Diaptomid Species Research Articles

The Diaptomidae (Copepoda, Calanoida) of Tunisia and the role of spatial and environmental factors as drivers of their distribution patterns

Even in a biodiversity hotspot such as the Mediterranean basin, aspects relating to the distribution of some groups of microcrustaceans still need clarification. In this paper, we critically analyse the available information on diaptomid copepods in Tunisian inland waters and, based on the largest sampling campaign to date carried out in the country, report new data on their distribution. In the frame of this study, 248 crustacean samples were collected from 190 sites, and 10 diaptomid species belonging to 7 genera and 2 subfamilies were found in the samples. Their distribution follows a climate gradient determined by precipitation, and ecological variables mainly affect diaptomid distribution in the study area, while pure spatial factors are of negligible importance. Diaptomid biodiversity is therefore strongly linked to the diversity of inland waters that characterise the country. This is especially true in the wetlands of the Medjerda alluvial plain, where six diaptomid species co-occurred sympatrically, with up to four or five species coexisting syntopically and synchronically in some sites. Unfortunately, the natural water bodies of this plain are currently strongly threatened by urban expansion and agricultural reclamation, and the risk of local extinction for the species they host is increasingly high.

An annotated checklist and bibliography of the Diaptomidae (Copepoda, Calanoida) of Italy, Corsica, and the Maltese islands

Calanoids of the family Diaptomidae are the most widespread copepods in the lentic inland waters of the Palearctic region. In Italy, studies on the family date back to the end of 19th century. Since then, several papers contributed to increasing the knowledge on their presence, distribution, and ecological preferences. Nevertheless, new records for the area and the discovery of putative new species stress that the current knowledge on these inland water crustaceans is still far from being exhaustive. This paper presents an updated and annotated checklist and bibliography of the Diaptomidae of the Italian peninsula and surrounding islands, including Corsica and the Maltese islands, compiled through a critical review of the existing literature and carrying out further field research. The doubtful records reported in the literature are discussed and clarified. The updated checklist includes 30 diaptomid species and subspecies; among them, an alien species and three putative new species pending formal description are reported. About 20% of the observed species are endemic or subendemic to the study area. The faunal provinces ascribed to the Mediterranean limnofaunistic region host the highest species richness and contribute to the checklist with rare species and unique occurrences. The high species richness observed in the Mediterranean area supports the hypothesis of a long-lasting persistence of an ancient and peculiar copepod fauna.

Redescription of the freshwater calanoid copepod <i>Neutrodiaptomus formosus</i> with key to females of diaptomid species in Japan

Redescription of the freshwater calanoid copepod <i>Neutrodiaptomus formosus</i> with key to females of diaptomid species in Japan

Diversity patterns and biogeography of Diaptomidae (Copepoda, Calanoida) in the Western Palearctic

Diaptomid copepods are an important component of biodiversity in inland aquatic ecosystems worldwide but to date little is known about the historical and ecological factors that determined their current distribution. In the present paper, a critical review of the available literature on diaptomid species distribution in the Western Palearctic was performed, and a biogeographical analysis was carried out on the roles that spatial, current environmental, and historical (paleoclimatic) factors played on their actual distribution in this large area. The results show a clear pattern of colonization which is only partially overlapping what has been recently proposed for other terrestrial and aquatic taxa. Disentangling beta diversity into its turnover and nestedness components, we hypothesized a complex post-glacial pattern of recolonization of the higher latitudes, encompassing the importance of extra-Mediterranean refugia in the West (due to mountain chains which represent effective barriers for recolonization coming from the Italian and Iberian peninsulas) and a more typical pattern of post-glacial recolonization from southern refugia in the East, where mountain chains are north–south oriented and therefore less effective as barriers.

Identification and characterization of five polymorphic microsatellite loci in the freshwater copepod Hemidiaptomus gurneyi (Copepoda: Calanoida: Diaptomidae)

Hemidiaptomus diaptomid copepods are known to be excellent biological indicators for the highly biodiverse crustacean communities inhabiting Mediterranean temporary ponds (MTPs), an endangered inland water habitat whose conservation is considered a priority according to the “Habitat Directive” of the European Union. This study reports on the characterization of five polymorphic microsatellite loci in Hemidiaptomus gurneyi, to be used as markers for fine-scale studies on the population genetic structure and metapopulation dynamics of a typical and obligate MTP dweller. The five selected loci proved to be polymorphic in the species, with three to five polymorphic loci per studied population. Overall, mean heterozygosity scored for all loci and populations was lower than that reported for the few other diaptomid species for which microsatellite loci have been to date described; this is possibly due to the intrinsically fragmented and isolated peculiar habitat inhabited by the species. Furthermore, the presence of indels within the flanking regions of selected loci was scored. This study, albeit confirming the technical difficulties in finding proper microsatellite markers in copepods, provides for the first time a set of useful polymorphic microsatellite loci for a Hemidiaptomus species, thus allowing the realization of fine-scale phylogeographic and population genetics studies of this flagship crustacean taxon for MTPs.

Historical biogeography of the neotropical Diaptomidae (Crustacea: Copepoda).

IntroductionDiaptomid copepods are prevalent throughout continental waters of the Neotropics, yet little is known about their biogeography. In this study we investigate the main biogeographical patterns among the neotropical freshwater diaptomid copepods using Parsimony Analysis of Endemicity (PAE) based on species records within ecoregions. In addition, we assess potential environmental correlates and limits for species richness.ResultsPAE was efficient in identifying general areas of endemism. Moreover, only ecoregion area showed a significant correlation with diaptomid species richness, although climatic factors were shown to provide possible upper limits to the species richness in a given ecoregion.ConclusionThe main patterns of endemism in neotropical freshwater diaptomid copepods are highly congruent with other freshwater taxa, suggesting a strong historical signal in determining the distribution of the family in the Neotropics.

Variation in Body Shape across Species and Populations in a Radiation of Diaptomid Copepods

Inter and intra-population variation in morphological traits, such as body size and shape, provides important insights into the ecological importance of individual natural populations. The radiation of Diaptomid species (~400 species) has apparently produced little morphological differentiation other than those in secondary sexual characteristics, suggesting sexual, rather than ecological, selection has driven speciation. This evolutionary history suggests that species, and conspecific populations, would be ecologically redundant but recent work found contrasting ecosystem effects among both species and populations. This study provides the first quantification of shape variation among species, populations, and/or sexes (beyond taxonomic illustrations and body size measurements) to gain insight into the ecological differentiation of Diaptomids. Here we quantify the shape of five Diaptomid species (family Diaptomidae) from four populations each, using morphometric landmarks on the prosome, urosome, and antennae. We partition morphological variation among species, populations, and sexes, and test for phenotype-by-environment correlations to reveal possible functional consequences of shape variation. We found that intraspecific variation was 18-35% as large as interspecific variation across all measured traits. Interspecific variation in body size and relative antennae length, the two traits showing significant sexual dimorphism, were correlated with lake size and geographic location suggesting some niche differentiation between species. Observed relationships between intraspecific morphological variation and the environment suggest that divergent selection in contrasting lakes might contribute to shape differences among local populations, but confirming this requires further analyses. Our results show that although Diaptomid species differ in their reproductive traits, they also differ in other morphological traits that might indicate ecological differences among species and populations.

Neodiaptomus prateek n. sp., a new freshwater copepod from Assam, India, with critical review of generic assignment of Neodiaptomus spp. and a note on diaptomid species richness (Calanoida: Diaptomidae)

Neodiaptomus prateek n. sp. is described based on a plankton sample collected from Deepor Beel, a floodplain lake in the north-eastern, Indian state of Assam, which falls within the key biodiversity area of the Indo-Burma Hotspot. The new species fulfils all the principal criteria of the genus NeodiaptomusKiefer, 1932, as revised by Kiefer (1939). It has, however, a spectacular autapomorphic feature, which is perhaps unparalleled in Diaptomidae as a whole – a massive coxal plate ending in a thumb-like spinulose structure on the caudal surface of the male left P5. The new taxon also has two homoplastic characters that are hitherto unknown within the genus: the female fourth pediger has a prominent mid-dorsal process, and the third endopodal segment of P2-P4 has six instead of seven setae, the proximal outer seta being absent. The affinities of the new species with its congeners are discussed. Furthermore, the generic assignment of all the 13 species of Neodiaptomus listed in the latest World Copepoda database (Walter, 2012) is critically reviewed. Of these, five species are recognised as valid, six are relegated to species inquirendae, and one each is a nomen dubium and a synonym. Two lineage groups are recognised within the genus, one belonging to Southeast Asia and the other mostly confined to India. Surprisingly, the new species was accompanied by a record number of seven other diaptomid species in the same sample; the probable biogeographic and ecological implications of this high species richness are briefly discussed.

Chorion Structure of Diapause and Subitaneous Eggs of Four Diaptomid Copepods (Calanoida, Diaptomidae): SEM Observations

Chorion Structure of Diapause and Subitaneous Eggs of Four Diaptomid Copepods (Calanoida, Diaptomidae): SEM ObservationsScanning electron microscopic examination of diapause eggs of freshwater CalanoidaHemidiaptomus amblyodonMarenzeller,Eudiaptomus vulgaris(Schmeil),E. graciloides(Lilljeborg) and subitaneous one s ofE. gracilis(Sars) is described. The chorion surface ornamentation and number of coated layers are revealed. Diapause eggs have a thick (0.6-4.8 μ), at least two-layered chorion with patterned surface, whereas subitaneous eggs have a thin (0.13-0.25 μ), single-layered chorion with smooth surface. The mean number of eggs in egg sac, diameter of eggs and thickness of chorion were measured. The significance of the egg chorion thickness for diaptomid species inhabited temporary and/or permanent water-bodies is discussed.

ALLEE EFFECT LIMITS COLONIZATION SUCCESS OF SEXUALLY REPRODUCING ZOOPLANKTON

Understanding the dynamics of populations at low density and the role of Allee effects is a priority due to concern about the decline of rare species and interest in colonization/invasion dynamics. Despite well-developed theory and observational support, experimental examinations of the Allee effect in natural systems are rare, partly because of logistical difficulties associated with experiments at low population density. We took advantage of fish introduction and removal in alpine lakes to experimentally test for the Allee effect at the whole-ecosystem scale. The large copepod Hesperodiaptomus shoshone is often extirpated from the water column by fish and sometimes fails to recover following fish disappearance, despite the presence of a long-lived egg bank. Population growth rate of this dioecious species may be limited by mate encounter rate, such that below some critical density a colonizing population will fail to establish. We conducted a multi-lake experiment in which H. shoshone was stocked at densities that bracketed our hypothesized critical density of 0.5-5 copoepods/m3. Successful recovery by the copepod was observed only in the lake with the highest initial density (3 copepods/m3). Copepods stocked into small cages at 3000 copepods/m3 survived and reproduced at rates comparable to natural populations, confirming that the lakes were suitable habitat for this species. In support of mate limitation as the mechanism underlying recovery failure, we found a significant positive relationship between mating success and density across experimental and natural H. shoshone populations. Furthermore, a mesocosm experiment provided evidence of increased per capita population growth rate with increasing population density in another diaptomid species, Skistodiaptomus pallidus. Together, these lines of evidence support the importance of the Allee effect to population recovery of H. shoshone in the Sierra Nevada, and to diaptomid copepods in general.

Taxonomic implications for diaptomid copepods based on contrasting patterns of mitochondrial DNA sequence divergences in four morphospecies

Morphological identification methods do not provide reliable and meaningful species identi- fications for taxa where morphological differences among distinct species are either absent or over- looked (i.e., cryptic species). For example, due to the minute nature of the morphological characters used to delineate diaptomid copepod species and the apparent potential for copepod speciation to occur with little or no morphological change (i.e., morphological stasis), morphological identifications of diaptomid species may not adequately capture their true species diversity. Here, we present results from a geographic survey of mtDNA sequences from populations across the geographic ranges of four North American diaptomid species— Leptodiaptomus minutus, Skistodiaptomus pallidus, Skistodiaptomus reighardi, and Onychodiaptomus sanguineus. Shallow mitochondrial DNA sequence divergences (maximum of 1.1%) among haplotypes of L. minutus from across its geographic range suggest that current morphological identification techniques reliably identify this species. In contrast, we found large mitochondrial DNA sequence divergences (14-22%) among populations within the currently recognized morphospecies of S. palli- dus, S. reighardi, and O. sanguineus. However, pairwise sequence divergences within four distinct S. pallidus clades and within populations of S. reighardi and O. sanguineus were similarly low (maximum of 1.5%) as found within L. minutus as a whole. Thus, the S. pallidus, S. reighardi, and O. sanguineus morphospecies may be considered best as cryptic species complexes. Our study therefore indicates that morphological identifica- tions, while sufficient for some species, likely underestimate the true species diversity of diapto- mid copepods. As such, we stress the need for extensive taxonomic revision that integrates genetic, morphological, reproductive, and ecological analy- ses of this diverse and important group of freshwater zooplankton. Furthermore, we believe an extensive taxonomic revision will shed important insight into major questions regarding the roles of geography, phylogeny, and habitat on the frequency of cryptic species on earth.

Length–weight relationships of eight freshwater planktonic crustacean species in Japan

1. The relationships between body length and dry weight were examined for eight species of freshwater planktonic crustacea common in Japan: Eodiaptomus japonicus, Acanthodiaptomus pacificus, Daphnia galeata, D. similis, D. magna, Scapholeberis mucronata, Simocephalus exspinosus and Bosmina longirostris.2. The relationships of two diaptomid species were similar and the approximate equation was lnW = 2.7 + 2.6*lnL, where L is prosome length (mm) and W is dry weight (μg). The carapace length–dry weight relationships in branchiopods were more variable, with the slope ranging from 1.9 to 2.9 and the intercept from 2.0 to 3.7.3. The effects of food conditions on the relationship were examined in the laboratory, and the seasonal changes in the field were also studied.4. Practical advice is presented for predicting crustacean weight from body length.

Larval stages of Neodiaptomus lindbergi Brehm, 1953 (Copepoda, Calanoida)

All the postembryonic developmental instars of Neodiaptomus lindbergi Brehm, 1953, reared in the laboratory from eggs, are described and illustrated. Further, the larval affinities of this species vis-a-vis certain other Indian diaptomid species are mentioned.

Postembryonic development of Phyllodiaptomus blanci (Guerne & Richard, 1896) (Copepoda, Calanoida)

All the postembryonic developmental instars of Phyllodiaptomus blanci (Guerne & Richard, 1896), reared in the laboratory, are described and illustrated. The larval affinities of this species vis-a-vis certain other diaptomid species are mentioned.

Aspects of mating, reproduction, and co‐occurrence in three freshwater calanoid copepods

SUMMARY. 1. We examined the seasonal distributions and mating behaviour of Epischura lacustris, Diaptomus minutus and Diaptomus oregonensis to evaluate several proposed mechanisms for reproductive isolation. There was no divergence in onset of maturity or timing of breeding periods between sympatric diaptomid populations; size displacement between co‐occurring diaptomid species did not result in concomitant reduction in mating frequency between heterospecific pairs in the laboratory.2. Divergence in mating behaviour was supported by observations that, in conspecific mating experiments, males of both diaptomid species discriminated between females bearing ripened ovaries (gravid) and those that did not (non‐gravid), and that, in heterospecific trials, males either mated indiscriminantly with all females, or engaged in mating very infrequently.3. In mating experiments with Epischura. males did not discriminate between gravid and non‐gravid females, but mated exclusively with virgins of a specific relative size. Divergence in timing of breeding seasons between Epischura and the two diaptomid species suggests that even if mating between genera is possible, it does not occur often in nature.4. We discuss the adaptive significance of different reproductive strategies of these three copepods and speculate on mechanisms that allow for coexistence of the closely related taxa in nature.

The naupliar instars of Diaptomus kenai (Copepoda, Calanoida) and their distinction from those of four other diaptomids

The development of the six naupliar instars of Diaptomus kenai from Loon Lake in the University of British Columbia Research Forest is described and illustrated. The nauplii of D. kenai and of four other diaptomid species from lakes in the reseach forest are distinguished using differences in caudal armature and body size.

A New Species of Diaptomus (Copepoda, Calanoida) from Oklahoma and Texas

A new species of calanoid copepod, Diaptomus (Aglaodiaptomus) kingsburyae, is described from temporary waters in Oklahoma -and Texas. The new species is closely related to D. clavipes and D. clavipoides. It is separated from these species by diagnostic features of the metasomal wings, the antennules, and the fifth legs. A general description of the armature on all the appendages of this species is presented. An examination of specimens of D. clavipes showed that this description also applies to this species. During previous studies of calanoid copepods (Robertson, 1970, 1972) a collection of zooplankton was obtained from McCurtain Co., Oklahoma, that contained representatives of an undescribed diaptomid species. This species, which has also been found in two locations in Texas, is described in the present report. The new species is named for Dr. Phyllis Kingsbury, whose work (1966, 1968) has contributed greatly to our knowledge of the distribution of calanoids in Oklahoma. Diaptomus (Aglaodiaptomus) kingsburyae, n. sp. Type locality.-Roadside ditch on E side of Oklahoma St. Hwy. 87 in NW quarter of SW quarter of SW quarter of Sec. 19, R27E, T1OS, McCurtain Co., Okla. Specimens examined.-Oklahoma: McCurtain Co., type locality, approximately 200 adults of both sexes, many ovigerous females and many attached spermatophores, 9 May 1970. Texas: Bowie Co., a small pool approximately I/4 mile (0.4 km) from bridge over the Red River along E side of Texas St. Hwy. 8, many adults of both sexes, 27 June 1970; Brazos Co., pond approximately 10 miles (16.1 km) SE of 'College Station, many adults of both sexes, 25 April 1970. Disposition of type.-The holotypic male (U.S.N.M. 136110) and allotypic female (U.S.N.M. 136111) of this species have been deposited in the U.S. National Museum of Natural History, Washington, D.C., as have a series of 10 male and 10 female paratypes (U.S.N.M. 136112). Diagnosis.-With the diagnostic characters of the subgenus Aglaodiaptomus as presented by Wilson (1955). Length (from front of head to base of caudal setae): Male (12 animals examined), range 1.80 1.98 mm, mean 1.90 mm; female (17 animals examined), range 1.83 2.17 mm, mean 2.06 mm. Greatest width of body in region of segment 2 of metasome. Metasomal wings of female not expanded laterally but quite markedly asymmetrical; left wing strongly bifid with inner lobe prominent and clearly reaching beyond outer lobe; right wing much less bifid with the inner lobe only slightly larger than the outer portion and not reaching noticeably beyond it (Figs. 1 and 2). 1 Present address: National Oceanic and Atmospheric Administration, 2300 Washtenaw, Ann Arbor, Mich. 48104.

DIAPTOMID COPEPODS FROM TWO MOUNTAIN PONDS IN ALBERTA

Two occurrences of coexisting populations of diaptomid copepods were investigated in two mountain ponds in Alberta. Diaptomus shoshone was found to be predaceous on smaller diaptomid species. Structural differences and their relationships to differences in feeding habits were examined. Certain anomalous structures were noted and some possible explanations regarding these anomalies are offered.