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Evolutionary Relationships and Biogeography of the Ant-Epiphytic Genus Squamellaria (Rubiaceae: Psychotrieae) and Their Taxonomic Implications.

Chomicki G, Renner SS - PLoS ONE (2016)

Bottom Line: Our field and phylogenetic work results in a new circumscription of the genus Squamellaria, which now contains 12 species (to which we also provide a taxonomic key), not 3 as in the last revision.Some of these ant-housing epiphytes must have dispersed with their specialized ants, for instance attached to floating timber.Others acquired new ant symbionts on different islands.

View Article: PubMed Central - PubMed

Affiliation: Systematic Botany and Mycology, University of Munich (LMU), Menzinger Str. 67, 80638, Munich, Germany.

ABSTRACT
Ecological research on ant/plant symbioses in Fiji, combined with molecular phylogenetics, has brought to light four new species of Squamellaria in the subtribe Hydnophytinae of the Rubiaceae tribe Psychotrieae and revealed that four other species, previously in Hydnophytum, need to be transferred to Squamellaria. The diagnoses of the new species are based on morphological and DNA traits, with further insights from microCT scanning of flowers and leaf δ(13)C ratios (associated with Crassulacean acid metabolism). Our field and phylogenetic work results in a new circumscription of the genus Squamellaria, which now contains 12 species (to which we also provide a taxonomic key), not 3 as in the last revision. A clock-dated phylogeny and a model-testing biogeographic framework were used to infer the broader geographic history of rubiaceous ant plants in the Pacific, specifically the successive expansion of Squamellaria to Vanuatu, the Solomon Islands, and Fiji. The colonization of Vanuatu may have occurred from Fiji, when these islands were still in the same insular arc, while the colonization of the Solomon islands may have occurred after the separation of this island from the Fiji/Vanuatu arc. Some of these ant-housing epiphytes must have dispersed with their specialized ants, for instance attached to floating timber. Others acquired new ant symbionts on different islands.

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Geographic distribution of the 12 Squamellaria species.
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pone.0151317.g006: Geographic distribution of the 12 Squamellaria species.

Mentions: (A-D)Squamellaria grayi. (A) Mature adult with flowers closed during the day. (B) Seedling. (C) Fruits. (D) CT scanning image of the functionally unisexual flowers of S. grayi lacking the squamellae at the inner base of the flower tube (see also Fig 4B, 4E and 4F). (E-H) Squamellaria huxleyana. (E) Habit of a mature adult. (F) Shoot with calyx nectaries visited by Philidris nagasau workers. Inset shows details of nectary and fruits (see also Fig 6E). (G) Habit of two young individuals growing adjacently. (H) Flowering shoot including one flower whose corolla has split and which is therefore secondarily zygomorphic. (I) CT-scanning optical cross-section of S. grayi bud, with reduplicate petal margins (see also Fig 4C). (J) CT-scanning optical cross-section of S. grayi fruit, with three carpels. (K) CT-scanning cross-section of S. huxleyana bud, showing the four carpels. (L) CT-scanning longitudinal 3D reconstruction of an S. huxleyana fruit showing the curved pyrenes. (M) CT-scanning longitudinal section of S. grayi fruit showing the straight pyrenes. (N-P) S. jebbiana. (N) Habit of a mature adult (fall on the ground). (M) Domatium cross-section. (O) Juvenile individual. Photographic credit: G. Chomicki except D, I-M: Y. Staedler. Scale bars: A: 10 cm; B: 1.5 cm; C-D: 1 cm; E: 20 cm; F: 2 cm; G: 7 cm; H: 2 cm; I,J: 1.5 mm; K: 3 mm; L-M: 2 mm; N: 20 cm; O: 6 cm; P: 2.5 cm.


Evolutionary Relationships and Biogeography of the Ant-Epiphytic Genus Squamellaria (Rubiaceae: Psychotrieae) and Their Taxonomic Implications.

Chomicki G, Renner SS - PLoS ONE (2016)

Geographic distribution of the 12 Squamellaria species.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4814088&req=5

pone.0151317.g006: Geographic distribution of the 12 Squamellaria species.
Mentions: (A-D)Squamellaria grayi. (A) Mature adult with flowers closed during the day. (B) Seedling. (C) Fruits. (D) CT scanning image of the functionally unisexual flowers of S. grayi lacking the squamellae at the inner base of the flower tube (see also Fig 4B, 4E and 4F). (E-H) Squamellaria huxleyana. (E) Habit of a mature adult. (F) Shoot with calyx nectaries visited by Philidris nagasau workers. Inset shows details of nectary and fruits (see also Fig 6E). (G) Habit of two young individuals growing adjacently. (H) Flowering shoot including one flower whose corolla has split and which is therefore secondarily zygomorphic. (I) CT-scanning optical cross-section of S. grayi bud, with reduplicate petal margins (see also Fig 4C). (J) CT-scanning optical cross-section of S. grayi fruit, with three carpels. (K) CT-scanning cross-section of S. huxleyana bud, showing the four carpels. (L) CT-scanning longitudinal 3D reconstruction of an S. huxleyana fruit showing the curved pyrenes. (M) CT-scanning longitudinal section of S. grayi fruit showing the straight pyrenes. (N-P) S. jebbiana. (N) Habit of a mature adult (fall on the ground). (M) Domatium cross-section. (O) Juvenile individual. Photographic credit: G. Chomicki except D, I-M: Y. Staedler. Scale bars: A: 10 cm; B: 1.5 cm; C-D: 1 cm; E: 20 cm; F: 2 cm; G: 7 cm; H: 2 cm; I,J: 1.5 mm; K: 3 mm; L-M: 2 mm; N: 20 cm; O: 6 cm; P: 2.5 cm.

Bottom Line: Our field and phylogenetic work results in a new circumscription of the genus Squamellaria, which now contains 12 species (to which we also provide a taxonomic key), not 3 as in the last revision.Some of these ant-housing epiphytes must have dispersed with their specialized ants, for instance attached to floating timber.Others acquired new ant symbionts on different islands.

View Article: PubMed Central - PubMed

Affiliation: Systematic Botany and Mycology, University of Munich (LMU), Menzinger Str. 67, 80638, Munich, Germany.

ABSTRACT
Ecological research on ant/plant symbioses in Fiji, combined with molecular phylogenetics, has brought to light four new species of Squamellaria in the subtribe Hydnophytinae of the Rubiaceae tribe Psychotrieae and revealed that four other species, previously in Hydnophytum, need to be transferred to Squamellaria. The diagnoses of the new species are based on morphological and DNA traits, with further insights from microCT scanning of flowers and leaf δ(13)C ratios (associated with Crassulacean acid metabolism). Our field and phylogenetic work results in a new circumscription of the genus Squamellaria, which now contains 12 species (to which we also provide a taxonomic key), not 3 as in the last revision. A clock-dated phylogeny and a model-testing biogeographic framework were used to infer the broader geographic history of rubiaceous ant plants in the Pacific, specifically the successive expansion of Squamellaria to Vanuatu, the Solomon Islands, and Fiji. The colonization of Vanuatu may have occurred from Fiji, when these islands were still in the same insular arc, while the colonization of the Solomon islands may have occurred after the separation of this island from the Fiji/Vanuatu arc. Some of these ant-housing epiphytes must have dispersed with their specialized ants, for instance attached to floating timber. Others acquired new ant symbionts on different islands.

Show MeSH
Related in: MedlinePlus