Record of Argyrodiaptomus bergi (Crustacea: Copepoda: Calanoida) after 36 years and first record in Brazil

The first record of Argyrodiaptomus bergi (Richard, 1897) from a small roadside pool at high altitude in the southern region of Brazil is presented. This is the ninth record of this species in South America (previously known from Argentina and Uruguay) since its original description, and a new occurrence after 36 years, extending its known distribution to the northeast. The environments where this species was found differ sharply, and possible explanations include the loss of habitat, high species selectivity or deficient sampling efforts. An additional description is provided, with scanning electron microscopy (SEM) photomicrographs and line drawings. Similarly to other species of Argyrodiaptomus, such as Argyrodiaptomus falcifer (Daday, 1905), Argyrodiaptomus denticulatus (Pesta, 1927) and Argyrodiaptomus granulosus (Brehm, 1933), this species shows a restricted distribution in the lower stretches of the Parana and Uruguay rivers, particularly in small pools. The importance of better understanding the dynamics and diversity of small water bodies is discussed.

At the time of sampling, the pool was approximately 70 m -2 in area and 1.5 m in maximum depth (Fig. 2). It was situated at an altitude of 1,400 m a.s.l. Water temperature was 10°C. Samples were obtained through horizontal hauls using a plankton net of 50-µm mesh size, with an aperture diameter of 25 cm, through open water. The filtered volume was estimated using the cylinder formula and the distance of haul. The material was concentrated and preserved in 90% ethanol.
Quantitative and qualitative analyses were performed in the laboratory. One sample was quantified from three subsamples of 10 ml each, and a minimum of 100 individuals was counted, in gridded acrylic chambers. The abundance was expressed as individuals.m -3 .
Subsequently, male and female copepods were sorted and washed with distilled water. Ten males and ten females were dissected and mounted on slides in lacto-phenol and glycerin. Measurements of the following structures (n = 30 for each sex) were made: 1) total body length excluding furcal setae; 2) total body length including furcal setae; 3) length of thoracic segments; 4) antennule length; 5) maximum thoracic segment width. All measurements were made with the aid of a Zeiss Discovery V-20 stereoscopic microscope, and the software Axio-Vision 6.0. Line drawings were made using a Zeiss AxioScope 25 light microscope equipped with a drawing tube.
Twenty specimens of both sexes were prepared for scanning electron microscopy (SEM) following protocols used by FELGENHAUER (1987) and HUYS & BOXSHALL (1991). Observations and photographs were taken with a Quanta 200 FEI electron microscope. Occurrences of A. bergi were plotted using ARCGIS 9.0 software.
Vials containing male and female specimens (10 of each) were deposited in the microcrustacean collections of the Universidade Estadual Paulista "Júlio de Mesquita Filho" (UNESP), Brazil; in the Museu de Zoologia da Universidade de São Paulo, Brazil (MZUSP No. 23473), and in the Instituto Nacional de Pesquisas do Amazonas, Brazil (INPA no. 1876).
The original description of RICHARD (1897)

RESULTS
The present record is the farthest north and east (approximately 950 km from the nearest previously recorded locality). All records are shown in table I and figure 1.
At the time of sampling, the copepods showed an intense red color, with a large body size. About 2,400 specimens including copepodids and adults (males and females) were collected.
Few other zooplankton species were observed. Cladocerans were represented by a large species, Simocephalus cf. semiserratus (3.0-4.0 mm) and some members of Chydoridae. A dense population of the green alga Volvox sp. was observed.
Mean and standard deviations of the measurements are presented in table II. The standard deviations of the structures were low; only antennule length varied more than the other structures. General views of the specimens are presented in figures 3-30. The morphological features, according to the original description of RICHARD (1897), are presented below.
Female. Last thoracic segments fused in dorsal region. Left lateral wing more developed than right. Modified sensil- lum of left lateral wing smaller than right. Genital segment longer than the remaining Ur. Left/anterior margin of GS longer than right. Presence of a small expansion at posterior third of Th5 in dorsal region. Ur2 and Ur3 similar in length. Fu very large and with inner (medial) margin plumose. Fu setae approximately equal to length of Fu and Ur together. Leg 5: enp clearly segmented, with the two segments of similar size. Leg 5: enp length exceeds half the exp length; the extremity bears two sub-apical spines, approximately one-third the enp length; the apical region shows a clear spinule crown. Leg 5: exp-2 cylindrical, distinct, and bears a small apical spine and one robust serrated spine medially, the latter twice the length of the former. Leg 5: exp-1 present on the lateral margin, near the insertion of the last segment, a very small spine, and the medial margin prolonged as a slightly curved claw, with the apex subacute and armed on the margins after the middle, with strong teeth (spinules), sharp and numerous.
Male. Left lateral wing larger than right. Right lateral wing with small spinules. Th5 right edge slightly shorter than right edge, so that right furca appears slightly warped laterally. Ur1: shorter than wide; with extremity on left posterior margin with two small lobes; and right extremity with a small spine, missing on left extremity. Ur3: elongated, all the same width; seta is part of the lateral distal end of the outer edge of the segment. Left antennule reaches middle of abdomen. Right antennule with segments 14 to 18 swollen. Right antennule, segment 13 bears a strong hook, segment 15 with spinous process; the penultimate segment has a curved clawlike extension, long, slender, and acute, and if straightened would reach almost to end of the antenna. Left P5: enp consisting of 1 sub-cylindrical segment, its apex reaching almost the beginning of the last segment of the endopod; enp apex with two spines and a series of spinules; exp1 with a small delicate seta on the last third of the external margin; exp1 inner border forms a terminal projection with coarse tubercles; end of left P5 reaches slightly beyond the middle of the last segment of the right leg; basis internal margin with small rounded chitinous projections; exp1 of left P5 inner surface with bilobed projection ornamented with setules; exp2 distal portion with subspherical projection ornamented with many setules; exp2 end with digitiform, denticulate process; Exp2 with spine slightly curved at its acute tip. Right P5 terminal claw strongly sigmoidal (clearly seen when it is in a perpendicular plane to the two legs).

DISCUSSION
The addition of the present record to the few previous records of A. bergi considerably extends its known distribution to the northeast. The paucity of records may indicate a very selective species; however, sampling efforts are not usually di-  rected to find this sort of organism in time and space. At present, small roadside pools are relatively poorly studied, due to the ease of transportation to large rivers, lakes and reservoirs. Pioneer studies in the beginning of the 20 th century, such as those of S. Wright and F. Kiefer, analyzed many small roadside pools, because of the ease of capturing typical lentic organisms.
Argyrodiaptomus bergi shows an endemic distribution in the lower La Plata River basin. The present record is nearly 1,000 km from the other known sites, and is probably near the northern limit of the species' distribution. However, compared to other species of the genus that are distributed over larger areas, such as A. azevedoi which occurs in northeastern, cen- tral-western and southeastern Brazil, and others distributed through the Amazon region, such as A. robertsonae, we can state that the distance observed in the present record is not so far, being within the limits of species distributions for this genus. Three other species of Argyrodiaptomus also occur only in the lower Paraná and Uruguay rivers, but they are more abundant in rivers and marginal lakes: A. granulosus, A. denticulatus, and A. falcifer. In Brazil, only A. denticulatus is recorded in state of Rio Grande do Sul, in Patos Lagoon, which is the northernmost record of the species. The Patos Lagoon is situated approximately 300 km from the site where A. bergi was found, which indicates that the Brazilian states of Rio Grande do Sul and Santa Catarina may be the limits of distribution for these two species of Argyrodiaptomus, typical of the lower La Plata basin. It is possible that A. granulosus and A. falcifer also occur in Brazil. However, further studies are necessary to elucidate this question. According to previous records, A. bergi occurs in different environments (rivers, lagoons and freshwater pools), with a high altitudinal variability (10-1,400 m a.s.l.), and also occurs during different seasons, between August (present study) and February. RICHARD (1897) found it in November, BRIAN (1926) in September and October;and PAGGI & JOSÉ DE PAGGI (1974) in January. Complete seasonal variations need to be studied, noting that in winter, the region has frosts and occasional snow, and pools may freeze. We suggest that this species is rather plastic in its environmental requirements.
Fish were not observed in the small pool during the sampling, and were probably absent. The large size of the copepods and their red color would certainly be a limiting factor for development, if fish were present in the pool. Another species that occurs in the same region, A. granulosus, has a larger body size. Predation by fish and invertebrates (such as Mesostoma) may have contributed to the low abundance and paucity of records for this species, as pointed out by AKOPIAN et al. (1999) and TROCHINE et al. (2006). Studies on ecology, reproduction and development of A. bergi are necessary. Other rare species reported from the lower La Plata River Basin, such as A. granulosus, Odontodiaptomus michaelseni (Mrázek, 1901) and Odontodiaptomus thomseni (Brehm, 1933), should also be rediscovered and studied. Small roadside pools require intensive studies, and if fish are absent, the possibility of collecting large copepods increases.