Naturally occurring triploids in contact zones between diploid/tetraploid Odontophrynus cordobae and O. americanus (Anura, Odontophrynidae)

in Amphibia-Reptilia
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Polyploidization plays an important role in speciation and evolution in anurans. However, a few stable triploid populations and some isolated triploid individuals have been reported. Here, we report the discovery of naturally occurring triploids in contact zones between diploid Odontophrynus cordobae and tetraploid O. americanus from Central Argentina, and propose values of erythrocyte area for the distinction of ploidy levels. A total of 101 individuals from three contact zones were studied and ploidy of each specimen was identified by mean chromosome count and erythrocyte size. Twenty three adult triploid specimens (males: n=21; females: n=2) from two contact sites were identified (percentage of individuals per ploidy level: site S2, 2n=40.6%, 3n=12.5%, 4n=46.9%; site S3: 2n=44.7%, 3n=40.4%, 4n=14.9%). The limit values of erythrocyte nuclear area used to distinguish between different ploidy levels were 23.62 μm2 (probability to be assigned to a respective ploidy level = 94.78%) for separating diploids and triploids and 27.67 μm2 (98.62%) for triploids and tetraploids. The high number of adult triploids occurring in more than one contact site between O. cordobae and O. americanus indicates that is not an isolated event. However, further studies are necessary to provide a hypothesis on the origin and evaluate the possible maintenance of triploids in syntopy with O. cordobae and O. americanus.

Naturally occurring triploids in contact zones between diploid/tetraploid Odontophrynus cordobae and O. americanus (Anura, Odontophrynidae)

in Amphibia-Reptilia



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    Geographic location of the known localities for Odontophrynus cordobae (white circles) and O. americanus (black circles) from south-central Córdoba according to Martino and Sinsch (2002) and Grenat et al. (2009, 2013). O. cordobae: VGB, Villa General Belgrano; SR, Santa Rosa de Calamuchita; EM, Embalse; BE, Berrotarán; EL, Elena; CÑS, Cañada del Sauce; RDS, Río de los Sauces; RV, Rodeo Viejo; CW, Camino W; SF, A° San Francisco. O. americanus: SP, Sampacho; HB, Holmberg; ACH, Achiras; CV, Camino Cuatro Vientos; RC, Río Cuarto; ES, Espinillo; BA, Baigorria; AG, Alcira Gigena; G1, Camino Gigena 1; G2, Camino Gigena 2; A1, Camino Alpa 1; A2, Camino Alpa 2; AC, Alpa Corral; LG, Las Guindas. Syntopic sites between the two species reported in this study are S1, S2 and S3 (black and white circles).

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    Metaphase of (A) a diploid Odontophrynus cordobae from S2; (B) a triploid individual from S3; and (C) a tetraploid O. americanus from S2.

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    Karyotypes of triploid individuals from the sites S2 and S3, Córdoba, Argentina.

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    Distribution curves of nuclear areas (μm2) from diploid, triploid and tetraploid individuals. Mean and standard deviation are shown within each curve. Dotted lines represent the values limits to distinguish between each ploidy level.

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    Comparison of nuclear areas of karyotyped (A) and non-karyotyped individuals (B) of Odontophrynus cordobae, triploid individuals and O. americanus. The dotted line represents the limit nuclear area to separate ploidy levels. Upper and lower ends of boxes represent 75th and 25th percentiles. Whiskers represent the minimum and the maximum values. The line within each box shows the locations of the sample median and the plus sign indicates the location of the sample mean. Outliers are shown as empty squares.

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    Discriminant function analysis based on erythrocyte measurements differentiating diploid (square), triploid (circles) and tetraploid (triangles) karyotyped (fill) and non-karyotyped (empty) individuals.

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