1. Abstract
Increase in global temperatures is causing great threat to global ecosystems. Adaptation to environmental stress has mainly been studied from a physiological standpoint, assuming populations to be
evolutionarily static. Comparing the range of plastic physiological responses1 and inherent genetic variation among populations across a geographical range can shed light on how quickly organisms
could adapt to climate change. Using PCR, sequencing and previous transcriptome data, genes upregulated under heat shock were compared across two populations of the copepod Tigriopus
californicus. Background genetic variation was compared to genetic variation of heat shock genes to assess the extent to which differences in heat adaptation were based on gene regulation vs.
differences in protein coding sequences. Percent sequence difference was similar between heat shock response genes and random genes, suggesting that gene regulation could play an important part
in adaptation to climate change.
Results
Conclusion and Discussion
• A higher dN/dS ratio in heat-shock response
genes suggests that selection has favored
amino acid differences between populations.
• Overall, similar levels of sequence differentiation
between heat shock response genes and
random genes suggest that gene regulation also
plays a role in adaptation to heat stress.
• Both sequence and regulatory changes involved
in stress response are likely to be important
drivers of adaptation to climate change.
Background
• Tigriopus californicus is a
harpacticoid copepod ranging
from Baja California to
Southeast Alaska1.
• Low connectivity between
populations makes it an ideal
model organism to study local
adaptation.
• The two populations under
study (SA and BD) from
northern and southern
California have different heat
tolerances (Fig. 2).
• Transcriptome sequencing was done for the two
populations to identify genes upregulated under heat
shock.
• Overall goal is to understand to what extent heat
adaptation is due to differentially expressed genes vs.
DNA sequence variation.
Research Question:
When comparing genes upregulated under heat shock
to random genes in transcriptome, is there more
genetic variation in heat shock genes than average?
Materials and Methods
• 20 PCR primers were designed using sequence alignment of the BD and SA
populations for genes upregulated during heat shock, and random genes from the
transcriptome.
• Primers were tested by doing multiple PCR runs to determine appropriate
annealing temperatures and extension times, followed by gel electrophoresis, PCR
clean-up and Sanger sequencing.
• Using previous transcriptome data and data from new primers, the % sequence
difference and dN/dS ratio between SA and BD were determined.
References and
Acknowledgements
1Kelly et al. (2011) Limited potential for adaptation to
climate change in a broadly distributed marine
crustacean. Proc. R. Soc. B; doi:10.1098/rspb.2011.0542
1471-2954.
Many thanks to my research mentor with LSU-HHMI Dr.
Morgan Kelly, my research mentor at Fairleigh Dickinson
University, Dr. Irwin Isquith and my team at the Kelly Lab:
Branden Lawson, Max Wheeler, Dustin DuSang, William
Murdock and Dr. Melissa DeBiasse.
This research was supported in part by a grant to Louisiana
State University from the Howard Hughes Medical Institute
through the Precollege and Undergraduate Science
Education Program.
Fig. 1: Tigriopus californicus
0
0.5
1
1.5
2
2.5
3
3.5
4
Random genes Heat shock response genes
%sequencedifference
Fig 3: Percent sequence difference between populations for genes responding to heat shock compared
0.00
0.20
0.40
0.60
0.80
1.00
1.20
Random genes Heat shock response genes
dN/dSratio
Fig. 4: Ratio of non-synonymous to synonymous SNPs in heat shock response genes and random genes
• Percent sequence difference was not very large between heat shock
response and background genes.
• Significant difference in dN/dS ratio between heat shock genes and
background genes.
Fig. 2: Mean thermal tolerance (LT50) of adult male T.californicus from eight
North American populations