Diversity and distribution of the free-living freshwater Cyclopoida ( Copepoda : Crustacea ) in the Neotropics

Cyclopoida species from the Neotropics are listed and their distributions are commented. The results showed 148 species in the Neotropics, where 83 species were recorded in the northern region (above upon Equator) and 110 species in the southern region (below the Equator). Species richness and endemism are related more to the number of specialists than to environmental complexity. New researcher should be made on to the Copepod taxonomy and the and new skills utilized to solve the main questions on the true distributions and Cyclopoida diversity patterns in the Neotropics.


Introduction
Cyclopoids are the most abundant and successful Copepoda in freshwater and they inhabit all kinds of freshwater environments such as rivers, streams, pools, lakes, reservoirs, wetlands and temporary pools.The Cyclopoida group commonly represents the main component of the zooplanktonic biomass in tropical water bodies (Rocha, et al., 1995;Santos-Wisniewski and Rocha, 2007).
The freshwater cyclopoids are distributed in two subfamilies, Eucyclopinae and Cyclopinae.There are some genera with high diversity, some are distributed mainly in temperate zones such as Cyclops and Diacyclops and others in tropical zones represented principally Mesocyclops and Thermocyclops.In the Neotropical region, the tropical genera prevail, with some species different from those found in Africa and Australia, and there are also cosmopolitan while introduced species (Reid and Pinto-Coelho, 1994;Suárez-Morales et al., 1999).
Cyclopoida studies in the neotropical region are scarce and in all revisions genera new species have been added to the region lists (Gutierrez-Aguirre and Suárez-Morales, 2001;Suárez-Morales, et al., 2004;Silva and Matsumura-Tundisi, 2005).Revisions on the distribu-do Sul, Mato Grosso do Sul State) and the Biota data bank (www.biota.org.br).

Diversity and Distribution
Table 1 shows the species and their distributions based on Figure 1 of the South and North neotropical regions.These results showed 148 species in the neotropics, where 83 species were recorded in the North region and 110 species in the South, these species being distributed in six genera of the sub-family Eucyclopinae and 14 genera of the sub-family Cyclopinae.

Eucyclops Claus, 1893
Genus with high diversity and with few studies on its taxonomy.E. serrulatus is the most common species being is described as a cosmopolitan and in the neotropics is distributed from Argentina to Mexico (Dussart and Dafaye, 1985;Rocha and Botelho, 1998;Suárez-Morales, 2004)
the neotropics restricted to South America, the species B. campaneri and B. Caroli.

Diacyclops Kiefer, 1927
The species of this genus is absent in most of the neotropical region, and are found mainly in the southern region of the Atlantic coast, in spite of this genus being the largest of the Cyclopidae group (Stoch, 2001).In the neotropics there are nine species, six of which are restricted to the north region: D. bernardi, D. hispidus, D. chakan, D. pilosus, D. ecabensis, D. puuc and three species restricted to the south above 40° S, D. andinus, D. bicuspidatus and D. urugaiensis.

Mesocyclops G. O. Sars, 1914
Most of the species from this genus have been recorded in the tropical region and it is one of the most studied groups, including revisions of African (Van de Velde, 1984), American (Suárez-Morales and Gutierrez-Aguire, 2001) and Australian (Holyska, 2000) species.Suárez-Morales and Gutierrez-Aguirre (2001) listed the 21 species and sub-species of Mesocyclops recorded in the neotropics, where one is pan-tropical, M. aspericornis, two neotropical M., M. longisetus longisetus and M. longisetus curvatus, two introduced species from the Afro-Asian region, M. ogunnus (the M. kieferi recorded in Brazil was a misidentification corrected by Matsumura-Tundisi and Silva, 2002

Paracyclops Claus, 1893
The genus Paracyclops has 28 species recorded in the world with eleven occurring in the neotropical region, and around 9 are American (Karaytug, 1999).In the neotropics the species P. poppei while P. chiltoni are considered cosmopolitan species, the first one being restricted to North America and the Caribbean zone and the second is restricted to South America and commonly misidentified as P. fimbriatus which does not exist in the Americas (Karaytug, 1999).

Homocyclops (Herrick, 1882)
This genus is monospecific, with only one species, Homocyclops ater, which is an American species and its distribution in the neotropics is from Argentina to Mexico (Rocha and Botelho, 1998).

Acanthocyclops G.O. Sars, 1863
This genus in the neotropics is represented by two cosmopolitan species and two endemic ones. A. robustus and A. vernalis are cosmopolitan and they are so close that they include a complex robustus-vernalis (Dodson, 1984).These species have been recorded in Eurasia, Australia and America.In the neotropics, they have been recorded from Argentina to Mexico (Reid, 1985;Dussart and Dafaye, 1985;Rocha andBotelho, 1998, Silva, 2003;Silva and Matsumura-Tundisi, 2002), and A. robustus is the most common form recorded in the neotropics.A. michaelseni and A. scottsbergi are both endemic to the south of Argentina and Chile.

Allocyclops Kiefer, 1932
Genus represented by two species in the neotropical region, one in the Cuba, A. botosaneanui (Dussart and Dafeyae, 1985) and another in Brazil, A. silvaticus (Rocha and Botelho, 1998).

Bryocyclops Kiefer, 1927
The species from this genus are essentially Afro-Asian (Dussart and Dafaye, 1985), with two species in The distribution showed a high number of species of Cyclopoida in the Southern region.In fact, these results were expected, because the south is bigger than the north in area and environmental diversity.Seventeen species are present in the whole neotropical region, which represents 10.8% of the total species.The high number of endemic versus the low number of widely distributed species for Cyclopoid a has been found in all recent taxonomic studies such as Kiefer (1981); Van-de-Velde (1984); Reid (1989) and Karaytug (1999) and Suárez-Morales (2002); Suárez-Morales et al. (2004).This fact has high evolutionary significance, because it shows that the speciation of Cyclopida is bigger than supposed some time ago.Endemism in the neotropics should be much higher than recorded; nowadays endemism is directly linked to the amount of research carried out at a given site.Reid, (1987;1989;1991) for central Brazil, Holynska, 2000 for Australia andSuárez-Morales et al. (2004) for the Yucatán Peninsula (Mexico), Silva and Mastsumura-Tundisi (2005) for São Paulo State (Brazil) give examples of endemism and discuss its relationship with research.
Amazonian sites are examples of less-understood environments, with thousands of different freshwater environments, in a giant area certainly having dozens (a conservative estimate) of endemic and new species of freshwater Cyclopoida.
Moreover, even with the well-studied Cyclopoida groups, such as Mesocyclops, there are many doubts about distribution, because of imprecise descriptions or morphological confusion (Suárez-Morales, 2001).Nowadays, new skills have been useful in taxonomy; Silva and Matsumura-Tundisi, 2004, found differences between Mesocylops longisetus longisetus from the United States and M. longisetus longisetus from Brazil using cytogenetic techiniques.This kind of study helps to understand distribution patterns and the speciation process has occurred in the neotropics.In the latter there are three variations for M. longisetus: M. longisetus longisetus var.north, M. longisetus longisetus var.south and M. longisetus curvatus.
Silva and Matsumura-Tundisi (2005), using molecular biology, observed that the genera Themocyclops and Mesocyclops are closely related genera, and that the morphological differences are not supported.This result alerts evolutionary researchers that the study of these genera might not have to be done alone, but together, and their distribution might be interrelated.
On the other hand, human activities usually represent a strong forcing function driving distribution and diversity.Tundisi et al. (1995) discuss the formation of hundreds of hydropower dams in Brazil, which is a country poor in natural lakes, and that before hydropower, the Cyclopoida species was adapted in marginal lakes with strong interannual pulses.Nowadays, there are hundreds of cascades of interlinked reservoirs multiplying environments for plankton.Silva and Matsumura-Tundisi (2002) and Nogueira et al. (2004), observed that in the cascade recorded in Venezuela and Brazil although in Brazil it is na incertae species (Rocha and Botelho, 1998).

Microcyclops Claus, 1893
The species of this genus present a low degree of endemism with many species recorded in more than one hydrographic basin.There are 12 recorded species in the neotropics (Dussart and Dafaye, 1985;Rocha, 1998;Rocha and Botelho, 1998)

Muscocyclops Kiefer, 1937
The species from this genus are all restricted to South America and are composed of three species: M. bidentatus, M. operculatus, M. therasiae.These species inhabit wet fields and organic soil (Rocha and Botelho, 1998).

Neutrocyclops (Lowndes, 1934)
This genus is monospecific, including only one species, N. brevifurca, distributed in the whole neotropical region.

Ponticyclops Reid, 1987
This genus is monospecific, including only one species, P. boscoi, recorded in the central Brazilian region.

Thermocyclops Kiefer, 1927
This genus, one of the most common in the planktonic environment, in the neotropics consists of eleven species (Silva and Matsumura-Tundisi, 2005).Thermocyclops tenuis is the most widely distributed species in the neotropics, but many records are probably erroneous (Reid, 1989).Thermocyclops decipiens, a pan-tropical species, is the most abundant in the neotropics followed by T. minutus a South American species.T. inversus is a species distributed between tropics in the Americas.The other Thermocyclops species are more geographically restricted, being: T. brehmi, T. crassus, T. hastatus antilhensis, T. iguapensis, T. tenuis longifurcatus, T. parvus.

Yancyclops Reid, 1988
This genus is monospecific, including only one species, Y. ferrarii, recorded in the northern region of Brazil, in the Amazonian region.

Discussion
The diversity and distribution of the Neotropical species is very likely linked to the pilocene events.Suárez-Morales (2004) observed that in the colonization of the Yucatán Peninsula in Mexico, South American species predominate.This way, the freshwater cyclopoid dispersion in the Neotropics should be starting from South American equatorial and tropical to the temperate zones and North America.systems, the Cyclopoida species are usually similar, differing in abundance among reservoirs, and that abundance is often related to the trophic state of the system and the retention time.This anthropic process might be homogenizing the systems and promoting extinction.
Concluding, in the last twenty years has been great improvement in the taxonomical knowledge of freshwater Cyclopoida with an emphasis on the impact of their distribution and diversity.Moreover, greater effort should be made to solve taxonomical doubts including the use of morphological, molecular and cytogenetic skills and in the geographical areas with a high deficit of studies.
In the revision of the Mesocyclops species in São Paulo State and in Samuel Reservoir in Rondônia State in Brazil, M. meridianus was identified as M. brasilianus), M. edax, M. evadomingoi with six species are endemic to islands, M. cahci, M. yutsil, M. intermedius, M. pescei, M. annulatus diversus, M. longisetus araucanus and species from the South above 40° S M. annulatus annulatus and M. paranaensis.