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論文

論文

Speciation, the process by which new species arise, is associated not only with the accumulation of molecular changes in DNA composition but often also with physical rearrangements in chromosome structure. Chromosome inversions, one common type of chromosomal rearrangement that occurs when a chromosome breaks at two points and the area between those breakpoints is repaired in the opposite orientation, are regularly observed as fixed differences between species and as polymorphisms segregating within species. Inversions were first discovered by Alfred Sturtevant in 1921 and have since been found to propel the evolution of sex chromosomes, supergene formation, local adaptation, and reproductive isolation. Despite their evolutionary significance, the widespread presence of inversions is in some ways puzzling, as new rearrangements may be initially disfavored due to structural underdominance in heterokaryotypes, if crossing over within the inverted region during meiosis results in the production of aneuploid gametes. Reconciling the widespread presence of chromosome inversions with possible selective disadvantages that a new inversion faces remains an unsolved problem and largely motivated this dissertation. Birds have long been used as models of speciation and are perhaps the best-studied group with respect to how behavior and ecology contribute to population divergence but little attention has been given to the role of chromosome rearrangements to bird speciation. Indeed, the gross physical structure of the avian genome is highly conserved with the most easily observed types of macro-rearrangements (fusions, fissions, translocations, etc.), which so often distinguish the karyotypes of species in other taxonomic groups, are relatively rare in birds. As such, karyotype evolution has generally been considered to be an unrelated and unimportant aspect of avian diversification. Chromosome inversions, however, appear to occur regularly in birds. Comparative cytological investigations of avian karyotypes regularly detect chromosome inversion differences between and within species based on rearrangement to chromosome banding patterns and/or centromere movement. Recent comparative genomic analyses of both distantly and closely related avian taxa support the findings of earlier cytological studies in detecting large numbers of inversions differences both pericentric, inversions that include the centromere, and paracentric, inversions that do not include the centromere, in nature. Here, I have made efforts in the course of this dissertation in order to better understand the evolutionary dynamics underlying chromosome inversion evolution in birds through i) a synthesis of classic cytological data placed in a phylogenetic context in order to evaluate support for alternative theoretical models of inversion evolution (Chapters 1 and 2) and ii) a genomic assessment of an avian hybrid zone where inversion polymorphism on the Z chromosome may underlie the maintenance of reproductive isolation between hybridizing taxa (Chapter 3).

Sample collection sites across the sky islands of the Western Ghats. Figure S2. Ancestral area analysis using Lagrange for Montecincla. Area codes for terminal taxa are A-Africa, B-peninsular India, C-Himalayas, D-Southeast Asia, E-China, F-Sundaland, G-Philippines, and H-Assam. The most likely ancestral range reconstruction for relevant nodes (in red) are shown. Figure S3. Ancestral area analysis using Lagrange for Sholicola. Area codes for terminal taxa are I-Peninsular India, H-Himalayas, A-Southeast Asia, D-Eurasia, E-Australasia F- Africaâ +â Southwest Asia, C-China, S-Sundaland, P-Philippines, E-Eurasia, and N-Australasia/New World. The most likely ancestral range reconstruction for relevant nodes (in red) are shown with their relative probabilities. Figure S4. Map showing the species distributions of Montecincla chilappans and Sholicola sholakillis. Figure S5. Photographs of Sholicola ashambuensis sp. nov. a) holotype in the Trivandrum Museum of Natural History; b) in comparison with other members of Sholicola: S. ashambuensis (right), with larger white belly contrasted with S. albiventris (middle), S. major (left). Figure S6. a) Discriminant Function Analysis of morphometric differences between Sholicola ashambuensis and S. albiventris based on 97 individuals shows 79.4% accurate classification and significant differences in the means (non overlapping 95% confidence interval circles); b) Box plots showing morphometric differences in bill and tarsus lengths in Sholicola ashambuensis and S. albiventris. Figure S7. Discriminant Function Analysis of Sholicola ashambuensis and S. albiventris songs based on 217 song recordings shows 80% accurate classification and significant differences in the means (non overlapping 95% confidence interval circles). Table S1: Samples used to reconstruct Montecincla phylogeny. Table S2: Samples used to reconstruct Sholicola phylogeny. Table S3: Morphometric variation in Montecincla species. Table S4: Morphometric variation in Sholicola species. Table S5: Song variation in Montecincla species in the Western Ghats Sky Islands. Table S6: Song variation in Sholicola species in the Western Ghats Sky Islands. Table S7: Comparison of morphometric measurements of Sholicola ashambuensis and S. albiventris. (PDF 3728 kb)

Sample collection sites across the sky islands of the Western Ghats. Figure S2. Ancestral area analysis using Lagrange for Montecincla. Area codes for terminal taxa are A-Africa, B-peninsular India, C-Himalayas, D-Southeast Asia, E-China, F-Sundaland, G-Philippines, and H-Assam. The most likely ancestral range reconstruction for relevant nodes (in red) are shown. Figure S3. Ancestral area analysis using Lagrange for Sholicola. Area codes for terminal taxa are I-Peninsular India, H-Himalayas, A-Southeast Asia, D-Eurasia, E-Australasia F- Africaâ +â Southwest Asia, C-China, S-Sundaland, P-Philippines, E-Eurasia, and N-Australasia/New World. The most likely ancestral range reconstruction for relevant nodes (in red) are shown with their relative probabilities. Figure S4. Map showing the species distributions of Montecincla chilappans and Sholicola sholakillis. Figure S5. Photographs of Sholicola ashambuensis sp. nov. a) holotype in the Trivandrum Museum of Natural History; b) in comparison with other members of Sholicola: S. ashambuensis (right), with larger white belly contrasted with S. albiventris (middle), S. major (left). Figure S6. a) Discriminant Function Analysis of morphometric differences between Sholicola ashambuensis and S. albiventris based on 97 individuals shows 79.4% accurate classification and significant differences in the means (non overlapping 95% confidence interval circles); b) Box plots showing morphometric differences in bill and tarsus lengths in Sholicola ashambuensis and S. albiventris. Figure S7. Discriminant Function Analysis of Sholicola ashambuensis and S. albiventris songs based on 217 song recordings shows 80% accurate classification and significant differences in the means (non overlapping 95% confidence interval circles). Table S1: Samples used to reconstruct Montecincla phylogeny. Table S2: Samples used to reconstruct Sholicola phylogeny. Table S3: Morphometric variation in Montecincla species. Table S4: Morphometric variation in Sholicola species. Table S5: Song variation in Montecincla species in the Western Ghats Sky Islands. Table S6: Song variation in Sholicola species in the Western Ghats Sky Islands. Table S7: Comparison of morphometric measurements of Sholicola ashambuensis and S. albiventris. (PDF 3728 kb)

2023

The Long-tailed Finch (Poephila acuticauda) is endemic to Australia’s northern tropics and comprises two sub-species differentiated by bill colour: yellow in the western sub-species acuticauda and red in the eastern sub-species hecki. We present an extensive survey of bill colour variation across the range of the Long-tailed Finch (more than 700 individuals collected across nearly 1500 km of range). Geographic clinal analysis using bill reflectance spectrophotometry data suggests that the greatest extent of bill colour admixture is only ~150 km wide and is centred approximately 50 km west of Katherine, Northern Territory (14.5° S, 132.3° E). Variation in bill colour is generally low outside of this zone, and across widely distributed allopatric populations of both sub-species. However, the best-fit clinal model supports a pattern of asymmetrical introgression of bill colour from the east into the west. The narrow geographic width of bill colour admixture between Long-tailed Finch sub-species and the estimated timing of secondary contact (14–21 kya) suggests a role for selection acting against hybrids and/or parentals in maintaining sub-species as independently evolving populations.

The Long-tailed Finch (Poephila acuticauda) is endemic to Australia’s northern tropics and comprises two sub-species differentiated by bill colour: yellow in the western sub-species acuticauda and red in the eastern sub-species hecki. We present an extensive survey of bill colour variation across the range of the Long-tailed Finch (more than 700 individuals collected across nearly 1500 km of range). Geographic clinal analysis using bill reflectance spectrophotometry data suggests that the greatest extent of bill colour admixture is only ~150 km wide and is centred approximately 50 km west of Katherine, Northern Territory (14.5° S, 132.3° E). Variation in bill colour is generally low outside of this zone, and across widely distributed allopatric populations of both sub-species. However, the best-fit clinal model supports a pattern of asymmetrical introgression of bill colour from the east into the west. The narrow geographic width of bill colour admixture between Long-tailed Finch sub-species and the estimated timing of secondary contact (14–21 kya) suggests a role for selection acting against hybrids and/or parentals in maintaining sub-species as independently evolving populations.

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