Salmoneus carvachoi

Oliveira, Mário Vitor, Baeza, Juan Antonio, Guéron, Rodrigo, Costa-Souza, Ana Carla, Mariano, Rodolfo, Zara, Fernando José & Almeida, Alexandre O, 2023, Protandric simultaneous hermaphroditism in Salmoneus carvachoi Anker, 2007 (Decapoda: Alpheidae): a new sexual system in alpheid shrimps, Zoological Journal of the Linnean Society 201 (3), pp. 1-18 : 10

Salmoneus carvachoi

Sex determination based on the presence/absence of the ap& pendio masculina is not possible in some alpheid genera, in contrast to most caridean shrimps* For instance, the appendio masculina (AM) is absent in all individuals in the alpheid genera Automate De Man, 1888 and Synalpheus Spence Bate, 1888 species (Banner and Banner 1973, Felder 1982, Dardeau 1984, Carvacho 1989, Tóth and Bauer 2007)* On the other hand, in Salmoneus and Yagerocaris Kensley, 1988 , the AM is present in all individuals regardless of the presence or absence of eggs brooded in their pleon ( Christoffersen 1982, Carvacho 1989, Holthuis 1990, Fransen 1991, Anker and Marin 2006, Anker 2007, 2010, 2011a, b, Olivera et al * 2015, Vera-Caripe et al * 2015)*

Carvacho (1989) stated that if the presence of the AM in Salmoneus was an expression of protandry, then, a gradual regression of this structure should be expected asser sexual inversion* Otherwise, it could not be a character indicating the sex of an individual in Salmoneus * Here we confirm that the AM is not useful for sex determination (e*g*, male-phase or hermaphrodite) in S. carvachoi , as it is in most carideans (see: Bauer 2004)* Asser sex change, there is no reduction in size or changes in the shape of the AM in this species* Our results showed that despite the negative allometric growth of the AM in both sexual phases, hermaphrodite shrimps have a longer AM than male-phase individuals* Experimental studies in gonochoric caridean species, in which pleopodal rami, presumably possessing copulatory function (e*g*, AM), have been ablated in males, have demonstrated the importance of the AM in sperm transfer (Bauer 1976, Berg and Sandifer 1984)* In the aforementioned experiments, males that had their AM ablated did not transfer spermatophores as efficiently as ‘normal’ males with intact AM* However, there is still no experimental evidence that the maintenance of the AM in the hermaphrodite phase of S. carvachoi is related to more efficient sperm transfer during mating*

Ŋe determination of different sexual forms based on secondary sexual characters in the studied species was only possible through the visualization of the gonopores using SEM* We noted that the visualization of the gonopores using a stereomicroscope is impractical in S. carvachoi due to the small size of the species, which prevents reliable sex identification from simple protocols commonly used in other carideans ( Berg and Sandifer 1984, Bauer 2004)* Male-phase individuals possess only male gonopores, whereas simultaneous hermaphrodites exhibit both male and female gonopores* Such a paưern has also been observed in other PSH species belonging to the families Lysmatidae Dana, 1852 and Barbouriidae Christoffersen, 1987 ( Bauer and Holt 1998, Bauer 2006, Baeza 2009, Braga et al * 2009, Onaga et al * 2012)* It is important to mention that we observed spermatophore residues containing spermatozoa in the male gonopore of a hermaphrodite that was brooding eggs* Ŋis observation supports the hypothesis that the male reproductive system in simultaneous hermaphrodites of S. carvachoi is functional*

Although we provide considerable evidence that supports PSH in S. carvachoi , experimental studies are necessary to test that the simultaneous hermaphrodites are functional, i*e*, capable

with spermatozoa immersed in the secretion type I surrounded by the secretion type II (arrow)* G, detail of the spermatozoon with tack morphology and a long spike* Ŋe secretion type I shows small granules, thin fibrils and some larger droplets (arrow)* H, thick musculature of the ampoule with many muscular fibres* Ŋe primordial spermatophore shows small amount of seminal fluid of the secretion type I and is surrounded by a thin layer of secretion type II (arrow)* I, male phase individual showing ovaries and testes forming the ovotestes, surrounded by blood capillaries (arrow)* Ŋe ovaries are filled with oogonia forming the germinal centre at the inner periphery of the ovarian lobe close the testes* Ŋe primary oocytes occupy the rest of the lobule while the spermatogenesis is still producing spermatozoa (arrowhead)* J, detail of the oogonia and primary oocytes arrested in the previtellogenic stage surrounded by follicle cells (black arrowhead)* Notice primary spermatocytes and spermatozoa (white arrowhead) in the testes* K, primordial ovaries found in male phase individuals* Ŋe ovarian wall cells are arranged in different strata around the ovary lumen forming a mandibulate type ovary* Detail of the ovarian wall cells showing long microvilli (arrowhead)* Ŋese cells are laying on the connective tissue shared with the testes* I–L, haematoxylin and eosin stain* M, ovarian wall cells with nucleus with mitotic prophase chromosome (arrow heads)* Toluidine blue stain* A *