Life Cycle variation including trimorphism in the foraminifer Trochammina inflata from North European salt marshes

Author(s)

Günther Lehmann, Rudolf Röttger, Johann Hohenegger

Abstract

The proloculus diameters were analyzed in 15 samples of

200 individuals each of the agglutinated foraminifer Trochammina

inflata from five salt marsh localities in Germany,

Denmark and Sweden. Accumulations of dead specimens

from the uppermost centimeter of sediment between the roots

of salt marsh halophytes include microspheric and, as

revealed by statistical analyses, two classes of megalospheric

individuals. These size classes are consistent with the

occurrence of three generations in a trimorphic life cycle as

has been described in several other foraminiferal taxa, and

they support the interpretation of a biologically trimorphic

life cycle in Trochammina inflata. The three size classes of

proloculi correlate with: agamonts (microspheric tests),

schizonts (smaller megalospheric tests) and gamonts (larger

megalospheric tests). This interpretation, however, has not

been confirmed by studies on cultivated specimens. Other

factors that may cause the bimodal size distribution of the

megalospheric proloculi are discussed. The sample means of

the agamonts range from 16.1-22 mm, those of the supposed

schizonts from 28.6-34.2 mm and those of the supposed

gamonts from 36.5-41.7 mm. The proportions of the three

generations are used to infer long-term life cycles in timeaveraged

assemblages. Samples from Bottsand (Kiel Bight,

Germany) contain particularly high proportions of schizonts,

indicating that schizogony may be the dominant or sole mode

of reproduction at the latter sites. Proportions of gamonts are

relatively high in the Heden saltmarsh (Swedish west coast)

and in the remaining localities, indicating a higher incidence

of the dimorphic cycle, relative to the trimorphic cycle. A

varying importance of the respective mode of reproduction

results in differing proportions of reproductive products,

agamonts, gamonts and schizonts in the sediment. Previous

investigations have focussed on trimorphism in tropical

environments; herein, we present an example from temperate

supralittoral-semiterrestrial habitats subject to strong fluctuations

in water content, temperature and salinity.

Organisation(s)

Department of Palaeontology

External organisation(s)

Christian-Albrechts-Universität zu Kiel

Journal

Journal of Foraminiferal Research

Volume

36

Pages

279-290

No. of pages

12

ISSN

0096-1191

Publication date

2006

Peer reviewed

Yes

Austrian Fields of Science 2012

105118 Palaeontology

Portal url

https://ucrisportal.univie.ac.at/en/publications/0eb243dc-e9d6-41c3-ac9d-7b0bff939083