A cladistic analysis of the genera of Macrothricidae Norman & Brady (Crustacea, Cladocera, Radopoda)

Análise cladística dos gêneros de Macrothticidae Norman & Brady (Crustacea, Cladocera, Radopoda)

A cladistic analysis of the genera of Macrothricidae Norman & Brady (Crustacea, Cladocera, Radopoda)

Análise cladística dos gêneros de Macrothticidae Norman & Brady (Crustacea, Cladocera, Radopoda)

Lourdes M. A. Elmoor-Loureiro

Laboratório de Zoologia, Universidade Católica de Brasília. QS 7 lote 1, Bloco M, sala 331, 71966-700 Taguatinga, Distrito Federal, Brasil. E-mail: [e-mail]

ABSTRACT

A cladistic analysis of the genera of the Macrothricidae (Crustacea, Cladocera, Radopoda) was performed based on 36 morphological characters, and including 15 terminal taxa (three as outgroups). The single tree obtained from this analysis supported the monophyly of Macrothricidae and Macrothricinae. The group called as "non-Macrothricinae" was indicated as paraphyletic. Neothricidae was also not supported.

Key words: Anomopoda, Macrothricinae, Macrothricoidea, phylogeny.

RESUMO

Foi conduzida uma análise cladística dos gêneros sul-americanos de Macrothricidae (Crustacea, Cladocera, Radopoda) com base em 36 caracteres morfológicos e incluindo 15 taxa terminais (três como grupos externos). Uma única árvore foi obtida pela análise, a qual suporta o monofiletismo de Macrothricidae e de Macrothricinae. O grupo chamado de "não-Macrothricinae" é indicado como parafilético. Neothricidae também não encontrou suporte.

Palavras chave: Anomopoda, filogenia, Macrothricinae, Macrothricoidea.

In its original definition, the family Macrothricidae Norman & Brady, 1867 (Branchiopoda, Anomopoda) embraced all littoral cladoceran genera with antennules long and attached near the tip of head, without rostrum, antenna with three endopodite and four expedite segments, and postabdomen with strong and numerous marginal dentils (for a detailed description, see Alonso 1996). According to FRYER (1974, 1995), most of the primitive anomopod characteristics were retained in this family.

In the last decade, Macrothricidae was redefined. At first, SMIRNOV (1992) transferred the genus Ilyocryptus Sars, 1892 to a new family, and more recently DUMONT & SILVA-BRIANO (1998) elevated the remaining group to superfamily status (Macrothricoidea). The Macrothricoidea embraces the families Macrothricidae strictu sensu, Acantholeberidae Smirnov, 1976, Neothricidae DUMONT & SILVA-BRIANO, 1997, and Ophryoxidae Smirnov, 1976. According to DUMONT & SILVA-BRIANO (1998), the Macrothricidae strictu sensu includes 11 genera, characterized by fork setae on trunk limb I and reduction of the number of trunk limb setae, if compared with more "primitive" macrothricid-like families. For example, the Acantholeberidae possess 8, 8, and 7 setae on exopodites of the trunk limbs III, IV, and V respectively, while the Macrothricidae have the maximum of 6, 6, and 3 setae on the same exopodites.

Although DUMONT & SILVA-BRIANO (1998) suggested a hypothetical evolutionary tree for the families of Macrothricoidea (and other Radopoda Dumont & Silva-Briano, 1997), the phylogenetic relationships within the Macrothricoidea have not yet been submitted to a cladistic analysis. As a starting point, the present study aims to investigate the phylogenetic relationships among the genera of the Family Macrothricidae, based on a formal cladistic analysis of 36 morphological characters.

MATERIAL AND METHODS

The ingroup taxa set consisted of 12 species representing the genera of Macrothricidae. The genus Cactus Vávra, 1900 was not included in the analysis because only a single specimen is known and its description is very vague. Three species of Macrothrix Baird, 1843 were included in the analysis in order to represent the synonymous genera Iheringula Sars, 1900 and Echinisca Liévin,1848. Streblocerus Sars, 1862 was represented by two terminal taxa because differences among species were observed. As outgroup, three genera of Macrothricoidea were included: two considered as "primitive" (Acantholeberis Lilljeborg,1846 and Ophryoxus Sars, 1862) and one considered as advanced (Neothrix Gurney, 1927) (DUMONT & SILVA-BRIANO 1998). The list of terminal taxa, the material examined, and the literature source are presented in table I.

The 36 selected morphological characters and the character states are summarized in table II. Most of these characters is traditionally used in cladoceran taxonomy and is well described in ALONSO (1996) and DUMONT & NEGREA (2002). The terminology used to describe the trunk limbs follows DUMONT & SILVA-BRIANO (1998) and DUMONT & NEGREA (2002). The abbreviation TLi is used to indicate the trunk limbs I to V, and endite i - TLi to indicate the endite 1 to 4 of the corresponding trunk limb. When samples were available, the character states were confirmed by direct observation of the specimens. Character 23 followed FRYER (1974). Some discrepancies were detected among Guernella Richard,1892 data from FRYER (1974), PAGGI (1976), and DUMONT & SILVA-BRIANO (1998), so in characters 10, 16, 20, and 27 the option was for the description of South American specimens (PAGGI 1976). The data matrix is presented in the table III.

Parsimony analysis was performed with PAUP 4 (SWOFFORD 1999), using the exhaustive search option. All characters were considered unordered and unweighted. ACCTRAN optimization was used and the tree was rooted using the outgroup method. The distribution of the characters states was further investigated using MacClade 3.04 (MADDISON & MADDISON 1992).

RESULTS AND DISCUSSION

The analysis produced a single most parsimonious tree (l = 79 steps; CI = 0.5696; RI = 0.6991; RCI = 0.3982), shown in figure 1. The apomorphy list is presented in table IV.

The monophyly of Macrothricidae is supported by 9 characters (Tab. IV). The presence of five pairs of trunk limbs, TL I without seta at exopodite base, TL II with duplication setae reduced and modified (Fig. 2), TL IV without pre-epipodite, and TL V with 1 or 2 setae on exopodite are constant characters within the family, but the other apomorphic characters (4, 22, 29, and 30) have their states changed in more advanced clades.

Within the Macrothricidae, Grimaldina Richard,1892 is the most basal genus and the sister group to a clade compounded by the remaining genera (Clade A in figure 1), which is supported by characters 17 (TL I with one seta on gnathobase or none) and 21 (TL II with 1 seta on exopodite). The reduction of the number of the TL I gnathobasic setae in more advanced clades also occurs in the Eurycercoidea (Eurycercidae have 3, while the Chydoridae have 0-2 setae). The present tree topology (Fig. 1), showing the non-Macrothricinae genera as paraphyletic, is in agreement with the supposition of DUMONT & SILVA-BRIANO (1998) and DUMONT & NEGREA (2002), who did not consider the non-Macrothricinae genera as a formal subfamily.

Two main clades could be recognized within Clade A (Fig. 1): the Macrothricinae and the Clade D (consists of the non-macrothricinae genera but Grimaldina). The Subfamily Macrothricinae (sensu Dumont & Silva-Briano, 1998) is supported by four synapomorphies: the presence of fork-like setae on TL I (Fig. 3), their occurrence on endite 1 (lost in Streblocerus pygmaeus, but not in Streblocerus serricaudatus), TL II with 5 or 4 gnathobasic filter comb setae, and the arrangement of the postabdominal marginal denticles in transversal rows (characters 8, 9, 22, and 32).

Within the Macrothricinae, Bunops Birge,1893 appears as the most basal genus (Fig. 1). Its sister group (Wlassicsia (Drepanothrix (Macrothrix + Streblocerus))), named as Clade B, is supported by three characters (10, 23, and 24). Of these, the presence of a fork-like seta on endite 2 of TL I have no parallel in other clades.

Macrothrix and Streblocerus are sister groups. The closest relationship between Macrothrix and Streblocerus, which was also found by Olesen (1998, 2000), is supported here by the sclerotized setae on endite 3-TL I and TL III with 3 or 4 setae on exopodite non filtratory setae on endite. Despite the differences observed among species, Streblocerus is well defined by the antennules curved outward, presence of scrapers on endite 3-TL I, and gut coiled (characters 1, 12 and 36). The monophyly of the genus Macrothrix is supported by the position of the distalmost seta endite 3-TL I, which is located apart from the others (character 13, Fig. 3). The present result suggests the maintenance of the synonymy of Macrothrix with Iheringula and Echinisca, but an analysis of the group including more terminal taxa is necessary to clarify this question.

The clade D (Pseudomoina (Guernella (Lathonura + Neothrix) is supported by presence of a seta on the second segment of antennal exopodite, TL III with 8 or more gnathobasic filter comb setae, and TL IV without internal series of setae (characters 3, 25, and 28). The close relationship between Guernella and Pseudomoina Sars 1912 was previously suggested by FRYER (1974), but here Guernella appears closer to (Lathonura + Neothrix).

According to the present analysis, Neothrix is a very derived genus of Macrothricidae, and its phylogenetic position (Fig. 1) conflicts with the proposition that it represents a separate family (DUMONT & SILVA-BRIANO 1998).

The present study has some limitations, beginning with the fact that information for many genera were collected from literature sources, that made the comparison difficult and limited the inclusion of more characters in data matrix. In addition, the characters used were limited by the optic microscopy resolution, which prevented the exploitation of the sensilar and glandular structures of the trunk limbs, as proposed by DUMONT & SILVA-BRIANO (1997).

Despite these limitations, the present analysis represents an advance for the comprehension of the relationships within the Macrothricidae. Moreover, not supporting the Neothricidae and suggesting the paraphyly of the non-Macrothricinae genera, this paper argues for the revision of the current classification (cf. DUMONT & NEGREA 2002).

ACKNOWLEDGEMENTS

I am very grateful to Dr. Reginaldo Constantino (Zoology Department, Universidade de Brasilia) for his advice on the cladistic analysis. I also thank Dr. Guarino G. Colli (Zoology Department, Universidade de Brasilia) and Ms. Vania Danigno for revising the English version of this manuscript. Thanks are also due to the Programa de Qualificação Docente of the Universidade Católica de Brasília for the financial support to the present study.

Received in 18.I.2005; accepted in 19.VIII.2005.

• ALONSO, M. 1996. Branchiopoda. Madrid, Museo Nacional de Ciencias Naturales, Consejo Superior de Investigaciones Científicas, 486p.
• DUMONT, H.J. & S.V. NEGREA. 2002. Introduction to the Class Branchiopoda. Leiden, Backhuys Publishers, 398p.
• DUMONT, H.J. & M. SILVA-BRIANO. 1997. Sensory and glandular equipment of the trunk limbs of the Chydoridae and Macrothricidae. Hydrobiologia, Dordrecht, 360: 33-46.
• DUMONT, H.J. & M. SILVA-BRIANO. 1998. A reclassification of the Anomopoda families Macrothricidae and Chydoridae, with the creation of a new suborder, the Radopoda (Crustacea, Branchiopoda). Hydrobiologia, Dordrecht, 384: 119-149.
• FRYER, G. 1974. Evolution and adaptative radiation in the Macrothricidae (Crustacea: Cladocera): a study in comparative functional morphology and ecology. Philosophical Transactions of the Royal Society of London (B), London, 269: 137-274.
• FRYER, G. 1995. Phylogeny and adaptative radiation within the Anomopoda: A preliminary exploration. Hydrobiologia, Dordrecht, 307: 57-68.
• FRYER, G. & J.C. PAGGI. 1972. A new cladoceran genus of the family Macrothricidae from Argentina. Crustaceana, Leiden, 23 (3): 255-262
• MADDISON, W.P. & D.R. MADDISON. 1992. MacClade: Analysis of phylogeny and character evolution, Version 3.04. Sunderland, Sinauer.
• OLESEN, J. 1998. A phylogenetic analysis of the Conchostraca and Cladocera (Crustacea, Branchiopoda, Diplostraca). Zoological Journal of the Linnean Society, London, 122: 491-536.
• OLESEN, J. 2000. An updated phylogeny of the Conchostraca-Cladocera clade (Branchiopoda, Diplostraca). Crustaceana, Leiden, 73: 869-886.
• PAGGI, J.C. 1976. Cladoceros Macrothricidae nuevos para la fauna Argentina. Physis, Buenos Aires, 35 (91): 103-112.
• PETKOVSKI, T.K. 1973. Zur Cladoceren-Fauna Australiens. II. Sididae und Macrothricidae. Acta Musei Macedonici Scientiarum Naturalium, Skopje, 13 (8): 161-192.
• SILVA-BRIANO, M. & H.J. DUMONT. 2001. Wlassicsia, Bunops & Onchobunops (Anomopoda), three related genera. Hydrobiologia, Dordrecht, 442: 1-28.
• SMIRNOV, N.N. 1992. The Macrothricidae of the world. Amsterdam, SPB Academic Publishing, 143p.
• SWOFFORD, D.L. 1999. PAUP: Phylogenetic Analysis Using Parsimony and other methods, Version 4. Sunderland, Sinauer.

Publication Dates

• Publication in this collection
  31 Oct 2005
• Date of issue
  Sept 2005

History

• Accepted
  19 Aug 2005
• Received
  18 Jan 2005