Elite Award: Distinction

The dual roles of niche conservatism in the speciation of tree lizards

Tzong-Han Lin
National Taiwan Normal University
Co-author: Zong-Yu Shen, Ming-Hsun Chou, Pei-Wei Sun, Chin-Chia Shen

Abstract

Taiwan’s complex topography and climatic history have generated high endemic biodiversity. Allopatric speciation is considered a major driver of diversification in montane organisms, while niche conservatism may reinforce divergence by limiting population contact. Using endemic Taiwanese tree lizards of the genus Diploderma, we integrated geographic isolation, climatic niches, and historical gene flow to reconstruct their speciation history. Genome-wide ddRAD-seq data identified seven genetically distinct lineages, suggesting underestimated diversity. Most sister lineages showed strong climatic niche overlap, supporting niche conservatism during early divergence. However, demographic analyses also revealed historical introgression, likely linked to climate-driven population expansion and secondary contact. Niche conservatism may therefore both promote initial isolation and later facilitate renewed contact and gene flow. This study advances understanding of speciation in Taiwan and supports cryptic species recognition, taxonomic revision, and conservation planning.

Keywords:
allopatric speciation, Diploderma, introgression, niche conservatism

Methodology and Implementation Steps

Overall workflobrw:
Sample collection 🡪 Phylogenetic analyses 🡪 Species delimitation 🡪 Gene flow evaluation 🡪 Niche analysis

Results

  1. We obtained 15,932 SNPs from 198 individuals through ddRAD-sequencing. The phylogenetic analysis indicated monophyletic lineage for described five species, while the results of population structure analyses concordantly exhibited seven lineages. Additional clusters were found in D. brevipes and D. polygonatum.
  2. Presence of ancestral gene flow was found between northern D. brevipes and western D. polygonatum. The ancestral and bidirectional introgression was occurred 1.33 million years ago.
  3. Our findings showed that niche conservatism was detected in most lineages underwent differentiation, and intriguingly, in closely distributed lineages with introgression signal (northern D. brevipes and western D. polygonatum).

Innovation and Cross-Disciplinary Collaboration

  1. 首次運用次世代定序資料進行攀蜥屬(Diploderma)的遺傳研究。
  2. 相較於過去僅依賴形態特徵或少量遺傳標記的研究，提供更高解析度的物種界定證據。
  3. 證實棲位保守性可能同時促進地理分化，並促成次級接觸與基因流。
  4. 揭示臺灣攀木蜥蜴存在隱蔽物種多樣性。
  5. 建立可應用於攀木蜥蜴及其他島嶼與山區類群的研究框架。

Expected Results and Contributions

  1. 提供評估保育單元與優先保育族群所需的重要遺傳資料。與短肢攀蜥(D. brevipes)相關的研究成果曾發表於 2023 年臺灣國家公園論文競賽。
  2. 揭示多稜攀蜥(D. polygonatum)與短肢攀蜥(D. brevipes)內部存在顯著遺傳分化及潛在隱蔽物種。
  3. 本研究結果可為分類修訂、保育等級評估及國家公園經營管理提供科學依據。
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