Name: Ana Heloisa de Carvalho
Type: PhD thesis
Publication date: 28/11/2017
Advisor:

Name	Role
Leonora Pires Costa	Advisor *
Valéria Fagundes	Co-advisor *

Examining board:

Name	Role
Ana Carolina Loss Rodrigues	Internal Examiner *
Bárbara Maria de Andrade Costa	External Examiner *
Leonora Pires Costa	Advisor *
Maria José de Jesus Silva	External Examiner *
Roberta Paresque	Internal Examiner *

Summary: Rhipidomys (Cricetidae, Rodentia) taxonomy is very complex, and the identification of
specimens is usually based on continuous morphological characters. In previous phylogenetic
studies, based in the Cytochrome B (Cytb) gene, among other lines of evidence, 12 of the 23
recognized species were sampled: three of them have been identified and described after these
studies and another one is not formally described yet. These data indicate that the
morphological variation may underestimate the diversity of the genus. Karyotype is usually a
reliable taxonomic character for rodents but, concerning Rhipidomys, many have been
described but not necessarily associated with a recognized species or misinterpreted.
Karyotypes of specimens from different localities, that were identified on basis of molecular
and/or morphological characters, were analyzed. We reviewed the karyotypic information
available in literature for Rhipidomys and some were reinterpreted. This genus presents three
karyological groups: a group presenting diploid number (2n) equal to 44, and low fundamental
number (FN) varying from 48 to 52; a group presenting 2n=44, FN high, FN=72–80; and a
group presenting 2n different from 44, 2n=48 and 50 and FN=66–72. Most species of this
genus presents 2n=44 and low FN, all of these karyotypes being very similar. We assume that
the ancestral karyotype of the genus should be similar to these, since are the ones recorded for
Rhipidomys basal clades and are registered for specimens nearest to Central America, region
of the cladogenesis event between Rhipidomys and Thomasomys probably occurs which
presents some species showing 2n similar to 44, including 2n=44, and low FN. In addition to
the 2n=44 and low FN karyotypes group, a single clade includes the other two groups: the
group presenting 2n=48 e 50, which currently only includes R. nitela, but presented five
distinct complements that can possibly comprise three taxonomic entities or distinctive
populations; and a group with 2n=44 and high FN, that currently includes R. ipukensis and R.
mastacalis. Molecular data, using two mitochondrial and four nuclear markers, associated with
karyotype data, revealed two clades in R. mastacalis: one north of the Jequitinhonha river and
another to the south. These clades correspond to two distinct species: R. mastacalis (2n=44,
FN=74) and probably R. cearanus (2n=44, FN=72), a taxon name currently available but not
current recognized. Within the clade characterized by high FN is R. emiliae that presents
karyotype with 2n=44, FN=52, due to an introgression event confirmed by nuclear
concatenated analysis. While karyotype analyzed by conventional staining does not
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distinguish well species with low FN, banding patterns suggest distinctions. We could not
differentiate the main cause of variation in FN: centromeric repositioning or pericentric
inversion. The explanation for the appearance of 2n=48 and 50 karyotype is more complex
than a simple fission. In the present study the karyotype of Rhipidomys emiliae, R. ipukensis
and R. tribei was described for the first time. Based on the molecular analysis, there is also the
indication of possible new species.
Keywords: introgression, geographic distribution, taxonomy, Rhipidomys cearanus,
molecular phylogeny, mitochondrial marker, nuclear marker, karyotype.

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