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Reproductive Components (reproductive + component)
Selected AbstractsSeed dynamics of the mast seeding tussock grass Ampelodesmos mauritanica in Mediterranean shrublandsJOURNAL OF ECOLOGY, Issue 3 2000Montserrat Vilà Summary 1,The Mediterranean perennial grass Ampelodesmos mauritanica may have the potential to expand its range. We analysed temporal variability of its reproductive components (seedfall, seed bank, seed predation, seed germination, seedling emergence, survival and growth) in three microsites (open areas, beneath Ampelodesmos and beneath shrubs) at two sites. 2,Reproductive components prior to seedling emergence were both closely linked and very similar between microsites within a site. Seedling survival and growth differed between microsites, being lowest in open areas. Recruitment patterns cannot therefore be predicted from seedfall. 3,Abundant seed production in 1996 was followed by successful germination and high seedling survival. In the following (non-masting) year, although Ampelodesmos has a low-density persistent seed bank, recruitment was much lower because germination was low and post-dispersal seed predation was high. 4,Our results suggest that Ampelodesmos reproduction is episodic. Expansion of its distribution may be triggered by intermittent seedling recruitment following masting, but is otherwise constrained by seed limitation, post-dispersal seed predation and a loss of viability in the seed bank. [source] Genetic and demographic responses of mercury-exposed mosquitofish (Gambusia holbrooki) populations: Temporal stability and reproductive components of fitnessENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2002Christopher Paul Tatara Abstract Two previous mesocosm studies showed changes in glucosephosphate isomerase-2 (Gpi-2) allele frequencies in mosquitofish populations exposed to mercury for 111 d or two years. A previous selection component analysis of single-generation populations exposed for 111 d to 18 ,/L Hg suggested that female sexual selection and fecundity selection could contribute to changes in Gpi-2 allele frequencies. The present multigeneration study was conducted to determine the stability of Gpi-2 allele frequencies over four years of mercury exposure, measure the reproductive fitness of Gpi-2 genotypes inhabiting control and mercury-contaminated mesocosms to determine a mechanism explaining changes in Gpi-2 allele frequencies, investigate differences in the demographic characteristics of mercury-exposed and control populations, and investigate the water quality of the mesocosms to determine if variables other than mercury show concordant patterns among mesocosms. Differences in Gpi-2 allele frequencies between control and mercury-exposed populations were stable over four years (, eight generations) of mercury exposure. Mercury-exposed female mosquitofish had a lower probability of being gravid than control females (p = 0.001). Mercury-exposed females also had lower fecundity (total number of eggs and embryos) than control females (p = 0.036). Unlike the results of the more intense mercury exposures in the single generation study, no strong evidence was found that Gpi-2 genotype influenced fecundity or the probability of being gravid in both control and mercury-exposed females. The quantification of fitness components is difficult but has the potential to enhance our understanding of how toxicants alter allele frequencies in exposed populations. [source] Reduced reproductive success in small populations of the self-incompatible Primula vulgarisJOURNAL OF ECOLOGY, Issue 1 2004Rein Brys Summary 1Habitat fragmentation and the resulting decline in population size can affect biotic interactions and reproductive success of plant species. We investigated the impact of habitat type, population size, morph type and frequency, plant density, floral display and predation on different reproductive components in 16 populations of the distylous self-incompatible perennial herb, Primula vulgaris , a rare, declining species in Belgium. 2Although habitat type accounted for significant variation in population size, we did not find any relation between habitat type and either reproductive and vegetative characteristics. Population size, however, strongly affected reproductive success, such that plants in small populations produced significantly fewer fruits per plant and seeds per fruit, and therefore fewer seeds per plant. 3No significant difference was found between morph types for any reproductive characteristic, nor an interaction with population size. However, when morph frequency was strongly biased (, 1 : 3), the proportion of flowers setting fruit and the number of seeds per fruit were significantly lower in individuals of the common morph type. 4Within populations, individual plants varied tremendously in size and floral display. Total number of fruits per plant significantly increased with floral display, but the highest fruit set per flower was found at intermediate flower number. 5The proportion of fruit suffering pre-dispersal predation per plant significantly increased with floral display, but this did not offset the potential fitness gains of producing a large display. Furthermore, the absolute number of predated fruits per plant was significantly and positively affected by the interaction of the total number of fruits per plant and the density of the population. [source] Seed dynamics of the mast seeding tussock grass Ampelodesmos mauritanica in Mediterranean shrublandsJOURNAL OF ECOLOGY, Issue 3 2000Montserrat Vilà Summary 1,The Mediterranean perennial grass Ampelodesmos mauritanica may have the potential to expand its range. We analysed temporal variability of its reproductive components (seedfall, seed bank, seed predation, seed germination, seedling emergence, survival and growth) in three microsites (open areas, beneath Ampelodesmos and beneath shrubs) at two sites. 2,Reproductive components prior to seedling emergence were both closely linked and very similar between microsites within a site. Seedling survival and growth differed between microsites, being lowest in open areas. Recruitment patterns cannot therefore be predicted from seedfall. 3,Abundant seed production in 1996 was followed by successful germination and high seedling survival. In the following (non-masting) year, although Ampelodesmos has a low-density persistent seed bank, recruitment was much lower because germination was low and post-dispersal seed predation was high. 4,Our results suggest that Ampelodesmos reproduction is episodic. Expansion of its distribution may be triggered by intermittent seedling recruitment following masting, but is otherwise constrained by seed limitation, post-dispersal seed predation and a loss of viability in the seed bank. [source] Life stages and reproductive components of the Marmorkrebs (marbled crayfish), the first parthenogenetic decapod crustaceanJOURNAL OF MORPHOLOGY, Issue 3 2004Günter Vogt Abstract Recently, we briefly reported on the first case of parthenogenesis in the decapod Crustacea which was found in the Marmorkrebs or marbled crayfish, a cambarid species of unknown geographic origin and species identity. Curiously, this animal is known only from aquarium populations, where it explosively propagates. By means of light and electron microscopic techniques we have now investigated the reproductive components of this crayfish, using more than 100 specimens ranging from hatchling to repeatedly spawned adult. Additionally, we documented its principal life stages. Our results revealed that the external sexual characters and also the gonads of the marbled crayfish are purely female, making this fast-reproducing species a good model for investigating female reproductive features in crayfish. Testicular tissues, ovotestes, or male gonoducts, gonopores, or gonopods were never found, either in small juveniles or large adult specimens, confirming the parthenogenetic nature of this crayfish. Parthenogenesis may have arisen spontaneously or by interspecific hybridization since Wolbachia -like feminizing microorganisms were not found in the ovaries. The external sexual characters of the marbled crayfish are first recognized in Stage 4 juveniles and are structurally complete ,2 months after hatching in specimens of ,2 cm total length. In the same life stage the ovary is fully differentiated as well, although the oocytes are in previtellogenic and primary vitellogenic stages only. The architecture of the mature ovary and also the synchronous maturation of cohorts of primary vitellogenic oocytes by secondary vitellogenesis are in general agreement with data published on ovaries of bisexual crayfish. New results were obtained with respect to the muscular nature of the ovarian envelope and its extensive proliferation after the first spawning, the distribution of hemal sinuses in the ovarian envelope and in the interstitium around the oogenetic pouches, the high transport activity of the follicle cells, and the colonization of oogenetic pouches by previtellogenic oocytes that originate in the germaria. Investigation of the nuclei of oocytes in the germaria and oogenetic pouches revealed no signs of meiosis, as usually found in females of bisexual decapods, suggesting that parthenogenesis in the marbled crayfish might be an apomictic thelytoky. The detection of new rickettsial and coccidian infections in the ovary and further organs raises fears that the marbled crayfish might endanger native European species by transmission of pathogens once escaped into the wild. J. Morphol. 261:286,311, 2004. © 2004 Wiley-Liss, Inc. [source] | ||||||||||