Chapter 5b supplement

Chapter 5b supplement - SupplementstoChapter5Bnotes

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Supplements to Chapter 5B notes We’ve already lectured on slides 1 15 from the Chapter 5B notes. This supplement begins with slide 16, the picture of the spotted antbird. Slide 16: Spotted antbirds are tropical residents (non migratory) that breed seasonally but have a very long and flexible breeding schedule. In Panama, where the latitude is about 9 degrees north of the equator, the photoperiod varies by about an hour from the shortest to the longest days of the year. These birds typically breed in May, during the rainy season, as the photoperiod is approaching the maximum for the year. Can they measure this relatively small change in photoperiod and use it to time preparation for breeding? 17: Both male (top panel of figure) and female (middle panel) spotted antbirds exposed to a 1 hour abrupt increase in photoperiod showed enhanced gonadal development compared with controls held on short days. They also grew the gonads faster than free living birds on naturally changing photoperiod (which was increasing, but more slowly than in the experimental treatment), consistent with the hypothesis that they can measure this modest change in day length and use it as a cue to regulate appropriate timing of reproductive development. This figure also shows that singing activity of males was higher when they had access to live crickets during the experiment than when they did not (bottom panel). 18: Further, an increase of only 17 minutes above short day controls induced reproductive development in the experimental birds (males, top pane., females, middle panel). The sample size here was smaller, but note that the experimental birds all showed increases in gonadal size whereas short day controls showed no change during the same time interval. This is consistent with the interpretation that these birds can detect and use a change in photoperiod of as little as about a quarter of an hour to anticipate the upcoming reproductive time. This figure also shows the effect of crickets on singing activity; the males sang much more when crickets were available to them than when not. We come back to this issue below. 19: Appropriate timing of the end of breeding can be just as important from a fitness standpoint as appropriate timing of the onset of breeding. What mechanism controls the end of breeding? A phenomenon called Photorefractoriness (already introduced) turns out to be widespread in seasonally breeding birds (it is also present in seasonally breeding mammals, but the definition and details are different – we’re not going to cover that here). In birds, photorefractoriness is defined as the reproductive unresponsiveness to the stimulatory effects of long days. As shown in some of the figures presented earlier, it facilitates the collapse of the gonads and therefore termination of reproductive competence. It can do this even if photoperiod remains long, which means that
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 8

Chapter 5b supplement - SupplementstoChapter5Bnotes

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online