External Sexual Dimorphism Research Articles

Molecular phylogeny and possible scenario of ponyfish (Perciformes:Leiognathidae) evolution

The family Leiognathidae, commonly known as ponyfish or slip mouth, comprises three genera, each being characterized mainly by mouth morphology. To date, however, neither the phylogenetic relationships within the family nor monophyly of the genera has been tested. The phylogenetic relationships among 14 species of Leiognathidae, inferred from two protein coding mitochondrial genes ( ND4 and 5), indicated monophyly of the studied species form genera Gazza and Secutor, and paraphyly of the genus Leiognathus, with L. equulus occupying a basal branch of the family. The relationships allowed phylogenetic analyses of mouthpart structures and light organ systems. The results suggested that the morphology of the upwardly and forwardly protractile mouth types (latter with canine-like teeth) are phylogenetically informative, and the downwardly protractile mouth type being ancestral in the family. The results also suggested that internal sexual dimorphism of the light organ system was present in the common ancestor of a sister clade to L. equulus, whereas external sexual dimorphism seems to have evolved subsequently in two monophyletic subgroups.

Reproductive biology, sexual dimorphism, and population structure of the deep sea hydrothermal vent scale-worm, Branchipolynoe seepensis (Polychaeta: Polynoidae)

The polychaete family Polynoidae (scale-worms) is well-represented at deep sea hydrothermal vents. Most species are free-living in a wide range of habitats: from high-temperature hydrothermal `chimney' walls to diffuse venting areas. Conversely, species of the genus Branchipolynoe live inside the mantle cavity of vent and seep mytilids. Specimens, morphologically close to Branchipolynoe seepensis, have been reported from all the known vent areas on the Mid-Atlantic Ridge (MAR), with varying infestation rates (0–6 individuals per host). Reproductive tract, gametogenesis and population structures were examined for specimens from the Lucky Strike vent field (MAR) in order to test whether this species displays dwarf males, protandric hermaphroditism or differential mortality between males and females. Observations of histological sections reveal the presence of fully developed ovaries in females which originate ventrally in segments 7–9 and of an unusual genital tract in which both sperm and mature oocytes are stored. Oogenesis is intraovarian and quasi-continuous. The vitellogenic oocytes are only free in the coelom at their terminal growing stage and are then transferred into an ovisac through spermathecae. The species displays an external sexual dimorphism in the number of genital papillae and the shape of the pygidial appendages. Sex ratios showed significant deviations from a 1:1 expected ratio, in favour of females. The modal decompositions of size–frequency histograms show the occurrence of three modes in females and only two modes in males, indicating discrete breeding periods. The two first modes were not significantly different between males and females. These results indicate that B. seepensis forms heterosexual pairs and uses internal fertilization to reproduce during discrete spawning periods. Differential mortality between males and females is likely to shape size-histograms as observed by preventing males from reaching the female proportions. Such an observation could be a result of either cannibalism on larger males, small sizes facilitating the male escape, or natural predation when males move from one bivalve to another to breed.

Ovarian development and cycles in cultured Siberian sturgeon, Acipenser baeri

Sturgeon lack external sexual dimorphism and have longer-than-annual ovarian cycles. Using gonadal biopsy of marked fish, we identified sex and monitored ovarian development in one cohort of cultured Siberian sturgeon over the age interval 8.5–12.5 year. Sex ratio in the population did not differ from 1:1 (268 females and 286 males). Each November, the females were separated into two groups: one with ovarian follicle diameter ≥ 2.8 mm (Group 2, spawnable) and another with smaller follicles in previtellogenic or vitellogenic growth (Group 1). During the 5 year period of observations, 11.2 % of the initial 268 females were lost. The oocytes of Group 2 exhibited migratory germinal vesicle but its position in animal hemisphere was not peripheral in November. The annual changes in proportions of Group 2 females, from 34.6 to 63.3 %, reflected ovarian cycles of different duration. Majority of 196 females, matured two or more times during a period of study, exhibited biennial ovarian cycle or recurring cycles of 1 and 2 years in the same individual. Annual and triennial cycles were also observed. Some abnormalities in oocyte pigmentation are described.

Sex identification of parrots, toucans, and curassows by PCR: Perspectives for wild and captive population studies

Methods for the identification of the sex of bird species without external sexual dimorphism are specially important in field studies and for captive breeding of endangered taxa. We confirmed the accuracy of a polymerase chain reaction (PCR)-based method to identify the sex in three disparate avian orders that included 31 species of parrot, two species of toucan, and eight species of curassow, for which many individuals were previously sexed. In each case, two DNA fragments were amplified in females and one in males with the use of a single set of primers. This method was also tested on unsexed birds of 13 other species of parrot and five species of toucan. The same kind of polymorphism was detected in each. The PCR products of parrots and toucans could be separated in simple agarose gels, while the curassows' products could only be distinguished in acrylamide gels. An advantage of this DNA test is that samples of blood or feathers can be easily collected and stored at room temperature, which is of particular importance for studies of wild birds. Zoo Biol 17:415–423, 1998. © 1998 Wiley-Liss, Inc.

Sex identification of parrots, toucans, and curassows by PCR: Perspectives for wild and captive population studies

Methods for the identification of the sex of bird species without external sexual dimorphism are specially important in field studies and for captive breeding of endangered taxa. We confirmed the accuracy of a polymerase chain reaction (PCR)-based method to identify the sex in three disparate avian orders that included 31 species of parrot, two species of toucan, and eight species of curassow, for which many individuals were previously sexed. In each case, two DNA fragments were amplified in females and one in males with the use of a single set of primers. This method was also tested on unsexed birds of 13 other species of parrot and five species of toucan. The same kind of polymorphism was detected in each. The PCR products of parrots and toucans could be separated in simple agarose gels, while the curassows' products could only be distinguished in acrylamide gels. An advantage of this DNA test is that samples of blood or feathers can be easily collected and stored at room temperature, which is of particular importance for studies of wild birds. Zoo Biol 17:415–423, 1998. © 1998 Wiley-Liss, Inc.

Juvenile Morphology and Appearance of Sexual Appendages in Two Porcellanid Crabs, Petrolisthes Rufescens (Heller, 1861) and Pisidia Gordoni (Johnson, 1970) (Decapoda, Anomura, Porcellanidae)

Abstract The porcellanid crabs in their larval phase show typical anomuran features but develop a crab-like form from megalopa through the juvenile instars. However, the adult species characters are not yet noticeable in the juvenile phase thus leading to confusion in identity both at specific or even at generic level. With attainment of the crab-like form, the reproductive appendages, like male pleopods, show a brachyuran pattern. In absence of external sexual dimorphism, sex determination is difficult in this group. Very little information is available as to how and when the sexual appendages start developing in Porccllanidae. With the purpose of tracing the development of the adult taxonomic characters and that of the reproductive appendages (and sex differentiation), the present paper describes the juvenile laboratory development of two porcellanid crabs, viz. Petrolisthes rufescens (Heller) up to instar III and Pisidia gordoni (Johnson) up to instar IV. Taxonomic features: In both the species the definitive adult features like those of the carapace front and its armature, the chelipeds and other pereiopods, the sternite of the third maxillipeds, etc., develop in the third instar. Sexual appendages: (a) In Petrolisthes rufescens the primary pleopods get totally reduced at least up to instar III and, therefore, the sexual appendages appear to be developing as a secondary series of pleopods, particularly in the female. (b) In Pisidia gordoni, at least in the male, differentiation starts from instar II onwards with the first pleopod modifying into a male appendage, while the remaining pleopods gradually become reduced.

Research Note: Effect of In Ovo 17-β-Estradiol or Tamoxifen Administration on Sexual Differentiation of the External Genitalia

The effect of in ovo administration of tamoxifen or 17β-estradiol on external sexual dimorphism in chickens was investigated. In two trials, fertile eggs were injected with either tamoxifen (200 μg per egg) or vehicle (100 μL corn oil) on Day 1 of incubation, or with 17β-estradiol (20 μg per egg) or vehicle on Day 11 of incubation. Sexes were determined by visual inspection of the external genitalia and by gonadal identification at Day 1 posthatch. Tamoxifen injection resulted in a significantly greater number of phenotypic male identifications, with male:female ratios of 76:24 (Trial 1) and 62:38 (Trial 2) based on external genitalia phenotype. Gonadal sexing corrected these ratios to 46:54 and 44:56, resulting in genital sexing errors of 27% (Trial 1) and 18% (Trial 2). These errors were significantly higher than genital sexing errors of the chicks treated with vehicle (2 and .6% for Trials 1 and 2, respectively). In ovo administration of 17β-estradiol resulted in an increased number of female identifications based on genital sex determination, with male:female ratios of 37:63 (Trial 1) and 46:54 (Trial 2). Gonadal sexing corrected these ratios to 54:46 and 51:49, resulting in genital sexing errors of 10 and 6% for Trials 1 and 2, respectively. These errors were significantly higher than genital sexing errors of vehicle-treated chicks (4 and .9% for Trials 1 and 2, respectively). The results of the present study indicate that early embryonic administration of estrogen or an estrogen antagonist alters chicken external sexual dimorphism near the time of hatch.

Functional morphology of the gonads of the articulate brachiopodTerebratulina retusa

The reproductive anatomy, and ultrastructural features of the gonads of the articulate brachiopodTerebratulina retusa (Linnaeus), are documented based on collections made between October 1985 and October 1986 from the Firth of Lorn, west coast of Scotland. This species is dioecious, and maturity is achieved in both sexes at shell lengths greater than ~5.5 mm. There is no obvious external sexual dimorphism except for slight differences in the coloration of the gonads; testes are white/cream, ovaries are yellow/orange. The gonads occur as four palmate lobes, a pair in each valve. Gonads are formed within a mantle sinus (vascula genitalia), which is an anterior extension of the coelom, that opens posteriorly into the visceral cavity and to the exterior via a pair of metanephridia. The latter serve as gonoducts during spawning. Gametes are borne on genital lamellae formed from a reticulate lattice of connective tissue. The lamellae are an extension of the ileoparietal band and are fused along one margin to the inner mantle membrane. Developing oocytes are closely affixed to the genital lamellae and originate from a pool of proliferating germ cells at its base. Vitellogenic oocytes that are at an advanced stage are released from the genital lamellae, but are retained within thevascula genitalia. Liberated oocytes continue to accumulate yolk and eventually occlude thevascula genitalia, before being spawned. Coelomocytes were identified within the gonads. In spent females these cells appear to be phagocytic and involved in the resorption of necrotic material, while in the male they may serve as nutritive cells.

Breeding the Abyssinian ground hornbill at San Diego Wild Animal Park

SummaryThe observations recorded during the three nestings at the San Diego Wild Animal Park make it possible to construct a growing picture of the nesting habits and requirements of the Abyssinian ground hornbill. It is of some importance to mention that at no time did we offer or construct any artificial potential nest sites. All sites utilized were chosen by the birds alone.The hornbills seemingly prefer to construct their nests in a bank of hardpacked yet workable soil. Sandy, rocky or other intermediate sites, including several available logs, were investigated but rejected. The man‐made culvert chosen in the preliminary nesting attempt was also located in the same hard‐packed material as the later two successful nests. The nest itself was carved out using the beak to break the soil loose, and the feet to scratch and push the loosened material from the growing hole. Both finished nests had approximately the same dimensions and were constructed in such a manner that direct sunlight never penetrated beyond the entrance. The floors were concave and covered with a litter composed of dead leaves, grasses and small twigs. Excavation of both sites took approximately two weeks.Prior to the selection of the nest site, the adult birds exhibited so‐called ‘searching behaviour’, which subsequently led to their thorough examination of suitable locations within an established ‘home’ or preferred range where they spent most of their time. Simultaneous with the appearance of searching was the ♂ s frequent presentation of food to the ♀. Once a suitable site was found, searching was replaced by digging, which in turn, with excavation completed, was supplanted by collection and arrangement of litter within the nest. The ♂ did most of the collecting and carrying and the ♀ arranged it until the floor was covered to a depth of 7–9 era.Although mating was observed only once, it is assumed from the birds' general behaviour that it occurred frequently before the ♀ laid one to two chalky white (c. 8 × 5 cm) eggs. Unlike other hornbill species, the ♀ ground hornbill was not walled into the nest nor was there any evidence that she moulted. After a 37–40 day incubation period, blind, naked chicks with purple‐grey skin were hatched, the second egg in all observed instances taking slightly longer, 39–40 days, to hatch.The chicks grew rapidly and left the nest after about three months. At the time of their emergence, they were fully capable of flight, but beak, general body size and plumage had still to develop further. External sexual dimorphism was also first apparent at this time, although it was not until the second chick emerged from the nest that we could compare the two. The latter had a definite reddish cast to its gular sac, the distinguishing feature of the ♂abyssinicus, while the sac of the first chick was grey. The second chick was also considerably larger than the first, another indication that they were of opposite sex.While the ♀ was incubating, she received all her food from the constantly foraging ♂ and continued to do so until 10–12 days after hatching. Then she left the nest for brief, but progressively lengthening periods and began to forage for herself, although still dependent on the ♂ for part of her food. The ♂ was also sole provider to the chicks, either giving food to the ♀ who in turn fed the chicks, or, once the ♀ had left the nest, feeding them directly.