scholarly journals Macroevolutionary Changes of Plants on Islands

2021 ◽  
Author(s):  
◽  
Patrick Kavanagh
Keyword(s):  
New Zealand ◽  
Seed Size ◽  
Growth Form ◽  
Plant Traits ◽  
Ontogenetic Changes ◽  
Dioecious Plants ◽  
Niche Variation ◽  
Evolutionary Changes ◽  
Evolutionary Pathways ◽  
Niche Variation Hypothesis

<p>Insularity is known to produce predictable evolutionary changes in plants. For example, herbaceous plants often evolve woodiness and seeds tend to have reduced dispersal capabilities on islands. However, our understanding of how other plant traits may evolve on islands is lacking. Furthermore, plants are modular organisms and by investigating evolutionary changes in specific plant traits we may better understand macroevolutionary processes on islands.  In this thesis, I investigate evolutionary changes in a range of plant traits on islands. First, I tested for evolutionary changes in seed size on islands (Chapter 2). Island plants consistently produced larger seeds than mainland relatives. Furthermore, this result was consistent regardless of differences in dispersal mode, growth form and evolutionary history. Selection may favour increased seed size to reduce dispersal distances. Additionally, selection may favour larger seeds due to the competitive advantage conferred to developing seedlings.  Many animal taxa exhibit increased sexual size dimorphism (SSD) on islands, as predicted by the niche variation hypothesis. However, patterns of SSD among dioecious plants on islands are unknown. In Chapter 3 I tested for differences in SSD of dioecious plants that colonized four island groups from New Zealand (mainland). The degree of SSD did not vary predictable between island and mainland plants, contrary to predictions of the niche variation hypothesis. However, SSD was consistently female biased on the mainland and results suggest selection is acting to increase the size of both sexes on islands.  Evolutionary changes in island plants may be a response to herbivory by unique large browsers. For example, the divaricate growth form is common in the New Zealand flora and may have deterred browsing moa. In Chapter 4 I tested for differences in traits associated with the divaricate growth form between plants from mainland New Zealand and Chatham Island. Results suggest that an absence of moa on Chatham Island has relaxed selection for traits associated with the divaricate growth form.  An emerging body of research suggests aposematism (warning signals to herbivores) may be common in plants. However, previous investigations have not appreciated the fact that the perspective of terrestrial herbivores changes as plants grown vertically. Furthermore, ontogenetic changes in the capacity of plants to defend themselves may influence the reliability of warning signals. In Chapter 5 I tested for ontogenetic changes in two potentially aposematic signals produced by Pseudopanax crassifolius. Aposematism on upper leaf surfaces peaked early in ontogeny, providing a dishonest signal of defense. Conversely, signaling on the underside of leaves peaked later in ontogeny and scaled positively with structural defenses.   The results of this thesis suggest selection is acting on specific plant traits on islands. Evolutionary pathways, such as the evolution of woodiness, may be better explained by considering selection acting on other plant traits. For example, selection acting on seed size may facilitate evolutionary size changes evident at later life-history stages. A lack of consensus exists regarding the role of insular herbivores in the evolution of island plants. The results of Chapters 4 and 5 suggest herbivory has played an important role in the evolution of novel morphology of island plants. Considering trait specific changes of plants on islands may further our understanding of prominent evolutionary pathways by pinpointing the action of selection.</p>

scholarly journals The repeated evolution of large seeds on islands

2014 ◽  
Vol 281 (1786) ◽  
pp. 20140675 ◽  
Author(s):  
Patrick H. Kavanagh ◽  
Kevin C. Burns
Keyword(s):  
Seed Size ◽  
Evolutionary History ◽  
Growth Form ◽  
Plant Traits ◽  
General Tendency ◽  
Long Distance Dispersal ◽  
Long Distance ◽  
Dispersal Mode ◽  
Evolutionary Pathway ◽  
Repeated Evolution

Several plant traits are known to evolve in predictable ways on islands. For example, herbaceous species often evolve to become woody and species frequently evolve larger leaves, regardless of growth form. However, our understanding of how seed sizes might evolve on islands lags far behind other plant traits. Here, we conduct the first test for macroevolutionary patterns of seed size on islands. We tested for differences in seed size between 40 island–mainland taxonomic pairings from four island groups surrounding New Zealand. Seed size data were collected in the field and then augmented by published seed descriptions to produce a more comprehensive dataset. Seed sizes of insular plants were consistently larger than mainland relatives, even after accounting for differences in growth form, dispersal mode and evolutionary history. Selection may favour seed size increases on islands to reduce dispersibility, as long-distance dispersal may result in propagule mortality at sea. Alternatively, larger seeds tend to generate larger seedlings, which are more likely to establish and outcompete neighbours. Our results indicate there is a general tendency for the evolution of large seeds on islands, but the mechanisms responsible for this evolutionary pathway have yet to be fully resolved.

Comparative ecology of seed size and dispersal

1996 ◽  
Vol 351 (1345) ◽  
pp. 1309-1318 ◽  
Keyword(s):  
Leaf Area ◽  
Seed Size ◽  
Specific Leaf Area ◽  
Growth Form ◽  
Plant Traits ◽  
Seed Mass ◽  
Site Quality ◽  
Common Mechanism ◽  
Dispersal Mode ◽  
Reserve Effect

Seed mass is correlated with a number of other plant traits, including dispersal mode, growth form and specific leaf area. Specific leaf area is the main determinant of potential relative growth rate and an indicator of the site quality to which a species is adapted. The relationships with dispersal mode and growth form have consistent form in five datasets from three continents, and each account for about 20-30 % of variation in log seed mass. Thus, there is also very substantial variation within growth form and dispersal categories. Much, but not all, of the 20-30% is associated with shifted family composition between growth forms or dispersal modes. Experiments have shown that seedlings of larger-seeded species are better able to survive hazards including deep shade, drought, physical damage and the presence of competing vegetation. If there is a common mechanism under these different hazards, it seemingly must be a ‘reserve effect’, whereby during deployment and early growth larger-seeded species hold a bigger percentage of seed reserves uncommitted to seedling structure and available to support respiration or repair damage. A reserve effect has not yet been demonstrated directly. It remains possible that different mechanisms operate under different hazards. Under a reserve effect, advantages of larger seed size should be temporary, and temporary advantage has indeed been observed with regard to seedling survival under dense shade. Although larger seed mass confers benefits on seedlings, larger seeds must necessarily be produced in smaller numbers per unit of resource allocated. Seed mass is presumed to have evolved as a compromise between these counterposed pressures. Yet there has proved to be surprisingly little difference in average seed mass between very different vegetation regions, at least in temperate climates. Rather, there is startlingly wide variation in seed mass among species growing interspersed with each other. Recent applications of game theory may be capable of accounting for this wide variation between coexisting species, but at present these models are driven by competition among seedling species (as opposed to between seedlings and adults). It remains unclear whether competition among seedlings is a decisive influence on species composition in most of the world’s vegetation types.

scholarly journals Community Ecology of Epiphytes and other Arboreal Plants in the New Zealand Eco-region

2021 ◽  
Author(s):  
◽  
Thomas Dawes
Keyword(s):  
New Zealand ◽  
Seed Size ◽  
Host Species ◽  
Spatial Ecology ◽  
Scale Insects ◽  
Tree Fern ◽  
Sooty Mould ◽  
Tree Ferns ◽  
Epiphytic Fern ◽  
Epiphyte Community

<p><b>Epiphytes and other structurally-dependent plants have a spatial ecology and community structure intrinsically linked to that of the host trees in the forest, unlike fully terrestrial plants. Understanding of the ecological implications of this from a theoretical perspective is in its infancy. New Zealand’s south temperate rainforest, whilst not as species rich as tropical forests, hosts one of the richest temperate epiphyte floras. Our understanding of the ecological processes structuring the epiphyte communities of New Zealand forests is however lacking. Here, I present four key studies seeking to add to our knowledge of epiphyte community structure, host specificity and spatial ecology in the New Zealand eco-region.</b></p> <p>First, I tested if seed size determined the likelihood of woody plant species occurring epiphytically on tree ferns (their arboreality) – Chapter 2. Arboreality was negatively related to seed size, with only smaller-seeded species commonly occurring on tree ferns. However, the effect of seed size reduced in later life history stages, as expected. These small-seeded species, most notably Weinmannia racemosa, appear to be utilising an alternative recruitment strategy by establishing epiphytically on the tree fern trunks.</p> <p>Second, on Cyathea dealbata host tree ferns, I tested patterns of species accumulation, metacommunity network structure, and differences in vertical stratification (Chapter 3). Epiphytes and climbers followed a species accumulation model of succession between tree ferns of different sizes and between older and younger portions of the tree fern. The metacommunity network showed patterns of species co-occurrence and nestedness consistent with null expectations. Epiphytes of different habits and different dispersal syndromes show different vertical profiles of occurrence, with bird-dispersed species occurring more often near the top of the tree fern than other taxa.</p> <p>To understand an unusual pattern in epiphyte between-host structuring, I quantified the relationship between epiphytic plant and sooty mould assemblages in New Zealand montane beech forest (Chapter 4). Due to the presence of host specific scale insects, the sooty mould was limited to two of three co-dominant canopy tree species. On these two host species, epiphyte richness was significantly reduced. The host size-richness relationship in these two species was also removed, with species composition significantly altered compared to the mould free host species. My results are consistent with the sooty mould amensally excluding the epiphytes and it can be considered as a part of a keystone species complex (with the host beeches and scale insects). This produces a strong pattern of parallel host specificity otherwise not seen in epiphyte assemblages.</p> <p>Lastly, I compared the differences in spatial niche and host species diversity between three arboreal plants, with divergent ecophysiology, on Lord Howe Island (Chapter 5). These focal species were a dwarf mistletoe, an epiphytic orchid and an epiphytic fern. The mistletoe was restricted to thinner branches, and had a significantly different niche to both epiphyte taxa. The host diversity of the mistletoe and orchid both differed significantly from null model expectations. However, the epiphytic fern (Platycerium bifurcatum) had a host diversity consistent with null expectations.</p> <p>Taken together, these studies increase our understanding of epiphyte community assembly in New Zealand and provide a platform to encourage further work in this field. They also provide results that expand understanding of spatial patterns between host and up vertical clines.</p>

scholarly journals A test of the Niche Variation Hypothesis in a ruminant herbivore

2020 ◽  
Vol 89 (12) ◽  
pp. 2825-2839
Author(s):  
Brett R. Jesmer ◽  
Matthew J. Kauffman ◽  
Melanie A. Murphy ◽  
Jacob R. Goheen
Keyword(s):  
Niche Variation ◽  
Niche Variation Hypothesis

scholarly journals The ubiquitin system affects agronomic plant traits

2020 ◽  
Vol 295 (40) ◽  
pp. 13940-13955 ◽  
Author(s):  
Katrina J. Linden ◽  
Judy Callis
Keyword(s):  
Seed Size ◽  
Agronomic Traits ◽  
Plant Traits ◽  
Vascular Plant ◽  
Crop Improvement ◽  
26S Proteasome ◽  
Plant Host ◽  
Ubiquitin System ◽  
Expression Of Genes ◽  
Effector Recognition

In a single vascular plant species, the ubiquitin system consists of thousands of different proteins involved in attaching ubiquitin to substrates, recognizing or processing ubiquitinated proteins, or constituting or regulating the 26S proteasome. The ubiquitin system affects plant health, reproduction, and responses to the environment, processes that impact important agronomic traits. Here we summarize three agronomic traits influenced by ubiquitination: induction of flowering, seed size, and pathogen responses. Specifically, we review how the ubiquitin system affects expression of genes or abundance of proteins important for determining when a plant flowers (focusing on FLOWERING LOCUS C, FRIGIDA, and CONSTANS), highlight some recent studies on how seed size is affected by the ubiquitin system, and discuss how the ubiquitin system affects proteins involved in pathogen or effector recognition with details of recent studies on FLAGELLIN SENSING 2 and SUPPRESSOR OF NPR CONSTITUTIVE 1, respectively, as examples. Finally, we discuss the effects of pathogen-derived proteins on plant host ubiquitin system proteins. Further understanding of the molecular basis of the above processes could identify possible genes for modification or selection for crop improvement.

A complex didemnid ascidian from Whangamata, New Zealand

2002 ◽  
Vol 82 (4) ◽  
pp. 625-628 ◽  
Author(s):  
Patricia Kott
Keyword(s):  
New Zealand ◽  
Growth Form ◽  
Vas Deferens ◽  
Three Dimensional ◽  
Present Species ◽  
Double Loop ◽  
Undescribed Species ◽  
Surface Test ◽  
Dimensional Growth ◽  
Eleven Species

An undescribed species of the genus Didemnum (Didemnidae) reported from installations in Whangamata Harbour (Coromandel Peninsula), has a unique and conspicuous three-dimensional growth form (possibly associated with vertical and undersurfaces it occupies). It is also distinguished by a combination of the few characters available to define these small, simplified, convergent organisms. Its stellate spicules are sparse except for a patchy layer in the surface test, primary common cloacal canals are the full depth of the zooids, nine vas deferens coils surround the testis, the gut is long forming a double loop, and larvae have six pairs of ectodermal ampullae. Eleven species said to belong to this genus have previously been reported from New Zealand, but only six are valid Didemnum spp., and they all are distinguished readily from the present species. Nevertheless, there is no evidence that the new species is introduced, and the simplest explanation of it occurrence is that it is part of the little known indigenous didemnid fauna of New Zealand.

Seed size, shape and persistence in soil: a test on Italian flora from Alps to Mediterranean coasts

2003 ◽  
Vol 13 (1) ◽  
pp. 75-85 ◽  
Author(s):  
Bruno Cerabolini ◽  
Roberta M. Ceriani ◽  
Marco Caccianiga ◽  
Rossella De Andreis ◽  
Barbara Raimondi
Keyword(s):  
New Zealand ◽  
Seed Size ◽  
Seed Fate ◽  
Key Factors ◽  
Seed Shape ◽  
Seed Persistence ◽  
Wide Range ◽  
Mediterranean Maquis ◽  
Italian Flora ◽  
The Relationship

AbstractSeed size is a good predictor of seed persistence in soil for British, Argentinean, Iranian and – to some extent – New Zealand species. It has been suggested that seed shape should also be linked to the ease of burial and, thus, to seed persistence, even if some studies failed to show this. The relationship between seed size and shape and persistence in soil was analysed for 259 species of the Italian flora, belonging to a wide range of habitats, from alpine pasture to limestone prairies and meadows of the Prealps, and from woodlands to Mediterranean maquis and garigues. Seed size was related to persistence in soil in the same way as in most other floras examined. Furthermore, seed shape was highly related to persistence in soil among the species analysed, when considered both altogether and divided among the different habitats. Our results suggest that not only seed size, but also seed shape, are key factors in determining seed fate and seed persistence in soil.

Sign in / Sign up

Export Citation Format

Share Document