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Data from: Climatic niche differences between diploid and tetraploid cytotypes of Chamerion angustifolium (Onagraceae)
Thompson, Ken A.; Husband, Brian C.; Maherali, Hafiz — 2015-09-23 Premise of the study: Polyploidy—the possession of more than two copies of each chromosome in the nucleus—is common in flowering plants. Polyploid plants can occupy different geographic ranges than their diploid progenitors, but the factors responsible for maintaining these range differences are poorly understood. Polyploidy can have significant physiological consequences, and the present study aims to determine whether previously described physiological differences between cytotypes are correlated with climatic niches and geographic distributions. Methods: Prior research indicates that tetraploid Chamerion angustifolium (Onagraceae) are more tolerant of drought and less tolerant of freezing than diploids, which suggests that they should occupy a niche that is warmer and drier than that of diploids. We extracted climate data for 134 C. angustifolium populations classified as pure diploid, pure tetraploid, or mixed-ploidy. We compared climatic conditions between these population categories, and generated ecological niche models to compare their geographic distribution with prior qualitative estimates. Key results: Pure tetraploid populations occupy habitats that are warmer and drier than pure diploid populations. Mixed-ploidy populations occur in habitats that are not strictly intermediate between pure diploid and pure tetraploid populations, but are as cold as pure diploid populations and have intermediate soil moisture deficits. Our niche models were similar to previous qualitative estimates of cytotype geographic distribution. Conclusions: The correspondence between the physiological tolerances of cytotypes, their climatic niches, and their geographic distributions suggests that physiological traits are at least partially responsible for differences in the realized climatic niches of diploid and tetraploid C. angustifolium. https://creativecommons.org/publicdomain/zero/1.0/
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Data from: No influence of water limitation on the outcome of competition between diploid and tetraploid Chamerion angustifolium (Onagraceae)
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Thompson, Kenneth A.; Husband, Brian C.; Maherali, Hafiz; Thompson, Ken A. — 2016-02-09 1. Polyploid plants often occupy different geographic ranges than their diploid progenitors, but the causes of this segregation are poorly understood. Differential competitive abilities of cytotypes across an environmental gradient could be responsible for these observed geographic range differences. 2. Cytotypes of Chamerion angustifolium (Onagraceae) are mostly allopatric, and prior research indicates that tetraploids are more physiologically tolerant of water limitation and occupy drier habitats than diploids. We hypothesized that tetraploids are stronger competitors than diploids in soils where water is limited, which allows them to persist in dry habitats while diploids cannot. 3. We grew both cytotypes together in competition under water-limited and well-watered conditions. We varied both total plant density and the relative frequency of cytotypes among pots, which allowed us to separate the effects of intra-cytotypic and inter-cytotypic competition. 4. Both diploid and tetraploid plants were smaller in the water-limited treatment than in the well-watered treatment. Nevertheless, there were no differences in the relative strength of intra-cytotypic and inter-cytotypic competition experienced by either cytotype across the watering treatments, indicating that diploids and tetraploids had equal competitive abilities in both treatments. 5. Synthesis. Competition for limiting resources is often proposed as a mechanism causing ecological and geographic segregation between diploid and polyploid cytotypes. Our results do not support the hypothesis that tetraploid Chamerion angustifolium plants are stronger competitors than diploids when water is limited. A differential ability to compete for water is likely not responsible for the observed ecological and geographic segregation between cytotypes in this species. Competition may not be a general mechanism that causes segregation between diploid and polyploid cytotypes in nature.
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Data from: Adaptation of diploid and tetraploid Chamerion angustifolium to elevation but not local environment
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Martin, Sara Lauretta; Husband, Brian C. — 2013-01-17 Polyploid organisms often have different geographic ranges than their diploid relatives. However, it is unclear whether this divergence is maintained by adaptation or results from historical differences in colonization. Here we conducted a reciprocal transplant experiment with diploid and autotetraploid Chamerion angustifolium to test for adaptation at the ploidy and population level. In the Rocky Mountains, pure diploid populations occur at high elevations and pure autotetraploid populations occur at low elevations with mixed-ploidy populations between. We planted 3134 seedlings in 2004 and 3890 juveniles (bolting) in 2005 among nine plots, three in each of the diploid, mixed-ploidy and tetraploid zones, and monitored survival until 2008. For both seedlings and juvenile plants, elevation significantly influenced survival. The juvenile plants also showed a significant ploidy by elevation interaction, indicating that diploids and tetraploids survived best at their native elevations. In contrast, we found no evidence of local adaptation to plot within elevation. This suggests that the current distribution of diploids and tetraploids across elevations is the result of adaptation and that genome duplication may have facilitated the invasion of lower elevation habitats by limiting the movement of maladapted alleles from diploid populations at higher elevations.
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Data from: Genetic and environmental determinants of unreduced gamete production in Brassica napus, Sinapis arvensis and their hybrids
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Sora, Dylan; Kron, Paul; Husband, Brian C. — 2016-07-19 Unreduced gametes, sperm or egg cells with the somatic chromosome number, are an important mechanism of polyploid formation and gene flow between heteroploid plants. The meiotic processes leading to unreduced gamete formation are well documented, but the relative influence of environmental and genetic factors on the frequency of unreduced gametes remain largely untested. Furthermore, direct estimates of unreduced gametes based on DNA content are technically challenging and hence, uncommon. Here, we use flow cytometry to measure the contribution of genetic (hybridization) and environmental (nutrient limitation, wounding) changes to unreduced male gamete production in Brassica napus, Sinapis arvensis, and two hybrid lines. Treatments were applied to greenhouse grown plants in a random factorial design, with pollen sampled at two time intervals. Overall the frequency of unreduced gametes averaged 0.59% (range 0.06%-2.17%), plus a single outlier with 27%. Backcrossed hybrids had 39% to 75% higher unreduced gamete production than parental genotypes, averaged across all treatments, although the statistical significance of these differences depended on sampling period and wounding treatment. Unreduced gamete frequencies were higher for the second sampling period than the first. There were no direct effects of wounding or nutrient regime. Our results indicate that both genetic and environmental factors can induce increased unreduced gametes, highlighting the potential importance of environmental heterogeneity and genetic composition of populations in driving polyploid evolution
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Data from: Reproductive system of a mixed-mating plant responds to climate perturbation by increased selfing
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Jones, Natalie T.; Husband, Brian C.; MacDougall, Andrew S. — 2013-07-10 How plants respond to climatic perturbations, which are forecasted to increase in frequency and intensity, is difficult to predict because of the buffering effects of plasticity. Compensatory adjustments may maintain fecundity and recruitment, or delay negative changes that are inevitable but not immediately evident. We imposed a climate perturbation of warming and drought on a mixed-mating perennial violet, testing for adjustments in growth, reproduction and mortality. We observed several plasticity-based buffering responses, such that the climatic perturbation did not alter population structure. The most substantial reproductive adjustments, however, involved selfing, with a 45% increase in self-pollination by chasmogamous flowers, a 61% increase in the number of cleistogamous flowers that produced at least one fruit and an overall 15% increase in fruit production from selfed cleistogamous flowers. Reproductive assurance thus compensated for environmental change, including low pollinator visitation that occurred independently of our climate treatment. There was also no immediate evidence for inbreeding depression. Our work indicates that plants with vegetative and reproductive flexibility may not be immediately and negatively affected by a climatic perturbation. The stabilizing effects of these reproductive responses in the long term, however, may depend on the implications of significantly elevated levels of selfing.
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Data from: Understanding the spectacular failure of DNA barcoding in willows (Salix): Does this result from a trans-specific selective sweep?
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Percy, Diana M.; Argus, George W.; Cronk, Quentin C.; Fazekas, Aron J.; Kesanakurti, Prasad R.; Burgess, Kevin S.; Husband, Brian C.; Newmaster, Steven G.; Barrett, Spencer C. H.; Graham, Sean W.; Barrett, Spencer C.H. — 2014-06-17 Willows (Salix: Salicaceae) form a major ecological component of Holarctic floras, and consequently are an obvious target for a DNA-based identification system. We surveyed two to seven plastid genome regions (~3.8 kb; ~3% of the genome) from 71 Salix species across all five subgenera, to assess their performance as DNA barcode markers. Although Salix has a relatively high level of interspecific hybridization, this may not sufficiently explain the near complete failure of barcoding that we observed: only one species had a unique barcode. We recovered 39 unique haplotypes, from more than 500 specimens, that could be partitioned into six major haplotype groups. A unique variant of group I (haplotype 1*) was shared by 53 species in three of five Salix subgenera. This unusual pattern of haplotype sharing across infrageneric taxa is suggestive of either a massive non-random coalescence failure (incomplete lineage sorting), or of repeated plastid capture events, possibly including a historical selective sweep of haplotype 1* across taxonomic sections. The former is unlikely as molecular dating indicates that haplotype 1* originated recently, and is nested in the oldest major haplotype group in the genus. Further, we detected significant non-neutrality in the frequency spectrum of mutations in group I, but not outside group I, and demonstrated a striking absence of geographic structure to the haplotype distributions in this group. The most likely explanation for the patterns we observed involves recent repeated plastid capture events, aided by widespread hybridization and long-range seed dispersal, but primarily propelled by one or more trans-species selective sweeps.

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(auteur : Husband, Brian C.)

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