Abstract
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 Karwar, west coast of India. The results indicate an inverse relationship between mean proloculus size and dextrality (% 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.
Highlights
Innature many organismssuchas gastropods,bacterialcolonies (Bacillus rnycoides), the spiral vascular conductors of some plants and the spiral distribution of leaves,show differencesin coiling direction
For some speciesarguments have been made in favour of their use as paleotemperature indicators, a number of contradictionshave been observed and they failto consistently correlate with cold and warm periods (Thiede, 1971; Parker, 1971;Olsson, 1974).For example,higher dextral/sinistralratios in the planktonic foraminiferal species G. truncatulinoides has been considered tobe an indicator of higher temperature in the North Atlantic (Bandy, 1960;Takayanagi et al, 1968;BC, 1969) and in the Pacific Ocean (Parker & Berger, 1971) off Portugal and Moroccomostly dextral G. truncatulinoides were found in glacial sediments (Thiede, 1971).Wollin et al (1971) had the same opinion
It is important to notice that in each core the average mean proloculus size of specimens showingdextralcoilingisinvariablysmallerthan thosecoiled sinistrally(Table5).Thisshowsthat dextrallycoiledspecimens are associatedwith smallerproloculus,which is a characteristic of sexually formed microspheric forms
Summary
Innature many organismssuchas gastropods,bacterialcolonies (Bacillus rnycoides), the spiral vascular conductors of some plants and the spiral distribution of leaves,show differencesin coiling direction. For some speciesarguments have been made in favour of their use as paleotemperature indicators, a number of contradictionshave been observed and they failto consistently correlate with cold and warm periods (Thiede, 1971; Parker, 1971;Olsson, 1974).For example,higher dextral/sinistralratios in the planktonic foraminiferal species G. truncatulinoides has been considered tobe an indicator of higher temperature in the North Atlantic (Bandy, 1960;Takayanagi et al, 1968;BC, 1969) and in the Pacific Ocean (Parker & Berger, 1971) off Portugal and Moroccomostly dextral G. truncatulinoides were found in glacial sediments (Thiede, 1971).Wollin et al (1971) had the same opinion This could be due to the disagreement concerning the temperature conditions of species, as some species appear to be more tolerant of low temperature in the southern hemisphere than in the northern hemisphere (Be, 1969;Boltovskoy,1969,1970;B6 & Tolderlund, 1971).Kennett & Huddlestun (1972) indicated that the same species may show more one response to a particular environment. In the North Atlantic, G. quinquelobn showed no preference between dextral and sinistral, G. pachyderm displayed a seasonal alternation in preferred coiling direction, whereas G. truncatulinoides had a distinctly preferred coiling direction regardless of season or temperature. (Tolderlund & BC, 1971)
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