Sexual dimorphism in resource acquisition and deployment: both size and timing matter.

Background and Aims The males and females of many dioecious plant species differ from one another in important life-history traits, such as their size. If male and female reproductive functions draw on different resources, for example, one should expect males and females to display different allocation strategies as they grow. Importantly, these strategies may differ not only between the two sexes, but also between plants of different age and therefore size. Results are presented from an experiment that asks whether males and females of Mercurialis annua, an annual plant with indeterminate growth, differ over time in their allocation of two potentially limiting resources (carbon and nitrogen) to vegetative (below-and above-ground) and reproductive tissues.Methods Comparisons were made of the temporal patterns of biomass allocation to shoots, roots and reproduction and the nitrogen content in the leaves between the sexes of M. annua by harvesting plants of each sex after growth over different periods of time.Key Results and Conclusions Males and females differed in their temporal patterns of allocation. Males allocated more to reproduction than females at early stages, but this trend was reversed at later stages. Importantly, males allocated proportionally more of their biomass towards roots at later stages, but the roots of females were larger in absolute terms. The study points to the important role played by both the timing of resource deployment and the relative versus absolute sizes of the sinks and sources in sexual dimorphism of an annual plant.

Desarrollo sexual del paiche (arapaima gigas) en las zonas reservadas del estado (ríos Pacaya y Samiria) 1971 - 1975

Desarrolla los datos registrados en la Reserva Nacional Pacaya - Samiria, de noviembre de 1971 a noviembre de 1975, efectuado con 697 paiches hembras; donde determinaron el ciclo de desove y la longitud que alcanza el paiche en su primera madurez sexual.

Reporte de datos de madurez sexual de la anchoveta peruana (engraulis ringens) durante el periodo 1961 - 1987

Se presentan datos de madurez sexual promedio mensual de la anchoveta peruana, Engraulis ringens por longitudes y sexos, para las Regiones Norte (06°-10°S), Centro (10°-14° S) y Sur (14°-18°20 ' S) para el período 1961-87. Estos se obtuvieron usando los datos de madurez sexual colectados macroscópicamente de ejemplares procedentes de los desembarques a lo largo del litoral peruano.

Efecto de la proporción sexual, densidad y edad de los reproductores en la producción de semilla de Tilapia nilotica (Pisces, Cichlidae)

En el Laboratorio de Huachipa del Instituto del Mar del Perú, en el período comprendido entre octubre de 1980 y agosto de 1982, se realizaron varios experimentos a fin de determinar el efecto del tipo de estanque, densidad de carga y calidad y cantidad de fertilizante en el crecimiento y la producción de Tilapia nilotica. Estos experimentos arrojaron una diferencia no significativa entre los tratamientos, por lo cual se halló una cifra general promedio de crecimiento y producción que permitió su comparación con las cifras de producción obtenidas en otras áreas del mundo, un peso individual promedio de 203.4 g, una producción total de 2,038 Kg/ha/272 días, y una producción neta de 5.6 Kg/ha/día. Cifras que quedan dentro del rango reportado por el ICA (International Center for Aquaculture) para clima templado; similares a las obtenidas en países de Europa Central y la China, y notablemente bajas comparadas con los 20 Kg/ha/día producidos en Israel. Se identifican la mala condición de los estanques utilizados, la baja densidad de carga aplicada, la baja calidad del fertilizante y el clima de la zona, específicamente la presencia de nubosidad, como los factores de mayor incidencia en los resultados poco satisfactorios.

Estudio de la fecundidad y ciclo sexual de la anchoveta (Egraulis ringens. J.) en la zona de Chimbote

La fecundidad de la anchoveta del Perú (Engraulis ringens J.) ha sido investigada en 83 ovarios colectados en varias localidades de la zona pesquera de Chimbote, durante la estación de desove.La fecundidad, considerada aquí como el número de huevos que la anchoveta elimina en una puesta ha sido estimada determinando el número de ovas en el grupo del tamaño modal más avanzado.

La madurez sexual de la anchoveta (Engraulis rigens J.) en los periodos reproductivos 1961/1968

Información sobre la madurez sexual de la Anchoveta peruana, que ha sido estudiado por el examen macroscópico de las gónadas durante 1961-1968, el material se recogió en Chimbote, Callao e Ilo y se comparó con datos similares de Chile. Las etapas más avanzadas de la madurez sexual fueron la base de la evaluación. El análisis pone de relieve las diferencias de tiempo de la temporada de desove entre las localidades en relación con la longitud y la edad. Los datos de Chimbote y Callao indican que la actividad sexual se extiende de agosto a marzo. Se producen dos picos de desove, uno en septiembre y otro en febrero. por otro lado, los datos de Ilo y Chile demuestran que la época de desove en la zona sur comienza en julio y termina en febrero. Estos resultados también demuestran dos puntos interesantes en relación con la longitud y la edad de anchovetas: el pico a la madurez sexual en verano es tan intenso como en el invierno, pero el predominante de pequeñas anchovetas durante el verano hace dificil de detectar la situación real y las anchovetas mayores desove durante un período más largo y con mayor intensidad que los más jóvenes. Por último, las anchovetas en la etapa más avanzada de madurez fueron más abundantes durante 1964, 1967 y que durante el resto de año cerca de Callao y Chimbote.

Madurez sexual, frecuencia de desove y fecundidad de la anchoveta peruana durante invierno-primavera de 1997

Analiza tres aspectos importantes en el estudio de la biología reproductiva de la anchoveta Engraulis ringens: el estado reproductivo por grado latitudinal (entre 16° y 5°S), la frecuencia de desove y la fecundidad parcial. El desove fue más intenso en el área comprendida entre los grados 10°S y 12°S. La frecuencia de desove fue 0,071, disminuyendo en 32,0% en comparación al cálculo del año anterior.

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

Impact of job insecurity on sexual desire: an exploratory analysis.

To explore, for the first time, the impact of job insecurity on sexual desire. Cross-sectional analysis of a nationally representative sample of 7247 individuals aged 20-64 years working as full or part-time employees in Switzerland. The logistic regression analysis showed that workers aged 20-49 years perceiving high levels of job insecurity are exposed to a significantly higher risk of decrease of sexual desire compared to the reference group. The risk is 53% higher among men (OR 1.53; 95% CI 1.16-2.01) and 47% for woman (OR 1.47; 1.13-1.91). No increased risk was found for employees aged 50-64 years old. An increasing fear of job loss is associated with a deterioration in sexual desire. These first preliminary findings should promote further epidemiological and clinical prospective studies on the impact of job insecurity on intimate relationships and sexual dysfunction.

Effects of female postmating odour on male sexual behaviour, in Heliconius butterflies /

The effects of the female postmating odour on male sexual behaviour were examined in Heliconius erato and H. charithonia (Lepidoptera: Nymphalidae). Predictions from the antiaphrodisiac hypothesis were tested using the two reproductive strategies of these species. Within the pupal mating strategy, results from behavioural experiments quantified and statistically tested dispersal rates of pupal-perched males to the presence of stimuli with and without the postmating odour. Results do not support an antiaphrodisiac function to the postmating odour. Similarly, within the adult courtship strategy, behavioural test results indicate that males do not alter their expenditure of energy in terms of either the duration or frequency of courtship behaviours elicited by females with and without the postmating odour. The data from both experiments did not support the antiaphrodisiac hypothesis for the function of the female postmating odour. A novel hypothesis predicting that the postmating female odour acts as an oviposition-deterring pheromone is presented.

An examination of the mediation process as it is used to resolve sexual harassment complaints in Canadian universities /

The ways in which the process of mediation affected those involved in the resolution of sexual harassment complaints in Canadian universities were explored. Questionnaires were sent to forty- six Canadian universities and interviews were conducted with fifteen advisors. An analysis of the twenty- two questionnaires returned indicated that mediation was utilized in 11% of the sexual harassment complaints and effected a successful resolution in 67% of these. Both complainants and those con^lained against were reported to have spoken more favourably than unfavourably about the process and outcome of mediation. Questionnaire respondents in general found mediation a slightly less than satisfactory method of complaint resolution. Those respondents who had successfully used mediation; however, describe its usefulness within a university context.

Parental care in the common tern (Sterna Nirundo): sexual roles in a monogamous seabird

The parental behaviour of male and female Common Terns (Sterna hirundo) was documented throughout two breeding seasons at a colony near Port Colborne , Ontario. Thirteen and fourteen pairs of terns were chosen for intensive study in 1982 and 1983, respectively. The delivery of fish by males to their mates ("courtship feeding") occurred prior-to, during, and following the egg-laying period. Following the laying of the second egg, courtship feeding rates declined significantly. There was a significant, positive correlation bebween courtship feeding rates and subsequent chick feeding rates by males. The incubation rates of females were significantly higher than those of males, especially during the first ten days of incubation. Territorial attendance rates during the incubation stage were similar for males and females. During the chick stage, territorial attendance rates of females were significantly higher than those of males. The size of fish fed to chicks by males increased as the chicks grew older and chick feeding rates of males were approximately three times higher than female rates. Based on these quantitative differences in parental care activities, the cumulative parental time investment by the two sexes was very similar. However, the energetic investment by males was likely greater than that by females, since male parental contributions (e.g. courtship feeding and chick feeding) often entailed extensive foraging behaviour.

Sexual behavior and factors affecting female reproduction in house and field crickets

The objective of this investigation was to clarify the adaptive significance of female sexual behaviours in the house cricket, Acheta domesticus, and the Texas field cricket, Gryllus integer. Experiments were focussed primarily on: nutritional factors affecting female reproductive success; the ontogeny of female sexual behaviours; female mating frequency and progeny production; and the pattern of sperm competition. Reproduction of singly mated female A. domesticus assigned to 3 nutritional regimes was compared . Females fed a vitamin and protein-enriched mouse chow, cannibalistic females, and starved females produced on the average, 513 , 200 and 68 offspring, respectively. Cannibals probably could not obtain the same amounts of essential nutrients as females fed mouse chow. Reabsorption of oocytes was likely the major factor contributing to the decreased reproduction of starved females. In addition, female !. domesticus fed mouse chow, but allowed constant access to males produced 11 times as many offspring than did females fed corn meal. Females fed corn meal probably could not absorb or synthesize enough dietary lipids, thus resulting in poor ovariole growth. Female !. domesticus first mate at an average adult age of 7 days, closely corresponding to when they first exhibit positive phonotaxis. Females mate repeatedly and often consume the externally attached spermatophore. In ~. domesticus, females allowed constant access to males produced significantly more offspring than did single maters. Similarly, doubly mated G. integer females produced more offspring than did single maters. This difference resulted largely from the failure of many single maters to reproduce. Remating by female crickets partly functions in offsetting the possibility of a failed initial mating. Nymph production increased significantly with the time the spermatophore was attached in singly mated ~. domesticus. Spermatophore consumption by the female was not affected by male guarding behaviour, and the interval between mating and eating of the spermatophore may often be shorter than the time required for maximum insemination. Some degree of sperm depletion in singly mated !. domesticus and G. integer may have occurred. The patterns of daily offspring production of singly and multiplymated females suggests that a factor provided by a male during mating stimulates female oviposition and/or egg production. Female crickets also might acquire nutrition from spermatophore consumption, a benefit that is augmented by female multiple mating. The electrophoretic examination of various allozymes in ~. integer did not permit determination of a pattern of sperm competition. However, the possibility of last male sperm predominance is related to male guarding behaviour.

Sexual selections in the northern fall field cricket, Gryllus pennsylvanicus: a manipulation of the adult sex ratio

The operational sex ratio has long been considered an important constraint on the structure of mating systems. The effects of an experimentally manipulated sex ratio on mating behavior and selection were investigated in a polygynous species, Gryllus pennsylvanicus, where the potential exists for spatial/temporal fluctuations in sex ratio of field populations. Four different sex ratios (males: females, 5:0, 5:2, 5:5, 5:10) were investigated. Observations were conducted in late summer over two field seasons, from 2400 h , to 1000 h EST. Several male characters thought to be associated with male reproduc.tive success were studied: calling duration, searching distance, weight, fighting behavior, courtship frequency, and mating success. Variance in male mating success was used as the indicator for the opportunity for sexual selection. Total selection was estimated as the univariate regression coefficient between relative fitness and the character of interest, while direct selection was estimated as standardized partial regression coefficients generated from a multiple regression of relative fitness on each character. The opportunity for sexual selection was highest at 5:2 and lowest at 5:10. The frequency of fighting behavior was highest at 5:2 and 5:5. Fighting ability (% wins) was determined to be an important correlate of male body weight. Direct selection for increased male body weight was detected at 5:2, while total selection for body weight was seen at 5:5. Selection on male body weight was not detected at 5: 10. Calling duration decreased as sex ratio became more female-biased. Total and direct selection were detected for increased calling at 5:2, only total selection for calling was seen at 5:5, whereas direct selection against calling was detected at 5: 10. Searching distance also decreased as sex ratio became more female-biased, however no form of selection was detected for searching at any of the sex ratios. Data are discussed in terms of sexual selection on male reproductive tactics, the mating system and maintenance of genetic variation in male reproductive behavior.