Taxonomy, ecology, and geographical distribution of the species of the genus Thermocyclops Kiefer, 1927 (Copepoda, Cyclopoida) in São Paulo State, Brazil, with description of a new species

Taxonomia, ecologia e distribuição geográfica das espécies do gênero Thermocyclops Kiefer, 1927 no estado de São Paulo, com a descrição de uma espécie nova

Taxonomy, ecology, and geographical distribution of the species of the genus Thermocyclops Kiefer, 1927 (Copepoda, Cyclopoida) in São Paulo State, Brazil, with description of a new species

Taxonomia, ecologia e distribuição geográfica das espécies do gênero Thermocyclops Kiefer, 1927 no estado de São Paulo, com a descrição de uma espécie nova

Silva, W. M.^I; Matsumura-Tundisi, T.^II

^IDepartamento de Hidráulica e Transporte, Universidade Federal do Mato Grosso do Sul

^IIInternational Institute of Ecology, Rua Bento Carlos, 750, CEP 13560-660, São Carlos, SP, Brazil

^{Correspondence}

ABSTRACT

The taxonomy and ecology of the cyclopoid copepod genus Thermocyclops were studied. Samples were collected in 207 water bodies located in the 22 hydrographic basins of São Paulo State, Brazil, including large reservoirs, small and shallow lakes, and ponds and rivers. The genus Thermocyclops inhabits mainly water bodies within a limnetic region. Four species were found, of which one is new: Thermocyclops iguapensis, which occurred in the reservoirs of the Ribeira do Iguape and Paraíba do Sul basins. The description of the new species and the geographical distribution of all four species in São Paulo State are presented. Thermocyclops decipiens was the most frequent species, occurring in 71% of the water bodies within a limnetic region. This species is characteristic of eutrophic environments where it can occur in great abundance, whereas Thermocyclops minutus is characteristic in oligotrophic systems. Thermocyclops inversus and Thermocyclops iguapensis n. sp. were not common but can occur together with Thermocyclops decipiens.

Key words: taxonomy, ecology, geographical distribution, Thermocyclops iguapensis n. sp. co-occurrence.

RESUMO

Foram realizadas coletas em 207 corpos de água, distribuídos em 22 unidades de gerenciamento de recursos hídricos (UHGRH) do estado de São Paulo no período de 1999 a 2002, abrangendo grandes e pequenos reservatórios, lagoas marginais e grandes rios. Nestas coletas foram analisadas as espécies do gênero Thermocyclops quanto à taxonomia, distribuição geográfica e freqüência de ocorrência. O gênero Thermocyclops ocorreu em corpos de água com zona limnética bem desenvolvida e com raras exceções em ambientes estritamente litorâneos. Foram registradas quatro espécies, sendo Thermcyclops iguapensis espécie nova, que ocorreu nos reservatórios das UHGRHs Ribeira do Iguape e Paraíba do Sul. A descrição da espécie nova e a distribuição das quatro espécies são apresentadas, mostrando que Thermocyclops decipiens foi a espécie mais freqüente, ocorrendo em 71% dos corpos de água com região limnética desenvolvida. Esta espécie é característica de ambientes eutróficos, onde ocorre em grande número, e a espécie Thermocyclops minutus é característica de ambientes oligotróficos. Thermocyclops inversus e Thermocyclops iguapensis n. sp. não são espécies freqüentes, mas podem co-ocorrer com a espécie Thermocyclops decipiens.

Palavras-chave: Copepoda Cyclopoida, distribuição geográfica, Thermocyclops, Thermocyclops iguapensis n. sp.

INTRODUCTION

The genus Thermocyclops Kiefer, 1927 (Copepoda, Cyclopoida) originated in the tropical region, in which it presents a high diversity of species (Dumont & Decraemer, 1977). In many tropical water bodies, this genus represents the most important component of the zooplankton biomass (Margalef, 1983). Despite the presence of the genus in South America, high diversity has not been recorded in this continent, as compared to the African and Asian continents (Rocha et al., 1995). In the Western Hemisphere, nine species and subspecies have been recorded (Reid, 1989), four of them occurring in Brazil (Rocha & Botelho, 1998).

Until 1998, three species of Thermocyclops had been recorded in the freshwater systems of São Paulo State (Rocha & Botelho, 1998; Matsumura-Tundisi & Silva, 1999). Thermocyclops decipiens (Kiefer, 1929) was the most frequent species, found in several reservoirs and ponds, followed by T. minutus. Thermocyclops inversus Kiefer, 1936, a rare species, was registered in one reservoir located in São Paulo, SP (Rocha & Botelho, op. cit.).

The aim of this work was to evaluate the occurrence of the species of the genus Thermocyclops in the water bodies of São Paulo State, located in 22 basins that are under hydrographic management and which are referred to as hydrographic management units (HMU).

MATERIAL AND METHODS

Fig. 1 includes two maps of São Paulo State showing its 22 hydrographic basins as well as the hydrographic network with the main rivers where several reservoirs have been constructed in cascade to generate hydroelectricity.

Samplings were carried out during the period of 1999-2002. For each UHGRH, a minimum of 3 and maximum of 29 water bodies were sampled, including the limnetic and littoral regions of large and small reservoirs, as well as ponds and rivers. Geographical coordinates were determined at each site using a Garmin III GPS.

Zooplankton was collected by making vertical and horizontal hauls using a standard plankton net of mesh size 68µm. The samples were preserved in 4% formaldehyde and deposited in the Plankton Museum of the International Institute of Ecology. Species identifications were performed using only adult females. Drawings and measurements were made using an optical microscope with image acquiring system and drawing software (TurboCAD Version 6.5).

Samples obtained from Barra Bonita Reservoir during the period of September 1983 to October 1984 at fortnightly intervals, were analyzed to study the seasonal fluctuations of two species of Thermocyclops.

RESULTS

Taxonomical studies

Thermocyclops iguapensis n. sp.

Types collected in Brazil, São Paulo State, Ibiuna County, Fumaça Reservoir (24º00'16"S and 47º15'40"W), collected by William M. Silva on 9/19/2001. All types were deposited in the USP museum.

Holotype : Body size: 720 µm, specimen dissected and mounted on 1 slide (MZUSP: 16196).

Allotype : Body size: 589 µm, specimen dissected and mounted on 1 slide (MZUSP: 16197).

Paratypes: 20 (average size: 735 µm ± 21) and 10 (average size: 585 µm ± 9), not dissected preserved in alcohol 70%, MZUSP 16198 and 16199 respectively.

Description of the female

Figs. 2 shows the general aspect of the female (Fig. 2a) and her appendages. Antennule (Fig. 2b): 17 segments, extending past 3^rd thoracic segment, 17^th segment without hyaline membrane. Antenna (Fig. 2c): 1^st segment with few rows of spinules and one seta on caudal side; 4^th segment with hyaline serrate ornamentation. Mouth appendages: mandibule (Fig. 2d), maxillule (Fig. 2e), maxilla (Fig. 2f), and maxilliped (Fig. 2g) with no special ornamentation. Legs 1-4 (Figs. 2h-2k): all of them with 3 articles, spine formula: 2,3,3,3 and intercoxal sclerite of the swimming legs without spine ornamentation on the distal margin. Endopodite 3 of leg 4 with terminal inner spine about 3.5 times longer than terminal external spine. Leg 5 (Fig. 2l): with spine in the inner article short, 1.4 time longer than distal article. Receptaculum seminis (Fig. 2m) with anterior margin of lateral arms not curved in the proximal part and the lateral canal jointed in the copulatory pore. Caudal rami (Fig. 2n) is 3.15 times longer than wide. Length of caudal setae: internal: 61 µm; medial internal: 243 µm; medial external: 131 µm; and external: 24 µm.

Description of the male

Fig. 3a shows the general aspect of the male. Antenna (Fig. 3b): 17 segments with geniculation in the 9^th and 15^th segments. Leg 5 (Fig. 3c): internal apical spine passing leg 6 insertion.

Etymology: A reference to the Ribeira do Iguape Hydrographic Basin where this species was found in high abundance.

Differential diagnosis: Thermocyclops iguapensis n. sp. differs from other American Thermocyclops species by a combination of characteristics such as intercoxal sclerite of legs 1-4 without spinular ornamentations on distal margins; ratio between the terminal spines of endopodite 3 of leg 4; and principally, the difference in the morphology of the receptaculum seminis.

Remarks: T. iguapensis n. sp. was recorded in the reservoirs of the Ribeira do Iguape Basin and in reservoirs of the Paraíba do Sul hydrographic basins by Sendacz & Kubo (1982) but was identified as T. minutus.

The figures (51 to 56) presented by the authors show characteristics similar to those presented by T. iguapensis n. sp. and differing from the characteristics of T. minutus, especially in the morphology of the receptaculum seminis.

Differential diagnosis and key for São Paulo Thermocyclops species

Fig. 4 shows the main differences presented by the four species of Thermocyclops found in São Paulo State: T. decipiens, T. inversus, T. minutus and T. iguapensis n. sp.

Thermocyclops decipiens: average size of 10 adult females: 823 µm ± 21. Leg 4: intercoxal sclerite with ornamental spines in prominences on distal margins (Fig. 4-a1) and 3^rd endopodite with outer apical spine 2.4 times as long as the inner (Fig. 4-b1). Receptaculum seminis (Fig. 4-c1): lateral arms slightly curved in the proximal and distal parts. Caudal rami (Fig. 4-d1): 2.28 times longer than wide, lateral setae nearly on the distal margin, and internal setae 3 times longer than the external.

Thermocyclops inversus: average size of 10 adult females: 637 µm ± 17. Leg. 4: intercoxal sclerite without ornamental spines in prominences on distal margins (Fig. 4-a2), and 3^rd endopodite with outer apical spine 0.8 time as long as the inner (Fig. 4-b2). Receptaculum seminis: lateral arms narrow (Fig. 4-c2). Caudal rami: 3.2 times as long as wide, lateral setae on the middle of the caudal rami, internal setae 2.16 times long than the external (Fig. 4-d2).

Thermocyclops minutus: average size of 10 adult females: 602 mm ± 18. Leg 4 (Fig. 4-a3): intercoxal sclerite without ornamental spines in prominences on distal margins, and 3^rd endopodite with outer apical spine 5 times longer than the inner (Fig. 4-b3). Receptaculum seminis (Fig. 4-c3): lateral arms slightly curved in the proximal part of anterior margin, pore canal curveted and posterior margin located above the lateral arms. Caudal rami (Fig. 4-d3): 2.4 times longer than wide, lateral spine on the middle of the caudal rami, internal setae 1.8 time longer than the external.

Thermocyclops iguapensis n. sp.: 4^th leg (Fig. 4-a4): intercoxal sclerite without ornamental spines in prominences on distal margins, 3^rd endopodite with outer apical spine 3.5 times longer than the inner (Fig. 4-b4). Receptaculum seminis (Fig. 4-c4): lateral arms slightly curved on the distal margin, pore canal short, and posterior margin located in the middle of the lateral arms. Caudal rami (Fig. 4-d4): 3.1 times as long as wide, lateral spine on the middle of the caudal rami, internal setae 2.6 times longer than the external.

Identification key for Thermocyclops species found in the hydrographic basins of São Paulo State

1.

Sclerite intercoxal of leg 4 with spine ornamentation on the distal margin (Fig. 4-a1)......................................................................................................2

Sclerite intercoxal of leg 4 without spine ornamentation on the distal margin (Fig. 4-a2 and a4)............................................................................................3

2. 3^rd endopodite of leg 4 with outer apical spine 2.4 times as long as inner (4- b1)...........................................................................................T. decipiens 3.

3^rd endopodite of leg 4 with apical outer spine longer than inner (Fig. 4-b2)........................................................................................T. inversus

3^rd endopodite of leg 4 with apical outer spine shorter than inner spine...............4

4.

3^rd endopodite of leg 4 with outer apical spine 5 times longer than the inner (Fig. 4-b3) and receptaculum seminis with anterior margin showing a depression in the proximal part (Fig. 4-c3) ............................................................ T. minutus

3^rd endopodite of leg 4 with outer apical spine 3.5 times longer than the inner (Fig. 4-b4) .................................................................................................... 5

5. Receptaculum seminis with anterior margin having no depression in the proximal part (Fig. 4-c4) .............................................................. T. iguapensis n. sp.

Geographical distribution and frequency of occurrence of Thermocyclops species of São Paulo State

Among the Cyclopoida, the genus Thermocyclops is characteristic of the limnetic region of lakes.

Table 1 shows the number of water bodies studied in the 22 hydrographic basins of São Paulo State, the number of water bodies that present a limnetic zone, and the frequency of occurrence of the four species in each hydrographic basin.

Thermocyclops decipiens was the most frequent species, having been found in 71% of the water bodies with a limnetic region, and occurring in all the hydrographic basins with the exception of the Mantiqueira. Thermocyclops minutus was found in 25% of the water bodies with a limnetic region. This species occurred in a large number of the water bodies considered oligotrophic. It was distributed in the three largest river basins: Tietê, Parapanema, and Rio Grande, but was not found in the Mantiqueira, Litoral Norte, Baixada Santista, and Ribeira do Iguape basins.

Thermocyclops inversus and the new species, Thermocyclops iguapensis, were rare, the former occurring in 8% and the latter in 6% of the limnetic samplings. Both species occurred in several reservoirs of the Ribeira do Iguape Basin. Thermocyclops inversus was recorded also in water bodies from the Pardo, Alto Tietê, Mogi, Tietê/Jacaré, Turvo Grande, and São José dos Dourados basins. Thermocyclops iguapensis was recorded only in the Ribeira do Iguape and Paraíba do Sul basins, so that its distribution was restricted to the hydrographic basins, which are coastal basins, located n. sp. in the east of São Paulo State where the rivers flow to the Atlantic Ocean.

Fig. 5 shows the distribution maps of Thermocyclops decipiens, Thermocyclops inversus, Thermocyclops minutus, and Thermocyclops iguapensis n. sp. in São Paulo State obtained from the SINBIOTA Atlas (www.biota.org.br).

Seasonal fluctuation of Thermocyclops populations in Barra Bonita Reservoir

Barra Bonita Reservoir is the first of six reservoirs constructed in cascade in the Middle Tietê River Basin (Fig. 1). The reservoir receives from the Tietê River all the domestic and industrial sewage produced in the metropolitan area of São Paulo, SP, as well as pollution from the Piracicaba River, another tributary. The reservoir presents eutrophic characteristics with high concentrations of phosphorus, nitrogen, and chlorophyll, and frequent presence of cyanobacterial blooms. The abundances in this reservoir of two species of Thermocyclops, T. deciepiens, and T. minutus, from September 1983 to September 1984, were analyzed at a time when the reservoir was meso-eutrophic. Both populations showed high abundances during the same periods (November-December and March-April). However, while Thermocyclops minutus disappeared completely in some periods (the end of July to October), Thermocylops decipiens occurred throughout the period (Fig. 6).

DISCUSSION

Thermocyclops iguapensis n.sp. was found only in two basins of São Paulo State: the Ribeira do Iguape and Paraíba do Sul. Sendacz & Kubo (1982) found it in the water bodies of those basins, but identified the species as Thermocyclops minutus. T. iguapensis n. sp. as well as T. inversus have narrow geographical distributions, being restricted to the hydrographic basins in the eastern part of São Paulo State.

The most frequent species, Thermocyclops decipiens, has wide geographical distribution occurring in many types of water bodies in all of the hydrographic basins, whereas Thermocyclops minutus is less widely distributed, thus indicating more restrictive ecological requirements. The occurrence of these two species in Barra Bonita Reservoir (which this time was meso-eutrophic) with similar abundances in some periods of the year and complete disappearance of Thermocyclops minutus in other periods (mainly in the winter and spring) indicates that the two species probably present some different ecological requirements. Much evidence shows that Thermocyclops minutus is common in oligotrophic and mesotrophic environments (Matsumura-Tundisi & Tundisi, 1976; Tundisi et al., 1997). Silva & Matsumura-Tundisi (2002) recorded clear patterns of dominance of Thermocyclops minutus over Thermocyclops decipiens in oligo-mesotrophic reservoirs and dominance of T. decipiens over T. minutus in eutrophic reservoirs.

The co-occurrence of Thermocyclops inversus and Thermocyclops decipiens in some eutrophic water bodies of the Ribeira do Iguape Basin (Iporanga and Jurupará reservoirs) showed that Thermocyclops inversus outnumbered Thermocyclops decipiens (Table 1). Thus, the former species probably has better adaptive strategies than does Thermocyclops decipiens in eutrophic systems.

Acknowledgements — This work is part of BIOTA/FAPESP- Virtual Institute of Biodiversity. The authors express their thanks to Dr. Kennedy F. Roche for an English revision and FAPESP for financial support (Thematic Project: 98/5091-2 and fellowship process: 99/05104-0).

Received July 3, 2003 – Accepted December 9, 2003 – Distributed August 31, 2005

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Publication Dates

• Publication in this collection
  13 Dec 2005
• Date of issue
  Aug 2005

History

• Accepted
  09 Dec 2003
• Received
  03 July 2003