Constraints upon the organisation and evolution of chromosomes in Allium

Summary In terms of chromosome morphology, karyotype organisation, taxonomy and genetic relationship as judged from chromosome pairing in the Fl hybrid, A. cepa and A.fistulosum are two closely related species. But large variation in nuclear DNA amounts has occurred during the evolution of the two species. A comparison of the molecular composition of DNA in the two species has confirmed that the excess DNA acquired during evolution was predominantly repetitive sequences (sequences which do not encode genetic information). However, its distribution within the chromosome complements was equal in all chromosomes irrespective of the differences in chromosome size. The even distribution of the excess DNA within complements suggests strong constraints underlying evolutionary changes in genome organisation. The nature of the constraints is discussed, and it is shown that such constraints can influence the direction of karyotype evolution during speciation.     

Rapid clinical effectiveness of MIF-I in the treatment of major depressive illness

A double-blind 28 day study was conducted to compare the anti-depressant efficacy of MIF-I with that of imipramine. Twenty patients hospitalized with major depressive illness participated. Clinical responses were measured by using the Hamilton Depression Rating Scale, the Global Severity of Illness Scale, the Zung Self-Rating Depression Scale as well as the 100 mm line self-rating for depression. The results indicate that MIF-I was at least as effective as imipramine in this study, and that its anti-depressive effect was a rapid and often dramatic one.     

A large proportion of pelvic neurons innervating the corpora cavernosa of the rat penis exhibit NADPH-diaphorase activity

Nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry, which indicates the presence of neural nitric oxide synthase, the enzyme responsible for the generation of nitric oxide, was used in combination with retrograde labelling methods to determine, in whole-mounts and sections of rat major pelvic ganglia, whether neurons destined for the penile corpora cavernosa were able to produce nitric oxide. In whole-mount preparations of pelvic ganglia, among the 607±106 retrogradely labelled neurons innervating the penile corpora cavernosa, 84±7% were NADPH-diaphorase-positive, 30±7% of which were intensely histochemically stained. In serial sections of pelvic ganglia, out of a mean count of 451 retrogradely labelled neurons, 65% stained positively for NADPH-diaphorase. An average of 1879±363 NADPH-diaphorase positive cell bodies was counted in the pelvic ganglion. In the major pelvic ganglion, neurons both fluorescent for Fluorogold or Fast Blue and intensely stained for NADPH-diaphorase were consistently observed in the dorso-caudal part of the ganglia in the area close to the exit of the cavernous nerve and within this nerve. This co-existence was much less constant in other parts of the ganglion. In the rat penis, many NADPH-diaphorase-positive fibres and varicose terminals were observed surrounding the penile arteries and running within the wall of the cavernous spaces. This distribution of NADPH-diaphorase-positive nerve cells and terminals is consistent with the idea that the relaxation of the smooth muscles of the corpora cavernosa and the dilation of the penile arterial bed mediated by postganglionic parasympathetic neurons is attributable to the release of nitric oxide and that nitric oxide plays a crucial role in penile erection. Moreover, the existence in the pelvic ganglion of a large number of NADPH-diaphorase-positive neurons that are not destined for the corpora cavernosa suggests that nitric oxide is probably also involved in the function of other pelvic tissues.     

Intrasexual selection and phylogenetic constraints in the evolution of sexual canine dimorphism in strepsirhine primates

The goals of this study were to analyze the origin and function of sex differences in the size of canine teeth among Malagasy lemurs and other strepsirhine primates. These analyses allowed me to illuminate interactions between different mechanisms of sexual selection and to elucidate constraints on this sexually-selected trait. In contrast to central predictions of sexual selection theory, polygynous lemurs lack both sexual dimorphism in body size and male social dominance, but the degree of sexual dimorphism in the size of their canines is not known. A comparison of male and female canine size in 31 species of lemurs and lorises revealed significant male-biased canine dimorphism in only 6 of 13 polygynous lemur species. This result is in contrast to predictions of a hypothesis that would explain the lack of size dimorphism in lemurs as a result of high viability costs because canine teeth presumably have low maintenance costs and because they are used as weapons in male-male combat. Moreover, because females had significantly larger maxillary canines than males in only one lemur species, female dominance is not generally based on female physical superiority and selective forces favoring female dominance do not constrain sexual canine dimorphism in the sense of a pleiotropic effect. Contrary to predictions of sexual selection theory, species differences in canine dimorphism across strepsirhines were neither associated with differences in mating system, nor with the potential frequency of aggression. Variation in canine dimorphism was also unrelated to differences in body size, but there were significant differences among families, pointing to strong phylogenetic constraints. This study demonstrated that polygynous lemurs are at most subject to weak intrasexual selection on dental traits used in male combat and that traits thought to be under intense sexual selection are strongly influenced by phylogenetic factors.     

An Exploration of the Effects of Constraints on the Phosphorylation of Synthetic Protein Tyrosine Kinase Peptide Substrates

We synthesized by classical solution methods three conformational constrained analogues of EDNEYTA, a heptapeptide sequence that represents the common major autophosphorylation site of the protein tyrosine kinases (PTKs) of the Src family. The correlation between the different structural properties induced by the modifications of the native sequence and the propensity of the peptides to act as PTK substrates was examined. The kinetic data obtained indicate that the introduction of the tyrosine-analogue constraints Tic(OH) and MeTyr, which block the ring flexibility, completely prevents the phosphorylation catalysed by the kinases Lyn and Fgr. On the other hand PTKIIB/p38^syk can phosphorylate the two derivatives albeit with an efficiency lower than that found with the native sequence. A third derivative contained side chain to side chain cyclization. This analogue, in which the freedom of the phenolic moiety is not altered, can be phosphorylated by all the PTKs tested with kinetic constants comparable to the parent peptide.     

Sexual cannibalism in the fishing spider and a model for the evolution of sexual cannibalism based on genetic constraints

Several hypotheses have been proposed for the evolution of sexual cannibalism by females. Newman and Elgar (1991) suggested that sexual cannibalism prior to mating by virgin female spiders may have evolved as a result of female foraging considerations. According to this model, an adult female's decision to mate or cannibalize a courting male should be based on an assessment of the male's value as a meal versus his value as a mate. The current study provides an empirical test of the assumptions and predictions of this model in the sexually cannibalistic fishing spider. Adult females were subjected to different food treatments, and exposed to adult males in the laboratory. However, only one of the assumptions of the model and none of its five predictions were upheld. We failed to find any effects of female foraging, female mating status, female size, male size or time of the season on females' behaviour towards courting males. Females behaved stereotypically, and many females were left unmated despite numerous mating opportunities. We also demonstrate costs of sexual cannibalism in a natural population. We propose that the act of sexual cannibalism in the fishing spider is non-adaptive, and develop a model for the evolution of premating sexual cannibalism in spiders based on genetic constraints. According to this hypothesis, sexual cannibalism by adult females may have evolved as an indirect result of selection for high and non-discriminate aggression during previous ontogenetic stages. Genetic covariance between different components of aggressive behaviour may constrain the degree to which (1) juvenile and adult aggression and/or (2) aggression towards conspecifics and heterospecifics can vary independently. We briefly review the support for our model, and suggest several critical tests that may be used to assess the assumptions and predictions of the model.     

The genetics of resistance to five races of downy mildew (Plasmopara halstedii) in sunflower (Helianthus annuus L.)

 These studies were undertaken to determine whether downy mildew resistance genes in sunflower were independent as first reported, or linked as suggested by more recent hypotheses. The segregations for downy mildew reaction of 111 F₃ progenies from a cross between a susceptible line and a line with Pl2 were used to locate this gene on the sunflower consensus RFLP linkage map. It was shown that Pl2 was linked to the same RFLP markers on linkage group 1 as Pl1 and Pl6, mapped earlier, and at a very similar distance. The F₃ progenies showed exactly the same segregation patterns when tested with race 1 and race D. One hundred and fifty four progenies from a cross between a susceptible line and HA335, containing Pl6 (considered as giving resistance to all Plasmopara halstedii races), were tested with the five French downy mildew races, 1, A, B, C and D. Two progenies were observed to show segregation for races 1 and D, while appearing homozygous-resistant to races A , B and C. Tests on F₄ progenies confirmed this separation of resistances with fixation of susceptibility to races 1 and D and resistance to races A, B and C. It is concluded that the Pl6 gene is not a “strong” gene, giving resistance to all downy mildew races, but rather a cluster of genes, each providing resistance to one, or a few, downy mildew races. The genes giving resistance to races 1 and D, on one hand, and to races A, B and C, on the other hand, must be very closely linked, with about 0.6 cM between the two groups. Received: 23 December 1996 / Accepted: 18 April 1997     

A PERFORMANCE CONSTRAINT ON THE EVOLUTION OF TRILLED VOCALIZATIONS IN A SONGBIRD FAMILY (PASSERIFORMES: EMBERIZIDAE)

Behavioral evolution can be influenced by constraints, for example, of phylogeny and performance. In this paper I describe a pattern in the evolution of birdsongs that may reflect a constraint on vocal performance. Trilled vocalizations from 34 species of songbirds (Passeriformes: Emberizidae) were analyzed. Two acoustic variables, trill rate and frequency bandwidth, were measured for different trill types. In most species, maximal values of frequency bandwidth were found to decrease with increasing trill rates. Further, trills with low trill rates exhibited wide variance in frequency bandwidth, and trills with high trill rates exhibited only narrow frequency bandwidths. The bounded nature of this pattern suggests that performance constraints have limited the evolutionary diversification of trills. In particular, I explore the role of constraints associated with vocal tract modulations during song production and evolution. Identification of this constraint may enhance our ability to explain particular patterns of trill evolution.     

Plant defence, an evolutionary dilemma: contrasting effects of (specialist and generalist) herbivores and natural enemies

Conclusions Contrasting effects of generalist and specialist herbivores can explain why all plants have not evolved high levels of defence. Maintenance of variation in concentration of defence substances can be explained by a shifting balance between natural selection for defence against herbivory by specialists and generalists. Generalist natural enemies will shift the optimal defence curve to lower concentrations of defences. Physiological costs of production of defence substances and selection by specialist herbivores of plant phenotypes with higher levels of defence compounds for sequestration are no essential elements of this model. They may, however, adjust the predicted optimum defence function and contribute to maintenance of variation of concentrations of defence substances.     

Evolutionary relationship ofHLA-DRB genes inferred from intron sequences

The major histocompatibility complex (Mhc) consists of class I and class II genes. In the humanMhc (HLA) class II genes, nineDRB loci have been identified. To elucidate the origin of these duplicated loci and allelic divergences at the most polymorphicDRBI locus, introns 4 and 5 as well as the 3′ untranslated region (altogether approximately 1,000 base pairs) of sevenHLA-DRB loci, threeHLA-DRBI alleles, and nine nonhuman primateDRB genes were examined. It is shown that there were two major diversification events inHLA-DRB genes, each involving gene duplications and allelic divergences. Approximately 50 million years (my) ago,DRBI ^*04 and an ancestor of theDRB1 ^*03 cluster (DRBI ^*03, DRBI^*15, andDRB3) diverged from each other andDRB5, DRB7, DRB8, and an ancestor of theDRB2 cluster (DRB2, DRB4, andDRB6) arose by gene duplication. Later, about 25 my ago,DRBI ^*15 diverged fromDRBI*03, andDRB3 was duplicated fromDRBI ^*03. Then, some 20 my ago, the lineage leading to theDRB2 cluster produced two new loci,DRB4 andDRB6. TheDRBI ^*03 andDRBI ^*04 allelic lineages are extraordinarily old and have persisted longer than some duplicated genes. The orthologous relationships ofDRB genes between human and Old World monkeys are apparent, but those between Catarrhini and New World monkeys are equivocal because of a rather rapid expansion and contraction of primateDRB genes by duplication and deletion. Correspondence to: Y. Satta