Deep sea gigantism
Deep sea gigantism (also abyssal gigantism ) describes in zoology the hypothesis that comparable taxa or fauna of the deep sea become larger with increasing water depth. The presumption of deep-sea gigantism comes from individual findings. However, systematic investigations cannot confirm that this effect is even present as a general trend, and it is discussed which influences it should be attributed to. In the oceans, the opposite is also known: gigantism of plankton eaters near the surface ( whale shark , baleen whales ).
verification
A trend towards deep sea gigantism can be investigated by systematic comparisons of the body sizes of related taxa in shallow water and deep sea.
A general deep-sea giant antism trend was identified when compared with smaller gastropods living in shallow water . A general trend could be observed for prey-seeking fish from the north-east Atlantic.
No trend towards deep-sea gigantism was noted for non-prey fish. For gastropods, which are already quite large in shallow water, the opposite trend can be observed.
The results as to whether there is actually a trend towards deep-sea gigantism are contradictory; depending on the study concept, there is no deep-sea gigantism, but also "deep-sea dwarfing".
The meio- and macrofauna of the benthos decrease with increasing water depth, which is not surprising due to the increasing scarcity of food, but the relationship between meio- and macrofauna of the benthos is not subject to any trend.
Selection pressure
In order to explain a general trend, a similar selection pressure over long periods of time is necessary. Environmental factors responsible as selection factors come here, for example. B. in question:
- Food shortage
- later sexual maturity
- Facilitating partner finding with low population density
- unequal distribution of macro foods
- even distribution of micro-food
- Coexistence with symbiotes
- Protection against predators
- permanently low temperatures (approx. 4 ° C)
- slower growth
- higher life expectancy
- Increased swimming speed and endurance
- hunt
- Claim against permanent currents
- Darkness
- reduced energy resources see food shortage
- reduced perceptibility by predators
- Water pressure
- other factors
- Combinations of several factors
Protection against predators was discussed as an explanatory model. Since it is assumed that food poverty on islands can cause the opposite trend , this frequently cited attempt to explain deep-sea gigantism does not seem generally convincing. It is of considerable importance whether the diet consists mainly of detritus or of (large) carrion or (large) live prey.
Examples
- Belt fish reach a length of up to 8 m
- Giant squids reach a length of up to 13 m ( Mesonychoteuthis hamiltoni : up to 14 m)
- Giant lice are fifty times larger than land lice
- Giant sponges of glass sponges in deep cold water
Similar and opposite trends
In the oceans there is gigantism of near-surface plankton eaters . Other general body size trends are known in polar regions ( macrofauna ). On islands, both island dwarfing and opposing island gigantism are assumed.
Single receipts
- ↑ a b c d Yoshihisa Shirayama: Size structure of deep ‐ sea meio ‐ and macrobenthos in the Western Pacific. International Review of the Entire Hydrobiology and Hydrography, Volume 68, No. 6, 1983, pp. 799-810. doi : 10.1002 / iroh.3510680605 .
- ↑ a b c d e f g h i j k l m MA Collins et al .: Trends in body size across an environmental gradient: a differential response in scavenging and non-scavenging demersal deep-sea fish. Proceedings of the Royal Society B: Biological Sciences, Volume 272, No. 1576, 2005, pp. 2051-2057. doi : 10.1098 / rspb.2005.3189 .
- ↑ a b c d e f g h i j k Craig R. McClain, Alison G. Boyer, Gary Rosenberg: The island rule and the evolution of body size in the deep sea. Journal of Biogeography, Volume 33, No. 9, 2006, pp. 1578-1584. doi : 10.1111 / j.1365-2699.2006.01545.x .