Does selfing provide reproductive assurance in the perennial herb Bulbine vagans (Asphodelaceae)?

Selection for selfing to provide reproductive assurance depends on the balance between increased reproductive output when pollinators or potential mates are scarce and the extent that inbreeding depression erodes such fertility gains. We use glasshouse and field experiments to examine the benefits of autonomous and facilitated selfing in Bulbine vagans . Autonomous selfing was delayed until after opportunities for outcrossing and reproductive output was 0.67 relative to manual selfing and open pollination. Values less than one probably reflected insufficient autonomous deposition of self pollen. In the field, reproductive output of emasculated flowers was 0.50 relative to intact flowers that could both outcross and self, indicating that outcross pollen was limited and that selfing boosted reproductive output. Because all pollen was removed from anthers before intact flowers closed, facilitated selfing rather than autonomous selfing occurred. In the glasshouse, inbreeding depression was 0.45, but under natural conditions would probably exceed 0.5. Values greater than 0.5 negate the automatic gene transmission advantage afforded by selfing and increasingly erode the benefits of reproductive assurance. We conclude that in B. vagans delayed and facilitated selfing can confer reproductive assurance, providing the latter does not usurp ovules that could be outcrossed.     

Can environmental factors explain size variation in the common shrew (Sorex araneus)?

Shrews are small mammals with a high metabolic rate and may potentially be greatly influenced by environmental factors. Several studies have indicated both morphological and genetical variation in the common shrew (Sorex araneus). The aims of this study were to study patterns in size variation and to test which environmental factors influence body size most. Most study sites were located to northern Norway, between 65° and 70°N, one study site in south Norway was also included (60°N). At one site shrews were studied for 10 consecutive years. Three body measurements (body length, tail length and body mass) and two combined estimates (tail proportion and body condition) were compared, where appropriate, among populations (sites), years and months, and along gradients of altitude (habitat), coast–inland and north–south. Effects of summer climate (temperature and precipitation) were also tested. Size variations among populations of common shrews were found in a number of respects; yearly, seasonal, local and regional. Regional variation was most significant, followed by yearly and seasonal variation. The results suggest a strong link between body size and a coast–inland gradient, with smallest shrews (up to 13% smaller) on inland locations. The main differences between coastal and inland sites are lower winter temperatures and less snow cover at inland sites (factors which are also associated with habitat productivity), which could favour smaller shrews with less energetic demands. Most other variation was relatively small (<5%). Most of the results indicate climate and habitat productivity as the most important factors, which may also vary between years at a single site. Bergmanns's rule, Allen's rule or Dehnel's phenomenon were not supported by this study. The insular syndrome was partly supported. Smaller variations in size may only be proximate adaptations to local food supply, but larger variations are likely to be ultimate adaptations.     

Can the pollination biology and floral ontogeny of the threatened Acacia carneorum explain its lack of reproductive success?

Many Acacia species in arid areas of eastern Australia have been severely impacted by grazing, habitat degradation and fragmentation. These factors have been at the core of proposed explanations for the reproductive failure and numerical decline of Acacia carneorum and other threatened acacias. Paradoxically, the sympatric Acacia ligulata is thriving and highly fecund. Although these species have superficially similar floral displays, differences in sexual reproductive success may reflect interactions between flower and inflorescence ontogeny and pollinator assemblages. We compared the floral biology and flower visitor assemblages of A. carneorum and A. ligulata at four sites per species. Both species displayed similar floral ontogeny and synchronicity of display, with inflorescences simultaneously hermaphroditic for 4–5 days. However, A. ligulata displayed a higher density of flowers than A. carneorum and, while both species received a range of flower visitors, A. ligulata was visited by relatively few species and was serviced primarily by the non-native honeybee Apis mellifera, which typically made many within-plant movements during foraging bouts. In contrast, A. carneorum was visited by a diverse suite of native insects that carried little pollen and made fewer within plant movements. On average, Apis mellifera carried 98.4 % A. ligulata pollen, whereas the native insect visitors of A. carneorum carried only 45 % A. carneorum pollen. Differing floral ontogeny or lack of native pollinators does not explain the reproductive failure of A. carneorum. The success of A. ligulata may reflect pollination services provided by A. mellifera and interactions with plant mating systems.     

Can pseudo entrainment explain the synchrony of estrous cycles among golden hamsters (Mesocricetus auratus)?

Synchrony among golden hamsters is often cited in the menstrual-cycle synchrony literature and has recently become a paradigm for explaining menstrual synchrony in humans (L. Weller, A. Weller, and S. Roizman (1999), J. Comp. Psychol. 113, 261-268). It has also stimulated further research on synchrony in Djungarian hamsters, for which no evidence of synchrony was found (G. E. Erb, H. E. Edwards, K. L. Jenkins, L. C. Mucklow, and K. E. Wynne-Edwards (1993), Physiol. Behav. 54, 955-959). The case for synchrony in the golden hamster is reexamined in this paper. It is demonstrated, with the help of computer simulation experiments, that the experimental method used by G. Handelmann, R. Ravizza, and W. J. Ray (1980, Horm. Behav. 14, 107-115) for detecting synchrony has a critical flaw. It does not distinguish synchrony that can occur by chance (pseudo entrainment) from synchrony due to a process of entrainment. It is suggested that the apparent entrainment of estrous cycles in hamsters and the role of social dominance may be due to the stress caused by moving animals to different rooms or grouping them. Thus, because we cannot reject the possibility of pseudo entrainment as an explanation for these results, it must be concluded that there is no evidence that golden hamsters synchronize their estrous cycles. Finally, an approach is briefly outlined for testing synchrony in golden hamsters.     

Can phenotypic selection on floral traits explain the presence of enigmatic intermediate individuals in sympatric populations of Platanthera bifolia and P. chlorantha (Orchidaceae)?

Pollinators represent one of the main agents of selection on floral traits. Here, we estimated phenotypic selection on floral morphology and phenology in a sympatric population of two orchid species, Platanthera bifolia and P. chlorantha, including enigmatic individuals with intermediate column morphology (as reflected by the distance between viscidia and caudicle length, two traits involved in assortative mating and reproductive isolation among Platanthera species), but genetically indistinguishable from P. bifolia. Our aim was to clarify whether the occurrence of intermediate phenotypes could be explained by the presence of selective pressures exerted by pollinators. Simple linear and quadratic regressions together with univariate and multivariate analyses were used to evaluate the strength of directional, disruptive and stabilizing selection. We found that selection on phenotypic traits varied between groups and sex functions. Contrary to our hypothesis, selection on the viscidia distance and caudicle length appeared to be consistent in the two P. bifolia groups. Interestingly, the viscidia distance was under significant stabilizing selection through female reproductive success in intermediate individuals. Based on these results, we conclude that, despite a significant selective pressure on some phenotypic traits, the presence of individuals with intermediate phenotype is not due to selection. Stabilizing selection on distance between viscidia in intermediate individuals may suggest that assortative mating play a role in the maintenance of this phenotypic polymorphism.     

Can mutation or fixation biases explain the allele frequency distribution of human single nucleotide polymorphisms (SNPs)?

One of the most abiding controversies in evolutionary biology concerns the role of neutral processes in molecular evolution. A main focus of the debate has been the evolution of isochores, the strong and systematic variation of base composition in mammalian genomes. One set of hypotheses argue that regions of similar GC are owing to localised mutational biases coupled with neutral evolution. The alternatives point to either selection or biased gene conversion as mechanisms to preferentially remove A or T bases, favouring G and C instead. Using a novel method, we compare models including such fixation biases to models based on mutation bias alone, under the assumption that non-coding, non-repetitive human DNA is at compositional equilibrium. While failing to fully explain the allele frequency distributions of recent single nucleotide polymorphism data, we show that the data are best fitted if the mutation bias is assumed to be constant across the genome, while fixation bias varies with GC content. We also attempt to estimate the strength of fixation bias, which increases linearly with increasing GC. Our approximation suggests that this force exists within the necessary parameter range: it is not so weak as to be drowned by random drift, but not so strong as to lead to exclusive use of G and C alone. Together these results demonstrate that mutation bias fails to explain the evolution of isochores, and suggest that either selection or biased gene conversion are involved.     

Can differences in phosphorus uptake kinetics explain the distribution of cattail and sawgrass in the Florida Everglades?

Background  

Cattail (Typha domingensis) has been spreading in phosphorus (P) enriched areas of the oligotrophic Florida Everglades at the expense of sawgrass (Cladium mariscus spp. jamaicense). Abundant evidence in the literature explains how the opportunistic features of Typha might lead to a complete dominance in P-enriched areas. Less clear is how Typha can grow and acquire P at extremely low P levels, which prevail in the unimpacted areas of the Everglades.     

Can diet composition estimates using stable isotope analysis of feathers predict growth and condition in nestling mountain bluebirds (Sialia currucoides)?

Insectivorous birds breeding in seasonal environments provision their dependent young during periods when prey diversity and abundance vary. Consequently, the composition and nutritional value of diets parents feed to their offspring may differ within and among broods, potentially affecting the condition of nestlings. In a population of mountain bluebirds (Sialia currucoides), we used two methods to estimate diet composition for individual nestlings: direct observation of provisioning using video recordings at 5 and 9 days post‐hatch, and stable isotopes of the δ¹³C and δ¹⁵N in nestling feathers and prey followed by analysis with mixing models. We determined the macronutrient content (% fat and lean mass) and estimated the metabolized energy from each type of prey. We evaluated whether different methods of estimating diet composition would produce similar results, and whether the types of prey nestlings ate at one or both ages affected their morphology, growth rates, or blood ketone concentration. We found that bluebirds fed their young 5 main types of prey: beetles, cicadas, grasshoppers, insect larvae, and spiders. Both observational and mixing model estimates of diet composition indicated that larvae are traded off with grasshoppers and that fewer larvae are provided to nestlings as the season progresses. In evaluating how diet influences individual growth and condition, estimates from direct observations had greater explanatory power than those from mixing models, indicating that diets rich in the most energy‐dense prey (greatest fat content; cicadas and larvae) were associated with larger size and higher body condition, and faster rate of mass gain and growth of tarsus. Lower value prey had more limited, specific effects on nestlings, but may still be important dietary components. While isotopic methods produced estimates of diet composition that were generally informative, when applied to explain the growth and condition of nestlings they proved less useful.     

Can reproductive traits help to explain the coexistence of mud crabs Panopeus (Decapoda: Panopeidae)? A case of two sympatric species inhabiting an impacted mangrove area of Southern Brazil

Coexistence among species is commonly related to niche divergence. However, congenerics usually are very similar in their microhabitat selection and food consumption. Thus, divergent life history strategies may represent the mechanism that allows sympatry in related species. Here, we describe and compare reproductive features in two sympatric mud crabs Panopeus americanus and P. occidentalis in an impacted mangrove area in Southern Brazil. As these species are ecologically similar, we hypothesize that these species diverge in their reproductive traits, which could explain their coexistence. Crabs were collected every two months from September 2004 to July 2006. Reproductive features such as number and size of ovigerous females, breeding season, fecundity, reproductive output, and embryo volume were assessed. Panopeus americanus produced embryos during the entire sampled period, while P. occidentalis produced only between September and March. Panopeus americanus produced more embryos considering the size of the species, had significantly lower embryo volume, and higher reproductive output than P. occidentalis. These data permit to classify P. americanus as an r-strategist and P. occidentalis as a K-strategist regarding their reproductive traits. In conclusion, our results support the hypothesis that divergent reproductive features may allow coexistence of these mud crabs.     

Do inbreeding depression and relative male fitness explain the maintenance of androdioecy in white mangrove, Laguncularia racemosa (Combretaceae)?

Mathematical models predict that to maintain androdioecious populations, males must have at least twice the fitness of male function in hermaphrodites. To understand how androdioecy is maintained in Laguncularia racemosa (white mangrove), outcrossing, inbreeding depression, and relative male fitness were estimated in two androdioecious populations and one hermaphroditic population. Outcrossing was estimated based on length of pollinator foraging bout and pollen carryover assumptions. Inbreeding depression was measured at three life stages: fruit set, seedling emergence, and seedling survivorship. The relative fitnesses of males and the male component of hermaphrodites were compared at these three stages and at the pollen production stage. Male frequency predictions generated by Lloyd's model were compared with observed frequencies in two androdioecious subpopulations. Outcrossing estimates were moderate for all populations (0.29-0.66). Inbreeding depression varied among populations (-0.03-0.86), but the strength of inbreeding depression did not increase with male frequency. Males produced significantly more flowers/inflorescence than hermaphrodites, but pollen production/flower did not differ. Male and hermaphroditic progeny did not differ significantly at other life stages. Populations of white mangrove with male plants were functionally androdioecious. Lloyd's model accurately predicted male frequency in one androdioecious subpopulation, but underestimated male frequency in the second subpopulation.     

Can the risk of parasite infection in fish cause the ecological differentiation in the population of roach Rutilus rutilus (Cyprinidae)?

Population characteristics of macroparasite infection (prevalence and intensity) in juvenile roach Rutilus rutilus have been studied in one of the tributaries of the Rybinsk Reservoir. The level of infection and parasite diversity is higher in the mouth part than in the upper reaches of the river. Habitats in the upper reaches are characterized by a high degree of irregularity of the risk of infection. The intensity of parasitic infection varies from the absence of parasites to 100% infection. Our data confirm the hypothesis about adaptaive value of the spawning migration to habitats with lower risk for the infection of offspring with parasites. Heterogeneous conditions in the upper reaches of the river make it possible for juvenile fish from a migrating part of the population to grow in relatively safe conditions. Differences in the strategy of the spawning migration can be based on the ecological differentiation as a result of which the groups oriented either at the local adaptation or at migration to the other habitat are formed in the population.     

Can phylogenetic signal,character displacement,or random phenotypic drift explain the morphological variation in the genus Geonoma (Arecaceae)?

Plant clades may exhibit little or wide morphological variation as a result of (1) the retention of ancestral characteristics or phylogenetic signal, (2) character displacement, or (3) random phenotypic drift or convergence. Understanding the taxonomy and systematics of many plant lineages has been challenging due to continuous intra‐ and interspecific morphological variation. To assess which evolutionary hypothesis could explain the morphological diversity in the genus Geonoma (Arecaceae), we performed a Mantel test between phylogenetic and morphological distances of 54 taxa, and tested for phylogenetic signal using Blomberg's K‐statistic on continuous variables, and a randomization of character states. To obtain a phylogenetic (patristic) distance matrix for Geonoma, we constructed a molecular phylogeny of tribe Geonomateae using three nuclear DNA regions. A positive relationship between the patristic and a 26‐discrete‐character distance matrix (R² = 0.55, P < 0.001) supported the phylogenetic signal hypothesis. The randomization test showed that signal was present in 16 characters. No relationship was evident using a 17‐quantitative‐variable distance matrix (R² = 0.07, P = 0.13), supporting the random drift hypothesis or convergence, and all 17 K‐values were close to 0, suggesting less phylogenetic signal than under the Brownian model. If most morphological variables traditionally used to classify Geonoma evolved randomly or convergently, it might explain Geonoma's challenging taxonomy. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 528–539.     

Is reproductive strategy a key factor in understanding the evolutionary history of Southern Ocean Asteroidea (Echinodermata)?

Life traits such as reproductive strategy can be determining factors of species evolutionary history and explain the resulting diversity patterns. This can be investigated using phylogeographic analyses of genetic units. In this work, the genetic structure of five asteroid genera with contrasting reproductive strategies (brooding: Diplasterias, Notasterias and Lysasterias versus broadcasting: Psilaster and Bathybiaster) was investigated in the Southern Ocean. Over 1,400 mtDNA cytochrome C oxidase subunit I (COI) sequences were analysed using five species delineation methods (ABGD, ASAP, mPTP, sGMYC and mGMYC), two phylogenetic reconstructions (ML and BA), and molecular clock calibrations, in order to examine the weight of reproductive strategy in the observed differences among phylogeographic patterns. We hypothesised that brooding species would show higher levels of genetic diversity and species richness along with a clearer geographic structuring than broadcasting species. In contrast, genetic diversity and species richness were not found to be significantly different between brooders and broadcasters, but broadcasters are less spatially structured than brooders supporting our initial hypothesis and suggesting more complex evolutionary histories associated to this reproductive strategy. Broadcasters' phylogeography can be explained by different scenarios including deep‐sea colonisation routes, bipolarity or cosmopolitanism, and sub‐Antarctic emergence for the genus Bathybiaster; Antarctic‐ New Zealand faunal exchanges across the Polar Front for the genus Psilaster. Brooders' phylogeography could support the previously formulated hypothesis of a past trans‐Antarctic seaway established between the Ross and the Weddell seas during the Plio‐Pleistocene. Our results also show, for the first time, that the Weddell Sea is populated by a mixed asteroid fauna originating from both the East and West Antarctic.     

Can heterochrony help explain the high morphological diversity within the genus Niphargus (Crustacea: Amphipoda)?

Postembryonic development of nine species of Niphargus (Crustacea: Amphipoda) was studied, with spine development and shifts in allometric growth being combined in developmental sequences that were compared across species. The developmental sequences show high diversity with respect to the position of individual events in the sequence, as well as a high frequency of events being inapplicable in some species. Within Niphargus, the highest degree of independence between events occurs mainly in early mid-aged instars, where the shifts in position are both the largest in magnitude and also the most frequent in occurrence. Constructive troglomorphic features of subterranean species were inferred to develop more because of accelerated growth rather than a delayed offset of growth. Shifts in both relative timing and growth rate appeared to have played a role in the evolution of sexually dimorphic elongated appendages. Growth patterns differed greatly between species for individual sexually dimorphic and troglomorphic traits, hinting at their possible independent origin. The independence between developmental events that was generally apparent might indicate the existence of an important genetic basis for the extreme intrageneric morphological variation arising from numerous highly variable body parts being combined in a ‘mosaic’ manner. Moreover, we suggest that the overall diversity of the genus might actually be underestimated in light of possible convergent features accompanied by ‘cryptic’ speciation. We conclude that both sequential and growth heterochrony appear to have played a key role in the evolution of Niphargus, the most diverse genus of freshwater amphipods. A preliminary list of heterochronic characters is provided.     

A nodding capitulum enhances the reproductive success of Cremanthodium campanulatum (Asteraceae) at high elevations in the Sino–Himalayan Mountains

Background: Flower orientation is considered an evolutionary response to pollinators and abiotic factors. Several members of the genus Cremanthodium (Asteraceae) growing in alpine habitats in the Sino–Himalayas have conspicuously nodding capitula, the function of which is not understood.

Aims: We investigated the influences of nodding capitula on floral thermal conditions, pollinator visitation rate, pollen viability and achene production in Cremanthodium campanulatum.

Results: (1) the nodding capitulum did not modify internal thermal conditions, but the elongated involucral bracts could shelter pollen from UV-B radiation; (2) water and UV-B radiation seriously reduced the viability of pollen grains; (3) capitula artificially held erect set significantly fewer achenes than nodding ones; and (4) no pollinator preference was observed between capitula that were artificially held erect and natural nodding ones.

Conclusions: This study indicated that the nodding capitulum of C. campanulatum may protect pollen from being damaged by UV-B radiation, being washed away from the anther and stigma, and enable it to avoid rain damage during the wet monsoonal period. Our results suggest that nodding capitula in C. campanulatum possibly confer a selective advantage and may be driven by non-biological agents rather than pollinator attractors.     

Can biomass supply meet the demands of bioenergy with carbon capture and storage (BECCS)?

To reach the reduced carbon emission targets proposed by the Paris agreement, one of the widely proposed decarbonizing strategies, referred to as negative emissions technologies (NETs), is the production and combustion of bioenergy crops in conjunction with carbon capture and storage (BECCS). However, concerns have been increasingly raised that relying on the potential of BECCS to achieve negative emissions could result in delayed reductions in gross CO₂ emissions, with consequent high risk of overshooting global temperature targets. We focus on two particular issues: the carbon efficiency and payback time of bioenergy use in BECCS and the potential constraints on the supply of bioenergy. The simplistic vision of BECCS is that 1 tonne of CO₂ captured in the growth of biomass equates to 1 tonne of CO₂ sequestered geologically, but this cannot be the case as CO₂ is emitted by variable amounts during the lifecycle from crop establishment to sequestration below ground in geological formations. The deployment of BECCS is ultimately reliant on the availability of sufficient, sustainably sourced, biomass. The two most important factors determining this supply are land availability and land productivity. The upper bounds of the area estimates required correspond to more than the world's harvested land for cereal production. To achieve these estimates of biomass availability requires the rapid evolution of a multitude of technological, social, political and economic factors. Here, we question whether, because of the limited sustainable supply of biomass, BECCS should continue to be considered the dominant NET in IPCC and other scenarios achieving the Paris targets, or should it be deemed no longer fit for purpose?     

Does genetic variation and gene flow vary with rarity in obligate seeding Persoonia species (Proteaceae)?

Theory predicts that genetic variation is a determinant of persistence, and that the abundance and distribution of variation is strongly dependent on genetic drift and gene flow. Small, isolated populations are expected to be less diverse and more differentiated than large, inter-connected populations. Thus rare species may be more at risk of extinction. We used 389 putative AFLP loci to compare genetic variation and structuring in two pairs of closely-related common (large populations geographically widespread) and rare (small populations spatially restricted) Persoonia species. We genotyped 15–22 adult plants, from four populations, covering the geographic range of each species. Although genetic diversity was low for all four species (for long-lived outcrossing perennials), we found significantly more diversity within populations of the rare species than within those of the common species. AMOVA revealed significant levels of structure both among species (21%) and populations (15%). The proportion of inter-population variation within species did not vary consistently with rarity (Pair 1 rare 21.1% versus common 16.5%; Pair 2 rare 15.8% versus common 20.6%). However populations of the rare species were more differentiated than common species with similar geographic separation, suggesting greater gene flow between populations of the common species. Therefore, even relatively small genetically isolated populations of rare Persoonia species were more diverse than large populations of common Persoonia species. We hypothesise that common Persoonia species have undergone a rapid range expansion from a narrow gene pool, while genetic diversity is maintained in the soil seed-bank of rare remnants.