Reproductive Biology of the Freshwater Shrimp Atya scabra (Leach, 1815) (Crustacea: Atyidae) in Ilheus, Bahia, Brazil

Alexandre Oliveira Almeida, Emerson Contreira Mossolin, and Joaldo Rocha Luz (2010) Reproductive biology of the freshwater shrimp Atya scabra (Leach, 1815) (Crustacea: Atyidae) in Ilheus, Bahia, Brazil. Zoological Studies 49(2): 243-252. Reproduction and population aspects of the freshwater shrimp Atya scabra in the Santana River, city of Ilheus, state of Bahia, Brazil, were studied from Apr. 2004 to May 2005. During these 14 mo, 3752 individuals were captured, with a sex ratio of 1.01 males for each female. The total number of individuals caught per month ranged 80-532. Males were generally larger than females. The smallest female found (5.40 mm in carapace length and 29.03 mm in total length) was ovigerous, which indicates that only adult individuals were caught. Ovigerous females were found every month, which indicates continuous reproduction and a high index of reproductive activity during the year. The highest reproduction indices were observed in May (94.3%) and Oct. (98.6%) 2004, and Mar. (93.7%) 2005. Fecundity ranged 870-8907 eggs, with a mean of 3811 (+/- 1992.87) eggs per female. The size of the females and their fecundity were positively correlated. The distribution of individuals in length classes by month showed that representatives of smaller classes occurred throughout almost the entire study period. This indicates a constant input of individuals into the population, which corroborates the characterization of the reproductive period as being continuous, and explains the large numbers of ovigerous females found each month. The 2nd abdominal segment is proportionally larger in females than in males, in width, height, and pleural length: these female secondary characteristics are related to an increased incubation area for eggs. http://zoolstud.sinica.edu.tw/Journals/49.2/243.pdf

Signal trait sexual dimorphism and mutual sexual selection in Drosophila serrata

The evolution of sexual dimorphism may occur when natural and sexual selection result in different optimum trait values for males and females. Perhaps the most prominent examples of sexual dimorphism occur in sexually selected traits, for which males usually display exaggerated trait levels, while females may show reduced expression of the trait. In some species, females also exhibit secondary sexual traits that may either be a consequence of a correlated response to sexual selection on males or direct sexual selection for female secondary sexual traits. In this experiment, we simultaneously measure the intersex genetic correlations and the relative strength of sexual selection on males and females for a set of cuticular hydrocarbons in Drosophila serrata. There was significant directional sexual selection on both male and female cuticular hydrocarbons: the strength of sexual selection did not differ among the sexes but males and females preferred different cuticular hydrocarbons. In contrast with many previous studies of sexual dimorphism, intersex genetic correlations were low. The evolution of sexual dimorphism in D. serrata appears to have been achieved by sex-limited expression of traits controlled by genes on the X chromosome and is likely to be in its final stages.

Male body size and breeding tubercles are both linked to intra-sexual dominance and reproductive success in the minnow

Male dominance hierarchies are usually linked to relative body size and to weapon size, that is, to determinants of fighting ability. Secondary sexual characters that are not directly used as weapons could still be linked to dominance if they reveal determination or overall health and vigour and hence, indirectly, fighting ability. We studied the mating behaviour of the minnow, Phoxinus phoxinus, a cyprinid fish in which males develop breeding tubercles during the spawning season. The function of these breeding tubercles is still not clear. Using microsatellite markers, we determined male reproductive success under controlled conditions. The minnows were territorial and quickly established a dominance hierarchy at the beginning of the spawning season. Dominance was strongly and positively linked to fertilization success. Although body size and number of breeding tubercles were not significantly correlated in our sample, both large males and males with many breeding tubercles were more dominant and achieved higher fertilization success than small males or males with few tubercles. We found multimale fertilization in most clutches, suggesting that sperm competition is important in this species. Females showed behaviour that may be linked to spawning decision, that is, male dominance might not be the only determinant of male reproductive success in minnows

Parasitism, host immune function, and sexual selection.

Parasite-mediated sexual selection may arise as a consequence of 1) females avoiding mates with directly transmitted parasites, 2) females choosing less-parasitized males that provide parental care of superior quality, or 3) females choosing males with few parasites in order to obtain genes for parasite resistance in their offspring. Studies of specific host-parasite systems and comparative analyses have revealed both supportive and conflicting evidence for these hypotheses. A meta-analysis of the available evidence revealed a negative relationship between parasite load and the expression of male secondary sexual characters. Experimental studies yielded more strongly negative relationships than observations did, and the relationships were more strongly negative for ectoparasites than for endoparasites. There was no significant difference in the magnitude of the negative effect for species with and without male parental care, or between behavioral and morphological secondary sexual characters. There was a significant difference between studies based on host immune function and those based on parasite loads, with stronger effects for measures of immune function, suggesting that the many negative results from previous analyses of parasite-mediated sexual selection may be explained because relatively benign parasites were studied. The multivariate analyses demonstrating strong effect sizes of immune function in relation to the expression of secondary sexual characters, and for species with male parental care as compared to those without, suggest that parasite resistance may be a general determinant of parasite-mediated sexual selection.

Predicting the mating system from phenotypic correlations between life-history and sperm quality traits in the Alpine whitefish Coregonus zugensis

The mating behavior and reproductive strategies of Alpine whitefish like Coregonus zugensis (Nusslin) are poorly understood, probably because they spawn in deep water where direct observations are difficult. In this study, we interpret life-history and sperm quality traits of fish that we caught from their spawning place. We found that males invest heavily into gonadal tissue (up to 5.6% of their body weight), which is, in comparison to other fish, consistent with external fertilization, distinct pairing and moderate to high communal spawning, or no pairing and low to moderate communal spawning. Sperm competition theory and recent experimental studies on other salmonids predict that males optimize ejaculate characteristics in relation to the costs of sperm and the level of competition they have to expect: dominant males are predicted to invest less into ejaculate quality and to have slower spermatozoa than subdominant males. We found that spermatozoa of older males are slower than those of younger males. Moreover, older males have larger breeding tubercles, a secondary sexual trait that has, in some previous studies, been found to be linked to good condition and to good genetic quality. Our results suggest that C. zugensis has age-linked reproductive strategies, that multimale spawning is common, i.e., that sperm competition plays a significant role, and that older males are on average dominant over younger males at the spawning place.

Importance and evolution of sexual dimorphism in different families of Collembola (Hexapoda)

A bibliographic revision of sexual dimorphism in different families of Collembola was performed in order to determine the most common patterns in each group. We list several examples of the sexual dimorphism in different families of Collembola, which illustrate from some of the smallest differences between males and females to major differences between both sexes in some families. We show different cases of sexual dimorphism in Spinactaletes, Sminthurides, and the remarkable morphology of Guthriella muskegis. It seems that most of the cases of strong sexual dimorphism are related to aquatic habitats or behaviour still not fully understood. Species belonging to primarily aquatic families (fresh water or marine water) have the most evolved morphology, where males have clasping antennae to attach the females in order to avoid loosing them with the movement of the water.

Bone properties and skeletal maturity in adolescent males, as assessed by quantitative ultrasound

ABSTRACT Background: Previous studies have implied that weight-bearing, intense and prolonged physical activities optimize bone accretion during the grow^ing years. The majority of past inquiries have used dual-energy X-ray absorptiometry (DXA) to examine bone strength and hand-wrist radiography to determine skeletal maturity in children. Recently, quantitative ultrasound (QUS) technologies have been developed to examine bone properties and skeletal maturity in a safe, noninvasive and cost-effective manner. Objective: The purpose of this study was to compare bone properties and skeletal maturity in competitive male child and adolescent athletes with minimallyactive, age-matched controls, using QUS technology. >. Methods: In total, 224 males were included in the study. The 115 pre-pubertal boys aged 10-12 years consisted of control, minimally-active children (n=34), soccer players (n=26), gymnasts (n=25) and hockey players (n=30). In addition, the 109 late-pubertal boys aged 14-16 years consisted of control, minimally-active adolescents (n=31), soccer players (n=30), gymnasts (n=17) and hockey players (n=31). The athletic groups were elite level players that predominantly trained year-round. Physical activity, nutrition and sports participation were assessed with various questionnaires. Anthropometries, such as height, weight and relative body fat percentage (BF%) were assessed using standard measures. Skeletal strength and age were evaluated using bone QUS. Lastly, salivary testosterone (sT) concentration was measured using Radioimmunoassay (RIA). Results: Within each age group, there were no significant differences between the activity groups in age and pubertal stage. An age effect was apparent in all variables, as expected. A sport effect was noted in all physical characteristics: the child and adolescent gymnasts were shorter and lighter than other sports groups. Adiposity was greater in the controls and in the hockey players. All child subjects were pubertal stage (fanner) I or II, while adolescent subjects were pubertal stage IV or V. There were no differences in daily energy and mineral intakes between sports groups. In both age groups, gymnasts had a higher training volume than other athletic groups. Bone speed of sound (50s) was higher in adolescents compared with the children. Gymnasts had signifieantly higher radial 50S than controls, hockey and soccer players in both age cohorts. Hockey athletes also had higher radial 50S than controls and soccer players in the child and adolescent groups, respectiyely. Child gymnasts and soccer players had greater tibial 50S compared with the hockey players and control groups. Likewise, adolescent gymnasts and soccer players had higher tibial SoS compared with the control group. No interaction was apparent between age and type of activity in any of the bone measures. » Lastly, maturity as assessed by sT and secondary sex characteristics (Tanner stage) was not different between sports group within each age group. Despite the similarity in chronological age, androgen levels and sexual maturity, differences between activity groups were noted in skeletal maturity. In the younger group, hockey players had the highest bone age while the soccer players had the lowest bone age. In the adolescent group, gymnasts and hockey players were characterized by higher skeletal maturity compared with controls. An interaction between the age and sport type effects was apparent in skeletal maturity, reflecting the fact that among the children, the soccer players were significantly less mature than the rest of the groups, while in the adolescents, the controls were the least skeletally mature. Summary and Conclusions: In summary, radial and tibial SOS are enhanced by the unique loading pattern in each sport (i.e, upper and lower extremities in gymnastics, lower extremities in soccer), with no cumulative effect between childhood and adolescence. That is, the effect of sport participation on bone SOS was apparent already among the young athletes. Enhanced bone properties among athletes of specific sports suggest that participation in these sports can improve bone strength and potential bone health.

Sexual maturity of Eurytium limosum (say 1818) from a subtropical mangrove in Brazil

The size at onset of maturity of Eurytium limosum from a subtropical mangrove in Brazil was investigated. In this species, sexual maturity for males can be indicated by the allometric growth and gonopod length. For females, the morphological sexual maturity can only be externally verified through the relative quantity of setae along the abdominal margins and pleopods. Internally, gonad development was also examined. The size at which half of the population is physiologically mature was 11.6 mm of CW for females and 12.3 mm of CW for males. The values for the morphological and physiological maturity are very similar, indicating that the development of the secondary sexual characters is synchronized with the achievement of the physiological maturity for E. limosum.

Dimorfismo sexual em Dasypops schirchi (Miranda-Ribeiro, 1924): aspectos morfológicos

Amphibians exhibit great morphological plasticity of habitat and life history. This heterogeneity contributes to the frequency of occurrence and diversity of sexual dimorphism (shape or size) is large. Dasypops schirchi is a species belonging to the subfamily and family Gastrophryninae Microhylidae and this endemic and endangered. Generally, very little is known about D. schirchi, much in part to its habit of living and cryptic small geographical distribution. In order to detect and characterize elements sexually dimorphic in this species was a survey of specimens of D. schirchi in major national zoological collections. We analyzed 16 morphometric variables were also searched and secondary sexual characters non-morphometric. Statistical analysis of the morphometric data, the results showed a clear distinction between males and females of D. schirchi, secondary sexual characters nonmorphometric were also found

The contagion indicator hypothesis for parasite-mediated sexual selection.

Hamilton and Zuk [Hamilton, W. D. & Zuk, M. (1982) Science 218, 384-387] proposed that females choosing mates based on the degree of expression of male characters obtain heritable parasite resistance for their offspring. Alternatively, the "contagion indicator" hypothesis posits that females choose mates based on the degree of expression of male characters because the latter indicate a male's degree of infestation of parasites and thus the risk that choosing females and their offspring will acquire these parasites. I examined whether parasite transmittability affects the probability that parasite intensity and male mating success are negatively correlated in intraspecific studies of parasite-mediated sexual selection. When females risk infection of themselves or their future offspring as a result of mating with a parasitized male, negative relationships between parasite intensity and male mating success are significantly more likely to occur than when females do not risk such infection. The direct benefit to females of avoiding parasitic infection is proposed to lead to the linkage between variable secondary sexual characters and the intensity of transmittable parasites. The direct benefits of avoiding associatively transmittable parasites should be considered in future studies of parasite-mediated sexual selection.

Juniperus navicularis - a study of Portuguese population structure and fitness

Juniperus navicularis Gand. is a dioecious endemic conifer that constitutes the understory of seaside pine forests in Portugal, areas currently threatened by increasing urban expansion. The aim of this study is to assess the conservation status of previously known populations of this species located on its core area of distribution. The study was performed in south-west coast of Portugal. Three populations varying in size and pine density were analyzed. Number of individuals, population density, spatial distribution and individual characteristics of junipers were estimated. Female cone, seed characteristics and seed viability were also evaluated. Results suggest that J. navicularis populations are vulnerable because seminal recruitment is scarce, what may lead to a reduction of genetic variability due solely to vegetative propagation. This vulnerability seems to be strongly determined by climatic constraints toward increasing aridity. Ratio between male and female shrubs did not differ from 1:1 in any population. Deviations from 1:1 between mature and non-mature plants were found in all populations, denoting population ageing. Very low seed viability was observed. A major part of described Juniperus navicularis populations have disappeared through direct habitat loss to urban development, loss of fitness in drier and warmer locations and low seed viability. This study is the first to address J. navicularis conservation, and represents a valuable first step toward this species preservation. 

A reclusão pubertaria no Kamayura de Ipawu : um enfoque biocultural

Universidade Estadual de Campinas. Faculdade de Educação Física

The ultrastructure and function of the silk-producing basitarsus in the Hilarini (Diptera : Ernpididae)

The tribe Hilarini (Diptera: Empididae), commonly known as dance flies, can be recognised by their swollen silk-producing prothoracic basitarsus, a male secondary sexual characteristic. The ultrastructure and function of the silk-producing basitarsus from one undescribed morphospecies of Hilarini, 'Hilarempis 20', is presented. Male H. 20 collect small parcels of diatomaceous algae from the surface of freshwater creeks that they bind with silk produced by the gland in the basitarsus. The gift is then presented to females in a nearby swarm, composed predominately of females. The basitarsus houses approximately 12 pairs of class III dermal glandular units that congregate on the ventral side of the cavity. Each gland cell has a large extracellular lumen where secretion accumulates. The lumen drains to the outside via a conducting canal encompassed by a canal cell and a duct extending through the shaft of a specialised secretory spine. The secretory spines lie in pairs in a ventral groove that runs the length of the basitarsus. A comparison of the basitarsal secretory spines with sensilla on the basitarsi of non gland-bearing legs of males, and with non gland-bearing prothoracic. basitarsi of females, suggests that the glandular units are derived from contact chemosensory sensilla. (C) 2003 Elsevier Ltd. All rights reserved.

Sexing the human skull through the mastoid process

OBJECTIVE: The purpose of this study was to evaluate the significance for sex determination of the measurement of the area formed by the xerographic projection of 3 craniometric points related to the mastoid process: the porion, asterion, and mastoidale points. METHOD: Sixty skulls, 30 male and 30 female, were analyzed. A xerographic copy of each side of the skull was obtained. On each xerographic copy, the craniometric points were marked to demarcate a triangle. The area (mm²) of the demarcated triangle for each side of the skull (right (D) and left (E) sides) was determined, and the total value of these measures (T) was calculated. RESULTS: Concerning the right area of the male and female skulls, 60% of the values overlapped; for the left area, 51.67% overlapped, and for the total area, 36.67% overlapped. The analysis of the differences between the sexes in the areas studied was significant for the 3 areas. Regarding the total area, which is the preferred measurement because of the asymmetry between the sides of the skull, the value of the mean was 1505.32 mm² for male skulls, which was greater than the maximum value obtained in the female skulls. The value of the mean for female skulls was 1221.24 mm², less than the minimum value obtained for the male skulls. CONCLUSIONS: This study demonstrates a significant result in the 3 studied areas, (D), (E), and (T). The total area values show less overlapping of values between the sexes, and therefore can be used for sexing human skulls. For the population studied, values of the total area that were greater than or equal to 1447.40 mm² belonged to male crania (95% confidence). Values for this area that were less than or equal to 1260.36 mm² belonged to female crania (95% confidence).

The evolution of sex determination

Sexual reproduction is a fundamental aspect of life. Sex-determination mechanisms are responsible for the sexual fate and development of sexual characteristics in an organism, be it a unicellular alga, a plant, or an animal. Surprisingly, sex-determination mechanisms are not evolutionarily conserved but are bewilderingly diverse and appear to have had rapid turnover rates during evolution. Evolutionary biologists continue to seek a solution to this conundrum. What drives the surprising dynamics of such a fundamental process that always leads to the same outcome: two sex types, male and female? The answer is complex but the ongoing genomic revolution has already greatly increased our knowledge of sex-determination systems and sex chromosomes in recent years. This novel book presents and synthesizes our current understanding, and clearly shows that sex-determination evolution will remain a dynamic field of future research. The Evolution of Sex Determination is an advanced, research level text suitable for graduate students and researchers in genetics, developmental biology, and evolution.