Spira mirabilis inHeterostegina: evolutionary and ecological perspectives

Morphometric analysis of the marginal spiral outline ofHeterosteginapopulations belonging to theocalana-matteucciilineage reveals that it fully fit with a logarithmic spiral identified by two variables: the initial radius (IRex) and the radius increase (Rinc). Spirals tend to become more looser through time as observable also in well-known Mediterranean lineages.Rinctends to increase along a phyletic line leading to the definition of a trend of neanic acceleration inHeterostegina, defined as the tendency of the marginal spiral to become looser. Ecophenotypical variations, with high value ofRincin respect to coeval populations, may occur as for other routinely employed biometric values for nummulitids, but the investigated populations can be well-constrained in aRinc-Xbivariate plot, whereXindicates the number of undivided chambers. The spiral outline, going looser, seems to tend become a golden spiral, a spiral defined by value ofRincof 0.306, leading to a recognition of golden selection in Heterostegininae.

Automated summary

The morphometric analysis of marginal spiral outlines in Heterostegina populations belonging to the ocalana-matteuccii lineage indicates a full fit with a logarithmic spiral defined by two variables, with the spirals tending to become looser over time. Additionally, there is an increase in Rinc along a phyletic line leading to a neanic acceleration trend in Heterostegina, and ecophenotypical variations are well-constrained in a Rinc-X bivariate plot. The spiral outline appears to tend towards a golden spiral, characterized by a Rinc value of 0.306, suggesting the presence of golden selection in Heterostegininae.