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PubMed1999

Sexual selection resulting from extrapair paternity in collared flycatchers.

Extrapair paternity has been suggested to represent a potentially important source of sexual selection on male secondary sexual characters, particularly in birds with predominantly socially monogamous mating systems. However, relatively few studies have demonstrated sexual selection within single species by this mechanism, and there have been few attempts to assess the importance of extrapair paternity in relation to other mechanisms of sexual selection. We report estimates of sexual selection gradients on male secondary sexual plumage characters resulting from extrapair paternity in the collared flycatcher Ficedula albicollis, and compare the importance of this form of sexual selection with that resulting from variation in mate fecundity. Microsatellite genotyping revealed that 15% of nestlings, distributed nonrandomly among 33% of broods (N=79), were the result of extrapair copulations. Multivariate selection analyses revealed significant positive directional sexual selection on two uncorrelated secondary sexual characters in males (forehead and wing patch size) when fledgling number was used as the measure of fitness. When number of offspring recruiting to the breeding population was used as the measure of male fitness, selection on these traits appeared to be directional and stabilizing, respectively. Pairwise comparisons of cuckolded and cuckolding males revealed that males that sired young through extrapair copulations had wider forehead patches, and were paired to females that bred earlier, than the males that they cuckolded. Path analysis was used to partition selection on these traits into pathways via mate fecundity and sperm competition, and suggested that the sperm competition pathway accounted for between 64 and 90% of the total sexual selection via the two paths. The selection revealed in these analyses is relatively weak in comparison with many other measures of selection in natural populations. We offer some explanations for the relatively weak selection detected. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1999

Determining the reproductive behaviour of individual brown-headed cowbirds using microsatellite DNA markers.

The reproductive behaviour of brood-parasitic birds has been of long-standing interest to evolutionary biologists but key features such as the mating system, patterns of host use and degree of overlap of female egg-laying ranges are largely unknown for particular species. Here we use microsatellite DNA markers to obtain such information for one of the best-studied brood parasites, the brown-headed cowbird, Molothrus ater. Parentage analyses of young and adults from a marked population at Delta, Manitoba for 1 year revealed the following key features of the reproductive behaviour of this species. (1) Monogamy is the predominant genetic mating system in this population, although matings by a single male with more than one female occur infrequently. (2) There is substantial variance in reproductive success among individuals, with only 23 out of 34 (68%) of all resident females and 21 out of 54 (39%) of all resident males in the study population identified as producing offspring. (3) Nonbreeding adults are seen less frequently and have shorter periods of residency on the study site suggesting they may form a subpopulation of 'floaters'. (4) Roughly half the females on site laid their eggs in the nests of a single host; most strikingly, the most fecund female laid all 13 of her eggs in red-winged blackbird, Agelaius phoeniceus, nests. This raises the possibility that cowbird populations may consist of combinations of females some of whom are host generalists and others host specialists. (5) Female egg-laying areas rarely overlap. (6) Realized annual fecundity of females may be lower than previously suggested. These results provide important information that can be used to clarify the mechanism and the selection pressures that have led to the evolution of different features of the reproductive behaviour of these birds. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2000

Sexual selection and the evolution of exclusive paternal care in arthropods.

Internal fertilization and anisogamy are thought to impede the evolution of exclusive paternal care by reducing paternity assurance and increasing male promiscuity. The potential role of sexual selection in easing these constraints is currently being examined in vertebrates but has not been seriously studied in most arthropods. To distinguish the effects of sexual from natural selection on the evolution of arthropod paternal care, I tested predictions of the state of several life history and behavioural traits under both forms of selection across all known taxa with exclusive paternal care. The results suggest parallels between prezygotic nuptial gifts and exclusive postzygotic paternal care and support the hypothesis that, in arthropods, male behaviours that enhance female reproductive success either directly by releasing females from the fecundity constraints of maternal care (enhanced fecundity hypothesis) or indirectly by identifying mates with superior genes (handicap principle) are traits on which sexual selection has acted. Under such conditions males willing to guard young become preferred mates for gravid females and enjoy greater promiscuity than males unable or unwilling to guard. Females use nest construction or the act of guarding another female's eggs as honest signals of paternal intent and quality. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1996

Effect of Zn, Cu, Pb, and Cd on fitness in snails (Helix aspersa).

Juveniles and adults of the Brown garden snail (Helix aspersa Müll.) were fed on an artificial diet contaminated with Zn (ca. 40-12,000 micrograms.g-1 dry wt), Cu (ca. 9-1600 micrograms.g-1 dry wt), pb (ca. 0.4-12,700 micrograms.g-1 dry wt), Cd (ca. 0.16-145 micrograms.g-1 dry wt), and all four metals mixed together for 120 days. Significant negative exponential regressions of food consumption and fecundity on concentrations were found for all treatments. Growth rate was affected significantly only by Zn and mixed treatments. The calculated EC20(consumption) values for juveniles were (in microgram.g1): Zn, 855; Cu, 248; Pb, 5290; Cd, 60; and for adults: Zn, 1240; Cu, 275; Pb, 3120; Cd, 147. In mixed treatment EC20(consumption) values were substantially lower indicating the additive effect of pollution with these four metals. EC20(consumption) for Zn in mixed treatment was 329 micrograms.g-1 for juveniles and 661 micrograms.g-1 for adults. The following EC20 values were estimated for fecundity (in micrograms.g-1): Zn, 1740; Cu, 533; Pb, 6140; Cd, 120; Zn in mixed treatment, 2210. The relative toxicities of the four metals were compared with their ratios in contaminated field sites. Comparing Zn and Cd, for example, even though Zn is ca. 13-24 times less toxic than Cd, it is usually present in plants and forest litter in concentrations ca. 100 times greater than those of Cd. Thus, of these two metals, Zn appeared to be potentially the most important pollutant in ecologically relevant situations. No effect of any treatment on mortality was found during the 4-month experiment. The calculated scenarios of population dynamics under the stress of chronic pollution with mixtures of the four metals revealed that the delayed reproduction due to estivation of snails may be the main cause of population decline at high metal concentrations in food. However, at concentrations at and below ca. 1000 micrograms Zn.g-1 in food, if the reproduction is not delayed the population may persist for a long time (0.25 control number after 50 years).

Aging↗
PubMed1996

Comparison between a normal and a Cr-tolerant strain of Scenedesmus acutus as a food source to Daphnia magna.

A normal (S2-N) and a Cr-tolerant (S2-T) strain of Scenedesmus acutus, grown in Cr-free medium or in the presence of 1, 5, or 10 mg/liter Cr(VI), were fed to Daphnia magna. An increase of growth and fecundity was observed in the daphnids when the algae had undergone an increase of dry mass following Cr treatment, which happened in S2-N in the presence of 1 mg/liter and in S2-T in the presence of 5 mg/liter. When the algae were pretreated with 10 mg/liter, growth and fecundity were reduced in the daphnids fed on S2-N, but remained normal in the daphnids fed on S2-T. It is concluded that the tolerant strain remains a good food source even if grown in the presence of a Cr concentration that reduces the nutritional value of the normal strain.

Animals↗
PubMed1997

Toxicity of 4-nonylphenol in a life-cycle test with the midge Chironomus tentans.

A life-cycle test with the macroinvertebrate Chironomus tentans was conducted with 4-nonylphenol. The chironomids were exposed to a series of concentrations of 4-nonylphenol via the water, in an intermittent (2 times/day) water renewal system. The test included evaluation of a number of developmental (e.g., growth) and reproductive (e.g., emergence, fecundity, viability) endpoints through parental and into F1 generations. Reductions in survival were observed in 20-day-old larvae at the highest test concentration, which corresponded to no-observable- and lowest-observable-effect concentrations of 42 and 91 microg/liter, respectively. No significant effects on larval growth (20 days), organism survival past 20 days, emergence success or pattern, sex ratio, fecundity, or egg viability were observed at any treatment level. Qualitative observations indicated an increase in deformed egg masses at the highest test concentrations; however, the biological significance of this is uncertain.

Animals↗
PubMed1998

Evaluation of a high-hardness COMBO medium and frozen algae for Daphnia magna.

A new high-hardness (H-H) COMBO medium for long-term culturing and bioassay testing of Daphnia magna was evaluated in 21-day survival, growth, and reproduction studies. The COMBO medium originally designed for softwater daphnid species (i.e., D. pulicaria) was modified for the hardwater species D. magna. This medium also allowed continuous culturing of a green algal food source for daphnids, Ankistrodesmus falcatus. After 12 generations of culturing in H-H COMBO medium, the mean fecundity was 128 +/- 12 (coefficient of variation = 9.4%). No significant observations of dead young, aborted eggs, or reduced antennas were made during the 6 months of continuous culturing. The no-observable-effect concentration (NOEC) for a reference toxicant standard, 3,4-dichloroaniline (3,4-DCA), was 8.3 micrograms/liter, which is similar to published values. These studies demonstrate that H-H COMBO is an acceptable medium for use for culturing and bioassay testing with D. magna. Additional experiments using frozen aliquots of A. falcatus were conducted. Although mean fecundity (64 +/- 7) and adult length were significantly decreased from the values for daphnids fed fresh algae, the NOEC for 3,4-DCA was > 25 micrograms/liter. The use of this alternative food source in bioassay testing appears promising, but further optimization of feeding rates is warranted.

Aniline Compounds↗
PubMed1997

Schistosoma mansoni: maturation rate and drug susceptibility of different geographic isolates.

The fecundities and drug susceptibilities of Schistosoma mansoni isolates from Senegal, Puerto Rico, and Kenya have been examined in mice. The Senegal parasite, obtained from the field in 1993, was shown to have a longer prepatent period (eggs first recovered in the faeces on Day 46 after infection) than those of two isolates, from Puerto Rico and Kenya, that had been maintained for a long period in the laboratory (faecal eggs recovered on Days 38 and 36 after infection, respectively). A Kenyan isolate, also collected from the field in 1994, was shown to mature more slowly than the laboratory-maintained Kenyan isolate. Tissue egg counts confirmed that early in infection the fecundity of the recently collected isolates from Senegal and Kenya was significantly lower than that of the long-term laboratory-maintained Kenyan isolate. Praziquantel and oxamniquine treatment of 8-week-old infections caused a significant (P < 0.001) reduction in worm burden in all isolates tested. However, the reduction in worm burden after praziquantel treatment of infections of the Senegal isolate (50% reduction) was significantly lower than the > 90% reductions in worm burdens after praziquantel treatment of mice infected with either of the Kenyan isolates (P < 0.001). The study confirms that despite being tolerant to praziquantel, the Senegal isolate is fully susceptible to oxamniquine. The praziquantel tolerance of the Senegal parasite is not solely attributed to the state of maturation of the parasite at the time of drug administration.

Animals↗
PubMed2000

Resource competition in stage-structured populations.

Two models are made to account for the dynamics of a consumer-resource system in which the consumers are divided into juveniles and adults. The resource grows logistically and a type II functional response is assumed for consumers. Resource levels determine fecundity and maturation rates in one model, and mortality rates in the other. The analysis of the models shows that the condition for establishment of consumers is that the product of per capita fecundity rate and maturation rates is higher than the product of juvenile and adult per capita decay rates at a resource level equal to its carrying capacity. This result imposes a minimal abundance of resource able to maintain the consumers. A second result shows an equilibrium stage structure, with a small instability when juveniles and adults mean saturation constants are different. The implications of these results for community dynamics are discussed.

Age Factors↗
PubMed1994

Transgenerational, ultrastructural analysis on the antioxidative effects of tocopherol on early gametogenesis in Caenorhabditis elegans grown in 100% oxygen.

The random, free-radical-mediated oxidations of biological molecules result in membrane degradation leading to cellular deterioration (B. Halliwell, Free Radical Res. Commun. 9, 1-32, 1990). External oxygen, prooxidants, and internally produced oxygen free radicals (oxyradicals), interact and alter the nature of biomembranes. Antioxidants, e.g., tocopherol (Vitamin E), inhibit such oxidative damage of free radicals. In the present study, the nematode Caenorhabditis elegans was grown under hyperoxia (100% oxygen) with or without the addition of Vitamin E to the growth media. The nematodes were viable under such conditions for at least eight generations, although fecundity gradually decreased through successive generations, presumably due to genetic load. Vitamin E was also shown to have a protective effect against paraquat, which is a strong, intracellular, oxidizing agent. Ultrastructural observations of early meiosis showed that the formation of synaptonemal complexes was compromised and that the telomeres failed to attach to the nuclear envelope. Those nematodes grown in 100% oxygen with 200 micrograms/ml Vitamin E had normal meiotic structures and normal fecundity. Thus, the presence of enhanced levels of intracellular Vitamin E resulted in protection against oxidative stress during gametogenesis.

Animals↗
PubMed1997

In utero and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces genital dysmorphogenesis in the female rat.

Recently, Gray and Ostby (Toxicol. Appl. Pharmacol. 133, 285-294, 1995) reported that in utero and lactational TCDD exposure causes striking abnormalities in the rat female reproductive system, including reduced fecundity and vaginal threads. The mechanism by which TCDD induces such abnormalities is unknown. Thus, we sought to determine: (1) whether TCDD reduced fecundity by destroying ovarian follicles and (2) whether the vaginal threads resulted from a TCDD-induced developmental defect during embryogenesis or abnormal vaginal opening at puberty. Pregnant Holtzman rats were treated with 1.0 microgram TCDD/kg or vehicle by a single oral dose on gestation day (GD) 11, 15, or 18. Female offspring were monitored for vaginal opening and terminated on postnatal days 2, 21, and 42. The reproductive tract was removed and evaluated for structural abnormalities. The number of primordial follicles also was determined for each ovary. TCDD exposure on GD 11, 15, or 18 did not change the day of vaginal opening, affect ovarian morphology, or reduce the number of primordial follicles. However, this exposure induced the cleft clitoris and vaginal thread originally described by Gray and Ostby (1995) in approximately 55-96% and 36-44% of the litters in our study, respectively. Histologically the thread presented as a thick cord of mesenchyme surrounded by epithelial cells. This defect was clearly visible in histological sections at birth and was noted in the closed vaginas of prepubertal animals. These data suggest that in utero and lactational exposure to TCDD does not reduce the size of the primordial follicle pool; however, it induces developmental abnormalities in the vaginal canal.

Animals↗
PubMed2002

Ecological and evolutionary conditions for fruit abortion to regulate pollinating seed-eaters and increase plant reproduction.

Coevolved mutualisms, such as those between senita cacti, yuccas, and their respective obligate pollinators, benefit both species involved in the interaction. However, in these pollination mutualisms the pollinator's larvae impose a cost on plants through consumption of developing seeds and fruit. The effects of pollinators on benefits and costs are expected to vary with the abundance of pollinators, because large population sizes result in more eggs and larval seed-eaters. Here, we develop the hypothesis that fruit abortion, which is common in yucca, senita, and plants in general, could in some cases have the function of limiting pollinator abundance and, thereby, increasing fruit production. Using a general steady-state model of fruit production and pollinator dynamics, we demonstrate that plants involved in pollinating seed-eater mutualisms can increase their fecundity by randomly aborting fruit. We show that the ecological conditions under which fruit abortion can improve plants fecundity are not unusual. They are best met when the plant is long-lived, the population dynamics of the pollinator are much faster than those of the plant, the loss of one fruit via abortion kills a larva that would have the expectation of destroying more than one fruit through its future egg laying as an adult moth, and the effects of fruit abortion on pollinator abundance are spatially localized. We then use the approach of adaptive dynamics to find conditions under which a fruit abortion strategy based on regulating the pollinator population could feasibly evolve in this type of plant-pollinator interaction.

Animals↗
PubMed2002

Effects of local interactions and local migration on stability.

Mathematical models can help to resolve the longstanding question of whether more diverse communities are more stable. Here, I focus on how local dispersal and local interactions--hallmarks of spatial communities--affect stability in a spatially implicit model with demographic stochasticity. The results are based on a novel way to analyze moment equations. The main conclusion is that the type and strength of density-dependent factors, such as fecundity and competition, determine whether local dispersal and local interactions increase or decrease stability. Local dispersal has a stabilizing effect when fecundity is high, interspecific competition is either low or high, and the number of species is small. Effects of local migration on stability are amplified when space is explicit.

Animal Migration↗
PubMed1987

Differences in life history traits between alcohol dehydrogenase genotypes of Drosophila mercatorum: background and maternal genotype effects.

The effects of genotype at the alcohol dehydrogenase (ADH) locus on developmental time and fecundity were studied using three strains of Drosophila mercatorum. All three strains had similar genetic backgrounds and two were homozygous for the same electrophoretic allele (F for fast). The third strain was homozygous for the slow allele (S). The life history traits of all possible progeny of these strains were studied. The results showed that for both mean developmental time and pattern of eclosion, strong maternal genotype and background effects were present. Fecundity among genotypes was not different, although there was an effect on the total number of offspring suggesting differences in egg-to-adult survivorship.

Alcohol Dehydrogenase↗
PubMed1988

Mdg-1 mobile element polymorphism in selected Drosophila melanogaster populations.

The changes in mdg-1 mobile element polymorphism that followed artificial selection for either high or low egg-to-adult viability in a Drosophila melanogaster population were investigated. The two selected subpopulations were thus characterized for fecundity, wing length, and number and location of the mdg-1 mobile element by in situ hybridization of the biotinylated--DNA on salivary gland chromosomes. The selected populations that differed greatly in egg-to-adult viability showed the same mean fecundity and identical values for intra and inter components of variances, intraclass correlation coefficient, and fluctuating asymmetry estimated on the wing length measurement. This indicates a non-correlated effect between deleterious mutations affecting viability and other fitness components. However, the two selected populations differed in their pattern of mdg-1 location, although the mean number of insertions per genome was not different from that of the initial population; hence, the number of insertions of the mdg-1 mobile element was independent of the effective population size. These results suggest that the mdg-1 copy number was regulated, and that during the selection process, drift and inbreeding made up new insertion patterns of the mdg-1 element in the selected populations. The results are discussed in the light of some recent theoretical models of the population dynamics of transposable elements.

Animals↗
PubMed1992

Selenium and other trace elements in bluegills from agricultural return flows in the San Joaquin Valley, California.

The effects of water quality and exposure to trace elements in irrigation return flows on bluegills (Lepomis macrochirus) were studied in the Merced River and Salt Slough, tributaries to the San Joaquin River, California, during 1988. Our study revealed that conductivity, turbidity, pH, total filterable residue, total hardness, and alkalinity were significantly greater in the Salt Slough, which receives tile drainage, then in the Merced River, which does not receive tile drainage. The concentrations of all trace elements, except aluminum and selenium, were below levels that are expected to have significant chronic toxic effects on bluegills. Selenium body burdens in bluegills from the Salt Slough have increased over fourfold since 1973. Age 1 bluegills from the Salt Slough were significantly shorter than age 1 bluegills from the Merced River. No other significant differences were noted in length by age. The mean length of age 1 bluegills from the Merced River has been increasing since 1983. In contrast, the length of age 1 bluegills from the Salt Slough has been decreasing. Fecundity of bluegills was lower in the Salt Slough than in the Merced River. The concurrent rise in selenium body burdens in bluegills from the Salt Slough and the decreasing total length of age 1 bluegills suggest a causal link between the two. In addition, the apparent depressed fecundity may also be related to the increased body burdens of selenium.

Animals↗
PubMed1976

Studies on host-flea relationship. IV. Progesterone and cortisone do not influence the reproductive potentials of rat fleas Xenopsylla cheopis (Rothschild) and X. astia (Rothschild).

Experiments carried out to study the influence of progesterone and cortisone on the initiation of ovarian maturation, fecundity rate and fertility of the two species of rat fleas Xenopsylla cheopis (Rothschild) and X. astia (Rothschild) indicated that these hormones do not exert any influence on their reproductive potentials. This along with earlier observations show that the factors which regulate ovarian maturation and fecundity in these rat fleas are different from those of the rabbit flea Spilopsyllus cuniculi (Dale).

Animals↗
PubMed1988

An experimental analysis of the relationships between fitness components and malic enzyme genotypes in Tribolium confusum.

The hypothesis that natural selection is capable of maintaining allozyme variation in natural populations was tested using a species of flour beetles, Tribolium confusum. We selected a polymorphic locus (a locus encoding variation for malic enzyme) in an experimental population of T. confusum and scored the genotypes at this locus for a series of fitness components on different flour types. Measurements included survival rate, development time, fecundity, and rate of egg cannibalism. Flour type had significant effects on most traits. Significant differences among genotypes for fecundity and rates of egg cannibalism and the presence of genotype x flour type interactions for development time were demonstrated. Thus, changes in allele frequencies at the malic enzyme locus could in part be under the influence of natural selection. The existence of genotype x flour type interactions suggests that environmental heterogeneity could maintain allozyme variation at the malic enzyme locus.

Animals↗