Growth Rates of Marine Ciliates on Diverse Organisms Reveal Ecological Specializations within Morphospecies

Abstract

The growth rate of 31 stocks of Euplotes, a cosmopolitan, marine, unicellular protist, on six food species representing two different food types, microalgae and bacteria, has been determined. The 31 stocks represented nine reproductively isolated groups (biological species?) based on breeding relationships. Three morphospecies, E. vannus, E. crassus, and E. minuta, each with both autogamous and cross-breeding breeding groups, were included. The mean number of fissions completed in 5 days of a breeding group growing on one of the six food species varied from zero to 17.06. There is a strong interaction between morphospecies and food type. The largest morphospecies, E. vannus, translates the nutritional content of algae into growth better than it translates that of bacteria, while the reverse is true for E. minuta, the smallest morphospecies. Autogamous breeding groups grow more rapidly on algae than on bacteria when compared to cross-breeding groups in the same morphospecies. Two breeding groups cannot grow on Escherichia coli. ANOVA of fissions completed in 5 days revealed significant main effects and interactions between many hierarchical levels of stocks and food species. These significant interactions indicate that genetically determined ecologically important information is present at all taxonomic levels-morphospecies, breeding system, breeding group, and stock. As all these levels are biologically meaningful, measuring biodiversity in the E. vannus-crassus-minuta complex solely on morphospecies will inadequately represent the ecological diversity present in the organisms and their environment.

Differences in species richness patterns between unicellular and multicellular organisms

“…On the other hand, almost all data on protist species richness rely entirely on morphological species concepts (Fenchel et al 1997;. For both diatoms and ciliates, the validity of morphospecies has been questioned on the basis of molecular differences (Medlin et al 1991;Manhart and Court 1992), reproduction barriers (Mann 1989), and different physiology (Dini and Nyberg 1999). Structural and molecular classification may be congruent at the level of phylogenetical lineages (Taylor 1999), but may differ at the species level (Costas et al 1995).…”

A Molecular Approach to the Tangled Intrageneric Relationships Underlying Phylogeny in Euplotes (Ciliophora, Spirotrichea)

“…Chen et al, unpublished) as E. vannus SSrDNA corresponds instead to our E. crassus sequence. The diversity among E. vannus, E. crassus, and E. minuta is also clearly indicated by ecological specialization (Dini and Nyberg, 1999) and secondary metabolite production . For species determination, we used both these criteria and morphological characters.…”

Antimicrobial Activity of Euplotin C, the Sesquiterpene Taxonomic Marker from the Marine Ciliate Euplotes crassus

“…These strains have already been used in ecotoxicological studies (16,42) and were available as part of the personal collection of one of the authors of the present paper (F.D.). These ciliates were cultured at 23 Ϯ 1°C in sterile, defined artificial seawater (Allen's formula) (3) inoculated with the microalga D. salina as a food organism (17); in this medium these protozoa divide twice in 24 h. Leishmaniae. L. major (strain LRC-L137) and L. infantum (strain MHOM/ TN/80/IPT1) were maintained in vitro at 25°C in Tobie's diphasic medium modified according to the work of Taylor and Baker (46).…”