Inbreeding and heterogamic mating: An alternative to Averhoff and Richardson

An alternative explanation to the pheromonal control of mating through chemoreceptor saturation proposed by Averhoff and Richardson (1974) is offered for the apparent rise in heterogamic mating in their experiments, after several generations of full-sib mating. In a multiple-choice mating between two genotypic strains differing in their level of sexual vigor, there is a sequence from heterogamic to homogamic mating. It is proposed that, by reducing mating speed, inbreeding changes the rate of this sequence but not its pattern, so the apparent level of heterogamic mating will increase during inbreeding, for a fixed observation period. This hypothesis was tested using the Kence-Bryant model of mating success.A portion of this study was carried out during the tenure of a grant from the National Institutes of Health (5-RO1-AI-10988-02 TMP).     

The effects of joint stress on sticklebacks

The effects on the three-spined stickleback, (Gasterosteus aculeatus L.), of various combinations of stresses due to parasitism bySchistocephalus solidus, dietary restriction, and exposure to cadmium (0.032 mg l^–1) were investigated. Sticklebacks exposed to a combination of all three stressors died first with a median period of survival significantly shorter than that for fish subjected to fewer stressors. Compared with fish on a restricted diet alone, parasitism plus dietary restriction also reduced survival; however, the combination of cadmium exposure and restricted diet did not. A possible explanation for this finding is proposed.     

Variation in sexual behavior and negative assortative mating inDrosophila melanogaster

The hypothesis that negative assortative mating occurs as a mechanism limiting inbreeding between genetically related individuals ofDrosophila melanogaster was tested. In order to avoid bias linked to using inbred lines, experiments made use of the F₁ hybrid progeny between lines rendered homozygous on chromosomes 1, 2, and 3. No negative assortative mating was found, but significant additive variation was observed between lines for orientation, vibration, copulation latencies, and copulation duration. There was no consistency of results, either among parameters or between sexes from the same line. It is therefore unlikely that the variations observed are due merely to quantitative differences in vigor. Since all lines originated from the same wild population, these differences are a possible estimate of natural variation in sexual behavior.     

Inbreeding and copulatory behavior in house mice: A further consideration

Comparisons were made of the copulatory behavior of randomly bred (one population: WRL) and inbred wild (five strains: PAA, PAB, PAC, PAD, and PAE) male house mice. All inbred and randomly bred stocks were derived from a single foundation population. The inbred males tended to have shorter latencies to the first mount and intromission, longer latencies to ejaculation, and more preejaculatory mounts and thrusts than randomly bred males. All these effects parallel those observed in a previous study in which a wild population was compared with various domestic inbred strains. If inbreeding depression is related to adaptive significance, these data suggest that, although rapid initiation of copulation in a novel environment may not be adaptive, it may be adaptive for mice to ejaculate rapidly once copulation is initiated.This work was supported by Grant BMS75-08658 from the National Science Foundation.     

Female song preference and theperiod gene inDrosophila

Mutations at theperiod (per) locus inDrosophila melanogaster alter rhythmic components of the male courtship song. We have examined the mating speed of females homozygous for mutantper alleles when presented with artificial mutant songs. Mutant females retain a preference for wild-type over mutant songs, thus male song and female preference are probably under separate genetic control. In contrast,per-mutant females from an established laboratory stock which had been maintained for nearly two decades appear to have an enhanced response to the corresponding mutant song in that they no longer discriminate against mutant song. These results are discussed in terms of the genetic coupling and coevolution theories of complementarity between male and female components of communication systems.     

Variation of Female Preference for Male Coloration in the Eastern Mosquitofish Gambusia holbrooki

The preference for melanistic males was studied in two populations of eastern mosquitofish (Gambusia holbrooki, Pisces: Poeciliidae), one from Florida and one from northern Italy. Melanism in the eastern mosquitofish is a Y—linked character, expressed in males only. Melanistic males have black spots varying in size and number. In the Florida population, melanistic males are common, whereas in the Italian population they have never been observed. Females were male-deprived for at least 2 months before being tested in a dichotomous choice chamber. Italian females showed a significant preference for unpigmented males from their own population, whereas Florida females preferred melanistic males. When given the choice between males with few (<10% of the body surface) and males with many (>50%) black spots, Italian females preferred males with few black spots and Florida females those with many black spots. The preference of the Italian females for unpigmented males was confirmed in females reared from birth to maturity in the presence of only melanistic males. The preference of Florida females for melanistic males was also confirmed in females reared from birth to maturity in the presence of only unpigmented males. Altogether, these results demonstrate that in the eastern mosquitofish there is polymorphism in female preference and that this preference does not have an environmental basis.     

Genetic Variation in Male and Female Reproductive Characters Associated with Sexual Conflict in <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

Recent studies have shown that elevated mating, courtship and seminal substances affect female fitness negatively in Drosophila melanogaster. It has also been shown that males vary with respect to these characters and that male harm to females correlates positively with components of male fitness. These results suggest that there is sexual conflict over the effect of such male characters. An important component of this scenario is that females have evolved counteradaptations to male harm, but so far there is limited evidence for this. Here I define female resistance as the ability to withstand an increased exposure to males. Across 10 genetically differentiated lines of D. melanogaster, I found genetic variation among females in the reduction of lifespan that followed from exposure to males of different durations. There was also genetic variation among males with regards to the degree to which they decrease the lifespan of their mates. These results suggest that genetic variation for female ability to endure male sexually antagonistic adaptations exists and may play an important role in male–female coevolution.     

Frequency-dependent sexual selection among wild-type strains ofDrosophila melanogaster

Frequency-dependent sexual selection was studied using three geographically isolated strains ofDrosophila melanogaster. The Oregon-R and Canton-Special wild-type strains were essentially homogeneous, having been maintained in laboratories since 1925; the wild Macomb strain was relatively genetically heterogeneous, having been collected in September 1972, immediately prior to this investigation. All possible double combinations of the three strains were placed in separate chambers of a modified Elens-Wattiaux observation apparatus at ratios of 520, 1212, and 205. Allowing 2 hr observation time for each chamber, data were collected to detect mating preference between these strains. There was no sexual isolation between the strains. However, frequency dependence, where rare males have a definite mating advantage in a population, was exhibited by the strains studied. Sexual vigor appeared to be a factor when the heterogeneous Macomb strain was mated to either of the two homogeneous strains in equal numbers.     

Selection for increased female sexual receptivity inRaised stocks ofDrosophila melanogaster

Two third-chromosome mutations inraised (rsd) stocks, when homozygous, cause the wings ofDrosophila melanogaster adults to be held upright. Males expressing these mutations cannot vibrate their wings to produce the courtship song, which functions to increase female receptivity to copulation. As expected,rsd males are less successful when courting wild-type females. However, females from long-establishedrsd stocks are more receptive to courtship stimuli and mate more readily with bothrsd and wild-type males than do wild-type females. Genetic analysis reveals dominant factors on the X and third chromosomes that, in combination, are responsible for the increased receptivity ofrsd females. These observations suggest that the lack of courtship song inrsd stocks, which would be expected to reduce the vigor of the stock, may have functioned as a selective force, favoring mutations that increased female receptivity. Possible consequences of selection favoring the development of differential female receptivity on speciation are discussed.     

Sexual behavior in laboratory strains ofDrosophila mercatorum that have spontaneously adopted parthenogenesis

Three instances are described in which bisexual laboratory strains spontaneously adopted an exclusively parthenogenetic mode of reproduction, even in the presence of fertile, bisexual males. The few males produced by the parthenogenetic strains lack a Y chromosome and are sterile but, nevertheless, showed no correlated impairment of normal mating behavior. In contrast, females show a strong reluctance to accept copulation. This behavioral correlate of parthenogenesis also has been observed previously in experimentally produced parthenogenetic lines. We suggest that genetic breakdown in female mating behavior may contribute to an evolutionary stimulus that results in a selective increase in the frequency of diploidizing events in unfertilized eggs. This ultimately might lead to the origin of an exclusively parthenogenetic reproductive mode.This work was supported by NSF Grant DEB79-26692.     

Female sexual receptivity is defective in juvenile hormone-deficient mutants of theapterous gene ofDrosophila melanogaster

During reproductive maturation of female insects, the acquisition of sexual receptivity is coordinated with ovarian development. Juvenile homone regulates vitellogenesis in the ovaries, but the action of this hormone in the development of sexual behavior is less well-understood. A strain ofDrosophila melanogaster carrying a mutation in theapterous gene(ap ⁴) was known to exhibit arrested vitellogenesis (rescuable by applying exogenous juvenile hormone), sterility of both sexes, and a deficiency of juvenile hormone. In this study, we examined the effects of mutations ofap on female receptivity and its relationship to juvenile hormone. We observed abnormally low female receptivity in homozygousap strains, and heteroallelic combinations ofap mutations exhibited low receptivity. For female receptivity,ap showed no dominance (i.e.,ap/ap ⁺ was intermediate betweenap/ap andap ⁺/ap ⁺). Low receptivity mapped genetically to theap locus. The reduction in female receptivity in these mutants is positively correlated with levels of juvenile hormone synthesized by their corpora allata.This work was supported in part by The Scheinfeld Center for Humans Genetics in the Social Sciences (J.R.), The National Science Foundation (BNS-882 1339 to J.R.), BARD (No. IS-1664-89R to D.S.), The Israel Cancer Research Fund (grant to D.S.), The Rekanati Foundation of Tel Aviv University (grant to D.S.), and The Israeli Fruit Council (award to M.A.)     

Female Remating in Drosophila ananassae: Bidirectional Selection for Remating Speed

In Drosophila ananassae, artificial selection was carried out for fast and slow remating speed for 10 generations. Response to selection resulted in rapid divergence in remating time in each of two replicates of both fast and slow lines. There were significant differences in mean remating time in females among fast, slow, and control lines. Regression coefficients for both fast and slow lines are significantly different from zero. The realized heritability over 10 generations of selection is from 0.26 to 0.33 for two replicates of fast line and from 0.23 to 0.27 for two replicates of slow line. These findings suggest that female remating time in D. ananassae is under polygenic control. Remating frequency of females showed a correlated response in both fast and slow lines. At generation 10, correlated response to selection was also investigated. Mating propensity of D. ananassae of fast and slow lines was observed in an Elens-Wattiaux mating chamber. Fifteen pairs per test showed that on the average, the fast lines (11.20, 11.60) were more successful in mating than those of slow (6.40, 5.60) and control (8.00) lines. Productivity of once-mated females was measured in terms of number of progeny produced per female and the results of productivity analysis indicate that females of fast lines (157.83, 130.83) produced more progeny compared with slow (72.70, 85.83) and control (109.23) lines.     

Genetic variability of sexual behavior in a natural population ofDrosophila melanogaster

Although many experiments on laboratory stocks ofDrosophila have suggested that mate choice is a major feature of sexual selection in this organism, few attempts have been made to measure its extent in wild populations. In this study, a crossing design was used to obtain a set of 13 genetically identical independent lines representative of genotypes from an African population ofDrosophila melanogaster. They were tested for variation in sexual behavior using dyadic tests. Significant variation in orientation and vibration latencies was found for males, and in mating speed and copulation duration for both sexes. No evidence of assortative mating, either positive or negative, was found. The absence of a correlation in mating speed between males and females sharing the same genotype leads us to doubt the applicability of the notion of male eagerness and female reluctancy inDrosophila and the importance of vigor as a factor in mating speed. The absence of mate choice in natural populations ofDrosophila seems to us the most likely hypothesis on the basis of both theory and empirical evidence.     

Cloning and sequence analysis of a cDNA for cellulase (FI-CMCase) from Aspergillus aculeatus

Summary Wa have cloned and characterized the cDNA coding for a major component of cellulase, endoglucanase (FI-CMCase), produced by Aspergillus aculeatus. The cDNA was isolated from a A. aculeatus cDNA library using synthetic oligonuceotide mixtures that correspond to the internal amino acid sequence of the mature FI-CMCase protein. Nucleotide sequence analysis of the cloned cDNA insert revealed a 711 bp open reading frame that encoded a protein of 237 amino acid residues. The primary structure of FI-CMCase deduced from the nucleotide sequence of cDNA agreed with that found by amino acid sequencing of peptide fragments obtained by digestion with several proteinases and cyanogen bromide cleavage. There may be a signal peptide sequence of 16 amino acid residues at the N-terminus. The molecular mass of the mature protein calculated from the cDNA is 24002 daltons, which compares favorably with molecular mass estimates of purified FI-CMCase obtained from SDS-PAGE (25000 Da). No distinct homology was found between the amino acid sequence of FI-CMCase and known cellulase sequences of other microorganisms. This study is the first example of cDNA cloning of an endoglucanase from the genus Aspergillus.The sequence reported in this paper has been submitted to the EMBL/GenBank through DDBJ (accession no, X52525).     

Sexual Selection and Speciation in Hawaiian <Emphasis Type="Italic">Drosophila</Emphasis>

Many ideas about sexual selection and speciation have been stimulated by considering Hawaiian Drosophila. In turn, the ideas and models have stimulated research with the flies, particularly members of the planitibia group. This paper describes high points of some of the models and reviews data that are relevant to understanding sexual selection and speciation in this species group.     

Quantitative Genetic Variation for Oviposition Preference with Respect to Phenylthiocarbamide in Drosophila melanogaster

Seven isogenic strains of Drosophila melanogaster were assayed for oviposition preference on food with phenylthiocarbamide (PTC) versus plain food. There was significant variation among strains for the percentage of eggs oviposited on each medium, ranging from 70±4% (SE) preference for plain food to no significant preference. Reciprocal hybrid, backcross, and F₂ generations derived from two extreme parent strains revealed significant additive and nonadditive genetic variation but no evidence of maternal, paternal, or sex-chromosome effects.     

A compartmental model for oxygen transport in brain microcirculation

A compartmental model is formulated for oxygen transport in the cerebrovascular bed of the brain. The model considers the arteriolar, capillary and venular vessels. The vascular bed is represented as a series of compartments on the basis of blood vessel diameter. The formulation takes into account such parameters as hematocrit, vascular diameter, blood viscosity, blood flow, metabolic rate, the nonlinear oxygen dissociation curve, arterial PO₂, P₅₀ (oxygen tension at 50% hemoglobin saturation with O₂) and carbon monoxide concentration. The countercurrent diffusional exchange between paired arterioles and venules is incorporated into the model. The model predicts significant longitudinal PO₂ gradients in the precapillary vessels. However, gradients of hemoglobin saturation with oxygen remain fairly small. The longitudinal PO₂ gradients in the postcapillary vessels are found to be very small. The effect of the following variables on tissue PO₂ is studied: blood flow, PO₂ in the arterial blood, hematocrit, P₅₀, concentration of carbon monoxide, metabolic rate, arterial diameter, and the number of perfused capillaries. The qualitative features of PO₂ distrbution in the vascular network are not altered with moderate variation of these parameters. Finally, the various types of hypoxia, namely hypoxic, anemic and carbon monoxide hypoxia, are discussed in light of the above sensitivity analysis.     

Mating ability in laboratory-adapted and field-derivedDrosophila melanogaster: The stress of domestication

Mating ability differences between flies of different alcohol dehydrogenase (Adh) genotypes have been assessed in the temperature range 15 to 29°C for laboratory-adapted and field-derivedDrosophila melanogaster. Significant differences amongAdh genotypes were detected principally for the laboratory-adapted strains due to departures from random mating associated with heterozygote superiority at the relatively extreme temperature of 29°C, although mating ability differences could not be attributed directly to theAdh locus. The difference between the laboratory and the field populations can be explained by the effects of genetic back-ground manifested in the form of fitness differences, being enhanced for the laboratory-adapted flies as a consequence of the stress of laboratory culture. In contrast with larval survival and development time, laboratory and field flies do not differe appreciably in their overall abilities to obtain mates, which indicates that mating ability is a direct fitness character not greatly affected by laboratory culture. It follows that direct fitness traits are the least amenable to change under domestication.     

Regulation of cardiac function in prepubertal rats

Prepubertal period in rats is characterized by some peculiarities of the cardiac regulatory mechanisms. In 6-week-old rats atropine produced bradycardia instead of tachycardia. Similar reaction was not observed in chemically sympathectomized age-matched rats. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 129, No. 6, pp. 611–613, June, 2000