Ctenomys lami, Freitas, 2010
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publication ID |
https://doi.org/ 10.1076/snfe.36.1.1.8882 |
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persistent identifier |
https://treatment.plazi.org/id/03DB687B-FFA8-FFB6-FF17-92E5FDEBB1B8 |
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treatment provided by |
Juliana |
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scientific name |
Ctenomys lami |
| status |
sp. nov. |
Ctenomys lami View in CoL spec. nov.
Holotype
Adult ♀, 2n = 54 and FN (Fundamental Number) = 76. Skin and skull number 094, collected by Vitor H. Travi and Thales R.O. Freitas. Deposited in the Departamento de Genética, Instituto de Biociências, Universidade Federal do Rio Grande do Sul. Total length 257 mm; tail 79 mm; hind foot (with claws) 36 mm and hind foot (without claws), 32 mm. Total length of skull, 46.45 mm; condylobasal length, 44.40 mm; nasal length, 16.80 mm; nasal width, 7.20 mm; zygomatic breadth, 28.45 mm; bimeatal breadth, 26.50 mm; interorbital breadth, 10.05 mm; mastoid breadth, 25.90 mm; rostral breadth, 11.40 mm; pre orbital foramen length, 10.50 mm; condylopremolar length, 31.10 mm; diastema length 13.25 mm; braincase breadth, 18.10 mm; length of maxillary toothrow, 9.90 mm; palatal length, 22.20 mm; upper incisive breadth 3.30 mm; IV premolar length, 4.40 mm; auditory bulla width, 7.50 mm; auditory bulla length, 15.85 mm; mandibular width, 33.40 mm; and palatal length, 22.20 mm.
Description
Total length, 231–310 mm; length of tail, 67–92 mm; length of hind foot (with claws), 30– 45 mm; hind foot (without claws), 31– 42 mm, weight, 170–307 g. Table 1 View Table 1 summarizes the skull measurements. Skull ( Fig. 2 View Fig ) wide. In dorsal view ( Fig. 2A View Fig ) nasal bones wide anteriorly and tapering posteriorly; frontal presenting a flat surface from the inter-orbital constriction to the posterior region; front-parietal suture round; braincase oval-shaped, length of brancaise 1 / 3 of length of the skull; zygomatic arch square and robust. Incisive foramina small in ventral view ( Fig. 2B View Fig ). Mesopterygoid fossa wide posteriorly and flared anteriorly. Nasal tip in the same plane as the incisor edge in the lateral view ( Fig. 2C View Fig ). Tympanic bullae large and inflated ventrally. The mandible ( Fig. 2D View Fig ) with long and narrow coronoid process; heavy condyloid process and large angular process. Four kidneyshaped molariform teeth; large and orange orthodont incisors, M3 and m3 much reduced. Pelage dark brownish dorsally, each hair dark grayish basally and brownish near the tip, ventral pelage lighter.
Karyotype
Seven diploid numbers: 2n = 54, 55a, 55b, 56a, 56b, 57, and 58, the FN varying from 76 to 82. This karyotype with 2n = 54 is formed by 12 biarmed and 14 acrocentric pairs ( Fig. 3A View Fig ). The sexual pair in males is formed by X-submetacentric and Y-acrocentric chromosomes.
Type locality
Beco dos Cegos (point 1 in Fig. 1B View Fig ), Lami Beach in the Guaíba river, near Porto Alegre, at 30°51¢S; 51°10¢W, characterized as sandy grasslands disturbed by agricultural activities.
Paratypes
34 additional specimens deposited in the Departamento de Genética, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Brazil, listed by locality ( Fig. 1B View Fig ): Brazil, Rio Grande do Sul, Beco dos Cegos (1) ♂♂: N o.77; N o.78, N o.88, N o.107, N o.112, N o.118, N o.405. ♀♀: N o.79, N o.86, N o.87, N o.89, N o.94, N o.95, N o.108, N o.109, N o.110, N o.111, N o.113, N o.114, N o.115. Chico Lomã (2), ♂♂: N o.TR.15, N o.TR.16, N o.TR.17, N o.TR.18, N o.TR.19, N o.TR.456, N o.TR.394. ♀♀: N o.TR.9, N o.TR.10, N o.TR.11, N o.TR.12, N o.TR.13, N o.TR.14, N o.TR.455, N o.TR.532.
Etymology
The name ‘lami’ refers to the Guaíba river beach named Lami, near Porto Alegre, where Beco dos Cegos is located.
Geographic distribution
Ctenomys lami can be found in an almost isolated region named Coxilha das Lombas ( Fig. 1B View Fig ), northeast of the Guaíba river, which extends up nearly 80 km to the southwestern banks of Barros lake. This area is bordered in the northwest by the Pachecos swamp and on the southeast by the Touros swamp. This region originated in the early Pleistocene, from the first marine transgressionalregressional event, through marine and eolian deposits ( Villwock et al., 1986). Nowadays, it is characterized by pastures and an anthropogenic vegetation typical of sandy soils. Ecologically C. lami occurs only in sandy fields.
Diagnosis
Fossorial rodent of medium size and brownish color with 2n = 54, 55, 56, 57 and 58. Other characteristics are listed under Description.
Reproduction
Collections were made between 1981 and 1990; 25 pregnant females were observed from June to December. The litter size is 1–3 embryos (x¯ = 2.04 ± 0.73; N = 25).
The sperm has symmetric form.
Comparisons
Comparison of skull measurements between C. lami and C. minutus separately ( Table 1 View Table 1 ) revealed 9 significantly different characters in ♂♂ and 12 in ♀♀ (T-test).
Discriminant Analysis was performed with 20 characters ( Table 1 View Table 1 ), separately for males and females of C. lami and C. minutus . The analysis among males from localities 1 and 2 for C. lami and 3 and 4 for C. minutus showed a correct classification in almost 100% of the 32 cases. The variable influence shows that condylobasal length, nasal width, bimeatal length, mastoid length, interorbital constriction, frontal length, auditory bullae length, incisive breadth, and IV premolar length are different in both species. The first axis of Canonical Variate Analysis shows an eigenvalue of 27.43 (Wilk’s Lambda = 0.001), and the second axis shows 6.28 (Wilk’s Lambda = 0.03). Two scores of classification resulted from the Canonical Analysis for males ( Fig. 4A View Fig ) showing that males of C. lami from population 1 and 2 are grouped closer and separated of populations 3 and 4 of C. minutus .
The Discriminant Analysis among females from localities 1 and 2 for C. lami , and 3 and 4 for C. minutus showed a correct classification in almost 100% of the 43 cases. Condylobasal length, nasal length. Nasal width, bimeatal length, mastoid length, interorbital constriction, frontal length, rostral breadth, braincase width, pre orbital foramen, auditory bullae length, and incisive breadth are different in both species. The first axis of Canonical Variate Analysis shows eigenvalues of 10.94 (Wilk’s Lambda = 0.003), and the second axis shows 6.54 (Wilk’s Lambda = 0.03). Two scores of classification resulted from the Canonical Analysis for females ( Fig. 4B View Fig ) showing that females of C. lami from population 1 and 2 are separated from C. minutus’ populations 3 and 4.
C. lami spec. nov. presents different diploid numbers, varying due to centric fusions and pericentric inversions, and higher FN’s than C. minutus (2n = 42, 46a, 46b, 47, 48, 49, and 50, with FN = 76, Fig. 3B View Fig ). The karyomorph 2n = 54 is formed by 12 biarmed and 14 acrocentric pairs with the sexual pair formed by sub-metacentric chromosomes ( Fig. 3A View Fig ), whereas in C. minutus the karyomorph 2n = 46a consists of 16 biarmed and 6 acrocentric pairs with the sexual pair formed by a metacentric X-chromosome and a sub-metacentric Y-chromosome ( Fig. 3B View Fig ). Comparison between the two species through G-banding pattern revealed 4 chromosomic differences due to centric fusion in C. minutus ( Fig. 3C View Fig ). The chromosome 1 results from a fusion between chromosomes 23 and 13, while chromosome 3 is formed by a fusion between chromosomes 24 and 16. In C. lami 2 other fusions form chromosome 4 (18 and 25) and 6 (19 and 22).
Discussion
Three other species of Ctenomys occur in Rio Grande do Sul, C. torquatus , C. minutus , and C. flamarioni ( Freitas, 1995) . However, only C. minutus shows similarities with C. lami . C. torquatus presents a different skull and its karyotype shows 2n = 44 and 46 ( Freitas & Lessa, 1984). The same occurs with C. flamarioni , characterized by a strong skull, white hair, and a very different karyotype (2n = 48). C. flamarioni is similar to C. australis , both presenting 2n = 48 and belonging to the Mendocinus-group ( Travi & Freitas, 1984; Freitas, 1994).
Reig et al. (1990) supposed that the genus Ctenomys originated in the Pliocene. Since C. minutus has a lower chromosome number than C. lami and presents more rearrangements ( Freitas, 1997), it can be deduced that C. lami is the more ancient of these two species. This is enforced by results from Villwock et al. (1986) that show that the region of Coxilha das Lombas has been isolated since the beginning of the Pleistocene due to regressional and transgressional events of the coastline. C. lami is restricted to this region, while C. minutus is a species which occurs from Santa Catarina to Southern Rio Grande do Sul. Reig et al. (1966) stated that although displaying 2n = 50 (which is the ‘ minutus ’ cytogenetic pattern) the specimens collected in Santo Antonio da Patrulha showed large morphological differences in relation to other populations of minutus . Thus, the forms considered to be ‘ minutus ’ by these authors could be different taxonomic entities. At the same location where these authors collected the specimens classified as ‘ minutus ’, a karyotype occurs with 2n = 56; it is now classified as C. lami . C. minutus with 2n = 50 was also observed by Freitas (1997), but in Jaguaruna beach, Santa Catarina State about 300 km away to the northeast from Santo Antonio da Patrulha.
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