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Diapause in aquatic invertebrates
- 1. Diapause in Aquatic Invertebrates Done by : Lamya Alsadhan
- 2. A form of dormancy, Diapause is a programmed state of developmental arrest that typically occurs as part of the natural developmental progression of organisms that inhabit seasonal environments. Diapause : Quiescence : Is a form of dormancy that begins or ends practically immediately after a change in the depressive factor, e.g. Temperature.
- 3. Why diapause is different? It is considered to be a physiological state of dormancy with very specific initiating and inhibiting conditions. Diapause does not occur as an immediate response to a simple worsening of conditions. It may last from weeks, to decades and hundreds of years in some environments such as lake sediments. The rapid improvement of environmental conditions cannot initiate the termination of diapause.
- 4. Types of Diapause Obligatory Facultative ReproductiveEmbryonic Larval Adult
- 5. Undergo this period of arrested development at the predetermined point in their life cycle, regardless of the environmental conditions. Diapause occurs in every generation. Ex: synchaeta pectinata (species of rotifers) Obligatory Diapause : Facultative Diapause : Undergo a period of suspended development only when conditions require it for survival. Ex : most copepods.
- 6. A temporary arrest of embryo development and hatching. Ex: Brine shrimp (Artemia franciscana) Embryonic Diapause : Reproductive Diapause : Which is a suspension of reproductive functions in adult. Rare in aquatic invertebrates but frequent in terrestrial insects, ex : monarch butterfly in north america
- 7. A temporary arrest and growth hold in the larval stage. Ex : occurs in numerous invertebrates, including copepods, cladocerans and rotifers. Larval Diapause : Adult (Postembryonic) Diapause : A period of suspended development in the adult form during unfavorable environmental conditions, and the halt of metabolism and other vital processes.
- 8. What causes diapause? Seasonal fluctuations. Temperature. Trophic conditions. Declining oxygen concentrations. The pressure of predators.
- 9. Stages of Diapause : Induction phase Maintenance phase Termination phase Development has ceased but physiological preparation continues, typically with a regulated decrease in metabolic rate. The metabolic rate is low and constant. diapause intensity decreases and direct development subsequently resumes, either spontaneously or in response to environmental cues
- 10. Induction phase: Its occurs at a genetically predetermined stage of life and occurs well in advance of the environmental stress. During this phase, invertebrates are responsive to external cues called token stimuli. Token stimuli can may be any change in photoperiod, thermoperiod, or allelochemicals from food source. Invertebrates that undergo Obligatory diapause don’t undergo induction phase, since they start diapuasing spontaneously.
- 11. Maintenance phase: During the maintenance phase, invertebrates experience lowered metabolism and developmental arrest is maintained. At this stage, invertebrates are unresponsive to changes in the environment that will eventually trigger the end of diapause.
- 12. Termination phase: In invertebrates that undergo obligate diapause, termination may occur spontaneously, without any external stimuli. In facultative diapausers, token stimuli must occur to terminate diapause. To emerge from diapausing state it must receive one or more token stimuli informing it that the environmental conditions (temperature, light, oxygen concentration) are acceptable. The effect of diapause slowly decreases until the insect can resume its developmental process under favorable condition.
- 13. Regulation of diapause: Environmental stimuli interact with pre defined genetic pathway to effect neural signals, endocrine pathways and metabolic and enzymatic changes. Environmental regulators of diapause generally display a characteristic seasonal pattern. Depending upon the season, invertebrates respond to the photoperiodism and thermoperiodism.
- 14. Embryonic diapause in Brine shrimp
- 15. Embryonic diapause in copepods : The production of resting eggs has been described as an adaptation to the relatively large environmental variability in these environments Most marine copepods that produce diapausing eggs occur in estuaries and other coastal waters where seasonal environmental changes are substantial.
- 17. Postembryonic (adult) diapause in copepods: Several species undergo diapause during late development as a life history strategy to avoid adverse environmental conditions, such as extreme temperatures, poor food availability, or abundant predators. Late-development diapause is characterized by: The accumulation of substantial lipid reserves. An ontogenetic vertical migration. Prolonged starvation during dormancy at depth. And emergence from dormancy to continue development and/or begin reproduction.
- 18. Significance of diapause in the aquatic invertebrates: The aquatic invertebrates are highly successful and are among the planet’s most numerous animals because diapause allows them to survive long periods of unfavorable environmental conditions. Aquatic invertebrates that undergo postembryonic diapause, the accumulation of substantial lipid reserves in preparation for diapause also makes them exceedingly nutritious prey for a wide variety of predators in the ocean. Diapause can be a key determinant of dispersal ability in aquatic invertebrates. Diapausing stages facilitate species survival during movement across geographical barriers under extreme conditions.
- 19. References: • Baumgartner, M. F., &Tarrant, A. M. (2017).The physiology and ecology of diapause in marine copepods. Annual review of marine science, 9, 387-411. • Podrabsky, J. E., & Hand, S. C. (2015). Physiological strategies during animal diapause: lessons from brine shrimp and annual killifish. Journal of Experimental Biology, 218(12), 1897-1906. • Alekseev,V. R. (2010). Physiological and molecular biological mechanisms underlying diapause in aquatic invertebrates. Russian journal of developmental biology, 41(2), 61-70. • Alekseev,V. R., De Stasio, B., & Gilbert, J. J. (Eds.). (2007). Diapause in aquatic invertebrates: theory and human use (Vol. 84). Springer Science & Business Media.
Editor's Notes
- So diapause is actually programmed in the genes of the organism, and it happens in case of less favorable conditions.
- Crustaceans have fewer diapausing stages, including embryonal, larval, and adult diapauses. In monogonont rotifers, only embryonic diapause exists, while Bdelloid rotifers spend dormancy in the adult stage
- The seasonal rhythms of meteorological conditions observed at most latitudes on the earth, lead to cyclical pulses of the main factors important for life in continental and oceanic waters. The warm season of the year is the most favorable for the overwhelming majority of aquatic organisms, and at high latitudes it is often the only period when organisms are active. Temperature optima and tolerance limits are generally similar and rather narrow for different groups of crustaceans developing during summer. Appearance of favorable temperatures is determined by one of the most stable processes, the movement of the earth around the sun. Seasonal fluctuations of temperature should be regarded as one of the fundamental factors creating the need for diapause among aquatic invertebrates. Trophic conditions are the other periodic factor essential for aquatic animals. The periodic food supply for filter feeders and their predators at latitudes with temperate and arctic climates is a result of the greater amount of solar energy in summer and the action of correlated processes such as the income of bio-organic material from deeper layers due to mixing by wind or thermal dynamics. The significance of trophic factors in the induction of diapause has been proven experimentally many times. Declining oxygen concentrations in the deepest part of highly eutrophic basins in winter and summer may be regarded as one of the causes of the interruption of active development by diapause in many crustaceans, especially those that live near the bottom. The pressure of predators, especially juvenile fish, is also a seasonal and periodic factor. Some authors consider it as the main cause of the appearance of diapause.
- During the summer months, females of the brine shrimp Artemia franciscana reproduce ovoviviparously by releasing free-swimming nauplius larvae directly from the brood pouch into the water column. With the onset of shorter days in the autumn, ovigerous females begin reproducing oviparously. Encapsulated (encysted) embryos are introduced into the brood pouch and then released into the lake. These embryos enter diapause at the gastrula stage. Although the developmental cessation is complete by the time embryos are released by the female into the water column, the metabolic depression requires several days post release. For habitats such as the Great Salt Lake, these events serve to prevent hatching and preserve nutrient stores while the embryo floats on the lake or after it has washed ashore. Whereas most of these encysted embryos overwinter on the shoreline, a fraction overwinter as floating cysts in the lake. Shoreline-deposited embryos may be subjected to cycles of dehydration and rehydration. Cold exposure and/or dehydration eventually break diapause in overwintering embryos, whether on the lake or shore. Commonly in the spring, the shoreline-deposited embryos (now post diapause) are washed back into the lake and resume active metabolism and development. However, it should be noted that some of these embryos may become entrapped in sediments/decaying algal mats along the shoreline and experience hypoxia or anoxia for varying lengths of time.
- At least 49 species of marine and estuarine copepods in the order Calanoida have been shown to produce resting or dormant eggs . The production of resting eggs by species inhabiting estuarine and neritic habitats has been described as an adaptation to the relatively large environmental variability in these environments Most marine copepods that produce diapausing eggs occur in estuaries and other coastal waters where seasonal environmental changes are substantial The diapause phase is critical to these species; many disappear altogether from the water column for months at a time when the entire population is composed of benthic diapausing eggs.
- Within a species, females may produce either subitaneous eggs, which hatch within a few days at ambient temperatures, or one or more types of resting eggs. adults are present in the water column only from November through April, Females produce subitaneous eggs during the winter and diapausing eggs during the spring. Subitaneous eggs may develop continuously or may sink into the anoxic and sulfidic sediments, where they become quiescent. The diapausing eggs sink into at least the upper 5 cm of the sediments, remain dormant throughout the summer, and do not resume development until the eggs are mixed into cool oxygenated water in the late fall Under anoxic and sulfidic conditions, diapausing eggs remain viable for extended periods relative to quiescent subitaneous eggs.
- including many species of invertebrates, fish, seabirds, and a few baleen whales.