Population genetics of the invasive ascidian Botryllus schlosseri from South American coasts

Ben‐Shlomo, Rachel; Reem, Eitan; Douek, Jacob; Rinkevich, Baruch

doi:10.3354/meps08688

Cited by 35 publications

(32 citation statements)

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“…The population differentiation at the housekeeping loci confirms the significant genetic structure seen at microsatellite loci (Ben‐Shlomo et al 2010; Bock et al 2012). These results are in sharp contrast to the lack of significant population differentiation at FuHC.…”

Section: Discussionsupporting

confidence: 62%

Evidence for Selection on a Chordate Histocompatibility Locus

2012

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Allorecognition is the ability of an organism to differentiate self or close relatives from unrelated individuals. The best-known applications of allorecognition are the self-incompatibility (SI) systems in plants, vertebrate immune response to foreign antigens mediated by MHC loci, and fusion, where two genetically independent individuals physically join to become a single individual. Fusion occurs in a wide diversity of organisms (Buss 1982), including anemones (Mercier et al.

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Section: Discussionsupporting

confidence: 62%

Evidence for Selection on a Chordate Histocompatibility Locus

2012

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“…The population differentiation at the housekeeping loci confirms the significant genetic structure seen for neutral markers (microsatellites) in B. schlosseri [33,34]. These results are in sharp contrast to the lack of significant population differentiation at fester and FuHC.…”

Section: Discussionsupporting

confidence: 63%

The fester locus in Botryllus schlosseri experiences selection

Nydam

Tomaso

2012

BMC Evol Biol

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BackgroundAllorecognition, the ability of an organism to distinguish self from non-self, occurs throughout the entire tree of life. Despite the prevalence and importance of allorecognition systems, the genetic basis of allorecognition has rarely been characterized outside the well-known MHC (Major Histocompatibility Complex) in vertebrates and SI (Self-Incompatibility) in plants. Where loci have been identified, their evolutionary history is an open question. We have previously identified the genes involved in self/non-self recognition in the colonial ascidian Botryllus schlosseri, and we can now begin to investigate their evolution. In B. schlosseri, colonies sharing 1 or more alleles of a gene called FuHC (Fusion Histocompatibility) will fuse. Protein products of a locus called fester, located ~300 kb from FuHC, have been shown to play multiple roles in the histocompatibility reaction, as activating and/or inhibitory receptors. We test whether the proteins encoded by this locus are evolving neutrally or are experiencing balancing, directional, or purifying selection.ResultsNearly all of the variation in the fester locus resides within populations. The 13 housekeeping genes (12 nuclear genes and mitochondrial cytochrome oxidase I) have substantially more structure among populations within groups and among groups than fester. All polymorphism statistics (Tajima's D, Fu and Li's D* and F*) are significantly negative for the East Coast A-type alleles, and Fu and Li's F* statistic is significantly negative for the West Coast A-type alleles. These results are likely due to selection rather than demography, given that 10 of the housekeeping loci have no populations with significant values for any of the polymorphism statistics. The majority of codons in the fester proteins have ω values < 1, but 15–27 codons have > 95% posterior probability of ω values > 1.ConclusionFester proteins are evolving non-neutrally. The polymorphism statistics are consistent with either purifying selection or directional selection. The ω statistics show that the majority of the protein is experiencing purifying selection (ω < 1), but that 15–27 codons are undergoing either balancing or directional selection: ω > 1 is compatible with either scenario. The distribution of variation within and among populations points towards balancing selection and away from directional selection. While these data do not provide unambiguous support for a specific type of selection, they contribute to our evolutionary understanding of a critical biological process by determining the forces that affect loci involved in allorecognition.

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“…) and 3–29% in introduced populations in South America (Ben‐Shlomo et al. ) and New Zealand (Ben‐Shlomo et al. ).…”

Section: Discussionmentioning

confidence: 99%

Investigating the widespread introduction of a tropical marine fouling species

Sheets

Cohen

Ruiz

et al. 2016

Ecology and Evolution

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Little is known about the number and rate of introductions into terrestrial and marine tropical regions, and if introduction patterns and processes differ from temperate latitudes. Botryllid ascidians (marine invertebrate chordates) are an interesting group to study such introduction differences because several congeners have established populations across latitudes. While temperate botryllid invasions have been repeatedly highlighted, the global spread of tropical Botrylloides nigrum (Herdman, 1886) has been largely ignored. We sampled B. nigrum from 16 worldwide warm water locations, including around the Panama Canal, one of the largest shipping hubs in the world and a possible introduction corridor. Using mitochondrial (COI) and nuclear (ANT) markers, we discovered a single species with low genetic divergence and diversity that has established in the Atlantic, Pacific, Indo‐Pacific, and Mediterranean Oceans. The Atlantic Ocean contained the highest diversity and multilocus theta estimates and may be a source for introductions to other regions. A high frequency of one mitochondrial haplotype was detected in Pacific populations that may represent a recent introduction in this region. In comparison to temperate relatives, B. nigrum displayed lower (but similar to temperate Botrylloides violaceus) genetic divergence and diversity at both loci that may represent a more recent global spread or differences in introduction pressures in tropical regions. Additionally, chimeras (genetically distinct individuals sharing a single body) were detected in three populations by the mitochondrial locus and validated using cloning, and these individuals contained new haplotype diversity not detected in any other colonies.

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Population genetics of the invasive ascidian Botryllus schlosseri from South American coasts

Cited by 35 publications

References 35 publications

Evidence for Selection on a Chordate Histocompatibility Locus

Evidence for Selection on a Chordate Histocompatibility Locus

The fester locus in Botryllus schlosseri experiences selection

Investigating the widespread introduction of a tropical marine fouling species

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