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Gayana (Concepción)

versión impresa ISSN 0717-652Xversión On-line ISSN 0717-6538

Gayana (Concepc.) v.66 n.2 Concepción  2002

http://dx.doi.org/10.4067/S0717-65382002000200002 

Gayana 66(2): 97-101, 2002

REDISCOVERY OF ECHINISCUS RUFOVIRIDIS DU BOIS-RAYMOND
MARCUS 1944 (HETEROTARDIGRADA, ECHINISCIDAE). NEW CONTRIBUTIONS
TO THE KNOWLEDGE OF ITS MORPHOLOGY, BIOECOLOGY AND DISTRIBUTION

REDESCUBRIMIENTO DE ECHINISCUS RUFOVIRIDIS DU BOIS-RAYMOND 
MARCUS 1944 (HETEROTARDIGRADA, ECHINISCIDAE). CONTRIBUCIONES AL
CONOCIMIENTO DE SU MORFOLOGIA, BIOECOLOGIA Y DISTRIBUCION

Julio Peluffo1, María C. Moly de Peluffo1 & Alejandra M. Rocha1

ABSTRACT

Numerous specimens of Echiniscus rufoviridis (Heterotardigrada, Echiniscidae) were recorded and studied from urban localities in Argentina. Since the first description of this species by Du Bois-Raymond Marcus in 1944 on Brazilian specimens, it had not been recorded again. The validity of the species is confirmed, its geographic distribution is extended to Argentine localities and new data are provided on its morphology (optical and SEM) and its bioecology. Echiniscus rufoviridis can be clearly separated from the E. viridis, the closest species within the "viridis group", by the possession of depressions with pores on the surface of the cuticle, instead of papillae. On the other hand, an ecological similarity with E. testudo is proposed. This latter species occupies, albeit with low tolerance, urban environments in Europe.

KEYWORDS: Urban environments, Argentina, Heterotardigrada, Echiniscidae, Echiniscus rufoviridis, geographic distribution, morphology, rediscovery.

RESUMEN

Se presenta el hallazgo y estudio de numerosos ejemplares de Echiniscus rufoviridis (Heterotardigrada, Echiniscidae) en localidades urbanas de Argentina. Esta especie no había sido citada desde su descripción por Du Bois-Raymond Marcus en 1944 sobre ejemplares de Brasil. Se confirma la validez de la especie, se amplía el área de su distribución a localidades de Argentina y se aportan nuevos datos sobre su morfología (con microscopía óptica y electrónica de barrido) y sobre su bioecología. Echiniscus rufoviridis se diferencia claramente de E. viridis, la especie más afín dentro del "grupo viridis", por la posesión de depresiones con poros en la superficie de la cutícula en lugar de papilas. Por otra parte, se propone una semejanza ecológica con E. testudo, especie que en Europa ocupa, con baja tolerancia, ambientes urbanos.

PALABRAS CLAVES: Ambientes urbanos, Argentina, Heterotardigrada, Echiniscidae, Echiniscus rufoviridis, distribución geográfica, morfología, redescubrimiento.

INTRODUCTION

Echiniscus rufoviridis was proposed by du Bois-Raymond Marcus in 1944 based upon material coming from mosses growing over trees in the cities of São Paulo and Campos de Jordão, in the state of São Paulo (Brazil). Its description, although detailed, does not reflect the intraspecific and ontogenetic variability.

Ramazzotti and Maucci (1983), in their monograph on tardigrades, place Echiniscus rufoviridis within the "viridis group", composed of green-cuticled Echiniscus, with no other appendages than the cephalic ones and the cirrus A. Within the group, they differentiate it by the restriction of the green coloration to the posterior part of the body and the short cirrus A.

Since 1944, the year in which it was formally described, there have been no further records of the species. Numerous specimens have been found recently in urban, suburban and rural areas of Central and Western Argentina. The purpose of this study is to contribute new data towards a better characterization of the species, enlarge the known geographic area and record some aspects of its biology and ecology.

MATERIAL AND METHODS

Echiniscus rufoviridis was found in moss and lichen communities growing on different tree species in the Argentine cities of Santa Rosa and General Pico (province of La Pampa), Trenque Lauquen and La Plata (province of Buenos Aires) and Las Rosas (province of Santa Fe).

Sampling took place in Santa Rosa during February of 1999 and January of 2000; in General Pico during February and May 2001; in Trenque Lauquen during May 1999; in La Plata during November 2001; and in Las Rosas during November 2001.

For separation of the tardigrades, the usual method of Ramazzotti and Maucci (1983) was used. Specimens were studied using optical microscope and SEM. For observation under an optical microscope, specimens were mounted in Faure's medium or in polyvinyl-lactophenol. Adults were previously treated with KOH. Measurements were done with a micrometer eyepiece on a Kyowa Medilux-12 microscope. For SEM observation, the animals were fixed in neutral buffered formalin and/or ethanol, then dehydrated by critical point and finally coated in gold. Photographs and images were taken with a JEOL JSM35CF SEM in the SEM Laboratory of the "Centro Regional de Investigaciones Básicas y Aplicadas de Bahía Blanca" (CRIBABB, Regional Center for Basic and Applied Research at Bahía Blanca), Argentina.

For the description of the external morphology the terminology of Ramazzotti and Maucci (1983) was used.

Observation of color was done using stereoscopic microscopy, by episcopy. To analyze the degree of distribution of the green color throughout the dorsal plates, an ordinal scale was formulated.

To determine the degree of association among the studied variables, the following coefficients were used: Pearson´s Correlation Coefficient (between total length and the length of cirrus A and claw length), and Spearman´s Rank Correlation Coefficient (between total length and the extension of colored area).

RESULTS

DESCRIPTION

Body length: 125-298 µm. Stage 1 (with two claws): 125-208 µm. Stage 2 (with four claws, but without gonopore): 143_228 µm. Stage 3 (with four claws and gonopore) (Fig. 1): 172-298 µm.

Cuticle color: Green on the posterior part of the body. Colorless in small specimens. Extension of green color increasing towards the anterior region, in relation to the total length of body, reaching the scapular plate in larger individuals. Spearman rank correlation coefficient rs=0.782365 (N=94, p<0,001).

In the areas of the body with colorless cuticle, the orange color of the cavitary granules can be observed by transparency.

Eyes: reddish.

Lateral appendages: The only lateral appendage is cirrus A, which is rather short. Size varies from 18 to 63 µm. Cirrus A length and body length are positively correlated (r=0.870611; N=113; p<0.05).

Legs: Claws length of leg IV ranges from 11-26 µm. Claws length and body length are positively correlated (r=0.785332; N=44; p<0.05). The dentate collar of leg IV is irregularly developed and carries 7 to 10 teeth.

Sculpture: Under optical microscopy a double sculpture can be observed, i.e. a base of fine uniform punctuation and an irregularly distributed coarser punctuation (Fig. 2). Under SEM, it is seen that the fine punctuation appears superficially as very low papillae, only in the areas in which the cuticle is thinner. In areas in which the cuticle is thicker there is an irregular and slightly depressed reticulation. Superimposed to this reticulation and frequently at the intersection points, appear conical depressions with a pore at the bottom (Fig. 3). These depressions correspond to the coarser punctuations observed under LM and, in general, are missing along the plate edges.


Fig.1-5. Echiniscus rufoviridis, 1-2. LM. Scales: 15 mm, 3-5. SEM. Scales: 10 mm, 1. dorsal view, 2. double sculpture, 3. depressions with pores on the scapular plate, 4. cephalic plate, 5. plate II, lateral view.

Fig.1-5. Echiniscus rufoviridis, 1-2. MO. Escalas: 15 mm, 3-5. MEB. Escalas: 10 mm, 1. vista dorsal, 2. doble escultura, 3. depresiones con poros sobre la placa escapular, 4. placa cefálica, 5. placa II, vista lateral.

Cephalic plate: The depressions are distributed over a pair of lenticular zones and a triangular mid-zone. It shows an extended reticulate nape area with few small pores irregularly distributed (Fig. 4).

Scapular plate (I), median plates (1 and 2) and terminal plate (IV): depressions are present throughout the surface. Plate IV shows a faceted appearance, with a pair of lateral-caudal cuticular folds.

Paired plates (II and III): they show two distinct areas, an anterior one with a large number of low papillae and a posterior one with the typical depressions with pores (Fig. 5).

Areas between plates: they show low papillae similar to those observed on the anterior portion of the paired plates.

Eggs: spherical, reddish-orange, diameter of 50-60 µm, without ornamentation, free or in the exuvium of the adult.

DISTRIBUTION

Brazil: Campos de Jordão (22°44' S, 45°35' W) and São Paulo (23°32' S, 46°37' W). Argentina: Santa Rosa (36°37' S, 64°17' W), General Pico (35°40' S, 63°44' W), Las Rosas (32°29' S, 61°35' W), Trenque Lauquen (35°58' S, 62°42' W) and La Plata (34°56' S, 57°57' W).

ECOLOGICAL DATA

The smallest egg-bearing female measured 172 µm of total length. One to six eggs were observed in each exuvium. Free eggs were occasionally found adhered together or to the body of the adults in number of one to three. Eggs or stage 1 individuals were found during all seasons.

Studied populations were found in urban, suburban and rural environments, exposed to any or some of the following factors: motor vehicle exhaust gases, high sun radiation, abundant solid material suspended in the air by the wind. Echiniscus rufoviridis was associated to one or more of the following species of tardigrades: Milnesium cf. tardigradum, Ramazzottius cf. oberhaeuseri, Macrobiotus cf. areolatus and an undescribed species of Macrobiotidae. In some of the suburban and rural area samples E. rufoviridis was the dominant tardigrade species, while it appears in low proportions when it does so in urban areas.

DISCUSSION

The original description (du Bois-Raymond Marcus 1944) provided a unique value for each one of the different characters (total length, length of cirrus A, etc.). The numerous specimens studied from Argentina agree with the description and reaffirm the validity of the species. Actually, the variation range described for the different characters of the studied samples includes the values corresponding to the specimens from Brazil. The abundance of material and the use of SEM as a study technique allow an enhanced description of the species and explain some of the differences encountered with the original description.

Du Bois-Raymond Marcus (1944) indicated that the cuticle "é verde na região posterior" (is green on the posterior region), for specimens of 190 µm in length. This agrees with our data: In the studied material, specimens of that length present green terminal plates. This color, in some individuals, also extends over the second paired plates.

Length of cirrus A is another varying character that varies with specimen size. According to the original description the size of the cirrus is 30 µm for specimens 190 µm long, a value that agrees with our data.

The same author (du Bois-Raymond Marcus 1944) described a third intercalated plate (3) in which "faltam covinhas" (pores are missing). According to our observation under LM and SEM, the space corresponding to that plate should be interpreted as an interplate.

Among the other species of Echiniscus, E. rufoviridis can be compared with E. viridis by its morphological traits and with E. testudo by its ecology.

Within the species that Ramazzotti and Maucci (1983) call the "viridis group", Echiniscus viridis Murray 1910 is the most similar one, as they both share the possession of a short cirrus A. However, plate sculpture is very different in the two species, as the coarse punctuation in E. rufoviridis corresponds to depressions with pores while in E. viridis it represents papillae (Crowe et al. 1970).

From an ecological point of view and according to Séméria (1982), tardigrades in the urban "lichen desert" can exhibit high, medium or low tolerance to environmental conditions. Their frequency is the criterion used to place them in one or other category. According to what can be observed in Argentine cities, E. rufoviridis fits in the low tolerance group. It accompanies highly tolerant species such as Milnesium cf. tardigradum and Ramazzottius cf. oberhaeuseri.

In European urban surveys, the only echiniscid found was E. testudo (Séméria 1981, 1982; Steiner 1994), which exhibited low tolerance to urban pollutants. This species was not found in any of the samples studied herein, which come from several Argentine cities. Studies under way on the ultrastructure of the cuticle of E. rufoviridis should help to elucidate if this ecological similarity is reflected at a structural level.

ACKNOWLEDGEMENTS

The authors wish to thank M. Martin (UNLPam, Argentina) for help with statistical analyses. They also thank M.F. Izaguirre (UNER, Argentina) and S. Echaniz (UNLPam, Argentina) for their photographic work.

REFERENCES

Crowe, J.H., I.M. Newell & W.W. Thomson. 1970. Echiniscus viridis (Tardigrada): Fine structure of the cuticle. Trans. Amer. Microsc. Soc., 89 (2):316-325.         [ Links ]

Du Bois-Raymond Marcus, E. 1944. Sobre tardigrados brasileiros. Com. Zool. Mus. Hist. Nat. Montevideo, 1(13):1-19.         [ Links ]

Ramazzotti, G. & W. Maucci. 1983. II Phylum Tardigrada. Memorie dell Istituto Italiano di Idrobiologia. 41:1-1012.         [ Links ]

Séméria, Y. 1981. Recherches sur la faune urbaine et suburbaine des tardigrades muscicoles et lichenicoles. I. Nice-Ville. Bull. Soc. Linn. Lyon, 50(7):231-237.         [ Links ]

Séméria, Y. 1982. Recherches sur la faune urbaine et sub-urbaine des tardigrades muscicoles et lichenicoles. II. L'espace sub-urbain: Les hauteurs orientales de Nice-Ville. Bull. Soc. Linn. Lyon, 51(10):315-328.         [ Links ]

Steiner, W.A. 1994. The influence of air pollution on moss-dwellig animals. 2. Aquatic fauna with emphasis on Nematoda and Tardigrada. Revue Suisse Zool., 101(3):699-724.         [ Links ]

Fecha de recepción: 28.08.02
Fecha de aceptación: 16.10.02

1Facultad de Ciencias Exactas y Naturales, Universidad Nacional de La Pampa, Uruguay 151, 6300 Santa Rosa, La Pampa, Argentina. E-mail:molpel@cpenet.com.ar

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