The reciprocity between coiling direction and dimorphic reproduction in benthic foraminifera

Abstract

There are various opinions as to what parameter influences the coiling directions in foraminifera. "Do microspheric and megalospheric generations have different coiling ratios?" is an unanswered question in foraminiferal studies. Per view of this, an attempt is made to study the relationship between mode of reproduction (sexual/asexual) and coiling direction (dextral/sinistral) in the benthic foraminiferal species Rotalidium annectens (Parker & Jones). Proloculus (initial chamber) size is taken as an indicator of changes in reproductive behaviour.The present study is based on the observations made on 17722 specimens of this species from 186 samples, obtained from 3 sediment cores (representing a time span of about 9,500 years) from the shallow water region off Kanvar, west coast of India. The results indicate an inverse relationship between mean proloculus size and dextrality (YO of dextral forms) which is statistically confirmed. The correlation value (r = -0.57) between the two parameters is above the level of significance at 99% level. Therefore, it is inferred that microspheric generation (smaller proloculus) prefers dextral coiling and coiling in benthic foraminifera appears to be influenced by mode of reproduction. J. Micropalaeontol., 11 (2), 221-228, December 1992. INTRODUCTIONInnature many organisms suchas gastropods, bacterial colonies (Bacillus rnycoides), the spiral vascular conductors of some plants and the spiral distribution of leaves, show differences in coiling direction. Many trochospiral foraminiferal species possess asymmetric tests in which chambers are arranged in a cone-like spiral. This spiral may coil either in an anti-clockwise, sinistral (left handed) or in a clockwise, dextral (right handed) direction.These changes in coiling direction are the most commonly studied morphological variable exhibited by foraminifera (reviews by Scott,

Colonization of over a thousand Cibicidoides wuellerstorfi (foraminifera: Schwager, 1866) on artificial substrates in seep and adjacent off-seep locations in dysoxic, deep-sea environments

“…Two prominent mechanisms have been identified which may control benthic foraminiferal coiling direction: heritability (genetically derived) and influence by environmental conditions such as temperature (e.g., Collins, 1990;Nigam and Rao, 1989). On all SEA 3 s in this study individuals of both coiling directions were observed attached directly adjacent to one.…”

“…It has been suggested that environmental variations in bottom-water temperature can influence coiling direction in some benthic foraminiferal species (e.g., Collins, 1990;Nigam and Rao, 1989). Although bottom water temperature measurements were not recorded for the duration of these colonization experiments, no previous temperature fluctuations have ever been recorded at Hydrate Ridge and bottom-water temperatures are thought to be very consistent (~4-5°C; Tryon et al, 2002;Torres et al, 2002).…”

Relationship between abundance and morphology of benthic foraminifera Epistominella exigua: Paleoclimatic implications

“…Boltovskoy and Wright (1976) expressed similar views about the benthic foraminifera in general while stating that under normal condition number of megalospheric specimens always outnumber the microspheric specimens. As the morphological variations of the test, as well as the variation in distribution of benthic foraminifera have previously been applied to infer past climatic variations from the west coast of India (Nigam and Rao, 1989;Nigam and Khare, 1992;Nigam and Khare, 1999) the present study suggests that morphologic variations of E. exigua can also be applied to infer paleoclimatic conditions.…”

“…Besides assemblage, isotopic and elemental composition, abundance and morphology of a few foraminiferal species vary with ambient conditions and are used as paleoclimatic proxy (Thiede, 1971;Prell, 1984;Nigam and Rao, 1987;1989;Anderson and Prell, 1993;Nigam and Khare, 1999;Peeters et al 2002;Zaric et al 2005;Saraswat et al 2005a, b). The abundance and morphology of benthic foraminifera is closely associated with the reproduction which depends on the ambient environmental conditions.…”

Palaeoceanographic implications of abundance and mean proloculus diameter of benthic foraminiferal speciesEpistominella exigua in sub-surface sediments from distal Bay of Bengal fan

“…Though, in nature, the microspheric and megalospheric forms of various benthic foraminifers are always present, their relative abundance is reportedly affected by physico-chemical conditions, thus their relative abundance is utilized to study palaeoclimate (Nigam 1986). However, distinction between dimorphic forms is not always possible (Nigam and Rao 1987;Nigam and Khare 1992). In such cases, instead of ratio of dimorphic forms, mean proloculus diameter will be more useful as it will have a direct relationship with the ratio of microspheric to megalospheric forms, because higher ratio will normally be reflected in lower mean size of the proloculus (Nigam and Rao 1987).…”