skip to main content


Title: Evolution of apetaly in the cosmopolitan genus Stellaria
Premise

Apetaly is widespread across distantly related lineages of flowering plants and is associated with abiotic (or self‐) pollination. It is particularly prevalent in the carnation family, and the cosmopolitan genusStellariacontains many lineages that are hypothesized to have lost petals from showy petalous ancestors. But the pollination biology of apetalous species ofStellariaremains unclear.

Methods

Using a substantial species‐level sampling (~92% of known taxonomic diversity), we describe the pattern of petal evolution withinStellariausing ancestral character state reconstructions. To help shed light on the reproductive biology of apetalousStellaria, we conducted a field experiment at an alpine tundra site in the southern Rocky Mountains to test whether an apetalous species (S. irrigua) exhibits higher levels of selfing than a sympatric, showy petalous congener (S. longipes).

Results

Analyses indicated that the ancestor ofStellariawas likely showy petalous and that repeated, parallel reductions of petals occurred in clades across much of the world, with uncommon reversal back to showy petals. Field experiments supported high rates of selfing in the apetalous species and high rates of outcrossing in the petalous species.

Conclusions

Petal loss is rampant across major clades ofStellariaand is potentially linked with self‐pollination worldwide. Self‐pollination occurs within the buds inS. irrigua, and high propensities for this and other forms of selfing known in many other taxa of arctic‐alpine habitats may reflect erratic availability of pollinators.

 
more » « less
Award ID(s):
1637686
NSF-PAR ID:
10387846
Author(s) / Creator(s):
 ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
American Journal of Botany
Volume:
108
Issue:
5
ISSN:
0002-9122
Page Range / eLocation ID:
p. 869-882
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    The amphicarpic annual legumeAmphicarpaea bracteatais unusual in producing aerial and subterranean cleistogamous flowers that always self‐fertilize and, less commonly, aerial chasmogamous flowers that outcross. Although both morphologic and genetic variants are known in this highly selfing species, debate continues over whether this variation is continuous, reflecting the segregation of standing genetic variation, or discontinuous, reflecting distinct taxa that rarely intercross. We characterizedSNPvariation in 128 individuals in southern Wisconsin to assess within‐ and among‐population variation at 3928SNPs. We also assessed genotype and leaf morphology in an additional 76 individuals to connect phenotypic variation with genetic variation. Genetic variation maps onto three strongly divergent and highly inbred genetic groups showing little relation to site location. Each group has a distinct phenotype, but the divergence of these groups differs from the varietal divisions previously identified based on morphological characters. Like previous authors, we argue that the taxonomy of this species should be revised. Despite extensive sympatry, estimates of among‐group migration rates are low, and hybrid individuals were at low frequency (<2%) in our dataset. Restricted gene flow likely results from high selfing rates and partial reproductive incompatibility as evidenced by the U‐shaped distribution of pairwiseFSTvalues reflecting “islands” of genomic divergence. These islands may be associated with hybrid incompatibility loci that arose in allopatry. The coexistence of lineages within sites may reflect density‐dependent attack by species‐specific strains of pathogenic fungi and/or root‐nodulating bacteria specializing on distinct genotypes.

     
    more » « less
  2. Abstract

    Fusion of petals to form a corolla tube is considered a key innovation contributing to the diversification of many flowering plant lineages. Corolla tube length often varies dramatically among species and is a major determinant of pollinator preference. However, our understanding of the developmental dynamics underlying corolla tube length variation is very limited. Here we examined corolla tube growth in theMimulus lewisiispecies complex, an emerging model system for studying the developmental genetics and evo‐devo of pollinator‐associated floral traits. We compared developmental and cellular processes associated with corolla tube length variation among the bee‐pollinatedM. lewisii, the hummingbird‐pollinatedMimulus verbenaceus, and the self‐pollinatedMimulus parishii. We found that in all three species, cell size is non‐uniformly distributed along the mature tube, with the longest cells just distal to the stamen insertion site. Differences in corolla tube length among the three species are not associated with processes of organogenesis or early development but are associated with variation in multiple processes occurring later in development, including the location and duration of cell division and cell elongation. The tube growth curves of the small‐floweredM. parishiiand large‐floweredM. lewisiiare essentially indistinguishable, except thatM. parishiitubes stop growing earlier at a smaller size, suggesting a critical role of heterochrony in the shift from outcrossing to selfing. These results not only highlight the developmental process associated with corolla tube variation among species but also provide a baseline reference for future developmental genetic analyses of mutants or transgenic plants with altered corolla tube morphology in this emerging model system.

     
    more » « less
  3. Abstract Background

    Mammalian skeletons are largely formed before birth. Heterochronic changes in skeletal formation can be investigated by comparing the order of ossification for different elements of the skeleton. Due to the challenge of collecting prenatal specimens in viviparous taxa, opportunistically collected museum specimens provide the best material for studying prenatal skeletal development across many mammalian species. Previous studies have investigated ossification sequence in a range of mammalian species, but little is known about the pattern of bone formation in Carnivora. Carnivorans have diverse ecologies, diets, and biomechanical specializations and are well-suited for investigating questions in evolutionary biology. Currently, developmental data on carnivorans is largely limited to domesticated species. To expand available data on carnivoran skeletal development, we used micro-computed tomography (micro-CT) to non-invasively evaluate the degree of ossification in all prenatal carnivoran specimens housed in the Harvard Museum of Comparative Zoology. By coding the presence or absence of bones in each specimen, we constructed ossification sequences for each species. Parsimov-based genetic inference (PGi) was then used to identify heterochronic shifts between carnivoran lineages and reconstruct the ancestral ossification sequence of Carnivora.

    Results

    We used micro-CT to study prenatal ossification sequence in six carnivora species:Eumetopias jubatus(Steller sea lion,n = 6),Herpestes javanicus(small Indian mongoose,n = 1),Panthera leo(lion,n = 1),Urocyon cinereoargenteus(gray fox,n = 1),Ursus arctos arctos(Eurasian brown bear,n = 1), andViverricula indica(small Indian civet,n = 5). Due to the relatively later stage of collection for the available specimens, few heterochronic shifts were identified. Ossification sequences of feliform species showed complete agreement with the domestic cat. In caniforms, the bear and fox ossification sequences largely matched the dog, but numerous heterochronic shifts were identified in the sea lion.

    Conclusions

    We use museum specimens to generate cranial and postcranial micro-CT data on six species split between the two major carnivoran clades: Caniformia and Feliformia. Our data suggest that the ossification sequence of domestic dogs and cats are likely good models for terrestrial caniforms and feliforms, respectively, but not pinnipeds.

     
    more » « less
  4. Abstract Aim

    High‐elevation plants are disproportionally affected by climate change. As temperatures rise, the amount of available alpine habitat in the Rocky Mountains will decrease resulting in potential local extinctions of plant species. In addition to the direct effects of climate‐driven habitat loss, alpine plants must also respond to indirect effects, such as changes in disturbance regimes. One notable shift is the increase of wildfire frequency in regions where fire was previously rare or absent, including the alpine. We hypothesized that direct climatic changes compounded with increased wildfire frequency will reduce the future suitable habitat of high‐elevation plants more than if climate was considered alone.

    Location

    Rocky Mountain Floristic Region, western North America.

    Taxon

    Saxifraga austromontana(Saxifragaceae), a wildflower endemic to high elevations of the Rocky Mountain Floristic Region.

    Methods

    Our approach integrated historical herbarium records, field surveys, remote sensing, species distribution models, historic wildfire data, and predictive models.

    Results

    Our results indicate wildfire has significantly reduced the abundance and increased the likelihood of extirpation forS. austromontana. Increased fire frequency compounded with direct climatic changes will likely reduce the range of the species by approximately 43% by 2050 compared to 38% due to climate alone, under a moderateCO2emissions scenario. The influence of wildfire varies regionally. For instance, the Middle Rockies will likely lose 74% of its suitable habitat of which 16% may be lost due to fire, while other regions, such as the northern range, will be less negatively affected by direct and indirect effects.

    Main Conclusions

    Our evidence that increased wildfire frequency will compound the impacts of climate change on alpine taxa in North America led to the development of a new, general hypothesis on the fundamental interaction between direct and indirect effects of climate change on species range reductions.

     
    more » « less
  5. PREMISE

    Hybridization plays a key role in introgressive adaptation, speciation, and adaptive radiation as a source of evolutionary innovation. Hybridization is considered common inArctostaphylos, yet species boundaries are retained in stands containing multiple species.Arctostaphyloscontains diploids and tetraploids, and recent phylogenies indicate two clades; we hypothesize combinations of these traits limit or promote hybridization rates.

    METHODS

    We statistically analyzed co‐occurrence patterns of species by clade membership and ploidy level from 87 random 0.1 ha plots. We sampled multiple sites to analyze for percent hybridization based on morphology. Finally, phenophases were analyzed by scoring herbarium sheets for a large number of taxa from both clades as well as tetraploids, and second, surveying three field sites over two years for divergence in phenological stages between co‐occurring taxa.

    RESULTS

    Most taxa inArctostaphylosare allopatric relative to other congenerics. When two taxa co‐occur, the patterns are a diploid with a tetraploid, or two diploids from different clades. When three taxa co‐occur, the pattern is two diploids from different clades and a tetraploid. Field and herbarium data both indicate flowering phenology is displaced between diploids from the two clades; one of the diploid clades and tetraploids overlap considerably.

    CONCLUSIONS

    The two deep clades inArctostaphylosare genetically distant, with hybrids rare or non‐existent when taxa co‐occur. Reproductive isolation between clades is enhanced by displaced flowering phenology for co‐occurring species. Within clades, taxa appear to have few reproductive barriers other than an allopatric distribution or different ploidy levels.

     
    more » « less