Potential inbreeding in a small population of a mass flowering species, Xanthorrhoea johnsonii (Xanthorrhoaceae): is your mother my father?

Xanthorrhoea johnsonii is a long lived slow growing perennial understorey species, that produces a large quantity of passively dispersed seed every 3-5 years. Reproductive maturity is not reached until 20-30 years of age. The temporal asynchrony of the flowering event in this population was analogous to geographic isolation through fragmentation. A small population of plants flowering in isolation provided the opportunity to examine outcrossing rates, genetic diversity and the paternity of progeny at a small spatial scale (0.2 ha). The geographic location and physical characteristics of the adult plants were recorded, and both adults and their seed were sampled for genetic analysis. Four microsatellite loci were screened for genetic diversity and spatial structure analysis. A population outcrossing rate was estimated, as well as the number of paternal parents required to resolve the progeny multilocus genotypes. High genetic diversity was found in both adults and progeny with an estimated 97% outcrossing rate. All maternal lines required several paternal contributors, with no evidence of dominant paternal genotypes. Pollen transfer occurred between both geographically close and distant plants

Phenotypic differentiation among native, expansive and introduced populations influences invasion success

Aim: Humans influence species distributions by modifying the environment and by dispersing species beyond their natural ranges. Populations of species that have established in disjunct regions of the world may exhibit trait differentiation from native populations due to founder effects and adaptations to selection pressures in each distributional region. We compared multiple native, expansive and introduced populations of a single species across the world, considering the influence of environmental stressors and transgenerational effects. Location: United States Gulf and Atlantic coasts, United States interior, European Atlantic and Mediterranean coasts, east coast of Australia. Taxon: Baccharis halimifolia L. (eastern baccharis). Methods: We monitored seed germination, seedling emergence, survival and early growth in a common garden experiment, conducted with over 18,200 seeds from 80 populations. We also evaluated the influence of environmental stress and maternal traits on progeny performance. Results: Introduced European Atlantic populations had faster germination and early growth than native populations. However, this was not the case for the more recently naturalized European Mediterranean populations. Introduced Australian populations grew faster than native populations in non-saline environments but had lower survival in saline conditions commonly encountered in the native range. Similarly, expansive inland US populations germinated faster than coastal native populations in non-saline environments but grew and germinated more slowly in saline environments. Maternal inflorescence and plant size were positively related with seed germination and seedling survival, whereas flower abundance was positively correlated with seedling early growth and survival. However, maternal traits explained a much lower fraction of the total variation in early demographic stages of B. halimifolia than did distributional range. Main conclusions: Phenotypic differentiation could allow B. halimifolia to adapt to different biotic and abiotic selection pressures found in each distributional range, potentially contributing to its success in introduced and expansive ranges

Outcrossing rates and reproductive success in xanthorrhoea johnsonii (xanthorrhoeaceae), in south east Queensland, Australia

Outcrossing rates and seed set were estimated at both the population and individual plant scale within four populations of Xanthorrhoea johnsonii. Sites differed with respect to habitat disturbance (time since fire), plant density, mean plant height, and mean inflorescence length. Allozyme data from progeny arrays of 24 seeds per plant from ten plants at each site were used to determine maternal outcrossing rates, which were found to be consistently high at all sites (>90%). Small but significant levels of inbreeding were recorded at three of the four sites. There was close agreement between tm and ts measures, which indicated that most inbreeding was a result of within plant selfing rather than biparental inbreeding. Outcrossing rates were estimated within top, middle, and bottom thirds of spikes on six plants at a fifth site. Significant differences from complete outcrossing were recorded in the middle and/or bottom sections of three plants. Total seed set per plant and seed set per flower varied significantly among the four sites. Xanthorrhoea johnsonii appears to be able to maintain relatively high outcrossing rates under different ecological conditions, although levels of both seed set per plant and seed set per flower are much more variable

Monarchs in decline: a collateral landscape level effect of modern agriculture

We review the postulated threatening processes that may have affected the decline in the eastern population of the monarch butterfly, Danaus plexippus L. (Lepidoptera: Nymphalidae), in North America. Although there are likely multiple contributing factors, such as climate and resource-related effects on breeding, migrating, and overwintering populations, the key landscape-level change appears to be associated with the widespread use of genetically modified herbicide resistant crops that have rapidly come to dominate the extensive core summer breeding range. We dismiss misinterpretations of the apparent lack of population change in summer adult count data as logically flawed. Glyphosate-tolerant soybean and maize have enabled the extensive use of this herbicide, generating widespread losses of milkweed (Asclepias spp.), the only host plants for monarch larvae. Modeling studies that simulate lifetime realized fecundity at a landscape scale, direct counts of milkweeds, and extensive citizen science data across the breeding range suggest that a herbicide-induced, landscape-level reduction in milkweed has precipitated the decline in monarchs. A recovery will likely require a monumental effort for the re-establishment of milkweed resources at a commensurate landscape scale

Plant reproductive phenology and floral resources of an Australian subtropical rainforest

Volume: 55Start Page: 463End Page: 47

Microsatellite records for volume 10, issue 2 (vol 10, pg 269, 2018)

The author group of the article is not displayed in the web/online version, though the information appeared in print version