David G. Frey

The taxonomy and biogeography of the Cladocera

For a variety of reasons, including the analysis of a number of taxa having the same names on different continents, we have concluded overwhelmingly that the chydorid Cladocera are not cosmopolitan in distribution but instead are restricted to smaller regions by their specific ecological requirements for habitat type and also by long-term events in earth history. Recent study of Chydorus faviformis and species resembling it indicates there has been no effective exchange of genetic material between North America and South America, nor between Australia and Asia, nor even between China, Malaysia, and India in southern Asia. Moreover, the patterns of distribution are even narrower than this, as in North America, for example, taxa having the same names in the southern states as in the northern states are differentiated at the species level in some instances, possibly in most. Southern species push northward along the Atlantic Coast for varying distances, one species having reached Nova Scotia and Newfoundland probably during the warm interval in mid-Postglacial time. Thus, when species are studied closely to define their morphological limits, cosmopolitanism disappears, and patterns of distribution emerge that are very similar to those of other animals and plants.

On the plurality of Chydorus sphaericus (O. F. Müller) (Cladocera, Chydoridae), and designation of a neotype from Sjaelsø, Denmark

Two readily distinguishable species of Chydorus sphaericus sens. lat. occur in Salmon Lake, Montana, differing from each other in size and shape of rostrum, headpore configuration, frequency of doubling of teeth on the postabdomen, pattern of reticulation of the shell, and morphology of the mature male, especially the postabdomen, postabdominal claws, copulatory hooks, and rostrum. In any such comparisons, individual specimens are not sufficient; populations are needed to sort out morphological characters associated with instar and sex and characters that change with increasing body size. Comparison of population structure and stage of reproduction can be accomplished by a size-frequency distribution and by specific morphological characters that enable the three male instars to be recognized individually.One species, thought at first to be Chydorus herrmanni, is very close to Chydorus sphaericus sens. str. from Denmark. The other taxon with a short, generally blunt labrum, is described as the new species Chydorus brevilabris. Because of morphological diversity among the entities currently listed as Chydorus sphaericus from around the World, it is certain that a complex of species is represented. To facilitate the eventual resolution of this problem, the population in Sjaelsø, Sjaelland, Denmark has arbitrarily been selected as the standard of comparison, and from this population a neotype and several allotypes have been designated. Cursory examination of various available populations suggests that C. sphaericus sens. str. and C. brevilabris represent a major dichotomy in the sphaericus complex, each branch consisting of an unknown number of closely-related species. Cautions are voiced against assuming that Chydorus sphaericus is a single cosmopolitan and ubiquitous species.

The penetration of cladocerans into saline waters

Cladocerans are essentially freshwater organisms, many of which have been able to penetrate slightly saline waters (up to 5‰ salinity), both thalassic and athalassic, some of which occur at high salinities, and a few of which, mostly non-chydorids, penetrate still higher salinities (15–30‰ and even higher) and may be confined to these salinities. Three previous studies from Saskatchewan, Iran, and Germany (the latter including thalassic waters) have been analyzed, and records for the athalassic saline waters of the World have been summarized; all results show a decline, at some point, in species number against increasing concentration of salinity.Examination of samples for 67 waterbodies in southern Australia and 167 in South Africa, covering the full salinity range over which cladocerans occur, reveals much the same relationships. Graphical analysis was carried out using salinity intervals defined along a logarithmically-scaled conductivity axis.The mean number of chydorid taxa per site was considerably greater in Australia than in South Africa, and this was true for both freshwater (< 5 mScm−1) and saline (> 5 mScm−1) sites. In both countries, the number of chydorid taxa per site showed little variation with conductivity over the freshwater range but declined rather abruptly at conductivities > mScm−1. For South Africa, there was also some indication of reduced numbers of chydorid taxa in the most dilute (< 0.2 mScm−1) waters.Non-chydorid taxa, which were analysed only on a generic basis, averaged much more numerous in Australian saline sites than in either South Africa saline sites or Australian freshwater ones. Mean number of non-chydorid taxa per site was about the same for Australian and South African freshwater sites.Plots of total number of taxa observed per conductivity interval had maxima in the 0.2–0.7 mScm−1 conductivity range and decreased at higher and lower conductivities. This trend to some extent only reflected the effect of the variation in number of sites per interval; a negative impact on chydorids of very low conductivities (<0.2 mScm−1) is nevertheless suggested.

Pollen Succession in the Sediments of Singletary Lake, North Carolina

In ail attempt to unravel the complicated ontogeny of some natural lakes in the North Carolina Coastal Plain on the basis of their accumulated sediments, the writer was led into the analysis of the plant and animal remains contained ill them. Pollens and spores, primarily those of aerial plants. are by far the most abundant of all microfossils in these sediments, and because of their diversity and very long period of accumulation they afford an excellent means of determining the relative total age of the sediments and of correlating the sediments from various parts of the basin as to contemporaneity. Pollen studies in eastern North America have been confined largely to the glaciated portion because of the abundance there of glacial basins filled with peat deposits. Similar studies south of the glacial boundary are few and scattered. The first of these by Lewis and Cocke (1929) and later by Cocke, Lewis, and Patrick (1934) describes the pollen and spores at various levels in the recent deposits of the Dismal Swamp near Lake Drummond in Virginia. Buell (1945) made some investigations on the sediments of Jerome Bay near Singletary Lake, but never published any comprehensive quantitative account of his findings. Cain (1944) reported on the pollen content of some buried soils in South Carolina, but these at present cannot be fitted into an overall chronology of the region for the determination of their relative age. Sears (1935) presented a few diagrams for Arkansas and eastern Tennessee. Darlington (1943) recorded the pollen sequence in a bog in West Virginia. Potzger (1945) shows a few diagrams from southern New Jersey. And finally, Potzger and Tharp (1947) present a significant pollen diagram from a bog in Texas. These analyses are still too scattered and often too fragmentary for one to draw generalizations or to try to find south of the glacial boundary the several postglacial climatic periods that have been established for the glaciated region. (See Deevey 1949, for a review of this problem.) The one generalization that can be made is that all of these southern diagrams which extend back far enough show spruce, and sometimes fir, in the lowermost horizons. It has been surmised that such horizons are from the Pleistocene.

Relocation of Chydorus barroisi and related species (Cladocera, Chydoridae) to a new genus and description of two new species

Five taxa already in the literature are here removed from Chydorus to their own genus Ephemeroporus, and two new species — E. acanthodes and E. archboldi — are described, with E. acanthodes being designated the type species of the genus. These taxa, plus at least nine undescribed species and others undoubtedly waiting to be sorted out, constitute a tightly circumscribed group of species morphologically. The first two species described — E. barroisi and E. poppei — are nomina dubia for the present, as no specimens exist from the original collections, nor are any available from the type localities or reasonably close thereto. E. hybridus from Brazil has been characterized in greater detail through the availability of specimens from the type series, which has enabled one of the species in the E. hybridus group from North America to be judged conspecific with reasonable certainty. E. tridentatus, from Brazil, has been restored as a valid species, and the highly distinctive E. phintonicus from Sardinia and Algeria constitutes the seventh species in the genus. Chydorus nitidulus and Chydorus tilhoi, which have been suggested to be members of the barroisi complex, are not. What are presently called E. barroisi and E. hybridus, except for E. hybridus, sens. str., each consists of a cluster of species sharing the same number of teeth on the labrum and shell. Because of their wide, distribution, abundance, and frequency of occurrence, especially in South Asia, the species in the E. barroisi group will be especially meaningful to sort out.

A new genus of alonine chydorid cladocerans from athalassic saline waters of New South Wales, Australia

A new genus (Celsinotum) and three new species are described from intermittent athalassic saline waters in the Paroo region of northwest New South Wales, which have TDS varying from 2.8 to 14.0 g l-1. The species are large, thin, high-bodied, and have a pronounced keel on the shell but not on the head. The marginal armature of the postabdomen consists entirely of clusters of fine spinules. Most strikingly, the males have 12 terminal aesthetascs on the antennule, and in addition have 5 or 6 equally long accessory aesthetascs arising laterally. Alona taraporevalae from India presumably also has this character, but a comparison of the two species indicates they are not closely related.The taxa bear a general similarity to Alona diaphana from Australia, but a close comparison shows that they, too, are unrelated. A. diaphana has a prominent spine arising from the basal segment of the antennal exopod, the two IDL (= inner distal lobe) setae on trunklimb I have a much coarser setulation distally than in Celsinotum, and on the postabdomen the postanal portion is always considerably longer than the anal, and the marginal armament consists of single setae distally and clusters of only a few setae proximally. Besides, the species is smaller, the body is wider and less high, and the shell although weakly ridged is not keeled. The male has 9 terminal aesthetascs and no accessory lateral ones.In athalassic saline waters around the world the number of anomopod species declines negative exponentially in relation to salinity. Many of the freshwater species persist into the 3 to 10‰ range without any difficulty, some occur in abundance up to 30‰, and a few even extend into the hypersaline range. Chydorids, though, except for a very few species, do not tolerate salinities higher than about 15‰, and none of them seem adapted to these salinities and confined to them. Celsinotum, though, possibly is so adapted, as it did not occur in other basins of the region with lower salinities, and it is not presently known from other regions.Having different but closely related congeneric taxa in nearby lakes of the same region seems surprising. The three species of Celsinotum are very similar in most details of morphology, but they vary significantly in body proportions, the number of denticle clusters on the postanal portion of the postabdomen, and in such seemingly minor details as the amount of expansion of the labral plate. Such taxonomic differentiation, which has been observed in other groups of organisms as well, is believed to have arisen from the extreme temporal isolation of these waterbodies, those in the Paroo region normally containing water only once every 5 to 20 years.

Differentiation of Alona Costata Sars From Two Related Species (Cladocera, Chydoridae) 1)

[Die drei Arten der Gattung Alona, welche in dieser Arbeit behandelt werden, sind nahe verwandt aber leicht voneinander zu unterscheiden. A. rustica Scott, welche hier zum ersten Mal von ausserhalb Grossbritanniens gemeldet wird, hat eine weite Verbreitung in Nordamerika. A. iheringi Sars aus Brasilien und A. estonica Maemets aus Estland reprasentieren Angehorige der gleichen Art und wurden hier daher mit A. rustica vereinigt. A. bicolor sp. nov. unterscheidet sich von den beiden anderen Arten durch folgende Merkmale: 1) das Rostrum uberragt das Ende der Borsten der ersten Antennen, 2) das Nebenauge ist grosser als das Auge, 3) der vordere Lippenanhang hat einen grossen, rundlichen Einschnitt an der vorderen Oberkante, 4) die Schale ist zweifarbig, und 5) die Individuen sind gewohnlich grosser. A. bicolor ist bis heute nur aus Neu-England bekannt, wo sie in denselben Gewassern wie die anderen beiden Arten vorkommen kann. A. costata und A. rustica leben auch in anderen Gegenden zusammen in denselben Seen., Die drei Arten der Gattung Alona, welche in dieser Arbeit behandelt werden, sind nahe verwandt aber leicht voneinander zu unterscheiden. A. rustica Scott, welche hier zum ersten Mal von ausserhalb Grossbritanniens gemeldet wird, hat eine weite Verbreitung in Nordamerika. A. iheringi Sars aus Brasilien und A. estonica Maemets aus Estland reprasentieren Angehorige der gleichen Art und wurden hier daher mit A. rustica vereinigt. A. bicolor sp. nov. unterscheidet sich von den beiden anderen Arten durch folgende Merkmale: 1) das Rostrum uberragt das Ende der Borsten der ersten Antennen, 2) das Nebenauge ist grosser als das Auge, 3) der vordere Lippenanhang hat einen grossen, rundlichen Einschnitt an der vorderen Oberkante, 4) die Schale ist zweifarbig, und 5) die Individuen sind gewohnlich grosser. A. bicolor ist bis heute nur aus Neu-England bekannt, wo sie in denselben Gewassern wie die anderen beiden Arten vorkommen kann. A. costata und A. rustica leben auch in anderen Gegenden zusammen in denselben Seen.]

First subfossil records of Daphnia headshields and shells (Anomopoda, Daphniidae) about 10 000 years old from northernmost Greenland, plus Alona guttata (Chydoridae)

Silty pond sediments from Wulff Land in northernmost Greenland, radiocarbon dated 10480 BP, yielded many headshields, shells, and ephippia of Daphnia pulex, and headshields, shells, ephippia, and one postabdomen of Alona guttata. This is the first documentation of recognizable headshields and shells of Daphnia in the fossil record.

Subgeneric differentiation within Eurycercus (Cladocera, Chydoridae) and a new species from Northern Sweden

Eurycercus, although quite uniform in casual gross morphology, is now regarded as a highly differentiated group of Cladocera, split into three subgenera: Eurycercus for the species lamellatus, Teretifrons subgen. nov. for glacialis, and Bullatifrons subgen. nov. for macracanthus and pompholygodes sp. nov. At least four other species await description. E. pompholygodes differs from macracanthus most strikingly in having a less well developed clasping hook on trunk limb I and in having more teeth on the postabdomen. The latter character, being size-dependent like many others, can be described only by a regression. Other important characters are the regressions of the number of denticles on the postabdominal claw, the size of the median head pore, the number of setules in three clusters on trunk limb I, and the number of denticles on scraping spines 2, 3, and 4 of trunk limb II. Biologically the species has five pre-reproductive instars in parthenogenesis, six in gamogenesis. Once reproductive capacity is achieved, a brood of parthenogenetic young is produced each instar but a brood of gamogenetic eggs only every other instar, successive broods being separated by a barren instar. The gradual ontogeny of males, particularly of their antennule and trunk limb I, to functional maturity in instar III is described. Two parasites occur, both selective for large individuals, and one seemingly important in helping control population structure. The reproductive potential of all four species is described by regressions and related to egg size and size at maturity.

The reticulated species of Chydorus (Cladocera, Chydoridae): two new species with suggestions of convergence

Of the two small, compact, dusky, reticulated species of Chydorus from Sri Lanka, one arbitrarily has been selected as the taxon to which Dadays name reticulatus henceforward will be attached, the other herein being described as new. A third species from eastern North America, also described herein as new, resembles the two Asian species in certain gross features but otherwise is very distinct. Particularly noteworthy among these differences are the structure of the labrum and of the male postabdomen and copulatory hook. The question is raised whether the gross morphological features that seem to unite the taxa or the features of the labrum and of the male that separate them are the more conservative. No unequivocal answer is provided. Because of their obvious close similarity, the two Asian species are established as a species group, the one from North America being divergent and therefore not included. The possibility of convergence is considered.The North American taxon in north Florida occurs in waterbodies with a pH less than 5 (down to 4.2), conductivity less than 40 µS, and usually with no more than a trace of dissolved color. They are naturally acidic, non-bog lakes. The number of species of chydorids and of total littoral Cladocera in them are considerably greater than found by Fryer in waterbodies of comparable acidity in England. The occurrence also of a diversity of macrophytes and fishes in these lakes indicates that pH per se is not the factor forcing the decreasing diversity associated with changes resulting from acid precipitation.