A multiple sex-chromosome system in Antarctic ice-fishes

Summary We have studied the chromosomes of 11 of the 15 known species of the notothenioid family Channichthyidae, the specialized whiteblooded Teleosts endemic to the Southern Ocean (ice-fishes). In the female sex, all studied species have the same diploid number of forty eight mostly acrocentric (uniarmed) chromosomes; however there is an interspecific variability in the chromosome morphology, type and quantity of repetitious DNA (usually seen as heterochromatin) localization of silver-stained nucleolar organizers. At least five of the studied species show a multiple sex-chromosome system possibly originated by the translocation of an autosome on an early Y gonosome morphologically similar to the X: the digametic males (2n = 47) show a X₁Y X₂ and the homogametic females (2n = 48) a X₁X₁X₂X₂ gonosomic constitution. This peculiar sex determining mechanism, otherwise rare in Teleosts, can be considered apomorphic in the same way as other morphofunctional characters usually interpreted as adaptive in these fishes.Some of the data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

A complex sex-chromosome system in the hare-wallaby Lagorchestes conspicillatus Gould

Among specimens of the spectacled hare-wallaby Lagorchestes conspicillatus Gould (Marsupialia, family Macropodidae) 4 males had 15 chromosomes and 2 females 16 chromosomes. The sex chromosomes are X₁X₁X₂X₂ in the female and X₁X₂Y in the male, the Y being metacentric and both X chromosomes are acrocentric. In about 96% of sperm mother cells at meiosis the sex chromosomes form a chain trivalent and in more than 99% of these this orients convergently so that the X₁ and X₂ move to the same pole. Evidence is presented that L. conspicillatus has evolved from a form with 22 chromosomes including a small X and a minute Y. Autoradiographic studies show that the proximal fifth of the X₁ chromosome replicates late. This is probably the ancestral X chromosome which has been translocated to an autosome. The fate of the original Y is obscure but an hypothesis is proposed that it forms the centromeric region of the Y. A single male had 14 chromosomes and was heterozygous for a translocation involving the centric fusion of two acrocentric autosomes. In about 30% of sperm mother cells the autosomal trivalent did not disjoin regularly but, despite this, all secondary spermatocytes observed at metaphase 2 had balanced complements of chromosomes. It is assumed that unbalanced secondary spermatocytes died before reaching metaphase.     

Multiple calmodulin genes in fish

In mammals, identical calmodulin (CaM) proteins are encoded by three nonallelic genes that differ in their promoter regions and untranslated regions (UTRs). The UTRs of each of these three genes are specific for each gene and are highly conserved. In this study, sequences obtained from the GenBank and EST databases and sequencing were examined for several species of fish to ascertain whether this multi-gene one protein system exhibited in mammals extends to other vertebrates. Three genes in zebrafish (Danio rerio) designated , , and were identified. As in mammals, these genes differ in the 3-UTR region but encode completely identical CaMs. PCR primers spanning the coding and the 3-UTR regions were designed based on the assembled sequences and used to confirm the presence of each gene in the cDNA library. Other species of fish were also found to contain homologous genes that were closely related as indicated by phylogenetic analysis. The 3-UTR of the , and particularly the CaM gene of fish were not found to be as conserved as the corresponding genes of mammalian species possibly due to the span of evolutionary time. Only a few short elements in the 3-UTR were observed to be similar in fish and mammals. These short regions of identity are shared primarily between the mammalian CaM II and CaM I and the gene and gene of fish, respectively. Thus, the multi-gene one protein system occurs among fish as well as among mammals.     

A sex-chromosome mutation in Silene latifolia

Silene latifolia is dioecious, yet rare hermaphrodites have been found, and such natural mutants can provide valuable insight into genetic mechanisms. Here, we describe a hermaphrodite-inducing mutation that is almost certainly localized to the gynoecium-suppression region of the Y chromosome in S. latifolia. The mutant Y chromosome was passed through the megaspore, and the presence of two X chromosomes was not necessary for seed development in the parent. This result supports a lack of degeneration of the Y chromosome in S. latifolia, consistent with the relatively recent formation of the sex chromosomes in this species. When crossed to wild-type plants, hermaphrodites performed poorly as females, producing low seed numbers. When hermaphrodites were pollen donors, the sex ratio of offspring they produced through crosses was biased towards females. This suggests that hermaphroditic S. latifolia would fail to thrive and potentially explains the rarity of hermaphrodites in natural populations of S. latifolia. These results indicate that the Y chromosome in Silene latifolia remains very similar to the X, perhaps mostly differing in the primary sex determination regions.     

Influence of autosome movements and of sex-chromosome movements on sex-chromosome segregation in crane fly spermatocytes

In crane fly spermatocyte meiosis 3 autosome half-bivalents normally move to each spindle pole in anaphase while the 2 amphitelic sex-chromosome univalents remain at the equator. The sex-chromosome univalents move to opposite poles after the autosomes reach the poles. — We used micromanipulation to detach half-bivalents in anaphase. When re-attached half-bivalents were syntelically oriented to the original pole, sex-chromosome segregation was usually not altered. When re-attached half-bivalents were amphitelically oriented, sex-chromosome segregation was usually altered: usually the amphitelic autosome segregated against one sex-chromosome while the other sex-chromosome remained at the equator. When re-attached half-bivalents were syntelically oriented to the opposite pole, sex-chromosome segregation was often altered: often one sex-chromosome moved normally to the spindle pole with 2 autosomal half-bivalents, while the other sex-chromosome did not move to the spindle pole with 4 autosomal half-bivalents, but remained at the equator. — The direction of motion of a sex-chromosome could be altered even after sex-chromosome segregation had begun, by suitable micromanipulation of the other sex-chromosome. — Amphitelic chromosomes that were not on the equator at the start of anaphase segregated predominantly to the closer spindle pole. Detached half-bivalents showed no preference for the closer pole when they re-attached with syntelic orientation. — We discuss some possible hypotheses for non-independent movements, and some implications of the results.     

An isthmo-optic system in a bony fish

This investigation reveals the existence of an isthmo-optic system in a bony fish for the first time. Two cell aggregates of the isthmic region project bilaterally to each eye in Polypterus. The crossed connections are significantly more developed than the uncrossed ones. These findings provide further evidence for the presence of bilaterally projecting isthmo-optic systems in early stages of vertebrate evolution. Furthermore, they suggest that a loss of one or all of these connections during evolutionary or ontogenetic development reflects a parcellation process as proposed by the parcellation theory.     

Nonlinear acoustic complexity in a fish 'two-voice' system

Acoustic signals play essential roles in social communication and show a strong selection for novel morphologies leading to increased call complexity in many taxa. Among vertebrates, repeated innovations in the larynges of frogs and mammals and the syrinx of songbirds have enhanced the spectro-temporal content, and hence the diversity of vocalizations. This acoustic diversification includes nonlinear characteristics that expand frequency profiles beyond the traditional categorization of harmonic and broadband calls. Fishes have remained a notable exception to evidence for such acoustic innovations among vertebrates, despite their being the largest group of living vertebrates that also exhibit widespread evolution of sound production. Here, we combine rigorous acoustic and mathematical analyses with experimental silencing of the vocal motor system to show how a novel swim bladder mechanism in a toadfish enables it to generate calls exhibiting nonlinearities like those found among frogs, birds and mammals, including primates. By showing that fishes have evolved nonlinear acoustic signalling like all other major lineages of vocal vertebrates, these results suggest strong selection pressure favouring this mechanism to enrich the spectro-temporal content and complexity of vocal signals.     

Multiple stable equilibria in a predator-prey system

Necessary and sufficient conditions are given for three equilibria to occur in a predatorprey model and conditions are given for two of these to be stable. The existence of two stable equilibria requires predator intraspecific competition for either space or food, and the lower the prey growth rate the stronger this predator self-regulation must be. A prey growth rate that is skewed to the right, the ability of a few predators to survive at low prey densities, and predators with high searching effectiveness, long handling times, and large maximum per capita rate of increase all make two stable equilibria more likely.     

Selective trade-offs and sex-chromosome evolution in Silene latifolia

Alleles of sexually antagonistic genes (i.e., genes with alleles affecting fitness in opposite directions in the two sexes) can avoid expression in the sex to which they are detrimental via two processes: they are subsumed into the nonrecombining, sex-determining portion of the sex chromosomes or they evolve sex-limited expression. The former is considered more likely and leads to Y-chromosome degeneration. We mapped quantitative trait loci of major effect for sexually dimorphic traits of Silene latifolia to the recombining portions of the sex chromosomes and found them to exhibit sex-specific expression, with the Y chromosome in males controlling a relatively larger proportion of genetic variance than the X in females and the average autosome. Both reproductive and ecophysiological traits map to the recombining region of the sex chromosomes. We argue that genetic correlations among traits maintain recombination and polymorphism for these genes because of balancing selection in males, whereas sex-limited expression represses detrimental alleles in females. Our data suggest that the Y chromosome of S. latifolia plays a major role in the control of key metabolic activities beyond reproductive functions.     

A pseudo-multiple sex-chromosome mechanism in an indian gryllid

Summary A sample of 55 testes of the Indian gryllidEuscyrtus sp. comprised 33 with 2n=19 chromosomes, 18 with 2n=20, two with 2n=21, and one with 2n=19 and 2n=20 in different follicles of the testis: the extra chromosomes in 20- and 21-chromosome individuals are, by definition, supernumeraries. They are transitorily heteropycnotic during meiosis and presumably genetically inactive. Their anaphase segregation is correlated with that of the X-chromosome (strongly, positively heteropycnotic) to an extent possibly determined by the degree to which they exhibit heteropycnosis.A precocious separation of the components of a pair of autosomes (P-chromosomes) produces a pseudo-multiple sex-determining mechanism through the precession of one and the X to one pole, the second to the other pole. Actually, this species ofEuscyrtus is, like the other cytologically known members of the genus, an XXXO type.The precocious movement of the P-chromosomes is conditioned by a pre-metaphase stretch, which is of extremely short duration but initiated with such violence as to culminate in the premature disjunction of these chromosomes and these only.The pre-metaphase stretch, previously established as a taxonomic attribute of the phasmid, mantid, and blattid components of the orthopteroid complex, is thus found to be a characteristic feature in the cytology of this member of the gryllid component: this is no more than a reflection of their common ancestry.Contribution number 86, Division of Forest Biology, Science Service, Department of Agriculture, Ottawa.     

性染色体微卫星标记在亲缘鉴定中的应用

性染色体短串联重复序列(short tandem repeat,STR),又称微卫星DNA(micro satellite DNA)作为一种特殊的遗传标记在法医学个体识别及亲缘鉴定中发挥着重要的作用。该文对亲子鉴定概念、原理和方法等基础知识以及性染色体STR的研究历史、特点以及局限性等进行综述,为性染色体STR在法医学、遗传学等方面的推广应用提供参考。     

Multiple origins of the green-sensitive opsin genes in fish

Vertebrate opsins are divided into four major groups: RH1 (rhodopsins), RH2 (rhodopsinlike with various absorption sensitivities), SWS (short-wavelength sensitive), and LWS/MWS (long and middle-wavelength sensitive) groups. The green opsin genes (g101 _Af and g101 _Af ) in a Mexican characin Astyanax fasciatus belong to the LWS/MWS group, whereas those in goldfish belong to the RH2 group (Yokoyama 1994, Mol Biol Evol 11:32–39). A newly isolated opsin gene (rh11 _Af ) from A. fasciatus contains five exons and four introns, spanning 4.2 kilobases from start to stop codons. This gene is most closely related to the two green opsin genes of goldfish and belongs to the RH2 group. In the LWS/MWS group, gene duplication of the ancestral red and green opsin genes predates the speciation between A. fasciatus and goldfish, suggesting that goldfish also has an additional gene which is orthologous to g101 _Af and g103 _Af .Correspondence to: S. Yokoyama