Francesc Mezquita

Exceptional cryptic diversity and multiple origins of parthenogenesis in a freshwater ostracod.

The persistence of asexual reproduction in many taxa depends on a balance between the origin of new asexual lineages and the extinction of old ones. This turnover determines the diversity of extant asexual populations and so influences the interaction between sexual and asexual modes of reproduction. Species with mixed reproduction, like the freshwater ostracod (Crustacea) morphospecies Eucypris virens, are a good model to examine these dynamics. This species is also a geographic parthenogen, in which sexual females and males co-exist with asexual females in the circum-Mediterranean area only, whereas asexual females occur all over Europe. A molecular phylogeny of E. virens based on the mitochondrial COI and 16S fragments is presented. It is characterised by many distinct clusters of haplotypes which are either exclusively sexual or asexual, with only one exception, and are often separated by deep branches. Analysis of the phylogeny reveals an astonishing cryptic diversity, which indicates the existence of a species complex with more than 40 cryptic taxa. We therefore suggest a revision of the single species status of E. virens. The phylogeny indicates multiple transitions from diverse sexual ancestor populations to asexuality. Although many transitions appear to be ancient, we argue that this may be an artefact of the existence of unsampled or extinct sexual lineages.

EFFECT OF EPISODIC AND REGULAR SEWAGE DISCHARGES ON THE WATER CHEMISTRY AND MACROINVERTEBRATE FAUNA OF A MEDITERRANEAN STREAM

Physical, chemical and biological parameters were used to investigate the effects of regular and episodic sewage inputs,either domestic or industrial, on the water quality of a smallMediterranean stream (River Magro, eastern Spain). Although results from chemical analyses were useful for monitoring waterquality in areas where sewage discharge was regular, episodic andlocalised discharges from industries or farms were not detected by chemical analyses because sampling was performed seasonally. An adequately small number of macroinvertebrate taxa were foundto indicate water quality changes within R. Magro, and the presence/absence and relative abundance of these taxa can be usedas a simple, rapid, low cost method for detecting changes in water quality. Macroinvertebrates are highly sensitive to episodic sewage discharges, which are difficult to detect by classical physical and chemical monitoring.

Food selection in Eucypris virens (Crustacea: Ostracoda) under experimental conditions

Ostracods have long been studied by scientists because their fossil remnants provide a valuable tool for the reconstruction of past environmental changes, including climate change and anthropogenic eutrophication. Relatively little is known about the physiology, behaviour and reproductive ecology of recent forms. We argue that filling this gap in knowledge requires stable cultures that can be used in laboratory studies. Here we provide quantitative information on the food preference of the common non-marine ostracod Eucypris virens. Using an experimental device allowing a free choice of eight food items, including both auto- and heterotrophic organisms, observations were carried out on groups of animals from different populations. Our results indicate that E. virens highly prefers spinach and the cyanobacterium Tolypothrix tenuis to other food items. The latter also plays an important role in maintaining the quality of the culture medium and provides a convenient substrate for moulting and egg-laying. As such, we recommend Cyanobacteria like T. tenuis as a food source for long-standing cultures of E. virens, and other non-marine ostracod species.

Endorheic versus karstic lakes: patterns of ostracod distributions and lake typology in a Mediterranean landscape (Castilla - La Mancha, Spain)

In a survey for conservation of non-marine aquatic systems, the ostracod compositions of 43 water bodies sampled in central Spain were analysed by multivariate ordination (DCA) and classification (TWINSPAN) methods, showing a clear division in lake typology. The wide variety of life modes and habitat requirements of non-marine ostracod species yields assemblages of species of value as ecological indicators. Endorheic shallow lakes, highly temporary, are characterized by an assemblage of circum-Mediterranean and endemic species. Karstic and more stable lakes are inhabited by northern Holarctic or Palaearctic species, depending on the history and environmental conditions of the water body. Between these two extremes, the study of ostracod assemblages permits the distinction, on a finer scale, of a gradient of lake types with different disturbance conditions, resulting from a combination of hydrological, climatic, chemical and anthropogenic factors. At the extreme of that gradient, highly tolerant cosmopolitan species play an important role in the ostracod community of sites severely affected by human activities.

The response of ostracod shell chemistry to seasonal change in a Mediterranean freshwater spring environment

We established the relationships between water chemistry changes in a pool fed by a permanent spring and seasonal variations in trace-element contents (Sr & Mg) in the shells of the ostracod species Herpetocypris intermedia, based on monthly collections of ostracod and water samples. The water chemistry of the investigated pool (Maïques, Valëncia, Spain) was dominated by calcium and bicarbonate, and showed marked seasonal variation in alkalinity, Ca2+ content, Sr/Ca and Mg/Ca ratios. Although the variability in the water chemistry was relatively low (~10% relative standard deviation over the entire period), the trace-element contents in the ostracod shells tracked the seasonal change in the water chemistry of Maïques pool. Moreover, due to the rapid renewal of H. intermedia population, this species is able torecord in its shells the evolution of the water chemistry at a monthly time scale. Our results also showed that, in the Maïques pool system, ostracod Sr/Ca and Mg/Ca ratios increased with the decrease in water salinity.To our knowledge, this is the first geochemical study of ostracods dwelling in spring environments. The results of this study may be applied to paleohydrological reconstruction using ostracods preserved in sediments deposited around springs (i.e. travertine and tufa deposits).

Microcrustacean and Rotiferan Communities of Two Close Mediterranean Mountain Ponds, Lagunas de Bezas and Rubiales (Spain)

ABSTRACT We compared two freshwater mountain ponds during an annual cycle by focusing on Rotifera and Crustacea. These ponds, Laguna de Bezas and Laguna de Rubiales, are located only 4.5 kilometers apart and share a similar altitude (ca. 1200 m.a.s.1) on the Iberian Mountain range, in Teruel (Spain). Bezas is near-permanent and dries out only in severe droughts; Rubiales is temporary, drying out periodically. They also show important differences in other limnological traits. Bezas has transparent water, harbors a fish population, and has a dense macrophyte cover, whereas Rubiales has elevated turbidity and neither fish nor macrophytes during most of the hydroperiod. These differences are probably why they have significantly different aquatic fauna. We found that rotifers were density-dominant in the zooplankton of Bezas, while Rubiales was dominated by microcustaceans. Ostracods were practically absent at Bezas, whereas the ostracod community at Rubiales was rich and variable.