Name: VICTOR HUGO COLOMBI
Type: PhD thesis
Publication date: 21/02/2018
Advisor:
Name |
Role |
|---|---|
| Valéria Fagundes | Advisor * |
Examining board:
| Name |
Role |
|---|---|
| Ana Carolina Loss Rodrigues | Internal Examiner * |
| Kátia Cristina Machado Pellegrino | External Examiner * |
| Lena Geise | External Examiner * |
| Sarah Maria Vargas | Internal Alternate * |
| Valéria Fagundes | Advisor * |
| Vander Calmon Tosta | External Alternate * |
| Yuri Luiz Reis Leite | Internal Examiner * |
Summary: Thaptomys Thomas, 1916 is a monotypic rodent genus endemic from Atlantic Forest. Despite the low
morphological differentiation, cytogenetic and molecular data suggest an underestimated diversity for this
taxon. Thus, the present work tested the hypothesis that Thaptomys is not monotypic, from an integrative
analysis, with cytogenetic, morphometric, molecular and niche modeling data, performing a broad
taxonomic revision for the genus. We analyzed 201 specimens (141 citogenectilly) of 26 localities, from
Una/BA to San Raphael, Paraguay. G and C banding, FISH with telomeric probes and chromosome
painting allowed the characterization of five new karyotypes, described for the first time: 2n=48/FNA=52,
2n=49a/FNA=52, 2n=49b/FNA=52, 2n=50/FNA=52, 2n=51/FNA=52. Our data suggest that centric fusions
of four acrocentrics pairs (1+15 and 3+4) generated a large metacentric and other submetacentric pairs,
in homozygous and heterozygous conditions, combinations at 2n=48-51/FNA=52. In addition, we refined
the mechanism of differentiation between karyotypes of 2n=50/FNA=48 and 2n=52/FNA=52, as a complex
rearrangement involving unequal centric fission of each small metacentric 25 homologue, followed by a
tandem fusion of each arm derived from 25 in the acrocentric pairs 2 and 23. Phylogenetic analyzes (Cytb)
recovered a "Noth Clade" of wide geographic range, from Una/BA (2n=50/FNA=48), Luminárias/MG
(2n=48-51/FNA=52) to Tapiraí/SP (2n=52/FNA=52) and the other samples formed a politomy ("South"),
from Tapiraí/SP (2n=52/FNA=52) to San Rafael and Limoy (Paraguay, without karyotype), which
diverged by 2.15%. Specimens with different karyotypes were not recovered as monophyletic, although
specimens with 2n=50/FNA=48 formed two distinct and exclusive clades. Population analysis (CytB and
six microsatellite loci) indicated Una/BA (2n=50/FNA=48) as a distinct population from the others,
diverging in 1.89% from 2n=52/FNA=52 and 1.2% of 2n=48-51/FNA=52, without sharing of haplotypes
with another karyotype or locality. Morphologically, specimens with 2n=48-51/FNA=52 did not present
any distinction of those with 2n=50/FNA= 48 and 2n=52/FNA=52 and that are geographically isolated.
The geographic distribution of the different karyotypes shows that they were never detected in sympatry,
that there is no evidence of hybrids between them and that they seem to be geographically isolated, since
Una/BA (2n=50/FNA=48) is distant in 938 km of Luminárias/MG (2n=48-51/FNA=52), and 500km from
Santa Teresa/ES (2n=52/FNA=52). The fixation of a chromosomal rearrangement with a high frequency
in a population, such as the central fissions and tandem fusions observed in specimens with
2n=50/FNA=48, would result in separation of Thaptomys populations into non interbreeding subgroups
(with and without chromosomal rearrangement), representing a barrier to gene flow, as suggested in the
peripatric speciation model. Thus, founding populations of small size would tend to represent distinct
species, the chromosome being the triggering factor of this process. The lack of phylogenetic resolution
in recovering specimens with different karyotypes as monophyletic, added to the subtle (not significant)
morphological distinction, may indicate a process of abrupt speciation, started by complex chromosomal
rearrangements in which the lineages did not have time to accumulate differences. In view of the data, a
much more complex interpretation is proposed, in which Thaptomys would be represented by two species,
being (I) Thaptomys sp. n., with 2n=50/FNA=48, exclusive from Una, Bahia; and (II) Thaptomys nigrita,
presenting chromosomal polymorphism, with three subspecies, being (III) Thaptomys nigrita ssp. n with
2n=48-52/FNA=52, exclusive from Luminárias, Minas Gerais, (IV) Thaptomys nigrita nigrita
(nominotypical subspecies; 2n=52/FNA=52), occurring from Santa Teresa (ES) to Tapiraí (SP) and (V)
Thaptomys nigrita subterraneus (2n=52/FNA=52), from Pilar do Sul (SP) to San Raphael (Paraguay).
Keywords: speciation, cytotaxonomy, integrative taxonomy, Atlantic Forest
