Collinsia sparsiflora in serpentine and nonserpentine habitats: using F2 hybrids to detect the potential role of selection in ecotypic differentiation

Our plain-English summary of Collinsia sparsiflora in serpentine and nonserpentine habitats: using F2 hybrids to detect the potential role of selection in ecotypic differentiation, by J.W. Wright, M.L. Stanton (The New Phytologist, 2007).

The study

• Authors: J.W. Wright, M.L. Stanton
• Journal: The New Phytologist
• Published: 2007;173(2):354-66
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Here we document phenotypic differences between serpentine and nonserpentine ecotypes of Collinsia sparsiflora, as well as patterns of selection in these contrasting soil habitats. We transplanted the two parental ecotypes and experimental F2 hybrids into six field sites, and collected morphological, phenological and fitness data on emergent plants. To focus on edaphically mediated selection, rather than on pollinator-mediated selection, we used pollinator-exclusion cages. Transplanted parentals of the two ecotypes showed genetic differentiation for floral traits, but not for phenological traits or cotyledon size. For the F2 hybrids growing on serpentine soils, there was significant directional selection on cotyledon size, flower size and flower shape. However, the pattern of selection did not differ significantly between serpentine and nonserpentine sites. Overall, we did not see evidence for divergent selection on the two soil types. We conclude that differences in floral traits between the ecotypes do not reflect adaptation to physical conditions associated with soil type, and that there are unmeasured traits that must be contributing to ecotypic differentiation.

In plain English

This field experiment studied the wildflower Collinsia sparsiflora on serpentine and nonserpentine soils at six California sites. The article does not discuss asbestos. In August 2002 the authors planted seeds of both locally adapted plant types (ecotypes) and of second-generation (F2) hybrids into all six sites; cages excluding pollinators were added once plants began forming flower buds. The two parental types did not differ significantly in emergence date, flowering date or seed-leaf (cotyledon) size, but the serpentine type had larger, darker flowers. Among F2 hybrids on serpentine soils, larger seed leaves, larger flowers, and narrower-petaled, longer-calyx flowers were linked to more fruit. Selection mostly pointed the same way on both soils; of 20 life-stage selection measures, only two differed significantly between soils and were opposite in sign, for emergence date and flower shape. On nonserpentine sites 61.8% of F2 seedlings survived to flower, compared with 86.9% on serpentine sites. The authors concluded that at least one, and probably several, unmeasured traits are relevant to maintaining the ecotype differences. They noted that the cages likely altered insect-driven selection on flowers.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Field transplant experiment: reciprocal transplant of parental ecotypes plus selection analysis on experimental F2 hybrids, with pollinator-exclusion cages added at flower-bud stage
• Who was studied: Plants of Collinsia sparsiflora, a native California winter annual, from six populations (three serpentine, three nonserpentine) at the University of California's McLaughlin Natural Reserve. Seeds were collected in 2000 and planted in the field in August 2002. F2 seed came from 27 of 32 hybrid crosses.
• Exposure: Soil habitat: serpentine soils (average calcium:magnesium ratio 0.3) versus nonserpentine soils (average 4.3). No asbestos or fiber exposure was studied.
• Main results:
  • Parental ecotypes showed no significant differences in emergence date, flowering date or cotyledon size. Four of five floral traits differed significantly between ecotypes, and the serpentine ecotype had larger, darker flowers.
  • For F2 hybrids in serpentine habitats (n = 389), there were significant positive selection gradients for larger cotyledons (0.1092, P = 0.0078), larger flowers (PC1, 0.1670, P less than 0.0001), and flowers with narrower petals and longer calyces (PC2, 0.1347, P = 0.0008).
  • Directional selection on the traits differed more in size than in direction between the two soil types, giving no indication of diversifying selection.
  • Of 20 selection differentials calculated for the four fitness components, two were significantly different between soil types and opposite in sign: emergence date (affecting survival to flowering) and flower shape (affecting fruit set).
  • Net selection for early flowering in F2 hybrids was significantly greater in nonserpentine habitats (selection intensity -0.4450) than in serpentine habitats (-0.1647), but was significant in both.
  • 61.8% of F2 seedlings on nonserpentine sites survived to flower, compared with 86.9% on serpentine sites.
  • Among F2 plants that flowered, fruit set had the greatest impact on variation in lifetime fruit production: partial R2 of 44.7% on nonserpentine soils and 39.9% on serpentine soils.
• The authors' conclusion: The authors concluded that the measured traits showed no compelling evidence of differential selection between soil types. They said this implies that at least one, and probably several, unmeasured traits are relevant to maintaining the differences between serpentine and nonserpentine ecotypes.
• Limitations the authors state:
  • The pollinator-exclusion cages are likely to have altered insect-mediated selection on floral traits.
  • High seedling mortality reduced statistical power to detect selection gradients when juvenile and adult traits were analyzed together.
  • Because of high seed dormancy, replication within families was insufficient to analyze genetic selection gradients.
  • The selection gradient analysis assumes that all relevant traits were measured, and the authors said this assumption was, in all likelihood, not met.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Serpentine Group.

Related studies

• Serpentine and non-serpentine ecotypes of Collinsia sparsiflora associate with distinct arbuscular mycorrhizal fungal assemblages — S.P. Schechter, T.D. Bruns (2008)
• Simultaneous evaluation of the effects of geographic, environmental and temporal isolation in ecotypic populations of Solidago virgaurea — S. Sakaguchi, K. Horie, et al. (2017)
• Bringing together evolution on serpentine and polyploidy: spatiotemporal history of the diploid-tetraploid complex of Knautia arvensis (Dipsacaceae) — F. Kolář, T. Fér, et al. (2012)
• Serpentine soils affect heavy metal tolerance but not genetic diversity in a common Mediterranean ant — F. Frizzi, A. Masoni, et al. (2017)
• Genetic analyses of nickel tolerance in a North American serpentine endemic plant, Caulanthus amplexicaulis var. barbarae (Brassicaceae) — A.M. Burrell, A.K. Hawkins, et al. (2012)
• Population resequencing reveals local adaptation of Arabidopsis lyrata to serpentine soils — T.L. Turner, E.C. Bourne, et al. (2010)

Browse return to medical research.