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ABSTRACT AimWe investigated the biogeographic consequences of chromosomal speciation, or structural changes in chromosome arrangement that lead to reproductive isolation, an intriguing speciation mechanism with implications for the phylogenetic and geographic distribution of species and chromosomal diversity. Location. North and Central America. Taxa. A species‐rich and chromosomally diverse clade of lizards in the genusSceloporuswhich are known to have coincident bursts of speciation and karyotype diversity, and coincident patterns of chromosomal change and branching order. Some workers have suggested that the tendency of communities ofSceloporuslizards to include species with different karyotypes is a signal of widespread chromosomal speciation, but given the high karyotypic diversity present inSceloporus, this may be due to chance rather than the effects of karyotypic speciation. MethodsWe gathered karyotypic, morphological, and biogeographic data on this chromosomally‐diverse clade in order to assess whether sympatry patterns ofSceloporusspecies are structured by karyotype. If karyotypic rearrangements contribute to the creation or maintenance of new species inSceloporus, then sympatric sister taxa should be more karyotypically diverged than allopatric sister taxa, and allopatric taxa should accumulate differences more gradually. We investigate whether species pairs with similar karyotypes are less likely to overlap geographically than expected by chance, and test whether karyotypic and geographic overlap between species pairs is related to divergence time. We pay special attention to cases of overlap between sister species. We also investigate whetherSceloporuscommunities are karyotypically overdispersed by comparing observed geographic distributions of karyotypic and phylogenetic diversity against phylogenetically‐informed modeled distributions. ResultsWe find little evidence for geographic signatures of chromosomal speciation and suggest that, while chromosomal speciation may have contributed historically to the spatial distributions ofSceloporusspecies, any geographic signature of this mode of speciation has been lost at long (> 10 Ma) temporal and broad (continental) spatial scales. Main ConclusionsThe spatial signature of chromosomal speciation is temporally restricted and the influences of other factors may have greater effects on species distributions over long time scales in this group.
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Chromosomal evolution, environmental heterogeneity, and migration drive spatial patterns of species richness in Calochortus (Liliaceae)
We used nuclear genomic data and statistical models to evaluate the ecological and evolutionary processes shaping spatial variation in species richness inCalochortus(Liliaceae, 74 spp.).Calochortusoccupies diverse habitats in the western United States and Mexico and has a center of diversity in the California Floristic Province, marked by multiple orogenies, winter rainfall, and highly divergent climates and substrates (including serpentine). We used sequences of 294 low-copy nuclear loci to produce a time-calibrated phylogeny, estimate historical biogeography, and test hypotheses regarding drivers of present-day spatial patterns in species number. Speciation and species coexistence require reproductive isolation and ecological divergence, so we examined the roles of chromosome number, environmental heterogeneity, and migration in shaping local species richness. Six major clades—inhabiting different geographic/climatic areas, and often marked by different base chromosome numbers (n = 6 to 10)—began diverging from each other ~10.3 Mya. As predicted, local species number increased significantly with local heterogeneity in chromosome number, elevation, soil characteristics, and serpentine presence. Species richness is greatest in the Transverse/Peninsular Ranges where clades with different chromosome numbers overlap, topographic complexity provides diverse conditions over short distances, and several physiographic provinces meet allowing immigration by several clades. Recently diverged sister-species pairs generally have peri-patric distributions, and maximum geographic overlap between species increases over the first million years since divergence, suggesting that chromosomal evolution, genetic divergence leading to gametic isolation or hybrid inviability/sterility, and/or ecological divergence over small spatial scales may permit species co-occurrence.
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- PAR ID:
- 10516261
- Editor(s):
- Schemske, D
- Publisher / Repository:
- Proceedings of the National Academy of Sciences, USA
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Edition / Version:
- 1
- Volume:
- 121
- Issue:
- 10
- ISSN:
- 0027-8424
- Page Range / eLocation ID:
- e2305228121
- Subject(s) / Keyword(s):
- California Floristic Province diversification environmental heterogeneity historical biogeography phylogenomics
- Format(s):
- Medium: X Size: 3.6MB Other: pdf/a
- Size(s):
- 3.6MB
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1073/pnas.2305228121
