Lecture 8 Survftxfhgjhghgxsival strategies.pptx

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1. Survival strategies

2. Dormancy Dormancy  is a period in an  organism's   life cycle  when growth, development, and (in animals) physical activity are temporarily stopped . It is a period of reduced metabolic activity that is adopted by various organisms under strenuous conditions. Dormancy helps these organisms conserve energy. Most organisms synchronize their entry to the dormancy state with the environmental changes via consequential or predictive means. Consequential dormancy takes place when an organism enters the dormancy state after the harsh conditions have started. Predictive dormancy occurs when they enter the dormancy phase right before the unfavorable conditions begin.

3. Types of dormancy Hibernation , Diapause , Aestivation , and Brumation .

4. Hibernation Hibernation  is a phase of metabolic depression and inactivity in endotherms . Hibernation is characterized by The following low metabolic rate, reduced heartbeat (by up to 95 %), slow breathing, and low body temperature.  Animals that hibernate  prepare for this phase by building up a thick body fat layer during late summer and autumn that will provide them with energy when they hibernate in winter . There are two types of hibernation : obligate hibernation and facultative hibernation.

5. obligate hibernation Obligate hibernators can sleep regardless of access to food and ambient temperatures. Obligate hibernators include European hedgehogs, mouse lemurs, various ground squirrel species, and butterflies among others. While hibernating, ground squirrels enter a state called  torpor . Their metabolism drops to as low as just 1% of summer levels and their body temperature can plummet to close to freezing. Torpor greatly reduces how much energy the animal needs to stay alive until springtime. Hibernating ground squirrel Active ground squirrel

6. facultative hibernation. Facultative hibernators hibernate when it’s too cold and food supply has reduced. Facultative hibernators include the black-tailed prairie dogs. Black-tailed prairie dogs  go into torpor for a few days at a time , and only hibernate on rare occasions during extreme cold weather conditions.

7. Brumation Brumation  is a state of dormancy in a reptile that resembles hibernation. Reptiles undergo brumation during the late stages of autumn, and they can wake up only to drink water and then go back to sleep. Reptiles consume a lot of food right before brumation since they can go for months without eating. The brumation phase can last for about eight months depending on the health, age, and size of the reptile. Brumation is usually triggered by decreased daylight hours and cold in winter. Reptiles don’t brumate fully in the first year of their lives; instead they eat less and slow down.

8. Diapause Diapause is a phase of delayed development that is marked by lower metabolic activity in response to recurring periods of severe environmental conditions. It is a predictive tactic which is determined by the animal’s genotype. Diapause is observed in all the life stages of arthropods like insects, but it’s quite common during the immobile stages like eggs and pupae . About 130 species of mammals and various oviparous fish species experience embryonic diapauses. Embryonic diapause is characterized by delayed attachment of embryos to the uterus lining resulting in the young ones being born in spring.

9. Aestivation   Aestivation  is a form of dormancy which is quite similar to hibernation, and it’s characterized by reduced metabolic rate and inactivity in response to arid conditions and high temperatures. Vertebrates and invertebrates can enter into the state of aestivation to avoid desiccation. Animals which aestivate look like they are in a lighter state of dormancy since they can reverse their physiological state rapidly and return to normal. The main concern of aestivating organisms is retaining water and conserving energy, ration the use of conserved energy while stabilizing their body organs and cells .

10. Examples of animals that undergo aestivation Lungfish ( Protopterus sp) Waterholding frogs (e.g. Cyclorana sp and Neobatracus sp, spade foot toads ( Scaphiopus  sp) Salamnder , and several species of land snails (e.g.  Helix   sp).

11. Aestivation Aestivation is typically defined as a summer or dry season dormancy. The word derives from the Latin for summer ( aestas ) or heat ( aestus ). Arid conditions that restrict water and food availability are the common trigger for aestivation, often but not always accompanied by hot summer temperatures. 

12. A form of ‘light’ dormancy involving no physiological changes that cannot be very rapidly reversed. Arousal in O. lacteal can occur within 10 min when aestivating snails are sprayed with water, as assessed both by enzymatic changes and emergence of the foot from the shell Gut tissue may regress during aestivation (e.g.  Cyclorana alboguttata  showed reduced mass and absorptive surface area of the small intestine) But skeletal muscle largely resists disuse atrophy and maintains its contractile capacity.

13. Strong metabolic rate depression during aestivation minimizes energy use to prolong total survival time, but this also means that the normal turnover of macromolecules (synthesis and degradation) is much reduced so that preservation strategies are needed to extend their functional lifespans . This is provided by mechanisms including enhanced antioxidant defenses and elevated chaperone proteins, strategies that are well-known components of the stress response but are also widely used across all forms of natural hypometabolism to support viability and life extension

14. What trigger eastivation ? Spurred on by ‘selfish genes’, all organisms are driven to grow, develop and reproduce. The primary inputs needed for this are water (the solvent of life), nutrients (both building blocks for biosynthesis and fuels for energy production) and energy (mainly ATP and reducing equivalents, mostly derived from oxygen-based respiration in animals). When one or more of these primary inputs for life is restricted or unavailable, organisms need a self-preservation strategy to help them avoid death . This frequently involves a strong suppression of metabolic rate and transition into a hypometabolic state

15. Physiological and biochemical adaptations Mechanisms to conserve energy, retain body water, ration use of stored fuels, deal with nitrogenous end products, and stabilize organs, cells and macromolecules of over many weeks or months of dormancy.

16. Diapause a period of suspended or arrested development and physiological activities are diminished in an insect, other invertebrate, or mammal embryo, especially during unfavourable environmental conditions. Considered to be a physiological state of dormancy Diapause is facultative and occurs only when induced by certain adverse environmental conditions. Insect diapause is usually triggered by environmental cues, like changes in daylight, temperature, or food availability. Diapause may occur in any life cycle stage—embryonic, larval, pupal , or adult—depending on the insect species. The first rains bring ants, mosquitoes and bugs out of diapause .

17. Diapause in mammals Embryonic diapause (ED) is a temporary arrest of embryo development and is characterized by delayed implantation in the uterus. ED occurs in blastocysts of less than 2% of mammalian species, including the mouse ( Mus musculus ).

18. First observed in the roe deer by observant hunters. They observed that there was a mystery in the roe deer between observations of the timing of mating and the time of birth, as the pregnancy seemed to continue for far longer than expected

19. Control of embryonic diapause

20. Cryptobiosis A physiological state in which metabolic activity is reduced to an undetectable level without disappearing altogether. It is known in certain plant and animal groups adapted to survive periods of extremely dry conditions.