Barcoding gene COI fails to distinguish between two fiddler crab species
(Brachyura: Ocypodidae: Uca) across their entire range of geographic overlap
RICHARD B. LANDSTORFER1, CHRISTOPH D. SCHUBART1, DARRYL L. FELDER2
1
Fakultät für Biologie I, Universität Regensburg, D-93040 Regensburg (r.landstorfer@gmx.de)
2
Dept. of Biology, University of Louisiana at Lafayette, Lafayette 70504, USA
The fiddler crab species Uca minax (Le Conte, 1855) and Uca longisignalis Salmon & Atsaides, 1968
are partially sympatric, with Uca longisignalis being endemic to the northern Gulf of Mexico from
northern Florida to Texas. The geographic range of Uca minax is wider and includes most of the
Amarican East Coast up to Massachusetts with a disjunct distribution across the Peninsula of Florida.
Following the description of Uca longisignalis in 1968, there was a long-standing debate on the validity
of this species. However, after a redescription in 1982, it has been accepted by most systematists.
Several diagnostic morphological traits, like differences in pubescence and in colour, allow us to
distinguish the two sister species. Intraspecific allozyme divergence in trans-Floridian populations of
Uca minax have also raised the question of whether the Gulf of Mexico hosts an endemic lineage of
this species. Our studies include populations in the region of sympatry for the two species as well as
regions where Uca minax (along the Carolinian Province) and Uca longisignalis (south-central Texas)
occur exclusively. Ten samples of at least ten specimens each from separate populations were
examined for morphological characters and color; thereafter, eight of each sample were used for
genetic examination with the barcoding gene cytochrome oxidase I (COI). Results are presented as
phylogenetic networks. Both species are characterized by high haplotype diversities, but limited
geographic structuring. The amount of gene flow within and between species was calculated with
AMOVA. As opposed to the morphology, our COI analysis does not allow distinction between these
two species, suggesting a very recent separation, possibly in different Pleistocene refugia. This is one
more example, where COI barcoding methods fail to recognize actual species diversity.