Parent Colony Research Articles

Qualitative bias in offspring investment in a superorganism is linked to dispersal and nest inheritance

How parents invest resources in offspring is a central aspect of life history. While investment strategies have been well studied in solitary organisms, comparatively little has been done on social species, including the many that reproduce by fission. Under colony fission, a parent colony divides resources (individuals) to form two or more offspring colonies. Because individuals differ in characteristics (e.g. size), there is opportunity for both quantitative and qualitative bias in their allocation. In this study we investigated the qualitative aspect of offspring investment during colony fission. Colonies of the ant Cataglyphis cursor fission into multiple offspring colonies as part of their lifecycle, and the distribution of workers is quantitatively biased. We found that investment is also qualitatively biased in terms of worker size and worker genetic characteristics (patrilines). This bias was mainly between the offspring colony that inherited the original nest and offspring colonies that dispersed to new nesting sites. In 74% of cases, dispersing colonies contained larger workers, and the distribution of genetic patrilines was biased in two of six cases in a manner that cannot be explained by the observed variation in worker size between patrilines. Fission also led to a reduction in diversity in offspring colonies compared to the parent colony, in terms of both worker size (70% of cases) and genetic diversity (40% of cases). These patterns are probably the result of differing dispersal probability between workers of different patrilines and of different size. This differential allocation may be adaptive because larger workers may be of disproportionate value to dispersing colonies, and their loss an acceptable cost to the colony inheriting the nest.

Selecting honeybees for worker brood that reduces the reproduction of Varroa destructor

We investigated an effect of Apis mellifera worker brood on the reproduction of Varroa destructor as a resistance trait by conducting seven generations of bidirectional selection. Initial tests showed twofold differences in mite fecundity (progeny per foundress mites) between colonies of different origins. In the first two generations of selection, low and high lines differed significantly in mite fecundity (2.6 vs. 2.9 and 2.3 vs. 2.8), but in five subsequent generations the average values of the low fecundity lines (ranges of 2.7 to 3.3) became indistinguishable from high lines (2.9 to 3.1). Similarly, the relationship between mite fecundity in 117 offspring colonies and in their 26 queen and 22 drone parent colonies was partly significant in the first three generations but not in subsequent generations. These findings suggest that adaptation of mites to host cues, loss of resistance alleles in a small breeding population, or environmental effects present challenges to breeding for this trait.

Development and Characterization of MIR604 Resistance in a Western Corn Rootworm Population (Coleoptera: Chrysomelidae).

mCry3A is one of only four proteins licensed for commercial use in Diabrotica control. Utilizing a colony of western corn rootworm, Diabrotica virgifera virgifera LeConte, selected for resistance to mCry3A, we evaluated how mCry3A resistance was inherited and whether fitness costs were associated with mCry3A resistance. Reciprocal crosses between a selected colony and a control colony were performed; resulting progeny along with parent colonies were evaluated in dose toxicity assays, greenhouse assays, and seedling assays. Dose toxicity assay results were inconclusive, as the highest dose of protein tested did not produce sufficient mortality for accurate LC50 calculation. In whole-plant greenhouse assays on mCry3A-expressing corn, larval relative survival of the selected female × control male reciprocal cross was similar to that of the selected colony, while that of the control female × selected male was intermediate between the mCry3-selected colony and the control colony. However, when adult relative survival in whole-plant greenhouse assays was examined, no significant difference between the reciprocal crosses and the two parent colonies was detected. Heritability calculations based on both larval (0.66) and adult (1.03) survival data indicate that resistance to mCry3A is not inherited in a recessive manner. The selected colony was removed from selection pressure and evaluated after three or eight generations of removal. At three generations of removal from selection, a slight decrease in larval relative survival was detected compared with the selected colony. At eight generations of removal from selection, larval relative survival was comparable with that of the selected colony.

Effect of Doping with Metals, Silicate, And Phosphate Ions on Fluorescence Properties and Morphology of Calcite Single Crystals Synthesized in Geobacillus thermoglucosidasius Parent Colonies

Geobacillus thermoglucosidasius cells grown on nutrient agar medium (parent colony) were placed on the surface of a calcite-promoting hydrogel containing acetate and calcium. After incubation at 60°C for 4 days, calcite single crystals of 110-130 μm in diameter were synthesized within the parent colony. The calcite contained 6.6% (atom%) Mg and showed striking fluorescent properties. Changes in the morphology and development of fluorescence intensity of calcite synthesized on calcite-promoting hydrogel doped with different metal ions, silicate ion, and phosphate ion were investigated. Doping with Mg, P, or Sr ions yielded calcite lattices with the respective metal ions substitutionally dissolved into calcium sites. On calcite-promoting hydrogel containing 2 mM Mg ion, the calcite Mg content increased to 22 atom%. Doping of the hydrogel with Al, Si, or P ions yielded calcites with increased fluorescence intensity (190-196% of that of control calcites). Contrary to expectations, doping of the hydrogel with Mn, Sr, Fe, or Co ions yielded calcites with decreased fluorescence intensity (64.4-96.9% of that of control calcites). When the hydrogel was doped with Mg or P ions, the calcite surface became smooth or sheet-like, respectively, in contrast to the rough-surfaced spherical morphology of control calcites. Distinctive crevice structures were observed on the surfaces of calcites synthesized on hydrogel doped with Mn or Al ions. Fluorescence microscopy showed that calcites emitted blue, green, or red fluorescence when illuminated with light at wavelengths of 360-370, 460- 500, or 530-560 nm, respectively. Calcites synthesized on hydrogel doped with Al, Si, and P ions emitted stronger fluorescence than control calcites when illuminated with light at 360-370 nm. Our studies have demonstrated that G. thermoglucosidasius is useful for the preparation of calcite phosphors in the absence of rare earth elements.

Tolerance of eCry3.1Ab in Reciprocal Cross Offspring of eCry3.1Ab-Selected and Control Colonies of Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae).

Two new insect colonies were created by separating virgin western corn rootworm, Diabrotica virgifera virgifera LeConte, males and females from both a selected laboratory colony that was being reared on eCry3.1Ab-expressing corn (Zea mays L.) and a control colony reared on its near-isoline corn. Females from the selected colony were paired with males of the control colony and vice versa to create both a selected female by control male colony (Sel♀) and control female by selected male colony (Con♀). Both colonies along with their parental colonies (eCry3.1Ab-selected and control) were evaluated on eCry3.1Ab-expressing corn and its near-isoline in seedling assays. Larvae from each colony were also used in diet toxicity experiments in order to determine the LC50 and EC50 values for the eCry3.1Ab toxin for each. Statistical analysis of seedling assay experiments did not indicate any significant colony×corn interaction but did show a significant main effect of corn type for both larval recovery and larval head capsule widths. Results from the diet toxicity assays showed the control colony to have a significantly lower LC50 value than the selected and cross colonies and a significantly lower EC50 than the selected and Con♀ colonies. Calculations of dominance values (h) of eCry3.1Ab resistance traits from seedling assays indicated that the two reciprocal cross colonies have a dominance value (h) of ∼1, suggesting dominance of the eCry3.1Ab resistance trait.

Eggs and larvae of Acropora palmata and larvae of Porites astreoides contain high amounts of dimethylsulfoniopropionate

Coral holobionts, including their symbionts, are known to produce large amounts of dimethylsulfoniopropionate (DMSP), a compound which some corals use to mitigate oxidative stress; however, very little work has been done on the presence and use of DMSP in early life history stages of coral, such as in eggs and larvae. This study shows that eggs and larvae, from Acropora palmata, and brooded larvae, from Porites astreoides, also contain high amounts of DMSP. Eggs and larvae of wild A. palmata were collected and contained extremely high levels of DMSP: 1.2μmol per larva and 359μmol per 100μL eggs. Larvae of P. astreoides were collected in flow-through laboratory tanks, from wild-collected parent colonies, over the course of the larval release cycle. In brooded larvae of P. astreoides, the amount of DMSP in larvae ranged from 11.6 to 1510nmol per larva; larval DMSP peaked by the second night of release and then decreased over the following release nights. These high levels in aposymbiotic eggs and larvae of A. palmata and the peaking trend in symbiotic larvae of P. astreoides are suggestive of parental provisioning. Given the large amounts of DMSP found in eggs and larvae, this study provides further evidence that even early life stages of the coral holobiont may benefit from the presence of DMSP.

Dispersal Flights of the Formosan Subterranean Termite (Isoptera: Rhinotermitidae).

The Formosan subterranean termite, Coptotermes formosanus Shiraki, is a pest of major economic concern. This termite is particularly known for its tendency to establish populations in nonendemic areas via maritime vessels as well as human-aided transport of infested materials. The natural spread of this species after new introductions occurs in part by dispersal flights originating from mature colonies. Dispersal flight activity is also the primary variable for the evaluation of area-wide management programs. Few studies exist describing the dynamics and distribution of a typical dispersal flight for this species. The present study used data collected by mark-recapture of C. formosanus alates over 12 individual evenings of dispersal flights in the New Orleans French Quarter. In this study, we found that for one selected flight dispersal location, which was not affected by a high density of trap locations nearby, alates flew on average 621 m from their parent colony. A new record of a 1,300-m dispersal flight was recorded. Spatial analysis showed that neither wind nor light affected the direction of flight, which may, however, be attributed to scarce light and wind measurements in the study region.

Botryllus schlosseri, an emerging model for the study of aging, stem cells, and mechanisms of regeneration

The decline of tissue regenerative potential with the loss of stem cell function is a hallmark of mammalian aging. We study Botryllus schlosseri, a colonial chordate which exhibits robust stem cell-mediated regeneration capacities throughout life. Larvae, derived by sexual reproduction and chordate development, metamorphose to clonal founders that undergo weekly formation of new individuals by budding from stem cells. Individuals are transient structures which die through massive apoptosis, and successive buds mature to replicate an entire new body. As a result, their stem cells, which are the only self-renewing cells in a tissue, are the only cells which remain through the entire life of the genotype and retain the effects of time. During aging, a significant decrease in the colonies’ regenerative potential is observed and both sexual and asexual reproductions will eventually halt. When a parent colony is experimentally separated into a number of clonal replicates, they frequently undergo senescence simultaneously, suggesting a heritable factor that determines lifespan in these colonies. The availability of the recently published B. schlosseri genome coupled with its unique life cycle features promotes the use of this model organism for the study of the evolution of aging, stem cells, and mechanisms of regeneration.

Growth dynamics of the threatened Caribbean staghorn coral Acropora cervicornis: influence of host genotype, symbiont identity, colony size, and environmental setting.

BackgroundThe drastic decline in the abundance of Caribbean acroporid corals (Acropora cervicornis, A. palmata) has prompted the listing of this genus as threatened as well as the development of a regional propagation and restoration program. Using in situ underwater nurseries, we documented the influence of coral genotype and symbiont identity, colony size, and propagation method on the growth and branching patterns of staghorn corals in Florida and the Dominican Republic.Methodology/Principal FindingsIndividual tracking of> 1700 nursery-grown staghorn fragments and colonies from 37 distinct genotypes (identified using microsatellites) in Florida and the Dominican Republic revealed a significant positive relationship between size and growth, but a decreasing rate of productivity with increasing size. Pruning vigor (enhanced growth after fragmentation) was documented even in colonies that lost 95% of their coral tissue/skeleton, indicating that high productivity can be maintained within nurseries by sequentially fragmenting corals. A significant effect of coral genotype was documented for corals grown in a common-garden setting, with fast-growing genotypes growing up to an order of magnitude faster than slow-growing genotypes. Algal-symbiont identity established using qPCR techniques showed that clade A (likely Symbiodinium A3) was the dominant symbiont type for all coral genotypes, except for one coral genotype in the DR and two in Florida that were dominated by clade C, with A- and C-dominated genotypes having similar growth rates.Conclusion/SignificanceThe threatened Caribbean staghorn coral is capable of extremely fast growth, with annual productivity rates exceeding 5 cm of new coral produced for every cm of existing coral. This species benefits from high fragment survivorship coupled by the pruning vigor experienced by the parent colonies after fragmentation. These life-history characteristics make A. cervicornis a successful candidate nursery species and provide optimism for the potential role that active propagation can play in the recovery of this keystone species.

Spatial patterns of social spider colonies in Namibia reflect habitat features and dispersal modes

Colonies of web building social spiders may persist at a site for several generations; therefore, their placement in the habitat is critical for survival. This study focuses on the development of spatial distribution patterns by means of different dispersal modes in a social spider species (Stegodyphus dumicola Pocock, 1898, Eresidae) in central Namibia. Social spiders disperse varying distances from the parent colony by ballooning or short distances by budding. Using spatial point pattern analyses we aimed to identify the dispersal pattern from source colonies and what drivers affect the resulting distribution patterns. The distribution of suitable vegetation constrained pattern development in the three study plots with mapped colonies. In a plot with isolated large trees, colonies were only aggregated over short distances and the average cluster size was small. First generation colonies were established within the same clusters by solitary ballooning females. In the two study plots with more evenly distributed shrubs, clusters were generally larger and new colonies were formed mainly by budding. In these plots, newly established colonies and older source colonies were either associated in suitable habitat patches or segregated from each other. Possible explanations include high mortality of either older colonies and replacement by newly established colonies or of dispersers in the vicinity of established colonies, or selection of “empty” sites by dispersing individuals based on cues from conspecific colonies. In conclusion, both the distribution of the vegetation and the mode of dispersal may explain the development of spatial patterns in S. dumicola. Our results highlight the importance of spatial pattern analyses for inferring underlying causes of distribution of sedentary organisms.

Workers' Extra-Nest Behavioral Changes During Colony Fission in Dinoponera quadriceps (Santschi).

Ant colonies can reproduce by two strategies: independent foundation, wherein the queen starts a new colony alone, and dependent foundation, in which workers assist the queen. In the queenless species Dinoponera quadriceps (Santschi), the colony reproduces obligatorily by fission, a type of dependent foundation, but this process is not well understood. This study describes a colony fission event of D. quadriceps in the field and analyzes the influence of the fission process on workers' extra-nest behavior. Based on observations of workers outside the nest, five distinct stages were identified: monodomic stage, polydomic stage, split stage, conflict stage, and post-conflict stage. The colony was initially monodomic and then occupied a second nest before it split into two independent colonies, indicating a gradual and opportunistic dependent foundation. After the fission event, the daughter colony had aggressive conflicts with the parental colony, resulting in the latter's disappearance. Colony fission affected workers' extra-nest behavior by increasing the frequency of rubbing the gaster against the substrate (which probably has a chemical marking function) and by decreasing the frequency of foraging during the split stage. After the fission event, the number of foragers was halved and foragers remained nearer to the nest during extra-nest activity. The spatial closeness of the parental and daughter colonies led to competition that caused the extinction or migration of the parental colony. Intraspecific competition was indicated by foraging directionality at the colony level, whereby areas of neighbor colonies were avoided; this directionality was stronger while both colonies coexisted.

Reproductive strategies of two invasive sun corals (Tubastraeaspp.) in the southwestern Atlantic

The azooxanthellate sun coralsTubastraea coccineaandT. tagusensisare invasive species which were introduced into Brazilian shallow-water tropical rocky reefs by oil and gas platforms. Both species are simultaneous hermaphrodites and brooders. Histological analysis shows a continuous reproduction with the presence of different stages of development of oocytes, spermatic cysts and larvae occurring together in the same polyps (overlapping). Gametogenesis, embryogenesis, planulation and settlement were observed. Although most of the colonies showed only oocytes, none had only testes. Spermatic cysts were observed in 8.3% ofT. coccineacolonies and in 5.5% of colonies ofT. tagusensis. The maximum diameter of oocyte ofT. tagusensis(1252.5 µm) was greater thanT. coccinea(901.8 µm) and mature spermaries 700 µm in diameter formed the typical arrangement of ‘bouquets’. Although all colonies showed oocytes throughout the year, two reproductive peaks of 3–4 months duration were observed. The larvae ofT. coccineaandT. tagusensishad a competency period of 18 d in aquaria and settled near the parental colony. The investigation of gametogenesis, temporal patterns of reproduction, fecundity and sexual maturation helps to explain the rapid expansion in to new habitats and high population growth in these invasive sun corals.

New “missing link” genus of the colonial volvocine green algae gives insights into the evolution of oogamy

BackgroundThe evolution of oogamy from isogamy, an important biological event, can be summarized as follows: morphologically similar gametes (isogametes) differentiated into small “male” and large “female” motile gametes during anisogamy, from which immotile female gametes (eggs) evolved. The volvocine green algae represent a model lineage to study this type of sex evolution and show two types of gametic unions: conjugation between isogametes outside the parental colonies (external fertilization during isogamy) and fertilization between small motile gametes (sperm) and large gametes (eggs) inside the female colony (internal fertilization during anisogamy and oogamy). Although recent cultural studies on volvocine algae revealed morphological diversity and molecular genetic data of sexual reproduction, an intermediate type of union between these two gametic unions has not been identified.ResultsWe identified a novel colonial volvocine genus, Colemanosphaera, which produces bundles of spindle-shaped male gametes through successive divisions of colonial cells. Obligately anisogamous conjugation between male and female motile gametes occurred outside the female colony (external fertilization during anisogamy). This new genus contains 16- or 32-celled spheroidal colonies similar to those of the volvocine genera Yamagishiella and Eudorina. However, Colemanosphaera can be clearly distinguished from these two genera based on its sister phylogenetic position to the enigmatic flattened colonial volvocine Platydorina and external fertilization during anisogamy. Two species of Colemanosphaera were found in a Japanese lake; these species are also distributed in European freshwaters based on a published sequence of an Austrian strain and the original description of Pandorina charkowiensis from Ukraine.ConclusionsBased on phylogeny and morphological data, this novel genus exhibits a missing link between Platydorina and the typical spheroidal colonial volvocine members such as Pandorina or Yamagishiella. Considering the external obligate anisogamy, oogamy evolution may have been preceded by the transition from external to internal fertilization during anisogamy within the volvocine green algae.

Evidence to support natural hybridization between Anopheles sinensis and Anopheles kleini (Diptera: Culicidae): possibly a significant mechanism for gene introgression in sympatric populations

BackgroundMalaria caused by Plasmodium vivax is still a public health problem in the Republic of Korea (ROK), particularly regarding the recent re-emergence of this malarial species near the demilitarized zone in northwestern Paju City, Gyeonggi-do Province. Currently, at least 4 species (An. kleini, An. pullus, An. belenrae and An. lesteri) of the Hyrcanus Group are reported as possible natural vectors of vivax malaria in the ROK, and An. sinensis, which is the most dominant species, has long been incriminated as an important natural vector of this P. vivax. However, An. sinensis was ranked recently as a low potential vector. According to the discovery of natural hybrids between An. sinensis (a low potential vector for P. vivax) and An. kleini (a high potential vector for P. vivax) in Paju City, intensive investigation of this phenomenon is warranted under laboratory conditions.MethodsMosquitoes were collected during 2010-2012 from Paju City, ROK. Hybridization experiments used iso-female line colonies of these anophelines together with DNA analysis of ribosomal DNA [second internal transcribed spacer (ITS2)] and mitochondrial DNA [cytochrome c oxidase subunit I (COI)] of the parental colonies, F1-hybrids and repeated backcross progenies were performed intensively by using a PCR-based assay and pyrosequencing technology.ResultsThe results from hybridization experiments and molecular investigations revealed that the mitochondrial COI gene was introgressed from An. sinensis into An. kleini. The An. sinensis progenies obtained from consecutive repeated backcrosses in both directions, i.e., F2-11 progeny [(An. sinensis x An. kleini) x An. sinensis] and F3-5 progeny [(An. kleini x An. sinensis) x An. kleini] provided good supportive evidence.ConclusionsThis study revealed introgression of the mitochondrial COI gene between An. sinensis and An. kleini through consecutive repeated backcrosses under laboratory conditions. This new body of knowledge will be emphasized in reliable promising strategies in order to replace the population of An. kleini as a high potential vector for P. vivax, with that of a low potential vector, An. sinensis, through the mechanism of gene introgression in nature.

Revisiting the connectivity puzzle of the common coral Pocillopora damicornis

Understanding levels of connectivity among scleractinian coral populations over a range of temporal and spatial scales is vital for managing tropical coral reef ecosystems. Here, we use multilocus microsatellite genotypes to assess the spatial genetic structure of two molecular operational taxonomic units (MOTUs, types α and β) of the widespread coral Pocillopora damicornis on the Great Barrier Reef (GBR) and infer the extent of connectivity on spatial scales spanning from local habitat types to latitudinal sectors of the GBR. We found high genetic similarities over large spatial scales spanning > 1000km from the northern to the southern GBR, but also strong genetic differentiation at local scales in both MOTUs. The presence of a considerable number of first-generation migrants within the populations sampled (12% and 27% for types α and β, respectively) suggests that genetic differentiation over small spatial scales is probably a consequence of stochastic recruitment from different genetic pools into recently opened up spaces on the reef, for example, following major disturbance events. We explain high genetic similarity among populations over hundreds of kilometres by long competency periods of brooded zooxanthellate larvae and multiple larval release events each year, combined with strong longshore currents typical along the GBR. The lack of genetic evidence for predominantly clonal reproduction in adult populations of P.damicornis, which broods predominantly asexually produced larvae, further undermines the paradigm that brooded larvae settle close to parent colonies shortly after the release.

Bacterial Competition Reveals Differential Regulation of the pks Genes by Bacillus subtilis

Bacillus subtilis is adaptable to many environments in part due to its ability to produce a broad range of bioactive compounds. One such compound, bacillaene, is a linear polyketide/nonribosomal peptide. The pks genes encode the enzymatic megacomplex that synthesizes bacillaene. The majority of pks genes appear to be organized as a giant operon (>74 kb from pksC-pksR). In previous work (P. D. Straight, M. A. Fischbach, C. T. Walsh, D. Z. Rudner, and R. Kolter, Proc. Natl. Acad. Sci. U. S. A. 104:305-310, 2007, doi:10.1073/pnas.0609073103), a deletion of the pks operon in B. subtilis was found to induce prodiginine production by Streptomyces coelicolor. Here, colonies of wild-type B. subtilis formed a spreading population that induced prodiginine production from Streptomyces lividans, suggesting differential regulation of pks genes and, as a result, bacillaene. While the parent colony showed widespread induction of pks expression among cells in the population, we found the spreading cells uniformly and transiently repressed the expression of the pks genes. To identify regulators that control pks genes, we first determined the pattern of pks gene expression in liquid culture. We next identified mutations in regulatory genes that disrupted the wild-type pattern of pks gene expression. We found that expression of the pks genes requires the master regulator of development, Spo0A, through its repression of AbrB and the stationary-phase regulator, CodY. Deletions of degU, comA, and scoC had moderate effects, disrupting the timing and level of pks gene expression. The observed patterns of expression suggest that complex regulation of bacillaene and other antibiotics optimizes competitive fitness for B. subtilis.

Increased brood viability and longer lifespan of honeybees selected for propolis production

Propolis has been proposed to affect honeybee health. To test this hypothesis, we initially evaluated propolis production in 36 honeybee colonies. The three highest (HP) and three lowest propolis-producing (LP) colonies had mean yields of 16.0 and 0.64 g, respectively. Queens and drones from these parental colonies were crossed by artificial insemination to produce five colonies each of the following crosses: HP♀ × HP♂, HP♀ × LP♂, LP♀ × HP♂, and LP♀ × LP♂. Colonies headed by HP♀ × HP♂ queens produced 34 times more propolis than those headed by LP♀ × LP♂ queens and five times more than those from the other two crosses. Newly emerged bees were marked to measure longevity, and egg and brood counts were made to determine brood survival rates. The colonies with queens derived from crosses between high-propolis-producing colonies had significantly higher brood viability and greater worker bee longevity. We conclude that colonies that collect more propolis are healthier and have longer-living bees.

Phenotypic variation in the plant pathogenic bacterium Acidovorax citrulli.

Acidovorax citrulli causes bacterial fruit blotch (BFB) of cucurbits, a disease that threatens the cucurbit industry worldwide. Despite the economic importance of BFB, little is known about pathogenicity and fitness strategies of the bacterium. We have observed the phenomenon of phenotypic variation in A. citrulli. Here we report the characterization of phenotypic variants (PVs) of two strains, M6 and 7a1, isolated from melon and watermelon, respectively. Phenotypic variation was observed following growth in rich medium, as well as upon isolation of bacteria from inoculated plants or exposure to several stresses, including heat, salt and acidic conditions. When grown on nutrient agar, all PV colonies possessed a translucent appearance, in contrast to parental strain colonies that were opaque. After 72 h, PV colonies were bigger than parental colonies, and had a fuzzy appearance relative to parental strain colonies that are relatively smooth. A. citrulli colonies are generally surrounded by haloes detectable by the naked eye. These haloes are formed by type IV pilus (T4P)-mediated twitching motility that occurs at the edge of the colony. No twitching haloes could be detected around colonies of both M6 and 7a1 PVs, and microscopy observations confirmed that indeed the PVs did not perform twitching motility. In agreement with these results, transmission electron microscopy revealed that M6 and 7a1 PVs do not produce T4P under tested conditions. PVs also differed from their parental strain in swimming motility and biofilm formation, and interestingly, all assessed variants were less virulent than their corresponding parental strains in seed transmission assays. Slight alterations could be detected in some DNA fingerprinting profiles of 7a1 variants relative to the parental strain, while no differences at all could be seen among M6 variants and parental strain, suggesting that, at least in the latter, phenotypic variation is mediated by slight genetic and/or epigenetic alterations.

Optimal colony fissioning in social insects: testing an inclusive fitness model with honey bees

In most species of social insects, when a queen departs from her parental nest to found a new colony, she leaves on her own. In some species, however, the departing queen leaves accompanied by a portion of the parental colony’s workers and there is a permanent fissioning of the worker force. Little is known about how the adult workers in colonies of fissioning species distribute themselves between the old and the new colonies. We examined this problem, building on Bulmer’s (J Theor Biol 100: 329–339, 1983) model for the optimal splitting of a colony’s adult workforce during colony reproduction. We first created an inclusive fitness model of optimal colony fissioning that applies to species in which fissioning gives rise to two autonomous colonies. The model predicts the optimal “swarm fraction”, which we define as the proportion of the adult workers in a fissioning colony that join the departing queen. We then tested the model by comparing the predicted and observed swarm fractions in honey bees. We found a close match between predicted (0.76–0.77) and observed (0.72 ± 0.04) swarm fractions. Evidently, worker honey bees distribute themselves between the old and new colonies in a way that jointly maximizes the inclusive fitness of each worker. We conclude by discussing additional ways to test the model.

Phlebotomus orientalis Sand Flies from Two Geographically Distant Ethiopian Localities: Biology, Genetic Analyses and Susceptibility to Leishmania donovani

Background Phlebotomus orientalis Parrot (Diptera: Psychodidae) is the main vector of visceral leishmaniasis (VL) caused by Leishmania donovani in East Africa. Here we report on life cycle parameters and susceptibility to L. donovani of two P. orientalis colonies originating from different sites in Ethiopia: a non-endemic site in the lowlands - Melka Werer (MW), and an endemic focus of human VL in the highlands - Addis Zemen (AZ).Methodology/Principal FindingsMarked differences in life-cycle parameters between the two colonies included distinct requirements for larval food and humidity during pupation. However, analyses using Random Amplified Polymorphic DNA (RAPD) PCR and DNA sequencing of cytB and COI mitochondrial genes did not reveal any genetic differences. F1 hybrids developed successfully with higher fecundity than the parental colonies. Susceptibility of P. orientalis to L. donovani was studied by experimental infections. Even the lowest infective dose tested (2×103 per ml) was sufficient for successful establishment of L. donovani infections in about 50% of the P. orientalis females. Using higher infective doses, the infection rates were around 90% for both colonies. Leishmania development in P. orientalis was fast, the presence of metacyclic promastigotes in the thoracic midgut and the colonization of the stomodeal valve by haptomonads were recorded in most P. orientalis females by day five post-blood feeding.ConclusionsBoth MW and AZ colonies of P. orientalis were highly susceptible to Ethiopian L. donovani strains. As the average volume of blood-meals taken by P. orientalis females are about 0.7 µl, the infective dose at the lowest concentration was one or two L. donovani promastigotes per sand fly blood-meal. The development of L. donovani was similar in both P. orientalis colonies; hence, the absence of visceral leishmaniasis in non-endemic area Melka Werer cannot be attributed to different susceptibility of local P. orientalis populations to L. donovani.