Phylogeny Problem Research Articles

Genomic and Cytogenetic Analysis of Synthetic Polyploids between Diploid and Tetraploid Cotton (Gossypium) Species.

Cotton (Gossypium spp.) is the most important natural fiber source in the world. The genetic potential of cotton can be successfully and efficiently exploited by identifying and solving the complex fundamental problems of systematics, evolution, and phylogeny, based on interspecific hybridization of cotton. This study describes the results of interspecific hybridization of G. herbaceum L. (A1-genome) and G. mustelinum Miers ex Watt (AD4-genome) species, obtaining fertile hybrids through synthetic polyploidization of otherwise sterile triploid forms with colchicine (C22H25NO6) treatment. The fertile F1C hybrids were produced from five different cross combinations: (1) G. herbaceum subsp. frutescens × G. mustelinum; (2) G. herbaceum subsp. pseudoarboreum × G. mustelinum; (3) G. herbaceum subsp. pseudoarboreum f. harga × G. mustelinum; (4) G. herbaceum subsp. africanum × G. mustelinum; (5) G. herbaceum subsp. euherbaceum (variety A-833) × G. mustelinum. Cytogenetic analysis discovered normal conjugation of bivalent chromosomes in addition to univalent, open, and closed ring-shaped quadrivalent chromosomes at the stage of metaphase I in the F1C and F2C hybrids. The setting of hybrid bolls obtained as a result of these crosses ranged from 13.8-92.2%, the fertility of seeds in hybrid bolls from 9.7-16.3%, and the pollen viability rates from 36.6-63.8%. Two transgressive plants with long fiber of 35.1-37.0 mm and one plant with extra-long fiber of 39.1-41.0 mm were identified in the F2C progeny of G. herbaceum subsp. frutescens × G. mustelinum cross. Phylogenetic analysis with 72 SSR markers that detect genomic changes showed that tetraploid hybrids derived from the G. herbaceum × G. mustelinum were closer to the species G. mustelinum. The G. herbaceum subsp. frutescens was closer to the cultivated form, and its subsp. africanum was closer to the wild form. New knowledge of the interspecific hybridization and synthetic polyploidization was developed for understanding the genetic mechanisms of the evolution of tetraploid cotton during speciation. The synthetic polyploids of cotton obtained in this study would provide beneficial genes for developing new cotton varieties of the G. hirsutum species, with high-quality cotton fiber and strong tolerance to biotic or abiotic stress. In particular, the introduction of these polyploids to conventional and molecular breeding can serve as a bridge of transferring valuable genes related to high-quality fiber and stress tolerance from different cotton species to the new cultivars.

Tardigrade Augean stables—a challenging phylogeny and taxonomy of the family Ramazzottiidae (Eutardigrada: Hypsibioidea)

Abstract Tardigrade taxonomy is most often hindered by prevalent outdated species descriptions, lack of integrative redescriptions, scarce genetic information, and fragmentary sampling. Here, we diagnose the problems obscuring phylogenetic inference and the taxonomy of the cosmopolitan family Ramazzottiidae. We carried out the most extensive phylogenetic analysis of this family to date, with a considerable influx of new genetic data from poorly sampled regions of the world. We found two new distinct evolutionary lineages defined by distinct morphological traits (dorsal cuticular sculpturing and/or body shape), characterized by restricted geographic distributions, and we delineated them as new species complexes: the Neotropical Ramazzottius baumanni complex and the Afro-Oriental Ramazzottius szeptyckii complex. Nevertheless, we could not confidently ascertain the taxonomic status of both complexes due to: (i) the current state of the ramazzottiid taxonomy, with outdated and/or imprecise species descriptions with heterogeneous terminology and, in many cases, without accounting for intraspecific variation; (ii) the missing genetic information for key taxa; and (iii) the possible lack of monophyly of Cryoconicus and Ramazzottius as suggested by our results. In addition to diagnosing the problems of ramazzottiid phylogeny and systematics, we also propose possible solutions that could accelerate the progress in our understanding of the evolution of this group.

Morphoanatomic description of Trigonella foenum-graecum L. seeds

The color and anatomical structure of the seed kernel are different. For the seed to ripen, it is necessary to go through certain processes, that is, it takes time. It depends on many external and internal factors. Morphological signs of fruits and seeds are different in each species, but at the same time, these signs are relatively constant at the level of the genus, therefore, the importance of these signs in systematics is increasing now. The morpho-anatomical study of angiosperms fruit and seed kernel was of great interest both practically and theoretically. The study of the morpho-anatomy of seeds and fruits of representatives of different taxa provides great material for solving controversial problems of systematics and phylogeny. That is why it is necessary to study the morphology, anatomy and biology of the seeds of this plant and this is the demand of the time. The following diagnostic signs were determined and the anatomical structure of seeds in the conditions of the Tashkent oasis during introduction was analyzed. The presence of densely arranged parenchymal cells, 50% of the volume of the embryo seed. These identified diagnostic signs can be used in the process of seed identification.

Comprehensive taxon sampling and vetted fossils help clarify the time tree of shorebirds (Aves, Charadriiformes)

Shorebirds (Charadriiformes) are a globally distributed clade of modern birds and, due to their ecological and morphological disparity, a frequent subject of comparative studies. While molecular phylogenies have been key to establishing the suprafamilial backbone of the charadriiform tree, a number of relationships at both deep and shallow taxonomic levels remain poorly resolved. The timescale of shorebird evolution also remains uncertain as a result of extensive disagreements among the published divergence dating studies, stemming largely from different choices of fossil calibrations. Here, we present the most comprehensive non-supertree phylogeny of shorebirds to date, based on a total-evidence dataset comprising 353 ingroup taxa (90% of all extant or recently extinct species), 27 loci (15 mitochondrial and 12 nuclear), and 69 morphological characters. We further clarify the timeline of charadriiform evolution by time-scaling this phylogeny using a set of 14 up-to-date and thoroughly vetted fossil calibrations. In addition, we assemble a taxonomically restricted 100-locus dataset specifically designed to resolve outstanding problems in higher-level charadriiform phylogeny. In terms of tree topology, our results are largely congruent with previous studies but indicate that some of the conflicts among earlier analyses reflect a genuine signal of pervasive gene tree discordance. Monophyly of the plovers (Charadriidae), the position of the ibisbill (Ibidorhyncha), and the relationships among the five subfamilies of the gulls (Laridae) could not be resolved even with greatly increased locus and taxon sampling. Moreover, several localized regions of uncertainty persist in shallower parts of the tree, including the interrelationships of the true auks (Alcinae) and anarhynchine plovers. Our node-dating and macroevolutionary rate analyses find support for a Paleocene origin of crown-group shorebirds, as well as exceptionally rapid recent radiations of Old World oystercatchers (Haematopodidae) and select genera of gulls. Our study underscores the challenges involved in estimating a comprehensively sampled and carefully calibrated time tree for a diverse avian clade, and highlights areas in need of further research.

Finding Optimal Triangulations Parameterized by Edge Clique Cover

We consider problems that can be formulated as a task of finding an optimal triangulation of a graph w.r.t. some notion of optimality. We present algorithms parameterized by the size of a minimum edge clique cover (texttt {cc}) to such problems. This parameterization occurs naturally in many problems in this setting, e.g., in the perfect phylogeny problem texttt {cc} is at most the number of taxa, in fractional hypertreewidth texttt {cc} is at most the number of hyperedges, and in treewidth of Bayesian networks texttt {cc} is at most the number of non-root nodes. We show that the number of minimal separators of graphs is at most 2^texttt {cc}, the number of potential maximal cliques is at most 3^texttt {cc}, and these objects can be listed in times O^*(2^texttt {cc}) and O^*(3^texttt {cc}), respectively, even when no edge clique cover is given as input; the O^*(cdot ) notation omits factors polynomial in the input size. These enumeration algorithms imply O^*(3^texttt {cc}) time algorithms for problems such as treewidth, weighted minimum fill-in, and feedback vertex set. For generalized and fractional hypertreewidth we give O^*(4^m) time and O^*(3^m) time algorithms, respectively, where m is the number of hyperedges. When an edge clique cover of size texttt {cc}' is given as a part of the input we give O^*(2^{texttt {cc}'}) time algorithms for treewidth, minimum fill-in, and chordal sandwich. This implies an O^*(2^n) time algorithm for perfect phylogeny, where n is the number of taxa. We also give polynomial space algorithms with time complexities O^*(9^{texttt {cc}'}) and O^*(9^{texttt {cc}+ O(log ^2 texttt {cc})}) for problems in this framework.

Classifications of Iris L. genus at the biological and molecular levels as a basis for modern phylogenetic studies

Aim. To analyze and summarize literature data on the state of classification and taxonomy of Iris genus plants of Iridaceae family.Results and discussion. The genus Iris L. is one of the largest species of Iridaceae Juss family, which includes 1,800 species of 80 genera. Despite the fact that plants are very common as ornamental plants, there is currently no single classification for both horticultural and wild species of Iris genus. Various classifications and systems of irises have been proposed, the main difference between them is related to the understanding of the genus scope. The taxonomy of Iris genus underwent dramatic changes in the last century, especially in recent decades after the introduction of molecular methods. This paper deals with the analysis of current literature data on the existing classifications of Iris genus plants, the correspondence between taxonomic studies and the results of recent molecular studies. The data presented summarize the traditional classifications according to Rodionenko and Matthew, and also describe modern achievements in phylogenetic studies of this genus using functional genomic studies, involving molecular markers in irises. Conclusions. The data analyzed and summarized in the article can be useful for solving issues of taxonomy, phylogeny, genetics and practical problems of selection of plants of Iris genus; in addition, they will contribute to a more appropriate use of the Iris raw material in practical pharmacy.

Chloroplast genomes of five Oedogonium species: genome structure, phylogenetic analysis and adaptive evolution

BackgroundThe order Oedogoniales within the single family Oedogoniaceae comprised of three genera, Oedogonium, Oedocladium, and Bulbochaete based on traditional morphological criteria. While several molecular phylogenetic studies have suggested that both Oedogonium and Oedocladium may not be monophyletic, broader taxon sampling and large amounts of molecular data acquisition could help to resolve the phylogeny and evolutionary problems of this order. This study determined five chloroplast (cp) genomes of Oedogonium species and aimed to provide further information on cp genome for a better understanding of the phylogenetic and evolutionary relationships of the order Oedogoniales.ResultsThe five Oedogonium cp genomes showed typical quadripartite and circular structures, and were relatively conserved in their structure, gene synteny, and inverted repeats boundaries in general, except for small variation in genome sizes, AT contents, introns, and repeats. Phylogenetic analyses based on 54 cp protein-coding genes examined by maximum likelihood and Bayesian analyses using amino acid and nucleotide datasets indicated that both Oedocladium and Oedogonium are polyphyletic groups. A positively selected gene (psbA) was identified in the two Oedocladium species and the terrestrial Oedogonium species, indicating that terrestrial Oedogoniales taxa may have undergone adaptive evolution to adjust to the difference in light intensity between aquatic and terrestrial habitats.ConclusionsOur results enrich the data on cp genomes of the genus Oedogonium. The availability of these cp genomes can help in understanding the cp genome characteristics and resolve phylogenetic and evolutionary relationships of the order Oedogoniales.

Finding Most Compatible Phylogenetic Trees over Multi-State Characters

The reconstruction of the evolutionary tree of a set of species based on qualitative attributes is a central problem in phylogenetics. In the NP-hard perfect phylogeny problem the input is a set of taxa (species) and characters (attributes) on them, and the task is to find an evolutionary tree that describes the evolution of the taxa so that each character state evolves only once. However, in practical situations a perfect phylogeny rarely exists, motivating the maximum compatibility problem of finding the largest subset of characters admitting a perfect phylogeny. Various declarative approaches, based on applying integer programming (IP), answer set programming (ASP) and pseudo-Boolean optimization (PBO) solvers, have been proposed for maximum compatibility. In this work we develop a new hybrid approach to solving maximum compatibility for multi-state characters, making use of both declarative optimization techniques (specifically maximum satisfiability, MaxSAT) and an adaptation of the Bouchitt'e-Todinca approach to triangulation-based graph optimization problems. Empirically our approach outperforms in scalability the earlier proposed approaches w.r.t. various parameters underlying the problem.

PhISCS: a combinatorial approach for subperfect tumor phylogeny reconstruction via integrative use of single-cell and bulk sequencing data.

Available computational methods for tumor phylogeny inference via single-cell sequencing (SCS) data typically aim to identify the most likely perfect phylogeny tree satisfying the infinite sites assumption (ISA). However, the limitations of SCS technologies including frequent allele dropout and variable sequence coverage may prohibit a perfect phylogeny. In addition, ISA violations are commonly observed in tumor phylogenies due to the loss of heterozygosity, deletions, and convergent evolution. In order to address such limitations, we introduce the optimal subperfect phylogeny problem which asks to integrate SCS data with matching bulk sequencing data by minimizing a linear combination of potential false negatives (due to allele dropout or variance in sequence coverage), false positives (due to read errors) among mutation calls, and the number of mutations that violate ISA (real or because of incorrect copy number estimation). We then describe a combinatorial formulation to solve this problem which ensures that several lineage constraints imposed by the use of variant allele frequencies (VAFs, derived from bulk sequence data) are satisfied. We express our formulation both in the form of an integer linear program (ILP) and—as a first in tumor phylogeny reconstruction—a Boolean constraint satisfaction problem (CSP) and solve them by leveraging state-of-the-art ILP/CSP solvers. The resulting method, which we name PhISCS, is the first to integrate SCS and bulk sequencing data while accounting for ISA violating mutations. In contrast to the alternative methods, typically based on probabilistic approaches, PhISCS provides a guarantee of optimality in reported solutions. Using simulated and real data sets, we demonstrate that PhISCS is more general and accurate than all available approaches.

Does Relaxing the Infinite Sites Assumption Give Better Tumor Phylogenies? An ILP-Based Comparative Approach.

Most of the evolutionary history reconstruction approaches are based on the infinite sites assumption, which states that mutations appear once in the evolutionary history. The Perfect Phylogeny model is the result of the infinite sites assumption and has been widely used to infer cancer evolution. Nonetheless, recent results show that recurrent and back mutations are present in the evolutionary history of tumors, hence the Perfect Phylogeny model might be too restrictive. We propose an approach that allows losing previously acquired mutations and multiple acquisitions of a character. Moreover, we provide an ILP formulation for the evolutionary tree reconstruction problem. Our formulation allows us to tackle both the Incomplete Directed Phylogeny problem and the Clonal Reconstruction problem when general evolutionary models are considered. The latter problem is fundamental in cancer genomics, the goal is to study the evolutionary history of a tumor considering as input data the fraction of cells having a certain mutation in a set of cancer samples. For the Clonal Reconstruction problem, an experimental analysis shows the advantage of allowing mutation losses. Namely, by analyzing real and simulated datasets, our ILP approach provides a better interpretation of the evolutionary history than a Perfect Phylogeny. The software is at https://github.com/AlgoLab/gppf.

SPhyR: tumor phylogeny estimation from single-cell sequencing data under loss and error.

MotivationCancer is characterized by intra-tumor heterogeneity, the presence of distinct cell populations with distinct complements of somatic mutations, which include single-nucleotide variants (SNVs) and copy-number aberrations (CNAs). Single-cell sequencing technology enables one to study these cell populations at single-cell resolution. Phylogeny estimation algorithms that employ appropriate evolutionary models are key to understanding the evolutionary mechanisms behind intra-tumor heterogeneity.ResultsWe introduce Single-cell Phylogeny Reconstruction (SPhyR), a method for tumor phylogeny estimation from single-cell sequencing data. In light of frequent loss of SNVs due to CNAs in cancer, SPhyR employs the k-Dollo evolutionary model, where a mutation can only be gained once but lost k times. Underlying SPhyR is a novel combinatorial characterization of solutions as constrained integer matrix completions, based on a connection to the cladistic multi-state perfect phylogeny problem. SPhyR outperforms existing methods on simulated data and on a metastatic colorectal cancer.Availability and implementationSPhyR is available on https://github.com/elkebir-group/SPhyR.Supplementary information Supplementary data are available at Bioinformatics online.

Multispecies coalescent analysis confirms standing phylogenetic instability in Hexapoda.

The multispecies coalescent (MSC) has been increasingly used in phylogenomic analyses due to the accommodation of gene tree topological heterogeneity by taking into account population-level processes, such as incomplete lineage sorting. In this sense, the phylogeny of insect species, which are characterized by their large effective population sizes, is suitable for a coalescent-based analysis. Furthermore, studies so far recovered short internal branches at early divergences of the insect tree of life, indicating fast evolutionary radiations that increase the probability of incomplete lineage sorting in deep time. Here, we investigated the performance of the MSC for a phylogenomic data set of hexapods compiled by Misof etal. (2014, Science 346:763). Our analysis recovered the monophyly of most insect orders, and major phylogenetic relationships were in agreement with current insect systematics. We identified, however, some evolutionary associations that were consistently problematic. Most noticeable, Hexapod monophyly was disrupted by the sister group relationship between the remiped crustacean and Insecta. Additionally, the interordinal relationships within Polyneoptera and Neuropteroidea were found to be phylogenetically unstable. We show that these controversial phylogenetic arrangements were also poorly supported by previous analyses, and therefore, we evaluated their robustness to stochastic errors from sampling sites and terminals, confirming standing problems in hexapod phylogeny in the genomics age.

Prickly problems of cacti phylogeny

Cactus Genomics![Figure][1] The genomes and relationships of columnar cacti, such as the saguaro, have been resolved. PHOTO: JAYPIERSTORFF/SHUTTERSTOCK The evolutionary history of cacti has been difficult to resolve. Copetti et al. sequenced the genomes of four species of columnar cacti,

The Complexity of Phylogeny Constraint Satisfaction Problems

We systematically study the computational complexity of a broad class of computational problems in phylogenetic reconstruction. The class contains, for example, the rooted triple consistency problem, forbidden subtree problems, the quartet consistency problem, and many other problems studied in the bioinformatics literature. The studied problems can be described as constraint satisfaction problems , where the constraints have a first-order definition over the rooted triple relation. We show that every such phylogeny problem can be solved in polynomial time or is NP-complete. On the algorithmic side, we generalize a well-known polynomial-time algorithm of Aho, Sagiv, Szymanski, and Ullman for the rooted triple consistency problem. Our algorithm repeatedly solves linear equation systems to construct a solution in polynomial time. We then show that every phylogeny problem that cannot be solved by our algorithm is NP-complete. Our classification establishes a dichotomy for a large class of infinite structures that we believe is of independent interest in universal algebra, model theory, and topology. The proof of our main result combines results and techniques from various research areas: a recent classification of the model-complete cores of the reducts of the homogeneous binary branching C-relation, Leeb’s Ramsey theorem for rooted trees, and universal algebra.

Compromise or optimize? The breakpoint anti-median.

BackgroundThe median of k≥3 genomes was originally defined to find a compromise genome indicative of a common ancestor. However, in gene order comparisons, the usual definitions based on minimizing the sum of distances to the input genomes lead to degenerate medians reflecting only one of the input genomes. “Near-medians”, consisting of equal samples of gene adjacencies from all the input genomes, were designed to restore the idea of compromise to the median problem.ResultWe explore adjacency sampling constructions in full generality in the case k=3, with given overlapping sets of adjacencies in the three genomes, where all adjacencies in two-way or three-way overlaps are included in the sample. We require the construction to be maximal, in the sense that no additional proportion of adjacencies from any of the genomes may be added without violating the local linearity of the genome. We discover that in incorporating as many adjacencies as possible, evenly from all the input genomes, we are actually maximizing, rather than minimizing, the sum of distances over all other maximal sampling schemes.ConclusionsWe propose to explore compromise instead of parsimony as the organizing principle for the small phylogeny problem.

Phylogenetic relationships between Palaearctic species of the Anopheles maculipennis complex (Diptera: Culicidae) revealed by different approaches and markers. The problem of consensus

A study of phylogenetic relationships in closely related groups of epidemically important species is an important task of parasitology and evolutionary theory. One of these species groups is the maculipennis complex, with its members widespread in Eurasia, North Africa and North America. We studied phylogenetic schemes of the Palaearctic part of this Complex, which are based on crossability of species, polytene chromosomes, isoenzymes, cuticular hydrocarbons and ITS2 of rRNA genes. The lack of high compliance between them prompted us to create a consensus scheme of phylogenetic relationships in the Palaearctic part of this Complex. We constructed phylogenetic schemes on the sequences of a COI gene fragment, the D2 variable region of 28S rDNA and ITS2 of rRNA genes using various algorithms (Neighborjoining, Minimum Evolution, Maximum parsimony and Maximum likelihood). Two consensus schemes of the Palaearctic branch of the maculipennis complex were constructed, validated and discussed. The first scheme was based mostly on molecular genetics data. The second scheme relies on polytene chromosome, geographical spread and ecological data. Phylogenetic relationships of An. beklemishevi are contradictory. This species is similar to other Palaearctic species by molecular markers but it is far from them by fixed chromosome inversions. It was shown that this species is distant from Neoarctic species of the An. quadrimaculatus branch. The proposed schemes show two possible scenarios of the maculipennis complex evolution. Differences between them are explained by facts and associated speculations as well as by assumptions made under different phylogenetic reconstruction methods. A hypothesis about a significant role of the disparity between the astronomical and biological times in the interpretation of evolutionary processes was proposed. To address the phylogeny problem of the Palaearctic branch of the maculipennis complex at a more detailed level, it is required to increase our knowledge about the underlying species.

Ginkgoales: Some problems of systematics and phylogeny

The rudimentary outgrowths in fixed positions on the collars of Nagrenia samylinae Nosova (plant closely related to Ginkgo biloba L.) and similar rudiments in extant Ginkgo suggest that the collar of Ginkgo was initially a bilateral structure with directional growth, which bore ovule on its abaxial side. The collar of Ginkgo is interpreted as a vestigial organ. In the light of the data obtained, the origin and phylogeny of Ginkgoales are discussed; the most probable ancestors of Ginkgoales are Umkomasiales (Corystospermales) and allied plants. Thus, the new data confirm the interpretation of the collar of Ginkgo proposed by Meyen (1984) and are consistent with his hypothesis of the origin of Ginkgoales.

Bilateral Accessory Renal Arteries: A Case Report

Anomalous blood vesseles are always interesting from a purely scientific point of view, especially since they so often shed light on obscure problems of phylogeny and ontogeny. The evolutionary history of kidney and renal artery is recapitulated during embryonic development. Most of the variations of human renal vesseles can be explained on the basis of phylogeny as many conditions which are anomalous in human are normally present in some animals. The most common variation or renal artery is the presence of an accessory renal arteries, occuring in approximately 30% of cases. The precise knowledge of renal vascular pattern is significant in conduct of various renal surgeries, interventional radiology, and urologic procedures. Variations in renal vascularization have assumed greater importance in conservative surgeries; hence the presence of accessory arteries cannot be overlooked during surgical resection, partial nephrectomy and renal transplant. The present case report aims at highlighting the possible variation in renal vasculature and its embryological and clinical significance.

A review on the molecular characterization of digenean parasites using molecular markers with special reference to ITS region

Abstract The rDNA region of eukaryotes has the immense potential to resolve the evolutionary and phylogeny problems using molecular markers. As evident from the present review, ITS region data is considered for interpretation of inter and intra-specific variations of 136 studies of 33 families including 78 genus and 114 species affecting individuals worldwide. Along with ITS-1 and ITS-2 region in 29 studies 18S region, in 38 studies 28S region and in 43 studies mitochondrial genes (COI and NDI) were also analyzed. Three new genera (Allobilharzia gen. nov., Caulanus gen. nov., and Latuterus gen. nov.) and 49 new species were discovered. Only 47 studies expressed variations at intra-specific and inter-specific level in complete ITS region, ITS-1 and ITS-2 rDNA sequences due to differences in nucleotide positions. According to the findings ITS region is more reliable and precise marker for demarcation and identification of species in combination of other DNA markers. Major studies were involved around the parasites of families Fasciolidae, Schistosomatidae, Opisthorchidae, Paragonimidae and Paramphistomidae, Clinostomidae, Diplostomidae, Haploporidae, among others infecting humans, farm animals, birds, fishes, reptiles and amphibians on the clinical basis. In future, molecular and bioinformatics aspects based on genetic variations will lead to explore the untouched areas of trematodes.

Genetic history of salmonid fishes of the genus Oncorhynchus

This review discusses genetic approaches to solving important problems of evolutionary biology of salmonid fishes with special reference to Pacific salmon and trout. The problems of the genetic phylogeny of salmonid fishes, including issues of the consistency/inconsistency of phylogenetic tree topologies built using genetic and phenotypic characteristics, the timing of the main phylogenetic events, the relationships among different taxa, including the mutual status of Pacific salmon and trout, and others are discussed. The problems of the tetraploidization of the salmonid fishes, as well as,the dilemma of their freshwater/marine origin, and the semelparity of some of the species are reviewed.