Sexual dimorphism, sex ratio and spatial distribution of male and female shrubs in the dioecious speciesPistacia lentiscus L.

The population sex ratio, spatial distribution, relative growth rate, canopy size and morphology, and nitrogen content of leaves of male and female individuals were compared in seven populations of the dioecious shrubPistacia lentiscus L. occurring in different localities of the Serra da Arrábida Natural Park, Portugal. The expected pattern of male preponderance in stressful habitats was tested. Less perturbed areas, with a well developed vegetation cover, had male-biased sex ratios, while in former agricultural areas there were no significant differences between the number of male and female plants. Our results failed to reveal any significant differences in the morphological variables between sexes except in the number of basal stems. Male plants also had a significantly higher chlorophyll content (chl a+b) than female plants. But when plants were sorted into large and small individuals, larger plants showed a significantly higher leaf area index and a significantly higher number of basal stems. There were no significant differences in the leaf nitrogen content between male and female plants from June to August, but such differences appeared (P<0.001) in September and October corresponding to the production of mature fruits. Differences in sex-ratio may be explained by different resource allocation patterns of the two sexes, which favoured male plants in the less perturbed environments. In agricultural areas farmers could also have favoured female plants in former times.     

ISSR marker-assisted selection of male and female plants in a promising dioecious crop: jojoba (Simmondsia chinensis)

Simmondsia chinensis (Link) Schneider, a multipurpose and monogeneric dioecious shrub from arid zones, has emerged as a cash crop all over the globe. Its seed propagation poses severe problems due to its male-biased population: the male:female ratio is 5:1. Investigations have been carried out to generate a sex-specific Inter-simple sequence repeat (ISSR) marker for the early detection of male and female plants. Of the 42 primers analysed with a bulk sample of pooled male DNA and a bulk sample of pooled female DNA, only one primer, UBC-807, produced a unique ~1,200 base-pair fragment in the male DNA. To validate this observation, this primer was re-tested with individual male and female samples from eight cultivars. A similar unique ~1,200 bp fragment was present in the male individuals of all eight cultivars and completely absent in the female individuals tested. This is the first report of the use of ISSR markers to ascertain sex in physiologically mature S. chinensis plants.     

Sexual size dimorphism and male combat in snakes

Summary This paper reviews published literature on snakes to test the hypothesis that large male size, relative to female size, evolves because of the advantage it confers in male combat. Analysis of the data reveals a high correlation between the occurrence of male combat, and sexual dimorphism in which the male is the larger sex. This correlation holds (i) within the total sample of snake species (n=224), (ii) within the family Colubridae (n=134), and (iii) in a comparison between the eight families of snakes for which data are available. These results strongly support the hypothesis that large male size is an adaptation to intrasexual competition. The analysis also shows that females are larger than males in about 66% of snake species, that male combat is known in only about 15% of species, and that both sexual size dimorphism and the incidence of male combat tend to be distributed along taxonomic lines.     

Patterns of resource allocation in male and female plants of Rumex acetosa and R. acetosella

Summary Patterns of resource allocation in the dioecious Rumex acetosa and R. acetosella were investigated. Males were found to allocate more to reproduction during flower production than females, whereas females invested considerably more in reproduction during seed production. Altogether, females allocated both a higher total amount and a higher proportion of energy to reproduction than did males. By regression analysis, the influence of plant size on reproductive effort was examined separately for males and females. The results indicated that while reproductive effort is sometimes lower for tall plants than for small plants, size-independent effects have a greater influence on reproductive effort than size distribution. An analysis of variance was conducted to investigate the effects of population, season, sex and their interactions on plant size, and an analysis of covariance was used to study differences in resource allocation patterns. Different interaction effects were found to be most important in the two species of Rumex.     

Sexual size dimorphism and male contest in wild Siamese fighting fish

Larger males of the wild Siamese fighting fish Betta splendens were more successful in male contests. There were no differences in fighting duration among treatments. Comparing agonistic behaviour between large and small males in ±1 and ±2 S.D treatments, larger males attacked, chased and performed total agonistic behaviour more than smaller males. There were no differences between larger and smaller males concerning other agonistic behaviour during fighting. Females presented with two potential mates of different sizes did not prefer larger males.     

Size-dependent resource allocation among vegetative propagules and male and female functions in the forest herb Laportea bulbifera

Reproductive resource investment among vegetative propagules and male and female sexual function and their size-dependence were investigated in a perennial forest herb, Laportea bulbifera . A theoretical model based on fitness gain curves predicts that optimal investments in three reproductive modes will increase with plant size if fitness returns in all three modes increase but become saturated with investment. In a field population, large plants of L. bulbifera produced both male and female inflorescences with propagules, while small plants produced only vegetative propagules. Biomass of propagules, male inflorescences, and infructescences with achenes were all positively correlated with plant size. The increase in investment with plant size was larger for propagule production than for sexual reproduction. The relationship between propagule biomass and plant size was constant irrespective of year, while the relationship between the biomass of sexual reproductive organs and plant size differed between two successive years. Annual change of individual sex expression was investigated for 25 transplanted plants. Although each plant changed its sex expression variously among male, female and bisexual from year to year, 23 out of 25 plants produced both male and female inflorescences in at least one year. The number of viable (germinated and survived) offspring from seeds was not significantly different from the number from propagules. The production cost of a propagule was higher than that of a seed. Resource allocation theory does not seem to be applicable to size-dependent resource allocation, especially the allocation between seeds and propagules in this species.     

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.     

青海沙蜥的两性异型和雌性繁殖

作者研究了青海沙蜥(Phrynocephalus vlangalii)形态特征的两性异形和雌体繁殖特征。蜥蜴于2005年5月初捕自西宁以西约150km的倒淌河,被检形态特征包括体色、体长、腹长、尾长、头长和头宽,新排卵雌体维持在实验室梯度热环境中直至产仔。成体两性异形显著,而性未成熟个体缺乏两性异形。最大的成年雄体和雌体分别为70.2mmSVL(snout-vent length)和82.8mmSVL。雄性成体具有相对较大的头长、头宽和尾长,雌性成体SVL大于雄体且具有相对较大的腹长。对4个形态特征进行主成分分析(特征值≥0.5)区分出2个主成分,共解释83.9%的两性相关形态特征的变异。去除SVL差异的影响后,尾长、头长和头宽在第一主成分有较高的正负载系数(解释57.8%的变异),腹长在第二主成分有较高的负负载系数(解释26.1%的变异)。实验室梯度热环境下的雌体于6月下旬至7月中旬产单窝、2-6个后代。窝仔数和窝仔重与母体SVL呈正相关,幼仔重与母体SVL无关。未在青海沙蜥中检测到后代数量与大小之间的权衡。     

Mating frequency and resource allocation to male and female function in the simultaneous hermaphrodite land snail Arianta arbustorum

Sex allocation theory predicts that mating frequency and long‐term sperm storage affect the relative allocation to male and female function in simultaneous hermaphrodites. We examined the effect of mating frequency on male and female reproductive output (number of sperm delivered and eggs deposited) and on the resources allocated to the male and female function (dry mass, nitrogen and carbon contents of spermatophores and eggs) in individuals of the simultaneous hermaphrodite land snail Arianta arbustorum. Similar numbers of sperm were delivered in successive copulations. Consequently, the total number of sperm transferred increased with increasing number of copulations. In contrast, the total number of eggs produced was not influenced by the number of copulations. Energy allocation to gamete production expressed as dry mass, nitrogen or carbon content was highly female‐biased (>95% in all estimates). With increasing number of copulations the relative nitrogen allocation to the male function increased from 1.7% (one copulation) to 4.7% (three copulations), but the overall reproductive allocation remained highly female‐biased. At the individual level, we did not find any trade‐off between male and female reproductive function. In contrast, there was a significant positive correlation between the resources allocated to the male and female function. Snails that delivered many sperm also produced a large number of eggs. This finding contradicts current theory of sex allocation in simultaneous hermaphrodites.     

Sexual dimorphism of heads and abdomens: Different approaches to ‘being large’ in female and male lizards

Sexual‐size dimorphism (SSD) is widespread in animals. Body length is the most common trait used in the study of SSD in reptiles. However, body length combines lengths of different body parts, notably heads and abdomens. Focusing on body length ignores possible differential selection pressures on such body parts. We collected the head and abdomen lengths of 610 lizard species (Reptilia: Squamata: Sauria). Across species, males have relatively larger heads, whereas females have relatively larger abdomens. This consistent difference points to body length being an imperfect measure of lizard SSD because it comprises both abdomen and head lengths, which often differ between the sexes. We infer that female lizards of many species are under fecundity selection to increase abdomen size, consequently enhancing their reproductive output (enlarging either clutch or offspring size). In support of this, abdomens of lizards laying large clutches are longer than those of lizards with small clutches. In some analyses, viviparous lizards have longer abdomens than oviparous lizards with similar head lengths. Our data also suggest that male lizards are under sexual selection to increase head size, which is positively related to winning male–male combats and to faster grasping of females. Thus, larger heads could translate into higher probability to mate. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 665–673.     

Sexual dimorphism in proconsul

One of the more important sources of variability in primate species is sexual dimorphism. Most Primates heavier than five kilos bodyweight are sexually dimorphic, both in body size and in shape of certain hard tissues. Despite these facts, most of the fossil Primates from East African Miocene deposits were originally perceived as being monomorphic, a perception which has propogated through the literature. Re-examination ofProconsul from various sites in Western Kenya results in the view that it was as dimorphic in its splanchonocranium and in bodyweight as chimpanzees and gorillas. The clearest evidence comes from Rusing Island, where adequate samples are known of two morphs, traditionally identified as two species, but more likely to represent two sexes of a single species,P. nyanzae. Co-occurrence of the two morphs is 100% at the various Rusinga sites. Less complete samples have been collected from the Tinderet sites os Koru and Songhor, yet what is available shows that similar patterns of dimorphism characterise the speciesP. africanus andP. major, and that the co-occurrence of the two morphs in each species is 100%. The identification of fossils taking into consideration the role of sexual dimorphism clarifies many of the old debates in which individual specimens frequently shifted between different species, mainly on the basis of metric rather than morphologic evidence. Consequently, the distribution of the species ofProconsul is rather different after accounting for dimorphism, than it was before.     

Sexual and male horn dimorphism in Copris ochus (Coleoptera: Scarabaeidae)

Copris ochus (Coleoptera: Scarabaeidae), an endangered species, is the largest dung beetle in Japan. In C. ochus, males have a long head horn, while females lack this long horn (sexual dimorphism). Very large males of C. ochus have disproportionately longer head horns than small males, suggesting male horn dimorphism, although the dimorphism has not been investigated quantitatively. To clarify sexual and male horn dimorphism in C. ochus quantitatively, we examined the scaling relationship between body size (prothorax width) and head horn length in 94 females and 76 males. These beetles were captured during July 1978 from a natural population on Mt. Aso in southwestern Japan using a light trap. Although the horn length of the females and males scaled with prothorax width, the scaling relationship differed between the sexes, i.e., the relationship was linear in females and nonlinear in males. Statistical tests for dimorphism in male horn length showed a significant discontinuous relationship, thus indicating distinct sexual and male dimorphism in head horns. Long- and short-horned C. ochus males may have different reproductive behaviors, as described in other horned dung beetles.     

昆虫的雌雄二型现象

对发生雌雄二型现象的昆虫类群、生态因子及进化进行了概括总结;还特别介绍了长足虻科昆虫雌雄二型的相关方面;并简要讨论了雌雄二型与性选择的关系。     

Chemical components of male and female flowers of Schisandra chinensis

Schisandra chinensis (Turcz.) Baill. is one of the important traditional medicinal plants in East Asia. It is a dioecious plant with aromatic flowers. The female and male flowers of S. chinensis possess slightly different fragrance characteristics. The overall scent of S. chinensis flowers is quite similar to that of Syringa dilatata (Korean lilac) flowers. Hence, this study aimed to understand the aromatic profile of the hexane extract from female and male flowers of S. chinensis and to compare their profile with the hexane extract of Korean lilac flowers. The chemical composition of hexane extract was determined by gas chromatography and mass spectrometry (GC-MS) analysis. In total, 67 different components were detected in the hexane extract of female (48) and male flowers (51) of S. chinensis; 32 of which were common to both female and male flowers. In regards to gender difference, 16 components were found only in female flowers, and 19 components were found only in male flowers. The results revealed that the most abundant components in the hexane extract of both female and male flowers were lilac alcohol C (9.53 and 7.00%), lilac alcohol A (6.55 and 5.71%), n-hexadecanoic acid (6.21 and 6.96%), linoleic acid (5.14 and 7.61%), β-elemene (5.12 and 1.99), and lilac aldehyde D (4.13 and 4.97%). The data suggest that the major compounds in the hexane extract of S. chinensis flowers were generally similar, but they varied quantitatively according to gender. The presence of 10 components in both S. chinensis and Korean lilac flowers may be responsible for their similar fragrance characteristics. It could be concluded that the different fragrance characteristics of these flowers may be due to the presence of several gender-specific aromatic compounds in minor percentages.     

Genetic association between male attractiveness and female differential allocation

Differential allocation of reproductive effort towards offspring of attractive mates is a form of post-copulatory mate choice. Although differential allocation has been demonstrated in many taxa, its evolutionary implications have received little attention. Theory predicts that mate choice will lead to a positive genetic correlation between female preference and male attractiveness. This prediction has been upheld for pre-copulatory mate choice, but whether such a relationship between male attractiveness and female differential allocation exists has never been tested. Here, we show that both female pre-copulatory mate choice and post-copulatory differential allocation are genetically associated with male attractiveness in house crickets, Acheta domesticus. Daughters of attractive males mated sooner and laid more eggs when paired with larger males. These forms of mate choice are strongest in large females, suggesting that costs decrease with increasing female size. The genetic association between attractiveness and differential allocation suggests potential for differential allocation to become exaggerated by coevolutionary runaway processes in an analogous manner to pre-copulatory choice. Sexual selection is thus likely to be stronger than predicted by pre-copulatory choice alone.     

密点麻蜥的两性异形和雌性繁殖

蜥蜴繁殖成功率与其形态特征有密切的关系。作者在内蒙古乌拉特后旗采集密点麻蜥(Eremias multio-cellata) ,定量研究该种形态特征的两性异形和雌体繁殖特征,检验与成体形态特征相关的两性繁殖成功率差异是否能促进两性异形的进化。密点麻蜥成体个体大小无显著的两性差异,但头部大小两性差异显著;雄性个体的头长和头宽均大于体长相同的雌性成体。繁殖雌体于五、六月份排卵;在实验室条件下,雌体在六月下旬至七月下旬之间产仔。该种雌体年产单窝仔,每窝2 -4仔。窝仔重与雌体体长呈正相关,但雌体体长仅能解释很少一部分(约19 %)窝仔重的变异。窝仔数和幼仔重均与雌体体长无关。幼仔重与相对生育力(相对于雌体体长的窝仔数)呈显著的负相关,表明该种蜥蜴存在后代数量-大小之间的权衡。密点麻蜥雄体和雌体向较大体型方向进化的选择压力均相对较弱,与成体头部大小相关的两性繁殖成功率的差异是导致该种蜥蜴头部大小两性异形进化的主要原因[动物学报52 (2) : 250 -255 , 2006]。     

Influence of certain environmental factors on photosynthesis and photorespiration in Simmondsia chinensis

The response of net photosynthesis and apparent light respiration to changes in [O₂], light intensity, and drought stress was determined by analysis of net photosynthetic CO₂ response curves. Low [O₂] treatment resulted in a large reduction in the rate of photorespiratory CO₂ evolution. Lightintensity levels influenced the maximum net photosynthetic rate at saturating [CO₂]. These results indicate that [CO₂], [O₂] and light intensity affect the levels of substrates involved in the enzymatic reactions of photosynthesis and photorespiration. Intracellular resistance to CO₂ uptake decreased in low [O₂] and increased at low leaf water potentials. This response reflects changes in the efficiency with which photosynthetic and photorespiratory substrates are formed and utilized. Water stress had no effect on the CO₂ compensation point or the [CO₂] at which net photosynthesis began to saturate at high light intensity. The relationship between these data and recently published in-vitro kinetic measurements with ribulose-diphosphate carboxylase is discussed.Abbreviations C _w intracellular CO₂ concentration - F _gross gross photosynthesis - F _net net photosynthesis - I light intensity - R _L light respiration rate - r _c carboxylation resistance - r ₈ leaf gas-phase resistance - r _i intracellular resistance; to CO₂ uptake - r _t resistance to CO₂ flux between the intercellular spaces and the carboxylation sites - T _L leaf temperature - _t leaf water potential - CO₂ compensation point