Long‐term balancing selection on chromosomal variants associated with crypsis in a stick insect

How polymorphisms are maintained within populations over long periods of time remains debated, because genetic drift and various forms of selection are expected to reduce variation. Here, we study the genetic architecture and maintenance of phenotypic morphs that confer crypsis in Timema cristinae stick insects, combining phenotypic information and genotyping‐by‐sequencing data from 1,360 samples across 21 populations. We find two highly divergent chromosomal variants that span megabases of sequence and are associated with colour polymorphism. We show that these variants exhibit strongly reduced effective recombination, are geographically widespread and probably diverged millions of generations ago. We detect heterokaryotype excess and signs of balancing selection acting on these variants through the species’ history. A third chromosomal variant in the same genomic region likely evolved more recently from one of the two colour variants and is associated with dorsal pattern polymorphism. Our results suggest that large‐scale genetic variation associated with crypsis has been maintained for long periods of time by potentially complex processes of balancing selection.     

小麦浆片在开花过程中的结构与作用观察

小麦可育株系和杂种F1花期早,开花张角大,开闭花持续时间短,其浆片吸胀快,体积大,增重幅度大,浆片解剖结构有3个部分;表皮层细胞外壁厚,有角质层,无气孔（器）;基本组织薄壁细胞（GPC）含丰富的原生质,在浆片吸胀和萎缩过程中,GPC体积增大至内膜系统破裂,细胞自溶后内溶物撤离;维管束分散于基本组织中,由导管,筛管薄壁细胞所组成。     

Courtship and Spawning Behavior in the California Sheephead, Semicossyphus Pulcher (Pisces: Labridae)

We recorded the courtship and spawning behavior of a protogynous fish, the California sheephead, Semicossyphus pulcher, throughout their spawning season at Bird Rock, Santa Catalina Island, California. We made additional observations at the Monterey Bay Aquarium and confirmed the details of behavior seen in the field. Large males held spawning territories in which females congregated approximately 1 h before sunset. Courtship commenced shortly before sunset and involved the male approaching each female, making lateral contact and leading her in a circular pattern. Smaller males attempted to court females within the territories, prompting large males to abort spawns and engage in chasing behavior with small males. Females visited several territorial males throughout the day, indicating that they are not part of a strict harem. Both field and aquarium observations confirm that the mating system can be successfully predicted from the size advantage model. Current regulations on the sheephead fishery, which allow for the removal of large, rare males, could have significant effects on the social structure, reproductive output, and mating processes of local populations. Moreover, understanding the mating system of the California sheephead illustrates the need for creating management strategies that better complement the unique life histories of marine fishes with alternative reproductive strategies.     

Genetic correlation of wing polymorphism between females and males in the oriental chinch bug,Cavelerius saccharivorus Okajima (Heteroptera: Lygaeidae)

Genetic correlations of the wing form and the relative wing length between females and males were estimated in the oriental chinch bug, Cavelerius saccharivorus, by calculating the correlation between the sexes of the proportion macropterous or the mean relative wing length in full-sib families obtained from different wing forms of parents emerged in a high density population. There was a significantly positive genetic correlation between the sexes in both the proportion macropterous and the mean relative wing length. However, the appearance rate of macropters tended to be much lower in males than in females under the rearing conditions which promote the appearance of macropters. This was evident especially in the offspring of brachypterous parents. These indicated that in C. saccharivorus the wing polymorphism of males is not a simple result of the genetic correlation of wing morphology between the two sexes. It was considered that both of the female and male fitness advantages to wing reduction, as well as the genetic correlation between the sexes, would influence the evolution of wing polymorphism in this species.     

Modification of phenotypic and functional gender in the monoecious Arum italicum (Araceae)

Other than studies on sex-labile Arisaema species, studies of gender patterns in Araceae are scarce. The modification of phenotypic and functional gender was investigated in three populations of the monoecious Arum italicum Miller. The probability of reproduction and the number of inflorescences produced increased with plant size, and flower number (total, male, staminodes, female, pistillodes) increased with both plant and inflorescence sizes. However, plant and inflorescence sizes were poor predictors of floral sex ratio (female to male flower ratio). In contrast, change in floral sex ratio towards increasing femaleness was found among inflorescences sequentially produced by a plant. This change could not be explained by either a decrease in inflorescence size or a change in the mating environment. Differences in functional gender did not appear to be related to plant size or stage in the flowering period. Instead, different patterns of functional gender were found between plants with different number of inflorescences. Multi-inflorescence plants showed a functional gender around 0.5, while plants with one inflorescence showed a more extreme functional gender (either male, female, or functionally sterile). Sex of flowers in this species did not seem to exhibit a phenotypic trade-off.     

Chloroplast movement

Abstract. Chloroplasts redistribute and/or reorientate in the cell as a response to the light direction, resulting in patterns typical for light of low or high fluence rate, respectively. Usually, the main photoreceptor pigment is a blue-UV-absorbing pigment ('cryptochrome'), but in a few exceptional cases, the reversible red/far-red system phytochrome is involved. Detection of light direction is based on light refraction and/or on dichroic orientation of photoreceptor molecules. Membrane effects, intracellular calcium redistribution and calcium-calmodulin interaction are discussed as likely steps in signal transduction . In the response mechanism the actin-myosin system is involved. However, several details of perception, transduction and response are still unsolved and open for discussion. Particularly interesting are the cases of multiple photoreceptor systems , i.e. those where separate transduction chains are started which coact or interact with each other. This raises the question as to the evolution of multiple photoreceptor systems under the assumption that light-oriented chloroplast movements serve to optimize photosynthesis.     

Alternative models for species replacement of pelagic fishes

It is well known that the stock abundance of a pelagic fish usually fluctuates and a species of pelagic fish which was dominant in abundance is often taken over by another species. Several alternative models for species replacement among pelagic fishes are presented and analyzed: (A) environmental fluctuation, (B) strong density-dependent reproduction rate, (C) a two-species system with phase variation (density-dependent change of life history traits), (D) a two-species competition system with environmental fluctuation, (E) cyclic advantage relationship among three competitive species, and (F) a two-prey, one-predator system. Different model requires different number of species for the occurrence of species replacement. Three criteria to test each hypothesis from qualitative properties of species replacement are proposed. Possible management policies to decrease the amplitude of stock fluctuations are discussed. As a result, if the catching effort to mackerels which is rare now is large, or if the catching effort to the sardine is still large when it begins to decline in stock abundance, fisheries may be strong destabilizing effect on the stock abundance.     

Biochemical homeostasis of the heterozygote at the lysozyme locus in Japanese Quail

The egg-white lysozyme in the Japanese quail shows electrophoretic polymorphism, there being two allelic forms (F and S). The proportions of the three phenotypes (FF, FS and SS) in three different populations agree with the expected values of the Hardy-Weinberg law in panmictic equilibrium. In the three populations examined the proportions of heterozygotes are close to the maximal expected value. The pH optima of the two homozygotes are different. Maintenance of this polymorphism is explained on the basis of Haldane's concept of the heterozygote advantage by biochemical homeostasis.     

Pathogen burden,co‐infection and major histocompatibility complex variability in the European badger (Meles meles)

Pathogen‐mediated selection is thought to maintain the extreme diversity in the major histocompatibility complex (MHC) genes, operating through the heterozygote advantage, rare‐allele advantage and fluctuating selection mechanisms. Heterozygote advantage (i.e. recognizing and binding a wider range of antigens than homozygotes) is expected to be more detectable when multiple pathogens are considered simultaneously. Here, we test whether MHC diversity in a wild population of European badgers (Meles meles) is driven by pathogen‐mediated selection. We examined individual prevalence (infected or not), infection intensity and co‐infection of 13 pathogens from a range of taxa and examined their relationships with MHC class I and class II variability. This population has a variable, but relatively low, number of MHC alleles and is infected by a variety of naturally occurring pathogens, making it very suitable for the investigation of MHC–pathogen relationships. We found associations between pathogen infections and specific MHC haplotypes and alleles. Co‐infection status was not correlated with MHC heterozygosity, but there was evidence of heterozygote advantage against individual pathogen infections. This suggests that rare‐allele advantages and/or fluctuating selection, and heterozygote advantage are probably the selective forces shaping MHC diversity in this species. We show stronger evidence for MHC associations with infection intensity than for prevalence and conclude that examining both pathogen prevalence and infection intensity is important. Moreover, examination of a large number and diversity of pathogens, and both MHC class I and II genes (which have different functions), provide an improved understanding of the mechanisms driving MHC diversity.     

Within-population variability in a moth sex pheromone blend: genetic basis and behavioural consequences

Evolutionary diversification of sexual communication systems in moths is perplexing because signal and response are under stabilizing selection in many species, and this is expected to constrain evolutionary change. In the moth Heliothis virescens, we consistently found high phenotypic variability in the female sex pheromone blend within each of four geographically distant populations. Here, we assess the heritability, genetic basis and behavioural consequences of this variation. Artificial selection with field-collected moths dramatically increased the relative amount of the saturated compound 16:Ald and decreased its unsaturated counterpart Z11–16:Ald, the major sex pheromone component (high line). In a cross between the high- and low-selected lines, one quantitative trait locus (QTL) explained 11–21% of the phenotypic variance in the 16:Ald/Z11–16:Ald ratio. Because changes in activity of desaturase enzymes could affect this ratio, we measured their expression levels in pheromone glands and mapped desaturase genes onto our linkage map. A delta-11-desaturase had lower expression in females producing less Z11–16:Ald; however, this gene mapped to a different chromosome than the QTL. A model in which the QTL is a trans-acting repressor of delta-11 desaturase expression explains many features of the data. Selection favouring heterozygotes which produce more unsaturated components could maintain a polymorphism at this locus.