Elucidating the evolution and diversity of the Southern Ocean ophiuroids with reference to present day ecosystem management

摘要

The evolution of life on our small world has a long and tumultuous history,
beginning as self-replicating molecules and evolving into complex organisms
able to consciously and deliberately alter their planet’s natural order. Over the
epochs, periods of slow, evolutionary development have been punctuated by
explosive diversification and catastrophic collapse. After 3.8 billion years the
bewildering array of life, and its ability to persist through the most difficult of
circumstances, is facing another period of lineage extinction out-pacing lineage
divergence. However, this time, the difference is that the primary cause is a
single species, humans.
A question asked in this thesis is, “will we be able to capture the extent of
diversity loss?”. Given the unknowns regarding the number of species on Earth,
and the increasing evidence that many species are likely to harbour
unappreciated genetic diversity, it is probable that many lineages and species
will not be recorded before their demise. Nowhere is this more likely than in the
least studied areas, one of which is also one of the biologically richest areas on
Earth, the seafloor of the Southern Ocean.
The studies presented here delve into the genetic diversity of Southern Ocean
brittle stars (Class Ophiuroidea), based on two exemplar species, Amphiura
belgicae and Ophioplinthus gelida, both common across the Southern Ocean
shelf regions, that have been sampled over several expeditions across a wide
spatial scale. Mitochondrial DNA sequences were used to identify patterns of
divergence that differ from expectations of what is expected from a good
“biological species” and are directly compared with two other similar published
studies on the species Astrotoma agassizii and Ophiuroglypha lymani.
Some interesting, and consistent, patterns of diversity emerge. Genetic
divergences, possibly consistent with being unrecognised or cryptic species, are
found in all four species, indicating that each has undergone a recent radiation.
Many of the clades had discrete geographical distributions, often limited to the
shelf regions of a single Southern Ocean island or archipelago. In each
radiation, one or more clades identified a priori as a sister species, or, in the The evolution of life on our small world has a long and tumultuous history,
beginning as self-replicating molecules and evolving into complex organisms
able to consciously and deliberately alter their planet’s natural order. Over the
epochs, periods of slow, evolutionary development have been punctuated by
explosive diversification and catastrophic collapse. After 3.8 billion years the
bewildering array of life, and its ability to persist through the most difficult of
circumstances, is facing another period of lineage extinction out-pacing lineage
divergence. However, this time, the difference is that the primary cause is a
single species, humans.
A question asked in this thesis is, “will we be able to capture the extent of
diversity loss?”. Given the unknowns regarding the number of species on Earth,
and the increasing evidence that many species are likely to harbour
unappreciated genetic diversity, it is probable that many lineages and species
will not be recorded before their demise. Nowhere is this more likely than in the
least studied areas, one of which is also one of the biologically richest areas on
Earth, the seafloor of the Southern Ocean.
The studies presented here delve into the genetic diversity of Southern Ocean
brittle stars (Class Ophiuroidea), based on two exemplar species, Amphiura
belgicae and Ophioplinthus gelida, both common across the Southern Ocean
shelf regions, that have been sampled over several expeditions across a wide
spatial scale. Mitochondrial DNA sequences were used to identify patterns of
divergence that differ from expectations of what is expected from a good
“biological species” and are directly compared with two other similar published
studies on the species Astrotoma agassizii and Ophiuroglypha lymani.
Some interesting, and consistent, patterns of diversity emerge. Genetic
divergences, possibly consistent with being unrecognised or cryptic species, are
found in all four species, indicating that each has undergone a recent radiation.
Many of the clades had discrete geographical distributions, often limited to the
shelf regions of a single Southern Ocean island or archipelago. In each
radiation, one or more clades identified a priori as a sister species, or, in theThe evolution of life on our small world has a long and tumultuous history,
beginning as self-replicating molecules and evolving into complex organisms
able to consciously and deliberately alter their planet’s natural order. Over the
epochs, periods of slow, evolutionary development have been punctuated by
explosive diversification and catastrophic collapse. After 3.8 billion years the
bewildering array of life, and its ability to persist through the most difficult of
circumstances, is facing another period of lineage extinction out-pacing lineage
divergence. However, this time, the difference is that the primary cause is a
single species, humans.
A question asked in this thesis is, “will we be able to capture the extent of
diversity loss?”. Given the unknowns regarding the number of species on Earth,
and the increasing evidence that many species are likely to harbour
unappreciated genetic diversity, it is probable that many lineages and species
will not be recorded before their demise. Nowhere is this more likely than in the
least studied areas, one of which is also one of the biologically richest areas on
Earth, the seafloor of the Southern Ocean.
The studies presented here delve into the genetic diversity of Southern Ocean
brittle stars (Class Ophiuroidea), based on two exemplar species, Amphiura
belgicae and Ophioplinthus gelida, both common across the Southern Ocean
shelf regions, that have been sampled over several expeditions across a wide
spatial scale. Mitochondrial DNA sequences were used to identify patterns of
divergence that differ from expectations of what is expected from a good
“biological species” and are directly compared with two other similar published
studies on the species Astrotoma agassizii and Ophiuroglypha lymani.
Some interesting, and consistent, patterns of diversity emerge. Genetic
divergences, possibly consistent with being unrecognised or cryptic species, are
found in all four species, indicating that each has undergone a recent radiation.
Many of the clades had discrete geographical distributions, often limited to the
shelf regions of a single Southern Ocean island or archipelago. In each
radiation, one or more clades identified a priori as a sister species, or, in the case of O. gelida, where Ophioplinthus martensi was included as a more distant
outgroup, the sister species (and O. martensi) were found to be an element of
the radiating clades. This indicates that the depth of divergence of a recognised
morphospecies was equivalent to the depth of divergence of the other
geographically explicit clades.
The key implications of these studies are that there is a large quantity of
unappreciated diversity that may represent considerably higher species
richness than recognised in the currently-available estimates. Furthermore, the
current biogeographic paradigm of four Southern Ocean biogeographic regions
– Antarctic, sub-Antarctic, shallow and deep – is a concerning simplification that
has led to a generally unquestioned suggestion of large, well-connected
populations in these regions with the implication of species resilience. The
reality of much smaller populations being present in small, localised areas with
little or no connectivity, implies vulnerability and the need for careful
consideration from conservation managers and policy makers.
Finally, the results of these studies question the current hypothesis explaining
the unusually high diversity across the Southern Ocean benthic fauna. The
biodiversity pump of the Milankovitch cycles implies that diversity increases with
each glacial cycle, while the results presented here strongly suggest that the
last diversification event predated the onset of Milankovitch cycles, and that
there has likely been a net loss of lineages over the past one million years.

奖励日期	9 12月 2025
源语言	English
奖励机构	University of the Highlands and Islands
赞助人	British Antarctic Survey
导师	William Goodall-Copestake (Supervisor) & Bhavani Narayanaswamy (Supervisor)