Giampaolo Rossetti

How ancient are ancient asexuals

Ancient asexual animal groups, such as bdelloid rotifers and darwinuloid ostracods, are excellent model organisms to study the effects of long–term asexuality. However, the absolute length of time that these groups have been fully asexual is mostly ignored. In the case of the darwinuloid ostracods, the fossil record shows that sexual reproduction disappeared almost completely after the end of Permian mass extinction (ca. 245 Myr ago), although several putative records of males from the Mesozoic obscure the exact time-frame of obligate asexuality in darwinuloids. Here, we re–examine the Mesozoic darwinuloid records, with regard to the reproductive mode of the assemblages. Three criteria to distinguish males in fossil populations (lack of brood pouch, position of muscle scars and size dimorphism) are used here to test for the presence of males in darwinuloid assemblages. A large, well-preserved assemblage of Darwinula leguminella (Forbes 1885) from the latest Jurassic (ca. 145 Myr ago) of England is found to be markedly variable in size and shape, but nevertheless turns out to be an all female assemblage. The exceptional preservation of the material also allows the re–assignment of this species to the extant darwinuloid genus Alicenula. All other putative dimorphic darwinuloid records from the Mesozoic are re–examined using the same criteria. The hypothesis that these assemblages represent bisexual populations is rejected for all post-Triassic (ca. 208 Myr ago) records.

Animal xenodiversity in Italian inland waters: distribution, modes of arrival, and pathways

The paper provides a list of the non-indigenous animal species occurring today in Italian inland waters. Xenodiversity was found to amount to 112 species (64 invertebrates and 48 vertebrates), which contribute for about 2% to the inland-water fauna in Italy. Northern and central regions are most affected, and Asia, North America, and the rest of Europe are the main donor continents. The large majority of non-indigenous species entered Italy as a direct or indirect effect of human intervention. A difference between invertebrates and vertebrates was found for their mode of arrival (unintentional for invertebrates and intentional for vertebrates). Accidental transport, in association with both fish (for aquaculture or stock enhancement) and crops, has been the main vector of invertebrate introductions, whereas vertebrates were mostly released for stocking purposes. Overall stock enhancement (47.92%) and culture (37.5%) prevailed over the other pathways. Seventeen and 7 species of our list are included among the 100 worst invasive species of Europe (DAISIE) and of the world (IUCN), respectively. For some (but not all) non-indigenous species recorded in Italy the multilevel impact exerted on the recipient communities and ecosystems is known, even if rarely quantified, but knowledge on their chronic impact is still missing. Additional research is needed to provide criteria for prioritizing intervention against well established invaders and identify which new potential invader should be targeted as “unwanted”.

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.

Detecting Stress at the Whole-Ecosystem Level: The Case of a Mountain Lake (Lake Santo, Italy)

Detecting the early signs of stress is imperative for the conservation of natural ecosystems. They may, however, go unrecognized because ecosystems, when disturbed, may act as sinks that absorb the external impact without showing any evident changes. This seems to be the case for Lake Santo, a small water body located in a mountainous area of northern Italy. Tourism activity in this area began to develop in the early 1970s and grew continuously over the following 20 years. This activity caused a continually increasing nutrient load into the waters, but surprisingly the lake has remained oligo-mesotrophic, as it was before human pressure became a stressor to the lake. To anticipate possible severe damage to the ecosystem, we searched for early signs of stress by carrying out a retrospective analysis based on a whole-ecosystem approach using trophic flow networks. Ecosystem properties of the lake as calculated from network analysis for the disturbed (year 1991) and unimpacted (year 1973) configurations were compared, with the support of sensitivity analysis and statistical tests. We found evidence that in the period 1970–90 nutrient enrichment did change the course of normal development as the observed increase in system throughput was accompanied by a drop in the level of mutual organization of flows, which instead would be expected to increase during the natural progression of the ecosystem. The scenario that emerged from the comparison of system-level indices, cycling activity, trophic structure, and trophic efficiency indicates that the ecosystem has been subjected to stress. In particular, the type of disturbance corresponds to a quantitative definition of eutrophication.

Ontogenetic changes in the carapace shape of the non-marine ostracod Eucypris virens (Jurine)

Developmental changes in carapace form (size+shape) during ontogeny have been explored in Eucypris virens (Crustacea, Ostracoda) using elliptic Fourier analysis. Clones from different geographic localities raised under controlled constant conditions (temperature and photoperiod) were used to characterize developmental pathways in the species. A larger data set including field populations and laboratory populations cultured under a range of environmental conditions were used to infer influence of environmental factors on carapace shape changes during ontogeny. Size changes between consecutive juvenile stages support empirical laws describing the doubling of ostracod volume at each moult. Ontogenetic changes point out the remarkable influence of environmental conditions on carapace shape.

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.

On the Darwinulidae (Crustacea : Ostracoda) from Oceania

This paper reviews the darwinulid ostracods from Australia and Oceanian islands. Eleven species in three genera have thus far been found in Australia, only the genera Microdarwinula and Alicenula are absent. Vestalenula matildae, sp. nov. is here described from Western Australia. Some taxonomic notes on other species, as well as a preliminary discussion on the distribution of the group on this continent, are also offered.

Pleistocene and Recent species of the family Darwinulidae Brady & Norman, 1889 (Crustacea, Ostracoda) in Europe

Six species in two genera of Darwinulidae are herereported from Europe; two of these are known fromfossils only.Microdarwinula zimmeri (Menzel) is, in Europe,an interstitial species. Darwinula stevensoni(Brady & Robertson), the type species of thegenus, is also the most common darwinulid. Althoughit abounds in the shallow littoral of lakes, it canalso occur in rivers, bogs and springs, both infresh and saline waters. Darwinula boteaiDanielopol is found in interstitial habitats inRumania. Darwinula pagliolii Pinto & Kotzian,originally described from Recent South Americanpopulations, is reported from fossil, Germanlocalities. Darwinula brasiliensis Pinto &Kotzian, originally described as D. africanabrasiliensis, also from South America, is hereelevated to specific rank. It has been found extantin a bog in southern France and is reported from amuseum collection from a Scottish lake. The latterspecies is here reported from Europe for the firsttime. Finally, Darwinula danielopoli n.sp. isalso described from German Holocene (Subrecent)fossils. This species represents the first nominaltaxon of a distinctly separate lineage within Darwinula s.l.Global and European distribution, history,ecological tolerance ranges, brooding and clonaltaxonomy in this group are discussed.

Molecular and morphological phylogeny of the ancient asexual Darwinulidae (Crustacea, Ostracoda)

The Darwinulidae are the only surviving post-Palaeozoic darwinulocopine family of an extensive radiation that reached its maximum in the Permian. Whereas at least some Palaeozoic darwinulids are known from sexual populations, the surviving lineages after the end-Permian mass extinction have abandoned sex since 200 million years ago. This makes the extant family Darwinulidae one of the few putative ancient asexual groups. Only about 30 species in 5 genera are presently known. The phylogeny of these taxa is here analysed using both morphological characters and molecular data. Twelve characters on valve morphology and 17 characters pertaining to appendages are used to construct the most parsimonious (unrooted) cladogram of 12 species in 5 genera. DNA sequences of one nuclear (ITS1) and a mitochondrial (COI) gene of 6 species in 5 genera are used to construct rooted maximum parsimony trees. Both molecular and morphological trees show a high degree of congruence, indicating that Alicenula and Vestalenula mostly cluster closely together, while Penthesilenula and Microdarwinula constitute a robust group. The position of the monospecific genus Darwinulais more variable, but is mostly closer to the two former genera. Congeneric species always cluster together in the morphological cladograms, and these results thus confirm that the five genera recognised by Rossetti & Martens (1998) are good phyletic units. An approximate molecular clock (calibrated with fossil data) indicates that the extant darwinulids share a common ancestor, which lived at least 100 million years ago.

Water quality and diversity of the Recent ostracod fauna in lowland springs from Lombardy (northern Italy)

The Po river plain (northern Italy) is delimited to two mountain ridges, the Alps and the Apennines. It hosts peculiar lowland man-modified springs, locally known as “fontanili”, which originate from natural resurgences occurring along the alluvial fans of the main watercourses, namely in the transition zone from the higher to lower plain which is characterized by changes in slope profile and sediment granulometry. These habitats usually show low variation in hydrological, hydrochemical and thermal conditions throughout the year. Twenty-eight springs, located in the provinces of Lodi and Cremona (Lombardy) in the alpine sub-catchment of the Po river were sampled in summer and autumn of 2004. Twenty-three of them were typical alluvial-fan springs, while the remaining five were terrace springs. The two groups of springs showed marked differences in their hydrochemical and hydrological characteristics. Sixteen ostracod species in three families (Candonidae, Ilyocyprididae, and Cyprididae) were identified. The most frequent species were Cypria ophtalmica (19 sites), Herpetocypris reptans (16), and Prionocypris zenkeri (13). Five species were found only once: Chlamydotheca incisa, Scottia pseudobrowniana, Pseudocandona compressa and Candona neglecta. Up to 6 taxa were recorded from a single site and the average number of taxa for each site was c. 3. The associations among ostracod taxa and their occurrence in relation to environmental factors were examined. Finally, the results of this survey were compared with a similar study previously conducted in 31 alluvial fan springs of the apennine sub-catchment of the Po river.