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

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

Name dc:type.qualificationname

Doctor of Philosophy (awarded by UHI)

Level dc:type.qualificationlevel

Doctoral Thesis

Grantor dc:publisher.institution

University of the Highlands and Islands

Year dc:date.issued

2025

Author dc:creator

• Sands, Chester J

Advisor dc:contributor.advisor

• Narayanaswamy, Bhavani

Language dc:language

eng

Identifier

oai:pure.atira.dk:studenttheses/08a0c865-6e72-4914-91a3-e7676ac2cefd

OAI identifier oai:identifier

oai:pure.atira.dk:studenttheses/08a0c865-6e72-4914-91a3-e7676ac2cefd