Showing 1 - 10 of 14 Items

• Embargo End Date: 2027-05-16

Date: 2024-01-01

Creator: Benjamin Sewell-Grossman

Access: Embargoed

Date: 2017-05-01

Creator: Robert Barron

Access: Open access

Hybrid zones and their dynamics are important in the understanding of the genetic basis of reproductive isolation and speciation. This study seeks to investigate the hybridization dynamics of a Scarus hybrid swarm within the Tropical Eastern Pacific (TEP) that includes four phenotypically distinct species: S. perrico, S. ghobban, S. rubroviolaceus, and S. compressus. Genetic and population structure analyses of four nuclear loci and a mitochondrial locus revealed that one of the four species, S. compressus, was the result of two different hybrid crosses: S. perrico ✕ S. rubroviolaceus and S. perrico ✕ S. ghobban. A NewHybrids model indicated that most of the S. compressus samples were F1 hybrids, but 21% of the S. compressus sample was classified as “parentals” which could also be explained by the presence of either F2 hybrids or backcrosses with S. compressus phenotypes, given the relatively low power of the nuclear data set (4 loci) to resolve complex hybrid genotypes. Significant mito-nuclear discordance in all three non-hybrid species is consistent with an evolutionary effect of backcrossing between F1 hybrids and “pure” species. This study reveals a relative ease of hybridization between parrotfish taxa separated by an estimated 4.5 million years of isolation and opens the door to further studies on the potential effects of gene flow across old species boundaries and perhaps the formation of new species by hybrid speciation in a diverse clade of tropical reef fish. Elucidating the nature of potentially “deep” F2 crosses and backcrosses within the TEP Scarus hybrid system will allow us to better understand the effects of hybridization on evolution and speciation on both a micro- and macro-ecological scale.

Date: 2024-01-01

Creator: Jared Lynch

Access: Open access

The mitochondrial genome has historically been relegated to a neutral genetic marker, but new evidence suggests mitochondrial DNA to be a target for adaptation to environmental stress. The invasive European green crab (Carcinus maenas) exemplifies this in the Gulf of Maine’s hybrid zone, where interbreeding populations exhibit thermal tolerances influenced by mitochondrial genotype. To better understand the mechanism behind this phenomenon, the effect of mitochondrial genotype on mitochondrial activity was tested by measuring mtDNA copy number (mtCN) and the activity of complex I, II, and IV of the electron transport system via high-resolution respirometry. Mitochondria isolated from frozen heart tissue were measured at three temperature points—5°C, 25°C, and 37°C—to represent thermal stresses and a control. It was predicted that cold-adapted haplogroups would exhibit both higher mtCN and increased activity for each complex, either across all temperatures or exclusively at 5°C compared to a warm-adapted haplogroup. Initial comparisons of mitochondria from fresh and frozen tissue at 25°C found lower activity for complex II and IV in frozen extracts, but they continued to be used for convenience. No differences were observed across haplogroups for mtCN or high-resolution respirometry, suggesting that mitochondrial activity does not underlie differences in thermal tolerance. However, temperature greatly influenced activity measurements with complex II and IV exhibiting the highest rates at 37°C while complex I exhibited optimal activity at 25°C. This study represents the first of its kind for C. maenas, providing a foundation for future experiments to continue exploring mitochondria in the context of adaptive evolution.

• Embargo End Date: 2026-05-18

Date: 2023-01-01

Creator: Holden D. Hadfield

Access: Embargoed

• Restriction End Date: 2025-06-01

Date: 2020-01-01

Creator: Diego Andres Villamarin

Access: Access restricted to the Bowdoin Community

Date: 2019-05-01

Creator: Natasha Ann Belsky

Access: Access restricted to the Bowdoin Community

Date: 2022-01-01

Creator: Garrison Asper

Access: Open access

The Extracellular Matrix (ECM) between plant cells is vital for structure, development, and intercellular adhesion. A pectin rich layer in between cells, the middle lamella, is largely responsible for regulating the adhesive properties of adjacent plant cells. Homogalacturonan (HG) pectin, the most common, is synthesized in the Golgi and secreted into the ECM where it undergoes calcium crosslinking, increasing its adhesive properties. Mutations in proteins essential for HG synthesis can reveal a severe adhesion defective phenotype, where the hypocotyls of dark grown Arabidopsis exhibit cell sloughing, curling, and general disorganization. A family of five ELMO proteins are suspected to act as scaffolds for pectin biosynthesis enzymes. ELMO1 and ELMO4 mutants exhibit an adhesion deficient phenotype, and a double mutant provides evidence of redundancy in function between ELMO1 and ELMO2. ELMO1-GFP co-immunoprecipitated with enzymes required for HG synthesis indicating its role as a scaffold protein. Double mutants of the other ELMO homologues were created to determine if they exhibit functional redundancy, and ELMO1 and ELMO3 appear partially redundant. A gene deletion of ELMO3 was also created using the CRSPR/Cas9 system, resulting in two distinct elmo3 deletion alleles, which were phenotypically identical to the original elmo3-/- mutant. All adhesion defective phenotypes can be partially suppressed by altering the osmoticum and hence turgor that provides pressure on adhesive cells. Lastly, ELMO3-GFP was localized to the Golgi, the site of pectin biosynthesis, further supporting a common role of the ELMOs in pectin biosynthesis.

• Embargo End Date: 2027-05-16

Date: 2024-01-01

Creator: Joanne Du

Access: Embargoed

Date: 2021-01-01

Creator: Andrew Close Bolender

Access: Open access

Plant cell adhesion is mediated by the extracellular matrix (ECM) or cell wall and plays an important role in plant morphogenesis and development. The amount, modification, and cleavage of pectin in the cell wall are major contributors to the adhesive properties of the ECM. To gain a more complete picture of plant cell adhesion processes, Arabidopsis thaliana seedlings were previously mutagenized and screened for hypocotyl adhesion defects. Genomic sequencing of one plant exhibiting an adhesion defect, isolate 242, showed that two mutations, one in cellulose synthase (CesA1) and another in a sugar transporter, are candidates for the causative mutation. This thesis reports that CesA1 is necessary for proper plant cell adhesion, while the sugar transporter encoded at At4g32390 is not. Dark grown seedlings homozygous for mutations in CesA1 stain in ruthenium red, indicating atypical adhesion, while those homozygous for null mutations in At4g32390 do not. Previous study of another adhesion mutant revealed ELMO1, a Golgi protein necessary for plant cell adhesion, and four additional homologs ELMO2-5 in the A. thaliana genome. Two of these homologs, ELMO2 and ELMO3, fused to GFP, colocalized with mCherry-MEM1 markers in the Golgi, but not mCherry-NLM12 ER markers, indicating that ELMO2 and ELMO3 are also Golgi proteins.

Date: 2014-05-01

Creator: Nicholas J Saba

Access: Access restricted to the Bowdoin Community