You've likely heard of polar bears (Ursus maritimus) and grizzly bears (Ursus arctos horribilis). Have you heard of a grolar bea
r or a pizzly bear? These might be unfamiliar because they are the offspring of matings between polar bears and grizzlies. A handful of these animals have been born in zoos: three have been documented in nature. Due to their rarity, only a few grolars (grizzly dad and polar bear mom) or pizzlys (polar bear dad and grizzly mom) have been studied in detail. Their fur color, head shape, and ear shape are striking intermediates between the phenotypes of their parents. It is thought that polar bears originated from a population of brown bears (Ursus arctos) that became geographically isolated during a glaciation event that occurred about 150,000 years ago (Lindqvist et al., 2010). Traditionally the territories of grizzly bears and polar bears did not overlap, as grizzlies ranged from Alaska to Mexico, whereas polar bears stayed on the annual sea ice over the Arctic continental shelf and within the Arctic archipelagos. Relatively recently (last 50 years or so) grizzlies and polar bears have begun to come in contact in the wild. Was the origin of polar bears an allopatric or sympatric speciation event? Briefly define both terms and explain your answer.
The circulatory and respiratory systems work together to pump blood and oxygen throughout the body. Air moves in and out of the lungs through the trachea, bronchi, and the bronchioles. Blood moves in and out of the lungs through the pulmonary arteries and veins that connect to the heart and thats how it works.
