Phase transformation and chiasma frequency variation in locusts

The hypothesis, proposed by Nolte, that all locusts undergo an increase in their chiasma frequency when swarming is examined in the Migratory Locust, Locusta migratoria, using (1) animals which have been isolated in the laboratory at hatching, (2) crowded and isolated animals supplied by an independent laboratory and (3) field solitaria material. Animals isolated in the laboratory at hatching did not show a reduced chiasma frequency when compared with crowded controls despite the fact that they did develop a solitaria phenotype. Likewise, crowded and isolated animals supplied by workers at the University of Paris showed no difference in their chiasma frequency. Finally, animals living at very low density on the flood plains of the River Niger in Mali, West Africa, and exhibiting extreme phase solitaria characteristics proved to have very high chiasma frequencies which is the exact antithesis of the hypothesis. — Thus there is no evidence that there is any relationship between phase status or density and chiasma frequency in Locusta migratoria. This is in direct contradiction to Nolte's claims but in agreement with a previous study by the present author on Schistocerca gregaria.     

Phase transformation and chiasma formation in locusts

The chiasmata in the eight longest of the eleven autosomes in spermatocytes of three species of locusts are greatly increased from the low basic number characteristic of the grasshopper-like or solitaria phase to higher numbers in the swarming or gregaria phase. Swarming in the field gives a greater impetus to the increase in chiasma frequency than crowding in cages. Although there seems to be some maternal effect acting on chiasma formation, the main correlation between population density and chiasma frequency seems to be effected during the last, or last two, instars of nymphal life. The effective factor is postulated to be present in the atmosphere, i.e. the air circulating in the locust breeding room and that circulating around a swarm in the field.In the species Locusía migratoria migratorioides three genetic factors have been found to control chiasma frequency. The first is a dominant factor reducing the frequency in one strain, the second is a possible polygenic complex reducing chiasma frequency in another strain selected for plasticity in hopper colour change, and the third is the recessive albino mutation which maintains chiasma frequency at the same level in crowded and solitary individuals.     

Effect of Paranosema (Nosema) locustae (Microsporidia) on morphological phase transformation of Locusta migratoria manilensis (Orthoptera: Acrididae)

Field and laboratory studies demonstrated that Paranosema (Nosema) locustae had significant effects on the morphological phase transformation of Locusta migratoria manilensis (Meyen 1835). In the field, spraying P. locustae on gregarious locusts caused a substantial population reduction by 16 days after treatment, with most of the surviving locusts being phase solitaria. However, the effects of P. locustae on locust phase transformation began before direct mortality had caused a substantial reduction in locust density: locust numbers were still high at day 10, but locusts had already transformed to phase transiens. Laboratory assays showed that while a low dose of P. locustae had no effect on phase transformation, at a higher dose of 1×10⁵ spores/mL, locusts had F/C ratios that were significantly (P<0.05) more solitaria than untreated locusts, with locusts having ratios that were either phase solitaria or on the solitaria side of phase transiens. In a second laboratory experiment that analysed the effects of locust density on phase transformation by P. locustae, there was no obvious effect of density on female locusts 10 days later as all were solitaria at all locust densities. At day 16, female locusts were transiens at higher densities, but were solitaria at 4/cage. With males there were lesser effects. These results provide new evidence for P. locustae having sub-lethal effects on locust phase transformation at a wide range of locust densities.     

The determination of larval phase coloration in the African armyworm, Spodoptera exempta and its consequences for thermoregulation and protection from UV light

Spodoptera exempta exhibits a density-dependent phase polyphenism in which caterpillars reared in isolation (phase solitaria) tend to be green/brown and cryptic while those reared in groups (phase gregaria) are black and highly visible. Differences in coloration between solitaria and gregaria phase larvae become apparent in the third instar and are pronounced by the final instar. Larval rearing densities as low as two larvae per 250 ml container are sufficient to induce gregaria coloration in 61% of the insects and at higher densities this is the only coloration expressed. Larvae transferred from isolated to crowded conditions or vice versa tend to retain or adopt gregaria phase coloration which suggests that this is highly advantageous. Black coloration is also induced in single larvae reared with other species of caterpillar (S. littoralis). Isolated larvae reared at low temperature tend to become melanic while crowded larvae reared at high temperature tend to be less melanised although they do not adopt the solitaria phase coloration. These results suggest that phase coloration is determined by non species-specific inter-larval contact, although it can be modulated by temperature. Under laboratory conditions, gregaria phase larvae heat up faster than solitaria; this is partially a consequence of their black coloration but their smaller size is a more important factor. The cuticles of the gregaria larvae absorb significantly more ultraviolet radiation than those of solitaria but this does not confer any protection when larvae are irradiated at 254 nm.     

Chiasmata and variability in Lolium and Festuca populations

There are significant differences in mean pollen mother cell chiasma frequencies between populations within Lolium perenne, L. multiflorum and Festuca pratensis. The differences are genotypically controlled. With low chiasma frequencies the chiasmata are distally located. With increasing chiasma frequency the frequency of chiasmata in interstitial segments increases. Shorter lived populations have higher chiasma frequencies than the more perennial. — The higher the chiasma frequency of a population the lower the phenotypic and genetic variance for characters under polygenic control, such as flowering time, and the less effective also is the response to selection for such characters. These observations are interpreted on the premise that high chiasma frequencies are instrumental in the breaking up of supergene sequences in interstitial chromosome segments.     

Chiasma frequency variation inCepaea hortensis (Müll.) and a comparison withC. nemoralis (L.)

Chiasma frequency variation has been studied in 12 populations ofCepaea hortensis and the results compared with those previously obtained forC. nemoralis from the same populations. Variation in chiasma frequency is effectively restricted to a single large bivalent. In both species there are significant differences between populations in chiasma frequency. Although mean population mean chiasma frequencies are similar inC. hortensis andC. nemoralis, C. hortensis is less variable thanC. nemoralis. This can be seen, to a greater or lesser extent, at several levels-(i) within cells, (ii) between cells, (iii) between snails, and (iv) between populations-and is most noticeable when interstitial chiasmata are considered separately from terminal chiasmata. Data from 6 populations suggest that chiasma frequency remains stable between successive years. It is suggested that, since sympatric populations were studied, the most likely explanation for differences in chiasma frequency statistics between the two species is thatC. hortensis andC. nemoralis are responding differently to similar selective pressures.     

Genetic and environmental factors affecting chiasma formation in locusts

By means of crosses with the African Migratory locust it has been demonstrated that various strains carry different segregations of genes which quantitatively condition the formation of chiasmata during meiosis. These genes occur in polygenic series, and in one low frequency strain the polygenes show an epistatic effect for low chiasma frequency, while another low frequency strain seems to have attained this property through gamma radiation. In reciprocal crosses between the lastnamed low and a medium frequency strain there appears to be a maternal effect, with heterosis and epistasis respectively in the reciprocal crosses. In one strain two lines were selected for plasticity and non-plasticity of hopper colour change in small populations, and this selection has resulted in multiple changes in that the two lines now diverge in the three main physical criteria of phase transformation, viz. hopper colour, adult morphometric ratios and chiasma frequencies; one line is now solitarious for these characteristics, the other more gregarious. The genotypes selected out could be related to the ability to utilize the gregarization pheromone.A 10° rise in temperature above 22° C has the effect of increasing chiasma frequencies significantly, but increase in the carbon dioxide content of the atmosphere has no effect. Male and female hoppers produce equivalent amounts of the chiasma-inducing pheromone, while solitarised hoppers do not lose the ability to produce this pheromone. The crucial stage for the action of this pheromone on chromosomes is during the fifth nymphal instar. The phase status of parents appears to affect chiasma frequencies in the offspring, more specifically that of the mother, so that there is further evidence of maternal effect on chiasma frequency.     

Population cytology of the genus Phaulacridium

Twenty seven populations of the grasshopper Phaulacridium marginale were sampled from South Island, New Zealand. An analysis of the chiasma frequency data showed that populations differed significantly for this metric. The populations appeared to fall into two distinct size groups. Morphological measurements confirmed this and a reanalysis of the chiasma frequency data revealed that although the two groups differed significantly for both mean cell chiasma frequency and between cell variances, there was no difference between populations within a group. Analysis of climatological data suggests that the “larger” individuals show different environmental (habitat) preferences from the smaller, which are restricted to one region of South Island. The taxonomic status of Ph. marginale as a single species is called into question.     

Seasonal variation of chiasma frequency in Phyllodactylus marmoratus (Gray) (Gekkonidae — Reptilia)

A study of the male meiotic system in two populations of the gekko Phyllodactylus marmoratus (Gray) has shown that both total and interstitial chiasma frequencies vary cyclically throughout the year. This variation is consistent in each population and was observed over a number of years. The total chiasma frequency (an index of the number of terminal chiasmata) has a different form of cyclic variation than does the interstitial chiasma frequency, and it is argued that they are under independent genetic controls. Reproductive studies suggest that only the sperm with the lowest total chiasma frequencies and greatest range of interstitial frequencies are used for fertilization. An experimental approach has shown that prolonged exposure to low temperature produces a significant increase in total chiasma frequency. It is believed that this environmental cue is responsible for the cyclic nature of total chiasma frequency.     

How Honey Bee Colonies Survive in the Wild: Testing the Importance of Small Nests and Frequent Swarming

The ectoparasitic mite, Varroa destructor, and the viruses that it transmits, kill the colonies of European honey bees (Apis mellifera) kept by beekeepers unless the bees are treated with miticides. Nevertheless, there exist populations of wild colonies of European honey bees that are persisting without being treated with miticides. We hypothesized that the persistence of these wild colonies is due in part to their habits of nesting in small cavities and swarming frequently. We tested this hypothesis by establishing two groups of colonies living either in small hives (42 L) without swarm-control treatments or in large hives (up to 168 L) with swarm-control treatments. We followed the colonies for two years and compared the two groups with respect to swarming frequency, Varroa infesttion rate, disease incidence, and colony survival. Colonies in small hives swarmed more often, had lower Varroa infestation rates, had less disease, and had higher survival compared to colonies in large hives. These results indicate that the smaller nest cavities and more frequent swarming of wild colonies contribute to their persistence without mite treatments.     

Chromosome polymorphism in populations of the grasshopper Trimerotropis pallidipennis from southern Argentina

Three populations of the grasshopper Trimerotropis pallidipennis from southern Argentina have been studied cytologically. A very characteristic B-chromosome was found in all three. They also showed geographical variability in respect of the presence of pericentric inversions, and the inversion system was found to influence chiasma frequency. The Laguna Blanca population, which is on the hypothetical pathway the species is believed to have followed during its migration from northern to southern latitudes, has the same karyotype composition as the N. American form, with fixed inversions in the 3 largest autosomes and the X-chromosome. Its members have a high total chiasma frequency and a great number of interstitial chiasmata. The Sierra de la Ventana population, situated at the absolute eastern border of the species distribution is highly polymorphic with respect to the presence of inversions in the medium chromosomes. Its members have the lowest total chiasma frequency and a greatly reduced number of interstitial chiasmata. Situated geographically between the other two, the Choele-Choel population has the highest frequency of inversions and many of them are homozygous. Its members have a higher total chiasma frequency than that observed in specimens from Sierra de la Ventana, and a greatly reduced number of interstitial chiasmata, similar to that observed in individuals from the latter population.     

Genetic population structure of Natterer's bats explained by mating at swarming sites and philopatry

During autumn 'swarming', large numbers of temperate bats chase each other in and around underground sites. Swarming has been proposed to be a mating event, allowing interbreeding between bats from otherwise isolated summer colonies. We studied the population structure of the Natterer's bat (Myotis nattereri), a swarming species in northern England, by sampling bats at seven sites in two swarming areas and at 11 summer colonies. Analysis of molecular variance (amova) and genetic assignment analyses showed that the swarming areas (60 km apart) support significantly different populations. A negative correlation was found between the distance of a summer colony from a swarming area and the assignment of bats to that area. High gene diversity was found at all sites (HE = 0.79) suggesting high gene flow. This was supported by a low FST (0.017) among summer colonies and the absence of isolation by distance or substructure among colonies which visit one swarming area. The FST, although low, was significantly different from zero, which could be explained by a combination of female philopatry and male-mediated gene flow through mating at swarming sites with bats from other colonies. Modelling suggested that if effective size of the summer colonies (Ne) was low to moderate (10-30), all mating must occur at the swarming sites to account for the observed FST. If the Ne was higher (50), in addition to random mating during swarming, there may be nonrandom mating at swarming sites or some within-colony mating. Conservation of swarming sites that support potentially large populations is discussed.     

Seasonal pattern in population dynamics and host plant use of non‐swarming Ruspolia differens Serville (Orthoptera: Tettigoniidae)

The edible Ruspolia differens (Serville) (Orthoptera: Tettigoniidae) is an important source of food in East Africa, but the seasonality of its population dynamics and host plant use are not fully understood. We studied seasonal patterns in the population density and relative frequency of developmental stages, sexes, colour morphs and host plants of the non‐swarming R. differens at two study sites in central Uganda over 15 months. Linear mixed models were used to study how precipitation and Enhanced Vegetation Index (EVI) predict population density and relative frequency of developmental stages, sexes, colour morphs and host plants. The results showed that all developmental stages of non‐swarming R. differens were found in the field throughout the year. The population densities of R. differens were high in wet seasons and low in dry seasons and were best predicted by the EVI of the previous month. The sex ratio of the non‐swarming R. differens populations was female biased. The proportion of males and green colour morphs increased during and after the rainy season. The use of host plants fluctuated seasonally so that during the greener seasons individuals used the more preferred host Panicum maximum more frequently. Overall, our work indicates that R. differens has a seasonal dynamic so that vegetation greenness can be used to forecast non‐swarming R. differens population densities. Our results also suggest that source populations for swarming individuals might have a local origin. This is important for the management of habitats for reproduction and conservation of viable populations of R. differens in East Africa.     

The chiasma-inducing pheromone of locusts

To the two quantitative criteria for phase transformation of locusts, viz. nymphal colour and adult morphometric ratios, the change in chiasma frequencies during meiosis in the male can now be added: gregarization or swarming induces an increase in chiasma formation. The atmosphere around crowded locusts contains a pheromone which is absorbed and causes a reactive haemolymph in locust hoppers. This haemolymph may be injected into solitarious hoppers or nymphs to induce increased chiasma formation. Certain solvents like risella oil and dimethyl sulphoxide will extract the pheromone from such an atmosphere, and bio-assays with these extracts have been demonstrated to be chiasma-inducing. Such extracts are, however, not chiasma-inducing in the albino mutant, but the haemolymph from crowded normal-coloured hoppers is reactive in the albino hopper. In addition the albino mutant is solitaria-like in both morphometric ratios and chiasma frequencies. These data indicate a relationship between the melanization cycle and chiasma induction: the previously postulated melanin-inducing pheromone and this chiasma-inducing pheromone are probably identical. On the other hand, this pheromone of nymphs and the sex-maturation pheromone of adults are not identical, although the latter may be a modified form of the other. The effect of the nymphal pheromone on adult morphometric ratios is not clear although some correlation has been shown to exist between raised chiasma frequencies in treated solitaries and advances towards gregaria ratios. It may be that in this pheromone we have, what may be called, a gregarizing principle.     

No evidence for transmission of antibiotic-resistant Escherichia coli strains from humans to wild western lowland gorillas in Lopé National Park, Gabon

The intensification of human activities within the habitats of wild animals is increasing the risk of interspecies disease transmission. This risk is particularly important for great apes, given their close phylogenetic relationship with humans. Areas of high human density or intense research and ecotourism activities expose apes to a high risk of disease spillover from humans. Is this risk lower in areas of low human density? We determined the prevalence of Escherichia coli antibiotic-resistant isolates in a population of the critically endangered western lowland gorilla (Gorilla gorilla gorilla) and other wild mammals in Lopé National Park (LNP), Gabon, and we tested whether the observed pattern could be explained by bacterial transmission from humans and domestic animals into wildlife populations. Our results show a high prevalence of antibiotic-resistant bacterial isolates in humans and low levels in gorillas and other wildlife. The significant differences in the genetic background of the resistant bacteria isolated from humans and gorillas suggest that transmission is low or does not occur between these two species. These findings indicate that the presence of antibiotic-resistant strains in wildlife do not imply direct bacteria transmission from humans. Thus, in areas of low human density, human-wildlife E. coli transmission seems to be low. The presence of antibiotic-resistant isolates in gorillas may be better explained by other mechanisms for resistance acquisition, such as horizontal gene exchange among bacteria or naturally acquired resistance.     

Chromosomal diversity and morphological dimorphism in Moroccan wild oat, Avena agadiriana

Chromosomal diversity and morphological dimorphism were examined by breeding the intraspecific hybrids among six accessions of Avena agadiriana Baum et Fedak. The accession M55 occasionally showed a quadrivalent, which indicated that it was heterogeneous for a reciprocal translocation. The chromosome pairings in the intra-early-flowering ecotype hybrids were almost normal with high chiasma frequency at metaphase I. However, the intra-late-flowering ecotype hybrids showed a quadrivalent or a trivalent with a univalent, similar to the inter-ecotype hybrids. The marginal population of the northeastern end, M74, always showed a quadrivalent or a trivalent in all the hybrids due to a unique large reciprocal translocation. This result was consistent with the late-flowering ecotype. There was a genocline of the chiasma frequency resulting from chromosomal rearrangements between adjacent populations. There was also a significant negative correlation between the mean chiasma frequency and the annual rainfall in each collection site (r = ?0.880). The two distinct ecotypes were characterized by the different magnitude and number of chromosomal rearrangements, reciprocal translocation and loss of satellite chromosomes, and they were adapted to the wide range of environments along the Atlantic coast of Morocco.     

Chiasma-induction and tyrosine metabolism in locusts

The production of a gregarization pheromone has been postulated in locusts, with effects on melanization of the hopper cuticle and increased chiasma frequency during meiosis in the adult on crowding or gregarization. Lack of chiasma-inducing effect of the pheromone on albino strains is correlated with the absence or deficiency of some of the products of the metabolic pathways of tyrosine. Some of these products, commercially obtainable, are the amino acids phenylalanine and tyrosine leading to both the melanization and sclerotization pathways; dopamine formed from dopa in the lastnamed pathway; three products of dopamine i.e. protocatechuic acid, noradrenaline and adrenaline. The injection of solutions of these metabolites into the haemolymph of solitary hoppers has shown that only dopa to some extent but noradrenaline to a large extent are effective in raising chiasma frequency in solitarised individuals of normal-coloured strains of Locusta, while in two albino strains, which differ genetically, the injection of dopa, dopamine, protocatechuic acid and noradrenaline proved effective; phenylalanine was effective in only one of these albino strains, while adrenaline was effective in neither. The chiasma-inducing effect of noradrenaline, common to the three strains, is accompanied in the normal-coloured strain by a greater retention of dark coloration during solitarization and by some attainment of the crowded type of morphometric ratios which is a third physical criterion of gregarization. The genetic blocks to the physical criteria of gregaria in the albino strains lie at the immediate level of dopa production or previous to this reaction; it may be construed that such a block in the solitaria of normal-coloured strains also lies at this early level, in this case being induced by too low a pheromone concentration.     

Social complementation and growth advantages promote socially defective bacterial isolates

Social interactions among diverse individuals that encounter one another in nature have often been studied among animals but rarely among microbes. For example, the evolutionary forces that determine natural frequencies of bacteria that express cooperative behaviours at low levels remain poorly understood. Natural isolates of the soil bacterium Myxococcus xanthus sampled from the same fruiting body often vary in social phenotypes, such as group swarming and multicellular development. Here, we tested whether genotypes highly proficient at swarming or development might promote the persistence of less socially proficient genotypes from the same fruiting body. Fast-swarming strains complemented slower isolates, allowing the latter to keep pace with faster strains in mixed groups. During development, one low-sporulating strain was antagonized by high sporulators, whereas others with severe developmental defects had those defects partially complemented by high-sporulating strains. Despite declining in frequency overall during competition experiments spanning multiple cycles of development, developmentally defective strains exhibited advantages during the growth phases of competitions. These results suggest that microbes with low-sociality phenotypes often benefit from interacting with more socially proficient strains. Such complementation may combine with advantages at other traits to increase equilibrium frequencies of low-sociality genotypes in natural populations.     

Asynapsis in Lolium perenne

Eighteen plants displaying varying degrees of asynapsis ranging from weak to very strong were found among four out of six populations of Lolium perenne L. (2n=14) which had been subjected to three cycles of directional phenotypic selection for productivity of green material. No plants were found displaying univalents in the original generation but the incidence increased with cycles of selection, indicating the genetic control and differential distribution of asynaptic genes among these populations. — The analysis of univalents and chiasma frequency of pollen mother cells (PMC) of six partially asynaptic plants chosen for detailed study revealed that univalents occurred throughout all PMC chiasma classes irrespective of chiasma frequency, but the higher the chiasma frequency of any PMC the less the likelihood of univalents occurring. The relationship between chiasma frequency and univalent frequency per PMC per plant was negative. — Mean chiasma frequency per bivalent increased for the asynaptic cells in comparison with the normal in both the weak and medium asynaptic groups which was explained by the availability of additional chiasmata for redistribution.     

Genetic Control of Meiosis in Rice, ORYZA SATIVA L. III. Effect of DS Genes on Genetic Recombination

The recombination frequency as influenced by five independent recessive ds genes was measured on three segments of different chromosomes of rice, Oryza sativa L. Each ds gene in the homozygous condition resulted in an almost equally reduced recombination frequency in the three segments. When the mean reduction in recombination frequency was related to the reduction of chiasma frequency, the five ds genes were divided into two types: in one type the reduction of chiasma frequency almost corresponded to the mean reduction of recombination frequency, and in the other the chiasma frequency was greatly reduced in comparison with the mean reduction of recombination frequency. Three of the five ds genes were found to belong to the former group. In both types, normal synaptonemal complexes were observed in pachytene cells homozygous for ds genes. This finding suggests that ds genes do not affect the formation of synaptonemal complexes which are regarded as the prerequisite structure for crossing over.