The effects of pool sediments on the egg morphology of Neotropical Eulimnadia (Branchiopoda : Limnadiidae)

Studying the species distribution of Limnadiidae, a family of crustaceans, in environments favourable to their growth and reproduction is made difficult by their extremely short life cycle and the transient existence of adult forms. However, the eggs of these branchiopods are highly resistant to environmental extremes and persist in the soil of humidified and dried pools. We therefore studied the capacity to detect populations of Limnadiidae and identify them at the species level using egg morphology. We investigated influences of pool sediments on Eulimnadia (clam shrimp) egg morphology and asked whether we could rely on this morphology after various lengths of time in the soil to recognise species. We studied sediment collected from temporary pools in four Neotropical areas: Minas Gerais and Bahia (Brazil), French Guiana, and Martinique. These samples represented diverse geographical regions and climates and allowed us to study the four most widely distributed Eulimnadia species in the Neotropics: E. colombiensis, E. cylindrova, E. geayi, and E. magdalensis. Our results indicated that soil abrasion is superficial and does not affect the general shape of the eggs (cylindrical or spherical). However, details of egg ornamentation can be severely affected by the combined effects of erosion and filling with sediments, which can lead to difficulties in species identification. In the particular case of the spherical eggs of E. magdalensis, this species cannot be unequivocally identified without clean eggs collected from adults after breeding or from eggs recently deposited in the field. This work and the investigative methods described herein should facilitate identification of Eulimnadia species and promote further study of Limnadiidae crustaceans in the field.