Genome Size Evaluation in Tetraodontiform Fishes from the Neotropical Region

Smooth pufferfish of the family Tetraodontidae had become pure genomic models because of the remarkable compaction of their genome. This trait seems to be the result of DNA loss following its divergence from the sister family Diodontidae, which possess larger genomes. In this study, flow cytometry was used for estimate the genome size of four pufferfish species from the Neotropical region. Cytogenetic data and confocal microscopy were also used attempting to confirm relationships between DNA content and cytological parameters. The haploid genome size was 0.71?±?0.03 pg for Sphoeroides greeleyi, 0.34?±?0.01 pg for Sphoeroides spengleri, 0.82?±?0.03 pg for Sphoeroides testudineus (all Tetraodontidae), and 1.00?±?0.03 pg for Chilomycterus spinosus (Diodontidae). These differences are not related with ploidy level, because 46 chromosomes are considered basal for both families. The value for S. spengleri represents the smallest vertebrate genome reported to date. Since erythrocyte cell and nuclear sizes are strongly correlated with genome size, the variation in this last is considered under both adaptive and evolutionary perspectives.     

The gas bladder of puffers and porcupinefishes (Acanthomorpha: Tetraodontiformes): Phylogenetic interpretations

The anatomy of the gas bladder of Diodontidae (porcupinefishes) and Tetraodontidae (pufferfishes) was studied on the basis of dissections and magnetic resonance imaging. Among the examined taxa of Tetraodontiformes, only puffers and porcupinefishes possess a thick walled and dorsally U‐shaped or crescent‐moon‐shaped gas bladder. In the tetraodontid genus Lagocephalus the gas bladder is reduced to a rudiment. The species belonging to the genera Canthigaster, Arothron, and some species of Tetraodon differ in the positioning of their crescent‐moon‐shaped gas bladder. These observations confirm the close relationship of: (i) Diodontidae and Tetraodontidae and (ii) Canthigaster, Arothron, and some species of Tetraodon. The heterogeneity of the genus Tetraodon is supported by the gas bladder morphology, as previously suggested by molecular studies. J. Morphol. 275:894–901, 2014. © 2014 Wiley Periodicals, Inc.     

暗纹东方鲀应激胀气行为功能形态学观察

该文以四齿鲀科(Tetraodontidae)的暗纹东方鲀(Takifugu obscurus)为对象,采用形态学解剖、X光透视和骨骼神经染色等方法,对其胀气行为的功能形态学进行研究。其结果发现,暗纹东方鲀腹部受到刺激后,口腔小幅高频将水或空气吞咽进入由食道腹壁特化成的气囊里,气囊与消化道的前后结合处由括约肌控制,腹壁肌呈束状,与此同时,高弹性的皮肤、脊柱和神经都会发生相应的位移变化,以保证胀气行为的快速完成。通过对暗纹东方鲀胀气行为及其吸、排水机制的深入了解,为进一步研究胀气行为的神经机理奠定基础,也将会丰富动物警戒逃避行为的理论。     

EVOLUTION OF PUFFERFISH INFLATION BEHAVIOR

The evolution of the extraordinary inflation mechanism of pufferfishes was studied in the light of an independently derived phylogenetic hypothesis of tetraodontiform fishes. Inflation behavior is found in all members of the puffer sister taxa Tetraodontidae and Diodontidae. However, most other tetraodontiform fishes exhibit two functionally similar behaviors. All taxa exhibit a “coughing” behavior and, with the exception of the sister-group to all other tetraodontiforms, represented by the Triacanthidae, all lineages “blow” strong jets of water out of their mouth to excavate prey. Functional specializations associated with the three behaviors were identified from anatomical analyses and electromyographic recordings of muscle activity in representatives of the major lineages of the order. The phylogenetic distribution of the three buccal compression behaviors and their functional bases indicates the following: (1) the evolution of inflation behavior involved major structural modifications of the head that function in a novel mechanism that links depression of the floor of the mouth to posterior expansion of the buccal cavity; (2) the contraction patterns of four key head muscles used in the three behaviors are generally similar both across behaviors and taxa; (3) however, the distribution of the two significant modifications of muscle activity are consistent with the hypothesis that the three behaviors represent a transformation series from coughing to water blowing to inflation. The motor pattern for water blowing is a slightly modified version of that seen in coughing, and the inflation motor pattern retains the blowing specialization and adds a single additional modification. The convergent evolution of a poorly developed inflation behavior in at least one genus of filefish provides evidence that tetraodontiform fishes are predisposed to the evolution of this unusual defensive behavior. The presence of a well developed water-blowing behavior in most tetraodontiform lineages may represent an intermediate functional specialization that increased the probability of the evolution of inflation.     

Genome size variation in butterflies (Insecta,Lepidotera, Papilionoidea): a thorough phylogenetic comparison

Butterflies have been of great interest to naturalists for centuries, and the study of butterflies has been an integral part of ecology and evolution ever since Darwin proposed his theory of natural selection in 1859. There are > 18 000 butterfly species worldwide, showing great diversity in morphological traits and ecological niches. Compared with butterfly diversity, however, patterns of genome size variation in butterflies remain poorly understood, especially in a phylogenetic context. Here, we sequenced and assembled the mitogenomes of 68 butterflies and measured the genome sizes (C-values) of 67 of them. We also assembled 10 mitogenomes using reads from GenBank. Among the assembled 78 mitogenomes, those from 59 species, 23 genera and one subfamily are reported for the first time. Combining with published data of mitogenomes and genome size, we explored the patterns in genome size variation for 106 butterfly species in a phylogenetic context based on analyses of mitogenomes from 264 species covering six families. Our results show that the genome size of butterflies has a 6.4-fold variation ranging from 0.203 pg (199 Mb) (Nymphalidae: Heliconius xanthocles) to 1.287 pg (1253 Mb) (Papilionidae: Parnassius orleans). Within families, the largest variation was found in Papilionidae (5.9-fold: 0.22–1.29 pg), followed by Nymphalidae (4.8-fold: 0.2–0.95 pg), Pieridae (4.4-fold: 0.22–0.97 pg), Hesperiidae (2.2-fold: 0.3–0.66 pg), Lycaenidae (2.6-fold: 0.39–1.02 pg) and Rioidinidae (1.8-fold: 0.48–0.87 pg). Our data also suggest that butterflies have an ancestral genome size of c. 0.5 pg, and some ancestral genome size increase or decrease events along different subfamilies or tribes produce the diversity of genome size variation in diverse butterflies. Our data provide novel insights into patterns of genome size variation in butterflies and are an important reference for future genome sequencing programmes.     

Toxin-resistant sodium channels: parallel adaptive evolution across a complete gene family

Approximately 75% of vertebrate proteins belong to protein families encoded by multiple evolutionarily related genes, a pattern that emerged as a result of gene and genome duplications over the course of vertebrate evolution. In families of genes with similar or related functions, adaptation to a strong selective agent should involve multiple adaptive changes across the entire gene family. However, we know of no evolutionary studies that have explicitly addressed this point. Here, we show how 4 taxonomically diverse species of pufferfishes (Tetraodontidae) each evolved resistance to the guanidinium toxins tetrodotoxin (TTX) and saxitoxin (STX) via parallel amino acid replacements across all 8 sodium channels present in teleost fish genomes. This resulted in diverse suites of coexisting sodium channel types that all confer varying degrees of toxin resistance, yet show remarkable convergence among genes and phylogenetically diverse species. Using site-directed mutagenesis and expression of a vertebrate sodium channel, we also demonstrate that resistance to TTX/STX is enhanced up to 15-fold by single, frequently observed replacements at 2 sites that have not previously been implicated in toxin binding but show similar or identical replacements in pufferfishes and in distantly related vertebrate and nonvertebrate animals. This study presents an example of natural selection acting upon a complete gene family, repeatedly arriving at a diverse but limited number of adaptive changes within the same genome. To be maximally informative, we suggest that future studies of molecular adaptation should consider all functionally similar paralogs of the affected gene family.     

Sauropod dinosaurs evolved moderately sized genomes unrelated to body size

Sauropodomorph dinosaurs include the largest land animals to have ever lived, some reaching up to 10 times the mass of an African elephant. Despite their status defining the upper range for body size in land animals, it remains unknown whether sauropodomorphs evolved larger-sized genomes than non-avian theropods, their sister taxon, or whether a relationship exists between genome size and body size in dinosaurs, two questions critical for understanding broad patterns of genome evolution in dinosaurs. Here we report inferences of genome size for 10 sauropodomorph taxa. The estimates are derived from a Bayesian phylogenetic generalized least squares approach that generates posterior distributions of regression models relating genome size to osteocyte lacunae volume in extant tetrapods. We estimate that the average genome size of sauropodomorphs was 2.02 pg (range of species means: 1.77–2.21 pg), a value in the upper range of extant birds (mean = 1.42 pg, range: 0.97–2.16 pg) and near the average for extant non-avian reptiles (mean = 2.24 pg, range: 1.05–5.44 pg). The results suggest that the variation in size and architecture of genomes in extinct dinosaurs was lower than the variation found in mammals. A substantial difference in genome size separates the two major clades within dinosaurs, Ornithischia (large genomes) and Saurischia (moderate to small genomes). We find no relationship between body size and estimated genome size in extinct dinosaurs, which suggests that neutral forces did not dominate the evolution of genome size in this group.     

Review of spino-occipital and spinal nerves in Tetraodontiformes,with special reference to pectoral and pelvic fin muscle innervation

The spino-occipital nerve (SO) and ventral rami of the spinal nerves (SV) in 10 tetraodontiform families and 5 outgroup taxa were examined, with special reference to pectoral and pelvic fin muscle innervation. Compared with the outgroup taxa, tetraodontiforms were characteristic in having SO3 + SV1 (SO3 in tetraodontids) that gave off several lateral subbranches to the pectoral fin base and SO participation in infracarinalis anterior innervation. SO and SV1 were connected with one another (6 patterns) before entering the pectoral fin muscles in most species, including the outgroup taxa, resulting in the participation of SV1 in the innervation of almost all of the pectoral fin muscles. SO3 + SV1 was present in all tetraodontiforms (except in 2 tetraodontids having only SO3) and the outgroup taxa, an upper dorsal branch uniformly extending dorsally into the pectoral fin base. The pectoral fin base also received a branch ventrally, but its identity differed (participation or nonparticipation of SV2). SV1 alone constituting the branch was a derived condition occurring in Aracanidae, Ostraciidae, Tetraodontidae, Diodontidae, and Molidae. No strong characters supporting a tetraodontiform sister group were recognized among the spino-occipital nerve and ventral rami of spinal nerves.     

The shortened spinal cord in tetraodontiform fishes

In teleosts, the spinal cord generally extends along the entire vertebral canal. The Tetraodontiformes, in which the spinal cord is greatly reduced in length with a distinct long filum terminale and cauda equina, have been regarded as an aberration. The aims of this study are: 1) to elucidate whether the spinal cord in all tetraodontiform fishes shorten with the filum terminale, and 2) to describe the gross anatomical and histological differences in the spinal cord among all families of the Tetraodontiformes. Representative species from all families of the Tetraodontiformes, and for comparison the carp as a common teleost, were investigated. In the Triacanthodidae, Triacanthidae, and Triodontidae, which are the more ancestral taxa of the Tetraodontiformes, the spinal cord extends through the entire vertebral canal. In the Triacanthidae and Triodontidae, the caudal half or more spinal segments of the spinal cord, however, lack gray matter and consist largely of nerve fibers. In the other tetraodontiform families, the spinal cord is shortened forming a filum terminale with the cauda equina, which is prolonged as far as the last vertebra. The shortened spinal cord is divided into three groups. In the Ostraciidae and Molidae, the spinal cord tapers abruptly at the cranium or first vertebra forming a cord‐like filum terminale. In the Monacanthidae, Tetraodontidae, and Diodontidae, it abruptly flattens at the rostral vertebrae forming a flat filum terminale. The spinal cord is relatively longer in the Monacanthidae than that in the other two families. It is suggested by histological features of the flat filum terminale that shortening of the spinal cord in this group progresses in order of the Monacanthidae, Tetraodontidae, and Diodontidae. In the Balistidae and Aracanidae, the cord is relatively long and then gradually decreased in dorso‐ventral thickness. J. Morphol. 276:290–300, 2015. © 2014 Wiley Periodicals, Inc.     

A new perspective on phylogeny and evolution of tetraodontiform fishes (Pisces: Acanthopterygii) based on whole mitochondrial genome sequences: Basal ecological diversification?

Background  

The order Tetraodontiformes consists of approximately 429 species of fishes in nine families. Members of the order exhibit striking morphological diversity and radiated into various habitats such as freshwater, brackish and coastal waters, open seas, and deep waters along continental shelves and slopes. Despite extensive studies based on both morphology and molecules, there has been no clear resolution except for monophyly of each family and sister-group relationships of Diodontidae + Tetraodontidae and Balistidae + Monacanthidae. To address phylogenetic questions of tetraodontiform fishes, we used whole mitochondrial genome (mitogenome) sequences from 27 selected species (data for 11 species were newly determined during this study) that fully represent all families and subfamilies of Tetraodontiformes (except for Hollardinae of the Triacanthodidae). Partitioned maximum likelihood (ML) and Bayesian analyses were performed on two data sets comprising concatenated nucleotide sequences from 13 protein-coding genes (all positions included; third codon positions converted into purine [R] and pyrimidine [Y]), 22 transfer RNA and two ribosomal RNA genes (total positions = 15,084).     

Lateral line system and its innervation in Tetraodontiformes with outgroup comparisons: Descriptions and phylogenetic implications

The lateral line system and its innervation in ten tetraodontiform families and five outgroup taxa were examined. Although some homology issues remained unresolved, tetraodontiforms were characterized by having two types (at least) of superficial neuromasts (defined by the presence or absence of supporting structures) and accessory lateral lines and neuromasts (except Molidae in which “accessory” elements were absent). The preopercular line in Tetraodontiformes was not homologous with that of typical teleosts, because the line was innervated by the opercular ramule that was newly derived from the mandibular ramus, the condition being identical to that in Lophiidae. Within Tetraodontiformes, the number of neuromasts varied between 70 and 277 in the main lines and between 0 and 52 in accessory elements. Variations were also recognized in the presence or absence of the supraorbital commissure, mandibular line, otic line, postotic line, ventral trunk line, and some lateral line nerve rami, most notably the dorsal branch of the opercular ramule, being absent in Aracanidae, Ostraciidae, Tetraodontidae, Diodontidae, and Molidae. Morphological characteristics derived from the lateral line system and its innervation provided some support for a sister relationship of tetraodontiforms with lophiiforms. J. Morphol., 2010. © 2009 Wiley‐Liss, Inc.     

Do phosphorus requirements for RNA limit genome size in crustacean zooplankton?

As for most other organisms, genome size in zooplankton differs widely. This may have a range of consequences for growth rate, development, and life history strategies, yet the causes of this pronounced variability are not settled. Here we propose that small genome size may be an evolutionary consequence of phosphorus (P) allocation from DNA to RNA under P deficiency. To test this hypothesis we have compared the two major groups of zooplankton, copepods and cladocerans, that have overlapping niches and body size. Relative to the cladocerans, copepods have a more complex life history and a lower mass-specific P content, while cladocerans tend to have higher P and RNA contents and higher specific growth rates and frequently experience P-limited growth, likely due to a shortage of P for ribosome synthesis. Cladocerans also generally have smaller genomes than copepods (1C = 0.17-0.63 pg DNA.cell-1 vs. 1C = 0.10-10 pg DNA.cell-1). Furthermore, cladocerans have a higher slope of the relationship of body size with DNA content (1.5 vs. 0.28 in copepods) and present almost 15-fold higher RNA:DNA ratios (24.8 in cladocerans vs. 1.6 in copepods). Hence, small genome size in cladocerans could reflect an evolutionary pressure towards "efficient" genomes to conserve a key element needed to maximize growth rate. We do not claim that this is a universal cause of genome size variability, but propose that streamlining of genomes could be related to P conservation rather than energy conservation. This could be relevant for a range of organisms that may suffer P-limited growth rates.     

Multiple invasions into freshwater by pufferfishes (teleostei: tetraodontidae): a mitogenomic perspective

Pufferfishes of the Family Tetraodontidae are the most speciose group in the Order Tetraodontiformes and mainly inhabit coastal waters along continents. Although no members of other tetraodontiform families have fully discarded their marine lives, approximately 30 tetraodontid species spend their entire lives in freshwaters in disjunct tropical regions of South America, Central Africa, and Southeast Asia. To investigate the interrelationships of tetraodontid pufferfishes and thereby elucidate the evolutionary origins of their freshwater habitats, we performed phylogenetic analysis based on whole mitochondrial genome sequences from 50 tetraodontid species and closely related species (including 31 newly determined sequences). The resulting phylogenies reveal that the family is composed of four major lineages and that freshwater species from the different continents are independently nested in two of the four lineages. A monophyletic origin of the use of freshwater habitats was statistically rejected, and ancestral habitat reconstruction on the resulting tree demonstrates that tetraodontids independently entered freshwater habitats in different continents at least three times. Relaxed molecular-clock Bayesian divergence time estimation suggests that the timing of these invasions differs between continents, occurring at 0-10 million years ago (MA) in South America, 17-38 MA in Central Africa, and 48-78 MA in Southeast Asia. These timings are congruent with geological events that could facilitate adaptation to freshwater habitats in each continent.     

Conifer genome sizes of 172 species,covering 64 of 67 genera,range from 8 to 72 picogram

Nuclear genome size of conifers as measured by flow cytometry with propidium iodide was investigated, striving to collect at least a single species from each genus. 64 out of 67 genera and 172 species were measured. Of the 67 genera, 21 are reported here for the first time and the same is true for 76 species. This nearly doubles the number of measured genera and adds 50% to the number of analyzed species. Conifers have chromosome numbers in the range of n = (7)10–12(19). However, the nuclear DNA content (2C‐value) is shown here to range from 8.3 to 71.6 picogram. The largest genome contains roughly 6 × 10¹⁰ more base pairs than the smallest genome. Genome sizes are evaluated and compared with available taxonomic treatments. For the mainly (sub)tropical Podocarpaceae small genome sizes were found with a 2C‐value of only 8–28 pg, with 13.5 pg on average. For the Taxaceae 2C‐values from 23–60 pg were determined. Not surprisingly, the genus Pinus with 97 species (39 species measured here) has a broad range with 2C = 38–72 pg. A factor of 2 difference is also found in the Cupressaceae (136 species) with nuclear DNA contents in the range 18–35 pg. Apart from the allohexaploid Sequoia, ploidy plays a role only in Juniperus and some new polyploids are found. The data on genome size support conclusions on phylogenetic relationships obtained by DNA sequencing. Flow cytometry is applicable even to young plants or seeds for the monitoring of trade in endangered species.     

Investigation of loss and gain of introns in the compact genomes of pufferfishes (Fugu and Tetraodon)

We have investigated intron evolution in the compact genomes of 2 closely related species of pufferfishes, Fugu rubripes and Tetraodon nigroviridis, that diverged about 32 million years ago (MYA). Analysis of 148,028 aligned intron positions in 13,547 gene pairs using human as an outgroup identified 57 and 24 intron losses in Tetraodon and fugu lineages, respectively, and no gain in either lineage. For comparison, we analyzed 144,545 intron positions in 12,866 orthologous pairs of genes in human and mouse that diverged about 61 MYA using dog as an outgroup and identified 51 intron losses in mouse and 3 losses in human and no gain. The rate of intron loss in Tetraodon is higher than that in fugu, mouse, and human but lower than the previous estimates for other eukaryotes. The introns lost in pufferfishes and mammals are significantly shorter than the mean size of introns in the genome. One intron deleted in fugu and another in Tetraodon have left behind 6 and 3 nucleotides, respectively, suggesting that they were lost due to genomic deletions. Such losses of introns are likely to be the result of a higher rate of DNA deletions experienced by the genomes of pufferfishes compared with mammals. The shorter generation time of Tetraodon compared with fugu, and the rich diversity and higher activity of transposable elements in pufferfishes compared with mammals, may be responsible for the higher rate of intron loss in Tetraodon. Our findings indicate that overall very little intron turnover has occurred in pufferfishes and mammals during recent evolution and that intron gain is an extremely rare event in vertebrate evolution.     

Genome size in Bulgarian Centaurea s.l. (Asteraceae)

Thirty-nine species and subspecies of the genera Centaurea, Colymbada, Psephellus and Cyanus (all included in Centaurea s.l.) including many rare and endemic taxa of preponderantly Bulgarian distribution have been investigated with Feulgen DNA image densitometry for holoploid and monoploid genome size (C- and Cx-values). Cyanus varies gradually 2.17-fold between 0.74 pg and 1.56 pg (1Cx). In the remaining taxa two major genome size groups are found, which differ about 1.8-fold in Cx-value. Low values occur in Centaurea subgenera Acrolophus, Solstitiaria, Phalolepis (0.77 pg to 0.90 pg, 1Cx) and Jacea (0.95 pg to 1.09 pg, 1Cx), high values in the genera Colymbada (1.65 pg to 1.93 pg, 1Cx) and Psephellus (1.79 pg, 1Cx, in P. marschallianus). Cx-values support a distinction of Colymbada from Centaurea. Genome size variation is discussed with regard to phylogeny, life form (annual versus perennial), polyploidy, chromosome basic numbers, altitude of occurrence and climate, endemism, and rarity.     

A molecular analysis of the interrelationships of tetraodontiform fishes (Acanthomorpha: Tetraodontiformes)

Tetraodontiform fishes (e.g., triggerfishes, boxfishes, pufferfishes, and giant ocean sunfishes) have long been recognized as a monophyletic group. Morphological analyses have resulted in conflicting hypotheses of relationships among the tetraodontiform families. Molecular data from the single-copy nuclear gene RAG1 and from two mitochondrial ribosomal genes, 12S and 16S, were used to test these morphology-based hypotheses. Total evidence (RAG1+12S+16S), RAG1-only, and mitochondrial-only analyses were performed using both maximum parsimony and Bayesian criteria. Total evidence and RAG1-only analyses recover a monophyletic Tetraodontiformes. However, the relationships recovered within the order differ, and none completely conform to previous hypotheses. Analysis of mitochondrial data alone fails to recover a monophyletic Tetraodontiformes and therefore does not support any of the morphology-based topologies. The RAG1 data appear to give the best estimate of tetraodontiform phylogeny, resulting in many strongly supported nodes and showing a high degree of congruence between both parsimony and Bayesian analyses. All analyses recover every tetraodontiform family for which more than one representative is included as a strongly supported monophyletic group. Balistidae and Monacanthidae are recovered as sister groups with robust support in every analysis, and all analyses except the Bayesian analyses of the mitochondrial data alone recover a strongly supported sister-group relationship between Tetraodontidae and Diodontidae. Many of the intrafamilial relationships recovered from the molecular data presented here corroborate previous morphological hypotheses.     

Enormous gill chambers of deep-sea coffinfishes (Lophiiformes: Chaunacidae) support unique ventilatory specialisations such as breath holding and extreme inflation

Deep sea habitats tend to favor species with low energetic demands, and therefore we predict that deep sea fishes will have behavioral and morphological specializations of the gill ventilatory system to reduce the energetic cost of pumping water across the gills. However, it is difficult to study functional morphology of deep sea fishes due the lack of ability to conduct laboratory experiments with living fishes. For this study, we combined analysis of publicly available video recorded by remote-operated vehicles (ROV) with detailed anatomical study of museum specimens to document the functional morphology of the massive gill chambers that are observed in coffinfishes (Lophiiformes: Chaunacidae). Chaunacids, like other lophiiforms, exhibit highly specialised ventilatory anatomy such as an enlarged branchiostegal apparatus and restricted gill openings, but videos show them using this anatomy in a new and unusual way. We observed eight individuals ventilating extremely slowly at rates of 0.03–0.004 Hz, during which the gill chambers were full yet we saw no inhalation or exhalation for periods of 26 to 245 s. This holding breath behaviour has not been observed in any other fishes and is probably highly energetically efficient. This inflation of the gill chambers also increases body volume by up to 30%, making them more globose and difficult to be taken as prey, much like stomach inflation in pufferfishes (Tetraodontidae). We also used micro computed-tomography (CT) scans to document the enormous branchiostegal rays and associated muscles that support this unique behaviour.     

Divergent genome sizes reflect the infrafamilial subdivision of the neotropical woody Marcgraviaceae

Neotropical Marcgraviaceae comprise about seven genera and 130 species of lianas and shrubs. They predominantly occur in lowland or montane rainforests and are characterized by a variety of pollination systems. Early classifications subdivided Marcgraviaceae into subfamilies Marcgravioideae and Noranteoideae, a concept supported by molecular data. Using flow cytometry and chromosome numbers, we investigated the role of genome size and polyploidization in the evolution of Marcgraviaceae and how genome sizes are distributed between the proposed infrafamilial groups. To do this we determined genome sizes and chromosome counts for six genera and 22 species for the first time. Our study supports the subfamilial classification of the family, revealing contrasting genome sizes in Noranteoideae (2C = 5.5–21.5 pg) and Marcgravioideae (2C = 2.3–6.2 pg). Polyploidy is considered to be the main source of genome size variation as in each subfamily the higher nuclear DNA amounts were associated with higher ploidy. In addition, genome size changes independent of polyploidy were also observed in some genera, suggesting an additional role for changes in repetitive DNA abundance in the evolution of Marcgraviaceae. A high chromosome base number (x = 18; 2n = 36 to ～70) points to an undetected lower diploid level or to palaeopolyploidy. Marcgraviaceae show a remarkable (nine‐fold) variation in genome size, and several Noranteoideae have genome sizes among the highest reported for tropical woody angiosperms worldwide. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 1–14.     

Genome sizes for 71 species of Zamia (Cycadales: Zamiaceae) correspond with three different biogeographic regions

Nuclear DNA contents (2C‐value) are reported for 71 out of 76 accepted species of Zamia (Zamiaceae) using flow cytometry with propidium iodide. Nuclear DNA content in Zamia ranges between 33.7 and 45.7 pg. Despite this small range, the largest genome contains roughly 10¹⁰ more base pairs than the smallest genome. The results for Zamia point to two centers of biogeographic distribution: Mexico and Colombia. Nicaragua seems to be the biogeographic boundary for these two centres for Zamia. To the north, genome sizes of 33.7–38.0 pg (average 35.6 pg) are found and to the south (Costa Rica, Panama and South America) 41.2–45.7 pg (average 42.9 pg). Plants from the Caribbean islands (including Florida) have intermediate genome sizes with 37.3–40.9 pg (average 38.7 pg). Costa Rica and Panama are in a transition zone and its species can be divided into three subsections: four species with ‘Caribbean’ values of 38.4–39.5 pg (average 39.0 pg), six species with ‘South American’ values with 42.7–43.6 pg, (average 42.9 pg, and six species with intermediate values ranging between 40.1–41.0 pg (average 40.4 pg). The latter values are nearly absent in other areas, suggesting that they could be the products of (introgressive) hybridization. This study represents the first, nearly complete overview of the genome sizes of the genus Zamia and their relationship with biogeography.