Deep phylogeny o f the am phipod super-fam ily Eusiroidea
Verheye M. and C. d ’Udekem d ’Acoz
D epartm ent o f Recent Invertebrates, Royal Belgian Institute o f Natural Sciences,
B-1000 Brussels, Belgium
E-mail: mverheve@ naturalsciences.be
The super-fam ily Eusiroidea is tra d itio n a lly divided into 4 fam ilies, nam ely C alliopiidae, Eusiridae,
Gammarellidae and Pontogeneiidae (De Broyer e t al., 2007), but recent phylogenetic data suggests
th a t the eusiroid clade form s a much broader assemblage (Englisch, 2001). Representatives are
found in all oceans, inh ab iting every tro p h ic niches and a wide bathym etric range. With 216
described species in the Southern Ocean (i.e. a bo ut 24% o f its known am phipod fauna), eusiroids
constitute a sign ifican t fraction o f the A n ta rctic and sub-Antarctic bio dive rsity (De Broyer e t al.,
2007).
The eusirid concept is very inadequately defined m orphologically. The super-fam ily fo rm s a diverse
assemblage o f taxa o f gam m aroid fo rm , g lo ba lly characterized by the loss or reduction o f the
accessory fla ge llu m (Bousfield & Hendrycks 1995). The fa m ily assignm ent o f genera is often
challenging, since there is no consistent set o f diagnostic characters defin in g m ost o f them . The 6
fam ilies fo rm e rly com prised in the non-validated taxon Iphim edioidea (Lowry & Myers 2000), as well
as the Astyridae and Stilipedidae were recently considered as eusiroids. Moreover, previous 18S
phylogenetic reconstructions revealed th a t the Astyridae, Iphim ediidae, Epimeriidae and Pleustidae
are nested w ith in the eusiroid clade (Englisch 2001).
With the aim o f clarifying those m ajor nom enclatural uncertainties and discussing the phylogenetic
relationships, a deep phylogeny o f the super-fam ily Eusiroidea, including representatives o f all the
aforem entioned fam ilies, was reconstructed using tw o d iffe re n t gene fragm ents (28S rRNA and 1 8S
rRNA). The analysis was perform ed at a global scale, m ostly w ith A n ta rctic taxa, but also European
and A rctic species.
The study confirm s th a t the Eusiroidea fo rm s a m ust broader
clade than
claimed inclassical
literature. It revealed th a t m ost o f the tra d itio n a lly d elim ited fam ilies are not m onophyletic and that
a few taxa previously considered as eusiroids {Gam m arellus, Cleippides) are in fa ct very d ista n tly
related, and therefore should be excluded fro m them . Eusiroids com prise several independent
arm oured and spiny lineages nested am ongst taxa w ith plesiom orphic m orphologies, suggesting
convergent evolutions and rapid m orphological specializations under intensive selection pressures.
The lim its o f the super-fam ily and its com posing clades have to be com pletely re-established in the
lig h t o f th is new genetic dataset. This study enables a clearer understanding o f the ta xon om y o f
one o f the m ajor am phipod assemblage in the Southern Ocean and gives us insights into the
patterns o f its phenotypic evolution. It proposes a solid fram e fo r fu rth e r analysis o f the systematics
o f various A n ta rctic eusiroid lineages, especially the epim eriid and iphim ediid clades, which w ill be
studied in more depth.
References
Bousfield E.L. and E.A. Hendrycks. 1995. The am phipod superfam ily Eusiroidea in the North
Am erican Pacific region. I. Family Eusiridae: system atic and d is trib u tio n a l ecology.
A m phipacifica l(4 ):3 -5 9 .
De Broyer C., J.K. Lowry, K. Jazdzewski and H. Robert. 2007. Volum e 1: Part 1. Catalogue o f the
Gammaridean and C orophiidean A m phipoda (Crustacea) o f the Southern Ocean w ith
d istrib u tio n and ecological data. Bulletin de I’In stitu t Royal des Sciences Naturelles de Belgique
77(1): 47-64.
Englisch U. 2001. Analyse der Phylogenie der A m phipoda (Crustacea, Malacostraca) m it Hilfe von
Sequenzen des Gens der RNA der kleinen ribosom alen Untereinheit. Phd thesis. RuhrUniversität Bochum, Germany.
LowryJ.K. and A.A. Myers. 2000. A fa m ily level phylogeny o f iphim edioid am phipods (Crustacea,
Am phipoda). [Abstract] Xth International C olloquium on A m phipoda, H eraklion, 16-21 A p ril
2000: 30.
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