Penile shape discriminates the two cryptic species of Akodon (Mammalia, Rodentia, Cricetidae) from eastern Brazil
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Wild caught and captive born specimens of Akodon cursor, Akodon montensis and your Hybrids
|Bounding Coordinates||South West [-25.046, -53.877], North East [-5.878, -29.575]|
Glans penis morphology has been used as a powerful tool in mammal’s taxonomy to differentiate cryptic species. Neotropical rodent species Akodon cursor and A. montensis are cryptic and interspecific hybrids are like their parental species. We investigated non-metric and metric phallic characters aiming to differentiate A. cursor from A. montensis. We also evaluated the parental species’ influence of the phallic characters on hybrids. We analysed 96 male adults, being 56 A. cursor, 27 A. montensis and 13 hybrids, subgrouping species by locality and hybrids by parental species (paternal vs. maternal). We verified that A. cursor and A. montensis are distinguishable by penile shape morphology: A. cursor has elongated penile form with a flare in distal portion and A. montensis has a barrel shape. Also, dark spots in ventral view, if present in A. montensis, distinguish A. montensis from A. cursor. Although the non-metric characters differentiate the species, they do not distinguish the subgroups of A. cursor, A. montensis and hybrids. The metric phallic characters indicated a significant difference between species and hybrids. These characters also differentiate the population groups of A. cursor. However, A. montensis subgroups and hybrids subgroups did not present a significant difference. . This study showed the importance of penis morphology in the taxonomy of rodent cryptic species A. cursor and A. montensis, representing a powerful tool to discriminate male specimens in mammal collections without karyotyping or sequencing, even though the specimens occurred in sympatric areas. Since most taxidermy protocols do not preserve the penis in mammals’ preparations, liquid preservation of some specimens or the removal of the penis before taxidermy for liquid preservation could represent an alternative. We also recommend the organisation of a penis bank for A. cursor species group (or even all rodent species) in museum collections to avoid losing this important information about species identification.
|Title||Penile shape discriminates the two cryptic species of Akodon (Mammalia, Rodentia, Cricetidae) from eastern Brazil|
|Funding||This work was funded by the Foundation for Research and Innovation of the state of Espírito - FAPES (grant #80600417/17 to VF) and the National Council for Scientific and Technological Development - CNPq (undergraduate bursary to LC and LRC and research bursary to VF). We thank the Laboratory of Cellular Ultrastructure Carlos Alberto Redins at UFES (LUCCAR-UFES) for assistance with Scanning Electron Microscopy. We are indebted to all field and the crossbreeding lab teams that, without them, this study would not be possible. We also thank Dr Wesley D. Colombo for assistance with photographing using the extended focus imaging system. In this study the collecting and processing specimens as well as access to the genetic heritage was duly registered with SisGen - Sistema Nacional de Gestão do Patrimônio Genético e dos Conhecimentos Tradicionais Associados, as required by Brazilian law. The authors have declared that no competing interests exist.|
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We used 96 male adults (Table 1, Figure 1a, Supplementary data S1), being 14 wild types (11 A. cursor, and 3 A. montensis) and 82 captive-born (56 A. cursor, 27 A. montensis, and 13 hybrids). The penises were extracted by scissors, fixed in a 10% formalin solution for 24 hours and stored in a solution of 70% ethanol. Before analysis, they were air-dried at room temperature, and then ventral and dorsal views were photographed using an extended focus imaging system GT-Vision (©Leica microsystems). We used digital pictures with a scale bar to determine the linear measurements of each specimen.
|Study Extent||Pernambuco, Bahia, Espírito Santo, Minas Gerais and São Paulo states, Brazil|
|Quality Control||For captive-born grouping, we analysed individuals aged at least 3-month-old. The species identification and their hybrids was based on karyotype features: diploid number (2n), the number of autosomal arms or fundamental number (FN) and the morphology of autosomes.|
Method step description:
- Firstly, six non-metric characters of the penile morphology were described to identify the character states. We focused on the following characters: spines morphology, dorsal cleft, dorsal cleft depth, ventral cleft, glans shape, and presence/absence of at least one dark spot on the ventral view of the glans (Table 2). Then, using the software TPSDig2 Version 2.31 (Rohlf 2009), we took seven glans penis’ linear measurements of the ventral and dorsal given by photographic views, as follow: Total length (TL), i.e. the distance from the beginning of the dorsal base of the spined area to the distalmost point on the glans; Spined Area Length (SAL), i.e. the distance from the beginning of the dorsal base of the spined area to the distalmost point on the spined area; Base Width (BW) i.e. diameter of the glans on the beginning of the base of the spined area; Meddle Width (MW) i.e. the greatest diameter of the glans penis, usually on the middle part of the spined area; Tip Width (TW) i.e. diameter of the distal end of the spined area; Dorsal Cleft Width (DCL) i.e. distance from the distalmost point to the proximal-most point of the dorsal cleft; Medial Bacular Mound Width (MBMW) i.e. diameter of the base of the medial bacular mound (Figure 1b). To guarantee the reliability of the measuring methods, the measurements were taken five times by the same researcher.