2011 Oct 3

Meeting Notes from October 3rd, 2011 by Emmett Fitzpatrick:

Presenter: Matthew Paul
The Influence of the Seasons on Behavior
- The seasons are caused by the earth’s rotational axis being on a tilt
- This leads to drastically different environment in the same geographical location depending on the time of the year
- Organisms have 2 choices, either Adapt to the changes or Leave during the changes
- There are examples of Summer Specific VS Winter Specific Behaviors
Soay Sheep: All births are within 2 months from Late March to early June. There is a 5 month gestation of the sheep, so the sheep mate in November to anticipate when the seasons change for the offspring to be born during for food availability Arctic Ground Squirrel: While hibernating, the body temperature drops below 0°C, and yet their blood does not freeze and crystallize - Humans have seasonal rythms too
Loss of virginity: Highest from May – July in Caucasians and Black. Latinos show a delayed peak. One possible explanation is prom as the highest age correlation is in 16-18 year olds Suicides: Highest from March – June. The seasonality is disappearing with the accessibility of knives, firearms, and poison, but this is because the rates of hanging, drowning, and jumping go up during the warmer months Births: There are many more in the last week of December than in the first week of January. They are mainly cesarean sections, and are probably caused by the tax break of being able to write it off for that year than having to wait until next year for the write off Androgens: Have seasonal rhythms that affect beard growth and hair loss - There are 3 types of seasonal rhythms. A) Hourglass Timer, B) Circannual Clock, and C) Passive Response to the Environment
- Siberian Hamsters are a widely accepted effective model for circadian rhythms
- Their bodies run on a Summer/Winter clock that can be controlled in a lab setting by manipulating the Long Day/Short Day stimuli. When they are put in a Short day cycle, their body mass decreases and their fur changes color as they get ready for winter, and this change resets after 11 weeks as the hamsters start to revert back to the summer phenotype. The Change to the winter phenotype must be reset by being exposed to Long Day photoperiods for weeks even if the hamsters are held in an environment that stays in the Short Day cycles. Other animals like birds also have seasonal changes in phenotype, but are reset by being exposed to a short day cycle instead of the long day cycle
- The SCN (Suprachiasmatic nucleus) plays an essential role in the internal clock of the brain
- Light enters the brain through the eye to the SCN to the Pineal Gland which breaks down Melatonin, a hormone released during the night and sleep in the brain. It breaks down in light (half life = 30 minutes)
- The Pars Tuberalis is thought to be the major driver of the Circadian Clock as there is significant levels of melatonin in this area across many divergent species from humans to hamster and deer to birds
- Other factors that affect Circadian rhythms (Nonphotic cues) are temperature
Common Starling: Testes size and molting are affected by temperature changes from 5°C to 20°C. - How do animals integrate Photic Cues Socially?
The internal clock has the animals start returning to the summer phenotype (Siberian Hamsters) in anticipation of the summer There are marked increases in vegetation. There is little variability in this. Animals must time to something other than photoperiod because photoperiods are consistent from year to year while ideal times of vegetation/food and breeding are not Food restrictions had no effect on testes size in summer phenotype hamsters (Kept in 16hr Day:8hr Night) but it had a significant effect in decreasing the size of testes in animals kept in moderate days (13.5hr day/10.5hr night) Animals housed in 3-4 animals per group show significant differences in reproductive development from solitary animals (Kept in a cage by themselves). It takes longer for the latter to reach reproductive development. This effect is more significant in females than males, but is removed in summer photoperiods. Do nonphotic cues act through the HPA axis (stress) on the HPG axis? Testosterone is low in suppressed animals while Cortisol is high. FSH is low in these animals. Is it due to the lew levels of testosterone? Is this affected by the gonads? Gonadextomized animals show an increase in GnRH and FSH. Further work would be to look at the Hypothalamus and GnRH neurons