Reproduction,predation, sexual dimorphism and diet in Agama anchietae (Reptilia: Agamidae) from Namibia

Agama anchietae is one of eight species of agama found in Namibia, its distribution range in the upper half of the country covers desert, Karoo and savannah type biomes and overlaps with that of some of its congeners. Here, we describe its sexual dimorphism, reproductive traits, predation, diet and nematode infection, and compare and contrast each aspect among the three biomes as well as to published findings for three other Namibian congenerics, Agama etoshae, Agama aculeata aculeata and Agama planiceps planiceps. Interesting similarities and differences were found among the biomes as well as with the three congenerics. Our hypothesis that the aspects studied in A. anchietae would be more in line with those of A. a. aculeata and A. etoshae, with which it shares similarities in body colouration, social organisation and microhabitat utilisation, was only partially confirmed. This cautions against using morphological and ecological similarities between agamas as proxies for making life-history strategy inferences.     

Some new African Milichiidae (Diptera: Cyclorrhapha) having pronounced sexual dimorphism of the frons

Enigmilkhia dimorphka gen. et sp. nov. and Milkhia distinctipennis, fumicoslata, savannaticola and sylvicola spp. nov. are described from tropical Africa. These forms, though belonging to different subfamilies, exhibit a very similar sexual dimorphism in the shape and chaetotaxy of the frons. Such a dimorphism is unknown within the Milichioidea.     

The ontogeny of sexual dimorphism in the African apes

The relationship between the growth spurt and the onset of sexual maturity is problematic in nonhuman primates. Growth data on the cranium and postcranium of dentally aged pygmy chimpanzees, common chimpanzees, and gorillas are reported here. In all three species, male means generally exceed female means throughout growth, with the exception that females exhibit a spurt during one dental-age stage when they become generally larger than the males. This female spurt occurs earlier in an absolute and relative sense in the gorillas than the chimpanzees. These growth data support field and laboratory observations suggesting that female gorillas become sexually mature earlier than do female chimpanzees. Gorillas are thus characterized by a greater degree of “sexual bimaturism” than are the chimpanzees. Implications of these differences in terms of size dimorphism, mating systems, and morphology are discussed.     

浙江丽水中国石龙子的食性、两性异形和雌性繁殖

丽水分布的中国石龙子（Ｅｕｍｅｃｅｓ ｃｈｉｎｅｎｓｉｓ）摄入的食物均为无脊椎动物,分别属于环节、软体和节肢动物,涉及３０余科,成体和幼体的食物生态位宽度分别为７．２６和６．６９,成体的幼体的食物生态们重叠度为０．５９。性成熟雄性个体大于雌体。成雄和幼体的头长和头宽随体长ＳＶＬ的增长速率大于成雌,成雄头长随ＳＶＬ的增长速度显著大于幼体,成雌和幼体的头长随ＳＶＬ的增长速率无显著差异。成雄头部大于成雌     

Differential sexual dimorphism in bone diameters of subjects of European and African ancestry

The 1,589 low-income adult subjects of primarily African ancestry (American Negroes or “Blacks”) showed systematically less sexual dimorphism in total subperiosteal area (TA), medullary area (MA) and cortical area (CA) than did 4,379 low-income adult subjects of European derivation (“Whites”). These systematic findings have implications both to the sexing of skeletal remains from diverse populations and to an understanding of population divergences in bone remodeling.     

Reproduction and growth in three species of West African fruit bats

This study outlines the reproduction periods of the African fruit bats Epomops buettikoferi, Epomophorus garnbianus , and Micropteropus pusillus at two West African savanna sites: a wet southern Guinea savanna and a drier southern Sudanese savanna. At both sites the two annual birth periods were timed such that both lactation by only one weaning period coincided with the rainy season peaks in fruit availability. On this basis we propose that lactation rather than weaning was the important determinant of the timing of reproduction. There was no evidence of cycling of testes size in males corresponding with the seasonal mating periods. E. buettikoferi and M. pusillus females mated at six months and gave birth at the age of 12 months. Males of the two species reached puberty by 11 months and seven months, respectively. Growth rates did not differ between cohorts growing through the wet and dry season and E. buettikoferi and M. pusillus grew at rates of 276 mg/day and 116 mg/day, respectively.     

Costs of reproduction in Nyssa sylvatica: sexual dimorphism in reproductive frequency and nutrient flux

Summary We examined the influence of differential reproductive frequency between the sexes on tertiary (phenotypic) sex ratios in the the dioecious tree Nyssa sylvatica (Nyssaceae). Reproduction was evaluated in relation to sex, size and canopy exposure using flowering data collected from 1229 marked trees over a four year period. For subsets of each population we used data on flower number, fruit crop size, fruit/flower ratios, and individual flower and fruit mass to compare biomass invested in reproductive structures of males and females. We also examined seasonal changes in stem nitrogen and soluble carbohydrate content in relation to flower and fruit production for trees of each sex. Our results indicate that: 1) Male-biased tertiary sex ratios could be explained by more frequent reproduction by male trees; 2) Estimated secondary sex ratios based on sums of all known males and females were not significantly different from 1:1; 3) Flowering frequency of males and females was significantly related to plant size (DBH) and exposure of the canopy to light; 4) Estimtes of reproductive biomass allocation ranged from 1.36 to 10.8 times greater for females relative to males; 5) Flower production was related to stem nutrient status for both sexes, but nutrient depletion and its effect on subsequent flowering was much more pronounced for female trees. We conclude that less frequent flowering by female trees may result from depletion of stored reserves, and that differential flowering frequency in N. sylvatica may ultimately reduce apparent sexual differences in the costs of reproduction.     

Testosterone,growth and the evolution of sexual size dimorphism

The integration of macroevolutionary pattern with developmental mechanism presents an outstanding challenge for studies of phenotypic evolution. Here, we use a combination of experimental and comparative data to test whether evolutionary shifts in the direction of sexual size dimorphism (SSD) correspond to underlying changes in the endocrine regulation of growth. First, we combine captive breeding studies with mark‐recapture data to show that male‐biased SSD develops in the brown anole lizard (Anolis sagrei) because males grow significantly faster than females as juveniles and adults. We then use castration surgeries and testosterone implants to show that castration inhibits, and testosterone stimulates, male growth. We conclude by reviewing published testosterone manipulations in other squamate reptiles in the context of evolutionary patterns in SSD. Collectively, these studies reveal that the evolution of SSD has been accompanied by underlying changes in the effect of testosterone on male growth, potentially facilitating the rapid evolution of SSD.     

Sexual selection,sexual dimorphism and plant phylogeny

Summary Darwin examined sexual dimorphism in animals, arguing that sexual selection was important in the evolution of such dimorphism. Sexual dimorphism in plants may have parallel causes and costs.The processes that contribute to sexual dimorphism may also lead to speciation and morphological differences among related species, as argued originally by Darwin. Where sexes are separate and dimorphism is well-developed, males of related animal species (both vertebrate and invertebrate) are often strikingly different from each other, while females may be virtually indistinguishable. A similar pattern may exist in plants: it is frequently the males (of dioecious taxa) or the male portions of the flower (in co-sexual flowers) that apparently have diversified. I suggest that the similarity of pattern may be accounted for by a similarity of process.In addition, sexual selection may have contributed to certain evolutionary trends within the angiosperms and, indeed, to angiosperm radiation.     

Precopulatory mating behavior and sexual dimorphism in the amphipod Crustacea

Accounts in the literature of precopulatory mate-guarding in gammaridean amphipods are that males use one of two strategies for mating: either they mate-guard by carrying or attending their mates until they are ready to molt and be fertilized, or they do not guard, instead searching benthically or swarming pelagically at the time that females are ready to molt. Mate-guarding by carrying has been documented for species of the superfamilies Gammaroidea, Talitroidea, and Hadzioidea. Mate-guarding by attending has been found in the more sedentary Corophioidea and Caprellidea. Non-mate-guarders that search pelagically are species of Ampeliscoidea, Lysianassoidea, Phoxocephaloidea, Oedicerotoidea, and Pontoporeioidea. Non-mate-guarders that mate-search benthically are species of Eusiroidea, Crangonyctoidea, and Haustorioidea. Mate-guarding and non-mate-guarding males develop different secondary sex characters at maturity. Mate-guarding males have enhancements for fighting and signalling. These alterations are more elaborate in males that attend their mates than in males that carry their mates. Non-mate-guarders that search pelagically develop enhancements for swimming and sensing. Non-mate-guarders that remain benthic exhibit little change at maturity. Most mate-guarding males develop their secondary sexual characters over several molts and mate over more than one instar. Pelagic mate-searchers develop their secondary sexual characters at the last molt and mating is confined to the last instar. Females of most mate-guarding species are iteroparous, while fewer than half of non-mate-guarding species are so. It is hypothesized that mate-guarding arose more than once in the evolutionary history of amphipod Crustacea.     

Population variation in sexual dimorphism in the human innominate

In the adult human innominate, pubis length and sciatic notch width are generally considered to offer the best prospect for reliable sex identification. Population variation in the extent of sexual dimorphism in these features was examined in two temporally distinct European skeletal collections of documented age and sex. (English and Dutch). A complex relationship was found to exist between pubis length and sciatic notch width with body size; these relationships differed both between the sexes and between the groups. Caution is therefore urged in the use of both metric and non-metric standards derived from one population and subsequently applied to other populations of differing origin.     

Gamete production and sexual size dimorphism in an insect (Orchesella cincta) with indeterminate growth

Abstract 1. The relationship of growth and body size with reproductive effort in animal species has been studied much less for males than for females. This imbalance applies to Orchesella cincta (L.) (Collembola), an insect with indeterminate growth, in which egg production is related positively to body size and negatively to growth.
2. To allow a comparison of the reproductive effort of male and female O. cincta , development and growth in immature stages of both sexes, and growth and spermatophore production for adult males were studied.
3. Embryonic development time and hatchling size did not differ between prospective males and females, but from hatching on the trajectories diverged, with males growing more slowly and maturing earlier and at a much smaller body size than females.
4. Neither the number of spermatophores deposited in the first adult instar (= inter-moult period) nor the total number of spermatophores deposited during seven instars was related to body size or growth.
5. Differences in growth rate between instars with and without spermatophore deposition indicated that the physiology of spermatophore production inhibits growth, which, however, was compensated for during the next instar.
6. The difference in the relationship of gamete production with body size and growth between males and females explains the divergence of their size at maturity.     

Environmental enrichment,sexual dimorphism,and brain size in sticklebacks

Evidence for phenotypic plasticity in brain size and the size of different brain parts is widespread, but experimental investigations into this effect remain scarce and are usually conducted using individuals from a single population. As the costs and benefits of plasticity may differ among populations, the extent of brain plasticity may also differ from one population to another. In a common garden experiment conducted with three‐spined sticklebacks (Gasterosteus aculeatus) originating from four different populations, we investigated whether environmental enrichment (aquaria provided with structural complexity) caused an increase in the brain size or size of different brain parts compared to controls (bare aquaria). We found no evidence for a positive effect of environmental enrichment on brain size or size of different brain parts in either of the sexes in any of the populations. However, in all populations, males had larger brains than females, and the degree of sexual size dimorphism (SSD) in relative brain size ranged from 5.1 to 11.6% across the populations. Evidence was also found for genetically based differences in relative brain size among populations, as well as for plasticity in the size of different brain parts, as evidenced by consistent size differences among replicate blocks that differed in their temperature.     

Sexual dimorphism in human skulls. A comparison of sexual dimorphism in different populations

Application and comparison of sex discriminant functions in different populations led to the conclusion that a certain combination and weighting of a few sex dimorphism variables (in this study we only used craniometric variables) can give a good discrimination between male and female individuals, independent of the racial group to which this function is applied. In our study, the sex-discriminatory power of five discriminant functions which were based on different ordination and selection procedures (e.g. professional knowledge, stepwise discriminant analysis, literature) of the cranial variables is compared. These discriminant functions were applied to three different data sets, the first being skull measurements from an Amsterdam series (Europids), the second skull measurements of a Zulu series (Negrids) and the third skull measurements of a Japan series (Mongolids). Our decision as to whether a function is a good or less good sex-discriminating function is determined by the Dt values (these values give an idea about the discriminatory value of the discriminant function when applied to a new test sample), the number of variables necessary to obtain this Dt and the location of the sectioning point (i.e. comparison between the estimation of the sectioning point and the ”real” sectioning point). These discriminant functions were compared withGiles Elliot's (1962, 1963) “race-independent” sex function.     

Craniofacial sexual dimorphism in Alouatta palliata, the mantled howling monkey

Ontogenetic scaling has been hailed as an explanation of the differences in craniofacial morphology between adult males and females of a number of non human primate species. This inference has implications for the evolutionary processes underlying patterns of sexual variation, as several heterochronic processes (rate and time hypo- and hypermorphosis) predict ontogenetic scaling. Primary among species for which ontogenetic scaling of craniofacial dimensions has been claimed is Alouatta palliata , the mantled howling monkey. This study uses a variety of analytical tools to explore the efficacy of ontogenetic scaling as an explanatory paradigm for this classic example. Multivariate analysis captures shape far better than does bivariate analysis. However, multivariate analysis does not support the traditional inference of ontogenetic scaling. Explanations for contradictory results are considered.     

Ecological selection and sexual dimorphism in the sooty oystercatcher,Haematopus fuliginosus

Male and female sooty oystercatchers (subspecies Haematopus fuliginosus fuliginosus; Haematopodidae) have an average difference in bill length of 19%. We studied the relationship between this sexual dimorphism and foraging ecology at coastal sites in southern New South Wales, Australia. Intersexual foraging divergence was most striking in diet, with seven prey classes eaten exclusively by one sex (male: 4, female: 3), and all shared prey classes eaten in different proportions. Intersexual diet partitioning was also observed in energetic rewards gained from foraging, with females gaining highest energetic benefits from eating ascidians and males from eating limpets. Furthermore, within the most commonly consumed prey item, limpets, females gained higher energetic benefit from eating smaller sizes while males gained greater rewards from the largest limpet sizes. Intersexual divergence was also observed in several aspects of foraging behaviour. Finally, there was a significant effect of tidal cycles upon intersexual niche partitioning in this species; the degree of diet divergence varied between tide conditions and females had a consistently more efficient dietary intake on neap tides than males. Diet divergence in the sooty oystercatcher is greater than previously observed in any oystercatcher, and is correlated with the largest sexual bill dimorphism recorded in this family. It is argued that intersexual competition between territorial pairs is operating to diverge male and female bill morphology.     

Directional changes in sexual size dimorphism in shorebirds, gulls and alcids

The Charadrii (shorebirds, gulls and alcids) are one of the most diverse avian groups from the point of view of sexual size dimorphism, exhibiting extremes in both male-biased and female-biased dimorphism, as well as monomorphism. In this study we use phylogenetic comparative analyses to investigate how size dimorphism has changed over evolutionary time, distinguishing between changes that have occurred in females and in males. Independent contrasts analyses show that both body mass and wing length have been more variable in males than in females. Directional analyses show that male-biased dimorphism has increased after inferred transitions towards more polygynous mating systems. There have been analogous increases in female-biased dimorphism after transitions towards more socially polyandrous mating systems. Changes in dimorphism in both directions are attributable to male body size changing more than female body size. We suggest that this might be because females are under stronger natural selection constraints related to fecundity. Taken together, our results suggest that the observed variation in dimorphism of Charadrii can be best explained by male body size responding more sensitively to variable sexual selection than female body size.