Olivia Hagen and Maeve Kolk
BIO 342: Animal Behavior
Hibernation in Endotherms
Phylogeny
Evolution
Over time, the consistent need to hibernate during times of lacking resources and low temperatures caused a few different ways of surviving such as, having food catches in burrows and using only body fuel reserves to last for months.
SCN Differences Between Endotherms and Ectotherms
The hypothalamic suprachiasmatic region (SCN) mentioned in our Mechanism section is also an example of phenotypic divergence. In endothermic animals, decreases in external temperature do not directly induce torpor and largely do not affect circadian oscillators. Ectothermic animals, without homeostatic thermoregulation, are affected by external temperature change through circadian oscillators. This shows a phylogenetic divergence between endothermic and ectothermic animals. The SCN of endotherms has evolved to entrain circadian rhythms using photo periods instead of external temperature.
Metabolism Across Evolutionary Clades
Hypo metabolism (metabolic rate suppression) is widely conserved across phylogenies as a survival strategy to deal with extra environmental stress. Most endotherms experience hypometabolism during hibernation and create triglyceride storages in adipose tissues for later use. However, many anoxia-tolerant species amass glycogen for glycolysis during hypometabolism; similarly anhydrobiotic organisms also do this but glycogen goes into synthesis of polls and sugars. A Story and Storey (2007) paper suggested that the mechanisms of hypo metabolism and hibernation are perhaps present in all species but latent in those that have abandoned them (e.g. humans) as defense strategies against stressful environments.