Penile shape discriminates the two cryptic species of Akodon (Mammalia, Rodentia, Cricetidae) from eastern Brazil

Study Extent

Pernambuco, Bahia, Espírito Santo, Minas Gerais and São Paulo states, Brazil

Sampling

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.

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 steps

1. 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.

Wild caught and captive born specimens of Akodon cursor, Akodon montensis and your Hybrids