International Botanic Congress (IBC) in Melbourne, 24-31 July 2011
NZPRN IBC Symposium: A perspective on species radiation - The New
Zealand story
Abstracts for our six talks are attached here:
1) The importance of New Zealand for understanding the phenomenon
of species radiation
Ilse Breitwieser, Josephine Ward
In recent years, molecular phylogenetic analyses of the New Zealand flora
have changed our understanding of its diversity and origins. These studies
have challenged the traditional view that New Zealand’s biota has been
isolated since the breakup of the southern supercontinent, Gondwana. Under
this “Moa’s Ark” hypothesis, New Zealand is thought of as the home to relic
species undergoing slow changes over long periods of time. However, we
now realize that this view is far too simplistic and a more dynamic, almost
tumultuous, view of New Zealand’s biodiversity is emerging. Contemporary
research demonstrates that much of the New Zealand flora is the result of
late-Tertiary (Pliocene-Pleistocene) species radiations.
Species radiation has been inferred in numerous plant groups in New
Zealand, raising questions of both evolutionary and conservation interest.
Reconstructing the evolutionary history of these radiations is important for
understanding the present day distribution and diversity of the flora.
Considering species radiation, what factors have contributed to the diversity
present in the New Zealand flora? Key factors in the evolutionary success of a
radiation may include innovations in morphology, reproductive features, and
physiology, and variation in these traits among closely related species is often
related to differences in resource utilization. Abiotic factors are also potential
drivers for generating and maintaining floristic diversity, and in New Zealand
these include uplift of the Southern Alps, diversity of geological parent
materials, Pleistocene glacial cycles, and steep environmental gradients.
Studies of the genetic basis of diversification increase our understanding of
how evolution on the molecular level has shaped our current biodiversity.
Hybridisation and polyploidy have long been thought important for
understanding New Zealand’s plant biodiversity. Testing the consequences of
these processes requires studies that demonstrate the occurrence of
reticulate evolution, and field studies to determine the evolutionary potential of
natural hybrids and polyploids.
The New Zealand flora provides an ideal system for understanding plant
evolutionary and ecological processes as they operate in a more global
context. An introduction to recent progress in our understanding of the
phenomenon of species radiation in New Zealand will be presented.
2) Species delimitation in recent New Zealand species radiations
Heidi M. Meudt
Plant species radiation is an important process of diversification in New
Zealand, a biodiversity hotspot with a unique flora. Even though many New
Zealand species may be morphologically and/or ecologically distinct,
delimiting the boundaries of species within these radiations and evaluating
their conservation status has been difficult for several reasons. For example,
many closely-related species are not reproductively isolated, and interspecific
hybridization-- especially when combined with polyploidy--may create new or
intermediate phenotypes. In addition, the phylogenetic relationships of
species, as well as the genetic characteristics that distinguish them, are often
poorly understood and difficult to establish due to reticulation and low levels of
genetic diversity. All these events may obscure species boundaries, and can
result in polymorphic and/or paraphyletic species.
Although resolving species boundaries in plant species radiations can be
challenging, the issue is of particular significance in New Zealand. This is
because more than 80% of species are endemic, exhibit highly restricted
geographic ranges, and/or are threatened. Taxonomists need to be explicit
regarding which operational criteria they use to define species boundaries for
their study groups. Emphasis by different taxonomists on different criteria
(e.g., monophyly at one or multiple DNA loci, morphological diagnosability,
ecological distinctiveness) can lead to different conclusions regarding species
limits and taxonomy. On the other hand, different types of criteria may be
required for delimiting species in different plant groups. Open debate
regarding which criteria are most objective and which species concepts are
most appropriate is very important.
In this talk, I will provide a literature review and synthesis regarding species
delimitation in New Zealand plant species radiations, paying particular
attention to operational criteria (whether implicit or explicit), difficulties with
and resolution of obscure species boundaries, trends over time, and current
practice. I will compare and contrast species delimitation of different plant
species radiations and discuss interesting trends where possible (e.g., alpine
vs. lowland, species radiation vs. non-radiating groups). In addition, I will
focus on specific examples of New Zealand radiations for which genetic,
morphological and ecological data are being generated in diverse and
integrative evolutionary studies, including Pachycladon (Brassicaceae),
Craspedia and other Gnaphalieae (Asteraceae), and Ourisia, Plantago, and
Veronica s.l. (which includes the Hebe complex; Plantaginaceae), among
others.
3) Reconstructing the evolutionary history of species radiations – the
impact of hybridisation
Rob Smissen
Since the early twentieth century botanists have marvelled at the prominence
of wild interspecific hybrids in the New Zealand flora. Cockayne and Allan’s
pioneering work documented many putative hybrid combinations and later
authors including Dansereau and Rattenbury mused on the causes and
evolutionary importance of hybrids in New Zealand. During the latter years of
last century botanical focus shifted away from studies of hybridisation, partly
as a result of the prioritisation of economic botany, but the adoption of
molecular systematic methods has created resurgent interest in the subject.
DNA sequencing and fingerprinting now allow not only robust tests of the
parentage of putative hybrids but also allow for the discrimination of first- from
later-generation hybrids in wild populations and the potential to measure
geneflow between species. Moreover, many authors have attributed
phylogenetic incongruence among independent DNA sequence data sets, or
between DNA-based and morphology-based phylogenies to the influence of
hybridisation, either through introgressive hybridisation (particularly
chloroplast capture) or hybrid speciation.
The impacts of hybridisation on the evolution of New Zealand species
radiations can be observed at all historical stages, from contemporary
geneflow between recently diverged species back to ancient hybrid events
preceding the radiation of a group in New Zealand, or even predating its
arrival. In this talk I will use examples from recent literature (eg Ranunculus,
Asplenium, Pachycladon, everlasting daisies, Ourisia, Pseudopanax) to
illustrate the evolutionary importance of hybridisation in New Zealand plants
and examine progress in resolving related problems in phylogenetic
reconstruction of species radiations. This will include discussion of the
putative hybrid origins of paleopolyploid lineages in New Zealand, methods for
distinguishing between lineage sorting and hybridisation as sources of
phylogenetic incongruence, untangling reticulate relationships among species
as a result of hybrid speciation, and the estimation of species trees from AFLP
data.
While reconstructing the one true species tree is probably an unrealistic and
perhaps even inappropriate goal for many species radiations, there is real
promise for progress in identifying major clades within species radiations and
a more precise understanding of the importance of hybridisation during
different phases of species radiation
4) Diversification of New Zealand alpine plants: Are these radiations
adaptive?
Carlos A. Lehnebach
Alpine areas in the North and South Island of New Zealand harbour a number
of plant groups that, despite their recent origin and low genetic diversity, have
undergone considerable morphological and ecological diversification. Two of
the most outstanding examples of plant species radiation in New Zealand are
the genera Ranunculus and Myosotis, each with over 40 species. Species
within both genera have colonised different habitats, or micro-habitats, within
the alpine areas, and exhibit diverse growth habits and leaf and floral
characteristics.
The extent of phenotypic diversification observed in these two genera has
provided the grounds to suggest both radiations are adaptive. This means that
diversification of these plant groups has been driven by differential utilisation
of resources available in these mountain environments. In general, adaptive
radiations of plant, animal and insect groups are common on islands, and in
particular oceanic islands. So far, whether plant radiations in the New Zealand
archipelago are adaptive has not been fully demonstrated.
Adaptive radiations can be detected by the presence of four features; rapid
speciation, recent common ancestry, phenotype-environment correlation and
trait utility. Molecular phylogenetic investigations of alpine Ranunculus and
preliminary phylogenetic evidence from Myosotis have shown that the New
Zealand species of both genera display two of the four features adaptive
radiations commonly exhibit: common ancestry (both groups are
monophyletic) and rapid speciation (c. 3-5Myr ago for the alpine Ranunculus).
The other two features, namely phenotype-environment correlations and the
adaptive significance of the different phenotypic traits, however, have not
been fully investigated.
In this talk I will focus on the morphological, anatomical and ecological
diversification that both plant groups have undergone and, by taking a
comparative approach, I will discuss the morphological and anatomical
evidence to support phenotype-environment correlations. Specifically, I will
address the following questions: How phenotypically diverse are these
radiations? Are phenotypically similar species found in similar habitats? Are
vegetative characters more diverse than reproductive characters? I will
conclude my talk with an introduction to current studies on these genera
aiming to understand the physiological and adaptive advantages of such
phenotypes.
5) Evolutionary significance of polyploidy in the New Zealand flora
Brian Murray
There is increasing evidence from sequenced plant genomes that whole
genome duplication or polyploidy has been a feature of genome evolution in
the angiosperms. However, this process is ongoing and more recent polyploid
events (neopolyploidy) can be recognized by comparative studies of the
morphology, cytogenetics and phylogenetics of polyploids and their diploid
relatives. Ancient or paleopolyploids show extensive duplication of syntenic
blocks of genes coupled with diploid-like chromosome behaviour and these
are recognized by their high basic chromosome number and extensive gene
duplication.
With chromosome numbers now known for at least one individual from c. 80%
of the New Zealand endemic and indigenous angiosperm flora it is clear that
polyploidy, both neo- and paleo-, has been a key element in the evolutionary
process. The vast majority of species have basic numbers greater than seven
- 10 and many of these are paleopolyploids. Neopolyploidy is also
widespread and is a feature of many of the most species-rich genera such as
Veronica (Hebe), Celmisia, Ranunculus and Coprosma in the endemic flora.
These neopolyploids present interesting questions for analysis. One involves
whether they are autochthonous or whether the initial colonizers were
polyploid; both of these scenarios would appear likely with genera such as
Lobelia and Veronica showing clear examples of recent polyploidy though
others, like Celmisia, are only represented by polyploids. A second major
question is whether the polyploids are autopolyploids that have arisen
following genome duplication within species or are allopolyploids, the products
of hybridization between species with different genomes followed by
polyploidy. The phylogenetic analysis of many genera suggests the relatively
recent arrival of one or a very few ancestors with consequently low levels of
sequence divergence between species. This suggests low levels of genome
differentiation and consequent autoploid events. However, this appears to be
contradicted by the presence of diploid-like meiotic pairing in c. 95% of the
polyploids studied, which suggests alloploidy. One way to resolve this
question is to use molecular cytogenetic techniques coupled with phylogenetic
analyses of genera that contain both diploid and polyploid species. This is
underway in Plantago, where there are six ploidy levels, and the results show
complex patterns of genomic evolution suggesting significant genomic change
despite low levels of sequence divergence.
6) Cenozoic plant radiations in New Zealand: species, habitats, and
timing – what drives plant diversification?
William G. Lee and Daphne E. Lee
On island systems, in marked contrast to continental regions, plant radiations
are important because they frequently contribute much of the biodiversity. For
example, in New Zealand, angiosperm genera with more than ten species
make up more than half of the flora. There are now more than 50 phylogenetic
lineages available for plant groups in New Zealand. These, coupled with more
detailed information about Cenozoic vegetation history and
paleoenvironmental changes, and better distribution, trait and life-history data
for most plant groups, enables us to test several long-standing hypotheses
about the factors driving plant radiations. Previous explanations for radiations
and uneven lineage diversification include phylogenetically constrained
differences in evolutionary potential (e.g., hybridisation ability, polyploidy), and
ability to exploit ecological events? (e.g., novel habitats). More recently,
priority effects and the evolution of plant functional traits to match habitat
availability have been proposed as key mechanisms. Using examples from
plant radiations in New Zealand, we will explore the macro-evolutionary role of
biotic interactions, environmental change, extinction episodes within biomes,
the emergence of new habitats, and the intrinsic properties of different groups
of biota in facilitating radiations within ecologically important clades. The aim
is show how diversification mechanisms in island radiations can contribute to
understanding the key processes determining large-scale patterns of
biodiversity elsewhere.