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Rogers RL, Grizzard SL, Titus-McQuillan JE, Bockrath K, Patel S, Wares JP, Garner JT, Moore CC. Gene family amplification facilitates adaptation in freshwater unionid bivalve Megalonaias nervosa. Mol Ecol 2021; 30:1155-1173. [PMID: 33382161 DOI: 10.1111/mec.15786] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Revised: 12/01/2020] [Accepted: 12/14/2020] [Indexed: 01/05/2023]
Abstract
Freshwater unionid bivalves currently face severe anthropogenic challenges. Over 70% of species in the United States are threatened, endangered or extinct due to pollution, damming of waterways and overfishing. These species are notable for their unusual life history strategy, parasite-host co-evolution and biparental mitochondrial inheritance. Among this clade, the washboard mussel Megalonaias nervosa is one species that remains prevalent across the Southeastern United States, with robust population sizes. We have created a reference genome for M. nervosa to determine how genome content has evolved in the face of these widespread environmental challenges. We observe dynamic changes in genome content, with a burst of recent transposable element proliferation causing a 382 Mb expansion in genome content. Birth-death models suggest rapid expansions among gene families, with a mutation rate of 1.16 × 10-8 duplications per gene per generation. Cytochrome P450 gene families have experienced exceptional recent amplification beyond expectations based on genome-wide birth-death processes. These genes are associated with increased rates of amino acid changes, a signature of selection driving evolution of detox genes. Fitting evolutionary models of adaptation from standing genetic variation, we can compare adaptive potential across species and mutation types. The large population size in M. nervosa suggests a 4.7-fold advantage in the ability to adapt from standing genetic variation compared with a low diversity endemic E. hopetonensis. Estimates suggest that gene family evolution may offer an exceptional substrate of genetic variation in M. nervosa, with Psgv = 0.185 compared with Psgv = 0.067 for single nucleotide changes. Hence, we suggest that gene family evolution is a source of 'hopeful monsters' within the genome that may facilitate adaptation when selective pressures shift. These results suggest that gene family expansion is a key driver of adaptive evolution in this key species of freshwater Unionidae that is currently facing widespread environmental challenges. This work has clear implications for conservation genomics on freshwater bivalves as well as evolutionary theory. This genome represents a first step to facilitate reverse ecological genomics in Unionidae and identify the genetic underpinnings of phenotypic diversity.
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Affiliation(s)
- Rebekah L Rogers
- Department of Bioinformatics and Genomics, University of North Carolina, Charlotte, NC, USA
| | - Stephanie L Grizzard
- Department of Bioinformatics and Genomics, University of North Carolina, Charlotte, NC, USA.,Department of Biological Sciences, Old Dominion University, Norfolk, VA, USA
| | | | - Katherine Bockrath
- Department of Genetics, University of Georgia, Athens, GA, USA.,U.S. Fish and Wildlife Service, Midwest Fisheries Center Whitney Genetics Lab, Onalaska, WI, USA
| | - Sagar Patel
- Department of Bioinformatics and Genomics, University of North Carolina, Charlotte, NC, USA.,Department of Biology, Saint Louis University, St. Louis, MO, USA.,Donald Danforth Plant Science Center, St. Louis, MO, USA
| | - John P Wares
- Department of Genetics, University of Georgia, Athens, GA, USA.,Odum School of Ecology, University of Georgia, Athens, GA, USA
| | - Jeffrey T Garner
- Division of Wildlife and Freshwater Fisheries, Alabama Department of Conservation and Natural Resources, Florence, AL, USA
| | - Cathy C Moore
- Department of Bioinformatics and Genomics, University of North Carolina, Charlotte, NC, USA
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Perkins MA, Johnson NA, Gangloff MM. Molecular systematics of the critically-endangered North American spinymussels (Unionidae: Elliptio and Pleurobema) and description of Parvaspina gen. nov. CONSERV GENET 2017. [DOI: 10.1007/s10592-017-0924-z] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
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Hove MC, Sietman BE, Berg MS, Frost EC, Wolf K, Brady TR, Boyer SL, Hornbach DJ. Early life history of the sheepnose (Plethobasus cyphyus) (Mollusca: Bivalvia: Unionoida). J NAT HIST 2015. [DOI: 10.1080/00222933.2015.1083059] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Harriger KM, Knight JR, Wegener MG. Host-Fish Identifications for Two Gulf Coast-Drainage Freshwater Mussels, Lampsilis straminea(Southern Fatmucket) and Quadrula succissa(Purple Pigtoe). SOUTHEAST NAT 2015. [DOI: 10.1656/058.014.0204] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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