Reproductive biology and ecology of Pacific hagfish (Eptatretus stoutii) and black hagfish (Eptatretus deani)

The reproductive biology of Pacific hagfish Eptatretus stoutii (Lockington, 1878) and black hagfish Eptatretus deani (Evermann & Goldsborough, 1907) was assessed using current and historical data. Our results found that the reproductive characteristics of both hagfish species reflect those of K-selected species, which tend to live long and exhibit slow growth rates, low fecundity (approximately 20 eggs per female) and late maturity. Additionally, females of both species commence maturation prior to males. This study provides a population profile for both species of hagfish, but further assessments are needed to effectively manage a sustainable hagfish fishery.     

Morphological analysis of the hagfish heart. I. The ventricle,the arterial connection and the ventral aorta

We have studied the heart in three species of hagfish: Myxine glutinosa, Eptatretus stoutii, and Eptatretus cirrhatus and report about the morphology of the ventricle, the arterial connection and the ventral aorta. On the whole, the hagfish heart lacks outflow tract components, the ventricle and atrium adopt a dorso‐caudal rather than a ventro‐dorsal relationship, and the sinus venosus opens into the left side of the atrium. This may indicate a “defective” cardiac looping during embryogenesis. The ventral aorta is elongated in M. glutinosa and E. stoutii but sac‐like in E. cirrhatus. The ventricles are entirely trabeculated. The myocytes show a low myofibrillar content and junctional complexes formed by fascia adherens and desmosomes. Gap junctions could not be demonstrated. Myocardial cells in M. glutinosa contain numerous lipid droplets. These droplets are less numerous in E. stoutii and practically absent in E. cirrhatus, suggesting different metabolic requirements. Other cell types present in the ventricle are chromaffin cells and granular leukocytes that contain rod‐shaped granules. The ventricle‐aorta connection is guarded by a bicuspid valve with left and right, pocket‐like leaflets. The leaflets extend from the cranial end of the ventricle into the aorta but the junction is asymmetrical. This junction contains a ganglion‐like structure in E. cirrhatus. The ventral aorta shows endothelial, media, and adventitial layers. The media contains smooth muscle cells surrounded by dense bands formed by tightly‐packed extracellular filaments. In addition, a short number of elastic fibers are observed in M. glutinosa and E. stoutii. Cellular and extracellular elements are more loosely organized in the aorta of E. cirrhatus. The collagenous adventitia contains ganglion‐like cells in the three species. In the absence of nerves, chromaffin and ganglion‐like cells may control the activity of the myocardium and that of the aortic smooth muscle cells, respectively. J. Morphol. 277:326–340, 2016. © 2015 Wiley Periodicals, Inc.     

Seasonal concentrations of reproductive steroids in the gonads of the Atlantic hagfish, Myxine glutinosa

Changes in gonadal morphology, gonadal estradiol, and progesterone were examined in Atlantic hagfish, Myxine glutinosa, during a period of 17 months, beginning in April, 2001. Atlantic hagfish were captured from the ocean on a monthly basis. A total of 60 hagfish were divided into three different size classes of twenty hagfish each (small 20-35 cm, medium 35-45 cm, large 45-55+cm) and transported to the University of New Hampshire for sampling. Overall, in the medium and large size hagfish, estradiol and progesterone had significantly elevated peaks in January, 2001. There were significant increases in estradiol concentrations in January, with relatively low fluctuations in levels for the rest of the sampling period. Progesterone concentrations increased significantly in January, 2002, in medium and large hagfish, and remained elevated until June and April, 2002, for the two size classes respectively. The majority of hagfish sampled were females or hermaphrodites; few true males were identified in any of the samples. The number of females with large eggs increased following the estradiol peak in January and hermaphrodites with mature sperm were identified in the July, 2002, sample. These data represent the first evidence for a seasonal reproductive cycle in M. glutinosa and only the second seasonal reproductive cycle identified in any hagfish species.     

Reproduction in context: Field testing a laboratory model of socially controlled sex change in Lythrypnus dalli (Gilbert)

Social interactions can have profound effects on reproduction and the proximate mechanisms involved are just beginning to be understood. Lythrypnus dalli, the bluebanded goby, is an ideal organism for analyzing the dynamics of socially controlled sex change both in the laboratory and field. As with most research species, the majority of its behavioural and physiologic study has been performed in the laboratory. The goal of our study was to induce sex change of L. dalli in a more natural environment and compare field dynamics with our laboratory-based model. Groups of L. dalli, composed of one large male and three females of varying sizes, were introduced into artificial habitats in the field. After male removal, the dominant, largest female underwent protogynous sex change in the majority of the groups. Within 15 days, 9 of 15 of the dominant females (focal fish) successfully fertilized eggs as males, compared to 13 of 17 in the laboratory. Focal fish displayed the distinctive temporal sequence of behaviour changes consisting of a dominance, quiescent, and courtship phase. In addition, focal fish had gonads, genital papillae, and accessory gonadal structures with morphology in between that of females and males. Those fish that fertilized eggs had this transitional morphology, but were functionally male. Steroids of focal fish were assayed by water sample, and morning samples of free 11-ketotestosterone (11-KT) positively correlated with the percent of male tissue in the gonad, with the size of the accessory gonadal structure but not the genitalia (genital papilla), and with aggressive displacement behaviour on the last day before the fish were sacrificed. These morphological, physiological, and behavioural patterns parallel those seen in the laboratory. Lower rates of behaviour and the dramatic effects of ambient temperature in the field provide insights as to how the environmental context modifies the behaviour and, subsequently, the reproductive function of individuals within a social group.     

The effect of heated effluent on egg production in the estuarine prawn Upogebia Africana (Ortmann)

Egg production of a population of Upogebia africana (Ortmann) in a pond containing water heated by a thermal power station at Knysna, South Africa was compared with that of the population in the adjacent estuary and in two other estuaries. The breeding cycle, proportions of ovigerous females, incubation time for eggs at different temperatures, number of eggs produced, sex ratios, and size-frequency of males and females were all investigated. The number of eggs produced/100 prawns was found to be nearly twice as high in the population exposed to heated effluent as compared with the population in the adjacent estuary. The increase was due to a combination of a change in sex ratio resulting in more females in the population and a greater proportion of larger females in the pond. Since the number of eggs produced/female is positively related to the size of the prawn, large females in warmer water produced more eggs than smaller females in the adjacent estuary. Exposure to heated effluent did not alter the initiation or duration of the breeding season, nor cause precocious maturity; nor did it alter the number of eggs carried per female at various sizes.     

Morphological analysis of the hagfish heart. II. The venous pole and the pericardium

The morphological characteristics of the venous pole and pericardium of the heart were examined in three hagfish species, Myxine glutinosa, Eptatretus stoutii, and Eptatretus cirrhatus. In these species, the atrioventricular (AV) canal is long, funnel‐shaped and contains small amounts of myocardium. The AV valve is formed by two pocket‐like leaflets that lack a papillary system. The atrial wall is formed by interconnected muscle trabeculae and a well‐defined collagenous system. The sinus venosus (SV) shows a collagenous wall and is connected to the left side of the atrium. An abrupt collagen‐muscle boundary marks the SV‐atrium transition. It is hypothesized that the SV is not homologous to that of other vertebrates which could have important implications for understanding heart evolution. In M. glutinosa and E. stoutii, the pericardium is a closed bag that hangs from the tissues dorsal to the heart and encloses both the heart and the ventral aorta. In contrast, the pericardium is continuous with the loose periaortic tissue in E. cirrhatus. In all three species, the pericardium ends at the level of the SV excluding most of the atrium from the pericardial cavity. In M. glutinosa and E. stoutii, connective bridges extend between the base of the aorta and the ventricular wall. In E. cirrhatus, the connections between the periaortic tissue and the ventricle may carry blood vessels that reach the ventricular base. A further difference specific to E. cirrhatus is that the adipose tissue associated with the pericardium contains thyroid follicles. J. Morphol. 277:853–865, 2016. © 2016 Wiley Periodicals, Inc.     

Sex‐specific differences in gonopore and gonadal growth trajectories in the brooding sea urchin,Abatus cavernosus (Spatangoida)

The heart urchin Abatus cavernosus shows sexual dimorphism characterized by the development of external brood pouches and the enlargement of gonopores in brooding females. Relationships between body size, gonopore size, and gonadal maturation in each sex were examined for inflection points using piecewise regression models (PRM). Opening of the gonopore occurred at 15.5 mm test length. Inflection points in the gonadal growth and gonopore diameter trajectories were clustered at smaller sizes in males (23 and 24.2 mm, respectively) than in females (25.1 and 25.9 mm), indicating sex‐specific differences in sexual maturation. Gonopore growth showed positive allometry at pre‐adult stages of development in both sexes, but isometry and negative allometry in adult females and males, respectively. Gonadal growth was initiated at smaller sizes and proceeded at a higher rate with increasing body size in males than in females. Identification of inflection points in gonopore and gonadal growth trajectories, using objective PRM, allows the determination of life stages and sexual maturation for individuals, thus providing a complementary tool for population studies.     

Male-male interactions and their influence on the mating behavior and success in the fountain darter, <Emphasis Type="Italic">Etheostoma fonticola</Emphasis>

Behavioral interactions between individuals of the same sex can affect the outcome of intersexual selection. For this reason, intrasexual selection is oftentimes examined independently from intersexual selection in studies aimed at understanding mating behaviors. However, a more complete understanding of sexual selection effects within a population can only come from exploring both intrasexual and intersexual selection and the potential interactions between the levels of selection. Association preferences in male and female Etheostoma fonticola do not reveal a size preference for same sex or opposite-sex individuals. However, male-male interactions may influence female choice in E. fonticola. We examined whether male E. fonticola that differ in body size exhibit differences in agonistic behaviors and mating success. Larger males do exhibit higher rates of aggressive behaviors and smaller males, in turn, exhibit more defensive behaviors. However, differences between larger and smaller males in male-male interactions did not translate into differences in spawning success. These results suggest that male size influences dominance relationships in E. fonticola but not mating success. There were also no differences between large and small males in mating attempts, which could be an outcome of the year-round breeding season found in this species, females laying eggs singly, or males fertilizing eggs individually.     

Sex differences and hormone influences on tyrosine hydroxylase immunoreactive cells in the leopard frog

We examined sex differences in tyrosine hydroxylase immunoreactive (TH-ir) cell populations in the preoptic area (POA), suprachiasmatic nucleus (SCN), posterior tuberculum (TP), and caudal hypothalamus (Hy) in the leopard frog (Rana pipiens), in addition to the effects of natural variation in sex steroid hormones on these same populations in both sexes. All four of these populations have been shown to be dopaminergic. Gonadal sex, androgens, and estrogen all influenced TH-ir cell numbers, but in a complicated pattern of interactions. After factoring out the effects of sex steroids by multiple regression, TH-ir cell numbers in all four areas differed between the sexes, with males having a greater number of TH-ir cells. The influence of androgens and estrogen differed by region and sex of the animals. Androgens were the main influence on TH-ir cell numbers in the POA and SCN. Plasma androgen concentrations were positively correlated with TH-ir cell numbers in both areas in males. In females, androgen concentration was negatively correlated with TH-ir cell numbers in the POA; there was no significant relationship in the SCN in females. In the more caudal populations, estrogen (E2) levels were positively correlated with TH-ir cell numbers in the TP of both males and females. In the caudal hypothalamus, E2 levels were positively correlated with TH-ir cell numbers in females, but there was no significant correlation in males. The results indicate that gonadal sex imposes a baseline sex difference in the four TH-ir (dopamine) populations, resulting in a higher number of such cells in males. Individual and sex-linked differences in gonadal steroid hormones lead to variation around this baseline condition, with androgens having a greater influence on rostral populations and estrogen on caudal populations. Last, an individual's gonadal sex determines the effect that androgens and estrogen have on each population.     

Factors affecting sex ratio in rearing ofCoeloides sordidator (Hym.: Braconidae)

Five factors known to affect the sex ratio (% of males) in parasitic Hymenoptera were investigated forCoeloides sordidator, a parasitoid ofPissodes weevils. The host age, the age of ovipositing females, and the host of origin had a significant impact on the sex ratio of offspring. In contrast, the number of ovipositing females had an insignificant effect on sex ratio whereas the effect of host density could not be clearly defined. The sex ratio decreased with host age, probably because, like many other hymenopteran parasitoids, females tend to lay male eggs on small hosts and female eggs on larger hosts in order to maximize the size and fitness of their female offspring. The sex ratio also varied with the age of the mother, younger females laying more male eggs and older females more female eggs. The host of origin also had an influence on sex ratio. The strain fromPissodes castaneus was significantly more male-biased than the strain fromP. validirostris, which corroborates previous observations made on field populations     

Age-based demography and reproductive biology of three <Emphasis Type="Italic">Epinephelus</Emphasis> groupers, <Emphasis Type="Italic">E. polyphekadion,E. tauvina,</Emphasis> and <Emphasis Type="Italic">E. howlandi</Emphasis> (Serranidae), inhabiting coral reefs in Okinawa

The demography and reproductive biology of three Epinephelus groupers (Serranidae), namely E. polyphekadion, E. tauvina, and E. howlandi in the Yaeyama Islands, Okinawa, were examined based on age assessment using otoliths and gonadal histology. The maximum ages for these three species were 26 year, 23 year, and 17 year. The von Bertalanffy growth functions were also determined for each species. The size and age at 50% female maturity were estimated to be 358 mm in total length (TL) and 6.0 year for E. polyphekadion, 371 mm TL and 6.7 year for E. tauvina, and 327 mm TL and 4.1 year for E. howlandi, respectively. Significant differences between the sexes in size and age frequencies were found in all three species, with males being larger and older than females, or transitional individuals. These results strongly indicated that the population of these three grouper species showed monandric protogynous hermaphroditism. The sex ratios of E. polyphekadion and E. tauvina were biased in favor of females, but that of E. howlandi was equivalent between sexes. The relative sizes of ripe testes indicated that the intensity of sperm competition varied among species suggesting different mating system of each species. Reproductive seasonality was similar among species, with active vitellogenesis coinciding with the annual rise in water temperature. The active spawning period was determined to be between April and May for E polyphekadion, in May for E. howlandi, and from March to June for E. tauvina.     

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.     

Sex differences in juvenile mouse social behavior are influenced by sex chromosomes and social context

Play behavior in juvenile primates, rats and other species is sexually dimorphic, with males showing more play than females. In mice, sex differences in juvenile play have only been examined in out-bred CD-1 mice. In this strain, contrary to other animals, male mice display less play soliciting than females. Using an established same-sex dyadic interaction test, we examined play in in-bred C57BL/6J (B6) 21-day-old mice. When paired with non-siblings, males tended to be more social than females, spending more time exploring the test cage. Females displayed significantly more anogenital sniffing and solicited play more frequently than did males. To determine if the origin of the sex difference was sex chromosome genes or gonadal sex, next we used the four core genotype mouse. We found significant interactions between gonadal sex and genotype for several behaviors. Finally, we asked if sibling pairs (as compared to non-siblings) would display qualitatively or quantitatively different behavior. In fact, XX females paired with a sibling were more social and less exploratory or investigative, whereas XY males exhibited less investigative and play soliciting behaviors in tests with siblings. Many neurobehavioral disorders, like autism spectrum disorder (ASD), are sexually dimorphic in incidence and patients interact less than normal with other children. Our results suggest that sex chromosome genes interact with gonadal hormones to shape the development of juvenile social behavior, and that social context can drastically alter sex differences. These data may have relevance for understanding the etiology of sexually dimorphic disorders such as ASD.     

H-Y Antigen Expression in Temperature Sex-Reversed Turtles (Emys orbicularis)

H-Y antigen has been used as a marker for the heterogametic sex and is assumed to be an organizing factor for the heterogametic gonad. In the turtle Emys orbicularis , H-Y antigen is restricted to the female cells, indicating a female heterogamety (ZZ/ZW) sex-determining mechanism. Moreover, the sexual differentiation of the gonads is temperature sensitive, and complete sex reversal can be obtained at will. In this framework the relationships between H-Y antigen, temperature, and gonadal phenotype were studied. Mouse H-Y antiserum was absorbed with blood and gonadal cells of control wild male and female adults, and with blood and gonadal cells from three lots of young turtles from eggs incubated at 25–26°C (100% phenotypic males), at 30–30.5°C (100% phenotypic females), or at 28.5–29°C (majority of females with some males and intersexes). The residual activity of H-Y antiserum was then estimated using an immunobacterial rosette technique. In adults, both blood cells and gonadal cells were typed as H-Y negative in males and as H-Y positive in females. In each of the three lots of young, blood cells were H-Y negative in some individuals and H-Y positive in others. The proposed interpretation is that the H-Y negative individuals were genotypic males (ZZ) and the H-Y positive were genotypic females (ZW). The gonads of these animals were then pooled in different sets according to their sexual phenotype and to the presumed genotypic sex (i.e., blood H-Y phenotype). Testicular cells were typed as H-Y negative in genotypic males as well as in the presumed sex-reversed genotypic females; likewise, ovarian cells were typed as H-Y positive in genotypic females as well as in the presumed sex-reversed genotypic males. These results provide additional evidence that H-Y antigen expression is closely associated with ovarian structure in vertebrates displaying a ZZ/ZW sex-determining mechanism.     

Hormones and social behavior in the lizard, Anolis carolinensis

The purpose of this experiment was to study the effects of homologous and heterologous gonadal hormones on sexual and aggressive behavior in a reptilian species. Thirty adult male and thirty adult female lizards (Anolis carolinensis) were divided into 10 groups of six each (five groups per sex) and each group was given one of five treatments: either left intact, sham-castrated and injected with the hormone vehicle, castrated and injected with the hormone vehicle, castrated and injected with estradiol benzoate, or castrated and injected with testosterone propionate. After a week of visual isolation and daily hormone injection, animals were tested four times, twice with a stimulus animal of each sex. Females treated with estrogen were receptive, but did not court. Females treated with androgen were receptive and also courted and pursued stimulus females as frequently as males given androgen. No males in any group were receptive, and thus the female appears to be more capable of heterotypical sexual behavior than the male. Castrated males failed to court. Courtship and pursuit of stimulus females was readily stimulated in males with testosterone, and weakly stimulated by estrogen. Intact males were very aggressive, but lower levels of aggression were independent of gonadal hormones, as was subordination (head-nodding). The results for aggression and subordination are interpreted with reference to naturally-occurring Anolis behavior, and the results for sexual behavior are compared with similar experiments with mammals and birds.     

Is egg carrying attractive? Mate choice in the golden egg bug (Coreidae,Heteroptera)

In several species of fish, females select males that are already guarding eggs in their nests. It is a matter of debate as to whether a female selects a good nest site for her offspring (natural selection) or a male for his attractiveness (sexual selection). The golden egg bug, Phyllomorpha laciniata Vill, resembles fish in the sense that mating males carry more eggs than single males, but in the bugs, female mate choice is decoupled from egg site choice. The sexual selection hypothesis predicts that if females select males using male egg load as a cue for male quality, they should not mate with a male when eggs are removed, regardless of his mating attempts. When individual females were enclosed with an egg-loaded male and an unloaded male, they mated equally often with both males, although the loaded males courted more. In addition, when only successful males were used, females mated equally often with the loaded male and the unloaded male irrespective of sex ratio. Male choice rather than female choice affected mating frequency when sex ratio was equal. Therefore, females do not select the male by the eggs he carries, but successful males may receive many eggs due to egg dumping by alien females while they mate or as a consequence of mate guarding.     

The relationship of age,sex, and reproductive state to assimilation efficiency in the adult milkweed bug, Oncopeltus fasciatus

The influence of age, sex, and reproductive state on efficiency of assimilation was examined in the milkweed bug Oncopeltus fasciatus. Amounts of food ingested and excreted decline with age in virgin males and females. Mated females laying eggs ingest significantly more food than virgin animals of either sex and also maintain a consistently higher assimilation efficiency. A qualitative analysis of the level of assimilation required for reproductive effort is discussed.     

Sources contribution for benthic invertebrates: an inter-lake comparison in a flood plain system

Dwarfism in males is a common phenomenon in planktonic monogonont rotifers. Considering the small body size of males, some studies suggested that the development time of male rotifers is faster than that of females. However, empirical studies associated with such a speculation are scarce. In this study, we used two common rotifer species, Brachionus calyciflorus and Brachionus plicatilis (each with two geographical populations), to test the hypothesis that the development time of dwarf males is significantly shorter than that of females. Results showed that male eggs (embryos) were deposited much faster than female eggs (embryos) in both Brachionus species. However, the embryonic development time of these small male eggs (embryos) was longer than that of large female eggs (embryos). As a result, males needed significantly longer total development time than females. The total development time of males was 2–3 h longer than that of females in both Brachionus species. Male-producing and female-producing females in the two Brachionus species did not show any difference in development time. Because sexual reproduction begins at high population densities in both species, postponement of development in males will be advantageous by decreasing mating costs in male rotifers.     

Lack of gonadal control of the dorsal gland and sandbathing in male and female bannertail kangaroo rats (Dipodomys spectabilis)

Previous studies have demonstrated gonadal control of mammalian scent glands; castration leads to reduced scent-marking rates and smaller gland sizes. I investigated whether gonadal hormones control the size of the dorsal gland (a specialized sebaceous gland) and sandbathing as a scent-marking behavior in adult male and female bannertail kangaroo rats (Dipodomys spectabilis). Gland sizes of males and females were similar in all age classes, except adult males with larger body weights had proportionately larger glands than females. Male gland sizes declined 18% following castration but were not significantly smaller than those of intact males; females showed no change in dorsal gland size either as a result of ovariectomy or after estradiol benzoate implants. Sandbathing rates also did not decline as a result of gonadectomy. Rather, castrated males and overiectomized females sandbathed at higher frequencies than intact males and ovariectomized females with estradiol benzoate implants, respectively. Gonadal hormones apparently have little influence on the function of a specialized scent gland and may inhibit sandbathing as a scent-marking behavior in adult D. spectabilis.