Benefits Of Sexual Reproduction Research Articles

Strong marine heatwaves trigger flowering in seagrass

AbstractIn recent decades, the global intensification of marine heatwaves has impacted several ecosystems and species, including the endemic Mediterranean seagrass Posidonia oceanica. However, the scarcity of research in Eastern Mediterranean meadows, where historical and present thermal conditions differ from those of the Western Mediterranean, hampers our ability to draw comprehensive conclusions regarding the species' response to elevated sea temperatures. Here, we studied flowering patterns of P. oceanica meadows (3–15 m depth) of the Greek seas and assessed their potential association with marine heatwaves, while also examining the effects on plant growth associated with the transition from vegetative to sexual reproduction. To do so, we reconstructed flowering patterns from 2007 to 2021 across 58 meadows using lepidochronology and estimated summer marine heatwave metrics and categories using satellite sea surface temperature. The results revealed that flowering, while sporadic in most meadows (mean flowering frequency: 0.15), it was triggered by strong (Category II) summer marine heatwaves and a cumulative intensity exceeding 30°C days. Nevertheless, flowering density was low (mean flowering density: 11 inflorescences m−2) and not fuelled by frequency, intensity, or duration of marine heatwaves. Despite the potential long‐term benefits of sexual reproduction, annual rhizome production of flowering shoots decreased 1.5‐fold for at least 2 yr postflowering. This study uncovers the susceptibility of Eastern Mediterranean P. oceanica meadows, akin to their western counterparts, to marine heatwaves induced stress and its effects on reproductive strategies, raising concerns about the prospective plant growth and reproductive fitness to the escalating trend in marine heatwaves.

Control of plastid inheritance by environmental and genetic factors

The genomes of cytoplasmic organelles (mitochondria and plastids) are maternally inherited in most eukaryotes, thus excluding organellar genomes from the benefits of sexual reproduction and recombination. The mechanisms underlying maternal inheritance are largely unknown. Here we demonstrate that two independently acting mechanisms ensure maternal inheritance of the plastid (chloroplast) genome. Conducting large-scale genetic screens for paternal plastid transmission, we discovered that mild chilling stress during male gametogenesis leads to increased entry of paternal plastids into sperm cells and strongly increased paternal plastid transmission. We further show that the inheritance of paternal plastid genomes is controlled by the activity of a genome-degrading exonuclease during pollen maturation. Our data reveal that (1) maternal inheritance breaks down under specific environmental conditions, (2) an organelle exclusion mechanism and a genome degradation mechanism act in concert to prevent paternal transmission of plastid genes and (3) plastid inheritance is determined by complex gene–environment interactions.

A general structured model of a hermaphrodite population

Both empirical and theoretical studies, have dealt with the question how to best optimize reproductive fitness for hermaphrodites, using models such as game theory or complicated energetic costs and benefits of mating displays. However, hermaphrodites exhibit a broad spectrum of sexual behaviors like simultaneous, sequential or lifetime gonochorist that cannot be explained using a unique formalism.A possible explanation of this diversity relies on the way these species maximize their fitness: Does the individual hermaphrodite split its time between strategies maximizing its instantaneous reproductive fitness or its evolutionary fitness?Here, we compare these two points of view and extend a game theoretical formalism to a sex allocation model that underlies all sexual behaviors as a result of a dynamic game whose payoff depends on the costs and benefits of sexual reproduction. Using this formalism, we prove that a simultaneous hermaphrodites strategy is stable even for high values of sex changing costs. Moreover, we prove that the stability of a sequential hermaphrodite is linked to the average energy allocated to the pure female strategy.

Investigation of evolutionary effects on the relative frequency of sexual reproduction in freshwater diatoms

There are substantial ecological and evolutionary costs to sexual reproduction and there is only a narrow range of conditions that favors the evolution of high rates of sexual reproduction in species that are capable of both sexual and asexual reproduction. Considering the evolutionary costs and benefits of sexual reproduction, it was hypothesized that the frequency of sexual reproduction relative to asexual reproduction in diatoms would be greater for attached pennates and lower for planktonic centrics. This was investigated by comparison of the size-class distributions of the attached pennate, Rhopalodia gibba (Ehrenberg) Müller 1895 and the planktonic centric Cyclotella meneghiniana Kützing 1844 collected from the littoral zone of Lake Phalen in St. Paul Minnesota, USA. Numerical combination of binomial functions was used to infer the number of significant occurrences of sexual reproduction contributing to the size-class distribution of each population, with the frequency of sexual reproduction relative to asexual reproduction inferred from the number of binomial curves contributing to the distribution. The size-class profile of C. meneghiniana was unimodal, dominated by a single peak at 12 µm, with additional contributing curves with peaks at 15 µm and 18 µm. The size-class profile of R. gibba was bimodal, dominated by peaks at 46 µm and 60 µm, with additional contributing curves with peaks at 36 µm, 73 µm, and 84 µm. The results of this investigation were robust with respect to difference between the species in sample size and number of size-classes, although the analysis method is sensitive to differences in the number of size-classes. The results supported the hypothesis, and demonstrate the principle that size-class analysis of diatom populations can be used to investigate evolutionary hypotheses about differences among taxa in the relative frequency of sexual and asexual reproduction.

Fecundity, Offspring Longevity, and Assortative Mating: Parametric Tradeoffs in Sexual and Life History Strategy

Genetic diversification of offspring represents a bet-hedging strategy that evolved as an adaptation to unpredictable environments. The benefits of sexual reproduction come with severe costs. For example, each offspring only carries half of each parent's genetic makeup through direct descent. The lower the reproductive rate, the more substantial the cost when considering the proportion of genes represented in subsequent generations. Positive assortative mating represents a conservative bet-hedging strategy that offsets some of these costs and preserves coadapted genomes in stable and predictable environments, whereas negative assortative mating serves the inverse function of genetic diversification in unstable and unpredictable environments.

Coerced group collaborative evolution as an explanation for sexual reproduction’s prevalence

The prevalence of sexual reproduction has long been an outstanding problem of evolutionary biology. Different explanations have been offered to explain the prevalence of sexual reproduction. These explanations mainly focus on the benefits of sexual reproduction’s ability to shuffle and recombine genes. In this paper, we propose an alternative and comprehensive point of view to this important problem. We first hypothesize that sexual reproduction leads to genetic homogeneity and maintains adaptational advantages of organisms. In stable conditions with strong selective pressures, the maintenance of desired adaptational advantages is one benefit of sexual reproduction. We further hypothesize that sexual reproduction provides a mechanism by which entire populations of similar genomes can interact and collaborate with one another in order to improve the population’s average genomic fitness, a phenomena we call coerced collaborative group evolution. We show that groups of individuals will improve as a whole, even though each individual is still operating under their own best interests. We also argue that the so-called ‘two-fold cost of males’ is misguided if we take limited resources in any environment into consideration. Finally, we propose an intuitive and visualized view to connect different theories on sexual reproduction to establish a comprehensive theory to explain sexual reproduction’s prevalence.

Model of evolution with sexual and non-sexual reproduction

Using a previously introduced model (Refs. [9, 10]) of biological evolution, we study the role of the reproduction pattern on the fate of an evolving population. Each individual is under the selectional pressure from the environment and random harmful mutations. The habitat (“climate") is changing periodically. Evolution of populations following three reproduction patterns are compared - an asexual one (without recombination) and two with recombination - asexual (meiotic parthenogenesis) and sexual. We show, via Monte-Carlo simulations, that sexual reproduction leads to a better adaptation to the environment, slightly better survival rates for the individuals and higher probability that the population will not become extinct in difficult external conditions. The benefits of sexual reproduction are enhanced by higher birth rates and lower mutation rates. In the case of low birth rates and high mutation rates there is a small preference for the meiotic parthenogenesis.

Spatial and ecological overlap between coexisting sexual and parthenogenetic Schmidtea polychroa (Tricladida; Platyhelminthes)

Theoretical models on the costs and benefits of sexual reproduction usually assume that sexual and parthenogenetic individuals coexist and are identical, except for their mode of reproduction. Empirical studies, however, show that conspecific sexuals and parthenogens can differ in ecological preferences and geographical distribution, which complicates the investigation of the costs and benefits of sex. The freshwater planarian Schmidtea polychroa exists in a sexual and a sperm-dependent, parthenogenetic form. The latter produce fertile sperm and mate, but received sperm is used only to induce parthenogenetic embryo development. We compared the spatial and ecological distribution between forms within a lake from which both had been reported. Forty samples showed large differences in the relative frequencies of sexuals and parthenogens. Nineteen samples contained both biotypes. All but one of the 13 ecological parameters that we measured, could not explain a significant part of the variance in relative abundance of each type. Only leech abundance had a significant, negative effect on the presence of sexual individuals. The causes of this effect remained unclear. We also estimated the amount of genetic isolation between sites and between reproductive modes, using body coloration as a genetic marker. Large differences were found between sites, suggesting isolation of local populations by migration barriers. There were smaller differences between sexuals and parthenogens within sites, suggesting that genetic exchange between biotypes may be limited. We conclude that there appears to be weak niche differentiation between sexuals and parthenogens in Lago di Caldonazzo in late summer. Fluctuations in relative frequency appears to be a consequence of low dispersal between local populations and stochastic effects within them.

High Fecundity and Low Fertility in Parthenogenetic Planarians

High Fecundity and Low Fertility in Parthenogenetic Planarians

How to gain the benefits of sexual reproduction without paying the cost: a worm shows the way

Sexual reproduction is perhaps the greatest of all evolutionary puzzles. It's a puzzle because sexually reproducing species pay the cost of spending half their resources (over and above what is needed for vegetative growth) in producing males, whereas parthenogenetic species utilize all their resources meant for reproduction in producing only females (or hermaphrodites) like themselves. This twofold cost of sexual reproduction [1,2] is sometimes referred to as the twofold cost of producing males. Three advantages of sexual reproduction that might offset this cost have been proposed. Genetic recombination and cross fertilization permit sexually reproducing species to (1) bring together, in the same individual, mutations arising in different individuals [3,4]; (2) generate genetic variability and thus adapt to changing environments[2, 5, 6]; and (3) shuffle their genes in every generation and thus keep parasites at bay [7,8,9]. While evolutionary biologists are busy testing their favourite ideas for offsetting the twofold cost of producing males, recent work by Craig LaMunyon and Samuel Ward[10] shows that a nematode, Caenorhabditis briggsae, appears to have found a way of gaining the benefits of sexual reproduction without paying the cost of producing males.

A Model of Asexuality and Clonal Diversity: Cloning the Red Queen

Given benefits of sexual reproduction, the long term persistence of asexual lineages is hard to explain. The Red Queen—which states that sex is maintained by coevolutionary interactions between hosts and their harmful parasites—is one theory that can account for both the prevalence of sexual reproduction and the occasional persistence of long-term asexual reproduction. In this paper, I present a model to analyse the population structures of asexual populations under the Red Queen. The results of the model show that the long-term persistence of asexuality results in two distinct (and genetically diverse) population structures. These may be useful in predicting patterns of dispersal of ancient asexual organisms. Further, the results show in detail how it is that the long-term persistence of asexuality is compatible with the Red Queen theory of the maintenance of sexual reproduction in populations.

The Evolution of Sex

The cost of sexual reproduction is material used to produce sperm that is unavailable for eggs. Producing sperm causes a decline in a species' growth rate. This cost of sex evolves as a result of sperm-sperm competition, and its magnitude depends on the ratio of monogamous to promiscuous matings. The benefit of sexual reproduction is a higher long-term growth rate in a fluctuating environment. This benefit exists because a sexual population has a less variable growth rate from generation to generation than an asexual population under the same conditions. The benefit of sex may exceed the cost of sex.