Difference between revisions of "Dimorphism"
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| − | [[File:Fig 05.gif|thumb|<font size="2"> '''Fig. 1.''' Standard dimorphic or trimorphic reproductive cycle in benthic, medium- to large-sized foraminifera according to Goldstein, 1999. Schizogeny, eventually repeated several times, may be widespread in larger foraminifera from oligotrophic habitats. Planktic foraminifera seem to have no dimorphic life cycle. Life cycles are linked in various ways to seasonal cycles. Example: Heterostegina depressa d'Orbigny, equatorial sections, Gulf of Aqaba, Red Sea (from Hottinger, 1977); (Hottinger, 2006; fig. 5 [http://paleopolis.rediris.es/cg/CG2006_M02/index.html] '''CC'''/BY-NC-SA)]] | + | [[File:Fig 05.gif|thumb|<font size="2"> '''Fig. 1.''' Standard dimorphic or trimorphic reproductive cycle in benthic, medium- to large-sized foraminifera according to Goldstein, 1999. Schizogeny, eventually repeated several times, may be widespread in larger foraminifera from oligotrophic habitats. Planktic foraminifera seem to have no dimorphic life cycle. Life cycles are linked in various ways to seasonal cycles. Example: ''Heterostegina depressa'' d'Orbigny, equatorial sections, Gulf of Aqaba, Red Sea (from Hottinger, 1977); (Hottinger, 2006; fig. 5 [http://paleopolis.rediris.es/cg/CG2006_M02/index.html] '''CC'''/BY-NC-SA)]] |
[[File:Fig 70.jpg|thumb|<font size="2">'''Fig. 2.''' Odd association and polar structures in ''Praealveolina tenuis'' Reichel. From Alcantara, Lisbon; Cenomanian. Transmitted light micrographs. | [[File:Fig 70.jpg|thumb|<font size="2">'''Fig. 2.''' Odd association and polar structures in ''Praealveolina tenuis'' Reichel. From Alcantara, Lisbon; Cenomanian. Transmitted light micrographs. | ||
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*''according to Hottinger (2006):'' | *''according to Hottinger (2006):'' | ||
'''DIMORPHISM''' - coexistence of two discrete morphotypes representing different generations in the [[life cycle]] of a single species. They are expressed in the adult growth stages and/or in the [[protoconch]] and in the following nepionic chambers. The protoconch diameter is large ([[megalospheric]] = [[A - form]]) when the [[agamont]]'s protoplasm is distributed (including eventual symbionts) among the cloned offspring. The protoconch diameter is small ([[microspheric]] = [[B - form]]) when the [[gamont]]'s gametes fuse pairwise to form a [[zygote]] whith no protoplasm or symbionts from the mother. If there is dimorphism in the adult shell, the B - form becomes larger than the A - form. The compartments of the microspheric initial phases are small. It takes many growth steps to reach the initial shell size of the megalospheric generation. Reaching the adult oversize of the microspheric generation demands numerous additional instars. Consequently, the dimorphism of foraminiferal generations reflects different life times and thus different strategies of life within the same species: the microspheric generation is adapted to the permanent basic low-level carrying capacity of an oligotrophic and warm environment, while the megalospheric generation with its short life time adapts to both spring and eventual autumn seasonal peaks of carrying capacity. Nepionts with large megalospheres may have a particular architecture different from that of the adult (see [[megalospheric]] apparatus). In complex life cycles, a third ([[schizontic]]) generation may produce megalospheric shells with a morphology slightly different from that of the gamonts. | '''DIMORPHISM''' - coexistence of two discrete morphotypes representing different generations in the [[life cycle]] of a single species. They are expressed in the adult growth stages and/or in the [[protoconch]] and in the following nepionic chambers. The protoconch diameter is large ([[megalospheric]] = [[A - form]]) when the [[agamont]]'s protoplasm is distributed (including eventual symbionts) among the cloned offspring. The protoconch diameter is small ([[microspheric]] = [[B - form]]) when the [[gamont]]'s gametes fuse pairwise to form a [[zygote]] whith no protoplasm or symbionts from the mother. If there is dimorphism in the adult shell, the B - form becomes larger than the A - form. The compartments of the microspheric initial phases are small. It takes many growth steps to reach the initial shell size of the megalospheric generation. Reaching the adult oversize of the microspheric generation demands numerous additional instars. Consequently, the dimorphism of foraminiferal generations reflects different life times and thus different strategies of life within the same species: the microspheric generation is adapted to the permanent basic low-level carrying capacity of an oligotrophic and warm environment, while the megalospheric generation with its short life time adapts to both spring and eventual autumn seasonal peaks of carrying capacity. Nepionts with large megalospheres may have a particular architecture different from that of the adult (see [[megalospheric]] apparatus). In complex life cycles, a third ([[schizontic]]) generation may produce megalospheric shells with a morphology slightly different from that of the gamonts. | ||
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==See also== | ==See also== | ||
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* [[trimorphism]] | * [[trimorphism]] | ||
* [[zygote]] | * [[zygote]] | ||
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==References== | ==References== | ||
| − | Hottinger (2006), [http://paleopolis.rediris.es/cg/CG2006_M02/index.html Illustrated glossary of terms used in foraminiferal research]. [http://paleopolis.rediris.es/cg/uk-index.html Carnets de Géologie], [http://paleopolis.rediris.es/cg/CG2006_M02/index.html Memoir 2], ISSN 1634-0744 | + | Goldstein (1999), Foraminifera, a biological overview. In: SEN GUPTA B.K. (ed.), Modern Foraminifera, Kluwer Academic Publishers, Dortrecht, p. 37-55. |
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| + | Hottinger (1977), Foraminifères operculiniformes, Mémoires du Muséum National d'Histoire Naturelle, Paris, (Série C, Sciences de la terre), t. XL, 159 p. + 66 pls. | ||
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| + | Hottinger (2006), [http://paleopolis.rediris.es/cg/CG2006_M02/index.html Illustrated glossary of terms used in foraminiferal research]. [http://paleopolis.rediris.es/cg/uk-index.html Carnets de Géologie], [http://paleopolis.rediris.es/cg/CG2006_M02/index.html Memoir 2], ISSN 1634-0744 | ||
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| + | Reichel (1933), Sur une alvéoline cénomanienne du Bassin du Beausset, Eclogae geologicae Helvetiae, Basel, vol. 26, N° 2, p. 269-280. | ||
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| + | | [[Foraminifera]] | [[EForams-LINKS|FORAM-Links]] | [[CONTRIBUTORS|Contributors]] | ||
