Seasonal breeders reproduce when the weather conditions are good. This is why they need a cue for the prime conditions. Some cues can be temperature, food availability, and photoperiod. Some seasonally breeding birds hatch during the longer days of summer in photorefractory state. The HPA axis is unresponsive to long day length. Adult breeders become photorefractory around the time that molting occurs. Juveniles and adults are exposed to short winter axis before the HPG axis becomes photosensitive. When these breeders are exposed to the lengthening spring days, the HPA axis is photostimulated. Males will start to sing and females respond with a copulation solicitation display.
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Intrasex competition stimulated the avian HPA axis. Increased aggression during territory acquisition and just before egg-laying associated with the peaks in testosterone. Paired males have higher testosterone levels than unpaired males in times of breeding. If a male is removed from central territory, testosterone increases in neighbors. Otherwise testosterone is at low levels. Intrasex competition can also inhibit HPA axis. Sex steroid and gonadotropin levels often lower in subordinate members of a group.
The organizational effect of hormones occurs in early development and during a specific critical period. The activational effect is not developmental and temporary. This is seen during or soon after hormone administration. An example of these effects would be in the rat uterus, where testosterone masculinizes and defeminizes the brain. Giving estrogen does not elicit female typical sexual behaviors.
All organisms go through a developmental period that starts with reproduction. Reproduction is the production of eggs in females and sperm in males. Subsequent fertilization, or joining, occurs typically within females. There are many different types of reproductive patterns. Oviparity occurs when eggs develop outside of the mother. This is common in many fishes, most amphibians, many reptiles and all birds. Ovoviviparity occurs when eggs develop inside of the female, but without any other nutrients beyond the yolk. This happens in some fish, amphibians, and reptiles. The last reproductive pattern is viviparity which is when eggs develop inside the female’s reproductive tract with additional nutrients beyond the yolk.
The Relative Plasticity Hypothesis was developed in order to explain steroid effects in within-sex differentiation. This was created by Moore and Thompson in 1990. The organizational effects are the most important in fixed alternative systems. In this system, at least two phenotypes are possible. Animals differentiate during development to a permanent morph. Activational effects are the most important in plastic systems. In this system, animals are phenotypically the same when they are juveniles. Animals can change morphs at least once as adults.
Metabolic rate is described as energy metabolism per unit time. It is calculated in three ways. Energy metabolism is calculated when measuring oxygen levels in the oxidation processes. This assumes there is no anaerobic metabolism. This method is generally accurate as the amount of heat generated per liter of oxygen during metabolism is consistent. The source for this could be fat, protein, or carbohydrate. The second way to calculate energy metabolism is to quantify the total heat production of animal compared to food consumed. This is accurate but is also complex. The last way of calculating energy metabolism is through quantifying the difference between energy value of all food consumed and energy value from waste. This method assumes no change in the physiology of an animal and Is accurate only across a long period of time.
Dogs pant in order to cool the brain by breathing through the nose and out through the mouth. Panting occurs with many different frequencies compared to regular breathing. Normal breathing occurs at 30-40 respirations per minute whereas panting occurs at 300-400 respirations per minute. Fast panting will occur for short periods of time. fast frequency happens at resonant frequency within the respiratory system. This means that panting requires little energy.
Marine mammals have flippers that do not have blubber, meaning that they are poorly insulated. These appendages are well-supplied with blood vessels, where heat is lost to the environment. These flippers act as heat exchangers, where each artery is surrounded by veins. As the warm arterial blood flows into the flipper, it is cooled by the cold blood that surrounds it. The blood then reaches the periphery pre-cooled and loses little actual heat to the water. This counter-current system is found in many mammals such as manatees and white sharks.
Thermoregulation is a huge factor when it comes to flight in butterflies. This is also true for many winged insects. The wings need to achieve a specific temperature in order to fly. These large wings absorb heat. Thirty to forty degrees Celsius must be reached in order for a butterfly to fly. This is called a basking temperature, which is the maximum temperature achieved by a resting butterfly. A study was done to look at the physical determinants of thermoregulation in Colias butterflies along an elevational gradient. It was shown that butterflies shuttle in and out of critical temperature for flight and that the variation in temperature throughout the day effects variation in activity throughout the day.
Many living objects can emit radiation in the infrared. This is too long to be seen by humans. An example of this is a Red-headed Agama have dark bodies and light heads. This allows the lizards to have warm bodies and cool heads. An animal with black bodies absorb all types of wavelengths in the electromagnetic radiation. Polar bears have white fur and black skin. Their fur is fiber optic which means that it transports the UV radiation to and from their black skin.