TY - BOOK
T1 - Divergence and Adaptive Capacity of Marine Keystone Species
AU - Fietz, Katharina
PY - 2017
Y1 - 2017
N2 - A multitude of anthropogenic actions ranging from overexploitation, pollution, and
eutrophication to the introduction of invasive species impact the marine environment today
(Jansson & Dahlberg 1999; Islam & Tanaka 2004; Pauly et al. 2005; Molnar et al. 2008). In
combination with rapid environmental alterations brought about by climate change, these factors
confer increasing pressure on marine organisms. An understanding of population divergence
patterns, population sizes, and local adaptive capacities is an important baseline for the design of
sustainable resource management measures and effective conservation actions. In this thesis, I
took a population genetic approach to shed light on the above features of three different keystone
organisms in the North Atlantic and Baltic Sea ecosystems.
In Chapter 2, my colleagues and I combined modern and historic nuclear and mitochondrial
genetic markers with zooarchaeological, demographic, and life history data, in order to
investigate the processes that drove colonization, extinction, and re-colonization of two grey seal
subspecies (Halichoerus grypus grypus and Halichoerus grypus atlantica) in the Baltic Sea and
North Sea. We revealed that the two subspecies diverged ca. 4,200 yrs BP due to an isolation
process that was presumably initiated by cooling and increasing ice cover of the Baltic Sea
3,500-4,500 yrs BP, and upheld by continued anthropogenic disturbance. We further discovered
that the historic grey seal population in (the geographically intermediate) Danish waters was
genetically connected to the Central Baltic Sea, while recolonizers of the same region today stem
from either North Sea or Baltic Sea. Lastly, we identified one location in the southwest Baltic
Sea that harbors admixed individuals, suggesting that this might be a place of subspeciesreconnection
in the near future.
Chapter 3 focuses on the extent of gene flow between the only two known North Atlantic
humpback whale (Megaptera novaeangliae) breeding grounds, and its effect on the effective size
of the breeding population in Cape Verde. Humpback whales in the North Atlantic have
undergone a drastic depletion during the 19th and 20th century due to heavy whaling activity
(Smith & Reeves 2003). Only within the last 60 years have they had a chance to recover thanks
to dedicated conservation efforts (Best 1993). Our study was able to show that humpback whales
in Cape Verde have likely undergone several historic and more recent population declines, and
today may be at or below a minimum viable population size. In addition, we showed that the
amount of long-term average gene flow between Cape Verde and the only other known breeding
ground in the West Indies is very limited, and indeed is of the same level of magnitude as genetic
differentiation in humpback whales between ocean basins (Jackson et al. 2014).
In Chapter 4, my colleagues and I investigated genome-wide population divergence patterns in
two economically and ecologically important sand lance species (Ammodytes tobianus and
Hyperoplus lanceolatus) in the Baltic Sea and North Sea. This study further took one step
beyond focusing on the genome alone, and additionally drew on information about the associated
fish gut and environmental water bacterial communities. Three findings emerged: Firstly, the
Baltic Sea harbors unique genetic populations of sand lances that are differentiated from the
North Sea. Genomic regions showed elevated divergence not only as a potential response to
salinity- and SST-related natural selection, but these regions also correlated with the relative
bacterial composition of the water. This could hint at a potential influence of environmental
microbes on the adaptive genetic divergence of these marine fishes. Secondly, we confirmed that
Baltic Sea A. tobianus exist as two genetic stocks co-occurring in the same habitat. Thirdly, the
gut microbial communities of sand lances are not a mere reflection of environmental microbes,
but rather the fishes themselves seem to excerpt some degree of internal control and selection.
The application of a range of molecular tools and their integration with environmental, count,
life history, and microbial data in the thesis presented here hopefully demonstrate the usefulness
of applying genetic methodology to the investigation of marine populations. I believe that this
work further illustrates the wide utility of genetic and genomic methodology in a conservationmanagement
framework. In the case of the Northern European grey seal, the findings of our
study highlight the importance of distinguishing grey seals as different genetic and demographic
units in Skagerrak, Kattegat, and the southwest Baltic when setting annual decimation quota
(Chapter 2). Regarding the small North Atlantic humpback whale breeding population in Cape
Verde, our work suggests that this population requires particular management attention, as it may
be vulnerable to stochastic effects of inbreeding and to anthropogenic disturbances (Chapter 3).
Lastly, our sand lance study results suggest that the different sand lance species differ in their
population divergence patterns, and that as a result connectivity of different areas might not be
comparable across species (Chapter 4). As such, it might be advisable to reconsider the current
management scheme that is treating all occurring sand lance species as one.
AB - A multitude of anthropogenic actions ranging from overexploitation, pollution, and
eutrophication to the introduction of invasive species impact the marine environment today
(Jansson & Dahlberg 1999; Islam & Tanaka 2004; Pauly et al. 2005; Molnar et al. 2008). In
combination with rapid environmental alterations brought about by climate change, these factors
confer increasing pressure on marine organisms. An understanding of population divergence
patterns, population sizes, and local adaptive capacities is an important baseline for the design of
sustainable resource management measures and effective conservation actions. In this thesis, I
took a population genetic approach to shed light on the above features of three different keystone
organisms in the North Atlantic and Baltic Sea ecosystems.
In Chapter 2, my colleagues and I combined modern and historic nuclear and mitochondrial
genetic markers with zooarchaeological, demographic, and life history data, in order to
investigate the processes that drove colonization, extinction, and re-colonization of two grey seal
subspecies (Halichoerus grypus grypus and Halichoerus grypus atlantica) in the Baltic Sea and
North Sea. We revealed that the two subspecies diverged ca. 4,200 yrs BP due to an isolation
process that was presumably initiated by cooling and increasing ice cover of the Baltic Sea
3,500-4,500 yrs BP, and upheld by continued anthropogenic disturbance. We further discovered
that the historic grey seal population in (the geographically intermediate) Danish waters was
genetically connected to the Central Baltic Sea, while recolonizers of the same region today stem
from either North Sea or Baltic Sea. Lastly, we identified one location in the southwest Baltic
Sea that harbors admixed individuals, suggesting that this might be a place of subspeciesreconnection
in the near future.
Chapter 3 focuses on the extent of gene flow between the only two known North Atlantic
humpback whale (Megaptera novaeangliae) breeding grounds, and its effect on the effective size
of the breeding population in Cape Verde. Humpback whales in the North Atlantic have
undergone a drastic depletion during the 19th and 20th century due to heavy whaling activity
(Smith & Reeves 2003). Only within the last 60 years have they had a chance to recover thanks
to dedicated conservation efforts (Best 1993). Our study was able to show that humpback whales
in Cape Verde have likely undergone several historic and more recent population declines, and
today may be at or below a minimum viable population size. In addition, we showed that the
amount of long-term average gene flow between Cape Verde and the only other known breeding
ground in the West Indies is very limited, and indeed is of the same level of magnitude as genetic
differentiation in humpback whales between ocean basins (Jackson et al. 2014).
In Chapter 4, my colleagues and I investigated genome-wide population divergence patterns in
two economically and ecologically important sand lance species (Ammodytes tobianus and
Hyperoplus lanceolatus) in the Baltic Sea and North Sea. This study further took one step
beyond focusing on the genome alone, and additionally drew on information about the associated
fish gut and environmental water bacterial communities. Three findings emerged: Firstly, the
Baltic Sea harbors unique genetic populations of sand lances that are differentiated from the
North Sea. Genomic regions showed elevated divergence not only as a potential response to
salinity- and SST-related natural selection, but these regions also correlated with the relative
bacterial composition of the water. This could hint at a potential influence of environmental
microbes on the adaptive genetic divergence of these marine fishes. Secondly, we confirmed that
Baltic Sea A. tobianus exist as two genetic stocks co-occurring in the same habitat. Thirdly, the
gut microbial communities of sand lances are not a mere reflection of environmental microbes,
but rather the fishes themselves seem to excerpt some degree of internal control and selection.
The application of a range of molecular tools and their integration with environmental, count,
life history, and microbial data in the thesis presented here hopefully demonstrate the usefulness
of applying genetic methodology to the investigation of marine populations. I believe that this
work further illustrates the wide utility of genetic and genomic methodology in a conservationmanagement
framework. In the case of the Northern European grey seal, the findings of our
study highlight the importance of distinguishing grey seals as different genetic and demographic
units in Skagerrak, Kattegat, and the southwest Baltic when setting annual decimation quota
(Chapter 2). Regarding the small North Atlantic humpback whale breeding population in Cape
Verde, our work suggests that this population requires particular management attention, as it may
be vulnerable to stochastic effects of inbreeding and to anthropogenic disturbances (Chapter 3).
Lastly, our sand lance study results suggest that the different sand lance species differ in their
population divergence patterns, and that as a result connectivity of different areas might not be
comparable across species (Chapter 4). As such, it might be advisable to reconsider the current
management scheme that is treating all occurring sand lance species as one.
UR - https://rex.kb.dk/primo-explore/fulldisplay?docid=KGL01010615587&context=L&vid=NUI&search_scope=KGL&tab=default_tab&lang=da_DK
M3 - Ph.D. thesis
BT - Divergence and Adaptive Capacity of Marine Keystone Species
PB - Natural History Museum of Denmark, Faculty of Science, University of Copenhagen
ER -
