On age morphological changes of males of Chydoridae (Cladocera)

Summary Young and adult males of 11 species of Chydoridae are studied, their figures being published here (fig. 1–15). The necessity is stressed to distinguish young forms of males and gynandromorphic individuals.Pleuroxus balatonicus is considered to be described from the population ofPleuroxus unicatus having under Balaton Lake conditions retarded transformation of young males into adult form, and accordingly having unusually numerous young males. \qO\qs\qn\qo\qv\qn\qy\ye \qr\ye\qz\qu\ql\Qj\qt\qa\qt\qy 11 (. 1–15). . , Pleuroxus uncinatus , Pleuroxus balatonicus.     

Life histories of some species of Chydoridae (Cladocera: Crustacea)

SUMMARY 1. Life history parameters of two species of Chydoridae ( Leydigia leydigi and Disparalona rostrata ) were studied in the field and in the laboratory.
2. For both species the number of juvenile instars was variable and tentatively related to initial size of neonate. Egg volume increased with increasing parent length and with decreasing temperature; possible advantages gained by the offspring are discussed in relation to invertebrate predation.
3. The life history strategy employed by the littoral Chydoridae is compared to that of large and small planktonic cladocerans. Small planktonic cladocerans and the Chydoridae (except the Eurycercinae and the Saycinae) produce large young relative to their size at maturity and mature early. However, unlike the small planktonic cladocerans, growth in the Chydoridae is curtailed after the onset of reproduction and in this they resemble the large planktonic cladocerans. This strategy may be related to vertebrate predation and the presence of vegetation in the habitat.     

Allozyme variation among natural populations of Holopedium gibberum (Crustacea; Cladocera)

• 1 Holopedium gibberum, from twenty lakes in Rhode Island and Maine, were examined for allozyme variation at five loci to determine the pattern and degree of generic variation among sites and the genetic structure within individual lakes.
• 2 There were significant differences in allele frequencies among sites. Most populations were fixed for a particular allele at each locus. Only five lakes had polymorphic populations.
• 3 Polymorphic populations showed significant deviation from expected Hardy-Weinberg genotype frequencies. In each case, there was an excess of homozygotes.
• 4 Two lakes were examined for intra-lake allele frequency differences. In one lake there were no differences. The other lake exhibited significant allele frequency differences between stations at the north and south ends of the lake.
• 5 Populations were examined for the frequency distribution of composite genotypes over three loci. Most populations were dominated by one or two genotypes.
• 6 The results suggest sporadic sexual recruitment and a high degree of genetic isolation among these populations of H. gibberum. In these respects they resemble the permanent pond populations of Daphnia magna examined by Hebert (1974a).

     

A contribution to the taxonomy ofC. sphaericus sens. lat. (Cladocera,Chydoridae)

Two distinct morphotypes ofChydorus sphaericus are recognised in Ireland. A reference collection of scanning electron micrographs of male and femaleC. sphaericus sens. str. has been compiled. This collection is used to compare the varying morphological features of Danish and Irish material to determine their taxonomic significance. However, no taxonomic decisions can be made about the Irish morphotypes until mature males and ephippial females become available. Comparison of population structures and stages of reproduction are accomplished by size-frequency distribution. This study illustrates the ever increasing value of scanning electron microscopy (SEM) in chydorid taxonomy, where characters such as shell-reticulation features may easily be misinterpreted using only light microscopy.     

The impact of conifer plantation forestry on the Chydoridae (Cladocera) communities of peatland lakes

Conifer plantation forestry is recognised as a potential source of diffuse pollution to surface waters and represents a risk to their ecological status. In this study, the water chemistry and Chydoridae (Cladocera) communities of 26 small blanket bog lakes were investigated to assess the impact of plantation forestry. The study was conducted over a 12-month period in 2009?C2010 by comparing lakes with three distinct catchment land uses: (i) unplanted blanket bog only present in the catchment, (ii) mature conifer plantation forests only present in the catchment and (iii) catchments containing mature conifer plantation forests with recently clearfelled areas. All three catchment land uses were replicated across two geologies: sandstone and granite. Lakes with afforested catchments had very high concentrations of plant nutrients (P and N), total dissolved organic carbon (TDOC) and heavy metals (Al and Fe), the highest concentrations being recorded from the clearfelled lakes. Similarly, the chydorid communities differed between lakes of contrasting catchment land use. The dominance of Alonopsis elongata in the unplanted blanket bog lakes shifted to dominance by the smaller bodied Chydorus sphaericus, along with Alonella nana, Alonella excisa and Alonella exigua, in the plantation forestry-effected lakes, consistent with a shift in lake trophy. Our findings have shown that plantation forestry can have a profound impact on the water quality of small peatland lakes, especially at the clearfell stage. The response of the chydorid communities is consistent with plantation forestry exerting a trophic, rather than an acidic or toxic, effect on lake ecosystems.     

Laboratory studies on the life cycle of Leydigia acanthocercoides Fisher (1854) (Cladocera: Chydoridae)

The biology of Leydigia acanthocercoides has been studied under laboratory conditions with reference to longevity, instar duration, growth, fecundity and embryonic development at a temperature range of 28–30 °C. It has three preadult and thirteen adult instars. Under the given laboratory conditions this species produces 20 eggs during a life span of 23 days. The number of eggs produced is uniformly constant in all adult instars. The growth rate seems to be exponential in the early phase of the life cycle as in other Cladocera. The general pattern of embryonic development of L. acanthocercoides is similar to those of other tropical cladocerans though differences in the duration of total developmental period have been recorded.Part of Ph.D. thesis.     

A hidden species becoming visible: biogeography and ecology of Rhynchotalona latens (Cladocera,Anomopoda, Chydoridae)

Hydrobiologia - A long hidden chydorid (Chydoridae, Cladocera) taxon, first found as fossil specimens and recently redefined as Rhynchotalona latens (Sarmaja-Korjonen et al., Hydrobiologia 436:...     

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 Daday's 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.     

Discovery of groundwater-inhabiting Chydoridae (Crustacea: Cladocera), with the description of two new species

The groundwater along the Couze (= river) Pavin in Auvergne, France, yielded four chydorid Cladocera, among which two are known but rare species, while two are new species. One of the new species, Alona phreatica, has reduced eye and ocellus-sizes, but no other adaptations to a groundwater-mode of life are apparent. The likelihood that more phreatic species exist in other parts of Europe and elsewhere is discussed.     

Assumed Amphi-Atlantic distribution of Oxyurella tenuicaudis (Cladocera,Chydoridae) denied by a new species from North America

Up to now the taxon Oxyurella tenuicaudis, described from Norway, has been claimed to occur in North America as well. However, our close study and comparison of populations from the two continents show them to be different in many major morphological details, involving principally the female and male postabdomens, labrum, headpore configuration, and the external sculpturing of the shell. The new species O. brevicaudis occurs from the Maritimes to Manitoba in southern Canada, southward throughout the region east of the Plains to Guatemala and possibly Panama. Two enigmatic outlier populations are known from the Northwest Territories and the State of Washington. A greater frequency of occurrence in the southeastern states compared with southern Canada, together with its extension of range into the Tropics, suggests that this taxon prefers the lower north temperate latitudes. Although widely distributed, its frequency of occurrence is very low. Just as interesting as the characters that separate these two species are those that unite them into the cohesive genus Oxyurella. Although the few other species in the genus have not been studied in sufficient detail, fragmentary information suggests that they also conform to the pattern of commonality emerging from this study. These potential generic characters include: 1) only one seta on the outer distal lobe of trunklimb I and two on the inner distal lobe; 2) 4 median headpores not connected to one another by any channel or raised chitinous ridge, although the light microscope shows irregular dark thickenings around each pore and occasional connections between the three anterior pores; 3) antennules of the male being very similar to those of the female except for the 2-segmented male seta and the addition of one more aesthetascs at the tip, for a total of 10 compared with the typical number of 12 in chydorid males; 4) a significant reduction in size of the seta arising from the middle endopodite segment of the male antenna as compared with the female; 5) use of the entire shell as an ephippium, without any external modification but with an internal foam-like mass secreted (?) into the brood pouch around the egg. Other populations outside western Europe claimed to be O. tenuicaudis need to be studied closely to evaluate their presumed conspecificity. Very likely at least some will be found to be different. As aids in this process of evaluation, besides specimens from Gjennestadvannet placed in various museums, including the Zoological Museum in Oslo, a lectotype has been selected and designated herein from among the few specimens mounted and studied by G. O. Sars.     

Separation of Leydigia louisi Jenkin, 1934 from L. leydigi (Schoedler, 1863) (Chydoridae, Anomopoda, Cladocera)

The aim of the present article was to contribute to the systematics of the leydigi-like species of Leydigia consisting of a few (probably 3) formal species with: (1) a large basal spine on the postabdominal claw (as long as claw thickness at the base); (2) a short setulation at anterior margin of labral keel; (3) no longitudinal striation on the female valves; (4) at least three lateral setae in each fascicle on the postabdomen; (5) three large lateral setae on exopodite III. The morphology of L. leydigi (Schoedler, 1863) and L. louisi Jenkin, 1934 are redescribed, and type material of L. macrodonta Sars, 1916 is studied. In contrast to previous suggestions (Jenkin, 1934; Smirnov, 1971), I found that: (1) L. louisi is a valid species, not a subspecies of L. macrodonta; (2) L. macrodonta is not a member of the L. leydigi-group. The third member of leydigi-group, Leydigia macrodonta longiseta Chen Shou-zhong, 1992, was described from China. It is not a subspecies of L. macrodonta, but a relative of L. leydigi; most probably, it is a valid species, but this opinion must to be confirmed by examination of original Asian material. In this article, the presence of L. leydigi in Palearctic only, and that of L. louisi in only Africa was confirmed. A new subspecies of L. louisi, found in Mexico, will be reported separately.     

Alona hercegovinae n. sp. (Cladocera: Chydoridae), a blind cave-inhabiting Cladoceran from Hercegovina (Yugoslavia)

Two interesting chydorid Cladocera were found in caves of Hercegovina and are described here. The pantropical Alona diaphana King, 1853 was already known in this part of Europe, but was found in a cave environment for the first time. Alona hercegovinae n. sp. is an eyeless and stygobiontic species, and was found in three caves.     

Worldwide distribution and ecology of Alonopsis (Cladocera: Chydoridae) with a description of Alonopsis americana sp. nov.

Whereas Alonopsis is widespread in Eurasia west of the Ural Mountains, in the Western Hemisphere Alonopsis has been recovered only in eleven lakes in New Hampshire and Maine and in two lakes in Newfoundland. The North American population is well differentiated from the Eurasian Alonopsis elongata and is described as a new species, A. americana. To test if the species were reproductively isolated, parthenogenetically reproducing stocks from England and New England were raised in the labaratory, and subsequently induced to undergo gamogenesis. Interspecific crosses were never successful.     

The population dynamics of Chydoridae and Macrothricidae (Cladocera: Crustacea) from the River Thames, U.K.

SUMMARY.

• 1 A study was made of the population dynamics of benthic cladocerans in the River Thames, U.K. These included three species of Chydoridae (Alona affinis Leydig, Disparalona rostrata (Koch 1841) and Leydigia leydigi Schodler) and one species of Macrothricidae Iliocryptus sordidus (Lievan).
• 2 The pattern of chydorid abundance was similar to that found in many lakes: a midsummer peak followed by a sharp decrease in numbers and subsequent low abundance. This was caused by a temporary decrease in natality, possibly due to food limitation, and a more permanent increase in mortality, thought to be due to predation.
• 3 Iliocryptus sordidus differed considerably from the chydorids, the major population peak occurring in the autumn. The lifestyle and adult size of Iliocryptus sordidus (Lievan) must render adults less vulnerable to invertebrate and fish fry predation.
• 4 A literature survey showed that the assemblage of species found in the unvegetated littoral of lakes and rivers included a taxocene of cladocerans.

     

The unique headpore of Monospilus dispar (Cladocera,Chydoridae) is not lonesome: new record of minute lateral pores

The headshield of Monospilus dispar (Cladocera, Chydoridae, Aloninae) was characterized by the presence of a unique headpore. Scanning Electron Microscopy shows the occurrence of minute pores close to the main headpore. The intimate structure of the main headpore is formed by concentric lamellae. This new information leads to new considerations about phylogeny.     

Estimating the size at maturity in field populations of Daphnia (Cladocera)

• 1 Two methods for estimating the average body size at the onset of reproduction were applied to populations of Daphnia hyalina. The first, ‘average maturation size’, assesses maturity by the relative length of abdominal processes of Daphnia; the second, ‘size at first reproduction’ (SFR), calculates the size class in which 50% of the maximum proportion of egg-bearing females is reached.
• 2 The influence of environmental factors on the expression of the difference in length between the first and the second abdominal process was tested in the laboratory. Neither temperature nor chemical cues from predators affected the difference in length, but the processes were indistinguishable at very low food concentrations.
• 3 During one season, D. hyalina exhibited pronounced changes in fecundity, proportion of egg-bearing adults and SFR. The pattern obtained by the two methods was similar in many cases, although maturation size estimated by the first method was slightly smaller than SFR obtained by the second method. Neither method gave reliable results during times of starvation (clear-water phase).