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Abstract

With increasing anthropogenic threats to the marine environment, it has become
a priority to improve our understanding and conservation of marine fauna. In Antarctic
waters, a rich and diverse benthic fauna thrives. However, the relative isolation of these
organisms and their adaptation to the unique Antarctic environment potentially
heightens their vulnerability to environmental change. Thorough research on the genetic
and ecological structure of Antarctic benthic invertebrate populations is lacking,
particularly for some of the most dominant taxa, such as the Amphipoda. This study
investigated genetic structure, diversity and population ecology in some common
Antarctic benthic amphipod species, to build a more rigorous understanding of the
Antarctic benthos that will aid in future management planning.
Genetic structure was explored over a circum-Antarctic scale in the widespread
amphipod species Eusirus perdentatus and Eusirus giganteus from the continental shelf,
using DNA sequences of two mitochondrial regions (COI and CytB) and one nuclear
region (ITS2). Phylogenies and haplotype networks provided strong evidence that E.
perdentatus harbours two previously undetected cryptic species, and E. giganteus
harbours at least three, highlighting our current misunderstanding of Antarctic benthic
diversity. There were clear differences in the distribution, genetic diversity and
connectivity of populations within each cryptic species, and it is proposed that this
reflects different modes of post-glacial recolonisation of the continental shelf. Within
one cryptic species, high genetic population differentiation (FST > 0.47, p < 0.01)
suggested a potential allopatric speciation process at play.
Genetic connectivity was explored over large (1000km) to very fine (100m)
distances in the ubiquitous nearshore amphipod Orchomenella franklini, using seven
highly polymorphic microsatellite markers. Genetic diversity differed significantly
among populations, potentially reflecting local environmental conditions including
anthropogenic pollution. Hierarchical AMOVA revealed marked genetic subdivision
(FST = 0.16, p < 0.001) across the largest geographical scale and evolutionary isolation
of these populations was inferred. Furthermore, three loci showed signs of selection
across this scale, providing evidence of locally adapted populations. Gene flow was also restricted at smaller scales, indicating a stepping-stone mode of dispersal consistent
with the brooded development of amphipods.
The ecology of O. franklini was investigated through length measurements, sex
and reproductive status of > 6000 individuals, spatial and temporal patterns in
abundance, and corresponding relationships with environmental data. The life history of
O. franklini revealed several traits that exemplify adaptation to the polar environment,
including delayed reproduction, longevity (> 2 years), and seasonal breeding linked to
the summer phytoplankton bloom. There was preliminary evidence of inter-annual and
spatial fluctuations in reproductive timing, potentially reflecting local sea-ice
conditions. O. franklini was found to reach astounding densities (> 65,000/m2) and
abundance was highly heterogeneous in space and time. The distribution of O. franklini
was related to various sediment properties although the relationship differed with
geographic region, highlighting a close association to the local environment as well as
broader Antarctic conditions.
This study has provided significant insight into the dynamics of Antarctic
benthic amphipod populations over a range of scales. Together the results emphasise a
considerable degree of heterogeneity largely overlooked in Antarctic benthic organisms
(from the taxonomy of entire species down to local-scale intraspecific population
dynamics), and thereby support predictions of their vulnerability to anthropogenicinduced
change. Results also shed light on speciation processes in Antarctic waters, and
will ultimately help inform future planning decisions regarding spatial management of
the Antarctic benthic ecosystem.

Item Type:	Thesis - PhD
Authors/Creators:	Baird, HP
Keywords:	genetic connectivity, peracarid crustacean, Antarctica, cryptic species, benthos
Copyright Holders:	The Author
Additional Information:	Chapter 2 is the equivalent of the peer reviewed version of the following article: Baird HP, Miller KJ and Stark JS (2011) Evidence of hidden biodiversity, ongoing speciation and diverse patterns of genetic structure in giant Antarctic amphipods. Molecular Ecology 20, 3439-3454, which has been published in final form at http://dx.doi.org/10.1111/j.1365-294X.2011.05173.x This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. Chapter 3 is the equivalent of a post-print version of an article later published as: Baird HP, Miller KJ and Stark JS (2012) Genetic Population Structure in the Antarctic Benthos: Insights from the Widespread Amphipod, Orchomenella franklini. PloS One 7(3), 1-10
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