Subfossil remains of an unknown chydorid (Anomopoda: Chydoridae) from Finland

Subfossil remains of an unknown chydorid taxon were found in sediments of three lake basins in Finland. Two of the sites lie in southern Finland and one in NW Finnish Lapland. Similar remains are also known from four lakes in eastern Finland. The headshields are small, with a broadly rounded posterior margin and an attenuated rostrum. The headshields resemble those of Rhynchotalona falcataSars, but have a unique pore arrangement. There is one oval median pore near the posterior margin and two lateral pores which are displaced quite far in position. The shell is very small and has faint, longitudinal striae. Also, unknown postabdomens were found. These resemble postabdomen of R. falcatain shape but had 5–6 pairs of teeth instead of the 2 seen in R. falcata. The age of the remains varies between ca. 8500 ¹⁴C yr BP and recent decades. The species appears to have been present in the entire country during most of the Holocene. On the basis of the pore arrangement, the new species cannot be put into any previously known genus. A tentative name Unapertura latensn. sp. is suggested until intact specimens are found and described.     

Eurycercus glacialis in Ireland (Cladocera,Chydoridae)

The taxon Eurycercus glacialis of Western Europe has been discovered living in the turloughs (tuar loch = dry lake) of Western Ireland. Only four populations were found during three field excursions, but because of the multitude of these waterbodies in the region, there must be many populations present. Turloughs are mainly periodic waterbodies occupying depressions in the drift overlying limestone. Most of them dry every year, and the bottoms are then used for grazing cattle. This periodicity prevents the establishment of fish populations, which would rapidly eliminate the cladoceran by size-selective predation. Only one of the many populations known from Western Europe survives in the presence of fishes. A species of the glacialis group in Newfoundland (not yet described), which is the southernmost known location of E. glacialis sens. lat. in the world, occurs commonly with salmonid or gasterosteid fishes, but this is a completely different species. Scanning electron micrographs of E. glacialis and E. lamellatus in Western Europe will aid in understanding their morphological differences.     

Benthic macroinvertebrate biomass and wildfires: evidence for enrichment of boreal subarctic lakes

1 We quantified the effects of forest fire on littoral benthic macroinvertebrate biomass on a boreal subarctic plateau in Alberta, Canada. Water chemistry and benthos were collected from six lakes, 1 and 2 years following a 1995 fire which burned about 91% of their catchments (i.e. recently burnt lakes), and from four other lakes whose catchments burned between 1961 and 1985 (i.e. previously burnt lakes). Seven lakes whose catchments had not burned since at least 1957 served as reference systems.
2 Total benthic macroinvertebrate biomass and biomass of Chironomidae were 1.5‐ and 2‐fold (P<0.05) greater within recently burnt lakes than in reference systems, whereas the biomass of Oligochaeta (P=0.06) and Amphipoda (P=0.07) were marginally higher in burnt than reference lakes. Burnt lakes had greater colour (P<0.05) and marginally (P=0.06) higher concentrations of soluble reactive phosphorus than reference lakes.
3 Nutrient diffusing substrata deployed in a previously and a recently burnt lake indicated that littoral epilithic communities were co‐limited by the availability of phosphorus (P) and nitrogen (N), although co‐limitation was stronger in the previously burnt than the recently burnt lake. Epilithic chlorophyll a on natural stone surfaces in the recently burnt lake was also 3.5 times higher (P<0.05) than that from the previously burnt lake.
4 Among all 17 lakes, total benthic biomass and biomass of Chironomidae, Amphipoda and Nematoda, were significantly (P<0.05) or marginally (P=0.06) related to soluble reactive phosphorus (SRP) but not dissolved inorganic nitrogen or colour. These regressions explained between 11% and 64% of variation in benthic biomasses.
5 Linear regressions and second‐order polynomials explained 18% and 24% of the variation in concentrations of SRP and water colour with time since fire, respectively, and between 22% and 70% of variation in total biomass and biomass of the five dominant invertebrate groups. These analyses suggest that benthic biomasses continue to be elevated for about 15–20 years following fire before declining to pre‐disturbance levels.     

Intensity of autumnal gamogenesis in chydorid (Cladocera,Chydoridae) communities in southern Finland,with a focus on <Emphasis Type="Italic">Alonella nana</Emphasis> (Baird)

The aim of this study was to examine whether there was variation in the intensity of gamogenesis (sexual reproduction) in communities of chydorid cladocerans during the autumnal sexual reproduction period. The proportions of gamogenetic individuals (i.e., intensity) in the chydorid communities of seven lakes in southern Finland were determined in weekly samples throughout the autumn of 2005. The period of gamogenetic reproduction began very synchronously in the lakes as a response to climatic forcing and proportions of gamogenetic individuals progressively increased towards winter. However, wide variation was found in intensity among the communities. The high intensity probably was a response to some environmental stressors (e.g., invertebrate predation, crowding, competition, or changes in water chemistry) to ensure genetic variability and future populations. One common species, Alonella nana showed exceptional, dualistic, gamogenetic behavior, since in some communities it reproduced with high and in others with extremely low gamogenetic intensity. It is possible that in the former it responded to environmental stressors by exhibiting high intensity of gamogenesis, thus renewing its genotypes, while in the latter it succeeded primarily by parthenogenetic (asexual) reproduction, and was possibly perennial. The high gamogenetic intensity in A. nana was related to dystrophic and mesotrophic conditions, but it correlated positively only with water conductivity.     

Alonella and Dunhevedia (Chydoridae,Cladocera): Morphology of trunk limbs

Summary The legs of some species of genera Alonella and Dunhevedia are described, including the type species of these genera. The structure of the endites and gnathobases is depicted and described in detail. The structure of legs of the studied species is compared with that of species of some other genera, including Eurycercus and Saycia.     

Zooplankton (Cladocera) in assessments of biologic integrity and reference conditions: application of sedimentary assemblages from shallow boreal lakes

Zooplankton are potentially powerful proxies for the assessments of biologic integrity. The paleolimnological perspective and use of fossil Cladocera also provide the means to reconstruct reference conditions and natural long-term community dynamics. Unfortunately, the use of zooplankton in lake quality assessments is currently underexploited. We studied a surface sediment dataset of 41 lakes in Finland to examine the relationship between Cladocera remains and environmental variables. Of the examined environmental variables, total phosphorus availability was found to be the most important variable in explaining the Cladocera community composition. Following the tests on species environment relations, we selected a lake trophic typology as the most suitable environmental variable for developing a new tool for limnoecological quality assessments. A test of the model on a modern and historic sample from a eutrophied lake showed that the test lake has proceeded from “mesotrophic/poor” to “eutrophic/bad” limnoecological state in agreement with previous independent evidence. The model developed here showed favorable performance that can be used to provide reliable estimates of ecological and environmental state of lakes.     

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.     

A New Species of the Chydorus sphaericus Group (Cladocera,Chydoridae) from Western Montana

Chydorus biovatus differs from C. sphaericus sens. str. in that the ephippial female carries two resting eggs, for which the brood pouch is expanded dorsally. resulting in a sharp angle in lateral contour near the junction of the head and shell and in the postpore distance being much elongated. The mature male has the pre-anal angle of the postabdomen rounded and the rostrum broadly rounded, both features being much different than in C. sphaericus sens. str. In North America there is a progressive replacement of C. brevilabris-group species in the South to C. sphaericus-group species in the Far North. Production of two resting eggs by Chydorus piger is recorded.     

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.     

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.

     

Subgeneric differences in head shield and ephippia ultrastructure within the genus Bosmina Baird (Crustacea,Cladocera)

Seven samples of roach (Rutilus rutilus L.) fromthe Austrian section of the Danube river, the Drauriver and lake Wallersee were examined to studypossible population genetic effects of anthropogenichabitat modification and subdivision. Geneticvariability was assessed using electrophoreticvariation of 11 enzyme systems coded by 14 gene loci.Genetic variation of roach was remarkably high, andwas mainly located within samples while differencesbetween them were weak. Morphometric analyses ofconventional external measurements revealedconsiderable morphological variation within samples.Significant differences between samples mainlyinvolved body depth and fin size, but did not allowadaptive ecomorphological interpretations in severalcases. The comparison of morphological and geneticvariation showed no significant correlations but waslimited by the narrow range of heterozygosityestimates.     

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.     

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.     

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.