Is the occurrence of a sigmoidal ventral border inCyprideis torosa(Jones) valves linked to salinity? A morphometrical analysis approach

F Grossi,S Da Prato,E Gliozzi

doi:10.1144/jmpaleo2016-018

Abstract

The living euryhaline species Cyprideis torosa (Jones) undergoes morphometric variations in size, noding and sieve-pore shape linked to environmental parameters. In particular it is known that salinity values around 8–9‰ represent the osmoregulation threshold and the turning point between smaller and greater valves and prevailingly noded as opposed to un-noded valves. Here, a character never studied before is analysed: the relationship between salinity and the C. torosa valve outlines, especially the morphology of the ventral border. Geometric–morphometric analysis was carried out on different populations of C. torosa collected in oligohaline (Massaciuccoli marsh, Tuscany, and Lake Trasimeno, Umbria) and hyperhaline waterbodies (Trapani–Paceco salt pans, Sicily). The results indicate that the species displays two morphotypes: a dominant one, characterized by a straight ventral border; and a morphotype with a sigmoidal profile ventral border. This latter morphotype seems to be related to higher salinity: the oligohaline waters are characterized only by C. torosa individuals with straight ventral outline, while the hyperhaline environments are marked by the occurrence of 17.6% of sigmoidal individuals. Furthermore, the sigmoidal ventral border is more emphasized in males than in females.

Highlights

Among benthic invertebrates, ostracods are sensitive to environmental changes, being strongly dependent on several physico-chemical parameters: temperature, waterbody turbidity, energy level, chemistry of the water, dissolved oxygen content, food supply and nature of the substrate (Rodriguez-Lazaro & Ruiz-Muñoz 2012)
Cyprideis torosa populations analysed in this work are from 5 samples collected on the NE shore of the lake at depths between 0.9 and 2 m, bottom temperature from 24.5 to 26°C, bottom pH 7.65 – 8 and salinity values between 0.6 and 0.77‰, in the oligohaline range
The results of the geometric–morphometric analyses carried out on different populations of Cyprideis torosa collected in oligohaline and hyperhaline waterbodies indicate that the species displays two morphotypes: a dominant one characterized by a straight ventral border, and a subordinate morphotype with a sigmoidal ventral profile in lateral view

Summary

Introduction

Ostracods are sensitive to environmental changes, being strongly dependent on several physico-chemical parameters: temperature, waterbody turbidity, energy level, chemistry of the water, dissolved oxygen content, food supply and nature of the substrate (Rodriguez-Lazaro & Ruiz-Muñoz 2012). The euryhaline species Cyprideis torosa (Jones) can withstand and thrive in a very wide range of salinity (from 0.4 to 150‰ according to Neale (1988) and Griffiths & Holmes (2000)), but its carapace records salinity variations through changes in some morphological traits. This species is commonly regarded as a valuable palaeosalinometer for the Quaternary marginal-marine and athalassic brackish deposits (Pint et al (2012) with references therein). The aim of this work is to evaluate the occurrence of this trait through geometric–morphometric analysis and look for possible correlations with the salinity range

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Conclusion