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 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.