pH-related Hatching Success of Triops cancriformis (Crustacea: Branchiopoda: Notostraca)

Six different pH ranges were tested for the hatching rate of Triops cancriformis cysts. Cumulative hatching numbers approach to approximately 50% of cysts. The highest hatching rates, co-occurring with the shortest hatching times, were recorded in the neutral range. No hatching took place at pH values 9 and above. This corresponds with the most frequent habitats of this species, snowmelt pools of river flood plains as well as aestival pools caused by heavy rainfalls. Occurrences in sodic alkaline pans can be explained by relatively low pH values at the time of inundation.     

Ultrastructural observations on the oogenesis of Triops cancriformis (Crustacea,Notostraca)

Summary The first stages of the oogenesis of Triops cancriformis have been studied. At the outset the oocyte is smaller than the nurse cells. Meiosis begins with typical synaptonemal complexes. The significance of these complexes and of some other peculiar structures of germ cells, i.e., pore complexes and annuli within the nucleus, and annulate lamellae within the cytoplasm are discussed. The morphofunctional uniformity of some cytoplasmic structures (annulate lamellae, concentrically arranged ER, and yolk globules) in the oocyte as well as its nurse cells is also discussed.     

Ultrastructural observations on the oogenesis of Triops cancriformis (Crustacea,Notostraca)

Summary Each ovarian follicle of Triops cancriformis is four-celled; these cells (one oocyte and three nurse cells) are interconnected by cytoplasmic bridges. In the course of differentiation, the nurse cells are early recognizable; they increase in size more than the oocyte and their nuclei contain many nucleoli. For the first time in Arthropoda, yolk globules are reported to be present in nurse cell cytoplasm; these globules arise from the smooth endoplasmic reticulum. The functional significance of the intercellular bridges and the trophic role of the nurse cells are discussed.The authors are grateful to Dr. Bruno Sabelli for his support and to Mr. Francesco Monte for his technical assistance     

Mitochondrial and nuclear DNA variability in the living fossil Triops cancriformis (Bosc, 1801) (Crustacea, Branchiopoda, Notostraca)

The living fossil Triops cancriformis comprises bisexual (either gonochoric or hermaphroditic) and unisexual populations. Genetic surveys have recently revealed a general trend of low differentiation of 12S and 16S mitochondrial genes. We, therefore, surveyed further mitochondrial (COI gene and control region) and nuclear markers (dinucleotide microsatellites) to assess the genetic variability and to establish any relationship with the different reproductive modes found in European populations. The mitochondrial analyses confirmed the pattern of low variability. Hence, the low mitochondrial genetic variability appears as a common feature of the genus Triops. The microsatellite analysis found that Italian populations are monomorphic or exhibit little polymorphism, while other European samples display a higher degree of polymorphism and private alleles. Spanish, Austrian and Italian populations show patterns of Hardy-Weinberg disequilibrium that could be explained by the mode of reproduction, or by a higher frequency of null alleles in these populations. The low diversity and differentiation among Italian populations lead us to question the Monopolization Hypothesis. One microsatellite locus appears to be sex-linked, with heterozygotes detected only in males and hermaphrodites.     

Sister species within the Triops cancriformis lineage (Crustacea, Notostraca)

We investigated the phylogenetic relationships among the three presently recognized subspecies of the tadpole shrimp, Triops cancriformis , using mitochondrial 16S and 12S rDNA sequences. Our results indicate that the taxon is divided into two distinct lineages. One lineage is formed of T. c. cancriformis populations and samples from northern Spain that had been classified as T. c. simplex in the most recent literature. The second lineage comprises all populations of T. c. mauritanicus and northern African populations of T. c. simplex . These two main lineages separated 2.3 to 8.9 million years ago, based on the range of inferred molecular clocks recognized for crustacean mtDNA sequence divergence. Percentages of divergence are in the range reported for recognized species in other notostracan lineages and we therefore propose to recognize them as two species, Triops cancriformis and Triops mauritanicus . The latter would comprise two subspecies in northern Africa, one consisting of the Moroccan populations of the former T. c. mauritanicus , the other comprising the African populations of the former T. c. simplex . It also includes three as-yet unnamed lineages. A comparison of morphological characters with the molecular data revealed that the former T. c. simplex cannot be reliably separated from T. c. cancriformis , using morphological characters that have hitherto been used to distinguish among subspecies of T. cancriformis . Our investigation is the first to demonstrate the presence of T. c. cancriformis in Africa (Tunisia). The genetic haplotypes of these populations are identical with haplotypes also occurring in Central and Western Europe, as well as in Sicily. Therefore, we hypothesize that the African populations of T. c. cancriformis represent a result of repeated long-distance dispersal across the Mediterranean Sea.     

SEM studies on the early larval development of Triops cancriformis (Bosc)(Crustacea: Branchiopoda, Notostraca)

We investigated early larval development in the notostracan Triops cancriformis (Bosc, 1801–1802) raised from dried cysts under laboratory conditions. We document the five earliest stages using scanning electron microscopy. The stage I larva is a typical nauplius, lecithotropic and without trunk limbs. The stage II larva is feeding and has trunk limb precursors and a larger carapace. Stage III larvae have larger trunk limbs and a more adult shape. Stage IV larvae have well developed trunk limbs, and stage V larvae show atrophy of the antennae. We describe the ontogeny of selected features such as trunk limbs and carapace, discuss ontogeny and homologization of head appendages, follow the development of the feeding mechanism, and discuss trunk limb ontogeny.     

Experimental test of the ecosystem impacts of the keystone predator Triops cancriformis (Branchiopoda: Notostraca) in temporary ponds

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Population dynamics of Triops cancriformis (Crustacea: Branchiopoda: Notostraca) of the Espolla temporary pond in the northeastern Iberian peninsula

The population dynamics of Triops cancriformis in Espolla temporary pond (NE Iberian peninsula) were studied during 1996 and 1997, which encompassed six flooded periods. Data were collected on each individual's size, sex, and, if female, on number of eggs in the oostegopodes. Male-biased sex ratios were found only in the drying-out phase and variations in fecundity were strongly related to hydroperiod duration. Sex ratio variation during the drying-out phase can be attributed to female mortality because the very low recruitment observed does not support the hypothesis of an increase of males. Two hypotheses are advanced to account for female mortality: (1) differential reproductive effort, and (2) size selective predation by herons. This population is characterised by low values of maximum densities compared with other notostracan populations, and by higher densities in the spring–summer hydroperiods than in the winter ones.     

R2 dynamics in Triops cancriformis (Bosc, 1801) (Crustacea,Branchiopoda, Notostraca): turnover rate and 28S concerted evolution

The R2 retrotransposon is here characterized in bisexual populations of the European crustacean Triops cancriformis. The isolated element matches well with the general aspects of the R2 family and it is highly differentiated from that of the congeneric North American Triops longicaudatus. The analysis of 5′ truncations indicates that R2 dynamics in T. cancriformis populations show a high turnover rate as observed in Drosophila simulans. For the first time in the literature, though, individuals harboring truncation variants, but lacking the complete element, are found. Present results suggest that transposition-mediated deletion mechanisms, possibly involving genomic turnover processes acting on rDNAs, can dramatically decrease the copy number or even delete R2 from the ribosomal locus. The presence of R2 does not seem to impact on the nucleotide variation of inserted 28S rDNA with respect to the uninserted genes. On the other hand, a low level of polymorphism characterizes rDNA units because new 28S variants continuously spread across the ribosomal array. Again, the interplay between transposition-mediated deletion and molecular drive may explain this pattern.     

Predation in a temporary pond with special attention to the trophic role of Triops cancriformis (Crustacea: Branchiopoda: Notostraca)

Temporary ponds are described as environments with a low predation pressure. Notostracans inhabit these types of ponds, and some populations acquire a high proportion of larger individuals, whose feeding behaviour is mainly predatory. The predation nature of Triops cancriformis is not widely accepted, because its diet is still partly controversial. We analysed the diet of one population of T. cancriformis in a Mediterranean temporary pond (Espolla pond, NE Iberian peninsula) to evaluate its predation behaviour. The gut content of the individuals bigger than 10 mm is mainly composed of detritus, plant fibres and microcrustaceans (cladocerans, ostracods and copepods). The prey number increases with the body size of individual T. cancriformis as previously described. Sex-biased predation was observed for one copepod prey, but not for the other. Predation pressure in that community was monitored along six hydroperiods as the percentage of predator biomass (not only T. cancriformis) in relation to the non-predator biomass. The proportion of predator biomass is high, and this contrasts with the low predation pressure expected for a temporary system with short hydroperiods.     

Ultrastructure of the male gonad and male gametogenesis in the clam shrimp Eulimnadia texana (Crustacea, Branchiopoda, Spinicaudata)

Abstract. The ultrastructure of the male gonad of Eulimnadia texana (Branchiopoda, Spinicaudata) has been observed for the first time to investigate the sexuality of a well-studied case of androdioecy in the animal kingdom. The male gonad is a double structure located in the hemocoel throughout the entire body length on each side of the midgut. Male gametes originate from the wall and mature centripetally toward the lumen; the proliferative activity is very high and continuous and therefore the mature gonad is full of numerous germ cells. Inside the lumen several degenerative stages are found mixed with sperm cells and spermatids, the latter two being not easily distinguishable because of the slight differences between them. The evolutionary meaning of the degenerative process in E. texana male gametes is difficult to explain, and we propose some hypotheses about its possible role or cause in the studied population: (a) to help build spermatophores, (b) to act as a trophic component for viable sperm, (c) as a manifestation of inbreeding depression, and/or (d) to regulate the number of sperm cells.     

Orientation responses of Triops granarius (Lucas) (Branchiopoda: Notostraca) and Streptocephalus ssp. (Branchiopoda: Anostraca)

Summary Triops granarius and Streptocephalus spp. show an orthokinetic response and swim faster in light than in darkness. Triops is negatively, Streptocephalus positively phototactic. The lethal temperature for 24 hours' exposure is 34°C for Triops, 35°C for Streptocephalus. Temperatures around 29°–30°C are preferred by both to 20°C or 33°C. Phototaxis overrides these temperature reactions in Streptocephalus but not in Triops. Both swim against water currents: Triops does not become habituated to mechanical stimuli upon responses to which its survival may depend.

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Résumé Le Triops granarius et le Streptocephalus spp. ont une réaction orthocinétique et se déplacent plus vite dans la lumière que dans le noir. Le Triops est négativement phototactique, le Streptocephalus l'est positivement. La température mortelle pour une exposition de 24 h. est 34°C pour le Triops et 35°C pour le Streptocephalus. Tous les deux préfèrent des températures de l'ordre de 29°–30°C plutôt que de 20°C ou 33°C. Le phototactisme domine ces réactions aux température chez le Streptocephalus mais pas chez le Triops. Tous les deux se déplacent contre les courants: le Triops ne peut pas s'accoutumer aux excitents méchaniques, même si sa vie dépend de sa réaction à ces excitents.

     

Adult Triops cancriformis (Pancrustacea: Notostraca) mediates the hatching rate of its resting eggs

Hydrobiologia - The resting eggs of large branchiopods do not hatch all at once during a hydroperiod; instead, a fraction of the eggs are left dormant to cope with unstable conditions in temporary...     

The formation of the nervous system during larval development in Triops cancriformis (Bosc) (crustacea,Branchiopoda): An immunohistochemical survey

We provide data of the development of thenervous system during the first five larval stages of Triops cancriformis. We use immunohistochemical labeling (against acetylated α‐tubulin, serotonin, histamine, and FMRFamide), confocal laser scanning microscopy analysis, and 3D‐reconstruction. The development of the nervous system corresponds with the general anamorphic development in T. cancriformis. In larval stage I (L I), all brain parts (proto‐, deuto‐, and tritocerebrum), the circumoral connectives, and the mandibular neuromere are already present. Also, the frontal filaments and the developing nauplius eye are already present. However, until stage L III, the nauplius eye only consists of three cups. Throughout larval development, the protocerebral network differentiates into distinct subdivisions. In the postnaupliar region, additional neuromeres and their commissures emerge in an anteroposterior gradient. The larval nervous system in L V consists of a differentiated protocerebrum including a central body, a nauplius eye comprising four cups, a circumoral nerve ring, mandibular‐ and postnaupliar neuromeres up to the seventh thoracic segment, each featuring an anterior and a posterior commissure, and two parallel connectives. The presence of a protocerebral bridge is questionable. The distribution of neurotransmitters in L I is restricted to the naupliar nervous system. Over the course of the five stages of development, neurotransmitter distribution also follows an anteroposterior gradient. Each neuromere is equipped with two ganglia innervating the locomotional appendages and possesses a specific neurotransmitter distribution pattern. We suggest a correlation between neurotransmitter expression and locomotion. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

Ultrastructural characterization of the gonads of Triops cancriformis (Crustacea, Notostraca) from populations containing both females and males: no evidence for hermaphroditic reproduction

 The gonads of female and male Triops cancriformis specimens from populations of the northern part of the species distribution area were examined by conventional transmission electron microscopy in order to gain insight into the complicated reproductive mode of the species. Ovarian follicles consisted of an oocyte and three nurse cells and were surrounded by a thin layer of follicular cells. Oocytes are initially smaller than nurse cells and contained mitochondria of the cristae type as well as many free ribosomes. The prominent nucleus contained a nucleolus. The cytoplasm of oocytes was filled with yolk globules that were surrounded by membranes of the endoplasmic reticulum. Nurse cells also contained yolk globules. The follicle duct walls consisted of closely packed elongated cells covered by a lamellar basal lamina. No distinct Golgi apparatus was found in the follicle duct cells. The passage of oocytes through the duct was accompanied by a marked flattening of the follicle duct cells. Simultaneously, the oocytes were wrapped in eggshell material before entering the longitudinal oviduct. Testicular lobes were not found in any of the investigated female specimens. In male animals, the epithelial wall of the testicular tubules consisted of both germinal and vegetative cells. Maturing spermatids formed multicellular nests located in clearly delimited cysts in the intercellular space of the testicular epithelium. The lumen of the testicular tubules contained, exclusively, free mature spermatozoa. These characteristics point to the cystic type of spermiogenesis. Mature spermatozoa were non-flagellate, had a regular ovoid shape of 4–5 μm diameter, and an acrosome was not found. Only a negligible amount of spermatozoa (< 5%) showed signs of degeneration. In conclusion, the results provide evidence for a parthenogenetic and/or bisexual reproduction mode rather than a hermaphroditic one in the populations examined. Accepted: 4 August 1997     

Molecular taxonomy and phylogeny of the 'living fossil' lineages Triops and Lepidurus (Branchiopoda: Notostraca)

Mantovani B. Cesari M. & Scanabissi F. (2004). Molecular taxonomy and phylogeny of the 'living fossil' lineages Triops and Lepidurus (Branchiopoda: Notostraca). — Zoologica Scripta , 33 , 367–374.
European Triops cancriformis and Lepidurus apus were analysed for 12S and 16S mitochondrial genes and compared to North American and Japanese taxa. There are no cryptic species among European T. cancriformis populations , which are highly homogeneous in comparison to conspecific Japanese samples. T. cancriformis differs from congeneric taxa all over its range, which can be explained by its antiquity. In contrast, the parapatric subspecies L. apus apus and L. apus lubbocki are morphologically conserved and differ substantially at the mtDNA level. The genetic distance values between them are of the same order of magnitude as those observed between American Lepidurus species. Their subspecific status therefore requires further analysis. L. apus apus is more closely related to a L. arcticus sample from Iceland than to L. apus lubbocki . It is also related to a Canadian L. couesii population. Further analyses of populations from the whole range of L. arcticus and the European range of L. couesii are needed to understand the relationships among these notostracan taxa. When considering the two genera, it is clear that Lepidurus is a well supported monophyletic unit, while Triops is polyphyletic, embodying very divergent taxa.     

Trypsin-like enzymes from two morphotypes of the 'living fossil' Triops (Crustacea: Branchiopoda: Notostraca)

Trypsin-like enzymes from two morphotypes (here called short and long) of the 'living fossil' Triops of Baja California Sur, Mexico were studied. Adults of both morphotypes were obtained from outdoor static cultures using dry soil from the natural habitats as a source of cysts and culture substrate. Individual and pooled extracts were made from dissected digestive tubes. The effect of pH and temperature on the trypsin activity was studied using N-alpha-benzoyl-DL-Arg-p-nitroanilide (BAPNA) as substrate. The highest proteolytic activity was found at the same pH with extracts of both morphotypes. At this pH, there was greater proteolytic activity at a lower temperature with the short morphotype extract than with the long morphotype extract. Substrate-SDS-PAGE zymograms showed bands of activity. Short morphotype extracts produced six bands; five of them were serine proteases of which three were trypsin-like enzymes. Long morphotype extracts revealed eight bands; six of them were serine proteases of which three were trypsin-like enzymes.     

Characterization of dinucleotide microsatellite loci in the living fossil tadpole shrimp Triops cancriformis (Crustacea Branchiopoda Notostrace)

Five dinucleotide markers were obtained from a microsatellite genomic library of the tadpole shrimp Triops cancriformis. The number of alleles at each locus was low (maximum three alleles) but all loci were polymorphic. The presence of null alleles could not be disregarded. Heterozygosity levels were indicative of selfing in the studied populations whose real sexuality will be further tested using these markers.     

Reproductive isolation and genetic differentiation in North American species of Triops (Crustacea: Branchiopoda: Notostraca)

Electrophoretic analysis of 31 populations, ranging from California to Kansas, indicates that the North American tadpole shrimp Triops longicaudatus (LeConte) is actually a mixture of at least two reproductively isolated species. In the central United States, the predominant species is T. longicaudatus, which is found typically in ephemeral prairie pools. In the southwestern United States, the predominant species is Triops newberryi (Packard), which characteristically inhabits large playa pools. The two species coexist occasionally and in sympatric situations they are reproductively isolated from each other. The two species are genetically distinct at a level greater than is typical of conspecific populations. These genetic differences are correlated with subtle morphological differences and profound differences in reproductive biology. Both species represent complexes of bisexual and unisexual populations. Bisexual populations of T. longicaudatus are usually composed of males and females in approximately equal frequencies; bisexual populations of T. newberryi are composed of males in low frequencies and self-compatible hermaphrodites. Unisexual populations of both species apparently consist entirely of self-compatible hermaphrodites. This revised version was published online in August 2006 with corrections to the Cover Date.