The supernumerary segment system of Stethophyma

Three species of the genus Stethophyma have been cytologically examined and all three show variation both for supernumerary heterochromatic segments and for the distribution of standard heterochromatin among the autosomes. The European species, S. grossum, for example, shows considerable interpopulation variation for standard heterochromatin while two of the populations, from Spain and Austria, show supernumerary segment polymorphism. The segments are located interstitially on the S₁₁ chromosome but occupy different positions in the different populations. — In all species, the presence of the extra heterochromatic segments increases the mean chiasma frequency. Moreover, the influence of the segments upon mean chiasma frequency is different in different populations and in different species. In the Spanish population, the increase is both intra- and interchromosomal whereas in Austria the influence of the segment is completely interchromosomal. — In the American species, S. gracile and S. lineatum, where supernumerary heterochromatic segments are carried on both S₁₀ and S₁₁ chromosomes, the effect on chiasma frequency shows a dosage relationship, an increase in the number of segments per individual being correlated with an increase in mean chiasma frequency. It is suggested that the interstitial segments found in all species have originated by direct duplication of chromosome material. By contrast the terminal segments in S. lineatum and S. gracile may be derived by translocation from a B-chromosome since such a chromosome has been found in one individual of the former species. — The variation in segment structure and the distribution of standard heterochromatin, among the European species of S. grossum suggests that these systems have evolved independently in different populations.On educational leave from the Forest Research Laboratory, Fredericton, N. B. Canada.     

The supernumerary segment system of Stethophyma

Three species of the genus Stethophyma carry supernumerary heterochromatic segments. The European species, S. grossa, has segments located close to the centromere on the S₁₁ chromosome pair, while the North American species, S. lineatum and S. gracile, have both interstitial and terminal segments on the S₁₀ and S₁₁ chromosomes. The latter species show a high degree of segment variation between individuals and the interstitial segments also show variation in size. The presence of segments on the S₁₀ and S₁₁ chromosomes, whether homozygous or heterozygous, modifies the pattern of chiasma distribution in these chromosomes when compared with that found in the basic homozygotes. When interstitial, they also lead to a high frequency of ring bivalents.Two points suggest that interstitially located supernumerary segments may prove to be more common than has previously been accepted. Firstly, combined equational and reductional segregation in unequal bivalents is only otherwise explicable in terms of chiasma formation in a short arm. Secondly the rod chromosomes of many Acridids may well be telocentric as in the case under study.It is proposed that these segments have arisen through a process of duplication with no evidence of interchromosomal movement.On educational leave from the Forest Research Laboratory, Canadian Forestry Service, Fredericton, New Brunswick, Canada.     

Parallel polymorphism for supernumerary segments inChorthippus parallelus (zetterstedt)

A complex and parallel pattern of polymorphism for heterochromatic supernumerary segments in the M₇ and S₈ chromosomes has been found in 14 populations of the meadow grasshopperChorthippus parallelus. Nine distinct karyotype classes for these two chromosome pairs occur though they are not equally represented in different populations. Populations differ also with respect to the frequency of supernumerary segments they contain. In all populations the presence of supernumerary segments leads to a significant elevation of mean cell chiasma frequency compared to individuals from the same population lacking such segments. The extent of the effect appears to differ in different populations. The observed frequencies of S₈ karyotypes conform to the expectations of a Hardy-Weinberg distribution. Those of the M₇, however, do not, and in all but one of the 14 populations there is a significant excess of homokaryotypes. In the Ashurst population 26% of the individuals sampled were characterised by germ-line polysomy for the M₄ chromosome, either in the form of entire tetrasomics or more usually as mosaics ranging from tri- to hepta-somics. In all these polysomics the M₄ chromosomes in excess of two were regularly heteropycnotic at first meiotic prophase from zygotene to diakinesis. As a consequence of this multivalents are rare. Extra M₄ chromosomes do not modify the chiasma characteristics of the other chromosomes in the complement. Nor do they modify the action of the supernumerary segments in any way.     

Male and female segregation distortion for heterochromatic supernumerary segments on the S8 chromosome of the grasshopper Chorthippus jacobsi

The mode of inheritance of supernumerary segments located on three different chromosome pairs was investigated in controlled crosses with specimens of the grasshopper Chorthippus jacobsi. While extra segments located on chromosomes M₅ and M₆ showed Mendelian inheritance, that on S₈ did not. Thus, the two supernumerary heterochromatic chromosome segments located distally on the S₈ chromosome accumulated through non-Mendelian transmission through both sexes. The observed transmission patterns may be explained by gametic selection for spermatozoa carrying segmented S₈ chromosomes, in addition to meiotic drive for segmented S₈ chromosomes in heterozygous females. The significance of these findings for the maintenance of these polymorphisms in natural populations is discussed.by S.A. Gerbi     

Evolutionary dynamics of 5S rDNA location in acridid grasshoppers and its relationship with H3 histone gene and 45S rDNA location

We analyze the chromosomal location of 5S rDNA clusters in 29 species of grasshoppers belonging to the family Acrididae. There was extensive variation among species for the number and location of 5S rDNA sites. Out of 148 sites detected, 75% were proximally located, 21.6% were interstitial, and only 3.4% were distal. The number of 5S rDNA sites per species varied from a single chromosome pair (in six species) to all chromosome pairs (in five species), with a range of intermediate situations. Thirteen chromosomes from eight species carried two 5S rDNA clusters. At intraspecific level, differences among populations were detected in Eyprepocnemis plorans, and some heteromorphisms have also been observed in some species. Double FISH for 5S rDNA and H3 histone gene DNA, performed on 17 of these 29 species, revealed that both markers are sometimes placed in a same chromosome but at different location, whereas they appeared to co-localize in five species (Calliptamus barbarus, Heteracris adpersa, Aiolopus strepens, Oedipoda charpentieri and O. coerulescens). Double fiber-FISH in A. strepens and O. coerulescens showed that the two DNAs are closely interspersed with variable relative amounts of both classes of DNA. Finally, no correlation was observed between the number of 5S and 45S rDNA clusters in 23 species where this information was available. These results are discussed in the light of possible mechanisms of spread that led to the extensive variation in the number of clusters observed for both rDNA types in acridid grasshoppers.     

Extra heterochromatin in natural populations of Gomphocerus sibiricus (Orthoptera: Acrididae)

Two types of extra heterochromatin, in the form of either supernumerary segments or B-chromosomes, have been observed in natural populations of Gomphocerus sibiricus. The presence of a heterochromatic supernumerary segment affecting the M₇ pair in a population from the Valle de Arán disturbs the normal separation of this bivalent at anaphase I of meiosis and non-disjunction products, respectively deficient or duplicate for the M₇, are present at metaphase II.A stable B_m chromosome has been detected in a second population from Formigal. In a single individual where a B_m is present together with a small unstable B_s supernumerary chromosome both the B_m and the M₅ are unstable in the germ line and in the case of the M₅ this unstability leads to a state of germ line polysomy.     

Worker size polymorphism and ethological role of sting associated glands in the harvester ant Messor barbarus

Summary: Though harvester ants are closely similar in ecology, species differ in their worker size polymorphism as well as in the glandular source of their trail pheromones and defensive compounds. In the harvester ant Messor barbarus, we find that the recruitment trail pheromone is located in the Dufour gland, while defence-alarm substances are produced in the poison gland. We also investigated how the glandular development and the ethological response to these abdominal glands are related to worker body size. For both glands, M. barbarus workers show monophasic and nonisometric growths with slopes of allometric regression lines lower than 1. The highest trail-following response is elicited by the Dufour gland secretion from media workers, responsible for most foraging activities in M. barbarus. Aggressive behaviour is more frequently observed in the presence of poison gland secretions from medium and large-sized workers. Differences between species and between worker size classes in the ethological role of sting associated glands are discussed in relation to the foraging ecology and defensive characteristics of harvester ants.     

Pseudoterminalisation,terminalisation, and non-chiasmate modes of terminal association

Terminal associations occur commonly between meiotic homologues of the two smallest (S10, S11) chromosomes in the northern race of Cryptobothrus chrysophorus when they are either heterozygous or homozygous for distal supernumerary heterochromatic segments. A detailed examination of the origin and behaviour of these associations provides convincing evidence that they are non-chiasmate in character and so cannot be explained by either pseudoterminalisation or terminalisation. The same is true of the terminal associations involved in the persistent pseudomultiples that develop between non-homologues of Heteropternis obscurella when one or both of these carry distal heterochromatic segments. In both situations the C-bands involved in such terminal associations are entire and are never interrupted by non-banded material. In Cryptobothrus, similar associations can also develop between centromere regions when these are heterozygous or homozygous for proximal supernumerary heterochromatic segments.     

SUPERNUMERARY CHROMOSOMES IN SAXIFRAGA VIRGINIENSIS (SAXIFRAGACEAE)

Acetocarmine squashes of root tips have demonstrated that 2n = 20 and 38 in Saxifraga virginiensis. These contrast with the earlier reported count of 2n = 28 for this species. In several populations supernumerary chromosomes were detected. Both intrapopulational and interpopulational variation in supernumerary chromosome number were detected, with the largest number of supernumerary chromosomes observed being six. Because these supernumerary chromosomes are equal in size to many of the smaller A chromosomes during mitotic metaphase, the presence of supernumerary chromosomes in this species could not be ascertained by analysis of mitotic metaphase preparations alone. During mitotic prophase, however, the supernumerary chromosomes of S. virginiensis are highly heterochromatic, appearing more densely coiled and darkly stained than the A chromosomes. This characteristic facilitated the recognition of supernumerary chromosomes in this species. The similarity in size of A and supernumerary chromosomes during mitotic metaphase and the observation of six supernumerary chromosomes in one population suggest that the count of 2n = 28 reported earlier for S. virginiensis may actually be a misinterpretation of 2n = 20 plus 8 supernumerary chromosomes. Furthermore, these findings and the observation of this same supernumerary chromosome phenomenon in other species of Saxifraga raise the possibility that some of the many disparate chromosome counts attributed to aneuploidy in the large genus Saxifraga may also be the result of misinterpretations of supernumerary chromosomes as A chromosomes.     

The inter-relationship between heterochromatin distribution and chiasma distribution

The distribution of chiasmata and their relationship to the presence of fixed and polymorphic heterochromatic segments is described in seven grasshopper species. In six of these, Cryptobothrus chrysophorus, Trimerotropis bilobata, Calliptamus wattenwylianus, Arcyptera fusca, Pezotettix giorni and Acrotylus insubricus, the presence of terminally located polymorphic heterochromatic segments leads to a radical redistribution of chiasmata away from the segments to more proximal sites. Polymorphisms for proximal heterochromatic segments exist in the first three of these species and they lead to a predominance of terminally associated homologues at male meiosis. In Oxya japonica where both polymorphic and fixed blocks are present, the polymorphic blocks have a similar pronounced effect on chiasma distribution, whereas the fixed blocks have no such effect.     

A polymorphism for heterochromatic supernumerary segments in Chorthippus parallelus

Supernumerary heterochromatic segments have been found in the S₈ bivalent of two populations of Chorthippus parallelus. These segments occur both in the heterozygous and the homozygous states. In both populations the frequencies of basic homozygotes, structural heterozygotes and structural homozygotes conform to a Hardy-Weinberg distribution. In the structurally heterozygous and homozygous states there is a significant increase in the chiasma frequency of the bivalents other than the S₈ itself. It is suggested that the adaptive role of these supernumerary segments can be explained in terms of this interchromosomal effect.To Professor J. Seiler in commemoration both of his 80th birthday and his many distinguished years of cytological service.     

Spontaneous chromosome mutations in Truxaline grasshoppers

Three distinct mutant conditions are described in single male individuals from three species of short horn grasshopper. Of these, one is an entire germ line mutant of Myrmeleotettix maculatus, heterozygous for a centric fusion between single M₄ and M₅ telocentric chromosomes. In contrast, the remaining two mutants are present in mosaic form. One is heterozygous for an L₁-M₄ interchange in Omocestus viridulus, the other tetrasomic for the M₄ chromosome in Chorthippus parallelus which in addition is characterised by the inclusion of a supernumerary heterochromatic segment on one S₈ homologue. Centric fusion in Myrmehotettix maculatus has neither disturbed the chiasma potential of the elements constituting the fusion multiple nor, has it apparently influenced the production of balanced gametes. The pattern of chiasma formation in the L₁-M₄ interchange multiple lends support to the contention that the process of chiasma formation originates near the distal end of chromosome arms in Omocestus viridulus. There is no interaction between the two mutant conditions of tetrasomy and the presence of supernumerary segments in Chorthippus parallelus. Moreover, because of the precocious nature of two of the four M₄ homologues there is little tendency to form multivalents. The two M₄ bivalents share a similar mean chiasma frequency.     

TWO MORPHOLOGICALLY SIMILAR BIOLOGICAL SPECIES: CHONDRUS PINNULATUS AND C. ARMATUS (GIGARTINACEAE,RHODOPHYTA)1

The nature of the relationship between Chondrus pinnulatus (Harvey) Okamura f. pinnulatus and C. pinnulatus f. armatus (Harvey) Yamada et Mikami (Gigartinaceae, Rhodophyta) was investigated by comparative analysis of their biogeography, phenologies, life histories, gross and vegetative morphology, crossability, and upper thermal tolerance. The forma pinnulatus has a more northerly distribution in Japan and adjacent waters, exhibiting adaptation to the cooler regions, whereas the forma armatus has a more southerly range. The latter may be the result of a higher thermal tolerance. Both formae have a Polysiphonia-type life history and are similar in their internal vegetative morphology. They can, however, be distinguished by gross morphology: forma pinnulatus has wide, flattened axes, compressed to flattened ultimate segments and proliferations, while forma armatus has narrow, compressed to subterete axes and subterete to terete ultimate segments and proliferations. These differences persist in laboratory culture. All intraformae crosses were positive, with carpospores from the cross developing into fertile F₁ tetrasporophytes releasing tetraspores that developed into dioecious F₁ gametophytes, the female gametophytes of which formed normal cystocarps. This suggests that members of populations of each forma freely interbreed. Among interformae crosses, only some offspring derived from geographically distant strains bore normal cystocarps in the F₁ female gametophytes. Other crosses showed that interbreeding between populations of these two formae was blocked by various isolating mechanisms: incompatibility, hybrid inviability, and hybrid sterility. Reproductive isolation between f. pinnulatus and f. armatus is virtually complete in wild populations, because hybrid populations have not been found in the wild. In addition, these two entities can be considered biological species that are also referred to the taxonomic species, C. armatus and C. pinnulatus, because they do not overlap with regard to the morphology of the ultimate segments and proliferations. Subtle (but significant) gross morphological differences, partial interfertility between the two species, and deleterious hybridization in the area in which they occur sympatrically suggest that their evolutionary divergence was relatively recent.     

A new type of fish olfactory organ structure in Periophthalmus barbarus (Oxudercinae)

Kuciel, M., ?uwa?a, K., Jakubowski, M. 2011. A new type of fish olfactory organ structure in Periophthalmus barbarus (Oxudercinae). —Acta Zoologica (Stockholm) 92 : 276–280. The study describes a new type of olfactory organ structure in teleost fish, the Atlantic mudskipper Periophthalmus barbarus (Gobiidae). The nasal cavity in this species consists of a tube‐like elongated canal widening to a chamber‐like sac in the preorbital part of the head. The olfactosensory epithelium (studied by light and electron microscopy) occurs only in the form of islets located along the medial wall of the tube‐like part of the organ. The presence of a chamber‐like sac without an olfactory rosette or olfactosensory epithelium suggests that a mechanism allowing water circulation is in operation.     

A molecular phylogenetic and phylogeographic study of two forms of Calliptamus barbarus (Costa 1836) (Orthoptera: Acrididae,Calliptaminae) from two regions of Algeria

Calliptamus barbarus (Orthoptera: Acrididae) is the most polymorphic species within the genus Calliptamus. It shows a morphological polymorphism (three hind femoral spots, or only one hind femoral spot). Several studies have been made in order to distinguish the two forms: morphometry, number of ovarioles, sound production, protein and enzyme system. The aim of our work is to assess whether the two forms can be considered as different taxa and to perform a molecular phylogenetic study of two populations of C. barbarus collected from two different Algerian localities. No clear genetic differentiation was found between the samples with different morphologies. Additionally, the samples from Algeria do not form a monophyletic sister clade compared to the one formed by the sequences from GenBank from other geographical regions. Despite the morphological differences shown between the two populations, our molecular study indicates that there are no differences at a molecular level using the two mitochondrial genes COI and 16S.     

Chromosomal mapping of the major and minor ribosomal genes, (GATA)<Subscript>n</Subscript> and U2 snRNA gene by double-colour FISH in species of the Batrachoididae family

In the present study dual-colour fluorescence in situ hybridization (FISH) was performed to study the chromosomal distribution of 18S and 5S rDNAs, (GATA)_n and 5S rDNA, and U2 snRNA and 18S rDNA in four species of Batrachoididae family: Amphichthys cryptocentrus, Batrachoides manglae, Porichthys plectrodon and Thalassophryne maculosa. The 18S rDNA signals were present in only one pair of chromosomes in all the four Batrachoididae species. The 5S rDNA was mapped on one pair of chromosomes, except in B. manglae, which showed a hybridization signal in two pairs. The two ribosomal genes are located on different chromosome pairs, except in A. cryptocentrus, in which they appear co-located. In all the cases, the (GATA)_n probe produced disperse hybridization signals in all four species. The U2 snRNA signals appear very widely scattered in A. cryptocentrus, P. plectrodon, but show a degree of clustering in a specific chromosome pair in B. manglae. In T. maculosa, they are thinly dispersed and strong hybridization signals are observed co-located to the 18S rDNA-bearing chromosomes. Finally, a double-colour FISH with U2 snRNA and 5S rDNA probes was performed in B. manglae, and this showed that these genes were not co-located. These results have been compared with those from another Batrachoididae species, and evolutive processes of these species are discussed.     

Taxonomy and distribution of species of Gastrocopta Wollaston 1878 (Mollusca: Gastropoda: Gastrocoptidae) from the Galápagos Islands (Ecuador)

ABSTRACT

A revision of Gastrocopta from the Galápagos Islands (Ecuador) is made. Four new species from Pinzón, Santa Cruz and Floreana Islands are described; species previously known are redescribed and new locations are added. Gastrocopta (Gastrocopta) reibischi is revalidated through new records from Floreana, Isabela and San Bartolomé Islands. Shell shape and the number, morphology and disposition of the apertural barriers support the discrimination of the taxa. The species have cylindrical to pupoid shells; the number of apertural barriers – differentiated as lamellae, folds and nodulae – varies between 4 and 11, almost completely occluding the aperture in the more complex cases. These structures are: angular-parietal, infraparietal, supracolumellar, columellar, subcolumellar lamellae, and supernumerary, basal, infrapalatal, lower-palatal, interpalatal, upper-palatal and suprapalatal folds. In addition to this classic scheme, a supernumerary fold and a nodule are added. Calcareous concretions – pustulae – are found in several species, mainly located in the peristome. The aulacognathous jaw and radular dentition formulae of Gastrocopta (Gastrocopta) clausa and Gastrocopta (Gastrocopta) munita, are described and photographed for the first time.     

The cytogenetic systems of grasshoppers and locusts

Two new cases of supernumerary heterochromatic segments are described. One of these, found in a heterozygous state in eight males of Chorthippus jucundus, is present terminally on the short arm of the longest autosome. The other, present in a single male heterozygote of Trimerotropis tolteca modesta, is again terminally sited, this time on the long arm of the second smallest auto-some. Both segments are considered to be products of tandem duplication rather than translocation. The segment system of C. jucundus, like that of a number of other categories of heterochromatic material, produces a striking increase in mean cell chiasma frequency compared to basic homozygotes from the same population. It is argued that this effect of the segment on recombination provides a potential basis for selection leading to altered fitness. This, in turn, may well have determined the evolution of at least some forms of supernumerary material in natural populations.     

Foraging behaviour of harvesting ants determines seed removal and dispersal

Harvesting ants can affect the regeneration of plants through at least two different processes: seed removal and seed dispersal. We analyse the role of different foraging strategies of ants on patterns of seed removal and dispersal by three Messor species with considerable differences in their foraging systems. Messor capitatus workers rarely leave the nest in well-formed columns, while the other two species form foraging trails, with M. bouvieri forming temporary trails and M. barbarus foraging on a stable system of permanent foraging trails. Overall seed intake of M. capitatus colonies is considerably less than that of the two group-foraging species. There are also differences in the size of seeds collected: M. barbarus and M. capitatus harvest similar amounts of large and small seeds, while M. bouvieri harvests small seeds more intensely than large ones, due to the smaller size of the worker caste. The three Messor species differ in the percent of seed dropping of the different seed type and in the seed dispersal distance. Moreover, M. bouvieri and M. capitatus redistributed dropped seeds preferentially in bare soil and low sparse vegetation habitats, while M. barbarus redistributed seeds mainly in the high vegetation habitat. These results show that the foraging systems of these harvesting ants determine different patterns of seed removal and dispersal and, thus, affect the abundance and redistribution of seeds in the area.