A tentative phylogenetic analysis of the genus pontoscolex (oligochaeta : glossoscolecidae)

Soil &al. Biochem. Vol. 24, No. I?. pp. 1207-I ?I I, 1992

0038-0717:92 55.00 + 0.00

Printed I” Great Britain. AlI rights reserved

Copyright c 1992 Pergamon Press Ltd

A TENTATIVE PHYLOGENETIC ANALYSIS THE GENUS PONTOSCOLEX (OLIGOCHAETA: GLOSSOSCOLECIDAE)

OF

SONIA BORGES Department

of Biology, University of Puerto Rico, Mayagiiez Campus, PR 00681, U.S.A.

phylogenetic analysis of the species of Pontoscolex has been made using PAUP with a data matrix of I5 characters. The results support Righi (Zoologische Mededelingen kiden 43, 3 14-3 15, 1984) and Borges and Moreno (Bollerino del Muse0 Regionale di Sciexe Naturali Torino, 1992) in their division of the genus into three subgenera, but challenge the diagnostic criteria used by Righi and the evolutionary implications of Borges and Moreno. The subgenera are redefined.

Summary-A

INTRODUCTION

Righi (1984) revised the genera Pontoscolex Schmarda, 1861 and Meroscolex Cernosvitov, 1934. Cernosvitov proposed that the genus Meroscolex differs from Pontoscolex because its setae are

arranged in regular rows and because of the structure of its calciferous glands. Nevertheless, Righi considered that these characters are not sufficient to distinguish Meroscolex from Pontoscolex at a generic level because some Meroscofex species have a partially irregular arrangement of the posterior setae and because some Pontoscolex have the same structure of the calciferous glands as some Meroscolex. Therefore, Righi grouped all their species under the genus Pontoscolex and separated then on a subgeneric level according to the position of the male genitalia among other characteristics. Based on the position of the male genitalia, parietal insertion of some anterior septa, and the arrangement of the setae, Righi divided the genus Pontoscolex into two subgenera, Pontoscolex and Meroscolex, and defined them as follows. Subgenus Pontoscolex. “Tubercula pubertatis extend for 3-5 segments in the region of XIX-XXIII. Table I. Ponroscolex subgenera and species

Posterior setae arranged in regular series, or some series regular and other irregular, or in quincux. Some anterior septa with unconventional parietal insertion”. Subgenus Meroscolex. “Tubercula pubertatis extend for 4f to 54 segments in the region of XXII-XXVIII. Setae disposed in regular series throughout the body. Septa with conventional insertion, rarely unconventional”. Borges and Moreno (1992) described three new species of the genus Pontoscolex, and using the criteria established by Righi (1984) included two of them in the subgenus Pontoscofex. The third species presented characteristics so distinct, that they created a new subgenus, Mesoscolex, which they defined as follows. Subgenus Mesoscolex. “Tubercula pubertatis extend from 6: to 7 segments in the region of segments (26$, 27-32. Septa with conventional insertion. Posterior setae irregular”. It is worth mentioning that, except for the position of the tubercula pubertatis (TP), the definitions of these subgenera are not exclusive. The 16 species belonging to Pontoscolex (see Table 1) were analyzed using PAUP (Phylogenetic Analysis Using Parsimony, version 2.4.1; Swofford, 1985) to evaluate the validity of this classification.

P. (Pontoscolex) corethrurus (Mitller. 1857)

P. (P.) canderrk-eni (Michaelsen, 1933) P. (P.) hingsroni (Stephenson, 1931) P. (P.) cuasi (Righi, 1984) P. (P.) marcusi (Righi and Ayres, 1976) P. (P.) lilljeborgi (Eisen, 1896) P. (P.) nogueirai (Righi, 1984) P. (P.) eudoxiae (Righi et al., 1978) P. (P.) moracoensis (Righi, 1984) P. (P.) spiralis (Borgcs and Moreno. 1991) P. (P.) me/issue (Barges and Moreno, 1991) P. (P.) Meroscolex) guianicus (Cemosvitov, 1934) P. (M.) longirsimus (Cemosvitov, 1934) P. (M.) hoogmoedi (Righi, 1969) P. (M.) roraimensir (Righi, 1984) P. (Mesoscolex) cvnthiae (Barges and Moreno. 1991)

SBB2412-c

METHODS

A character matrix of 15 characters for the 16 species considered was developed employing their original descriptions. (cited in Table l), except for P. corethrurus where an article by Gates (1973) was used. Characters 8, 13, 14 and 15 were not polarized and considered “unordered”. The rest of the characters were polarized using the criteria established by Brinkhurst (1981), Jamieson (1988), and Righi (1984). Table 2 shows the characters employed and their 1207

SONIA BOWES

1208

Table 2. Characters and character states used in the phylogenettc evaluation of Ponroscolex subgenera and species. States preceded by are plesiomorphic: Cl = consistency index; PI = phylogram I; PZ = phylogram 2 l

Table 4. Number of phylograms. their length and their consistency index (CI) for the different PAUP analyses carned out Analysis

CI

Characters employed regular (*A): irregular(B) (2) Number of irregular setal rows: 0 (*A); 2 (B); 3 (C): 4 (D) (3) First clitellar segment: 18 (*A); 16 (8); 15 (‘3: 14 (DI: I3 (E) (4) First intestki se&&t: 15 (*A); I6 (B); I7 (C); IS (D); 19 (E) (5) First TP segment: 26 (*A); 23 (B); 22 (C): 21 (D); 20 (E); 19 (F) (6) Seminal vesicles: present (*A); rudimentary or absent (B); absent(C) (7) Extension of seminal vesicles; 83 (*A); 60 (B); 45 (C); 33-31 (D); 26-21 (E); 19-12 (F); 0 (G) (8) First spermathecal pore: 8/9 (A); 7/S (B); 6/7 (C) (9) Pairs of spermathecae: 4 (*A); 3 (B) (IO) Irregular septa: absent (*A); present(B) (I I) Number of irregular septa: 0 (*A); I (8): 2 (C): 3 (D): 4 (E): 5 (F); 6 (G) (12) Position of male pore: 28 (*A); 24 (B); 22 (C): 21 (D); 20 (E): 19 (F) (I 3) First typhlosole segment: 3 I (A); 30 (B); 29 (C); 27 (D); 26 (E); 25 (F); 22 (G) (14) Extension of TP: 3 (A); 4 (8); 5 (C); 6 (D) 7 (E) (15) Extension of clitellum: 8 (A); 9 (B); IO (C) I I (D); I2 (E); I4 (F); I5 (G); I6 (H)

No. of phylograms

Phylogram length

CI

I

Sane

2

2 7

12.10 3,4 7 3.4.7 1.7

IO5 100 36 84 90 70 85

0.533 0 550 0.593 0.571 0.567 0.614 0.588

, 3 J

0.204

(I) Setae arrangement:

Character deleted

NO.

0.375 0.333 0.400

2

I

33 2 2 9 2

PI = 0.625 P2 = 0.714 0.667 0.500 0.667 0.500 0.333 0.500 0.833 0.857 PI = 0.677 P2 = 0.571 0.636

polarity. The data matrix appears in Table 3. In the computations, the following optional settings were constant: ADDSEQ = CONSTANT; SWAP = GLOBAL; MULPARS; OPT = DELTRAN; NOWEIGHTS; MAXTREE = 100; HYPANC = I; HOLD = 3. RESULTS

Initially, the data matrix was analyzed using all of 15 characters and rooted in a hypothetical ancestor with all the characters plesiomorphic. This analysis resulted in two equally parsimonious phylograms with a length of 105 steps and a consistency index

(CI) of 0.533. Character

number 1, 2, 3, 4, 7 and 10 had low CIs: 0.200, 0.300, 0.364, 0.444, 0.445 and 0.333, respectively. These low CIs could indicate that these characters’ contribution to the phylogenetic analysis may not be very significant. This leads to further analyses, this time deleting one or more of the low CI characters. The results of some of the analyses performed, i.e. the number of phylograms produced, the length of the phylograms and their CIs are shown in Table 4. Analyses 3 and 6, with the deletion of three characters, produced the highest CIs (0.593 and 0.614, respectively), as one would expect when less characters are used. However, they also had a high number of phylograms (33 and 9 respectively). All the other analyses resulted in phylograms with lower CIs. Analysis 4 produced the shortest and best resolved phylograms, with the highest CI. Therefore, the phylograms generated by this analysis were chosen as those that best represent the phylogenetical relationships between the species of Pontoscolex. Analysis 4 produced two equally parsimonious phylograms (length = 84), both with a CI of 0.571. The phylograms are very similar, differing only in the relationships between species P. m&sue, P. vandersleeni, and P. corethrurus (Fig. 1). In phylogram 1, P. candersleeni is more related to P melissae and in phylogram 2 it is closer to P. corerhrurus. The consistency index for each character in these two phylograms is listed in Table 2.

Table 3. Data matrix ROOT CUAS MARC NOGU RORA MEL1 SPIR CYNT GUIA LONG MARA HOOG CORE EUDO VAND HING LlLL

I

2

3

4

5

6

7

8

9

IO

II

12

I3

I4

I5

A B B A A B A B A A A A B A B B B

A B B A A D A C A A A A D A D B C

A C D D D C B A D A C D C E D B c

A C B E C D D E ? ? C C C A ? ? ?

A E F E B D E A C C E B F E F E ?

A A

A E C F B F E A F F E F F D ? D ?

A C C C C C C C C C C C C C C B A

A B B B B B B B B B B B B B

A B B B B B B A A A B B B A

A D B

.4 D F E B C ? A ? ? D B ? ?

A

C E E B D F B ? ? E ? G F

A B B B D A A

A D C E H C B G F D C H B E D B A

c” A A A A A A A A FJ A A A ?

’

: E D A A A G B B A

A

?

?

?

?

B B

B B

F B

E ?

? ?

: C B D B B A B ?

Columns represent characters and their states, and rows represent taxa. Binary characters are represented by an A when plesiornorphic and by B when apomorphic. multistate characters by the corresponding letters, and missing values are represented by ?. Species are identified by the first four letters of their specific name. ROOT = hypothetical ancestor.

Phylogenetic analysis of Ponrorcole.~

1209

ROOT

MARACAENSIS

HINCSTONI 12752

4-

I

6

NOGUEIRAI II

5

5

MLLISSAE

VANDERSLEENI

COREIHRURUS

7

I

ULLJEBORGl

1 43

1211107 r+++

+--I 9

I

2 I

5

11

-_ 11

1

LONGISSIMUS

L HOOGMOEDI

RORAIMENSIS

3

1

CYNTHIA&

2

,-

-

MELISSAE

LILWEBORGI

Fig. 1. Phylogenetical relationships between the species of Pontoscolex. This phylogram corresponds to phylogram 1 of analysis 4. The inset shows the difference between this and the other phylogram obtained in the analysis. Binary characters changing from A to B are indicated only by the number of the character. Other phyletic steps are indicated in full.

DISCUSSION

In order to determine which of the two phylograms produced in analysis four best represents the relationships among the species of Ponroscolex, it is first necessary to evaluate whether P. vandersleeni is closer to P. melissae as in phylogram 1, or to P. corethrurus, as in phylogram 2. The three species have irregular setal rows (character 2; CI = 0.375). The apomorphies that separate P. me/issue and P. vandersleeni in phylogram 1 are the number of spermathecae (9; CI = OSOO),the extension of the seminal vesicles (7; CI = OSOO),the number of unconventionally inserted septa (11; CI = 0.500), and the number of clitellar segments (15; CI = 0.636). The apomorphic characters that

separate P. vandersleeni and P. corethrurus are the presence or absence of seminal vesicles (6; CI = 0.667), the number of spermathecae (9; CI = O.SOO), the number of TP segments (14; CI = 0.57 I), and the number of clitellar segments (15; CI = 0.636). P. vandersleeni has a problem with the “missing values”, which add up to six out of the thirteen characters used. Therefore, of all the apomorphies mentioned before, only five could be used to compare these three species. P. vandersleeni is the only species in its genus which has four pairs of spermathecae while the rest have three pairs. Also, its number of clitellar segments (9) differs from P. melissue (10) and P. corerhrurus (11). Of the three characters left, P. candersleeni has two in common with P. melissae

lZI0

SANKA B0~Gi3

(6 and 14), and one in common with P. corethrurus (5). Thus, it can be assumed that P. oandersleeni is closer to P. melissae than to P. corethrurus, and therefore, phylogram 1 is chosen as the one that best represents the phylogenetical relationships among the 16 species of the genus Pontoscolex. Figure 1 shows that there is zero length between the species P. longissimus and P. ho~gmoed~ and their nodes. It is possible that the best explanation for these results is lack of information. P. hoogmoedi misses character 13 (CI = 857). P. longissimus differs from P. quiunicus by two characters (3 and 4), one of which (3) is deleted in this analysis and therefore was not included in length calculations. Both of these species have the same missing characters: 4 (which was also deleted in this analysis), 12, and 13. The last two characters seem to be significant for both have high CIs (0.833 and 0.857, respectively). This possibility would be easy to verify if specimens were available. Phylogram 1 may be divided into three groups. As observed in Table 1, all species in group 1 belong to the subgenus Pontoscolex, the only species present in group 2 pertains to the subgenus Meroscolex, and all the species in group 3 belong to the subgenus Meroscolex. It is possible to reason that the subgenus Mesoscolex is a monophyly as is also the subgenus Pontoscofex. The latter subgenus involves several subdivisions but the taxonomic implications of these subdivisions will not be considered here and will wait for additional information of the missing characters. The genus ~erosco~ex* which occupies a middle range between two monophylies, is not monophyletic. This could be due to the “missing” characters. Both P. guianicus and P. Iongissimus miss characters 4 (CI = 0.400), 12 (CI = 0.833), and 13 (CI = 0.857), and P, hoogmoedi misses character 13. Five of the seven missing characters had a very high CI, thus the groupings may have resulted differently if they had been available. The subdivision of this phylogram into three groups, each one containing only species belonging to a specific subgenus, supports, and is in complete agreement with, the opinions of Righi (1984) and Borges and Moreno (1992). The genus Pontoscolex had been divided into three subgenera according to the arrangement of the setal rows, the male genitalia, and the insertion of the septa (Righi, 1984; Borges and Moreno, 1992). As stated by Righi, the regular arrangement of the setal rows and conventional parietal insertion of the septa are considered primitive characteristics in the Oligochaeta. He considered the tendency towards cephalization, with an anterior disposition of male genitalia, as an advanced characteristic, especially in glossoscolecids. The subgenus Meroscolex, with its setae organized in regular rows, its septa conventionally inserted, and with a more posterior localization of its TP and male pores, was considered more primitive than the subgenus Pontoscolex in which the TP are localized

anteriorly, the setae may, or may not, be in longitudinal rows, and some of the anterior septa are not conventionally inserted. In the subgenus Mesoscolex the setae are irregular, the septa are inserted in a conventional way, and the TP and the male pores are localized even further behind those of Meroscofex. Because the subgenus Mesoscolex has both advanced and primitive characteristics, Borges and Moreno (1992) suggested it should occupy an intermediate position between Pontoseolex and Meroscolex. After this evaluation of the genus Pontoscolex, the opinions on the evolution of these subgenera will have to be reconsidered. Phylogram 1 (Fig. 1) has each branch length drawn proportionally to the number of changes assigned to the branch, allowing for inferences about the evolution of these subgenera. With this in mind, and in agreement with Righi, one could assume that, in effect, the subgenus Pontoscolex is the one with more advanced characteristics. It is also true that the subgenus Meroscolex has less advanced characteristics than Pontoscolex. But, contrary to expectation, the subgenus Mesoscolex does not occupy an intermediate position between Pontoscolex and Meroscolex, as suggested by Borges and Moreno. On the contrary, it appears to have the less advanced characters of all. This leads to the reconsideration of the criteria used by Righi and Borges and Moreno to distinguish between the subgenera. They used criteria that correspond to characters 1 (regular or irregular setal rows), 10 (septa inserted conventionally or not), and 14 (number of segments of the TP). They also used the position of the TP, but in this analysis, because of difficulties in codifying this characteristic, the first TP segment (character 5) was used instead. These characters have a CI of 0.200,0.333, 0.667, and 0.667, respectively. Characters 1 and 10, which were not exclusive in the subgenera descriptions, have low CIs, therefore, may not be the best characters to use to distinguish between subgenera. It is therefore suggested that the arrangement of the setal rows and septal insertions should not be considered as diagnostic criteria for these subgenera. Instead, and in addition to the extent of the TP already used by Righi, it is recommended that other characters with high CI, like the position of the male pores (CI = 0.833) and the first TP segment (CI = 0.625) be used. Based on these analyses, the subgenera should be redefined as follows: Subgenus Pontoscolex. TP extends over 3-5 segments beginning on segments 19-21; male pores in segments 19/20-22. Subgenus Meroscolex. TP extends over 4-6 segments beginning on segments 22-23; male pores in segment 24. Subgenus Mesoscolex. TP extends over 7 segments beginning on segment 26; male pores in segment 28. Acknowledgements--fn am indebted to DC Ralph Brinkhurst for reading the manuscript and offering many

Phylogenetic analysis of Ponfoscolex valuable suggestions, and to Dr Stuart J. Ramos for all his help. I would also like to thank Professor Fernando Bird for his comments.

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Jamieson G. M. (1988) On the phylogeny and higher classification of the Oligochaeta. Chzdtifics 4, 367-401. Michaelsen W. (1933) Die Oligochatenfauna Surinames. Tijdschri/I der Nederlandsche Dierkundige Vereeniging 3, 112-131.

Righi G. (1969) A new species of Meroscolex from Suriname (Oligochaeta, Glossoscolecidae). Zoiilogische Mededehngen

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Cemosvitov L. (1934jLes oh&h&es et d’autres navs de I’Amiriaue

de la Guyane francais du Sud. Buiietin du

Museum His;oi;e naturelie, Paris 2, 47-59.

Eisen G. (1896) Pontoscolex li&eborgi with notes on auditory sense cell of Pontoscolex corethrurus. Fesrskri/r Wilhelm Lilljeborg, 1-16. Gates G. E. <1973) Contribution to a revision of the earthworm family Glouoscolecidae. I. Ponfoscolex corerhrurus (Miiller, 1857). Bulletin Tall Timbers Research Station 14, I-12.

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Righi G. (1984) Pontoscolex (Oligochaeta, Glossoscolecidae), a new evaluation. Studies on Neotropical Fauna and Environmenl 19, 159-177. Righi G. and Ayres I. (1976) Meroscolex marcusi, sp.n. Oligochaeta, Glossoscolecidae da Amazonia. Bolerim Zo&ogia Uniuersidade Sao Paul0 1, 257-263.

Riahi G.. Avres I. and Bittencourt E. C. R. (1978) Gligochaeta-(Annelida) do Institute National de Pes&isas da Amazdnia. Acra Amazonica 8, I-49. Stephenson J. (1931) Oligochaeta from Burma, Kenya and other parts of the world. Proceedings Zoological Society of London 1931, 33-92. Swofford D. L. (1985) Phylogenetic Analysis Using Parsimony,

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