Reduction In Reproductive Fitness Research Articles

Meiotic pairing irregularity and homoeologous chromosome compensation cause rapid karyotype variation in synthetic allotetraploid wheat.

Allopolyploidization may initiate rapid evolution due to heritable karyotypic changes. The types and extents of these changes, the underlying causes, and their effects on phenotype remain to be fully understood. Here, we designed experimental populations suitable to address these issues using a synthetic allotetraploid wheat. We show that extensive variation in both chromosome number (NCV) and structure (SCV) accumulated in a selfed population of a synthetic allotetraploid wheat (genome Sb Sb DD). The combination of NCVs and SCVs generated massive organismal karyotypic heterogeneity. NCVs and SCVs were intrinsically correlated and highly variable across the seven sets of homoeologous chromosomes. Both NCVs and SCVs stemmed from meiotic pairing irregularity (presumably homoeologous pairing) but were also constrained by homoeologous chromosome compensation. We further show that homoeologous meiotic pairing was positively correlated with sequence synteny at the subtelomeric regions of both chromosome arms, but not with genic nucleotide similarity per se. Both NCVs and SCVs impacted phenotypic traits but only NCVs caused significant reduction in reproductive fitness. Our results implicate factors influencing meiotic homoeologous chromosome pairing and reveal the type and extent of karyotypic variation and its immediate phenotypic manifestation in synthetic allotetraploid wheat. This has relevance for our understanding of allopolyploid evolution.

Effects of ozone stress on flowering phenology, plant-pollinator interactions and plant reproductive success.

Tropospheric ozone is a highly oxidative pollutant with the potential to alter plant metabolism. The direct effects of ozone on plant phenotype may alter interactions with other organisms, such as pollinators, and, consequently, affect plant reproductive success. In a set of greenhouse experiments, we tested whether exposure of plants to a high level of ozone affected their phenological development, their attractiveness to four different pollinators (mason bees, honeybees, hoverflies and bumblebees) and, ultimately, their reproductive success. Exposure of plants to ozone accelerated flowering, particularly on plants that were growing in autumn, when light and temperature cues, that commonly promote flowering, were weaker. Simultaneously, there was a tendency for ozone-exposed plants to disinvest in vegetative growth. Plant exposure to ozone did not substantially affect pollinator preference, but bumblebees had a tendency to visit more flowers on ozone-exposed plants, an effect that was driven by the fact that these plants tended to have more open flowers, meaning a stronger attraction signal. Honeybees spent more time per flower on ozone-exposed plants than on control plants. Acceleration of flower production and the behavioural responses of pollinators to ozone-exposed plants resulted in retained reproductive fitness of plants pollinated by bumblebees, honeybees and mason bees, despite the negative effects of ozone on plant growth. Plants that were pollinated by hoverflies had a reduction in reproductive fitness in response to ozone. In a natural setting, acceleration of flowering by ozone might foster desynchronization between plant and pollinator activities. This can have a strong impact on plants with short flowering periods and on plants that, unlike wild mustard, lack compensatory mechanisms to cope with the absence of pollinator activity in the beginning of flowering.

Effects of Plasmodium gallinaceum on hemolymph physiology of Aedes aegypti during parasite development

Insect disease vectors show diminished fecundity when infected with Plasmodium. This phenomenon has already been demonstrated in laboratory models such as Aedes aegypti, Anopheles gambiae and Anopheles stephensi. This study demonstrates several changes in physiological processes of A. aegypti occurring upon infection with Plasmodium gallinaceum, such as reduced ecdysteroid levels in hemolymph as well as altered expression patterns for genes involved in vitellogenesis, lipid transport and immune response. Furthermore, we could show that P. gallinaceum infected A. aegypti presented a reduction in reproductive fitness, accompanied by an activated innate immune response and increase in lipophorin expression, with the latter possibly representing a nutritional resource for Plasmodium sporozoites.

Immune system activation affects male sexual signal and reproductive potential in crickets

Parasite-mediated sexual selection theory posits that individuals (usually females) choose mates by assessing the expression of costly secondary sexual signals, which provide reliable indications of parasite resistance. If these signals are indeed reliable, then immune-compromised males are predicted to exhibit changes in the sexual signal that are discernable by the female. Moreover, the mating pair is predicted to exhibit some reduction in reproductive fitness if the male is immune compromised. Here, we addressed these predictions in the ground cricket, Allonemobius socius, by injecting juvenile males with lipopolysaccarides, which allowed us to activate the immune system without the introduction of a metabolically active pathogen. As a consequence, we were able to disentangle the cost of immune system activation from the cost of infection. We found that immune activation had a long-term effect on male calling song and the males' ability to provide paternal resources, which can constrain male and female reproductive potential. We also found that song interpulse interval varied significantly with the male's immune treatment and may therefore provide choosy females with a way to avoid mating with immune-compromised males. In short, our data support the parasite-mediated theory of sexual selection, suggesting that female's gain direct benefits by mating with males who are immune competent. Copyright 2007.

Molecular abnormalities of FSH and LH action.

The identification of naturally occurring genetic mutations in individuals with disorders of reproductive function is the first logical step to therapy. To date, diagnostic investigations have been assisted by polymerase chain reaction and the development of an increasing number of effective screening techniques to scan genomic DNA (deoxyribonucleic acid) for causative mutations. The continued expansion of these technologies, coupled with high throughput gene sequencing, will ultimately result in automated DNA diagnosis for the practicing clinician at the point of care. At that time, the direct examination of a patient's DNA will be the definitive means of establishing the presence of specific genetic changes that cause or increase one's susceptibility to disease. This presentation selects important candidate genes in the human hypothalamic-pituitary-ovarian axis (HPG), reviews our knowledge of the spontaneously occurring human mutations that affect these genes, and reviews the biological implications of this information. To date, causative mutations in candidate genes have provided important insights into the transcription factors, receptors, and hormones that regulate the HPG axis at many levels. A major challenge in this field is that mutations in many of these genes and others remaining to be identified lead to infertility. The reduction in reproductive fitness due to these mutations limits the ability of investigators to use traditional genetic linkage and association studies to identify and clone important unidentified reproductive genes. Fortunately analysis of human gametes and new strategies that are being developed for the identification and mapping of complex human diseases will become increasingly important in continuing studies of idiopathic human infertility. At this time, it is helpful for the reader to become acquainted with some of the prototype mutations in candidate genes, their phenotypic consequences, and their prevalence. This presentation is designed to describe the known mutations in the gonadotropin genes and the genes encoding their respective receptors. The phenotypic effects of these mutations is compared, and evidence for causation is reviewed.

The costs of mounting an immune response are reflected in the reproductive fitness of the mosquito Anopheles gambiae

We have used Anopheles gambiae, a major vector of malaria in Africa, to test the hypothesis that the operation of a surveillance or immune system against microorganisms and parasites can be costly to the reproductive success of the host. Blood‐fed mosquitoes were challenged with an immune elicitor, lipopolysaccharide (LPS), and their resultant antimicrobial activity, accumulation of yolk protein in the ovary and egg production was monitored. Humoral activity against the Gram‐positive bacterium Micrococcus luteus was induced by LPS injection in a dose‐responsive manner. LPS treatment also caused a concomitant significant reduction in the accumulation of protein in ovaries 24 h after injection and in the production of eggs during the same gonotrophic cycle. Unlike immune stimulation, reduction in reproductive fitness was not dose responsive. Oral administration of LPS also significantly reduced ovarian protein content although we could not detect the presence of anti‐M. luteus activity in the gut tissue by using an inhibition zone assay. These findings indicate that immune stimulation imposed reproductive fitness costs on mosquitoes.

First Report of Colletotrichum gloeosporioides on Arceuthobium tsugense subsp. tsugense in Canada.

Although reports of Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. in Penz. occurring as a hyperparasite of western hemlock dwarf mistletoe (Arceuthobium tsugense (Rosend.) G.N. Jones subsp. tsugense) have been previously published (1), there are no collection or herbarium records to support this finding (B. Geils, personal communication). Given this ambiguity, this report is the first record of C. gloeosporioides on A. tsugense subsp. tsugense based on voucher collections deposited at the Pacific Forestry Centre (DAVFP #25277). Western hemlock dwarf mistletoe is a parasitic plant that occurs on western hemlock (Tsuga heterophylla (Raf.) Sarg.), causing growth reduction, degradation of merchantable wood, and reduction in reproductive fitness of its host. Dwarf mistletoe infections result in significant reduction in volume of mature stands of T. heterophylla in coastal British Columbia (B.C.). Aside from traditional silvicultural control methods, a potentially important control includes the use of fungi deleterious to the growth of dwarf mistletoe. C. gloeosporioides has been identified as a hyperparasite of numerous Arceuthobium spp., including A.tsugense subsp. mertensiana Hawksworth & Nickrent (1). In October 1996 and May 1997, lesions were observed on shoots of A. tsugense subsp. tsugense collected from two field sites, Cowichan Lake (48°56'N, 124°23'W) and Duncan (48°45'N, 123°50'W), B.C. Acervuli containing masses of spores and dark setae were observed within lesions, and conidia from the acervuli produced pure cultures of C. gloeosporioides. The fungus was identified based on conidial and cultural characteristics (2). Conidia were cylindrical to elliptical in shape and measured 12.5 to 15.0 × 2.5 to 4.0 μm. On potato dextrose agar, colonies developed a white to patchy, dark gray mycelial mat with conidia produced in mycelia and in distinct salmon-colored masses. Colony growth occurred at 10 to 30°C, with optimum growth at 20°C, while maximum germination was observed at 30°C after 24 h, with germination occurring between 10 and 35°C. Branches with healthy mistletoe shoots were cut from western hemlock trees and placed in Hoagland's nutrient solution. A spore suspension (106 conidia per ml) was brushed onto mistletoe shoots at a rate of approximately 1 ml per replicate, with 8 to 10 replicate branches, each containing a cluster of >5 shoots. Controls were treated with sterile, distilled water and branches were incubated in the greenhouse with 55% relative humidity. The fungus was re-isolated from acervuli that developed on inoculated shoots after 14 days, and these results were repeated in a second experiment. The fungus was not isolated from the controls. Koch's postulates were fulfilled by inoculating shoots of A. tsugense subsp. tsugense and re-isolating the pathogen from symptomatic stems. C. gloeosporioides could be an important control measure for western hemlock dwarf mistletoe.

The effects of infection with Plasmodium yoelii nigeriensis on the reproductive fitness of Anopheles stephensi.

Infection with the rodent malarial parasite Plasmodium yoelii nigeriensis caused a significant reduction in the reproductive fitness (number of eggs produced and proportion of eggs hatched) of two different generations of Anopheles stephensi. Overall fertility (number of larvae produced) was reduced by 38.3% in the generation containing smaller mosquitoes (with a wing length of 3.2 +/- 0.1 mm) with relatively larger parasite burdens, and by 48.81% in the generation containing larger mosquitoes (with a wing length of 3.4 +/- 0.1 mm). The contribution that reduction in egg production and egg hatching made to overall reduction in reproductive fitness differed in each experiment. No significant difference was observed in the egg size (length from tip to tip and breadth at the centre) of control and infected mosquitoes in another generation of infected An. stephensi.

The effect of Plasmodium yoelii nigeriensis infection on ovarian protein accumulation by Anopheles stephensi.

Both anopheline and culicine mosquitoes have been shown to incur a reduction in reproductive fitness when infected with malaria parasites. The agent of rodent malaria, Plasmodium yoelii nigeriensis, was used as a laboratory model to investigate changes in the accumulation of protein in the ovaries of Anopheles stephensi when infected with oocysts or when feeding on mice with heavy asexual parasitaemia but no mature gametocytes. Herein we report that during the early phases of the gonotrophic cycle the ovarian protein content increased normally; however, after 16 h post-blood-feeding there was a significant reduction in the total protein content in ovaries from infected mosquitoes. The development of ovaries from mosquitoes undergoing a second gonotrophic cycle and containing maturing oocysts was similarly affected. Ovarian protein profiles produced by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed a depletion of the yolk protein vitellin. Ovaries from mosquitoes feeding on a mouse with 31% parasitaemia, no detectable gametocytes and a low haematocrit (29% packed cell volume) also exhibited a reduction in protein content, although this did not occur until much later in the gonotrophic cycle. The role of blood-meal quality and malaria infection in the reduction in egg production is discussed.

Cytogenetic and reproductive studies of bulls born co-twin with freemartins.

Summary. The XX lymphocytes in peripheral blood of 22 bulls born co-twin with freemartins ranged from 5 to 95%. The difference of 1·2% between the means of XX percentages at initial and final karyotyping of 14 bulls over periods of 1–5 years was not significant (P > 0·25). Seven (58·3%) of the 12 A.I. chimaeric bulls were reproductive culls as compared to only 5·4% of their 128 controls (P < 0·001). The culled chimaeras produced no semen, had a low sperm output or had a high incidence of abnormal spermatozoa. The means for motility, sperm concentration and motile spermatozoa per ejaculate were significantly lower for the 12 chimaeric bulls than for a random sample of 12 controls (P < 0·025). The 60- to 90-day non-return rate for 30 814 services to 8 chimaeric bulls was 70% with a −0·1% mean deviation from contemporary breed average (P > 0·5). The 7 chimaeric bulls culled for poor reproductive performance had larger and more numerous focal areas of testicular degeneration. Areas of lymphocytic infiltration in testes of many of these bulls suggest a rejection phenomenon or the autoimmune response. No XX germ cells were detected in testes of 11 chimaeric bulls, aged 1–9 years. Differential haemolysis blood typing tests on one bull with 85% XX lymphocytes and 23 of his dam—daughter pairs provided no evidence of germ cell chimaerism. One bull with 33% XX cells sired an excess of daughters (71%) in a progeny group of 48, a significant deviation from a 1:1 ratio (P < 0·01). A disturbance in normal spermatogenesis in prenatal and postnatal life by transplanted XX primordial germ cells may contribute to the marked reduction in reproductive fitness of many chimaeric bulls.