Investigation of Sexes and Fertility Potential of Female Russian Sturgeon (Acipenser gueldenstaedtii) and Male American Paddlefish (Polyodon spathula) Hybrids

Abstract

In the present study, 10 allotriploid (3nALT) and 10 allopentaploid (5nALP) six-month-old hybrid fish and two 3nALT and four 5nALP 40-month-old hybrid fish, which resulted by crossing female Russian sturgeon Acipenser gueldenstaedtii (Brandt and Ratzeberg, 1833) and male American paddlefish Polyodon spathula (Walbaum, 1792), were investigated. It was revealed that six-month-old 3nALT and 5nALP hybrids initially had "undifferentiated" gonads, while in the 40-month-old hybrids, only testes were observed in one case of 3nALT and one case of 5nALP hybrids. The testis of 3nALT hybrids was partially developed with spermatogonia, while the testis of one 5nALP hybrid was in the second developmental stage with low spermatogonia density. We could not determine gonad differentiation in any of the cases when the hybrid individuals had the W sex chromosome. We concluded that the gonad differentiation of these interfamilial hybrids follows a similar pattern to interspecific hybrids of different ploidy parent species of the family Acipenseridae, which is consistent with the classical Haldane's rule. However, it cannot be excluded that the testis of this/these hybrid(s) may produce fertile sperm after sexual maturity, depending on additional genetic, hormonal and environmental factors, and further research is required for its evaluation.

Keywords: gonad; interfamilial hybrids; ploidy level; spermatogonia; testis.

Figure 1

Sex determination by SSM4 female-specific DNA sequence of purebred parent species and hybrid individuals on agarose gel. Symbols: ♀ female; ♂ male.

Figure 2

Microscopic view of an undifferentiated gonad (A/1) and macroscopic view of whole-body size (A/2) of six-month-old purebred Russian sturgeon. Microscopic view of undifferentiated gonad (B/1,C/1) and macroscopic view of whole-body size (B/2,C/2) of six-month-old 5nALP hybrids of male American paddlefish and female Russian sturgeon. Microscopic view of undifferentiated gonad (D/1,E/1) and macroscopic view of whole-body size (D/2,E/2) of six-month-old 3nALT hybrids of male American paddlefish and female Russian sturgeon. Black arrows: cells in the epithelium that have become columnar cells; yellow arrows: primordial germ cells (PGC) on the periphery of the gonad. 5nALP hybrid: male American paddlefish (Polyodon spathula) and female Russian sturgeon (Acipenser gueldenstaedtii) pentaploid hybrid; 3nALT hybrid: male American paddlefish (Polyodon spathula) and female Russian sturgeon (Acipenser gueldenstaedtii) triploid hybrid.

Figure 3

Microscopic view of pre-meiotic seminiferous tubules with normal spermatogonia density of 40-month-old purebred Russian sturgeon (A/1). Macroscopic view of 40-month-old purebred Russian sturgeon gonad (A/2) and whole-body size of purebred Russian sturgeon (A/3). Microscopic view of pre-meiotic seminiferous tubules with low spermatogonia density of 40-month-old 5nALP hybrid of male American paddlefish and female Russian sturgeon (B/1). Macroscopic view of gonad (B/2) and whole-body size (B/3) of 40-month-old 5nALP hybrid of male American paddlefish and female Russian sturgeon. Microscopic view of the partially developed gonad (C/1) of 40-month-old 3nALT hybrid of male American paddlefish and female Russian sturgeon. Macroscopic view of gonad (C/2) and whole-body size (C/3) of 40-month-old 3nALT hybrid of male American paddlefish and female Russian sturgeon. Black arrows: spermatogonia; yellow arrows: Sertoli cell; red arrows: gonad; red ellipse: exhibiting spaces without germ cells. 5nALP hybrid: male American paddlefish (Polyodon spathula) and female Russian sturgeon (Acipenser gueldenstaedtii) pentaploid hybrid; 3nALT hybrid: male American paddlefish (Polyodon spathula) and female Russian sturgeon (Acipenser gueldenstaedtii) triploid hybrid.