Mode Of Reproduction Research Articles

Reproduction mode and Strain effects on Rabbit Breeding Performances

This study was carried out to determine the impact of the mode of reproduction and the strain (male and female) of rabbits on some zootechnical and reproduction parameters. For that, monitoring was carried out in 2019 in the region of Setif (North Eastern Algeria) on a semi-intensive breeding of 25 crossbreed rabbits. The statistical analysis showed a very highly significant effect of the mode of reproduction on the number of mating per fertilizing mating (P= 0.0001) with an average of 1 ± 0 in AI (Fertility rate of 80%), while it was of 1.45 ± 0.51 in natural breeding with a fertility rate of 61%. The weight of the rabbits at weaning was higher in AI than in natural mating (587.25 ± 338.19 g vs. 575.0 ± 375.44 g, respectively). The results relating to the number of total born, born alive, weaned rabbits, the farrowing-mating interval and the farrowing-fertilizing mating interval in natural mode were respectively of (7.4 ± 3.12), (4.55 ± 3.12), (4.55 ± 3.12), (12.65 ± 2.30), (19.15 ± 3.58); and in AI: (6.90 ± 4.12), (5.75 ± 4 .12), (5.75 ± 4.12), (11.65 ± 2.05), (18.99 ± 3.2) (P>0.05). Furthermore, and regarding the strains, data revealed that the females did not have any significant effect on the variables studied. On the contrary, the male had a very highly significant effect on the number of mating per fertilizing mating (p = 0.000), while it had no impact on the other parameters (P>0.05). To conclude, the control and the management of reproduction is the key to success in rabbit breeding, thus the combination of rearing condition and genetic effects is the main tool for making rabbit farming successful.

Utjecaj sezone parenja i stanja tijela na zootehničke parametre ouled djellal ovaca u polupustinjskim područjima

In this study, a database was created by monitoring 3000 Ouled Djellal ewes, belonging to ten breeding farms and representing two modes of reproduction management. The data collected make it possible to measure the reproductive performance of females and to determine the influence of non-genetic factors on different parameters. The Body Condition Score (BCS) was calculated to compare performance in relation with breeding conditions. The results showed that fertility and prolificacy accounted for 91.1±0.1% and 116.4±0.2% in the reproduction mode respectively based on one lambing/year with exclusive spring control, and of 53.5±0.2% and 101.2±0.1% respectively in the traditional lambing system spread overthe year (with the ram permanently present in the flock) (P<0.05). The BCS varied according to mating season and feeding system. Indeed, as the BCS at mating increased, fertility, prolificacy and productivity improved. Ewes whose BCS at mating was equal to or greater than 3 obtained the best performance, while those with a lower BCS were less fertile, less prolific, and less productive. The average productivity of Ouled Djellal sheep was 107.0±0.1%, and 54.8±0.3%, respectively, in the first and second mode of reproduction management (P<0.05). This study highlights the main sources of variations and their interactions.

Convergent genomic signatures associated with vertebrate viviparity

BackgroundViviparity—live birth—is a complex and innovative mode of reproduction that has evolved repeatedly across the vertebrate Tree of Life. Viviparous species exhibit remarkable levels of reproductive diversity, both in the amount of care provided by the parent during gestation, and the ways in which that care is delivered. The genetic basis of viviparity has garnered increasing interest over recent years; however, such studies are often undertaken on small evolutionary timelines, and thus are not able to address changes occurring on a broader scale. Using whole genome data, we investigated the molecular basis of this innovation across the diversity of vertebrates to answer a long held question in evolutionary biology: is the evolution of convergent traits driven by convergent genomic changes?ResultsWe reveal convergent changes in protein family sizes, protein-coding regions, introns, and untranslated regions (UTRs) in a number of distantly related viviparous lineages. Specifically, we identify 15 protein families showing evidence of contraction or expansion associated with viviparity. We additionally identify elevated substitution rates in both coding and noncoding sequences in several viviparous lineages. However, we did not find any convergent changes—be it at the nucleotide or protein level—common to all viviparous lineages.ConclusionsOur results highlight the value of macroevolutionary comparative genomics in determining the genomic basis of complex evolutionary transitions. While we identify a number of convergent genomic changes that may be associated with the evolution of viviparity in vertebrates, there does not appear to be a convergent molecular signature shared by all viviparous vertebrates. Ultimately, our findings indicate that a complex trait such as viviparity likely evolves with changes occurring in multiple different pathways.

Regional inequalities among state universities in Chile: Perspectives on centralization and neoliberal development

Drawing on perspectives from top state-regional universities’ authorities (known as rectors) and public statistics on higher education, we discuss the sources of regional inequality in the Chilean university system. While there is scarce research on regional inequality for Chilean higher education, it is a well-recognized concern within global debates. In this study, the testimonies of rectors link perceptions of regional inequality to the historic, political, and managerial dimensions that have determined their institutions’ development. As the problem of regional inequality stems from a tradition of political centralization, the neoliberal transformations, imposed since 1981, were singled out by the rectors for institutionalizing patterns of marketization that reinforced “inequalities of origin” for state-regional universities. Since the 2000s, trends of massification, regulation, and student protests reshaped higher education, leading to sectorial reform in 2018. However, competitive disadvantages are seen to continue to hinder the public role of state-regional universities. Institutional development strategies emerged, under the direction of rectors, to compensate for such inequalities, differentiating between winners and losers of neoliberal higher education. This article characterizes the modes of reproduction and overcoming of regional inequalities among state universities under neoliberal policy.

Facultative parthenogenesis discovered for the first time in Jamaican boa (Chilabothrus subflavus) using novel microsatellite markers.

The mode of reproduction most often seen in snakes is sexual, but studies have noted facultative parthenogenesis in at least six families. Here, we provide evidence for the first observed case of facultative parthenogenesis in a captive Jamaican boa (Chilabothrus subflavus). A 7-year-old female Jamaican boa, isolated since birth, was found to have produced a litter of 15 offspring. To provide molecular DNA evidence of parthenogenesis, 13 new microsatellite loci were isolated in the species. All offspring were found to be homozygous at each locus and only possess alleles found in the dam, implicating that they were born from asexual reproduction. Several developmental abnormalities, including stillbirths and spinal deformities, were noted in the litter which may be explained by their increased level of homozygosity. To preserve genetic diversity in the captive population, research should be conducted to understand the prevalence of this mode of reproduction and to guide future management decisions of this IUCN listed Vulnerable species.

Nuclear gene introgressions in hybrid populations of water frog Pelophylax esculentus complex: geographical analysis of the phenomenon and its interpretation.

Reproduction of water frog hybrids Pelophylax esculentus (Pelophylax ridibundus x Pelophylax lessonae) is associated with hemiclonal reproduction and backcrossing. The hemiclonal mode of reproduction occurs within P. esculentus allodiploids. In this case, the unrecombined genome of one parental species is transmitted to the offspring after premeiotic elimination of the chromosome set of the second parental species. Usually, the chromosome set of P. lessonae is eliminated, and the altered genome of P. ridibundus is passed on to the progeny. The hemiclonal inheritance within diploid Pelophylax esculentus hybrids may be accompanied by certain aberrations of premeiotic elimination. As a result, the formation of P. ridibundus specimens with introgressions of the P. lessonae genetic material, or the formation of recombinant hybrids occurs, depending on which of the parental species backcrossing takes place. The aim of our study is to describe the aberration of premeiotic elimination within the water frog P. esculentus complex detected by the nuclear gene Ldh-B inheritance, with an attempt to find out the causes of this phenomenon. It has been established that aberrations of premeiotic elimination are widespread, but only within populations of water frog from the river system of Upper Dnieper within Ukraine. The highest level of introgression takes place in the water frog populations within Kiev metropolis under conditions of expressed anthropogenization, while the maximum frequency of recombinants was detected within populations from the basin of Desna River, that has preserved native ecosystems. It was demonstrated that the frequency of premeiotic aberrations does not correlate with the intensity of interspecific water frog hybridization. Populations with introgressions are more common than populations with recombinants, however, within the latter, the frequency of recombination events is higher. The primary factor of gametogenesis aberrations, most likely, is the genetic characteristics of the local populations of parental species, since unambiguous explanations of this phenomenon based on the action of environmental stress (pollution of water systems) are not obvious.

Patterns of Genomic Diversity in a Fig-Associated Close Relative of Caenorhabditis elegans.

The evolution of reproductive mode is expected to have profound impacts on the genetic composition of populations. At the same time, ecological interactions can generate close associations among species, which can in turn generate a high degree of overlap in their spatial distributions. Caenorhabditis elegans is a hermaphroditic nematode that has enabled extensive advances in developmental genetics. Caenorhabditis inopinata, the sister species of C. elegans, is a gonochoristic nematode that thrives in figs and obligately disperses on fig wasps. Here, we describe patterns of genomic diversity in C. inopinata. We performed RAD-seq on individual worms isolated from the field across three Okinawan island populations. C. inopinata is about five times more diverse than C. elegans. Additionally, C. inopinata harbors greater differences in diversity among functional genomic regions (such as between genic and intergenic sequences) than C. elegans. Conversely, C. elegans harbors greater differences in diversity between high-recombining chromosome arms and low-recombining chromosome centers than C. inopinata. FST is low among island population pairs, and clear population structure could not be easily detected among islands, suggesting frequent migration of wasps between islands. These patterns of population differentiation appear comparable with those previously reported in its fig wasp vector. These results confirm many theoretical population genetic predictions regarding the evolution of reproductive mode and suggest C. inopinata population dynamics may be driven by wasp dispersal. This work sets the stage for future evolutionary genomic studies aimed at understanding the evolution of sex as well as the evolution of ecological interactions.

Environmental sympatry through time: spatio-temporal distribution and conservation status of two sympatric anuran species (Leptodactylidae) in South America

Introduction: Leptodactylus latinasus and Physalaemus cuqui are sympatric anuran species with similar environmental requirements and contrasting reproductive modes. Climatic configuration determines distribution patterns and promotes sympatry of environmental niches, but specificity/selectivity determines the success of reproductive modes. Species distribution models (SDM) are a valuable tool to predict spatio-temporal distributions based on the extrapolation of environmental predictors. Objectives: To determine the spatio-temporal distribution of environmental niches and assess whether the protected areas of the World Database of Protected Areas (WDPA) allow the conservation of these species in the current scenario and future. Methods: We applied different algorithms to predict the distribution and spatio-temporal overlap of environmental niches of L. latinasus and P. cuqui within South America in the last glacial maximum (LGM), middle-Holocene, current and future scenarios. We assess the conservation status of both species with the WDPA conservation units. Results: All applied algorithms showed high performance for both species (X̅TSS = 0.87, X̅AUC = 0.95). The L. latinasus predictions showed wide environmental niches from LGM to the current scenario (49 % stable niches, 37 % gained niches, and 13 % lost niches), suggesting historical fidelity to stable climatic-environmental regions. In the current-future transition, L. latinasus would increase the number of stable (70 %) and lost (20 %) niches, suggesting fidelity to lowland regions and a possible trend toward microendemism. P. cuqui loses environmental niches from the LGM to the current scenario (25 %) and in the current-future transition (63 %), increasing the environmental sympathy between both species; 31 % spatial overlap in the current scenario and 70 % in the future. Conclusion: Extreme drought events and rainfall variations, derived from climate change, suggest the loss of environmental niches for these species that are not currently threatened but are not adequately protected by conservation units. The loss of environmental niches increases spatial sympatry which represents a new challenge for anurans and the conservation of their populations.

Genetic basis and expression of ventral colour in polymorphic common lizards.

Colour is an important visual cue that can correlate with sex, behaviour, life history or ecological strategies, and has evolved divergently and convergently across animal lineages. Its genetic basis in non-model organisms is rarely known, but such information is vital for determining the drivers and mechanisms of colour evolution. Leveraging genetic admixture in a rare contact zone between oviparous and viviparous common lizards (Zootoca vivipara), we show that females (N = 558) of the two otherwise morphologically indistinguishable reproductive modes differ in their ventral colouration (from pale to vibrant yellow) and intensity of melanic patterning. We find no association between female colouration and reproductive investment, and no evidence for selection on colour. Using a combination of genetic mapping and transcriptomic evidence, we identified two candidate genes associated with ventral colour differentiation, DGAT2 and PMEL. These are genes known to be involved in carotenoid metabolism and melanin synthesis respectively. Ventral melanic spots were associated with two genomic regions, including a SNP close to protein tyrosine phosphatase (PTP) genes. Using genome re-sequencing data, our results show that fixed coding mutations in the candidate genes cannot account for differences in colouration. Taken together, our findings show that the evolution of ventral colouration and its associations across common lizard lineages is variable. A potential genetic mechanism explaining the flexibility of ventral colouration may be that colouration in common lizards, but also across squamates, is predominantly driven by regulatory genetic variation.

Ultrastructural diversity in the shell of Artemia resting eggs.

The shell of Artemia resting egg, which is a delicate multilayered envelope surrounding the inside diapause embryo, plays an important role in the survival strategy of Artemia. To date, the ultrastructure of resting eggshell has been studied for only handful populations, and knowledge about the diversity of shell structure is still limited. In this paper, resting eggs from 13 Artemia populations were studied by transmission electron microscopy. Results show that the basic configuration of resting eggshell is quite conservative, but variations are not uncommon in the fine ultrastructure of each main layer of the shell (e.g., the shape and distribution of the radially oriented pores in the cortical layer; the size, number and arrangement of chambers in the alveolar layer; and the development state of outer cuticular membrane [OCM]). The ultrastructural variation of eggshell seems not to be linked with species and reproductive mode of Artemia. Resting eggs from very high habitats (4300+ m above sea level [a.s.l.]) on Qinghai-Tibet Plateau and certain tropical salterns have a hypoplastic OCM, which may be related to the adaptation to habitat conditions such as low oxygen concentration. RESEARCH HIGHLIGHTS: Comparative study on resting eggs from 13 Artemia populations reveals high diversity in the fine structure of eggshell. Resting eggs from very high (4300+ m a.s.l.) habitats commonly have a hypoplastic OCM.

Hardly Venus’s servant—morphological adaptations of Veneriserva to an endoparasitic lifestyle and its phylogenetic position within Dorvilleidae (Annelida)

Endoparasitic annelids living inside another annelid host are known, particularly with regard to Oenonidae, but in general are poorly studied. The dorvilleid Veneriserva pygoclava is known from southern California, and its genus name (Latin = Venus’s servant) alludes to the close association with the host aphroditid scaleworm Aphrodita longipalpa. Little is known on fundamental questions on the biology of Veneriserva pygoclava. What is its mode of reproduction? How do they feed? How do they penetrate the host? We have studied multiple parasitized hosts and V. pygoclava specimens, using an integrative approach, combining µCT, histology, and electron microscopy. 3D reconstructions from µCT data of a parasitized Aphrodita show the exact position of the parasites in their natural condition within the host’s coelomic cavity. Ultrastructural investigations of the parasites revealed interesting adaptations to their lifestyle such as the complete reduction of their gut, despite the presence of a functional jaw apparatus and a modified epidermis enabling nutrient uptake from the host’s coelomic fluid. In addition to these, we also investigated spermatogenesis and oogenesis in V. pygoclava. Sperm morphology indicates an external fertilization of eggs within the coelomic cavity of the host. Mature male and female parasites living inside the same mature host and the presence of juvenile V. pygoclava within juveniles of Aphrodita suggest an obligate form of parasitism with a very early penetration of the hosts. In addition to our detailed morphological investigation, we conducted a phylogenetic analysis showing the position of Veneriserva within Dorvilleidae and its position was recovered nested among taxa of the Iphitime. Our phylogenetic analyses also show that the taxation Ophryotrocha puerilis siberti should be given full species rank and referred to as Ophryotrocha siberti. Finally, we publish here the full mitochondrial genome of V. pygoclava and discuss its novel gene order with reference to other annelids.

Reproductive strategy response of the fungi Sarocladium and the evaluation for remediation under stress of heavy metal Cd(II)

Cadmium (Cd) is documented as one of the most lethal metals and poses a major threat to all life forms in the environment due to its toxic effects. Bioremediation of hazardous metals has received considerable and growing interest over the years. The functional fungi with tolerance to the heavy metal Cd were screened from the mining soil samples. Two fungi isolates from coal mine soil were characterized as Sarocladium sp. M2 and Sarocladium sp. M6 based on morphological and partial ITS sequencing analysis. M2 and M6 exhibited high levels of resistance to cadmium, and they were investigated for their micro-morphology and application in heavy metal removal with different concentration Cd(II) (0, 50, 100, 150 and 200 mg/L). The colony morphology of M2 and M6 gradually become very similar to that of bacteria with the increase of cadmium concentration (150–200 mg/L). Micro-morphological studies showed that Cd(II) exposure caused the disappearance of conidial heads and the occurrence of hyphae breakage (100–200 mg/L Cd(II), which is consistent to the colony morphology results. The surface/volume ratio of the spores decreased with the presence of Cd(II). The removal potential of fungi for cadmium was quantified by atomic absorption spectrometry. M2 and M6 showed great potential as bioremediators for highly Cd(II)-contaminated environment. The highest Cd(II) biosorption capacity was 5.13 ± 0.21 mg/g for M2 and 6.04 ± 0.21 mg/g for M6. The highest heavy metal sorption by M2 removed 57.11% ± 4.45% Cd(II) while that of M6 removed 48.35% ± 1.44% Cd(II) in 200 mg/L initial concentration Cd(II). To the best of our knowledge, this is the first report that cadmium induced the change of reproduction mode of the Sarocladium, from conidia to arthrospores, which made the colony morphological modifications, from the fungi colony morphology to the bacteria colony morphology. The arthrospore-modified (hyphae breakage) seemed to accumulate greater amounts of heavy metals than filamentous hyphae formation.

Antifungal Resistance in Pulmonary Aspergillosis.

Aspergilli may cause various pulmonary diseases in humans, including allergic bronchopulmonary aspergillosis (ABPA), chronic pulmonary aspergillosis (CPA), and acute invasive pulmonary aspergillosis (IPA). In addition, chronic colonization may occur in cystic fibrosis (CF). Aspergillus fumigatus represents the main pathogen, which may employ different morphotypes, for example, conidia, hyphal growth, and asexual sporulation, in the various Aspergillus diseases. These morphotypes determine the ease by which A. fumigatus can adapt to stress by antifungal drug exposure, usually resulting in one or more resistance mutations. Key factors that enable the emergence of resistance include genetic variation and selection. The ability to create genetic variation depends on the reproduction mode, including, sexual, parasexual, and asexual, and the population size. These reproduction cycles may take place in the host and/or in the environment, usually when specific conditions are present. Environmental resistance is commonly characterized by tandem repeat (TR)-mediated mutations, while in-host resistance selection results in single-resistance mutations. Reported cases from the literature indicate that environmental resistance mutations are almost exclusively present in patients with IA indicating that the risk for in-host resistance selection is very low. In aspergilloma, single-point mutations are the dominant resistance genotype, while in other chronic Aspergillus diseases, for example, ABPA, CPA, and CF, both TR-mediated and single-resistance mutations are reported. Insights into the pathogenesis of resistance selection in various Aspergillus diseases may help to improve diagnostic and therapeutic strategies.

The genetic basis of a recent transition to live-bearing in marine snails.

Key innovations are fundamental to biological diversification, but their genetic basis is poorly understood. A recent transition from egg-laying to live-bearing in marine snails (Littorina spp.) provides the opportunity to study the genetic architecture of an innovation that has evolved repeatedly across animals. Individuals do not cluster by reproductive mode in a genome-wide phylogeny, but local genealogical analysis revealed numerous small genomic regions where all live-bearers carry the same core haplotype. Candidate regions show evidence for live-bearer-specific positive selection and are enriched for genes that are differentially expressed between egg-laying and live-bearing reproductive systems. Ages of selective sweeps suggest that live-bearer-specific alleles accumulated over more than 200,000 generations. Our results suggest that new functions evolve through the recruitment of many alleles rather than in a single evolutionary step.

Diversification of the terrestrial frog genus Anomaloglossus (Anura, Aromobatidae) in the Guiana Shield proceeded from highlands to lowlands, with successive loss and reacquisition of endotrophy

Two main landscapes emerge from the Guiana Shield: the highlands to the west called the Pantepui region and the Amazonian lowlands to the east, both harbouring numerous endemic species. With 32 currently recognized species, the genus Anomaloglossus stands out among Neotropical frogs as one that diversified only within the Guiana Shield both in the highlands and the lowlands. We present a time-calibrated phylogeny obtained by using combined mitogenomic and nuclear DNA, which suggests that the genus originates from Pantepui where extant lineages started diversifying around 21 Ma, and subsequently (ca. 17 Ma) dispersed during the Miocene Climatic Optimum to the lowlands of the eastern Guiana Shield where the ability to produce endotrophic tadpoles evolved. Further diversification within the lowlands in the A. stepheni group notably led to an evolutionary reversal toward exotrophy in one species group during the late Miocene, followed by reacquisition of endotrophy during the Pleistocene. These successive shifts of reproductive mode seem to have accompanied climatic oscillations. Long dry periods might have triggered evolution of exotrophy, whereas wetter climates favoured endotrophic forms, enabling colonization of terrestrial habitats distant from water. Acquisition, loss, and reacquisition of endotrophy makes Anomaloglossus unique among frogs and may largely explain the current species diversity. The micro evolutionary processes involved in these rapid shifts of reproductive mode remain to be revealed.

Parthenogenomics: Insights on mutation rates and nucleotide diversity in parthenogenetic Panagrolaimus nematodes.

Asexual reproduction is assumed to lead to the accumulation of deleterious mutations, and reduced heterozygosity due to the absence of recombination. Panagrolaimid nematode species display different modes of reproduction. Sexual reproduction with distinct males and females, asexual reproduction through parthenogenesis in the genus Panagrolaimus, and hermaphroditism in Propanagrolaimus. Here, we compared genomic features of free-living nematodes in populations and species isolated from geographically distant regions to study diversity, and genome-wide differentiation under different modes of reproduction. We firstly estimated genome-wide spontaneous mutation rates in a triploid parthenogenetic Panagrolaimus, and a diploid hermaphroditic Propanagrolaimus via long-term mutation accumulation lines. Secondly, we calculated population genetic parameters including nucleotide diversity, and fixation index (F ST) between populations of asexually and sexually reproducing nematodes. Thirdly, we used phylogenetic network methods on sexually and asexually reproducing Panagrolaimus populations to understand evolutionary relationships between them. The estimated mutation rate was slightly lower for the asexual population, as expected for taxa with this reproductive mode. Natural polyploid asexual populations revealed higher nucleotide diversity. Despite their common ancestor, a gene network revealed a high level of genetic differentiation among asexual populations. The elevated heterozygosity found in the triploid parthenogens could be explained by the third genome copy. Given their tendentially lower mutation rates it can be hypothesized that this is part of the mechanism to evade Muller's ratchet. Our findings in parthenogenetic triploid nematode populations seem to challenge common expectations of evolution under asexuality.

Genome dosage alteration caused by chromosome pyramiding and shuffling effects on karyotypic heterogeneity, reproductive diversity, and phenotypic variation in Zea-Tripsacum allopolyploids.

We developed an array of Zea-Tripsacum tri-hybrid allopolyploids with multiple ploidies. We unveiled that changes in genome dosage due to the chromosomes pyramiding and shuffling of three species effects karyotypic heterogeneity, reproductive diversity, and phenotypic variation in Zea-Tripsacum allopolyploids. Polyploidy, or whole genome duplication, has played a major role in evolution and speciation. The genomic consequences of polyploidy have been extensively studied in many plants; however, the extent of chromosomal variation, genome dosage, phenotypic diversity, and heterosis in allopolyploids derived from multiple species remains largely unknown. To address this question, we synthesized an allohexaploid involving Zea mays, Tripsacum dactyloides, and Z. perennis by chromosomal pyramiding. Subsequently, an allooctoploid and an allopentaploid were obtained by hybridization of the allohexaploid with Z. perennis. Moreover, we constructed three populations with different ploidy by chromosomal shuffling (allopentaploid × Z. perennis, allohexaploid × Z. perennis, and allooctoploid × Z. perennis). We have observed 3 types of sexual reproductive modes and 2 types of asexual reproduction modes in the tri-species hybrids, including 2n gamete fusion (2n + n), haploid gamete fusion (n + n), polyspermy fertilization (n + n + n) or 2n gamete fusion (n + 2n), haploid gametophyte apomixis, and asexual reproduction. The tri-hybrids library presents extremely rich karyotype heterogeneity. Chromosomal compensation appears to exist between maize and Z. perennis. A rise in the ploidy of the trihybrids was linked to a higher frequency of chromosomal translocation. Variation in the degree of phenotypic diversity observed in different segregating populations suggested that genome dosage effects phenotypic manifestation. These findings not only broaden our understanding of the mechanisms of polyploid formation and reproductive diversity but also provide a novel insight into genome pyramiding and shuffling driven genome dosage effects and phenotypic diversity.

A microbial perspective on speciation

Abstract Understanding what a microbial species is and the process of speciation in microbes has been and still is a puzzle with many challenges. But there is now emerging consensus that speciation in microbes does follow certain rules and limitations. Just like in macrobes, it can be driven by divergent natural selection and is maintained by barriers to gene flow, either genetic or ecological in nature. However, whether microbial speciation mirrors that of sexually reproducing eukaryotes is up for debate, as extensive horizontal gene flow can blur patterns and processes. Here, I provide intriguing examples of speciation in bacteria, viruses, and yeast, which are arguably similar to what we see in eukaryotes. I synthesize recent insights from microbial evolutionary genomics, which may mitigate the traditional view that microbes are ‘messy’ and do not fit eukaryotic species concepts and speciation models. Finally, I highlight the benefits of microbial experimental evolution to answer fundamental questions in speciation research (especially why, how, and when speciation occurs). Speciation research with microbes, as opposed to the organisms traditionally used in this field, may suffer less from observational bias and the experimental control we have over selection types, gene flow, and reproductive modes in microbial systems may allow us to determine the mechanisms and timing of ecological divergence, reproductive isolation, and speciation.

Life cycles and reproduction of Rhizostomeae.

In the present study we reviewed the life cycles and reproduction strategies of the order Rhizostomeae. We found 28 species with described life cycles representing ∼30% of the valid species. The metagenetic life cycle of most scyphozoans, which includes the benthic asexually-reproducing polyp and the pelagic sexually-reproducing medusa, is exhibited by all rhizostome species. Rhizostomeae are dioecious with only two exceptions described as hermaphroditic. Sexual dimorphism can be found in species with special external structures utilised for brooding but others show no sexual dimorphism despite the colour of mature gonads. Six asexual reproduction modes have been described for the production of new polyps but rhizostome polyps propagate through a main mode that differs among taxa. Species belonging to Dactyliophorae produce new polyps by podocysts whereas the Kolpophorae new polyps develop from free-swimming buds. The number of ephyrae formed per strobila differs between taxa with monodisc and polydisc strobilation in the Kolpophorae and Dactyliophorae, respectively. Given the low number of studied species it is expectable that new reproductive strategies will be discovered when additional species are investigated. We recommend increasing (1) descriptions on life cycles and reproductive strategies for a greater number of species, (2) attempts to locate the polyps in the field, (3) the study of species in their natural environment, to understand the population dynamics of Rhizostomeae and to clarify the potential of artificial structures to increase medusa populations. In addition, experimental studies are needed to improve our understanding of the factors affecting transitions between life cycle stages and medusa production rates.

Comparative Genomics of Sex, Chromosomes, and Sex Chromosomes in Caenorhabditis elegans and Other Nematodes.

The nematode phylum has evolved a remarkable diversity of reproductive modes, including the repeated emergence of asexuality and hermaphroditism across divergent clades. The species-richness and small genome size of nematodes make them ideal systems for investigating the genome-wide causes and consequences of such major transitions. The availability of functional annotations for most Caenorhabditis elegans genes further allows the linking of patterns of gene content evolution with biological processes. Such gene-centric studies were recently complemented by investigations of chromosome evolution that made use of the first chromosome-scale genome assemblies outside the Caenorhabditis genus. This review highlights recent comparative genomic studies of reproductive mode evolution addressing the hybrid origin of asexuality and the parallel gene loss following the emergence of hermaphroditism. It further summarizes ongoing efforts to characterize ancient linkage blocks called Nigon elements, which form central units of chromosome evolution. Fusions between Nigon elements have been demonstrated to impact recombination and speciation. Finally, multiple recent fusions between autosomal and thesex-linked Nigon element reveal insights into the dynamic evolution of sex chromosomes across various timescales.