Sexual pattern ofNeocirrhites armatus (Cirrhitidae) with notes on other hawkish species

Synopsis We examined the gonads of eight species in five genera of hawkfishes. Histological preparations of ovaries and testes produced evidence for protogynous hermaphroditism inNeocirrhites armatus and suggested that hermaphroditism may also be expressed inCirrhitichthys oxycephalus, C. aprinus andC. falco, and possibly also by other species. Sexual patterns in hawkfishes are discussed in relation to environmental and ecological factors which influence mobility and length of spawning season.     

Evidence for protogynous hermaphroditism in some lethrinid fishes

An examination of the size/sex relationships and gonadial structure and histology of eight species of the commercially important family Lethrinidae from the North West Shelf of Australia and the Gulf of Carpentaria suggests that protogynous hermaphroditism is the typical mode of sexuality in these fishes. A linear relationship between size and sex ratio, in which females predominate at smaller sizes and males at larger sizes, was demonstrated in five species for which sufficient information was available. All five of these species showed a considerable overlap in the size distribution of the sexes but there was no evidence for the occurrence of primary males in the populations sampled. The tests of all species examined showed typical 'secondary male' morphology and the presence of atretic ovarian material ('brown bodies'). Individuals with intersex gonads were observed in five species. It is suggested that the effects of fishing on such protogynous fish stocks will depend on the precise mechanims, as yet unknown in lethrinids, that control the onset of sex change.     

The Evolution of Hermaphroditism from Dioecy in Crustaceans: Selfing Hermaphroditism Described in a Fourth Spinicaudatan Genus

The evolution of reproductive systems has intrigued evolutionary biologists for well over a century. Recent empirical and theoretical work has elucidated the evolution of dioecy (separate males and females) from hermaphroditism in many plant species. The reverse transition, evolving hermaphroditism from dioecy, has occurred many times in animals, and yet is poorly studied relative to its reverse analog in plants. Crustaceans in the sub-order Spinicaudata have evolved hermaphroditism from dioecy three separate times, in some cases forming all-hermaphroditic species and in others forming androdioecious (males + hermaphrodites) species. Herein we report evidence of hermaphroditism in a fourth spinicaudatan genus: the newly described Calalimnadia. We present sex ratio and anatomical evidence that Calalimnadia mahei comprises selfing hermaphrodites, with no males being found in over 10,000 offspring reared. We combine these reproductive results with those of other Spinicaudata to estimate the evolution of hermaphroditism in this crustacean sub-order. We use these genetic data combined with anatomical evidence to suggest that C. mahei represents a fourth, independent derivation of hermaphroditism from dioecy in these reproductively labile crustaceans.     

Hermaphroditism and gonochorism. a new hypothesis on the evolution of sexuality in crustacea

Most crustaceans are gonochoristic but hermaphroditism occurs in primitive classes as well as in different orders of higher Crustacea. Though studies have been carried out in plants and animals on the advantages of these two types of sexuality, it is not known how hermaphroditism can change into gonochorism and vice versa. The new hypothesis we report here is based on recent results on biased sex ratio in Crustacea. We suggest that ancestral sexuality was a simultaneous hermaphroditism as it exists still today in primitive groups. Gonochorism may have appeared following integration in the host genome of a parasitic xenogenous DNA inhibiting expression of ‘male genes’. Female sex would be anterior to male sex, and male heterogamety can be seen as a by-product of an intragenomic conflict in a species with an ancestral female heterogamety. Sequential hermaphroditism in higher Crustacea would be a secondary hermaphroditism resulting from other genetic conflicts between host genes and repressing heterochromosomic genes (parasitic DNA from xenogenous origin?)     

Characterization of the sexual pattern of Parastacus varicosus (Crustacea: Decapoda: Parastacidae)

Abstract. Freshwater crayfishes of the genus Parastacus are intersex, i.e., show characteristics of both sexes in the same individual; also, intersexuality has been documented in hermaphroditic species. The aim of this study was to analyze the gonads of Parastacus varicosus , characterizing its sexual pattern. The animals were collected at Cova do Touro, Gravataí, Rio Grande do Sul, Brazil. Three sexual forms were identified: intersex females, intersex males, and transitional specimens showing an ovotestes gonad that could only be identified by means of histological analysis. All specimens had two pairs of gonopores and gonoducts. The oviduct had a wider diameter in females, whereas in males the vasa deferentia were more developed. Gonads were composed of two parallel structures located in the cephalothorax. Female gonads were classified into three stages. The presence of transitional specimens may indicate that sex change occurs, with protandric hermaphroditism, as observed in other species of Parastacus . Because previous studies had demonstrated that P. varicosus is a gonochoristic species in a population from Uruguay, the present study addressed the possibility that the sexual pattern depends on differences in environmental factors among populations. To improve understanding of evolution of hermaphroditism in these crustaceans, their reproductive dynamics should be studied, including identification of the factors stimulating male and female functions.     

Protogynous hermaphroditism in the slinger, Chrysoblephus puniceus (Gilchrist & Thompson, 1908) (Teleosteir:Sparidae)

Hermaphroditism in the marine fishes is well documented, especially in the family Sparidae in which at least 35 species have been reported. Within this family sexuality ranges from gonochorism, through rudimentary, protogynous and protandrous hermaphroditism, to what is thought to be a single functional hermaphrodite.
A biological study of the economically valued Chrysoblephus puniceus revealed marked differences in the size of male and female fish, suggesting that this sparid undergoes sex reversal. Histology of gonads macroscopically classified as 'female', 'male' and 'hermaphrodite' were analysed. Degenerating pre-vitellogenic oocytes in the ovarian sections of hermaphroditic gonads confirm that C puniceus is a protogynous hermaphrodite.     

The gonadal anatomy and sexual pattern of the protandrous sex-reversing fish, Rhabdosargus sarba (Teleostei: Sparidae)

The gonadal anatomy and sexual pattern of Rhabdosargus sarba (Teleostei: Sparidae) was studied to provide some basic structural information for the subsequent investigations on the endocrinology of protandrous hermaphroditism in this fish. Evidence derived from relating sex to differences in body size, from gonadal histology and from biopsy, revealed the occurrence of natural sex reversal from male to female in this species. The gonad of R. sarba possessed topographically distinct male and female zones that were well separated by connective tissue. Based on gross-anatomical and histological observations, four types of gonad were distinguished and were designated as Types I-IV in the present study. Active spermatogenetic tissue was present in the Type I, II and IV gonads. Dormant oogonia and perinucleolar oocytes were found in the Type I (male) and II (intersex) gonads, respectively. In the Type III (female) gonad, a functional ovarian zone was observed and the testicular tissue was vestigial. The existence of ovarian tissue as an oogonial band in the Type IV (male) gonad, which was found more commonly in large specimens, suggested that these functional males might not undergo sex reversal in their life cycle. The interrelationship of the different types of gonad is discussed with reference to protandrous hermaphroditism.     

Sexual selection and simultaneous hermaphroditism among the Unionidae (Bivalvia: Mollusca)

Simultaneous hermaphroditism is an infrequent mode of reproduction among bivalves of the family Unionidae: only five of the 220 North American species are simultaneous hermaphrodites. However, hermaphroditic individuals of otherwise predominantly dioecious species have been encountered in 30 of I01 species examined. These hermaphroditic individuals as well as simultaneous hermaphrodites can exhibit considerable variability in the ratio of spermatogenic: oogenic tissue within the gonad, and the purposes of this paper are to determine the underlying causes of both this variability and the occurrence of occasional hermaphroditic individuals among dioecious species. Results indicate that the ratio of male: female gonodal tissue of a simultaneous hermaphrodite is bimodally distributed, and several hypotheses to account for this observation are presented. It is proposed that populations occurring in different habitats and under conditions of different individual density are subject to fundamentally different sexual selection pressures acting on ratios of allocation to male and female gametes. Occasional hermaphroditism among otherwise predominantly dioecious species was in this study associated with infection of the gonads by digenean trematodes. A model of sexual determination among unionids presented in this paper proposes that sex is determined by genetically controlled hormone levels: occasional hermaphrodites result from alterations in these hormone levels caused by developmental errors and trematodal infections which mimic the results of such errors. Predictions of this model are consistent with observed levels of variability in male: females gonadal tissue among occasional hermaphrodites.     

Hermaphroditism in fishes: an annotated list of species,phylogeny, and mating system

Fewer than 1% of vertebrate species are hermaphroditic, and essentially all of these are fishes. Four types of hermaphroditism are known in fishes: simultaneous (or synchronous) hermaphroditism (SH), protandry (male-to-female sex change; PA), protogyny (female-to-male sex change; PG), and bidirectional sex change (BS or reversed sex change in protogynous species). Here we present an annotated list of hermaphroditic fish species from a comprehensive review and careful re-examination of all primary literature. We confirmed functional hermaphroditism in more than 450 species in 41 families of 17 teleost orders. PG is the most abundant type (305 species of 20 families), and the others are much less abundant, BS in 66 species of seven families, SH in 55 species of 13 families, and PA in 54 species of 14 families. The recently proposed phylogenetic tree indicated that SH and PA have evolved several times in not-closely related lineages of Teleostei but that PG (and BS) has evolved only in four lineages of Percomorpha. Examination of the relation between hermaphroditism type and mating system in each species mostly supported the size-advantage model that predicts the evolution of sequential hermaphroditism. Finally, intraspecific variations in sexual pattern are discussed in relation to population density, which may cause variation in mating system.

     

Hermaphroditism in two populations of Chiton articulatus (Mollusca: Polyplacophora) from the eastern tropical coast of México

Through histological analyses, this study reveals an unusually high incidence of hermaphroditism in Chiton articulatus. Specimens were sampled every 30?days between September 2010 and September 2011 at two locations (Las Brisas and Jaramillo beaches, Acapulco) on the tropical eastern Pacific coast of Mexico. At both sites, hermaphroditism was found throughout the year, although in varying proportions. Higher percentages of hermaphroditism were found during the pre-spawning summer months (Las Brisas Beach 63%, Jaramillo Beach 68%). Two different kinds of hermaphroditic gonads were found, showing a preponderance of either male or female tissues but, commonly, female tissues occupied the greatest part of the gonad cross sections. Similar to other species of polyplacophorans, there was a predominance of males, although M:F sex ratios ranged from 0.7 to 4.5: 1 at Las Brisas Beach and 0.3–8: 1 at Jaramillo Beach.     

Female gonad of moles, genus Talpa (Insectivora, mammalia): ovary or ovotestis?

The female gonads of moles (genus Talpa) are composed of a cortex, functioning as an ovary, and a medulla, which is structurally similar to that of the testis. In the female reproductive apparatus there are masculine glandular annexes, such as a bilobate prostate, two Cowper glands, and a penis-like clitoris. All these features have recently led to the hypothesis of the presence of hermaphroditism due to sex-reversal in Talpa. The purpose of this study is to understand the functional significance of the structural organization of the female gonads in order to verify this hypothesis. Histological, histochemical and ultrastructural analyses have been carried out on several gonads of both sexes of two species: T. europaea and T. romana, including three fetuses. In both species, the cortical region of the female gonad shows a regular oogenetic activity. While the medulla is composed of interstitial cells that are partly organized in cord-like structures, no spermatogenetic activity has been ever observed inside of them. A histochemical analysis shows that in both sexes the interstitial cells secrete steroids, presumably estrogens as well as androgens. The presence of androgens in the female gonads would therefore explain the persistence of male glandular annexes in the female reproductive apparatus and both the sexual and behavioral monomorphism typical of the genus Talpa. Nonetheless, the female gonad of moles is a real ovary and a well-defined gonochorism exists. Therefore, there is no reason to assert the presence of hermaphroditism due to sex reversal.     

Monogamous mating system and sexuality in the gobiid fish, <Emphasis Type="Italic">Trimma marinae</Emphasis> (Actinopterygii: Gobiidae)

The mating system and sexuality of the gobiid fish Trimma marinae were investigated in aquaria and by gonadal histological examination. The male to female sex ratio in the study aggregation was female biased (14:27), and females were larger than males. T. marinae were monogamous because they established continuous pairs and spawned repeatedly with the same individuals. Observations of aggressive behavior suggested that the monogamous mating system resulted from female mate guarding. We also performed a rearing experiment to test whether sex change occurs in this species. None of the males or females reared separately in aquaria for 63 days changed sex. Additionally, gonadal histology revealed that mature fish had unisexual gonads (testis or ovary). These results strongly suggest that T. marinae is gonochoristic. However, immature fish had a bisexual gonadal structure, indicating juvenile hermaphroditism.     

Gonadal morphology of threadfin breams,Nemipterus bathybius andN. virgatus: Evidence of rudimentary hermaphroditism

Gonads of young and adultNemipterus bathybius andN. virgatus were examined histologically. In youngN. bathybius males, the testis is composed of a dorsal and a ventral zone separated by thin connective tissue. A duct runs through the center of the dorsal zone, and has an opening on the ventromedian surface of the body, separate from the male genital pore. Along with the start of spermatogenesis in the ventral zone, germ cells distributed in the dorsal zone also begin spermatogenesis and eventually develop into spermatozoa. Consequently, in mature testes the sperm sinuses are formed to enclose the dorsal duct, leaving a small number of germ cells, including oviform cells, retained in the lamellar projections of the duct. Testes ofNvirgatus also have essentially the same histological characteristics. No trace of testicular tissue is present in the ovaries, except in four cases of intersexual gonads found in both nemipterid species. It is concluded that the dorsal duct and its lamellar projections are remnants of the ovarian cavityoviduct system and ovigerous lamellae of the ovarian portion of the gonad, and that these two nemipterid species are rudimentary hermaphrodites in which males have bisexual gonads of the delimited type in their juvenile stages.     

Molecular analysis in true hermaphroditism: demonstration of low-level hidden mosaicism for Y-derived sequences in 46,XX cases

True hermaphroditism (TH) is an unusual form of sex reversal, characterized by the development of testicular and ovarian tissue in the same subject. Approximately 60% of the patients have a 46,XX karyotype, 33% are mosaics with a second cell line containing a Y chromosome, while the remaining 7% are 46,XY. Molecular analyses have demonstrated that SRY is present in only 10% of TH with a 46,XX karyotype; therefore, in the remaining 90%, mutations at unknown X-linked or autosomal sex determining loci have been proposed as factors responsible for testicular development. True hermaphroditism presents considerable genetic heterogeneity with several molecular anomalies leading to the dual gonadal development as SRY point mutations or SRY hidden gonadal mosaicism. In order to identify genetic defects associated with subjects with the disease, we performed molecular analyses of the SRY gene in DNA from blood leukocytes and gonadal tissue in 12 true hermaphrodites with different karyotypes. Our results using PCR and FISH analyses reveal the presence of hidden mosaicism for SRY or other Y sequences in some patients with XX true hermaphroditism and confirms that mosaicism for SRY limited to the gonads is an alternative mechanism for testicular development in 46,XX true hermaphrodites.     

Temperature regulates SOX9 expression in cultured gonads of Lepidochelys olivacea, a species with temperature sex determination

Although sex determination starts in the gonads, this may not be the case for species with temperature sex determination (TSD). Since temperature affects the whole embryo, extragonadal thermosensitive cells may produce factors that induce gonadal sex determination as a secondary event. To establish if gonads of a species with TSD respond directly to temperature, pairs of gonads were cultured, one at female-promoting temperature (FPT) and the contralateral at male-promoting temperature (MPT). Histological and immunohistochemical detection of SOX9 revealed that the response to temperature of isolated gonads was similar to that of the gonads of whole embryos. While gonads cultured at MPT maintained SOX9 expression, it was downregulated in gonads at FPT. Downregulation of SOX9 took longer in gonads cultured at stage 23 than in gonads cultured at stage 24, suggesting that a developmental clock was already established at the onset of culture. To find out if sex commitment occurs in vitro, gonads were switched from FPT to MPT at different days. Results showed that the ovarian pathway was established after 4 days of culture. The present demonstration that gonads have an autonomous temperature detector that regulates SOX9 expression provides a useful starting point from which the molecular pathways underlying TSD can be elucidated.     

Sexual strategy in the freshwater bivalve Galatea paradoxa (Donacidae) from the Volta River estuary,Ghana

The reproductive biology, sexual strategy and sex ratio of the freshwater donacid Galatea paradoxa in the Volta River estuary, Ghana, was studied from March 2008 to February 2010. Histological observations of the gonads showed that G. paradoxa is gonochoristic with dominance by females (80%) and a high incidence of hermaphrodites (9.4%) for individuals ranged between 20 and 82?mm in shell length. There was a single spawning event between July and October. Gametogenesis started in December, progressing steadily to a peak in June–July when spawning began, until November when individuals were spent. The dominance of females coupled with the high incidence of hermaphroditism may be a reflection of populations subjected to increasing fishing pressure and over-exploitation.     

Hermaphroditism and sexual function inCirrhitichthys aureus and the other Japanese hawkfishes (Cirrhitidae: Teleostei)

The present paper deals with gonadal formation, sex succession and sexual function in the Japanese hawkfishes,Cirrhitichthys aureus (Temminck et Schlegel),C. aprinus (Cuvier),C. falco Randall,Cirrhitops hubbardi (Schultz) andCyprinocirrhites polyactis (Bleeker). Detailed studies were made forC. aureus collected from Suruga Bay, central Japan. In this species the gonad of a young fish of 21.8 mm SL had begun to initially differentiate into an ovary forming an early ovarian cavity of the parovarian type. The gonadal structures of 63 further specimens ofC. aureus, ranging from 23.9 to 114.3 mm SL, could be separated into three categories: viz., ovaries (7), ambisexual gonads (54) and secondary testes (2). Reproduction ofC. aureus in Suruga Bay took place from June to November. Although ovaries which appeared throughout the year presented only in the immature stage and occurred only in small fish ranging from 25.1 to 46.6 mm SL, functional gonads occurred in 32 ambisexual fish ranging from 61.5 to 113.5 mm SL and in one secondary male of 101.5 mm SL, collected during the reproductive season. The smaller ambisexual fish, ranging from 61.5 to 92.0 mm SL, showed active oogenetic processes in the major ovarian zones with many ripened eggs ovulating into the ovarian cavity. These gynogenic gonads undoubtedly functioned as female; however, distinct meiosis proceeded partially in the minor testicular zones with a few spermatozoa occurring in the vas deferens. The larger ambisexual specimens, ranging from 71.5 to 113.5mm SL, had slender androgenic gonads, which showed active spermatogenesis in various testicular zones and which might function as males with reduced ovigerous lamellae. The secondary males had testes occupied by seminal lobules, but which retained the ovarian cavity within. According to aquarium rearing experiments, in a pair ofC. aureus twice crossed mutually after spawning, functional sex changes occurred in twice, opposite directions, in a single gonad, i.e., from female to male and from male to female. These gonadal aspects in captiveC. aureus seemed to show an intermediate phenomenon between consecutive and simultaneous hermaphroditism. This finding also suggested thatC. aureus had similar sex succession characteristics to those of the serranid,Serranus fasciatus, studied by Hasting and Petersen (1986) and the gobiid,Trimma okinawae, studied by Sunobe (1990). We also established that normal functional hermaphroditism occurred in the four other cirrhitid species, which showed almost identical gonadal characteristics toC. aureus.     

GENETIC EVIDENCE FOR MULTIPLE ORIGINS OF DIOECY IN THE HAWAIIAN SHRUB WIKSTROEMIA (THYMELAEACEAE)

Dioecy is unusually common in the Hawaiian Islands, yet little is known about the evolutionary biology of this breeding system. A native shrub, Wikstroemia, has an unusually diverse array of breeding systems: two forms of dioecy, cryptic and morphological dioecy, as well as hermaphroditism (perfect flowers). The existence of two forms of dioecy is significant for three reasons: 1) the presence of cryptic unisexuals that are functionally unisexual, but retain the appearance of hermaphroditism in both sexes, is strong evidence for the ancestral status of hermaphroditism; 2) the production of nonfunctional pollen, by female cryptic unisexuals, is a new instance of a phenomenon which has previously been reported for a few other species; 3) the two forms of dioecy are morphological markers which are useful in hybridization studies for tracing the genetic basis of their inheritance. Crosses were made between cryptically unisexual individuals (C), between morphologically unisexual individuals (M), and between the two types of unisexuality. The offspring of crosses between individuals with the same sex type usually resulted in offspring with that sex type, but most of the progeny of between-sex type crosses were, unexpectedly, perfect-flowered hermaphrodites. These results show that genetic control of sex determination is not homologous in all populations, suggesting that dioecy has evolved at least twice in Hawaiian Wikstroemia. The genetic data further suggest that males are the heterozygous sex.     

Environmental stressors affect sex ratios in sexually dimorphic plant sexual systems

• Revealing the environmental pressures determining the frequency of females amongst populations of sexually dimorphic plants is a key research question. Analyses of sex ratio variation have been mainly done in dioecious plants, which misses key plant sexual systems that might represent intermediate stages in the evolution of dioecy from hermaphroditism.
• We investigated female frequency across populations of sexually dimorphic plant species in relation to environmental stressors (temperature, precipitation), totaling 342 species, 2011 populations, representing 40 orders and three different sexual systems (dioecy, gynodioecy and subdioecy). We also included the biome where the population was located to test how female frequency may vary more broadly with climate conditions.
• After correcting for phylogeny, our results for gynodioecious systems showed a positive relationship between female frequency and increased environmental stress, with the main effects being temperature‐related. Subdioecious systems also showed strong positive relationships with temperature, and positive and negative relationships related to precipitation, while no significant effects on sex ratio in dioecious plants were detected.
• Combined, we show that female frequencies in an intermediate sexual system on the pathway from hermaphroditism to dioecy respond strongly to environmental stressors and have different selective agents driving female frequency.