Can the mass effect explain the mid-altitudinal peak in vascular plant species richness?

A mid-altitudinal peak in species richness is commonly observed and the mass effect (or source–sink effect) has been suggested as a possible cause. We test the importance of the mass effect for generating altitudinal patterns of plant species richness at two grain sizes using a simple estimate of sterility/fertility to indicate sinks and sources. To do this we identified species with fertile specimens (fertile species) and species with only sterile specimens (sterile species) in each sampling unit along altitudinal transects and assumed that the number of sterile species indicated the relative number of sink species, correspondingly that the number of fertile species indicated the relative number of source species when looking at the overall pattern of species richness along a transect. To evaluate this approach, we investigated the distribution of sterility and fertility of each species along the altitudinal transects. We found that sterile species are found more often at the edges and fertile species more often in the centre of the species altitudinal ranges than expected by chance. Using a fine grain, sterile species richness had a humped altitudinal pattern on all transects investigated at this scale, whereas using a coarse grain two of the three transects investigated had a humped pattern. At the fine grain, sterile species richness had a more pronounced peak than fertile species richness in two of the three transects investigated supporting the hypothesis of the mass effect, but this pattern did not persist at coarser grain. The observations at the fine grain are in accordance with the idea that the mass effect is important in shaping the mid-altitudinal peak in species richness, whereas the observations from the coarser grain are ambiguous.     

Nutrient foraging traits in 10 co-occurring plant species of contrasting life forms

1 Responses to spatial heterogeneity of soil nutrients were tested in 10 plant species that differ in life form and successional status, but which co-occur in the South Carolina coastal plain. The morphological responses of the root system were tested by assessing scale (represented by root mass and root length densities), precision (preferential proliferation of roots in nutrient-rich patches compared with less fertile patches) and discrimination (ability to detect and proliferate within the richest patches when patches vary in nutrient concentration). We also investigated sensitivity (growth benefits gained as spatial heterogeneity of nutrients increases, measured as total biomass).
2 Ten individuals of each species were grown in pots under four treatments that had differing nutrient distribution but the same overall nutrient addition. Plants were harvested when roots reached pot edge.
3 We observed high variation between species in scale, precision and sensitivity. No significant discrimination responses were observed, although greatest root mass density occurred at intermediate fertility levels for all species.
4 We rejected the hypothesis that scale and precision are negatively correlated. Indeed, in herbaceous species alone, scale and precision were positively correlated.
5 Sensitivity was not closely related to precision, indicating that proliferation of roots in fertile patches does not always yield growth benefits in heterogeneous soils. Further, some sensitive species had very low precision, suggesting that a positive growth response in heterogeneous environments may be related to plasticity in physiology or root life span, rather than morphology.
6 Plant life form was not correlated with precision or sensitivity. However, scale of response was greater in herbs than in woody plants, possibly because the two life forms develop root systems at different rates.     

Osmunda (Osmundaceae) from the Triassic of Antarctica: an example of evolutionary stasis

Compressed specimens of the fern Osmunda are described from the Triassic of the Allan Hills, Antarctica. The specimens consist of a once pinnate, deeply pinnatifid fertile frond as well as several sterile specimens. Six pinnae are present on the partial fertile rachis, with two sterile pinnae above four fertile pinnae. Both sterile and fertile specimens are virtually identical to the modern species Osmunda claytoniana. Entire fronds are fragmentary; the longest is 21 cm in length. Sterile pinnae are alternate and deeply pinnatifid, with slightly toothed pinnules and dichotomous venation. Fertile pinnae are 1-1.3 cm long, once pinnate, and lack vegetative lamina. Sporangia are clustered, each 300-375 um in diameter, and possess a transverse annulus 6-8 cells long; dehiscence is by a vertical slit. Fronds arise from a rhizome 4 cm long by 1 cm wide; two croziers are present on the rhizome. Two frond segments up to 6 cm long and three deeply pinnatifid pinnae are present on the uppermost part of one rachis. Pinnules are ~4 mm long and 2-3 mm wide. The presence of this Osmunda species in the Triassic demonstrates stasis of frond morphology, both fertile and vegetative, for the genus.     

Differential contribution of leucocytes and spermatozoa to the generation of reactive oxygen species in the ejaculates of oligozoospermic patients and fertile donors.

Cells isolated from the ejaculates of a high proportion of patients exhibiting oligozoospermia are characterized by generation rates of reactive oxygen species that considerably exceed those obtained for the normal fertile population. The purpose of this study was to resolve the cellular source of this enhanced activity. Semen samples from a cohort of oligozoospermic patients and a group of fertile controls were fractionated on discontinuous Percoll gradients to generate three cell populations (0, 50 and 100%) of differing density. For each fraction, both the steady-state and the phorbol-ester-induced chemiluminescent signals were significantly (P less than 0.001) greater for the oligozoospermic samples than for the fertile controls. In the fertile donors, leucocytes comprised the major source of reactive oxygen species, particularly in the low-density Percoll fractions; in oligozoospermic patients, however, spermatozoa were identified as a second major source of reactive oxygen species. Particularly striking was an intense phorbol-ester-induced chemiluminescent signal generated by oligozoospermic spermatozoa, purified by passage through isotonic Percoll and free of leucocyte contamination, which was 167 times greater than the median signal generated by the corresponding fraction from the fertile controls (P less than 0.001). These results emphasize the importance of spermatozoa as a major source of reactive oxygen species in oligozoospermia and have implications for the diagnosis and treatment of this condition, as well as for the design of appropriate diagnostic strategies.     

DNA barcoding in a biodiversity hot spot: potential value for the identification of Malagasy Euphorbia L. listed in CITES Appendices I and II

The island of Madagascar is a key hot spot for the genus Euphorbia, with at least 170 native species, almost all endemic. Threatened by habitat loss and illegal collection of wild plants, nearly all Malagasy Euphorbia are listed in CITES Appendices I and II. The absence of a reliable taxonomic revision makes it particularly difficult to identify these plants, even when fertile, and thereby compromises the application of CITES regulations. DNA barcoding, which can facilitate species‐level identification irrespective of developmental stage and the presence of flowers or fruits, may be a promising tool for monitoring and controlling trade involving threatened species. In this study, we test the potential value of barcoding on 41 Euphorbia species representative of the genus in Madagascar, using the two widely adopted core barcode markers (matK and rbcL), along with two additional DNA regions, nuclear internal transcribed spacer (ITS) and the chloroplastic intergenic spacer psbA‐trnH. For each marker and for selected marker combinations, inter‐ and intraspecific distance estimates and species discrimination rates are calculated. Results using just the ‘official’ barcoding markers yield overlapping inter‐ and intraspecific ranges and species discrimination rates below 60%. When ITS is used, whether alone or in combination with the core markers, species discrimination increases to nearly 100%, whereas the addition of psbA‐trnH produces less satisfactory results. This study, the first ever to test barcoding on the large, commercially important genus Euphorbia shows that this method could be developed into a powerful identification tool and thereby contribute to more effective application of CITES regulations.     

Genetic Architecture of Autosome-Mediated Hybrid Male Sterility in Drosophila

Several estimators have been developed for assesing the number of sterility factors in a chromosome based on the sizes of fertile and sterile introgressed fragments. Assuming that two factors are required for producing sterility, simulations show that one of these, twice the inverse of the relative size of the largest fertile fragment, provides good average approximations when as few as five fertile fragments are analyzed. The estimators have been used for deducing the number of factors from previous data on several pairs of species. A particular result contrasts with the authors' interpretations: instead of the high number of sterility factors suggested, only a few per autosome are estimated in both reciprocal crosses involving Drosophila buzzatii and D. koepferae. It has been possible to map these factors, between three and six per chromosome, in the autosomes 3 and 4 of these species. Out of 203 introgressions of different fragments or combinations of fragments, the outcome of at least 192 is explained by the mapped zones. These results suggest that autosome-mediated sterility in the male hybrids of these species is mediated by a few epistatic factors, similarly to X-mediated sterility in the hybrids of other Drosophila species.     

不同育性三角梅品种之间的形态、花粉活力、造访昆虫及黄酮醇含量的比较研究

三角梅高度不育,到目前为止其不育机理仍未理解透彻。本研究通过比较三角梅中可育和不育品种之间的生殖器官特征、花粉的活力、造访昆虫以及花粉中的类黄酮积累差异,为揭示其不育机理提供更多的证据。四个可育和两个不育三角梅品种的花萼管比较结果显示,可育品种的花萼管饱满呈长卵形,而不育品种的花萼管细长管状。可育品种的花粉形态均匀,而不育品种的花粉大小不一。花粉活性结果显示,可育品种的花粉萌发率在11.1%~46.5%,不育品种的花粉在相同的培养条件下几乎不萌发。在可育和不育品种间,共有七种昆虫造访,但昆虫的种类没有表现出明显的差异和偏好。类黄酮积累调查结果显示山奈酚/槲皮素糖苷衍生物是花粉中的主要类黄酮组分。利用花粉荧光染料DPBDA对四个可育和两个不育三角梅品种花器官中的黄酮醇含量比较显示,可育材料中的两种黄酮醇的含量显著高于不育材料,花粉管尖端的荧光信号相比花粉管的其他位置更丰富。我们推测黄酮醇含量差异,特别是槲皮素含量可能对三角梅花粉的活力有一定的积极作用。     

HYBRIDIZATION AND CYTOTAXONOMY OF DICENTRA

Biosystematic relationships among species assigned to three subgenera of the genus Dicentra were investigated with respect to hybridization and chromosomal constitution and fertility of the hybrids. Four species of subgenus Dicentra, D. formosa, D. eximia, D. nevadensis, and D. peregrina, were intercrossed in various ways to form diploid, triploid, and tetraploid hybrids. Hybrids at the tetraploid level in this subgenus invariably were highly fertile. Triploid hybrids, as expected, were mostly very sterile. Diploid hybrids varied in this respect, but none was highly fertile. Crosses with two of the remaining four species of subgenus Dicentra produced no hybrids, but abundant seed was obtained in one instance. The two species of the subgenus Chrysocapnos, D. chrysaniha and D. ochroleuca, cross to produce a partially fertile tetraploid hybrid, but cross-pollinations involving these species with those of other subgenera failed. The single species of subgenus Hedycapnos, D. spectablis (diploid) produced no hybrids when cross-pollinated with members of the other two sections. These results are fully concordant with presumed affinities based on morphological similarity In addition, preliminary results of hybridization between the monocotyledonous D. peregrina and a number of dicotyledonous species of Dicentra are reported.     

Genetic analysis of female mating recognition between Drosophila ananassae and Drosophila pallidosa: application of interspecific mosaic genome lines

Drosophila ananassae and Drosophila pallidosa are closely related species that can produce viable and fertile hybrids of both sexes, although strong sexual isolation exists between the two species. Females are thought to discriminate conspecific from heterospecific males based on their courtship songs. The genetic basis of female discrimination behavior was analyzed using isogenic females from interspecific mosaic genome lines that carry homozygous recombinant chromosomes. Multiple regression analysis indicated a highly significant effect of the left arm of chromosome 2 (2L) on the willingness of females to mate with D. ananassae males. Not only 2L but also the left arm of chromosome X (XL) and the right arm of chromosome 3 (3R) had significant effects on the females' willingness to mate with D. pallidosa males. All regions with strong effects on mate choice have chromosome arrangements characterized by species-specific inversions. Heterospecific combinations of 2L and 3R have previously been suggested to cause postzygotic reproductive isolation. Thus, genes involved in premating as well as postmating isolation are located in or near chromosomal inversions. This conclusion is consistent with the recently proposed hypothesis that "speciation genes" accumulate at a higher rate in non-recombining genome regions when species divergence occurs in the presence of gene flow.     

Developmental morphology of Odonthalia floccosa (Ceramiales, Rhodophyta) in laboratory culture

Material of the red alga Odonthalia floccosa (Esper) Fal-kenberg (Rhodomelaceae, Ceramiales), collected from California, was cultured in the laboratory and its life-history was completed. Tetraspores grew into bipolar sporelings that differentiated into a colorless rhizoidal portion and a pigmented upright shoot. The sporelings became compressed apically and formed lateral branches in a regularly distichous manner that were congenitally fused with the main axis. These tetraspore germlings grew into diecious gametophytes. Male ga-metophytes produced numerous spermatangia on modified fertile branchlets (male trichoblasts) that possessed three to four monosiphonous, proximal segments. Female gametophytes formed a single pro-carp on the suprabasal segment of unbranched female trichoblasts. Cystocarps developed on the female gametophytes cocultured with male gametophytes and released viable carpospores that developed into fertile te-trasporophytes. Tetrasporangia were produced from the third and fourth periaxial cells in each of 12–45 successive fertile segments and provided three (two lateral and one basal) cover cells. The occurrence of both spermatangia and procarps on fertile trichoblasts in O. floccosa suggests that the alga is the most derived in these two characters among the species of the genus Odonthalia. This species is distributed in cold temperate regions in the North Pacific, and it should be excluded from the North Atlantic marine algal flora.     

Odor discrimination in classical conditioning of proboscis extension in two stingless bee species in comparison to Africanized honeybees

Learning in insects has been extensively studied using different experimental approaches. One of them, the proboscis extension response (PER) paradigm, is particularly well suited for quantitative studies of cognitive abilities of honeybees under controlled conditions. The goal of this study was to analyze the capability of three eusocial bee species to be olfactory conditioned in the PER paradigm. We worked with two Brazilian stingless bees species, Melipona quadrifasciata and Scaptotrigona aff. depilis, and with the invasive Africanized honeybee, Apis mellifera. These three species present very different recruitment strategies, which could be related with different odor-learning abilities. We evaluated their gustatory responsiveness and learning capability to discriminate floral odors. Gustatory responsiveness was similar for the three species, although S. aff. depilis workers showed fluctuations along the experimental period. Results for the learning assays revealed that M. quadrifasciata workers can be conditioned to discriminate floral odors in a classical differential conditioning protocol and that this discrimination is maintained 15 min after training. During conditioning, Africanized honeybees presented the highest discrimination, for M. quadrifasciata it was intermediate, and S. aff. depilis bees presented no discrimination. The differences found are discussed considering the putative different learning abilities and procedure effect for each species.     

Empty seeds reduce seed predation by birds in Juniperus osteosperma

Utah juniper (Juniperus osteosperma) is one of many plant species that produce large numbers of fruits containing parthenocarpic or otherwise empty or inviable seeds. We tested the hypothesis that production of empty fruits in this species results in reduced levels of predation on fertile seeds. In a population in west-central Utah, we estimated the proportion of fruits with filled seeds in trees suffering high levels of fruit destruction by the seed-eating bird Parus inornatus and in neighbouring trees similar in crown and fruit-crop size but suffering negligible predation. We found that the heavily attacked trees had higher proportions of filled seeds. Thus, juniper may benefit from producing fruits that contain no offspring. This is the first study to demonstrate that empty seeds may reduce predation by vertebrate seed eaters and the first to demonstrate discrimination based on seed filling at the level of whole plants.     

Contrasting theory with the empirical data of species recognition

We tested hypotheses on how animals should respond to heterospecifics encountered in the environment. Hypotheses were formulated from models parameterized to emphasize four factors that are expected to influence species discrimination: mating and territorial interactions; sex differences in resource value; environments in which heterospecifics were common or rare; and the type of identity cues available for species recognition. We also considered the role of phylogeny on contemporary responses to heterospecifics. We tested the extent these factors explained variation among taxa in species discrimination using a meta-analysis of three decades of species recognition research. A surprising outcome was the absence of a general predictor of when species discrimination would most likely occur. Instead, species discrimination is dictated by the benefits and costs of responding to a conspecific or heterospecific that are governed by the specific circumstances of a given species. The phylogeny of species recognition provided another unexpected finding: the evolutionary relationships among species predicted whether courting males within species-but not females-would discriminate against heterospecifcs. This implies that species recognition has evolved quite differently in the sexes. Finally, we identify common pitfalls in experimental design that seem to have affected some studies (e.g., poor statistical power) and provide recommendations for future research.     

Fertilization competence and sperm size variation in sperm-heteromorphic insects

Between species, variation in sperm size has been related to male–female coevolution and male–male competition. In contrast, variation within species is poorly understood. A particular case of intraspecific sperm-size variation occurs in sperm-heteromorphic species, where males produce distinct sperm morphotypes, usually only one of which is fertile. This allows to investigate sperm size variation under different selection regimes. Nonfertile morphotypes, whose role is aside from fertilization, may have other functions, and this may be reflected by changes in developmental processes and a different phenotype compared to fertile sperm. We show that the intraspecific coefficient of variation in sperm length is up to four times lower for fertile than nonfertile morphotypes across 150 sperm-heteromorphic species (70 butterfly, 71 moth, 9 diopsid fly species). This is in agreement with a previous study on 11 species in the Drosophila obscura group. Significantly lower variation in fertile than nonfertile sperm morphometry may result from fertilization-related selection for optimal sperm size, novel functions of nonfertile sperm, or from tighter control of fertile sperm development. More data are needed to clarify the consequences and adaptive significance of within-morph variation, and its consistent pattern across sperm-heteromorphic insects.Co-ordinating editor: Hurst     

The structure, reproduction and taxonomy of Vidalia and Osmundaria (Rhodophyta, Rhodomelaceae)

Comprises species occurring mostly in subtidal habitats in tropical, subtropical and warm-temperate areas of the world. An analysis of the type species, V. spiralis (Sonder) Lamouroux ex J. Agardh, a species from Australia, establishes basic characters for distinguishing species in the genus. These characters are (1) branching patterns of thalli, (2) flat blades that may be spiralled on their axis, (3) width of the blade, (4) primary or secondary derivation of sterile and fertile branchlets and (5) position of sterile and fertile branchlets on the thalli. Application of the latter two characters provides an important basic method for separation of species into three major groups. Osmundaria , a genus known only in southern Australia, was studied in relation to Vidalia , and its separation from the Vidalia assemblage is not accepted. Species of Vidalia therefore are transferred to the older genus name, Osmundaria. Two new species, Osmundaria papenfussii and Osmundaria oliveae are described from Natal. Confusion in the usage of the epithet, Vidalia fimbriala Brown ex Turner has been clarified, and Vidalia gregaria Falkenberg, described as an epiphyte on Osmundaria pro/ifera Lamouroux, is revealed to be young branches of the host, Osmundaria prolifera.     

The evolution of reproductive isolation in the Drosophila yakuba complex of species

In the Drosophila melanogaster subgroup, the yakuba species complex, D. yakuba, D. santomea and D. teissieri have identical mitochondrial genomes in spite of nuclear differentiation. The first two species can be readily hybridized in the laboratory and produce fertile females and sterile males. They also form hybrids in natural conditions. Nonetheless, the third species, D. teissieri, was thought to be unable to produce hybrids with either D. yakuba or D. santomea. This in turn posed the conundrum of why the three species shared a single mitochondrial genome. In this report, we show that D. teissieri can indeed hybridize with both D. yakuba and D. santomea. The resulting female hybrids from both crosses are fertile, whereas the hybrid males are sterile. We also characterize six isolating mechanisms that might be involved in keeping the three species apart. Our results open the possibility of studying the history of introgression in the yakuba species complex and dissecting the genetic basis of interspecific differences between these three species by genetic mapping.     

The first compression fossils of Spencerites (Scott) emend., and its isospores, from the Bolsovian (Pennsylvanian) of the Kladno-Rakovník and Radnice basins, Czech Republic

Nearly 60 compression fossils of the vegetative stems and fertile zones of Spencerites (Scott) emend. are described from the Bolsovian of the Kladno-Rakovník and Radnice basins in the Czech Republic. Spencerites is re-interpreted as a pseudoherbaceous, repeatedly (minimum three times) dichotomously-branching, lycopsid with fertile apical zones. Vegetative stems are described for the first time. Two new species are proposed: Spencerites havlenae and Spencerites chaloneri. They are generally similar morphologically, and can be distinguished mainly by their isospores. Spencerisporites radiatus Felix and Parks, 1959 emend. isospores were isolated from Spencerites havlenae and Spencerisporites striatus sp. nov. from Spencerites chaloneri. Emendations are proposed for the generic diagnoses of Spencerites and Spencerisporites, and the specific diagnosis of Spencerisporites radiatus.     

Are 'preferences' and 'tolerances' in cichlid mate choice important for speciation?

Although early experience influences the development of preferences in cichlid mate choice, the same species can be very 'tolerant' and spawn with members of other species appearing very different from conspecifics. The conditions under which such interspecific spawnings occur in captivity are described, and are considered to exist in the field.
Many cichlid species are genetically similar, and interspecific spawning often produces fertile hybrids. Pre-mating behavioural barriers to hybridization are important. The ability of cichlids to develop preferences based on subtle cues, but also to produce fertile hybrids, is discussed in the context of speciation: genetic isolation of morphs (and possibly of hybrids) from their parental species, through social learning.