WHITHER OCTOCHAETIDAE?

- Its Family Status Reviewed

by

Rob Blakemore,COE fellow,

Soil Ecology Research

Group,Yokohama National University

Japan

After IOTM presentation at Cluj Romania September, 2005, and YNU seminar 10th November, 2005.

Introduction“The family-level classification of the megascolecid earthworms is in chaos” – Fender & McKey-Fender, (Soi

l Biology Guide, 1990: 369). - For an overview of the dispute, these authors cite the conflicting schemes of Gates (1959), Jamieson (1971), and Sims (1980).

The megadrile suborder Lumbricina comprises between 5 and 21 families under the various systems currently touted.

“Much breath & paper has been largely wasted arguing the appropriate rank of a group”. [http://www.palaeos.com/Systematics/Cladistics/incompatable.html July, 2005]

Inherited confusion distracts taxonomists hoping to service simple questions from increasingly frustrated field researchers such as:

“Which family does this genus belong to?”“How many families are found in Australia – just one, or ten?”

“What’re the differences and distributions of Acanthodrilidae and Megascolecidae?”“Is this species in Benhamiinae, Octochaetidae, or both?”

“Why can’t taxonomists agree, and progress to more important issues?”

The purpose of this presentation is to explore options for consensus, using both deductive (morphological) and objective (molecular) evidence, in an historical taxonomic context.

Family Characters eg.

BASIC Earthworm PATTERNS Female pore always on 14 Male pores on 18, prostatic pores o

n 17 & 19 (i.e., acanthodriline)• Prostates tubular

Setae – 8 per segment (lumbricine) Nephridia one pair per segment (ho

loic) Gizzard – single (mono-giceriate)

Any change – at all – from a “BASIC” (plesiomorphic) state MUST be a

“DERIVED” (apomorphic) state...

DERIVED Male PATTERN

Figure modifed from Lee, Blakemore & Fraser (2001) after Lee (1938)

DERIVED Setae PATTERN Setae Lumbricine (8) Non-lumbricine (>8 )

DERIVED Prostate PATTERN Prostates; tubular

non-tubular

DERIVED Nephridial PATTERNHoloic nephridia 　 (one

pair per segment)

Non-holoic (i.e., meroic or anything

other than a single pair)

DERIVED Gizzard PATTERNS Single Non-single (multiple or absent)

ProponentsEarthworm classification starts with Michaelsen (1900)

Herr Prof. Wilhelm Michaelsen (1860-1937) worked in Hamburg, assiduously naming >1,080 earthworm world species! His opus, Das Tierreich (1900), heralded a relatively stable Classical Systematics era.

Other propontents were:

Captain Dr John Stephenson (1871-1933) who mostly worked in British India (naming about 250 species), his great enduring monograph was The Oligochaeta (1930).

Dr Gordon Enoch Gates (1897-1987), an American schoolmaster in Burma in the 1930’s (ca. 369 species’ names) whose publications spanned nearly 60 years.

Family Classification 1Michaelsen (1900) – mainly based on male organs...

...then on intestinal and nephridial arrangements, etc..

Family Classification 2Michaelsen (1921) – modified several families from his earlier view.

Family Classification 3Stephenson (1930) – “Classical System” support of Michaelsen.

Family Classification 4Lee (1959) – simplifies by putting all Octochaetinae in Acanthodrilinae.

Family Classification 5Gates (1959) – objects to & rejects “Classical System”, proposes own.

Family Classification 5aGates (1959) – objects to & rejects “Classical System”, proposes own.

Family Classification 5bGates’ system was largely supported by Sims (1966/80/82) in UK, and Reynolds & Cook (1982/89/93) in USA; while James

(2005: 55) accepted “Acanthodrilidae” but, as he does not cite Blakemore (2000), possibly this is for Gates’ concept...

Family Classification 5cUnfortunately, Gates’ system was obviously false ...

Family Classification 5dUnfortunately, Gates’ system was obviously false ....

...based on a premise that only the prostate type separated Acanthodrilidae/*Octochaetidae (“tubular”) from Megascolecidae (“racemose”); and also that acanthodriline taxa (eg. Exxus) belong in the latter family...

*Gates (1972: 275) acknowledged that Octochaetidae was probably polyphyletic, but pragmatically maintained it for ‘convenience’ in lieu of better options from future research.

Family Classification 5eUnfortunately, Gates’ system was obviously false ....

Whereas, Megascolecidae is actually defined on non-acanthodriline male pores (i.e., megascolecine), and prostates may be either tubular or non-tubular - see the following Regulation Table...

CRASH!!

Family Classification 6aMeanwhile, Jamieson (1971, 1988, 2000, etc.) largely ignored the “Classical System” - and most other systems - strongly objected to Gates’ (flawed) scheme.....

... and devised his own scheme.

Family Classification 6bBut, Jamieson’s scheme was equally flawed ....

... based on highly environmentally adaptive or negative (and frequently absent!) fine ultra-structural details of meroic nephridia that varied within genera (and in some specimens!) so that it artificially merged Acanthodrilidae into Megascolecidae, had non-mutually-exclusive groups, and defied biogeographic (and phylogenetic) clarity...

[This scheme was criticised and rejected in whole or part by several other workers around the world eg., Gates, 1972, 1976; Reynolds & Cook, 1976, 1981, 1993; Edwards & Lofty, 1977; Easton, 1979: 9, 17-20; Sims, 1980: 104-5, 1982a, 1982b in Parker (1982); Easton, 1984; Sims & Gerard, 1985, 1999: 40; Fender & McKey-Fender, 1990; James, 1991: 339; Julka, 1988: 5, 368; Nakamura, 1994; Blakemore, 1994, 1999, 2000, 2002, 2004, 2005; Csudzi, 1996; Wetzel, 2003; etc., etc.].

CRASH!!

After a time-span of 30 years, Jamieson (2000) and Jamieson & Dyne (2004) now admit that Jamieson’s (1971) subfamiliar Tribes are defunct: “obsolete or restricted” being based on “highly homoplastic apomorphy of meronephridia” ; but these authors continue to reject ACANTHODRILIDAE and OCTOCHAETIDAE alternatives.

Family Classification 6cBut, Jamieson’s scheme was equally flawed ....

CRASH!!

Many, many authors yet refer to Acanthodrilidae and/or Octochaetidae, thus rejecting Jamieson’s scheme, but not all defer to Gates’ system; there are other options...

Family Classification 7Recently, Blakemore (2000) revised and updated the Classical systematics, raising most to Family status

Family Classification 8Revised systematics - raised to Family status

World distributions for these families pending....

Extended Families?Is it reasonable to have a larger number of Families?The terrestrial/aquatic Oligochaeta have ~8,535 species in 804 genera and 38 Families:

These are divided ca. 40 : 60 into aquatic microdriles/enchytraeids : terrestrial megadriles (eg. Dr Csaba Csuzdi’s database has ca. 5,500 megadrile names to May, 2004). Ratio of Species: Genera : Families is approximately 225:21:1

* The marine Polychaeta have ~13,000 species (ca. 8,000 valid), in 1,000 genera and 82 Families: Ratio of Species: Genera : Families is approximately 160:12:1 (or 100:12:1) - proportionally twice as many families as the Oligochaeta.

* [Data from Dr Chris Glasby: http://www.ea.gov.au/biodiversity/abrs/online-resources/polikey/index.html#history. Approximately 300 people work full-time on Polychaeta around the world, many countries have dedicated Marine Laboratories – one reason why they have more described species. Oligochaeta taxonomists are far fewer (look around the room!), and I know of no National Soil Biology Laboratory. Why is this?].

Phylogenetically Valid? -1Is a Linnean systematics compatible with Cladistics?

Probably not. An International Code regulates nomenclature to Family level (ICZN, 1999), but...

“Binomial/Linnaean classification without paraphyletic taxa is logically impossible. Every monophyletic genus in a Linnaean classification must be descended from something (probably a species) in a different genus, which must be paraphyletic.

Similarly every monotypic family must be descended from a species in a genus in a different family.  If one denies paraphyletic taxa, where do genera and families come from?

Ultimately, one would end up sinking everything into its ancestral taxon, and the whole classification would telescope into its original taxon....”

E.g., West African Wegeneriella is holoic and belongs in Acanthodrilidae (family precursor) to the similar, but derived, Amazonian meroic Wegeneriona that belongs in (Benhamiinae) Octochaetidae.

Phylogenetically Valid? -2Is a Linnean systematics compatible with Cladistics??

“... Hennig's proposal to eliminate paraphyletic taxa [from Cladistic studies] was based on a failure to see the difference between the Linnaean hierarchy in which all taxa are nested in the next higher taxon, and a phylogenetic hierarchy which is not so nested, the lower levels of the hierarchy being not equivalent to the higher levels”.

“Put another way, all the species of a genus together equal the genus,

but all the offspring of a parent do not equal the parent”.

Ernst Mayr and Walter J. Bock (2002) discuss these differences in detail....

「 This argument and discussion after Alan Kazlev/Toby White’s Palaeos website by Dr R.K. Brummitt http://www.palaeos.com/Systematics/Cladistics/incompatable.html July, 2005, see also Mayr & Bock (2002) http://www.blackwell-synergy.com/doi/full/10.1046/j.1439-0469.2002.00211.x]

Phylogenetically Valid? -3Is a Linnean systematics compatible with Cladistics?

Darwin’s Evolutionary Tree from his Notebook 1837 (for Galapagos finches).

Applied to primate phylogeny (from http://www.english.uga.edu/nhilton/4890/darwin/DarwinTree.html)

Phylogenetically Valid? -4Is a Linnean systematics compatible with Cladistics?- NO!

“The Hennigian system of cladification consists of the ordering of branches of the phylogenetic tree, strictly on the basis of a single criterion, the branching points of the phylogeny (holophyly) (Hennigian phylogeny). It is not a system of classification, as it does not lead to classes of entities possessing similar phenotypic attributes. A Darwinian classification, by using two criteria, similarity and common descent, leads to the recognition of classes (taxa) of similar entities consistent with common descent (monophyly) (Haeckelian phylogeny). ”.

.....from Ernst Mayr and Walter J. Bock (2002) discussion.

Systematics then is imperfect, but is a “convenience”, i.e, has informative natural groupings.

「 Mayr & Bock (2002) http://www.blackwell-synergy.com/doi/full/10.1046/j.1439-0469.2002.00211.x]

DNA evidence? -1Does the morphological data have a molecular basis?

YES! - The Family Classification system independently proposed by Blakemore (2000) has support of recent DNA Annelida studies, eg., Siddal et al. (2001) http://research.amnh.org/~siddall/pub/livanow.pdf and as reported in Dyne & Jamieson (2004, fig. 3), however these latter authors conclude differently.

DNA evidence? - 2Any alternative interpretations? Yes! The same molecular data can be used to support Csuzdi’s (1993) restoration of Benhamiinae, and

the resurrection of Michaelsen’s Diplocardiinae – here both elevated to Family status separate from Acanthodrilidae and Octochaetidae. [Note: data is lacking to confirm or disconfirm Exxidae].

OR all taxa could be “telescoped” into an Ocnerodrilidae clade, but this is rather “uniformative”.

SummaryMorphological classification supported by DNA

From the same data, which is limited and not based on type species, we can derive two alternative systems. The former one, initially based on morphology, is provisionally maintained for reasons of stability and universality, pending further analysis of the Diplocardiidae and Benhamiidae options. Nevertheless, Acanthodrilidae, Octochaetidae, Exxidae, and Megascolecidae appear to merit separate family status [unlike Jamieson’s (1971, 2000) schemes] but definitions differ greatly from Gates (1959, 　1972).

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All cited references may be found in Blakemore (2000; 2002; 2005).

Thank You!I thank the presenter and convener.

Hopefully, we can continue to discuss this topic another time.

Enjoy the IOTM symposium!

Cheers,Rob Blakemore

Please visit my COE website:http://bio-eco.eis.ynu.ac.jp/eng/database/earthworm/