matters and is a terrible signal, because a warm week in February means nothing. Day length is useless information about the present and perfect information about the date. Animals took the reliable signal, and climate change works by breaking the correlation between the signal and the thing it stood for.
- The cline and selection evidence is strongest in a small number of insect and small-mammal systems.
- Heritability estimates do not tell you whether adaptation will be fast enough in any particular case.
- Photoperiod interacts with temperature in ways this framing simplifies.
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Published by: Annual ReviewsPublished in an Annual Reviews journal.
doi.org/10.1146/annurev.ecolsys.37.091305.110115
This reference was resolved automatically against Crossref on 2026-08-11.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-08-11.