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Resting eggs bank and their hatching pattern in two co-occuring anostracans Phallocryptus spinosus and Branchinectella media (Crustacea) from saline lakes of the Aurès region (Northeastern Algeria)
Abstract
Phallocryptus spinosus (Milne-Edwards, 1840) and Branchinectella media (Schmankewitsch, 1873) are two anostracan species co-occurring in several saline lakes of the eastern steppic zone of Algeria. Both species produce resting eggs to persist in their temporary and unstable habitats, constituting a resting eggs bank. B. media has a wide and scattered distribution area, and it is known to prefer cold temperatures (16 °C max). Resting egg banks and hatching patterns of both species have been assessed in seven saline lakes. Results showed that densities of P. spinosus resting eggs were always higher than those of B. media, whatever the lake (F = 4.66, p = 0.0005). They range between 93,000 ± 75 and 1,495,000 ± 366.5 resting eggs m −2 for P. spinosus, and between 670 ± 30 and 365,000 ± 268 resting eggs m −2 for B. media. Hatching percentages of eggs incubated at temperatures of 16 °C and 22 °C, and salinities of 0 and 5 psu, showed that 16 °C and 5 psu was the most suitable combination for B. media, since 38.88 ± 1.93% of eggs hatched under these conditions. For P. spinosus, 81.11 ± 1.92% of eggs hatched at 22 °C and 5 psu. Resting eggs diameters measurements of both species as well as scanning electron micrographs of B. media are provided.
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The fairy shrimp Branchinectella media, because of its passive dispersal capacity and scarce and irregularly distributed habitats (temporary saline aquatic systems), is an intriguing organism from a population genomics and conservation per- spective. Stochasticity of dispersal events and the irregular distribution of its habitat might lead to low levels of population connectivity and genetic diversity, and consequently, populations with limited persistence through time. Indeed, by using genomic data (SNPs), we found a strong genetic structure among some of the geographically isolated Iberian populations of B. media. Interestingly, we also obtained high estimates of effective population sizes. Lack of suitable habitat between populations (absence of a “stepping stone” network) and strong genetic differentiation suggest limited dispersal success in B. media. However, the high effective population sizes observed ensure persistence of B. media populations against genetic stochasticity (genetic drift). These results indicate that rescue-effect might not be essential for population persistence if they maintain high effective population sizes able to hold adequate levels of genetic diversity. Should high population sizes be reported in other low dispersing Anostraca, one might be optimistic with regard to their conservation status and fate, provided that their natural habitats remain undisturbed.
1. We review progress in our understanding of the importance of waterbirds as dispersal vectors of other organisms, and identify priorities for further research.
2. Waterbirds are excellent for long-distance dispersal (LDD), whereas other vectors such as fish and mammals disperse similar propagules, but over shorter distances. Empirical studies of internal and external transport by waterbirds have shown that the former mechanism generally is more important. Internal transport is widely recognised for aquatic plants and aquatic invertebrates with resting eggs, but also is important for other organisms (e.g., terrestrial flowering plants not dispersed by frugivores, bryophytes, tardigrades, fish eggs).
3. Waterbird vectors also are important in terrestrial habitats, and provide con-nectivity across terrestrial-aquatic boundaries. There are important differences in the roles of different waterbird species, especially those using different habitats along the aquatic-terrestrial gradient. Early attempts to predict zoochory based on propagule morphology have been found wanting, and more research is needed into how the traits of vectors and vectored organisms (including life history , dormancy and growth traits) explain dispersal interactions. Experimental studies have focused on the potential of propagules to survive internal or external transport, and research into factors determining the establishment success of propagules after dispersal is lacking.
4. Recent spatially explicit models of seed dispersal by waterbirds should be expanded to include invertebrate dispersal, and to compare multiple bird species in the same landscape. Network approaches have been applied to plant-waterbird dispersal interactions, and these are needed for invertebrates. Genetic studies support effective LDD of plants and invertebrates along waterbird flyways, but there remains a lack of examples at a local scale. Next Generation Sequencing and genomics should be applied to waterbird-mediated dispersal across the landscape. More studies of biogeography, community ecology, or population genetics should integrate waterbird movements at the design stage.
The distribution, status, and phenology of the anostracan Phallocryptus spinosus in Sicily are described.
The only population of the species to date known to occur with certainty on the island inhabits a few temporary water bodies located within the Natura2000 site “ITA010006 - Paludi di Capo Feto e Margi Spanò”. In these sites, the species co-occurs with an interesting halophilous flora and crustacean fauna.
Based on available data, the concentration of dissolved salts in the water bodies seems to be the main driver of the life histories of the co-existing populations of the anostracans Artemia salina and Phallocryptus spinosus.
Invertebrate species from temporary aquatic ecosystems produce resistant dormant stages (i.e. eggs) that accumulate in long lived mixed egg banks in the sediment. These dormant eggs not only bridge dry phases but also act as propagules for passive dispersal. Large branchiopod crustaceans (e.g. Notostraca, Anostraca and Spinicaudata) produce dormant eggs of variable shapes, sizes and external ornamentation. While these characteristics are often species-specific and have been used in taxonomy, little is known about their ecological significance, for example, their contribution to colonisation success. Here, we explore the idea that variation in egg morphology may impact vector-mediated dispersal and colonisation success of large branchiopods. We studied egg banks from 98 temporary waters across the Northern Cape, South Africa and assessed whether distribution and densities of eggs carried a morphological signal. Overall, our results imply that both size and external structures may impact dispersal to and successful colonisation of temporary waters by large branchiopods. Specifically, our results show that small propagules (< 200 µm) and eggs with external traits (hooks or spines) that facilitate substrate adhesion were most confined in their distribution. In contrast, large (> 400 µm), smooth eggs and medium sized (200–300 µm), polygonal eggs were most widely distributed. Ultimately, our approach provides insight in actual colonisation success of species with different egg types and not only on the propensity of the eggs to be picked up and transported by vectors.
Organisms evolve to maintain fitness across generations, while short-term fitness in stochastic habitats such as temporary wetlands may be highly varied. As typical temporary wetland inhabitants, large branchiopods rely on bet hedging hatching that helps them survive throughout generations. An optimal hatching rate is predicted to be approximate to the successful reproduction probability (SRP). We tested the difference between hatching rate and SRP of large branchiopods Branchinella kugenumaensis and Eulimnadia braueriana in a temporary wetland in Taiwan, through field surveys and climatic records to evaluate their SRP. Comparisons were performed under two proposed scenarios, where a population’s hatching was bet hedged for a hydroperiod or for a wet season (with several hydroperiods), respectively. Population size fluctuations were simulated for these two scenarios under assumed egg mortalities and reproductive replenishments. Results showed that the hatching rates only fitted to SRP for E. braueriana under the scenario of bet hedging on a wet season, not for B. kugenumaensis, nor for both species under the scenario of bet hedging on a hydroperiod. Bet hedging on a wet season would have a smaller range of population size fluctuation and a lower rate of population size decrease. This implies that large branchiopods adopt a conservative hatching strategy, lowering the hatching fraction in each hydroperiod to reduce long-term egg bank size fluctuation. Bet hedging strategies could occur during other life cycle stages, coexist with other life history strategies, and lead to the diversified hatching fraction distribution rather than a single, optimal fraction throughout hydroperiods.
ABSTRACT. – The co-occurrence of two anostracan species Branchinectella media and
Phallocryptus spinosus have been surveyed monthly in four saline lakes from the Aures region
(Chott Tinsilt, Garaa El-Tarf, Sebkha Djendli and Garaa O’Lembarek), in North-East Algeria,
between 2013 and 2014. Branchinectella media occurred during the winter at low water temperatures
ranging between 5 and 16 °C and a salinity between 2.24 and 44 ppt (g/L), while
P. spinosus preferred spring with a temperature range between 18 and 22 °C and a salinity from
12.08 to 48.6 ppt. The presence of both species overlapped only in March in the four sites.
Phallocryptus spinosus always occurred with higher monthly densities between 5.2 ± 0.99 and
27.7 ± 3.81 ind.L–1 versus 1.65 ± 0.64 to 10.55 ± 0.78 ind.L–1 for B. media. Phallocryptus spinosus
was two times larger than B. media (F = 26.80, P < 0.001) and its females were two times more
fertile (t = 12.89, P < 0.0001) in the four sites. From the present study, we concluded that
B. media, which is considered as a rare species according to the literature, was sensitive to environmental
factors, mainly the temperature, and was dominated by P. spinosus, making it vulnerable,
especially to the effects of the predicted climate warming.
Spatial distribution of Branchinectella media (Crustacea, Branchiopoda) in a saline pond from "La Mancha
Húmeda": a case of habitat selection?
Branchinectella media is a commonly observed anostracan in Mediterranean temporary saline ponds. Despite its wide distribution, many aspects of its natural history are unknown or poorly studied. In this work, we seek to understand the main factors that influence the spatial distribution of juveniles and adults of B. media in a pond that belongs to the Manjavacas Pond Systems in the "La Mancha Húmeda" Biosphere Reserve in central Spain. We sampled on two dates, 29 November and 24 December, 2015. Environmental variables, such as pH, conductivity, temperature, depth and vegetation cover, were recorded at 20 defined sites in the pond. A hierarchical partition analysis was used to identify the independent contribution of each variable on the
density of juveniles and adults, and for each sampling date separately. On the first date, the predictive variables associated with the distribution of juveniles and adults were conductivity and depth, respectively. The density of juveniles was lower at sites with high conductivity, whereas adults occurred preferentially in deeper pond sectors. On the second date few adults were sampled, and only juvenile density was positively associated with depth. The use of deeper areas is possibly related to predation given the constant presence of waterfowl that feed on the littoral. Other causes, such as adaptation to temporary habitats with high evaporation rates and time stress to mate and produce resistant eggs, may play an important role.
Key words: Anostraca, environmental heterogeneity, hierarchical partitioning, temporary ponds
Higher temperatures and increased environmental variability under climate change could jeopardize the persistence of species. Organisms that rely on short windows of rainfall to complete their life-cycles, like desert annual plants or temporary pool animals, may be particularly at risk. Although some could tolerate environmental changes by building-up banks of propagules (seeds or eggs) that buffer against catastrophes, climate change will threaten this resilience mechanism if higher temperatures reduce propagule survival. Using a crustacean model species from temporary waters, we quantified experimentally the survival and dormancy of propagules under anticipated climate change and used these demographic parameters to simulate long term population dynamics.
By exposing propagules to present-day and projected daily temperature cycles in an eight month laboratory experiment, we showed how increased temperatures reduce survival rates in the propagule bank. Integrating these reduced survival rates into population models demonstrated the inability of the bank to maintain populations; thereby exacerbating extinction risk caused by shortened growing seasons.
Overall, our study demonstrates that climate change could threaten the persistence of populations by both reducing habitat suitability and eroding life-history strategies that support demographic resilience.
Mud from a temporary pool in Morocco was sequentially inundated and dried at the laboratory to follow the life history of Branchipus schaefferi. Once adult, each female was coupled to a male in order to study their life history and reproduction. The average percentage of hatching decreased during the successive inundations, presumably as an adaptation to the unpredictability of the habitat. However, there was no indication that the offspring of the first inundation would preferentially hatch during their first inundation too, neither was there any such preference in the offspring of the delayed hatchings. Each female reduced risk by spreading hatching time of her resting eggs over consecutive inundations. Eggs did not hatch all at the same moment, reducing the chance that a female’s entire offspring would die before reaching maturity if the pool would dry out too soon. There was a significant difference between the mean value of the number of resting eggs produced by the females from a large clutch size, and those produced by females from a small clutch size. There thus appears to be a genetic base for the clutch size of females.
Revue Synthèse N° 21, Janvier 2010 M. Amarouayache et M.H. Kara
29
Qualité et biomasse exploitable d’Artemia Salina (Crustacé,
Anostracé) du Chott Marouane (Nord-Est, Algérie)
Mounia Amarouayache et Mouhamed Hichem Kara
Laboratoire Bioressources Marines, Département de Biologie,
Université Badji Mokhtar, BP 12, Annaba 23000, Algérie.
Accepté le 31/31/2090
ملخص
ك ش سج هزِ انذساست ألسحًٍٍا سانٍُا )نٍٍُىس 3571 )نشظ يشواٌ، انىاقع فً والٌت انىادي. عشفج األَىاع عهى
أساس يعاٌٍش شكهٍت. حسعت يقاٌٍس بٍىيخشٌت جذٌذة اسخخذيج نخحذٌذ انخصائص انبٍىنىجٍت نبانؽً هزِ انسالنت، يٍ
بٍُها يخىسظ انحجى انزي هى 6 يهى عُذ انزكىس، وبٍٍ 7.7 يهى و7.5 يهى عُذ اإلَاد، بذالنت فخشة أخز انعٍُاث. بهػ
انقطش انًخىسظ نهكٍساث انًائٍت 116 يٍكشويخش ويخىسظ طىل انـ nauplii 811 يكشويخش نكم 17.1 يهػ وصٌ جاؾ.
اخخبشث َىعٍت انخفقٍس عهى عٍُاث يأخىرة فً فخشاث يخخهفت، حٍذ أعطج انعٍُت انًأخىرة فً ياي 1999 أفضم
انُخائج، يع َسبت 60 ٪ يٍ انفقس، وكفاءة حقذس بـ 350619 nauplii\غ يٍ األكٍاس انًحخضُت وعائذ ٌقذس بـ 88.9
ؼشاو يٍ nauplii .قذسث انكخهت انحٍىٌت انجافت نألكٍاس انًُخجت بـ 6.5 طٍ يٍ انىصٌ انجاؾ بعائذ 13.9 كؽى\هكخاس.
بٍٍ ححذٌذ وحقذٌش األحًاض انذهٍُت أٌ انسهسهت ٌ-1 هً انًهًٍُت، ألَها حًثم بٍٍ 53.13 و13.17 ٪ يٍ يجًىع
األحًاض انذهٍُت انخً حى ححهٍهها. ويع رنك، نىحظ كًٍاث صؽٍشة يٍ EPA( 17.3 )٪ وانؽٍاب انخاو نـ DHA.
الكلمات المفتاحية: أسحًٍا؛ انكخهت انحٍىٌت؛ حشبٍت األحٍاء انًائٍت؛ شظ؛ يشواٌ.
Résumé
Cette étude est consacrée à Artemia salina (Linnaeus 1758) du Chott Marouane, situé dans la Wilaya d’ElOued.
L’espèce est identifiée sur la base de critères morphologiques. Neuf paramètres biométriques ont
permis de caractériser les adultes de cette souche dont la taille moyenne est de 6 mm chez les mâles et entre
5,5 mm et 7,5 mm chez les femelles, en fonction de la période d’échantillonnage. Le diamètre moyen des
cystes hydratés est de 236 µm et la longueur moyenne des nauplii est de 428 µm pour un poids sec de 2,35
µg. La qualité de l’éclosion est testée sur des échantillons prélevés à différentes périodes. L’échantillon
prélevé en mai 2000 a donné les meilleurs résultats, avec un pourcentage d’éclosion de 69 %, une efficacité
de 179680 nauplii/g de cystes incubés et un rendement de 0,44 g de nauplii. La biomasse sèche de cystes
produits est estimée à 7,6 tonnes en poids sec et correspond à un rendement de 0,21 kg/ha. L’identification et
la quantification des acides gras montre que ceux de la série n-3 sont dominants, puisqu’ils représentent entre
21,71 et 25,21 % des acides gras totaux analysés. Cependant, nous notons les faibles quantités d’EPA (1,25
%) et l’absence totale de DHA.
Mots clés : Artemia; biomasse; aquaculture; Chott; Marouane; Nord-est algérien.
Abstract
This study concerns Artemia salina (Linnaeus 1758) from Chott Marouane, situated in the Wilaya of ElOued.
This species is identified using morphologic criteria’s. Nine biometric parameters have allowed to
characterize adults of this strain whose mean size is 6mm for males and varies between 5.5 and 7.5 mm for
females, depending on harvesting period. Mean hydrated cysts diameter is 236 µm and mean nauplius length
is 428 µm with a dry weight of 2.35 µg. The hatching quality of cysts is tested on samples harvested at
different periods. The sample of May 2000 brought the best results, with a hatching percentage of 69 %, an
efficiency of 179680 nauplius/g and a yield of 0.44 g. Dry biomass of cysts produced by the Chott Marouane
is estimated at 7.6 tons and corresponds to a yield of 0.21 kg/ha. The fatty acids identification shows that the
n -3 serial is strongly dominant since it represents 21.71 % to 25.21 % of the total fatty acids analysed.
However, it is noted a low level of EPA (1.25 %) and a total absence of DHA .
Key words: Artemia; biomass; aquaculture; Chott; Marouane; North-eastern of Algeria.
Auteur correspondant: m.derbal@yahoo.fr (Mounia Amarouayache)
The brine shrimp Artemia is a small crustacean of hypersaline lakes which is commonly used in larviculture. The parthenogenetic population of Artemia from El-Bahira Lake (10 ha area), situated in the High Plateaus of Northeastern Algeria (1034 m alt), has been characterized and surveyed during two hydroperiods of 2009 and 2013. Contrary to other known parthenogenetic populations, which develop in hot seasons and reproduce by ovoviviparity, Artemia from El-Bahira was found to develop only in cold seasons (winter and spring), even if the lake doesn’t dry in summer. It reproduces by oviparity and produces few cysts (5.69 ± 3.6 and 98.00 ± 28.32 offsprings/brood). Individual density was much lower during the hydroperiod of 2013, whereas fecundity was higher than in the previous hydroperiod (2009). Cyst reserve was estimated at 133.13 kg of dry weight which corresponds to a rate of 13.31 kg.ha-1.
Keywords : Artemia parthenogenetic, cold seasons, oviparity, cyst reserve
Phallocryptus spinosa (Thamnocephalidae) is a small primitive crustacean which lives in temporary saline pools of the Palaearctic region called Chott, Sebkha, Garâa or Daya in North Africa. Data on its biology and life history are very scarce despite its ecological importance in wetlands. Four populations living in the Northeastern High Plateaus of Algeria, Garâas Guellif, El-Tarf, Ank Djemel and Sebkha Ez-Zemoul, have been studied in point of view of their morphmetry (13 parameters) and their reproduction. The population of Sebkha Ez-Zemoul, living in higher salinities and in sympatry with Artemia salina was different from the 3 other populations that are close together. Its adults are the largest (21.77 ± 2.34 mm and 23.65 ± 2.36 mm for males and females respectively) and produce more cysts 771.47±8.45 cysts/brood of 293.11±10.41 μm diameter. Associated carcinological fauna and some behavioral traits are also approached.
Crustacean communities in saline lakes are regulated mainly by salinity, and a significant inverse correlation can be found between salinity and species richness. The aim of the present study is to compare the carcinological diversity of two distinct arid regions of the world: Algerian saline lakes, locally called "chotts" and "sebkhas", and their Chilean Altiplano counterparts, and to determine if there are similar regulator patterns that influence the composition of those communities. The main halophilic taxon common to both regions was the anostracan Artemia at high salinities. However, many other halotolerant crustaceansmay occur in Algerian chotts and sebkhas, such as Phallocryptus spinosa, Branchinectella media, Moina salina, Cletocamptus retrogressus, Arctodiaptomus salinus and Heterocypris sp. In Chilean saline lakes the calanoid copepod Boeckella poopoensis was an important component of zooplankton at high salinities, while ostracods were totally absent. The results of correlation analysis revealed a significant inverse correlation between salinity and species number (Algeria, τ= -0.39039, z = -2.9402, p-value = 0.0032; Chile, τ= -0.5868, z = -2.3973; p-value > 0.0165). The results of null model analysis describing species co-occurrence showed that the species communities are random for Algerian saline lakes due to the presence of many halotolerant species. For Chilean saline lakes, the species communities are structured.
Temporary ponds are the most peculiar and representative water bodies in the arid and semi-arid regions of the world, where they often represent diversity hotspots that greatly contribute to the regional biodiversity. Being indissolubly linked to these ecosystems, the so-called " large branchiopods " are unanimously considered flagship taxa of these habitats. Nonetheless, updated and detailed information on large branchiopod faunas is still missing in many countries or regions. Based on an extensive bibliographical review and field samplings, we provide an updated and commented checklist of large branchiopods in Tunisia, one of the less investigated countries of the Maghreb as far as inland water crustaceans are concerned. We carried out a field survey from 2004 to 2012, thereby collecting 262 crustacean samples from a total of 177 temporary water bodies scattered throughout the country. Large branchiopod crustaceans were observed in 61% of the sampled sites, leading to the identification of fifteen species. Among these, the halophilic anostracan Branchinectella media is here reported for the first time for the country; conversely, four of the species reported in literature were not found during the present survey. Based on literature
and novel data, the known large branchiopod fauna of Tunisia now includes 19 species, showing
a noteworthy species richness when the limited extension of the country is considered. For each
species, the regional distribution is described and an annotated list of references is provided.
Under a conservation perspective, the particular importance of the temporary ponds occurring in
the Medjerda river alluvial plain is further stressed. In this location, several large branchiopod taxa
with different ecological requirements converge and form unique and species-rich assemblages
that should be preserved.
The influence of spatial and environmental factors in explaining the structure of large branchiopod assemblages at different spatial scales is still poorly explored. We hypothesized that the extent of actual spatial connectivity, and thus the spatial distribution of a metacommunity, may depend on the environmental conditions as represented by climatic gradients and the structural characteristics of the landscape. To test this hypothesis, the distributional patterns of 14 large branchiopod species in a set of 177 temporary water bodies repeatedly sampled across Tunisia and on its main islands were analysed. Physical, chemical, morphological and climatic characteristics of the studied water bodies were collected as well, and spatial structures were described using distance-based Moran’s Eigenvector Maps. Distance based Redundancy Analysis and variance partitioning explained more than one-half of total variation. Mantel’s autocorrelograms demonstrated that species composition was spatially autocorrelated at shorter distances in the Mediterranean part of the country than in the southern, more arid part. These results suggest that both dispersal limitation and species response to
spatially structured environmental gradients might be involved in determining large branchiopod distribution in Tunisia and that these patterns may greatly vary on a regional basis.
Cyst shell morphology is described for 31 species and 4 genera of endemic Australian fairy shrimp. All four genera have distinctive cyst shell structure.
Anostracan bioregions were identified for Australia. These regions were quantitatively defined using species distributions compared through Jaccard's Coefficient of Community Similarity, and qualitatively defined using regional soils data. Community assemblages are quantified using Fager's Index of Recurring Species Groups. Substrate geochemistry was used to investigate additional relationships, but was limited by the constraints of available data. However, the highly salinized soils directly relate to Australia bearing the highest diversity of halophilic anostracan taxa. Three anostracan biogeographical regions are defined for Australia: Western, Eastern and Southern.
S. (2011). Morphometrics of the resting eggs of the Australian species of the fairy shrimp Branchinella (Anostraca: Thamnocephalidae). Proceedings of the Linnean Society of New South Wales 133, 53-70. Branchinella resting eggs are characterised by having surface ridges arranged more or less in polygons and by almost all species having few, if any, spines. The eggs of 33 out of a known possible 40 species (including 4 out of 6 undescribed species) were studied by SEM. A few species are distinctive by being adorned with lighter coloured surface membranes often strengthened by ribs or sparse spines and one (B. longirostris) is regularly spinose. Those species known to be morphological variable also have variable egg morphologies. This makes it diffi cult to characterise specifi c egg morphology, but even so in some species eggs are distinct : B. arborea, B. australiensis, B. budjiti, B. compacta, B. complexidigitata, B. hattahensis, B. kadjikadji, B. longirostris, B. lyrifera, B. occidentalis, B. pinderi and B. vosperi. Most of the remainder are easily confused with at least one or more species. Branchinella egg morphology seems of little value in taxonomical studies and of restricted use in distinguishing eggs in dried sediments.
Most freshwater zooplankton species produce dormant eggs or other long-lived resistant life stages to bridge periods that are unsuitable for growth and reproduction. One of the principal cues that determine activation of these dormant stages is light exposure. Contrary to the analogous process of seed germination in plants, relatively little is known about the mechanism of light activation and its potential adaptive value in freshwater zooplankton. We made use of a temporary pool model to investigate the hatching response of resting eggs of the fairy shrimp Branchipodopsis wolfi to a specific set of selected light regimes and to evaluate the importance of egg pigmentation for mediating susceptibility to light cues. Our results suggest the presence of a critical light threshold for activation leading to maximal hatching. Moreover, the process of light activation does not appear to be purely cumulative because light administered in a single continuous pulse resulted in much higher hatching than the same amount of light administered in several 2-h pulses. Last, darkly pigmented eggs were less sensitive than lightly pigmented eggs to light exposure, resulting in delayed hatching of darker eggs during an experimental inundation. This result indicates that natural variation in egg pigmentation could be a risk-spreading mechanism that trades off the risks of mortality caused by kin competition during the nutrient-limited conditions that typically prevail early during inundations on one hand and the risk of mortality from premature pond drying on the other hand. Overall, our results indicate that light-energy activation thresholds and variation in pigmentation of the eggshell can be important traits that may contribute to variation in hatching phenology among zooplankton lineages.
Fairy shrimps (Anostraca) live in temporary waters. Dominant among their predators are aquatic insects, especially diving beetles (Dytiscidae). Mastication of the eggs of the fairy shrimp Branchipus schaefferi and their passage through the digestive tract of smaller beetles, like Ilybius fenestratus, has a positive effect on hatching afterwards. Dytiscidae could be important vectors for aerial dispersal of diaspores among ponds which are not directly connected to a stream channel. Such long-distance dispersal can be of critical importance for population survival and gene flow among communities living in temporary habitats.
The presence of small trout together with fairy shrimp (Chirocephalus diaphanus) in isolated corrie lakelets in the French Pyrenees suggests that the fish might be agents of dispersal of the shrimp, if resting eggs could survive ingestion and freezing. Resting eggs in ovigerous females of Chirocephalus diaphanus can pass through the digestive tract of a trout and be subsequently frozen without losing their viability. Subsequently fecal pellets were collected from each fish. The gut passage time of C. diaphanus eggs were up to 4 days. Resting eggs recovered from fecal pellets were counted, frozen and then incubated. Hatching of nauplii began after 32 days, and 50.9% (sd. 29.4) hatched over the following 7 days. Ovigerous females of lab cultured C. diaphanus were administered to four trout Salmon trutta kept in separate tanks. Therefore, fish can aid upstream dispersion of these fairy shrimp.
The co-occurrence of Artemia parthenogenetica Bowen & Sterling, 1978 and Branchinella spinosa Milne-Edwards, 1840, was previously only supposed, on the basis of finding their cysts in the same lagoon, but active stages were never recorded together. In a saline lake in south eastern Italy, populations of the two species were observed for two years. A. parthenogenetica was typical of the early wet season (October–January), while B. spinosa, even if it was present before, developed in the late part of the wet season (February–May). Adult A. parthenogenetica were recorded only in the season 1999–2000. The seasonal distribution of A. parthenogenetica is probably controlled by abiotic conditions (i.e., photoperiod, temperature, conductivity, and rainfall); however, competition between specimens of similar body size (e.g., adults of A. parthenogenetica, and juveniles of B. spinosa) could explain the lower numbers of B. spinosa population in winter. The discovery of cysts of both species deep in the sediment of the lake suggests a long-lasting co-occurrence of these two Anostraca.
Eggs, including encysted embryos (cysts) of aquatic invertebrates may not only be thick-walled, but also provided with various external ornamentations such as spines and honeycombings. We argue that these provide protection, additional to that of the walls themselves, against invertebrate predators, and test this idea by offering intact (honeycombed) and decapsulated cysts of Chirocephalus diaphanus to the carnivorous flatworm Mesostomasp. Except at the lowest density of cysts, when intact as well as decapsulated cysts seem to be poorly detected by the (tactile?) searching system of the flatworms, intact cysts were relatively immune from predation. Similar causes elicit similar responses: the defences that occur in eggs are essentially similar to those present in adults of rotifers and various branchiopod microcrustaceans, copepods (marine species), and ostracods. Circumstantial evidence suggests that egg defences may vary in intensity with predation pressure. In some cases, they might be predator-inducible.
In temporary aquatic habitats, permanence and the severe disturbance associated with desiccation are strong selective agents
expected to lead to differentiation in life history strategies in populations experiencing different disturbance regimes.
Besides optimal timing of hatching of dormant life stages, maturation and reproduction, pool inhabitants also benefit from
the acquisition of reliable cues for the quality of the ambient environment. We investigated whether hatching patterns, life
history characteristics and egg bank size of Branchipodopsis fairy shrimp (Branchiopoda, Anostraca) inhabiting a cluster of temporary rock pools in South Africa reflect variation in
habitat stability and hatching cues. Long-term hydrological variation was used to select pools along a gradient of habitat
stability. Initial conductivity was a good indicator for the length of inundations. No hatching occurred under elevated conductivities,
which may present a mechanism to avoid abortive hatching. Egg bank size was unaffected by habitat size or habitat stability
but instead was related to cover by a protective sheet of dry aquatic vegetation, which presumably counteracts egg bank erosion
by wind when pools are dry. Life history but not hatching phenology reflected some aspects of habitat stability. Fairy shrimp
populations in ephemeral pools started reproduction earlier than populations in more stable habitats. Additional common garden
or transplant experiments, however, will be required to assess the relative importance of environmental and genetic components
in explaining the observed variation and acquire more insight into the trade-offs that lie at the base of the evolution of
life history strategies along the pond permanence gradient.
KeywordsHatching phenology-Hydroperiod-Hydroregime-Life history evolution-Temporary pools-Dormant egg banks
Romania is one of the most diverse countries for Anostraca in Europe. The Romanian Plain and the Black Sea coast are recognized as the most species-rich areas and harbour a high concentration of saline lakes and ponds. A short survey of ponds and small lakes was carried out in these areas of Romania during March 2019, with the aim of improving the knowledge of Anostraca diversity and distribution. Two species of Anostraca were found: Chirocephalus diaphanus romanicus Stoicescu, 1992, in Arge¸sArge¸s County, and Branchinectella media (Schmankewitsch, 1873), in Constan¸taConstan¸ta County. The record of B. media is the first for Romania, increasing the known diversity of Anostraca to 17 species. This discovery highlights the high diversity of large Branchiopoda in the country. RESUMEN Rumanía es uno de los países con mayor diversidad en Anostraca de Europa. La planicie rumana y la costa del Mar Negro se reconocen como las áreas que contienen una mayor riqueza de especies y de lagunas y lagos salinos. En marzo de 2019 se llevó a cabo un breve muestreo de lagunas y pe-queños lagos en estas áreas de Rumanía, con el objetivo de mejorar el conocimiento de la diversidad y distribución de Anostraca. Se encontraron dos especies de Anostraca: Chirocephalus diaphanus ro-manicus Stoicescu, 1992 en el distrito de Arge¸sArge¸s, y Branchinectella media (Schmankewitsch, 1873) en el distrito de Constan¸taConstan¸ta. El registro de B. media constituye el primero para esta especie en Rumanía, incrementando la diversidad conocida de Anostraca a 17 especies. Este descubrimiento destaca la elevada diversidad de grandes branquiópodos en el país.
Anostracan crustacean eggs were collected from various materials leaving and entering branchiopod habitats. The eggs were cultured from allochthonous dust and mud, bird faeces and stomach contents. Eggs that passed through aquatic bird digestive tracts hatched in significantly larger fractions than eggs dispersed by other vectors and eggs from resident habitat egg banks. Predator dispersed eggs would necessarily have a greater chance of reaching suitable habitat than eggs that are randomly dispersed (such as by wind). This larger hatching fraction would amplify the priority effects of habitat monopolisation should the eggs be deposited in unoccupied habitat.
1.Heat tolerance of dry cysts of the fairy shrimp Branchipus schaefferi and the brine shrimp, Artemia franciscana was studied using rapid (∼100°C/min) and slow (∼4°C/min) heating.2.Rapid heating caused much greater death than did slow, and we consider the possible causes.3.Although these primitive crustaceans are closely related, the major stress proteins of Artemia cysts (artemin and p26) were not detected in Branchipus cysts.4.The Arrhenius activation energy (Ea) for thermal killing of Branchipus cysts was found to be 5-fold higher than that of Artemia cysts over the range of 110–130°C.5.These major differences in stress proteins and Ea are especially interesting because the thermal tolerance of both kinds of cysts is very similar.
The cyst deposition behaviour of Streptocephalus torvicornis is described as the first documented case of active cyst deposition in Anostraca. The functional morphology of the brood pouch of S. torvicornis is described and illustrated using both Light Microscopy and Scanning Electron Microscopy. The brood pouch is an elongated tube-like structure with a subterminal crescent-shaped opening. During cyst deposition, the females insert this structure into the sediment to a depth of almost 10 mm, and deposit the resting cysts, analogous to an insect ovipositor. The opening mechanism of the genital pore is explained by contraction of a branched longitudinal muscle. The adaptive value of laying cysts into the soil and possible dispersal strategies are discussed.
1. In temporary aquatic habitats, time is probably the dominant environmental factor affecting community composition, mainly by setting constraints on colonization success and the replacement of taxa over time. The mechanism and effect of a decreasing inundation period on community development, mostly in terms of truncation, are still poorly documented. The permanent and ephemeral components of temporary communities are expected to be differently influenced by the degree of persistence of the habitat.
2. To study the effect of time on invertebrate community assembly and dynamics in a short duration type of temporary aquatic habitat, we monitored 16 ephemeral rock pools which persisted from less than a week to about 1 month at two rock pool sites in semi-arid south-eastern Botswana. Data were collected every 2 days during a full inundation cycle.
3. All communities were initially assembled by permanent residents recolonizing the habitat from egg banks and were later joined by actively dispersing ephemeral taxa. Species replacements only occurred in two pools. Concurrent with a decrease in the densities of Branchipodopsis wolfi, population sizes of Leberis sp. and Culicidae (Aedes sp. and Anopheles sp.) increased in these pools. Although it was possible to distinguish two successive phases at one rock pool site, community assembly was generally a gradual process determined by dispersal strategies of the inhabitants. Additional rains after initial filling triggered dispersal by ephemeral taxa, mainly Micronecta youngiana and Hydroglyphus infirmus, and positively influenced colonization success.
4. Decreasing persistence shortens community development down to a critical point below which lack of time eliminates the possibility of species replacement. Based on these findings, we define ephemeral waters as aquatic habitats lacking species replacements. Other temporary water types have a relatively longer persistence, permitting successional replacement of species.
To investigate their distribution and total numbers, resting eggs of the anostracan Chirocephalus ruffoi were collected from the bed of a temporary pool in southern Italy. Samples were taken at 0.5 m intervals along six transects oriented at 30° from each other, by means of a cylindrical core sampler. The horizontal distribution of intact resting eggs was extremely patchy, with cyst number per core ranging from 191 to 1,400 (CV = 32.7%), corresponding to a mean of between 0.8 and 4.3 cysts cm ⁻³ . Differences observed were related to core position and transect orientation, total cyst numbers being markedly higher in the leeward area of the pool compared to the windward area. Marked variation was also evident in vertical distribution, a significant, though weak correlation was recorded between egg density and sediment depth. Cyst‐bank size (± 95% confidence limits) of the pool bed, estimated from the mean cyst number cm ⁻³ obtained for the 6 transects, ranged between 1.0 × 10 ⁸ and 1.3 × 10 ⁸ cysts.
Hatching in the laboratory was very erratic. Despite significant differences in hatching, the observed variation was unrelated to most of the variables considered (position within sections, cores and transects, pre‐incubation treatment) and was explained only by initial sediment conditions (moist/dry). In none of the experimental conditions tested was synchronous hatching obtained.
Possible causal factors (mixing of the bottom sediments by cattle, egg age, storage conditions, differential exposure to environmental cues as well as variability in hatching response even at clutch level) are discussed. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cysts of three species of anostracans (Branchipusschaefferi, Chirocephalus diaphanus, and Tanymastigites perrieri), two species
of Notostracans (Triops numidicus and Lepidurus apus) and one species of Spinicaudata (Leptestheriamayeti) were collected
from the upper 2 cm of dry sediments at intervals along transects from a temporary pool in an arid zone of Morocco and from
two ditches in France. The horizontal distribution of viable cysts was patchy and is discussed in relation to several ecological
parameters prevailing during the aquatic phase. These include vegetation distribution, depth and morphometry of the pond,
dominant wind pattern, and granularity of the sediments.
The densities reached more than 1700 cysts of C. diaphanus per 100 cm2, and 1150 cysts of L. apus per 100 cm2 in the two ditches. The mean densities of cysts per 100 cm2 calculated for each transect ranged from 250 to 450 for C. diaphanous and 240 to 260 for L. apus (in the ditch populations)
and about 1–6 for T. perrieri and L. mayeti, 3–15 for B. schaefferi, and16–58 for T. numidicus in the pool in Morocco.
Occasional records of predation by freshwater fishes on Anostraca suggest these Crustacea to be a suitable live food in freshwater aquaculture.
Selection of species for this use should consider prey/predator size relations, biological characteristics of the prey, ecological requirements of the prey and of the predator, hatching characteristics of the species selected, hatching techniques, biochemical composition of the cysts and nauplii, and feasibility of mass culturing for commercial cyst production.
In light of this, biometrics, biological characteristics and ecological requirements of a number of fairy shrimp species from Italy are presented.
Most species examined have a suitable cyst diameter, particularly after decapsulation. Instar I nauplii sizes fall within the range considered optimum. The most suitable species are Chirocephalus ruffoi (0.263 mm mean diameter; 0.400 mm naupliar length), Branchipus pasai, and B. schaefferi (0.266 mm and 0.257 mm; 0.365 mm and 0.342 mm cyst and instar I naupliar sizes respectively).
A number of species seem to be tolerant of broad environmental variation, and are fast growing. However, there is great variability in fecundity and hatching success within and between species.
The extent to which dormancy in large freshwater branchiopods is controlled endogenously (diapause) or exogenously (quiescence) is not always clear. It is assumed that both processes occur even within the same brood. Based on the effectiveness of common diapause-deactivating processes such as desiccation, hibernation, and resting, it can be stated that diapause is not a general process controlling responsiveness of large freshwater branchiopod eggs. Only in limited cases unequivocal evidence for the positive influence of these treatments is found.With few exceptions, hatching of activated cysts is effected by specific conditions that may even differ among conspecific populations. Generally, each species (or even population) has a specific temperature range or regime for optimal hatching performance. In a suitable thermal environment with sufficient light and oxygen, hatching is invariably invoked by a low osmotic medium.The erratic hatching pattern in most species is thought to be an adaptation to the variable temporary habitat. Hatching is generally spread over several days or even weeks, but the highest peak usually occurs on the first or second day of hatching. Low hatching percentages were found only in subtropical/desert species and may be a reflection of the low chances for successful reproduction. Generation carry-over of propagules in the egg bank by dormancy, and hatching at low conductivity, are, together with obligate oviparity and absence of an asexual life cycle phase, thought to be highly adaptive to the temporary environment. This enabled large branchiopods to survive since the Upper Cambrian.
A study of 102 samples from almost all salt water bodies in Spain has allowed the preparation of a comprehensive list of anostracans, cladocerans and copepods living in such extreme environments. Among the 26 species recorded, 9 are halobionts, but 17 can exist in less saline waters. Of the halobionts, several are widely distributed throughout arid areas around the Mediterranean (Arctodiaptomus salinus, Cletocamptus retrogressus, Branchinectella media, Branchinella spinosa, Daphnia mediterranea, Moina salina); Branchinecta orientalis ( = B. cervantesi) only appears in Guadiana watershed and toward the east of Hungary, and the Alona belonging to the A. elegans complex is a Spanish endemic. In the second group are many typically freshwater species which also appear occasionally in saline waters, and colonizers of wetlands in steppes, characteristically adapted to a wide range of salinity; one of the formers, Diaphanosoma cf. mongolianum, deserves closer study. The Spanish halobiontic fauna seems to be very old judging by the existence of some isolated species, e.g. B. orientalis may be a Tertiary relic. Persistence through time could have resulted from the continuous aridity of some Iberian localities during the Pleistocene and the ecological constancy of wetlands maintained by regional groundwater discharges.
The anostracan Phallocryptus spinosa has an almost exclusively palearctic distribution. The Makgadikgadi Pans area in Botswana represents the only distribution
record south of the Sahara. In this ephemeral wetland, it is an important food item in the diet of migrating birds. By studying
egg bank characteristics (such as depth and density) and hatching requirements, we investigated the persistence of this sub-Saharan
population. At localities in the middle and north basin of Sua Pan, sediment cores were taken along a transect, and dormant
eggs were isolated. Densities of the active dormant egg bank ranged from 833 to 31449 dormant eggs m−2, indicating that this species is well established. Most of the dormant eggs were found in the top 4cm of the sediments,
and densities decreased to zero at a depth of 13cm. Considering the expected low sedimentation rate, the presence of dormant
eggs down to 13cm indicates long-time occurrence of P. spinosa in the Makgadikgadi Pans area. We observed high hatching fractions (up to 85%) at a temperature of 22°C and a salinity of
5ppt. A second anostracan species, Branchinella ornata, co-occurred with P. spinosa in our study site. This population also had a large active dormant egg bank (ranging from 6634 to 50557 dormant eggs m−2) with dormant eggs present until a depth of about 11cm. This pattern indicates a long-time co-occurrence of P. spinosa and B. ornata.
Survival and reproductive performance were measured at nine temperature–salinity (T–S) combinations (15°C, 24°C and 30°C/60 ppt, 120 ppt and 180 ppt) for four sexual (Artemia franciscana, A. salina, A. sinica and A. persimilis) and one parthenogenetic (A. parthenogenetica) species of brine shrimp. There was significant interaction between temperature and salinity for survival and reproductive traits. For most species there was disconcordance among seven performance estimators (LT50, 21-day survival, r, and four female reproductive traits) for the optimal T–S combination. We propose that the best ecological estimator of reproductive success is cohort reproductive output because it incorporates both survival (lx) and reproductive (mx) functions. All species had maximum reproduction at 24°C; at 120 ppt for A. parthenogenetica, A. sinica and A. franciscana, and at 180 ppt for A. salina and A. persimilis. There was only one T–S combination (24°C/120 ppt) where all species completed their life cycle. While at least one Artemia species reproduced at eight of the nine possible T–S combinations, sustainable reproduction (where Ro≥1) occurred at only five T–S combinations. A. parthenogenetica had the narrowest tolerance range of T–S combinations, contradicting the general purpose genotype hypothesis advanced for obligately parthenogenetic species.
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