Search results for "Reproduction"
showing 10 items of 752 documents
Optimal rates of bisexual reproduction in cyclical parthenogens with density‐dependent growth
1999
This work explores theoretical patterns of reproduction that maximize the production of resting eggs and the long-term fitness of genotypes in cyclical parthenogens. Our focus is on density-dependent reproduction as it influences the consequences of a trade-off between producing amictic daughters – which reproduce parthenogenetically and subitaneously – and producing mictic daughters – which undergo meiosis and bisexual reproduction. Amictic females increase competitive ability and allow the population to achieve a larger size; mictic females directly contribute to population survival through harsh periods by producing resting eggs. Although morphologically indistinguishable, the two types …
Experimental assessment of the fecundity of Eucypris virens (Ostracoda, Crustacea) under natural sex ratios
2007
Summary 1. The adaptive significance of the observed variations in sex ratios in non-marine ostracods is unclear. This study quantified the fecundity of females taken from a presumed fully sexual Eucypris virens population that were experimentally combined with different proportions of males (male : female sex ratios: 1 : 1, 1 : 2, 1 : 4, 1 : 8 and 0 : 1). 2. The results yielded no indications that female fecundity is altered by short-term variations in the proportion of males, at least not within the range of sex ratios that are common in natural ostracod populations. Complete removal of males, however, did strongly reduce hatching success of dried eggs. This suggests the need for multiple…
Allocation patterns in modes of reproduction in two facultatively sexual cryptic rotifer species
2015
Many zooplankters rely on diapausing stages to survive unsuitable conditions in time-varying habitats. In facultativesexualrotifers, reproductive effortallocatedtothe sexuallyproduced diapausingeggs isat the expenseofthe subitaneousparthenogenetic eggs, generatingatrade-offbetweencurrentand future population growth.Thetimingand the amountof sex (the sexual pattern) affect diapausing-egg production. This switch to sex is complex because the reproductivemode is separated in distinct females: asexual (female-producing), unfertilized sexual (male-producing) and fertilizedsexual (diapause-egg-producing). We studied sexual patterns and life-history variation of these females in two crypticspecies…
Selection on life-history traits and genetic population divergence in rotifers
2009
A combination of founder effects and local adaptation – the Monopolization hypothesis – has been proposed to reconcile the strong population differentiation of zooplankton dwelling in ponds and lakes and their high dispersal abilities. The role genetic drift plays in genetic differentiation of zooplankton is well documented, but the impact of natural selection has received less attention. Here, we compare differentiation in neutral genetic markers (FST) and in quantitative traits (QST) in six natural populations of the rotifer Brachionus plicatilis to assess the importance of natural selection in explaining genetic differentiation of life-history traits. Five life-history traits were measur…
Effects of defoliation on male and female reproductive traits of a perennial orchid, Dactylorhiza maculata
2000
1The effects of defoliation on male reproductive traits of plants have received little attention. We conducted two field experiments with Dactylorhiza maculata (L.) Soo to examine the effects of defoliation on both male and female reproductive traits. We removed 0, 50 or 100% of leaves prior to flowering. The quality of pollen was tested by transferring pollen from the differently treated plants to untreated plants of the same population. 2The non-defoliated plants did not differ from the defoliated plants in mass of pollinia. No differences were found in the weight of seed capsules or in the proportion of embryonic seeds raised by flowers receiving pollen from differently treated pollen do…
Mate recognition as a reproductive barrier in sexual and parthenogenetic Eucypris virens (Crustacea, Ostracoda)
2013
Mate selection is one of the motors of evolution and of particular importance in the case of organisms in which sexual and parthenogenetic populations coexist. Sexual populations of the ostracod species complex Eucypris virens are often mixed with parthenogenetic ones. A powerful mate selection mechanism must exist to avoid time, energy and sperm loss, for the maintenance and success of sexual reproduction in these mixed populations. There are four types of E. virens individuals: males (diploid), sexual females (diploid) and asexual females (parthenogenetic and either di- or triploid). From one parthenogenetic population and two populations with males of E. virens, we sampled early stage ju…
Minority Integration in a Western City: An Agent-Based Modelling Approach
2019
This chapter describes the design and construction of an agent-based model we refer to as the ‘Simulation of Extended Time Integration’ (SETI) model. This model was designed with the goal of obtaining a better understanding of the conditions and mechanisms leading to the structural, social, and cultural integration of minorities into large Western societies. SETI is a virtual society with structural (employment, income, education) and demographic (marriage, reproduction, life expectancy) variables typical of Westerns countries. Initialization occurs after a hypothesized immigration event in which a single minority population settles into the majority population, bracketing the first decade …
Ecological genetics of a cyclical parthenogen in temporary habitats
1995
Populations of the rotifer Brachionus plicatilis inhabiting three temporary ponds in Torreblanca Marsh (Castellon, Spain) were regularly screened for allozyme variation, sexual reproduction levels and population densities during an annual cycle. Relevant ecological parameters in the ponds were also recorded. The electrophoretic survey of the three ponds (Poza Sur, Poza Norte and Canal Central) revealed a high level of overall genetic polymorphism in four marker loci, but only 13 multilocus genotypes were found. We classified clones into three clonal groups (SS, SM, L) characterized by unique arrays of alleles in the four marker loci, and significant differences in body shape and size. Clona…
Invasive Alien Species and Their Effects on Marine Animal Forests
2020
Nonindigenous species are increasingly transported around the world through multiple pathways by a diversity of vectors. Invasive species are a subset of those that are introduced into the receptor community, where they establish and increase their population to a size where they impact the native system. Marine invasive species can therefore interact with and modify native animal forests and/or create novel ones resulting in simple-to-complex changes in material cycling, energy flow, ecosystem structure, and function. Despite the ever increasing number of studies dealing with marine invasive species, mostly biological invasions are mentioned generically as one of a number of threats of dir…
Food resources and intestinal parasites as limiting factors for boreal vole populations during winter
2014
Processes limiting the growth of cyclic vole populations have stimulated considerable research and debate over several decades. In Fennoscandia, the peak density of cyclic vole populations occurs in fall, and is followed by a severe winter decline. Food availability and intestinal parasites have been demonstrated to independently and synergistically limit wildlife populations. The purpose of this study was to directly compare competing food and parasite hypotheses on the limitation of overwintering high-density vole populations. Moreover, we evaluated the ability of food limitation and nematode infection to interact and thereby intensify population declines. A two-factor experiment with foo…