Sexual conflict and the alternation of haploid and diploid generations

Land plants possess a multicellular diploid stage (sporophyte) that begins development while attached to a multicellular haploid progenitor (gametophyte). Although the closest algal relatives of land plants lack a multicellular sporophyte, they do produce a zygote that grows while attached to the maternal gametophyte. The diploid offspring shares one haploid set of genes with the haploid mother that supplies it with resources and a paternal haploid complement that is not shared with the mother. Sexual conflict can arise within the diploid offspring because the offspring's maternal genome will be transmitted in its entirety to all other sexual and asexual offspring that the mother may produce, but the offspring's paternally derived genes may be absent from these other offspring. Thus, the selective forces favouring the evolution of genomic imprinting may have been present from the origin of modern land plants. In bryophytes, where gametophytes are long-lived and capable of multiple bouts of asexual and sexual reproduction, we predict strong sexual conflict over allocation to sporophytes. Female gametophytes of pteridophytes produce a single sporophyte and often lack means of asexual reproduction. Therefore, sexual conflict is predicted to be attenuated. Finally, we explore similarities among models of mate choice, offspring choice and segregation distortion.

A cytogenetic study on the rodent tapewormRodentolepis myoxi

The karyotype of glirid tapewormRodentolepismyoxi(Rudolphi, 1819) (Cestoda: Hymenolepididae) comprises six pairs of small bi-armed chromosomes (2n = 12). All pairs of chromosomes possess uniform morphology, i.e. metacentric, submetacentric or meta-submetacentric types of structures. The formula of the karyotype structure is n = 2m + 1m-sm + 3sm. The absolute chromosome length ranges from 3.78 to 2.00 μm. The mean total length of the haploid complement is 15.98 μm. The first pair (group A) is the largest, pairs 2 and 3 can be grouped into group B while pairs 4–6 are smaller and can be classified as group C. The number of chromosomes ofR.myoxiis the same for the congeneric species, however, karyological characteristics differ from all recently known karyotypes of rodent hymenolepidids.

Cytogenetics of Lathyrus palustris, a natural autohexaploid

American as well as British forms of the perennial plant Lathyrus palustris have 2n = 42 chromosomes with one group of 6 long submetacentric chromosomes, two groups of 6 medium-long subacrocentric chromosomes, three groups of 6 medium-long to medium-short submetacentric to subacrocentric chromosomes, and one group of 6 medium-short metacentric chromosomes. One haploid complement measures 45.8 μm at somatic metaphase. At meiotic first metaphase both forms show extensive multivalent formation. In 50 metaphase I cells of one plant of the British form there were 51 ring hexavalents, 80 chain and open-branched hexavalents of various forms, 2 quinquivalents, 41 ring quadrivalents, 58 chain quadrivalents, 20 branched quadrivalents of various forms, 1 trivalent, 128 ring bivalents, 280 open bivalents, and 9 univalents. It is concluded that L. palustris is most likely a natural autohexaploid with frequent multivalent pairing, many points of pairing initiation, several partner exchanges per multivalent, and many interstitial chiasmata. It may well be the first fully documented true natural autohexaploid reported. Pollen fertility was 56.2% and seed set 37%, apparently sufficient for a perennial plant species.Key words: Lathyrus, natural, autohexaploid, meiosis, multivalents.

Taxonomy, ecology, and karyology of a new species of Phagocata from Spain, with a discussion on the phylogenetic systematics of the genus Phagocata s.l. (Platyhelminthes, Tricladida, Paludicola)

The new species Phagocata ullala Sluys, sp.nov. is described from two localities in Spain, the Ebro delta and Pyrenean Massif. The species is characterized by brown dorsal pigmentation, principally ventral testes throughout the body length, vasa deferentia that fuse to form the ejaculatory duct in the proximal section of the cone-shaped penis papilla, and a basic haploid complement of 17 chromosomes. Animals from the Pyrenees may be polyploid, with complements of 4n, 8n, 10n, and 14n. At present, the genus Phagocata s.l. is diagnosed only by plesiomorphic features. The paper explores possible apomorphic characters of several groups within this genus. It is suggested that "Albiplanaria" and Atrioplanaria are monophyletic taxa and that together "Albiplanaria," Fonticola olivacea, and Phagocata s.str. form a monophylum.

JOINT SEGREGATION OF BIOCHEMICAL LOCI IN SALMONIDAE. II. LINKAGE ASSOCIATIONS FROM A HYBRIDIZED SALVELINUS GENOME (S. NAMAYCUSH x S. FONTINALIS)

ABSTRACT The results of more than 300 parwise examinations of biochemical loci for joint segregation in brook trout (Salvelinus fontinalis) and in the hybridized genome of lake trout (S. namaycush) × brook trout are summarized. Nineteen loci have been assigned to the following eight linkage groupings on the basis of nonrandom assortment, including cases of both classical linkage and pseudolinkage: ODH with PMI with PGI-3, PGI-2 with SDH, ADA-1 with AGP-2, AAT-(1,2) with AGP-1 with MDH-I, MDH-3 with MDH-4, LDH-3 with LDH-4, IDH-3 with ME-2 and GUS with CPK-I. Pseudolinkage (an excess of nonparental progeny types) was observed only for male testcross parents. The results suggest that this phenomenon involves homeologous chromosome arms as evidenced by the de novo association of presumed duplicate loci in each case. Classical linkage has not been found for the five pairs of duplicate loci examined in Salvelinus, suggesting that not all of the eight metacentrics in the haploid complement involve fusions of homeologous chromosomes. Females consistently showed a greater degree of recombination.

Meiosis and sporogenesis in a haploid plant of Pellaea glabella var. occidentalis

In spore mother cells of a sporophyte of Pellaea glabella var. occidentalis (E. Nelson) Butters resulting from induced apogamy, the chromosomes did not pair during prophase I and separated randomly, usually into two groups. Meiosis II generally produced tetrads with nuclei of unequal sizes. Spore walls began to form around these nuclei, but most of the spores eventually aborted. One apparently normal spore, which later germinated, is assumed to have resulted from the formation of a restitution nucleus at the end of meiosis I.The total lack of pairing among the 29 chromosomes of this plant is evidence that this number represents the basic haploid complement of the species.

THE CHROMOSOMAL COMPLEMENT OF THE YELLOW-CHEEKED VOLE: Microtus xanthognathus (Leach)

The karyotype of Microtus xanthognathus (Leach) is described, based on material from one female and one male vole. The diploid chromosomal number was found to be 54, and the fundamental number 62. The metacentric X-chromosome was of medium size and averaged 6.6% of the haploid complement. The designated Y-chromosome was near acrocentric. The specific distinction of M. xanthognathus and Microtus chrotorrhinus (Miller) was confirmed by the recognition of major differences in karyotype and differences in fundamental number. The distributional history of M. xanthognathus is briefly discussed.

NON-HOMOLOGOUS ASSOCIATIONS OF HAPLOID BARLEY CHROMOSOMES IN THE CYTOPLASM OF HORDEUM BULBOSUM L.

Haploids obtained from interspecific crosses between H. bulbosum (2n=14) and H. vulgare (2n=14) resembled the male parent (H. vulgare) with regard to vegetative and spike characteristics. The somatic chromosomes of these plants resembled those of the haploid complement (x=7) of the male parent H. vulgare. Thus, the haploids produced were considered androgenetic possessing the cytoplasm of H. bulbosum and the nucleus of H. vulgare. Detailed meiotic studies from pachytene to metaphase I in these haploids revealed non-homologous chromosome pairing, identical to that of haploids produced in the cytoplasm of H. vulgare. It was concluded that the influence, if any, of bulbosum cytoplasm on meiotic behavior of vulgare chromosomes is not different from that of vulgare cytoplasm.