Dr. Keith Sockman, an Associate Professor at University of North Carolina at Chapel Hill, participates in our latest installation of Insights by discussing with us his paper, co-authored with Dr. Allen Hurlbert, titled, “How the effects of latitude on daylight availability may have influenced the evolution of migration and photoperiodism”.

About the paper

What’s your paper about?

The paper that I authored, together with citizen science/eco-informatics expert and department colleague Allen Hurlbert, is about how the effects of latitude on daylight availability may have influenced the evolution of migration and photoperiodism. That is also the title.

What is the background behind your paper?

Daylight availability may play an important role in the evolution of avian migration. Photo by Chinmayee Mishra,  https://commons.wikimedia.org/wiki/File:A_clear_sunset_view.jpg#filelinks [commons.wikimedia.org]
Daylight availability may play an important role in the evolution of avian migration. Photo by Chinmayee Mishra

Photoperiod contributes to the regulation of the annual cycles of many organisms, especially birds. The field of photoperiodism in birds is old yet still very active, as its molecular mechanisms are unravelled. But throughout this long history of research, almost no attention has been given to the fact that annual photoperiod cycles vary by latitude and that migration between latitudes, something very common among birds, causes annual change not just in photoperiod but in the annual photoperiodic cycle, too. This is particularly pronounced in transequatorial migrants, which experience a semi-annual 180-degree phase shift in the cycle, which, in some cases, cannot be reconciled with known photoperiodic mechanisms regulating annual breeding cycles.

What are the key messages of your article?

The key messages are that latitudinal migration can dramatically affect an individual’s photoperiodic schedule and, in the vast majority of cases, increase an individual’s annual daylight exposure. This latter point led us to the hypothesis that daylight availability may have helped select for latitudinal migration in some species, a hypothesis we consider in detail in this paper.

How is your paper new or different from other work in this area?

Dynamic, user-interactive animation showing how migratory programme affects photoperiodic schedule. The parameter values reflect the Arctic tern's migratory programme. Screenshot by Keith W. Sockman
Dynamic, user-interactive animation showing how migratory programme affects photoperiodic schedule. The parameter values reflect the Arctic tern’s migratory programme. Screenshot by Keith W. Sockman

The ideas that daylight availability may have selected for latitudinal migration and that latitudinal migration may have influenced the evolution of photoperiodism (and vice versa) are not new. But the very thorough and quantitative approach we take in this paper is new. Moreover, we place it all in the context of a new proliferation of citizen science data on precise migratory programs for over 100 species, something that has never been done before. Perhaps the most novel aspect, however, is the inclusion of our dynamic, user-interactive models. Being computer animated models, they are not a usual part of the traditional scientific publication, in which graphic displays are static and not interactive. We think that the use of dynamic, user-interactive content will occur with greater and greater frequency in scientific publications.

Does this article raise any new research questions?

Many. In fact, as a Perspective, this paper is all about raising new questions. What are the photoperiodic mechanisms for long-distance latitudinal migrants, particularly transequatorial migrants? What is the evidence that daylight availability contributed to the selection for long-distance migration? It also raises fundamental questions about avian sensory ecology, including how individual sensory systems define daylight versus darkness.

Who should read your paper?

 This paper is for individuals interested in biogeographical ecology broadly, as well as those interested in photoperiodism and migration more specifically.

About the research

What is the broader impact of your paper?

The primary broader impact of this paper is in understanding the evolutionary causes and consequences of migration in this age of changing latitudinal distributions and phenologies driven by global change.

About the Author

How did you get involved in ecology?

The author, Keith W. Sockman. Photo by Keith W. Sockman.
The author, Keith W. Sockman. Photo by Keith W. Sockman.

As an undergraduate in the 1980s at Occidental College in Los Angeles, I was fortunate to work for two summers on the field crew of Marty Morton at Tioga Pass. His research program there served as a foundation for many studies over many decades and launched many careers in avian physiological ecology, one of which was mine.

What are you currently working on?

I am currently working on a grant proposal to test the hypotheses raised by this paper!

What project/article are you most proud of?

This might be one of the three articles of my career of which I am most proud. The other two include one on a proximate mechanism for plasticity in behavioural performance, defined broadly, that I published in 2016 in American Naturalist and one that I published in 2018 in Biology Letters confirming for the first time the 70-year-old hypothesis that oviposition drives hatching asynchrony in birds.

What do you do in your spare time?

As a father of two children, I am a family man. I enjoy taking the kids on long road trips camping and seeing as much of the natural world as we can.

You can read this paper here, along with other Perspective papers.