Theodore J. Abatzopoulos

Evolution and Speciation

The brine shrimp Artemia comprises a group of bisexual and parthenogenetic, morphologically similar, species very likely to have diverged from an ancestral form living in the Mediterranean area some 5.5 million years ago (Abreu-Grobois and Beardmore, 1982; Abreu-Grobois, 1987; Badaracco et al. 1987), though this estimate, based on allozymes, could be somewhat conservative as compared to that based on mitochondrial DNA (Perez et al. 1994). At that time the area was, according to geological indications, the only place in the world exhibiting for significant periods of time the very high salinity required for Artemia to thrive (Abreu-Grobois, 1987; Badaracco et al. 1987). The hypothesis of the Mediterranean as the centre of radiation for Artemia is also supported by the diversity of Artemia types currently found in the area, i.e. bisexuality and parthenogenesis on the one hand, together with diploidy and polyploidy on the other (see below).

International study on Artemia XLIX. Salinity effects on survival, maturity, growth, biometrics, reproductive and lifespan characteristics of a bisexual and a parthenogenetic population of Artemia

Two Artemia populations, a bisexual from San Francisco Bay (California, USA) and a parthenogenetic from Tanggu area (Tianjin province, Peoples Republic of China) are assayed for their tolerance and fitness in various salinity levels. This study was carried out under laboratory conditions where salinity effects upon special characteristics of the two Artemia populations, such as survival, growth rate, maturation, morphology, fecundity and life duration, were recorded. This evaluation revealed that the two populations examined exhibits significant differences in their response against elevated salinity levels. Furthermore, specific biometric parameters can be a useful tool for the discrimination and/or determination of their distribution in a mixed population, which, in fact, is the case in Tanggu salt works. Artemia franciscana seems to be a more effective colonizer at higher salinities. The data presented in this study may generate useful suggestions for proper management of the solar saltworks at Tanggu although further experimentation is needed.

Artemia sites in Iran

Field surveys were conducted in order to collect information on the occurrence of wild Artemia populations in hypersaline environments such as salt lakes, lagoons and salty rivers. The mating behaviour of Artemia populations and the presence or absence of males were carefully recorded. Sampling involved the use of plankton nets. Collected cysts were characterized on the basis of their diameter and chorion thickness, while nauplii (instar-I) were characterized on the basis of their total length. Artemia populations were found at 17 different geographical locations scattered over 12 Iranian provinces. All Iranian Artemia populations are parthenogenetic with the exception of Artemia urmiana from Urmia Lake. During the last five years severe salinity increase has caused a dramatic reduction of population sizes in several hypersaline settings in Iran. The study of cyst and naupliar biometry revealed substantial differences between populations and can be used, to some extent, for their discrimination. Cyst diameter mean values range from 243.2 to 285.4 μm. For some Iranian parthenogens, cyst diameters were among the smallest recorded so far for parthenogenetic Artemia . The total length of newly hatched nauplii ranges from 455.5 to 529.8 μm.

Artemia tibetiana: preliminary characterization of a new Artemia species found in Tibet (People's Republic of China). International Study on Artemia. LIX

In this study, we report on the existence of a new bisexual Artemia species, found in the high plateaus of Tibet (P. R. China). Different disciplines have been used to characterize this new population: biometrics of cysts and nauplii, morphometry of adults, cytogenetics, allozyme and DNA analyses and cross-breeding/fertility tests with known Artemia species. The results obtained justify that there is enough evidence to support the view that Artemia from Tibet is a new species with the proposed name Artemia tibetiana.

International study on Artemia. LIII. Morphological study of Artemia with emphasis to Old World strains. I. Bisexual populations.

A detailed morphological and allometrical study was performed withadult males and females of eleven bisexual populations of brineshrimp Artemia. Multivariate procedures, discriminant andcluster analysis, allowed to separate and group together populationswhich exhibit great genetic similarities. The eleven populationsstudied form four distinct groups: the A. franciscana group,the A. tunisiana group, the A. urmiana group and abroader group which includes Eastern Old World populations. Scanningelectron microscopy revealed differences in the male genital organsof an A. tunisiana population by lacking a medial protuberancein the base of the penes while the pattern of the ectodermal ridgesof the brood pouch of A. urmiana markedly differed from theother populations studied.

Is polyploidy a persevering accident or an adaptive evolutionary pattern? The case of the brine shrimp Artemia

Asexual organisms are confronted with substantial drawbacks, both immediate and delayed, threatening their evolutionary persistence. Yet, genetic associations with asexuality may refresh the gene pool promoting adaptation of clonal lineages; polyploidy is one of them. Parthenogenesis itself and/or polyploidy are responsible for the maintenance and spread of clones in Artemia, a sexual-asexual genus of halophilic anostracans. We applied flow cytometry, microsatellite genotyping, and mtDNA sequencing to 23 asexual populations. Artemia parthenogens have evolved multiple times either through hybridization or spontaneously. Nine out of 23 populations contained clones of mixed ploidy (2n, 3n, 4n). Most clones were diploid (20/31) while two and nine clones were triploid and tetraploid, respectively. Apomictic triploids and tetraploids formed two distinct groups of low genetic diversity compared with the more divergent automictic diploids. Polyploidy is also polyphyletic in Artemia, with triploids and tetraploids having independent origins from different sexual ancestors. We discern a pattern of geographical parthenogenesis with all clonal groups being more widespread than their closest sexuals. In favour of a specialist model, asexual diploids are restricted to single locations and are strikingly segregated from generalist triploids and tetraploids occupying a variety of sites. This is a rare pattern of mixed life-history strategies within an asexual complex.

The outcome of sperm competition is affected by behavioural and anatomical reproductive traits in a simultaneously hermaphroditic land snail.

Sperm competition is important in species with reproductive strategies that involve multiple mating and prolonged sperm storage such as the simultaneously hermaphroditic land snail Cornu aspersum. Double mating trials in this species have revealed that mating order and courtship behaviour affect paternity success. We investigated the effect of behavioural and anatomical reproductive traits on paternity success from triple mating trials. Triple mating resulted in triple fertilization in 58% of the cases whereas zero paternity was observed in 16% of sperm donors. Third sperm donors achieved higher paternity followed by first and second sperm donors. Snails with a longer epiphallus, the spermatophore forming organ, sired more offspring regardless of their mating order. Genetic compatibility between sperm donor and recipient did not influence paternity success. The results of the present study identified mating order and epiphallus length, as traits affecting the outcome of sperm competition in this species.

Salinity effects on maturation, reproductive and life span characteristics of four Egyptian Artemia populations (International Study on Artemia. LXVIII)

Three parthenogenetic Artemia populations, i.e. two coastal from Borg El-Arab and El-Max saltworks and one from the inland Qarun Lake, and a bisexual strain (Artemia salina) from the inland carbonate lake of Wadi El-Natrun, all from upper Egypt were assayed for their response in 5 salinities (i.e. 35, 80, 120, 150 and 200 g l−1). The experimental procedure was carried out under laboratory conditions, where the effects of salinity on maturation and ten reproductive and life span characteristics were investigated. The parthenogenetic Egyptian populations are more euryhaline compared to the bisexual one. The two coastal parthenogenetic populations appeared to be very similar in maturation rate and reproductive output at all salinities tested. The inland asexual strain showed a different reproductive response to the elevation of salinity from the two coastal populations. Discriminant function analysis has proven to be a useful tool in determining the differential response of closely related Artemia populations. The bisexual population showed significantly lower reproductive output compared to the parthenogenetic ones and performed best at 35 g l−1; this is the first record of an A. salina population inhabiting a carbonate lake. These findings may provide valuable information on Artemia biodiversity in an area where very little is known. %

Salinity effects on survival, growth and morphometry of four Egyptian Artemia populations (International Study on Artemia. LXVII)

Four Artemia populations from northern Egypt, a bisexual one from Wadi El-Natrun Lake, two coastal parthenogenetic ones from Borg El-Arab and El-Max saltworks and an inland parthenogenetic form from Qarun Lake, were assayed for their survival, growth and morphometric responses measured in laboratory experiments at salinities of 35, 80, 120, 150 and 200 g l−1. The survival rate was determined using regression analysis and analysis of covariance. The bisexual population (Wadi El-Natrun: WN) exhibited its best survival at 80 g l−1. All parthenogenetic strains studied performed similarly (in terms of survival) at all salinities investigated. The population growth rates were based on Von Bertalannfy’s equation. In all salinities, WN population had the lowest growth rate (based on K values) among all Artemia populations tested. It is obvious that parthenogenetic populations tolerate a broader range of salinities compared to the bisexual one. The two coastal asexual strains had similar survival, growth and morphometric characters at all salinities. Discriminant function analysis based on specific morphometric parameters permitted the assignment of adult Artemia individuals to their population of origin with a score as high as 84.6%. Furthermore, specific morphometric parameters (such as the furcal length and the number of setae in each furcal branch) are suitable discriminating characters among the populations studied.

Genetic structure and phylogeography of European catfish (Silurus glanis) populations

The genetic structure of Silurus glanis (Europe’s largest freshwater fish species) across most of its natural distribution was investigated using 10 microsatellite loci. The revealed levels of genetic diversity were much higher than previous allozyme and restriction fragment length polymorphism mitochondrial DNA analyses had shown; relative levels of variability among populations were however, in good agreement with the previous studies. Populations from large basins (Volga and Danube rivers) were the most polymorphic, while samples from the smaller Greek rivers, which are more prone to genetic bottleneck, exhibited the lowest levels of genetic diversity. Microsatellite multilocus genotyping permitted the assignment of individual fish to their population of origin with a score as high as 98.3%. Despite the great genetic differentiation of S. glanis populations, no consistent pattern of geographical structuring was revealed, in contrast to previous studies of European freshwater fish species. A model of isolation by distance seems more probable and a hypothesis of recent dispersion from only one glacial refugium is proposed. The discovery of the highest levels of microsatellite and mitochondrial diversity in the Volga sample and the presence of river connections, during the Pleistocene, between this area and all major areas of the present catfish distribution, place this refugium around the Ponto‐Caspian region. Combining these data with those from previous studies, a number of markers are now available to monitor wild and hatchery populations even at the individual level.