Reproductive interference in two ground-hopper species: testing hypotheses of coexistence in the field

Similar to resource competition, reproductive interference may hamper the coexistence of closely related species. Species that utilize similar signal channels during mate finding may face substantial fitness costs when they come into contact and demographic displacement of the inferior species (sexual exclusion) is a likely outcome of such interactions. The two ground‐hopper species Tetrix ceperoi and Tetrix subulata broadly overlap in their ranges and general habitat requirements, but rarely co‐occur on a local scale. Results from laboratory and field experiments suggest that this mosaic pattern of sympatry might be influenced by reproductive interference. Here, we examine the significance of sexual interactions for these species in the field and test hypotheses on mechanisms of coexistence. Our results show that heterospecific sexual interactions also occur under field conditions, but in contrast to the experiments T. ceperoi was not the inferior species. The number of male mating attempts of both species was strongly correlated with encounter frequencies. Males discriminated between the sexes but not between the species, suggesting an incomplete mate recognition system in both species. The analysis of microhabitat preferences and spatial distribution revealed that habitat partitioning is not a suitable mechanism of coexistence in this system. Instead, the costs of reproductive interference are substantially mitigated by different niche breadths leading to different degrees of aggregation. Despite a considerable niche overlap T. ceperoi displayed a stronger preference for bare ground and occurred more aggregated than T. subulata, which had a broader niche. These differences may reduce the frequencies of heterospecific encounters and interactions in the field. Our results demonstrate that coexistence in the presence of reproductive interference is comparable to resource competition, being strongly influenced by ecological traits of the involved species, such as niche breadth and dispersion pattern.     

Predicting the height of fossil plant remains: an allometric approach to an old problem

Interspecific correlations between plant height and basal stem diameter (the allometry of height) and between stem length distal to where diameter is measured (the allometry of stem taper) were determined for a total of 265 species with self-supporting stems and for the shoots of five conifers and 15 angiosperm vine species. The allometric equations obtained for these data are proposed as a method to predict the heights of fossil plants for which basal stem diameters are either known or inferred, and to predict the missing lengths of fragmented stems based on the most proximal stem diameters observed.     

Biomechanics of the columnar cactus Pachycereus pringlei

We report the longitudinal variations in stiffness and bulk density of tissue samples drawn from along the length of two Pachycereus pringlei plants measuring 3.69 and 5.9 m in height to determine how different tissues contribute to the mechanical stability of these massive vertical organs. Each of the two stems was cut into segments of uniform length and subsequently dissected to obtain and mechanically test portions of xylem strands, stem ribs, and a limited number of pith and cortex samples. In each case, morphometric measurements were taken to determine the geometric contribution each tissue likely made to the ability of whole stems to resist bending forces. The stiffness of each xylem strand increased basipetally toward the base of each plant where stiffness sharply decreased, reaching a magnitude comparable to that of strands 1 m beneath the stem apex. The xylem was anisotropic in behavior, i.e., its stiffness measured in the radial and in the tangential directions differed significantly. Despite the abrupt decrease in xylem strand stiffness at the stem base, the contribution made by this tissue to resist bending forces increased exponentially from the tip to the base of each plant due to the accumulation of wood. A basipetal increase in the stiffness of the pith (and, to limited extent, that of the cortex) was also observed. In contrast, the stiffness of stem rib tissues varied little as a function of stem length. These tissues were stiffer than the xylem in the corresponding portions of the stem along the upper two-fifths of the length of either plant. Tissue stiffness and bulk density were not significantly correlated within or across tissue types. However, a weak inverse relationship was observed for these properties in the case of the xylem and stem rib tissues. We present a simple formula that predicts when stem ribs rather than the xylem strands serve as the principal stiffening agents in stems. This formula successfully predicted the observed aspect ratio of the stem ribs (the average quotient of the radial and tangential dimensions of rib transections), and thus provided circumstantial evidence that the ribs are important for mechanical stability for the distal and younger regions of the stems examined.     

Signatures of antagonistic pleiotropy in a bacterial flagellin epitope

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The hSSB1 orthologue Obfc2b is essential for skeletogenesis but dispensable for the DNA damage response in vivo

We recently became aware of panel duplications in Supplementary Figures S6 and S7, due to pasting errors of similar flow cytometry images during figure preparation. This concerned the first two panels in the top row of Suppl. Fig S6A; second and third panel in the bottom row of Suppl. Fig S7B; and third and fourth panel in the bottom row of Suppl. Fig S7C.Furthermore, we noted a typographical error in Suppl. Fig S7B (top row, sixth plot), where the indicated percentage was wrongly given as 1.4%, instead of 1.1%. These errors did not change the results or the interpretation of the data. We deeply apologize to the scientific community for any confusion these errors may have caused. The updated appendix is published with this corrigendum.The original FlowJo analysis plots related to the affected figures are published as source data with this corrigendum. Please note that initial labelling of the experiments in these files referred to the official gene name Obfc2b informally as hSSB1, and Obfc2a‐shRNAs as ‘sh1’ and sh4’.Open in a separate windowFigure S6AOriginalOpen in a separate windowFigure S6ACorrectedOpen in a separate windowFigure S7BOriginalOpen in a separate windowFigure S7BCorrectedOpen in a separate windowFigure S7COriginalOpen in a separate windowFigure S7CCorrected     

Out-of-Africa again: A phylogenetic hypothesis of the genus Charaxes (Lepidoptera: Nymphalidae) based on five gene regions

Despite the long popularity of Charaxes among collectors and researchers, their evolutionary history is largely unknown. The current and accepted species groupings and relationships within the genus are based exclusively on adult morphology and life histories. Here, we examine the monophyly and evolutionary affinities of the species-groups within the genus Charaxes and explore how they relate to members of their closest genera (Euxanthe, Polyura and Palla) using 4167 bp of sequence data from five (1 mitochondrial and 4 nuclear) gene regions. Within the proposed phylogenetic framework, we estimate ages of divergence within the genus and also reconstruct their historical biogeography. We included representatives of all known species-groups in Africa and Asia, all known species of Euxanthe and Palla and two exemplar species of Polyura. We found the genus Charaxes to be a paraphyletic group with regard to the genera Polyura and Euxanthe, contrary to the earlier assumption of monophyly. We found that 13 out of 16 morphologically defined species-groups with more than one species were strongly supported monophyletic clades. Charaxes nichetes is the sister group to all the other Charaxes. Polyura grouped with the Zoolina and Pleione species-groups as a well-supported clade, and Euxanthe grouped with the Lycurgus species-group. Our results indicated that the common ancestor of Charaxes diverged from the common ancestor of Palla in the mid Eocene (45 million years ago) in (Central) Africa and began diversifying to its extant members 15 million years later. Most of the major diversifications within the genus occurred between the late Oligocene and Miocene when the global climates were putatively undergoing drastic fluctuations. A considerable number of extant species diverged from sister species during the Pliocene. A dispersal–vicariance analysis suggests that many dispersal rather than vicariance events resulted in the distribution of the extant species. The genus Polyura and the Indo-Australian Charaxes are most likely the results of three independent colonizations of Asia by African Charaxes in the Miocene. We synonymize the genera Polyura (syn. nov.) and Euxanthe (syn. nov.) with Charaxes, with the currently circumscribed Charaxes subdivided into five subgenera to reflect its phylogeny.     

Paleobiochemistry of North American fossil Liriodendron sp.

Organic geochemical analyses are presented for a fossil Liriodendron sp. from the Miocene, Clarkia Flora of Northern Idaho. Flavonoid profiles determined for the fossil and two extent species of Liriodendron (L. chinense and L. tulipifera) confirm the generic status of the fossil material, but owing to a generic uniformity in flavonoid composition, fail to resolve taxonomic affinities at the species level. Steroid and other cycloalkane-alkene profiles indicate that the fossil taxon has a greater chemical similarity with L. chinense than L. tulipifera, despite the general leaf outline similarity between the fossil species and extent L. tulipifera. The morphologic and chemical data are interpreted as evidence for mosaic evolution within the genus, and the non-canalization of character states in some Miocene species.     

Plant compensatory growth: a conquering strategy in plant–herbivore interactions?

We present a theoretical analysis that considers the phenotypic trait of compensatory growth ability in a context of population dynamics. Our model depicts a system of three interactors: herbivores and two different plant types referred to as ordinary and compensating. The compensating plant type has the ability to increase its intrinsic rate of biomass increase as a response to damage. This compensatory growth ability is maintained at the expense of a reduced growth rate in the absence of damage, where the ordinary plant type has the higher growth rate. Analysis of this system suggests that, even though a compensatory capacity of this kind will not imply an increase in equilibrium plant density, it will give a competitive advantage in relation to other plants, in the presence of a sufficiently efficient herbivore. Invasion of compensating plants into a population of non-compensating plants is facilitated by a high compensatory growth ability and a high intrinsic rate of plant biomass increase. Conversely, an ordinary plant can invade and outcompete a compensating plant when the herbivore is characterised by a relatively low attack rate, and/or when plant intrinsic growth rate is decreased.