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Benham PM, Cicero C, Escalona M, Beraut E, Fairbairn C, Marimuthu MPA, Nguyen O, Sahasrabudhe R, King BL, Thomas WK, Kovach AI, Nachman MW, Bowie RCK. Remarkably High Repeat Content in the Genomes of Sparrows: The Importance of Genome Assembly Completeness for Transposable Element Discovery. Genome Biol Evol 2024; 16:evae067. [PMID: 38566597 PMCID: PMC11088854 DOI: 10.1093/gbe/evae067] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2023] [Revised: 03/01/2024] [Accepted: 03/23/2024] [Indexed: 04/04/2024] Open
Abstract
Transposable elements (TE) play critical roles in shaping genome evolution. Highly repetitive TE sequences are also a major source of assembly gaps making it difficult to fully understand the impact of these elements on host genomes. The increased capacity of long-read sequencing technologies to span highly repetitive regions promises to provide new insights into patterns of TE activity across diverse taxa. Here we report the generation of highly contiguous reference genomes using PacBio long-read and Omni-C technologies for three species of Passerellidae sparrow. We compared these assemblies to three chromosome-level sparrow assemblies and nine other sparrow assemblies generated using a variety of short- and long-read technologies. All long-read based assemblies were longer (range: 1.12 to 1.41 Gb) than short-read assemblies (0.91 to 1.08 Gb) and assembly length was strongly correlated with the amount of repeat content. Repeat content for Bell's sparrow (31.2% of genome) was the highest level ever reported within the order Passeriformes, which comprises over half of avian diversity. The highest levels of repeat content (79.2% to 93.7%) were found on the W chromosome relative to other regions of the genome. Finally, we show that proliferation of different TE classes varied even among species with similar levels of repeat content. These patterns support a dynamic model of TE expansion and contraction even in a clade where TEs were once thought to be fairly depauperate and static. Our work highlights how the resolution of difficult-to-assemble regions of the genome with new sequencing technologies promises to transform our understanding of avian genome evolution.
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Affiliation(s)
- Phred M Benham
- Museum of Vertebrate Zoology, University of California Berkeley, Berkeley, CA 94720, USA
- Department of Integrative Biology, University of California Berkeley, Berkeley, CA 94720, USA
| | - Carla Cicero
- Museum of Vertebrate Zoology, University of California Berkeley, Berkeley, CA 94720, USA
| | - Merly Escalona
- Department of Biomolecular Engineering, University of California Santa Cruz, Santa Cruz, CA 95064, USA
| | - Eric Beraut
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, CA 95064, USA
| | - Colin Fairbairn
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, CA 95064, USA
| | - Mohan P A Marimuthu
- DNA Technologies and Expression Analysis Core Laboratory, Genome Center, University of California-Davis, Davis, CA 95616, USA
| | - Oanh Nguyen
- DNA Technologies and Expression Analysis Core Laboratory, Genome Center, University of California-Davis, Davis, CA 95616, USA
| | - Ruta Sahasrabudhe
- DNA Technologies and Expression Analysis Core Laboratory, Genome Center, University of California-Davis, Davis, CA 95616, USA
| | - Benjamin L King
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, ME 04469, USA
| | - W Kelley Thomas
- Department of Molecular, Cellular and Biomedical Sciences, University of New Hampshire, Durham, NH 03824, USA
| | - Adrienne I Kovach
- Department of Natural Resources and the Environment, University of New Hampshire, Durham, NH 03824, USA
| | - Michael W Nachman
- Museum of Vertebrate Zoology, University of California Berkeley, Berkeley, CA 94720, USA
- Department of Integrative Biology, University of California Berkeley, Berkeley, CA 94720, USA
| | - Rauri C K Bowie
- Museum of Vertebrate Zoology, University of California Berkeley, Berkeley, CA 94720, USA
- Department of Integrative Biology, University of California Berkeley, Berkeley, CA 94720, USA
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Benham PM, Walsh J, Bowie RCK. Spatial variation in population genomic responses to over a century of anthropogenic change within a tidal marsh songbird. GLOBAL CHANGE BIOLOGY 2024; 30:e17126. [PMID: 38273486 DOI: 10.1111/gcb.17126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Revised: 11/22/2023] [Accepted: 12/13/2023] [Indexed: 01/27/2024]
Abstract
Combating the current biodiversity crisis requires the accurate documentation of population responses to human-induced ecological change. However, our ability to pinpoint population responses to human activities is often limited to the analysis of populations studied well after the fact. Museum collections preserve a record of population responses to anthropogenic change that can provide critical baseline data on patterns of genetic diversity, connectivity, and population structure prior to the onset of human perturbation. Here, we leverage a spatially replicated time series of specimens to document population genomic responses to the destruction of nearly 90% of coastal habitats occupied by the Savannah sparrow (Passerculus sandwichensis) in California. We sequenced 219 sparrows collected from 1889 to 2017 across the state of California using an exome capture approach. Spatial-temporal analyses of genetic diversity found that the amount of habitat lost was not predictive of genetic diversity loss. Sparrow populations from southern California historically exhibited lower levels of genetic diversity and experienced the most significant temporal declines in genetic diversity. Despite experiencing the greatest levels of habitat loss, we found that genetic diversity in the San Francisco Bay area remained relatively high. This was potentially related to an observed increase in gene flow into the Bay Area from other populations. While gene flow may have minimized genetic diversity declines, we also found that immigration from inland freshwater-adapted populations into tidal marsh populations led to the erosion of divergence at loci associated with tidal marsh adaptation. Shifting patterns of gene flow through time in response to habitat loss may thus contribute to negative fitness consequences and outbreeding depression. Together, our results underscore the importance of tracing the genomic trajectories of multiple populations over time to address issues of fundamental conservation concern.
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Affiliation(s)
- Phred M Benham
- Museum of Vertebrate Zoology, University of California, Berkeley, Berkeley, California, USA
- Department of Integrative Biology, University of California, Berkeley, Berkeley, California, USA
| | - Jennifer Walsh
- Fuller Evolutionary Biology Program, Cornell Lab of Ornithology, Cornell University, Ithaca, New York, USA
| | - Rauri C K Bowie
- Museum of Vertebrate Zoology, University of California, Berkeley, Berkeley, California, USA
- Department of Integrative Biology, University of California, Berkeley, Berkeley, California, USA
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Clark JD, Benham PM, Maldonado JE, Luther DA, Lim HC. Maintenance of local adaptation despite gene flow in a coastal songbird. Evolution 2022; 76:1481-1494. [PMID: 35700208 PMCID: PMC9545442 DOI: 10.1111/evo.14538] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Revised: 03/09/2022] [Accepted: 03/19/2022] [Indexed: 01/22/2023]
Abstract
Adaptation to local environments is common in widespread species and the basis of ecological speciation. The song sparrow (Melospiza melodia) is a widespread, polytypic passerine that occurs in shrubland habitats throughout North America. We examined the population structure of two parapatric subspecies that inhabit different environments: the Atlantic song sparrow (M. m. atlantica), a coastal specialist, and the eastern song sparrow (M. m. melodia), a shrubland generalist. These populations lacked clear mitochondrial population structure, yet coastal birds formed a distinct nuclear genetic cluster. We found weak overall genomic differentiation between these subspecies, suggesting either recent divergence, extensive gene flow, or a combination thereof. There was a steep genetic cline at the transition to coastal habitats, consistent with isolation by environment, not isolation by distance. A phenotype under divergent selection, bill size, varied with the amount of coastal ancestry in transitional areas, but larger bill size was maintained in coastal habitats regardless of ancestry, further supporting a role for selection in the maintenance of these subspecies. Demographic modeling suggested a divergence history of limited gene flow followed by secondary contact, which has emerged as a common theme in adaptive divergence across taxa.
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Affiliation(s)
- Jonathan D. Clark
- Department of Environmental Science and PolicyGeorge Mason UniversityFairfaxVirginia22030,Current Address: Department of Natural Resources and the EnvironmentUniversity of New HampshireDurhamNew Hampshire03824
| | - Phred M. Benham
- Museum of Vertebrate ZoologyUniversity of California, BerkeleyBerkeleyCalifornia94720
| | - Jesus E. Maldonado
- Department of Environmental Science and PolicyGeorge Mason UniversityFairfaxVirginia22030,Center for Conservation GenomicsSmithsonian Conservation Biology InstituteWashingtonD.C.20013
| | - David A. Luther
- Department of BiologyGeorge Mason UniversityFairfaxVirginia22030
| | - Haw Chuan Lim
- Center for Conservation GenomicsSmithsonian Conservation Biology InstituteWashingtonD.C.20013,Department of BiologyGeorge Mason UniversityFairfaxVirginia22030
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Benham PM, Bowie RCK. The influence of spatially heterogeneous anthropogenic change on bill size evolution in a coastal songbird. Evol Appl 2021; 14:607-624. [PMID: 33664798 PMCID: PMC7896719 DOI: 10.1111/eva.13144] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2020] [Revised: 09/27/2020] [Accepted: 09/28/2020] [Indexed: 12/25/2022] Open
Abstract
Natural history collections provide an unparalleled resource for documenting population responses to past anthropogenic change. However, in many cases, traits measured on specimens may vary temporally in response to a number of different anthropogenic pressures or demographic processes. While teasing apart these different drivers is challenging, approaches that integrate analyses of spatial and temporal series of specimens can provide a robust framework for examining whether traits exhibit common responses to ecological variation in space and time. We applied this approach to analyze bill morphology variation in California Savannah Sparrows (Passerculus sandwichensis). We found that bill surface area increased in birds from higher salinity tidal marshes that are hotter and drier. Only the coastal subspecies, alaudinus, exhibited a significant increase in bill size through time. As with patterns of spatial variation, alaudinus populations occupying higher salinity tidal marshes that have become warmer and drier over the past century exhibited the greatest increases in bill surface area. We also found a significant negative correlation between bill surface area and total evaporative water loss (TEWL) and estimated that observed increases in bill size could result in a reduction of up to 16.2% in daily water losses. Together, these patterns of spatial and temporal variation in bill size were consistent with the hypothesis that larger bills are favored in freshwater-limited environments as a mechanism of dissipating heat, reducing reliance on evaporative cooling, and increasing water conservation. With museum collections increasingly being leveraged to understand past responses to global change, this work highlights the importance of considering the influence of many different axes of anthropogenic change and of integrating spatial and temporal analyses to better understand the influence of specific human impacts on population change over time.
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Affiliation(s)
- Phred M. Benham
- Museum of Vertebrate ZoologyUniversity of CaliforniaBerkeley, BerkeleyCAUSA
| | - Rauri C. K. Bowie
- Museum of Vertebrate ZoologyUniversity of CaliforniaBerkeley, BerkeleyCAUSA
- Department of Integrative BiologyUniversity of CaliforniaBerkeley, BerkeleyCAUSA
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Mikles CS, Aguillon SM, Chan YL, Arcese P, Benham PM, Lovette IJ, Walsh J. Genomic differentiation and local adaptation on a microgeographic scale in a resident songbird. Mol Ecol 2020; 29:4295-4307. [PMID: 32978972 DOI: 10.1111/mec.15647] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2019] [Revised: 08/24/2020] [Accepted: 09/01/2020] [Indexed: 11/30/2022]
Abstract
Elucidating forces capable of driving species diversification in the face of gene flow remains a key goal in evolutionary biology. Song sparrows, Melospiza melodia, occur as 25 subspecies in diverse habitats across North America, are among the continent's most widespread vertebrate species, and are exemplary of many highly variable species for which the conservation of locally adapted populations may be critical to their range-wide persistence. We focus here on six morphologically distinct subspecies resident in the San Francisco Bay region, including three salt-marsh endemics and three residents in upland and riparian habitats adjacent to the Bay. We used reduced-representation sequencing to generate 2,773 SNPs to explore genetic differentiation, spatial population structure, and demographic history. Clustering separated individuals from each of the six subspecies, indicating subtle differentiation at microgeographic scales. Evidence of limited gene flow and low nucleotide diversity across all six subspecies further supports a hypothesis of isolation among locally adapted populations. We suggest that natural selection for genotypes adapted to salt marsh environments and changes in demography over the past century have acted in concert to drive the patterns of diversification reported here. Our results offer evidence of microgeographic specialization in a highly polytypic bird species long discussed as a model of sympatric speciation and rapid adaptation, and they support the hypothesis that conserving locally adapted populations may be critical to the range-wide persistence of similarly highly variable species.
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Affiliation(s)
- Chloe S Mikles
- Fuller Evolutionary Biology Program, Cornell Lab of Ornithology, Cornell University, Ithaca, NY, USA
| | - Stepfanie M Aguillon
- Fuller Evolutionary Biology Program, Cornell Lab of Ornithology, Cornell University, Ithaca, NY, USA.,Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, USA
| | | | - Peter Arcese
- Department of Forest and Conservation Sciences, University of British Columbia, Vancouver, BC, Canada
| | - Phred M Benham
- The Museum of Vertebrate Zoology, University of California, Berkeley, Berkeley, CA, USA
| | - Irby J Lovette
- Fuller Evolutionary Biology Program, Cornell Lab of Ornithology, Cornell University, Ithaca, NY, USA.,Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, USA
| | - Jennifer Walsh
- Fuller Evolutionary Biology Program, Cornell Lab of Ornithology, Cornell University, Ithaca, NY, USA.,Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, USA
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