Family Tree and Flower Evolution in the Tropical Connaraceae Family

Jim Crocker
4th August, 2024

Family Tree and Flower Evolution in the Tropical Connaraceae Family

Image Source: Natural Science News, 2024

Key Findings

  • The study, conducted by the University of Basel, used phylogenomic data to revise the classification of the Connaraceae plant family
  • Researchers identified two main clades within Connaraceae, leading to the creation of a new subfamily, Manotoideae, for the African genus Manotes
  • The study suggests that tristyly, a complex floral polymorphism, may have been the ancestral reproductive system in Connaraceae, highlighting the family's diverse and labile floral evolution
Understanding the evolutionary relationships and floral diversity in the Connaraceae family has long been limited by the lack of comprehensive molecular data. This pantropical family, consisting of about 200 species, showcases a remarkable array of floral polymorphisms, including distyly, tristyly, homostyly, and dioecy. The University of Basel's recent study[1] leverages phylogenomic data to revise the family's classification and explore the evolution of these complex reproductive systems. The study employed the Angiosperms353 nuclear target sequence capture probes[2], which target 353 nuclear genes, to construct a detailed molecular phylogenetic tree. This method, which has been instrumental in advancing our understanding of angiosperm phylogeny, used herbarium specimens to sample all tribes and nearly all genera of Connaraceae. The resulting phylogenetic tree is almost entirely resolved, providing a robust framework for understanding the evolutionary history of the family. The study revealed two main clades within Connaraceae. One clade consists solely of the African genus Manotes, which the researchers have elevated to the subfamily level, named Manotoideae. This reclassification is supported by both vegetative and reproductive synapomorphies—shared derived characteristics that are unique to this group. The second clade, Connaroideae, includes the expanded tribe Connareae, which now incorporates the former Jollydoreae. However, the backbone of Cnestideae, containing more than half of the Connaraceae species, remains partially unresolved. One of the most intriguing aspects of this study is its exploration of the evolution of heterostyly within Connaraceae. Heterostyly refers to the presence of different floral morphs within a species, which typically promotes cross-pollination and genetic diversity. Previous studies have shown that heterostyly can break down under certain ecological and demographic conditions, leading to selfing or other outcrossing systems[3]. The new phylogenetic data tentatively supports the hypothesis that tristyly—where three floral morphs exist—was the ancestral state for the family. This finding aligns with earlier hypotheses but also highlights the phylogenetic lability and diversity of stylar polymorphisms within the family. The study's findings are significant in several ways. First, they provide a more accurate and detailed classification of Connaraceae, which has been hampered by reliance on morphological data alone. Second, the research underscores the value of herbarium specimens in phylogenomic studies, demonstrating that even historical collections can yield valuable genetic data. Lastly, the study enhances our understanding of the evolution of complex reproductive systems, making Connaraceae a promising model for future research on floral polymorphisms. Incorporating previous research, the study builds on the understanding of heterostyly and its evolutionary implications. For example, the genetic basis of transitions from tristyly to selfing in Eichhornia paniculata has been explored through whole-genome sequencing and genetic mapping[4]. These transitions are governed by independent sets of mating-system modifier genes, a pattern that is also observed in Connaraceae's diverse floral systems. In summary, the University of Basel's study provides a comprehensive phylogenetic framework for Connaraceae, revises its classification, and offers new insights into the evolution of its reproductive systems. By integrating phylogenomic data with previous findings, the research opens new avenues for understanding the complex mechanisms driving floral diversity and evolution in this fascinating plant family.

GeneticsPlant ScienceEvolution

References

Main Study

1) Phylogenomics of the pantropical Connaraceae: revised infrafamilial classification and the evolution of heterostyly

Published 3rd August, 2024

https://doi.org/10.1007/s00606-024-01909-y

Related Studies

2) A Comprehensive Phylogenomic Platform for Exploring the Angiosperm Tree of Life.

https://doi.org/10.1093/sysbio/syab035

3) 'A most complex marriage arrangement': recent advances on heterostyly and unresolved questions.

https://doi.org/10.1111/nph.16026

4) The genetic architecture of tristyly and its breakdown to self-fertilization.

https://doi.org/10.1111/mec.13946


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