Highlights d We sequenced 20 Native American Y chromosomes chosen for their genetic diversity d A Beringian Standstill of <4,600 years led to both Siberian and American Y-lineages d Y-lineage split times rule out occupation of the Americas before 19,500 years ago d Present-day male population structure in South America arose before 12,000 years ago

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 Abstract Godinho, H. P., Santos, J. E., Formagio, P. S. and Guimarães-Cruz, R. J. 2005. Gonadal morphology and reproductive traits of the Amazonian fish Arapaima gigas (Schinz, 1822). -Acta Zoologica (Stockholm) 86: 289-294An account of gonadal morphology and reproductive traits of the Amazonian arapaimatid, Arapaima gigas (Schinz 1822), is given. The only functional ovary (left) was foliaceous in shape having the ventral surface without an ovarian capsule. The absence of the ovarian capsule ventral portion, absence of oviduct and funnel-shaped coelomic cavity are features that imply that oocytes are freed in the coelomic cavity before being shed to the aquatic environment through a genital papilla. The only functional testis (left) was cord-like with a maximum diameter of 1-1.5 cm and was connected to the genital papilla through a spermatic duct. Size at sexual maturity was 145-154 cm and 115-124 cm, total length class, for females and males, respectively.

We studied the relationship between the morphology of the reproductive system and the reproductive strategies of six neotropical catfishes using macroscopic and microscopic analyses. The reproductive system of the examined Siluriformes showed diversified characteristics, but permitted their being grouped according to three reproductive strategies: pelagic spawning, demersal spawning, and internally fertilizing. The pelagic spawners Pseudoplatystoma corruscans and Conorhynchos conirostris have testes that are characterized by filiform lobes, absence of testicular secretion, full-grown oocytes of small diameter, thin zona radiata, and cuboidal follicular cells. Pimelodus maculatus is morphologically distinct from the other two pelagic spawners catfishes due to the presence of testicular secretion. The demersal spawners Lophiosilurus alexandri and Rhinelepis aspera possess homogeneous testicular secretion, large mature oocytes, and columnar follicular cells. The most specialized reproductive system was observed in the internally fertilizing Trachelyopterus galeatus, which possesses a seminal vesicle accessory to the testes, spermatozoa with elongated nuclei that form spermatozeugmata, and a secretory ovarian lamellar epithelium that is associated with sperm storage. The reproductive system observed in Neotropical catfishes showed a relationship associated with the type of fertilization and the reproductive strategies of the six species studied.

The gonad morphology and gametogenesis of Lophiosilurus alexandri Steindachner, 1877 from Santo Antônio river (Minas Gerais, Brazil) were studied through anatomical and histological techniques. Examination of the testis revealed that they were paired, fringed organs with two distinct regions: cranial spermatogenic and caudal spermatogenic and secretory. The cranial region represents ca. 60% of the mature/maturing testis, containing 41 to 73 fringes, while the caudal portion represents ca. 40% and contains 44 to 68 fringes. At the cranial portion the length of the fringes was 3.70 ± 1.70 mm and in the caudal portion was 0.20 ± 0.10 mm. The spermatogenesis was cystic, synchronic, and occurred throughout the whole extension of the seminiferous tubules. The ovaries were saculiforms, paired organs, which present ovigerous lamellae containing cells of the oogenic lineage. The oocytes were classified into four developmental stages according to their cytological characteristics and the characteristics of the cell layers that surround them.

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Lophiosilurus alexandri reproduces in captivity, has a high commercial value in Brazil and carries great potential for aquaculture. Research was carried out on L. alexandri larvae from days 1 to 30 post-hatch (DPH). Based on descriptions in the literature four developmental stages were observed using anatomic, histological and statistical techniques to provide useful data for the taxonomy, aquaculture and conservation of this species. In the yolk sac stage (1-2 DPH) the larvae presented myomeres (pre 17-23 and post anal 25-32) evident along the body, open mouth, the beginning of eye pigmentation and intestine with simple prismatic epithelium. The preflexion stage (3-4 DPH) was characterized by onset of body pigmentation and appearance of the pectoral fin bud. The oesophagus, stomach and intestine presented a folded mucosa. The flexion stage (5-7 DPH) was characterized by a flexion of the notochord, the chondrogenesis of the neural arches, formation of the dorsal and anal fins (11 rays) and appearance of the pelvic fin bud. In the postflexion stage (8-30 DPH) the formation of pelvic fin rays (6 rays) occurred along with the development of three different stomach regions. Except for the variables related to the yolk sac, all other studied variables presented significant differences between developmental stages.