DISTRIBUTION OF TRABECULAE AND ELYTRAL SURFACE STRUCTURES OF THE HORNED BEETLE, ALLOMYRINA DICHOTOMA (LINNÉ) (COLEOPTERA: SCARABAEIDAE)

Abstract To clarify the dynamic construction of Allomyrina dichotoma (Linné) elytra, the distribution of trabeculae and surface structures has been investigated using scanning electron microscopy and transmitted light. There are solid trabeculae in the elytron and under penetrating light these can be seen as black dots. It is clear that trabeculae arrangement is almost entirely irregular throughout the elytron, except for some approximately straight alignment near some trachea. This irregular arrangement is different from the longitudinal rows of striations that are well known in other species, and there are no hollowed striae (punctures) on the elytral surface of A. dichotoma . Throughout the internal architecture of the elytron, there are mesh-like (honeycomb) structures. Each honeycomb usually has 1–2 trabeculae mainly distributed at the corners of the honeycomb. The number of trabeculae present on each honeycomb is dependent on the size of the honeycomb.     

THE EVOLUTION OF FEMALE-BIASED SEXUAL SIZE DIMORPHISM: A POPULATION-LEVEL COMPARATIVE STUDY IN HORNED LIZARDS (PHRYNOSOMA)

Female-biased sexual size dimorphism is uncommon among vertebrates and traditionally has been attributed to asymmetric selective pressures favoring large fecund females (the fecundity-advantage hypothesis) and/or small mobile males (the small-male advantage hypothesis). I use a phylogenetically based comparative method to address these hypotheses for the evolution and maintenance of sexual size dimorphism among populations of three closely related lizard species (Phrynosoma douglasi, P. ditmarsi, and P. hernandezi). With independent contrasts I estimate evolutionary correlations among female body size, male body size, and sexual size dimorphism (SSD) to determine whether males have become small, females have become large, or both sexes have diverged concurrently in body size during the evolutionary Xhistory of this group. Population differences in degree of SSD are inversely correlated with average male body size, but are not correlated with average female body size. Thus, variation in SSD among populations has occurred predominantly through changes in male size, suggesting that selective pressures on small males may affect degree of SSD in this group. I explore three possible evolutionary mechanisms by which the mean male body size in a population could evolve: changes in size at maturity, changes in the variance of male body sizes, and changes in skewness of male body size distributions. Comparative analyses indicate that population differentiation in male body size is achieved by changes in male size at maturity, without changes in the variance or skewness of male and female size distributions. This study demonstrates the potential of comparative methods at lower taxonomic levels (among populations and closely related species) for studying microevolutionary processes that underlie population differentiation.     

INSECTARY STUDIES ON THE CONTROL OF DUNG BREEDING FLIES BY THE ACTIVITY OF THE DUNG BEETLE, ONTHOPHAGUS GAZELLA F. (COLEOPTERA: SCARABAEINAE)

i
The Afro-Asian dung beetle, Onthophagus gazella F., buries bovine dung as food for its larvae so rapidly that when beetle populations are of the order of 4 insects per 100 c.c. dung, entire cow pads are completely broken up and buried within 30 to 40 hours.
Insectary studies show that this rate of dung disposal caused 80 to 100 per cent. reduction in the numbers of the bushfly Musca vetustissima Walker emerging from the pads. Surviving maggots gave rise to small, stunted flies of low or nil reproductive capacity. Viable fly eggs or maggots were never found in brood balls, and it is presumed that they were destroyed in the course of the elaborate process by which the beetles convert lumps of dung into brood balls.
Speed of dung burial is the critical factor in fly control. If half of a cow pad is buried within the first 24 hours, few or no adult flies emerge. More rapid burial within this period resulting in the complete removal of the cow pad, produces complete fly control.     

SEXUAL SIZE DIMORPHISM AS A CORRELATED RESPONSE TO SELECTION ON BODY SIZE: AN EMPIRICAL TEST OF THE QUANTITATIVE GENETIC MODEL

We artificially selected for body size in Drosophila melanogaster to test Lande's quantitative genetic model for the evolution of sexual size dimorphism. Thorax width was used as an estimator of body size. Selection was maintained for 21 generations in both directions on males only, females only, or both sexes simultaneously. The correlated response of sexual size dimorphism in each selection regime was compared to the response predicted by four variants of the model, each of which differed only in assumptions about input parameters. Body size responded well to selection, but the correlated response of sexual size dimorphism was weaker than that predicted by any of the variants. Dimorphism decreased in most selection lines, contrary to the model predictions. We suggest that selection on body size acts primarily on growth trajectories. Changes in dimorphism are caused by the fact that male and female growth trajectories are not parallel and termination of growth at different points along the curves results in dimorphism levels that are difficult to predict without detailed knowledge of growth parameters. This may also explain many of the inconsistent results in dimorphism changes seen in earlier selection experiments.     

BODY SIZE AND SEXUAL SIZE DIMORPHISM IN MARINE IGUANAS FLUCTUATE AS A RESULT OF OPPOSING NATURAL AND SEXUAL SELECTION: AN ISLAND COMPARISON

Body size is often assumed to represent the outcome of conflicting selection pressures of natural and sexual selection. Marine iguana (Amblyrhynchus cristatus) populations in the Galápagos exhibit 10-fold differences in body mass between island populations. There is also strong sexual size dimorphism, with males being about twice as heavy as females. To understand the evolutionary processes shaping body size in marine iguanas, we analyzed the selection differentials on body size in two island populations (max. male mass 900 g in Genovesa, 3500 g in Santa Fé). Factors that usually confound any evolutionary analysis of body sizes—predation, interspecific food competition, reproductive role division—are ruled out for marine iguanas. We show that, above hatchlings, mortality rates increased with body size in both sexes to the same extent. This effect was independent of individual age. The largest animals (males) of each island were the first to die once environmental conditions deteriorated (e.g., during El Niños). This sex-biased mortality was the result of sexual size dimorphism, but at the same time caused sexual size dimorphism to fluctuate. Mortality differed between seasons (selection differentials as low as –1.4) and acted on different absolute body sizes between islands. Both males and females did not cease growth when an optimal body size for survival was reached, as demonstrated by the fact that individual adult body size phenotypically increased in each population under favorable environmental conditions beyond naturally selected limits. But why did marine iguanas grow “too large” for survival? Due to lek mating, sexual selection constantly favored large body size in males (selection differentials up to +0.77). Females only need to reach a body size sufficient to produce surviving offspring. Thereafter, large body size of females was less favored by fertility selection than large size in males. Resulting from these different selection pressures on male and female size, sexual size dimorphism was mechanistically caused by the fact that females matured at an earlier age and size than males, whereafter they constantly allocated resources into eggs, which slowed growth. The observed allometric increase in sexual size dimorphism is explained by the fact that the difference between these selective processes becomes larger as energy abundance in the environment increases. Because body size is generally highly heritable, these selective processes are expected to lead to genetic differences in body size between islands. We propose a common-garden experiment to determine the influence of genetic factors and phenotypic reaction norms of final body size.     

短尾猴下颌骨的性二型

对30个成年短尾猴下颌骨的8个有关变量作了性二型研究。单因子分析说明,8个变量均达到了显著差异水平。判别分析得到的第一判别式为:D=-11.013+1.151下颌骨髁长+0.269下颌骨髁宽。当D=-1.271±0.182时,标本为雌性;当D=0.973±0.290时为雄性。雄性下颌骨髁比雌性更长和更宽,且变化较为稳定,可作为种内性别间的鉴别特征。雄性比雌性具有较大咀嚼阻力臂(下颌长),但其他阻力臂则比雌性相对较短。与一些灵长类相同变量的比较说明,短尾猴下颌骨结构与猕猴较为接近,与长尾叶猴则相差甚远。这可反映它们食性和行为方面的亲疏关系。     

中国砚甲族分类概要(鞘翅目：拟步甲科)

对我国砚甲族Ａｋｉｄｉｎｉ的３属（齿砚甲属Ｅｏｃｙｐｈｏｇｅｎｉａ Ｍｅｄｖｅｄｅｖ,１９６８,砚甲属Ｃ工Ｓ１８３６和索砚甲属Ｓｏｌｓｋｉａ Ｓｏｌｓｋｙ,１８８２）共８种进行了修订,给出其属、种检索表和形态特征图;同时描述了１新种：拉萨索砚甲Ｓ．ｌｈａｓａｎａ Ｒｅｎ ｅｔ Ｙｕ,ｓｐ．ｎｏｖ．;发现我国一新纪录种：短脊砚甲Ｓ．ａｕｒｉｔａ（Ｐａｌｌａｓ,１７８１）。新种和新纪录标本保存在河北大     

SEXUAL SELECTION ON MATURATION TIME AND BODY SIZE IN SPHENARIUM PURPURASCENS (ORTHOPTERA: PYRGOMORPHIDAE): CORRELATED RESPONSE TO SELECTION

We measured in the field the intensity and mode (i.e., directional, stabilizing) of sexual selection acting jointly on body size and time of sexual maturity in the univoltine, polygamous grasshopper Sphenarium purpurascens. Statistical analyses indicated that selection favored large and protandrous males in terms of a higher mating success. At the same time, evidence of correlational selection acting simultaneously on body size and time to sexual maturity was found. Thus, selection should strengthen the relationship between body size and the time of sexual maturity. Theoretical work suggests the existence of a trade-off between reaching a large size and early sexual maturation in insects. The present study does not support the existence of this kind of trade-off. Recent theoretical and empirical work like the one reported here suggests that such a trade-off may not be necessarily expected if growth rates (which are often assumed to be invariable) are affected by environmental and genetic factors.     

SEXUAL DIMORPHISM,MATING SYSTEM AND BODY SIZE IN NEW WORLD BLACKBIRDS (ICTERINAE)

Although sexual selection is widely accepted as a primary functional cause of sexual size dimorphism in birds and mammals, results from some comparative studies have cast doubt on this conclusion. Chief among these contradictory results is the widespread association between body size and size dimorphism—large species tend to be more dimorphic than small species. This correlation is not directly predicted by the normal sexual selection scenario, and many hypotheses have been advanced to explain it. This paper reviews these hypotheses and evaluates them using data for the New World blackbirds (Icterinae). In this avian subfamily, (1) body size correlates with the intensity of sexual selection (as measured by mean harem size), and (2) size does not correlate with dimorphism if the effects of mating system are removed. Similar results are obtained when controlling for the confounding influence of phylogeny. Further, body size and mating system are associated with nesting dispersion. These results strongly argue that sexual dimorphism is a product of sexual selection in this subfamily, and suggest that either: (1) large body size itself, or the ecology of large species, promotes the development of coloniality and a polygynous mating system; or (2) polygyny and/or coloniality lead to the evolution of large size in both males and females. None of the other hypotheses examined predict an association between size and mating system, and all predict that size will correlate with dimorphism after the effects of mating system are removed. Thus, none of the other hypotheses seem applicable in this case. These results are compared to those obtained for other avian and mammalian taxa. Difficulties of analysis present in previous studies are discussed. I argue that it is inappropriate to assume that associations between a trait and body size or phylogeny are evidence of nonadaptive evolutionary “constraints.”     

EXOCRINE GLANDS IN THE FORELEGS OF DUNG BEETLES IN THE GENUS ONITIS F. (COLEOPTERA: SCARABAEIDAE)

Abstract
Two novel groups of exocrine glands on the forelegs of Scarabaeine dung beetles of the genus Onitis are described. One, located on the protrochanters and confined to the male, is present in most species of Onitis . The other, located on the procoxae in conjunction with disseminating structures on both the procoxae and the profemora, is present in both sexes and probably occurs throughout the scarabaeine dung beetles. It is speculated that the glands are involved in close range species recognition and sexual attraction.