Mating behaviour and reproductive isolation of three species of reptile tick

The mating behaviour of three species of reptile tick, Aponomma hydrosauri, Amblyomma albolimbatum and Amb. limbatum is similar and involves a female sex pheromone which activates males to detach from their hosts and search. After contacting females, a stereotyped six-phase courtship sequence occurs. There are qualitative differences between the species in courtship behaviour at phase 3 (reversal of position by dorsally mounted males) and phase 6 (the copulation position). On-host observations of non-conspecific mating show that females of the three species have species-specific activation pheromones, which is contrary to reports in other species of tick. Such specificity should result in reproductive isolation of the three species; however, under certain circumstances it may not prevent non-conspecific contacts between the sexes. Off-host observations of courtship behaviour show that once males of the three species contact non-conspecific females, they attempt courtship and are persistent with their courtship. Rarely did non-conspecific courtships proceed beyond phase 4 of the courtship sequence, as non-conspecific females did not lift their bodies to allow males venter contact. Differences between the species in leg orientation in the copulation position, together with body size differences, are responsible for a complete barrier to successful non-conspecific copulation. The observations illustrate the role that behavioural mechanisms play in reproductively isolating these three species of tick.     

Meiotic chromosomes and nucleolar behavior in testicular cells of the grassland spittlebugs Deois flavopicta, Mahanarva fimbriolata and Notozulia entreriana (Hemiptera, Auchenorrhyncha)

Spittlebugs annually infest pastures and cause severe damage, representing a serious problem for the tropical American beef cattle industry. Spittlebugs are an important biotic constraint to forage production and there is a lack of cytogenetic data for this group of insects. For these reasons, we conducted this work, in which the spermatogenesis and nucleolar behavior of Deois flavopicta, Mahanarva fimbriolata and Notozulia entreriana were studied. The males possessed testes in the shape of a "bunch of grapes"; a variable number of testicular lobes per individual and polyploid nuclei composed of several heteropycnotic bodies. A heteropycnotic area was located in the periphery of the nucleus (prophase I); the chiasmata were terminal or interstitial; metaphases I were circular or linear and anaphase showed late migration of the sex chromosome. The chromosome complement had 2n = 19, except for N. entreriana (2n = 15); the spermatids were round with heteropycnotic material in the center and elongated with conspicuos chromatin. The analysis of testes after silver nitrate staining showed polyploid nuclei with three large and three smaller nucleolar bodies. Early prophase cells had an intensely stained nucleolar body located close to the chromatin and another less evident body located away from the chromatin. The nucleolar bodies disintegrated during diplotene. Silver staining occurred in two autosomes, in terminal and subterminal locations, the latter probably corresponding to the nucleolus organizer regions (NORs). The spermatids were round with a round nucleolar body and silver staining was observed in the medial and posterior region of the elongated part of the spermatid head.     

Meek Males and Fighting Females: Sexually-Dimorphic Antipredator Behavior and Locomotor Performance Is Explained by Morphology in Bark Scorpions (Centruroides vittatus)

Sexual dimorphism can result from sexual or ecological selective pressures, but the importance of alternative reproductive roles and trait compensation in generating phenotypic differences between the sexes is poorly understood. We evaluated morphological and behavioral sexual dimorphism in striped bark scorpions (Centruroides vittatus). We propose that reproductive roles have driven sexually dimorphic body mass in this species which produces sex differences in locomotor performance. Poor locomotor performance in the females (due to the burden of being gravid) favors compensatory aggression as part of an alternative defensive strategy, while male morphology is coadapted to support a sprinting-based defensive strategy. We tested the effects of sex and morphology on stinging and sprinting performance and characterized overall differences between the sexes in aggressiveness towards simulated threats. Greater body mass was associated with higher sting rates and slower sprinting within sexes, which explained the greater aggression of females (the heavier sex) and, along with longer legs in males, the improved sprint performance in males. These findings suggest females are aggressive to compensate for locomotor costs of reproduction while males possess longer legs to enhance sprinting for predator evasion and mate finding. Sexual dimorphism in the metasoma (“tail”) was unrelated to stinging and sprinting performance and may best be explained by sexual selection.     

Sex-specific plasticity in body phosphorus content of Hyalella amphipods

Understanding the evolution of sexually dimorphic traits requires knowledge of the genetic and environmental sources of variation. However, we know surprisingly little about how the sexes differ in their responses to environmental nutrient supply. Here, we investigated how phosphorus (P) availability, a key metric of eutrophication, affects body composition in each sex of two Hyalella amphipod species. We also examined whether differences in food preference and acquisition are responsible for observed variation in body P. We discovered environmentally-driven changes in body P that were dependent on both species and sex. In both species, males contained less P when raised in low-P laboratory conditions compared to high-P field environments, while females exhibited no significant differences. Importantly, this difference was greater in the species that is known to have larger sexual traits and higher growth rates. Variation in P content was not due to differences in acquisition of P because both sexes preferred high-P food and consumed it at a similar rate. Our study illuminates potentially important sex- and species-specific evolutionary consequences of rapid alterations to P availability due to cultural eutrophication.     

Heterochromatin,repetitive DNS und Nukleolen in Leberzellen von Microtus agrestis

Zusammenfassung Die Zellstruktur von Leberzellen der Erdmaus, Microtus agrestis, wurde nach Giemsafärbung, Feulgenbehandlung, Behandlung mit Ribonuklease und nach Färbung des konstitutiven Heterochromatins untersucht. Das konstitutive Heterochromatin ist in Leberzellen nicht heteropyknotisch, das fakultative Heterochromatin ist im weiblichen Geschlecht als Sexchromatinkörperchen sichtbar. Bestimmungen des relativen DNS-Gehalts ergaben, daß die Zahl der Sexchromatinkörperchen der Ploidie der Zellkerne proportional ist. Die Nukleolen liegen in Hepatozyten oft randständig; in 59% der diploiden Zellkerne sind 2 Nukleolen enthalten. Nach Anfärbung der repetitiven DNS werden oft auch die Nukleolen gefärbt, nach Ribonukleasebehandlung tritt dieser Effekt nicht auf. Das konstitutive Heterochromatin wird in Form von 2 langen fädigen Strukturen sichtbar.

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Heterochromatin, repetitive DNA and nucleoli in liver cells of Microtus agrestis

Summary The nuclear structure of parenchymal liver cells of embryo and adult Microtus agrestis was studied in smear and section preparations after staining with Giemsa solution and treatment according to Feulgen, after treatment with ribonuclease and after specific staining of constitutive heterochromatin. In liver cell nuclei only the facultative heterochromatin is heteropycnotic, a sex chromatin body is observable in female but not in male animals. Constitutive heterochromatin is not heteropycnotic in liver cells. Measurements of the relative DNA content showed that nuclei with one sex chromatin body are diploid; tetraploid nuclei possess two and octoploid nuclei four sex chromatin bodies. Solely in the diploid cell nuclei of the intrahepatic gall ducts two large chromocenters are found. The nucleoli in hepatocytes often lie at the perimeter of the nucleus. 17% of the diploid nuclei contain one nucleolus, 59% two nucleoli, 23% three and 1% four. After staining of repetitive DNA, the nucleoli often become stained as well; after treatment with ribonuclease this effect does not occur. The constitutive heterochromatin becomes visible in form of two long, threadlike structures. After longer periods of dissociation the sex chromatin body ceases to be visible. Sex chromatin and constitutive heterochromatin are contiguous to the nucleoli.

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Mit dankenswerter Unterstützung durch das Bundesministerium für Bildung und Wissenschaft der Bundesrepublik Deutschland.     

Males vs. female meiotic prophase in a grasshopper,Arcyptera microptera (Orthoptera: Acridiae)

Female and male first meiotic prophase are analyzed in the grasshopper Arcyptera microptera with special reference to the heteropycnotic chromatin. Differences in the behaviour of the megameric and X-chromosomes, in nuclear size and in the response to C-banding treatment are described. The evidence for a distinctive meiotic prophase in both sexes is compared with results obtained in other species of grasshoppers by other authors using more advanced stages. The discussion centers around the role of the diffuse stage and the differential behaviour of the X-chromosome in the two sexes.     

Disturbance-dependent spatial distribution of sexes in a gynodioecious understory shrub

Several ecological conditions and processes occurring naturally in plant populations may lead to spatial aggregation of sexes within populations of sexually polymorphic species. In addition, ecological disturbances such as forest management or fire could also affect the spatial distribution of sexes within populations. Spatial aggregation of sexes can have important consequences for the fitness of the individuals in sex-biased patches through increased pollen limitation and/or variation in the male fitness of hermaphrodites. Therefore, spatial aggregation of sexes could be relevant for the maintenance of the sexual polymorphism in plant species. Here, we used point pattern analysis to study the spatial distribution of female and hermaphrodite individuals within a single population of the gynodioecious understory shrub Daphne laureola, inhabiting a young pine reforestation and the adjacent natural undisturbed area. In the undisturbed area, we found that hermaphrodites were distributed randomly whereas females were spatially aggregated at short distances. Such aggregation could result from narrower ecological amplitude, cyto-nuclear determination of sex and limited dispersal and/or increased cloning in females. In the reforested area, females were slightly more abundant and the two sexes were randomly distributed among all plants. Recolonization processes after certain forest disturbances could thus favour the establishment of females and alter the spatial distribution of sexes in this understory species.     

Body size dimorphism and sexual segregation in polygynous ungulates: an experimental test with Soay sheep

Sexual segregation in Soay sheep (Ovis aries) was investigated using an experimental approach in order to test the sexual dimorphism-body size hypothesis. Two corollaries of the sexual dimorphism-body size hypothesis were tested: (1) in dimorphic species males, the larger sex, have relatively smaller bite sizes on short swards because of the scaling of incisor arcade with body weight, and (2) they move off earlier to feed on taller but poorer-quality swards when such swards are patchily distributed on a scale which enables the spatial segregation of individuals. Patch choice between sexes was estimated using a matrix of grass patches which differed in both quality and biomass of grass on offer (HQ: high-quality-low-biomass; LQ: low-quality-high-biomass). Sex differences in patch choice and grazing behaviour were tested in short-term preference trials. Incisor breadth showed no significant difference between sexes. On the other hand, muzzle width was dimorphic, with females having a narrower muzzle than males. Bite size was significantly different between the sexes, being smaller in females than in males, although it was not significantly different between sward types. Females had a higher bite rate than males and the bite rate was higher in the HQ sward type than the LQ sward type. When the effect of body mass was removed, no sex differences in muzzle size, bite size or bite rate were found. The intake rate did not differ between the sexes or between sward types. Whilst both sexes preferred the HQ sward type, females spent a significantly longer time feeding on the LQ sward type than did males. The difference detected between the sexes in patch choice was not consistent directly with the sexual dimorphism-body size hypothesis. Alternative explanations based on sex differences in foraging behaviour in relation to body mass sexual dimorphism are discussed to explain the result. Received: 1 February 1999 / Accepted: 12 May 1999     

Fecundity and sexual size dimorphism of wolf spiders (Araneae: Lycosidae) along an elevational gradient in the Arctic

Fecundity and body size are central fitness-related traits, and their intra-specific responses to environmental variation are receiving increasing attention in the context of climate change. Recent results from Greenland indicate that temporal and spatial variation in body size differences between sexes (sexual size dimorphism) may be widespread among wolf spider species and could be related to climate. Here, we tested whether variation in elevation affected body size of three wolf spider (Araneae: Lycosidae) species in low-Arctic Canada, whether the sexes differed in their response to the cline, and whether changes in local density influenced this relationship. We also tested whether fecundity changed with elevation in two of the species, independent of body size variation. We found a significant sex–elevation interaction for Pardosa lapponica: female size decreased more in response to elevation than that of males. Males and females of Pardosa uintana decreased significantly in size with elevation at a similar rate. Alopecosa aculeata males increased in body size along the gradient while females did not. Pardosa lapponica females, but not P. uintana females, showed significant reduction in fecundity in response to elevation. P. uintana showed significant decreases in body size with increases in its population density. Changes in temperature and potential resource availability along the elevational gradient are probably causing these species- and sex-specific responses. Further summer warming of the region may alleviate current constraints on growth and reproduction of these species although sex-specific responses may affect their population dynamics.     

Size‐dependent mating pattern in a nuptial gift‐giving insect

The reproductive interests of females and males often diverge in terms of the number of mating partners, an individual’s phenotype, origin, genes, and parental investment. This conflict may lead to a variety of sex‐specific adaptations and also affect mate choice in both sexes. We conducted an experiment with the bush‐cricket Pholidoptera griseoaptera (Orthoptera, Tettigoniidae), a species in which females receive direct nutritional benefits during mating. Mated individuals could be assigned due to the genotype of male spermatodoses, which are stored in the female’s spermatheca. After 3 weeks of possible copulations in established mating groups which were random replications with four females and males we did not find consistent assortative mating preference regarding to body size of mates. However, our results showed that the frequency of within‐pair copulations (192 analyzed mating events in 128 possible pairwise combinations) was positively associated with the body size of both mated individuals with significant interaction between sexes (having one mate very large, association between body size and the number of copulations has weaken). Larger individuals also showed a higher degree of polygamy. This suggests that body size of this nuptial gift‐giving insect species is an important sexual trait according to which both sexes choose their optimal mating partner.     

Age Structure of Two Species of Odorous Frogs(Odorrana margaretae and Odorrana grahami)

Variation in age structure and body size benefits are identified to understand the evolution of life history. Here, we estimated the age structure and body size of two species of odorous frogs(Odorrana margaretae and Odorrana grahami) by using skeletochronology. The ages at sexual maturity of O. grahami and O. margaretae in both sexes were 1 and 2 years, respectively. For both sexes, the maximum age observed in O. margaretae was six years. For O. grahami, the maximum age observed in males and females were 4 and 5 years, respectively. Males and females did not differ in mean age in the two species.The average body size of both species considerably differed between sexes, with females being larger than males. The body size of females was also larger than that of males when the effect of age was removed. We also found positive correlations between body size and age within each sex in O. margaretae, but only for female in O. grahami. The female-biased sexual size dimorphism of the two species suggested that fecundity selection for larger female size may increase the reproductive output.     

On the sex chromosome trivalent in some Lepidoptera females

In four of the moth species investigated, viz. Witlesia murana, Scoparia arundinata (Pyraloidea), Bactra furfurana and B. lacteana (Tortricoidea) the metaphase plates of the first meiotic division of their oocytes show a trivalent in addition to the normal bivalents. It evidently has its rise in a transverse break in one of the conjugated chromosomes. Two sex chromatin bodies can be seen in the female somatic cells of three of these species, whereas other species with a normal XY bivalent have only one. These two sex chromatin bodies are unequal in size, and their sizes bear approximately the same relation to each other as do those of the two smaller chromosomes of the trivalent. The broken chromosome is evidently the Y chromosome. The sex chromosome designation for the four above-mentioned species is thus XY₁Y₂ for the females and XX for the males. The sex chromosomes of the four species are among the biggest of the respective complements. This supports the view that the big chromosome to be found in several Lepidoptera species is the sex chromosome. It seems that in animals with holokinetic chromosomes an excessive fragmentation is hindered, at least in the case of the sex chromosomes, by its deleterious effect on the balance of sex-determining genes.Dedicated to Doctor Sally Hughes-Schrader on the occasion of her seventy-fifth birthday.     

Evolutionary allometry reveals a shift in selection pressure on male horn size

How selection pressures acting within species interact with developmental constraints to shape macro‐evolutionary patterns of species divergence is still poorly understood. In particular, whether or not sexual selection affects evolutionary allometry, the increase in trait size with body size across species, of secondary sexual characters, remains largely unknown. In this context, bovid horn size is an especially relevant trait to study because horns are present in both sexes, but the intensity of sexual selection acting on them is expected to vary both among species and between sexes. Using a unique data set of sex‐specific horn size and body mass including 91 species of bovids, we compared the evolutionary allometry between horn size and body mass between sexes while accounting for both the intensity of sexual selection and phylogenetic relationship among species. We found a nonlinear evolutionary allometry where the allometric slope decreased with increasing species body mass. This pattern, much more pronounced in males than in females, suggests either that horn size is limited by some constraints in the largest bovids or is no longer the direct target of sexual selection in very large species.     

Function of nuchal humps of a cichlid fish from Lake Tanganyika: inferences from morphological data

Nuchal humps occur in various fish groups, but their functions are rarely studied. Both sexes of Cyphotilapia gibberosa, a cichlid fish endemic to Lake Tanganyika, possess nuchal humps. This study morphologically analysed the humps of this species to assess the primary factors responsible for hump development. Semi-landmarks showed that the size of male humps positively correlated with body condition, and thicknesses of hypodermises implied that the humps were larger in males than in females. These facts suggest that sexual selection on male humps is intense. Semi-landmarks showed that the humps were less prominent in females than in males, and that the transformation of nuchal humps with growth (becoming more prominent) ceased at medium body size in females. These facts suggest that sex recognition likely plays a role in the evolution of the uniform humps of large females, because, according to this hypothesis, a morphologically moderate hump may be favoured. If male humps also function as a sex recognition trait, the transformation of nuchal humps is expected to cease at a certain body size, as did female humps. However, the male humps became continuously more prominent from the smallest to the largest individuals examined. The body size at which hump transformation stops or at which extreme hump shape interferes with sex recognition may be outside of the size range of the present samples. A prominent nuchal hump may also function as a species recognition trait, because sympatric cichlid species do not develop nuchal humps as prominent as this species. In short, the present morphological analyses do not contradict the hypotheses that C. gibberosa individuals recognise conspecifics and their sex from the shapes of the nuchal humps, and that females prefer males with larger humps.     

The Nucleolar Chromosome in Hepatics. I.

Abstract

1. In six species of hepatics belonging to the Marchantiales and Acrogynae the large heteropycnotic chromosome found in addition to the sex chromosome or microchromosome is the nucleolar chromosome.

2. The sex chromosomes and microchromosomes in these species, and in four of the five species of which the nucleolar chromosomes have been described by other authors, are not nucleolar chromosomes. Riccardia pinguis (L.) Gray appears to stand alone in having a nucleolar orpnizer on the sex chromosome in addition to that on an autosome bearing a heteropycnotic trabant.

3. The large heteropycnotic sex chromosomes of certain species of Frullania belonging to the subgenus Galeiloba Steph. are not apparently homologous with the large heteropycnotic chromosome of Frullania africana Steph., belonging to the subgenus Chonanthelia Spr. This is not in accordance with the suggestion of Tatuno (1941) that all ' H-chromosomes' are phylogenetically homologous.

4. It is argued that the nucleolar chromosomes throughout the hepatics, with the exception of the sex chromosome of Riccardia pinguis, may be phylogenetically homologous.     

No evidence for color or size preference in either sex of a dichromatic stream fish, Percina roanoka

Sexual dimorphism is hypothesized to be the result of differential selection pressures between the sexes. Dimorphic traits can serve as indicators of mate quality, altering mate preferences in the opposite sex in favor of a conspicuous trait. Common indicators of mate quality include color and size, with traditional assumptions and evidence predicting a preference for more colorful and/or larger sized mates in many species. Both male and female preferences for more colorful and larger mates within a species are rarely examined simultaneously, however. We examined a sexually dichromatic freshwater fish, Percina roanoka and found that male coloration is positively correlated with size, suggesting color may function as an indicator of viability. We tested preferences for coloration and size in both sexes in a dichotomous mate choice setup in which only visual signals were exchanged. Neither females nor males exhibited a color or size preference in individuals of the opposite sex. Visual cues alone therefore appear to be insufficient to elicit a significant preference in both sexes of this species. Male coloration in P. roanoka does not appear to be driven solely by female preference.     

Sexual dimorphism and sexual selection in a montane scincid lizard (Eulamprus leuraensis)

Sex‐based divergences in body sizes and/or shapes within a species imply that selective forces act differently on morphological features in males versus females. That prediction can be tested with data on the relationship between morphology and reproductive output in females, and between morphology and realized paternity (based on genetic assignment tests) in males. In a sample of 81 field‐collected adult Blue Mountains water skinks (Eulamprus leuraensis), males and females averaged similar overall body sizes (snout–vent lengths (SVLs)). Reproductive success (based on 105 progeny produced by the females) increased with SVL at similar rates in both sexes (as expected from the lack of sexual size dimorphism). Multiple paternity was common. Males had larger heads than females of the same body size, and (as predicted) reproductive success increased with relative head size in males but not in females. Males also had relatively longer limbs and shorter trunks than females, but we did not detect significant sex differences in selection on those traits. Reproductive success in both sexes was increased by relatively longer hind limbs. Our data clarify mating systems in this endangered species, and suggest that mating systems are diverse within the genus Eulamprus.     

Replication of autosomal heterochromatin in man

Summary In interphase nuclei of leukocytes and oral mucosa cells of normal human males and f males, two types of heterochromatin can he distinguished according to their location in the nucleus. Firstly, nucleolus-associated heterochromatin which consists of one large mass of autosomal segments surrounding the nucleolus, or several large masses if there appears to be more than one nucleolus in the same nucleus. Secondly, scattered heterochromatin composed of a large number of positively heteropycnotic bodies scattered throughout the nucleus and not directly associated with the nucleolus. The correspondence of this type of heterochromatin with chromosome segments is obtained at late prophase where several positively heteropycnotic regions belonging to the autosomes are found scattered throughout the nucleus.In human females sex-chromatin is present in addition to these two types. In leukocytes the sex-chromatin cannot be easily identified due to the large size and number of the scattered heterochromatic bodies, but in oral mucosa cells such a distinction is more easily achieved due to the smaller amount of autosomal heterochromatin.Nucleolus-associated and scattered heterochromatin from leukocytes of both sexes synthesized their DNA at a different period of time from the euchromatin. The asynchrony of replication observed in the heterochromatin at interphase is in agreement with the asynchrony between autosomes and within autosomes described by many authors at metaphase. This does not mean, however, that every segment or chromosome found replicating asynchronously at metaphase contains necessarily heterochromatin.Dedicated to Professor H. Bauer on the occasion of his 60th birthday. — This investigation was supported by a research grant to A. Lima-de-Faria from the Swedish Natural Science Research Council.