Differences in environmental response between the sexes of the dioecious shrub Baccharis halimifolia (Compositae)

Summary Baccharis halimifolia (Compositae) is a dioecious shrub which grows on the upland fringe of tidal marshes along the Atlantic and Gulf Coasts of North America. We examined the responses of the two sexes to variation in nutrient and moisture availability plant density, and defoliation. By growing plants from seedlings to flowering adults under various combinations of soil type, fertilization rate and plant density, we were able to establish different rates of plant growth and mortality. Plants grown at high density and low nutrient and water supply grew the least, incurrent the most mortality and showed a male-biased sex ratio (73% male). At low density with abundant nutrients and water, plants grew more, survived well, flowered frequently, and were female-biased (75% female). Changes in sex ratio were probably the result of sex-related mortality rather than sexual lability of the seedlings. While changes in sex ratio occurred under experimental conditions in the green-house, no evidence for differences in habitat utilization between the sexes were found in the field and the sex ratio (59% female) did not vary across habitats. In the marsh habitats we sampled where water and nutrients were apparently available, there was no evidence for differential mortality between the sexes. When defoliated (75% of leaf tissue), both sexes showed similar reductions in reproductive effort (number of flower heads/shoot). Our results indicate that differences between the sexes of Baccharis in their response to environmental growing conditions is an important ecological factor associated with the separation of male and female function into separate individuals.     

Sex ratio variation and spatial segregation of the sexes in populations ofRumex acetosa andR. acetosella (Polygonaceae)

Populations ofRumex acetosa andR. acetosella were studied during two growth seasons. The ramet sex ratios ofR. acetosa were always female-biased. InR. acetosella the sex ratios expressed more variation but were mostly female-biased. In both species the sex ratios commonly varied between subpopulations reflecting a partial spatial segregation of the sexes. No marked differences between sexes in vegetative vigour were detected in either species. Interactions between sex ratios, various soil characteristics and population densities were determined. Possible mechanisms for causing biased sex ratios and partial spatial segregation of the sexes are discussed.     

Sex Differences in Captive Olive Baboon Behavior During the First Fourteen Days of Life

I discuss newborn baboon behavioral and proximity sex differences in a population of captive olive baboons (Papio anubis) living in a social group of >500 individuals. The data are based upon 20-min focal observations of 42 mother-newborn pairs (n = 27, n = 15) for infant-days 1–7 and 36 pairs (n = 23, n = 13) for infant-days 8–14 collected late-May through late-November 2001. I examined the first two weeks of infant life via behavioral, proximity, and approach-leave/contact analyses in order to determine whether behavioral sex differences exist during the first few days of life. I examine and analyze these 2 weeks independently due to different sample sizes. I used data from the total available sample population of 57 infants (n = 36, n = 21) to discuss birth, survivorship, and infant weight. Statistically significant age and/or age-sex interactions exist for all of the behavior and proximity measures during either infant-week 1 or 2. Moreover, there is a statistically significant difference in the birth sex ratio in the sample population but no significant difference in infant mortality by sex. There are also relative and significant differences in mothers' treatment of their newborn males and females. There are also some general tendencies for female newborns on average to suckle less and to explore more per focal observation than male infants do as they age. Conversely, male newborns average slightly more time per focal observation 1 m from the mother than do female infants. However, the observed differences may be influenced by maternal behavior in that mothers have higher rates of contact with their female than their male infants.     

Plasmid macro-evolution: selection of deletions during adaptation in a nutrient-limited environment

A study was made of the intra-and inter-population variability of the main traits involved in Trichogramma (T. brassicae and T. cacoeciae) efficiency in host exploitation: longevity, fecundity, progeny viability, progeny sex ratio and progeny allocation. The analysis of isofemale strains shows that differences in progeny viability, progeny sex ratio and progeny allocation are transmissible and relatively stable over two successive generations. Comparison of three strains of T. brassicae originating from different locations, demonstrates differences in fecundity, progeny sex ratio and progeny allocation. Differences in host exploitation strategies also exist between two sympatric populations of T. brassicae and T. cacoeciae. No significant correlation appears between the traits which discriminate populations. The ecological and evolutionary significance and the agronomical importance of the results are discussed.     

A rapid means of sex identification inSilene latifolia by use of flow cytometry

Sex identification in dioecious plants using nonflowering material would have broad applications in both basic and applied research. We present a method using flow cytometry for diagnosing the sex of the dioecious speciesSilene latifolia Poiret (Caryophyllaceae) by means of sexual differences in nuclear DNA content and base-pair composition. Males have a significantly larger genome, attributable to the known sex-chromosome heteromorphism. Males and females also differ in the AT/GC composition, attributable to differences in non-recombining portions of the sex chromosomes. The two measures enable assignment of individuals to sex with a combined error rate of 9%. These results forS. latifolia indicate useful directions for future research into sex diagnostics for other dioecious species.     

Sex differences in diet and foraging behavior in white-faced capuchins (Cebus capucinus)

I examined sex differences in diet and foraging behavior in two groups of white-faced capuchin monkeys (Cebus capucinus)in a tropical dry forest at Santa Rosa National Park, Costa Rica. I tested three hypotheses: sex differences in diet and foraging behavior are best explained by (1) sexual dimorphism, (2) the energy demands of pregnancy and lactation for females;and (3) avoidance of competition between the sexes. Sexual dimorphism offered the best explanation of sex differences in the diet and foraging behavior of C. capucinus,accurately predicting that males do more strenuous foraging activity, make less use of small foraging supports, and spend more time on or near the ground. Females spent more time foraging than males did but probably obtained a lower protein yield per unit foraging time. Females exploited more small and embedded invertebrates, while males ate more large invertebrates and vertebrate prey. Pregnant and lactating females spent more time resting and less time foraging than other females did, increasing their foraging return by focusing on foods requiring little handling. There was little evidence of competition avoidance between the sexes.     

Regional differences in the infection of wild Japanese macaques by gastrointestinal helminth parasites

A coprological survey of gastrointestinal parasites in wild Japanese macaques (Macaca fuscata), from 14 natural habitats was done. Ova of five nematode species (Trichuris trichiura, Strongyloides fuelleborni, Streptopharagus pigmentatus, Oesophagostomum aculeatum, andGongylonema species) and a worm of the cestode species,Bertiella studieri, were detected. Some differences found in rates of infection by sex were observed in the 14 areas. Differences based on age were found in only troops in which the infection rates ofStrongyloides fuelleborni, Streptopharagus pigmentatus, andTrichuris trichiura were higher in the juvenile monkeys. The number of parasite species was related to the geographical and climatic conditions of the habitat of the troop: troops living in areas cold in winter were infected by fewer parasite species than those in southern warmer areas.     

Behavioral Components of Sex Role Reversal in the Tettigoniid Bushcricket Ephippiger ephippiger

Facultative sex role reversal is found in species of tettigoniid bushcrickets in which males invest heavily in matings or offspring by producing large, nutritious spermatophores. On high-quality diets such species show conventional sex roles, but under low-quality diets males become the choosier sex. Comparative work suggests that Ephippiger ephippiger (Tettigoniidae, Ephippigerinae) has one of the largest described spermatophores (up to 40% of the male body weight). Here we examine the behavior of this species under variable diet conditions in the laboratory and find evidence of sex role reversal under poor-quality diet conditions. We also examine the behavioral components of sex role reversal. In the reversed condition, rejections of mating attempts are almost solely by the male and contests are almost solely between females. Role-reversed males sing less frequently and at a much reduced intensity. We use geographic variation in the calling song of this species to assess the strength of female phonotactic discrimination between races. This is not significantly reduced despite sex role reversal. We therefore suggest that the male and female aspects of the acoustic sexual communication system differ in that male components change most during facultative sex role reversal.     

Resource quality and spatial variation in sex ratios of a free-living solitary sawfly,Dineura virididorsata (Hym., Tenthredinidae)

The sex ratio in final-instar larvae of a birch-feeding, free-living solitary sawfly, Dineura virididorsata, was investigated in Finnish Lapland. The prepupal proportion of females, pooled over ten sites, was 56%, and at four individual sites the sex ratio was significantly female-biased. Larval survival from egg to prepupae did not differ between the sexes. This suggests a femalebiased primary sex ratio in the field. The sex ratio varied among the sites but not among host trees within sites. Contrary to previous results with hymenopterans, we did not find that differences in the sex ratio depended on forage quality: site-specific or tree-specific sex ratios did not correlate with the average prepupal weight. A literature search indicated that female-biased sex ratios are also common in other free-living sawflies. We are unable to explain sex ratios of Dineura virididorsata or other free-living sawflies with existing general models.     

Sex of incubation neighbours influences hatchling sexual phenotypes in an oviparous lizard

In many litter-bearing mammals and in a few viviparous reptiles the sex ratio of the entire brood or the sex of the adjacent fetuses induces sex-specific differences in the hatchling’s phenotype. This study examines whether the sex of incubation neighbours affects hatchling characteristics in oviparous common lizards (Lacerta vivipara). Oviparous common lizards lay eggs with thin eggshells and, therefore, are an optimal model organism for studying the effects of hormone leakage among developing embryos since the strongest evidence for prenatal sex ratio effects on offspring development comes from viviparous populations of the same species. Groups of three eggs were incubated together and were categorised according to the sex of the resulting hatchlings as either homosex (three hatchlings of the same sex) or heterosex (one male or one female hatchling plus two siblings of the opposite sex). Hatchlings incubated adjacent to siblings of the same sex had larger body mass and body condition. Males tended to have lower ventral scale counts when incubated with other males. Conversely, females tended to have more ventral scales when incubated with other females, indicative of a more feminised phenotype. There was also a significant interaction between hatchling sex and incubation environment with respect to the length of the fourth digit of the hindlimb, likely indicative of masculinisation in heterosex females. This study suggests steroid diffusion between adjacent eggs in a minimally manipulative experiment and provides the first evidence for developmental effects of the exogenous hormonal environment in near natural conditions in an oviparous amniote. Implications of these results for the evolution of within-clutch sex ratio are discussed.     

Ornamental colors reveal age in the king penguin

We investigated whether delayed plumage maturation occurred in king penguins (Aptenodytes patagonicus). Therefore we examined the relationships between age and sex on spectral properties and size of two colored plumage patches and a UV-reflective beak spot, using known-age cohorts. Unlike the colored patch on the breast, we found age differences in ear and beak coloration. These results suggest that head ornaments in king penguins could signal sexual maturity or social status. No sex differences were found in the intensity of colored ornaments, which can result from mutual mate choice or genetic correlation between sexes. Size of colored patches did not relate to age or sex.     

Female mating behavior in the field cricket,Gryllus pennsylvanicus (Orthoptera: Gryllidae) at different operational sex ratios

The influence of operational sex ratio on the mating behavior of female field crickets,Gryllus pennsylvanicus, was investigated. Females were predicted to be more discriminating under conditions of high mate availability and show less selectivity when males were rare. Such selectivity was indicated in this study with the proportion of courtships leading to a mating changing with sex ratio. Females accepted almost 70% of all courtships at the female-biased sex ratio, but only about half of all courtships were successful at even or male-biased sex ratios. Females moved least at the female-biased sex ratio. There was also a trend for females to be guarded more under male-biased conditions. Female weight did not influence any of the behaviors examined.     

Occurrence and detection of early sex-related differences inTelfairia occidentalis

The present study sought to assess the occurrence and early detection of sex-related differences for yielding ability inTelfairia occidentalis, using half-sib progenies from six diverse sources. Male plants flowered at 86 days after planting, 32 days earlier than females. Sex-related differences explained 12–43% of observed phenotypic variation for the measures of vegetable yielding ability. The strongest linkage with sex was observed for the size of the vine shoots harvested, with the effect of sex estimated at 1.29 standard deviations. There was, however, a significant heterogeneity in sex-related differences across families. Size per vine shoot and leaf yield per harvest showed early occurrence of sexual dimorphism, with sex-related differences occurring as early as 64 days after planting for size of vine shoots.     

The reproductive behavior of six species of Namib desert tenebrionid beetles (Coleoptera: Tenebrionidae)

The reproductive behavior of six species of tenebrionid beetles (Coleoptera: Tenebrionidae) was studied in the Namib Desert of southern Africa. In three species, males follow closely behind females (following behavior), while in the other three species, males mount females and remain clasped to them for extended periods (riding behavior). Following behavior occurs before and sometimes after copulation, while riding behavior occurs primarily after copulation. Males of all six species guard females from contesting males, although the effectiveness of guarding is greater in riding species. The evolution of the two male mating strategies does not appear to be related to operational sex ratio differences but, rather, to differential tendencies of females to remate. Variation in total pair duration within following and riding species may be attributed partly to species differences in operational sex ratio. However, pair durations are not affected by experimental manipulations of sex ratio in each species.     

Development of partner preferences in Japanese Macaques (Macaca fuscata): Effects of gender and kinship during the second year of life

Quantitative data are presented on the effects of subject sex, partner sex,and kinship on the social interactions of 18 juveniles of the Oregon troop of Japanese macaques (Macaca fuscata).Data on these subjects as infants were also used to detail maturational changes in partner sex preferences. Nine males and nine females, whose multiparous mothers represented a cross section of dominance ranks, were observed using a focal-animal technique. Juveniles of both sexes engaged in more proximity, contact, grooming, mounting, aggression, and social play with kin than with nonkin partners. They initiated less contact with females and more contact with males during their second year. They initiated more grooming and aggression during their second year than their first year, with females displaying a strong preference for grooming females and males specifically aggressing males more during the second year. Aggression was higher between same-sexed partners than between opposite-sexed partners. Males engaged in more social interactions with males during the second year than the first year of life. Males played more than females during both years. Males played more with males during the second year than the first year, and males played with males more than did females during the second year. We conclude that sex differences in behavioral frequencies become evident during the first year of life, and sex differences in partner preferences emerge during the second year of life.     

Sex ratio from germination through maturity and its reproductive consequences in the liverwort Sphaerocarpos texanus

Summary The dioecious winter ephemeral liverwort, Sphaerocarpos texanus disperses spore tetrads consisting of two males and two females. I examined the subsequent sex ratio of S. texanus at different stages in its life cycle to detect possible mechanisms affecting deviations from a 1:1 sex ratio and the effect of sex ratio on reproductive success. As S. texanus occurs in pure male, pure female and mixed sex clumps, I examined the proportions and sizes of these, the reproductive success of pure female and mixed sex clumps in the field and the sex ratio of germinating plants in a growth chamber. In both the field and the growth chamber the most abundant clump type was pure female followed by mixed sex and pure male clumps. These abundance patterns suggest that males have a lower survival rate than females before emergence and this lower survival rate continues through the gametophytic stage. This disadvantage may be due to the higher susceptibility of males to environmental conditions, to their competitive inferiority to females, and/or to differential resource allocation to the sexes within the spore tetrad. The female biased sex ratio at germination is consistent with predictions from sex ratio theory. Further my field data indicate that males may gain a survival benefit from growing in a mixed sex clump and both males and females benefit reproductively when they occur in mixed sex clumps.     

Larval sex identification in the paper wasp <Emphasis Type="Italic">Polistes dominulus</Emphasis> (Vespidae,Hymenoptera)

Identifying the sex of larvae is important in social Hymenoptera. Until now for Polistes wasps it has been necessary to genotype larvae at microsatellite loci, and assign their sex based on homozygosity at these loci. In our study on the paper wasp Polistes dominulus we have found morphological differences between larval sexes that can be used for larvae from the 3^rd instar on to easily and cheaply identify larval sex: the external gonopore and the shape and size of larval gonads. The robustness of these indicators was supported by genotype data at four microsatellite loci. Using gonopore and gonad features for sex assignment will assign diploid males as males, unlike techniques based on genetic loci or chromosomes. Received 12 July 2006; revised 4 January 2007; accepted 5 February 2007.     

Resource utilization and sex allocation in response to host size in two ectoparasitoid wasps on subcortical beetles

Patterns of host resource utilization and sex ratio manipulation in relation to host size were investigated for two solitary ectoparasitoid wasps,Atanycolus initiator andSpathius brevicaudis (Hymenoptera Braconidae). Both species parasitize subcortical beetles on the trunks of Japanese pine trees.A. initiator is on average 8 times larger in body weight and has an ovipositor that is 3.7 times longer than that ofS. brevicaudis. In both parasitoids, the size of emerging wasps was positively correlated with host size, but the host/wasp size regressions were linear for all three major host species inA. initiator, whereas inS. brevicaudis the regression was logarithmic for a relatively large host species. The sex ratios (proportion of males) of both parasitoids emerging from different host species decreased with increasing host size, but the overall sex ratio on each host species was male-biased inA. initiator, while female-biased inS. brevicaudis. How the proportion of host consumed changed in response to host size, differed between the two parasitoids for the same host species. In the field survey, the size and sex ratio of the emerging two parasitoids from a dead tree were closely related to host size. However, the spatial distribution of the two parasitoids depended on the bark thickness of the trunk. The data suggest that differences in the relative evaluation of host size and in ovipositor length may enable the coexistence of the two parasitoid wasps.     

Bi-directional sex change and gonad structure in the gobiid fish <Emphasis Type="Italic">Trimma yanagitai</Emphasis>

Bi-directional sex change in the deep-water gobiid fish Trimma yanagitai was examined. The gonads of all individuals consisted of ovarian and testicular elements, and an accessory gonadal structure. In no gonads were both testicular and ovarian parts simultaneously active. Bi-directional sex changes occurred during the rearing experiments in aquaria under conditions of which there was co-existence of two males or plural females. The sex of individuals could be determined by their relative body size or social dominance: the largest individuals acting as male and the remainder as female.     

Size-sex relationship and sexual dimorphism in JapaneseArisaema (Araceae)

The size-sex relationship and sexual differences of sixArisaema species native to Japan were investigated. The size-sex relationship showed almost the same pattern in all species. When the plant was small in size, the sex expression was male, and sex expression changed from male to female as the plant grew larger. Male ratios decreased rapidly around a critical size, but this critical size differed from one species to another. Sexual differences were detected in reproductive structures and behavior, although no difference was detected in vegetative structures. The stoutness, longevity and inner tissue of the scape showed remarkable differences between males and females, and this difference was represented most clearly as the size-weight relationship. Earlier initiation of flowering in males was also observed. No difference was found in resource allocation to reproductive structures between male and female plants at the flowering stage. However, a broad variation in the amount of resource allocation to reproductive structures was found at the fruiting stage in female individuals, which was attributed to differences in the setting rate of mature fruits.