Testes play a role in termination but not in initiation of the spring migration in the night-migratory blackheaded bunting

in Animal Biology
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Day length regulates the development of seasonal phenotypes linked with both the spring migration (e.g., premigratory body fattening and intense nighttime restlessness, called Zugunruhe, in captive birds) and reproduction (e.g., gonadal growth and maturation). The apparent overlap in these photoinduced seasonal phenotypes could be taken to suggest that they are causally linked. The present study investigates this, using the night-migratory blackheaded bunting (Emberiza melanocephala). We continuously monitored activity of male buntings exposed for 19 weeks to short (8 h light : 16 h darkness; 8L : 16D) and long (16L : 8D) photoperiods. Long, but not short, days induced the spring migratory phenotype. Another experiment investigated the role of testes in spring migration by comparing the development of Zugunruhe between intact and castrated buntings held on natural day lengths, at Meerut (India, 29°01′N, 77°45′E) during the period from March to October, thus covering the times of both the spring and autumn migrations. Testes were not involved in induction of the migratory phenotype but probably influenced the end of the migratory season, since castrates delayed the termination of the Zugunruhe.

Testes play a role in termination but not in initiation of the spring migration in the night-migratory blackheaded bunting

in Animal Biology



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    A. A double plotted activity record of representative of intact blackheaded bunting subjected to short days (8 h light : 16 h darkness, 8L : 16D, left) or was transferred to long days (16L : 8D, middle right) after three weeks for another 16 weeks. B. Daily activity profile (mean percent activity in half-hour bins) of blackheaded buntings exposed to short (broken line) and long (solid line) days for 10 days during the period from 11-20 days (i); 21-30 day (ii); 51-60 day (iii); 90-99 day (iv) and 121-130 day (v) of the experiment.

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    The activity hours (mean ± SE) during daytime (upper panel) and nighttime (lower panel) of blackheaded buntings under short (hollow bars) and long days (solid bars), calculated for 10-day bins, as indicated in fig. 1B. P<0.05 as compared to initial value.

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    A. A double plotted activity record of the representative intact and castrated blackheaded buntings held under to natural lighting conditions from March to October at Meerut (29°01′N, 77°45′E), showing 10-day bins for each month. B. Daily activity profile (mean percent activity in half hour bins) of intact (solid line) and castrated (broken line) blackheaded buntings during four months of a year (March, April, May and September), characterizing the transition in activity pattern over the seasons.

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    A. The amount (mean ± SE) of daytime and nighttime activity in intact and castrated buntings, P<0.05 levels, compared to initial value. B. Phase difference (mean ± SE) in the onset (Ψo) and end (Ψe) end of activity of intact and castrated buntings in relation to sunrise and sunset, respectively. P<0.05 levels, as compared to initial value.


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