David Ayre - Academia.edu (original) (raw)
Papers by David Ayre
International Journal of Plant Sciences, 2021
Premise of research. Worldwide, fire-sensitive shrubs have an important but underresearched life ... more Premise of research. Worldwide, fire-sensitive shrubs have an important but underresearched life history, and in Australia they are threatened by anthropogenic changes to fire regimes and habitat loss. Typically, adults are killed by fire, but they can also senesce and die if interfire intervals are prolonged. Populations can regenerate from seed banks displaying fire-stimulated germination; however, populations are ephemeral, and true population sizes and connectedness are difficult to estimate. Persoonia hirsuta ssp. evoluta is an endangered, inconspicuous, fire-sensitive shrub with a soil-stored seed bank currently known only from a small number of locations within the fire-prone Sydney Basin. Although it appears highly fragmented and populations are typically small, we predicted that its seed bank would buffer populations against loss of genetic diversity and population differentiation. Methodology. We used microsatellite markers to assess genetic variation within three aboveground populations of P. hirsuta separated by up to 25 km. The largest and most isolated population, at Appin, New South Wales, Australia, occurs on a mine site and may be subject to disturbance. We compared levels of genetic diversity and estimated the mating systems and genetic connectedness of plants within the three sites. Pivotal results. As predicted, all populations displayed similar genetic diversity, as judged by expected heterozygosity and allelic richness, and displayed little differentiation. All populations appear predominantly outcrossed. However, STRUCTURE and principal coordinates analyses showed that Appin individuals were distinct from those at the other locations. Conclusions. Our data imply that even for fire-sensitive species with few aboveground populations, genetic diversity can be maintained by the buffering effect of persistent seed banks with diversity reflecting historically greater interpopulation gene flow. While all P. hirsuta sites support comparable genetic diversity, the preservation of known populations is critical. Conservation efforts should include searches for additional populations, fire-stimulated germination of seed banks, and collection of seed for propagation in a nursery or direct sowing.
Oecologia, 2017
the importance of conserving the largest possible stands. However, additional work is needed to d... more the importance of conserving the largest possible stands. However, additional work is needed to determine (1) the proportion of recruits within small stands that originate within large stands, (2) how seedling performance varies with fruit size and genotype, and (3) how seedling size and performance vary with the abundance and diversity of pollen.
Geo: Geography and Environment, 2019
Research on rare and threatened plants is a major focus of conservation biology. We want to know ... more Research on rare and threatened plants is a major focus of conservation biology. We want to know why species are rare or declining, how best to arrest that decline and what is lost when species become locally extinct. Occasionally, understanding decline is straightforward - e.g. if the species is restricted to fertile soils that are desirable for cultivation. However, managing declining populations is more complex and requires knowledge of genetic diversity and interspecific interactions.
Biological Journal of the Linnean Society, 2015
Acacia loderi, the ecosystem engineer of the endangered Acacia loderi Shrublands in arid eastern ... more Acacia loderi, the ecosystem engineer of the endangered Acacia loderi Shrublands in arid eastern Australia, spans a persistent (> 15 000 year) but poorly studied landscape feature, the Darling River. We investigated the genetic structure of 19 stands of eight to > 1000 plants separated by < 300 km to test for variation in life histories between semi-arid and arid stands to the east and west of the Darling River, respectively. Eight of nine stands east of the Darling were exclusively sexual, whereas most of those to the west were clonal. Three western stands were monoclonal, two were polyploid, and one was a diverse mix of diploid and triploid phenotypes. Bayesian analysis revealed a complex genetic structure within the western stands, whereas the eastern stands formed only two genetic clusters. Conservation of small stands may require augmentation of genotypic diversity. However, most genotypic diversity resides within the eastern stands. Although arid zone stands of A. loderi are not always clonal, clonality and polyploidy are more common in the arid west. Clear demarcation of life histories either side of the Darling River may reflect ancient or contemporary effects of physical disturbance associated with the river channel, or cryptic environmental differences, with sexual and asexual reproduction, respectively, at a selective premium in the semi-arid east and arid west. The restricted distribution of clones and variation in clonality and polyploidy suggests that smaller stands may be vulnerable and warrant individual management.
Journal of Plant Ecology, 2016
Aims Worldwide, evidence suggests that exotic pollinators can disrupt plant mating patterns. Howe... more Aims Worldwide, evidence suggests that exotic pollinators can disrupt plant mating patterns. However, few studies have determined if pollination by the honeybee Apis mellifera (the world's most widely introduced pollinator) reduces offspring quality when compared with pollination by native birds. The Australian Proteaceae provides an excellent opportunity to test the impact of honeybees in pollination systems that are adapted to birds and non-flying mammals. Methods We compared the frequency of flower visitation and foraging behaviour of birds and insects within seven populations of Banksia ericifolia. Banksia ericifolia is hermaphroditic and has large nectar-rich, orange inflorescences typical of bird and mammal pollinated species. For a subset of the study populations, we compared the quality of seed produced via an exclusion treatment (that only allowed invertebrates to access flowers) with an open-pollination treatment (potentially visited by mammals, birds and invertebrates), by measuring seed weight, germination rates (T 50), percent germination, seedling height after 14 days since the emergence of the cotyledon and time to emergence of the cotyledon. Important Findings Apis mellifera was the only apparent insect pollinator and the most frequent flower visitor, while the open treatment inflorescences were also frequently visited by avian pollinators, primarily honeyeater species. The foraging behaviour of honeybees and honeyeaters showed striking differences that potentially affect patterns of pollen transfer. Honeybees made significantly greater proportions of within cf. among plant movements and only 30% (n = 48) of honeybees foraged for pollen (nectar foragers carried no pollen) whilst all birds were observed to contact both stigmas and anthers when foraging for nectar. Despite these fundamental differences in behaviour, there was little effect of treatment on seed set or quality. Our data show that while honeybees appear to alter patterns of pollen transfer within B. ericifolia populations, they do not impact reproductive rates or performance of early life-stages.
Australian Journal of Botany
Successful long-term conservation and management of populations of plants requires successful man... more Successful long-term conservation and management of populations of plants requires successful management of the suite of factors that determine their ‘realised’ mating systems. Within the genus Grevillea, mating systems are potentially complex. They may vary among species and among populations within a species, reflecting variation in pollinator behaviour and diversity (‘potential’ mating systems) and in breeding system (the ‘preferred’ mating system). We used a combination of pollinator observations, pollination experiments and electrophoretic analysis of seed from open pollinations, to examine variation in potential and preferred mating systems in two populations of each of two ‘spider-flowered’ Grevillea species: G. mucronulata (visited by honeyeaters and honeybees, although only birds effected pollen removal and transfer) and G. sphacelata (visited only by honeybees, which made frequent contact with pollen and stigmas). Almost all observed bird and insect foraging bouts on eithe...
Australian Journal of Botany
In southern New South Wales, a suite of widespread plant species exhibit short-statured ‘dwarf’ g... more In southern New South Wales, a suite of widespread plant species exhibit short-statured ‘dwarf’ growth forms on coastal headlands. It is unclear whether such populations are genetically distinct or whether dwarfism is a plastic response to the environment. We used four microsatellite markers to assess genetic differentiation among populations from coastal and inland sites for Banksia spinulosa var. spinulosa. We sampled plants from six locations, including from three ‘dwarf’ and three ‘normal’ populations. Mean levels of genetic diversity were slightly higher in the forest (Na = 7.07 ± 0.25; He = 0.80 ± 0.09) than on the coast (Na = 5.92 ± 0.70; He = 0.72 ± 0.10). In general, populations displayed genotypic diversity expected for outcrossed sexual reproduction, with 161 of 172 individuals displaying unique genotypes and mean values of FIS close to zero. However, we found evidence of at least limited clonal replication in each of four populations and, within one coastal population, 1...
Molecular ecology, 2018
Many plant species have pollination and seed dispersal systems and evolutionary histories that ha... more Many plant species have pollination and seed dispersal systems and evolutionary histories that have produced strong genetic structuring. These genetic patterns may be consistent with expectations following recent anthropogenic fragmentation, making it difficult to detect fragmentation effects if no prefragmentation genetic data are available. We used microsatellite markers to investigate whether severe habitat fragmentation may have affected the structure and diversity of populations of the endangered Australian bird-pollinated shrub Grevillea caleyi R.Br., by comparing current patterns of genetic structure and diversity with those of the closely related G. longifolia R.Br. that has a similar life history but has not experienced anthropogenic fragmentation. Grevillea caleyi and G. longifolia showed similar and substantial population subdivision at all spatial levels (global F' = 0.615 and 0.454; S = 0.039 and 0.066), marked isolation by distance and large heterozygous deficien...
Ecology and evolution, Nov 1, 2017
Long-lived, widespread plant species are expected to be genetically diverse, reflecting the inter... more Long-lived, widespread plant species are expected to be genetically diverse, reflecting the interaction between large population sizes, overlapping generations, and gene flow. Such species are thought to be resilient to disturbance, but may carry an extinction debt due to reproductive failure. Genetic studies of Australian arid zone plant species suggest an unusually high frequency of asexuality, polyploidy, or both. A preliminary AFLP genetic study implied that the naturally fragmented arid zone tree, Acacia carneorum, is almost entirely dependent on asexual reproduction through suckering, and stands may have lacked genetic diversity and interconnection even prior to the onset of European pastoralism. Here we surveyed microsatellite genetic variation in 20 stands to test for variation in life histories and further assessed the conservation status of the species by comparing genetic diversity within protected stands in National Parks and disturbed range lands. Using herbarium record...
Molecular Ecology Notes
We developed eight primer pairs for Banksia microsatellite markers (five using DNA from Banksia o... more We developed eight primer pairs for Banksia microsatellite markers (five using DNA from Banksia oblongifolia and three from Banksia robur) in order to study the processes of speciation within hybridizing B. oblongifolia , B. robur and Banksia paludosa complex. We genotyped four populations of B. oblongifolia and B. robur , and three of B. paludosa. Numbers of alleles ranged from 1 to 13 across the three species and observed average heterozygosities ranged from 0.000 to 0.833. At least four loci completely discriminated B. robur from B. oblongifolia and three discriminated B. paludosa from B. oblongifolia. Seven of these primers amplified DNA from at least two of three other local species.
Plant Ecology
Populations of the mangrove Avicennia marina in the Sydney region exist as stands of varying size... more Populations of the mangrove Avicennia marina in the Sydney region exist as stands of varying size, reflecting both natural and anthropogenic fragmentation. We hypothesised that, as observed in many terrestrial forests, small stands (plants) would experience lower pollinator densities and altered pollinator behaviour and visitation and, in consequence, would display reduced pollen deposition as compared with large stands (>10,000 plants). Nevertheless, we recognise that such predictions may be overly simplistic because within this region A. marina attracts a diversity of flower visitors, but its only significant pollinator is the exotic honeybee Apis mellifera. Moreover, it is unclear how readily A. mellifera moves among groups of plants within different mangrove stands of varying sizes separated either by water or urban habitat matrix. Our detailed surveys within pairs of large and small stands in two locations support the predictions that pollinator density and pollen deposition are reduced or altered within small stands. Within small stands honeybee abundance and pollen deposition were on average reduced significantly by 84 and 61 %, respectively. Moreover, within small stands there was a non-significant 12 % increase in the mean time that honeybees spent foraging on individual plants and hence potentially depositing self pollen. Taken together, our data indicate that fragmentation affects the performance of A. mellifera as a pollinator of A. marina and reduce pollinator abundance, leading to pollen limitation in small as compared to large stands, which may negatively affect reproductive output.
Ecology, 2016
The production of morphologically different seeds or fruits by the same individual plant is known... more The production of morphologically different seeds or fruits by the same individual plant is known as seed heteromorphism. Such variation is expected to be selected for in disturbance-prone environments to allow germination into inherently variable regeneration niches. However, there are few demonstrations that heteromorphic seed characteristics should be favored by selection or how they may be maintained. In fire-prone ecosystems, seed heteromorphism is found in the temperatures needed to break physical dormancy, with seeds responding to high or low temperatures, ensuring emergence under variable fire-regime-related soil heating. Because of the relationship between dormancy-breaking temperature thresholds and fire severity, we hypothesize that different post-fire resource conditions have selected for covarying seedling traits, which contribute to maintenance of such heteromorphism. Seeds with low thresholds emerge into competitive conditions, either after low-severity fire or in vegetation gaps, and are therefore likely to experience selection for seedling characteristics that make them good competitors. On the other hand, high-temperature-threshold seeds would emerge into less competitive environments, indicative of stand-clearing high-severity fires, and would not experience the same selective forces. We identified high and low-threshold seed morphs via dormancy-breaking heat treatments and germination trials for two study species and compared seed mass and other morphological characteristics between morphs. We then grew seedlings from the two different morphs, with and without competition, and measured growth and biomass allocation as indicators of seedling performance. Seedlings from low-threshold seeds of both species performed better than their high-threshold counterparts, growing more quickly under competitive conditions, confirming that different performance can result from this seed characteristic. Seed mass or appearance did not differ between morphs, indicating that dormancy-breaking temperature threshold variation is a form of cryptic heteromorphism. The potential shown for the selective influence of different post-fire environmental conditions on seedling performance provides evidence of a mechanism for the maintenance of heteromorphic variation in dormancy-breaking temperature thresholds.
Evolution International Journal of Organic Evolution, Sep 30, 2000
Marine Biology, Jul 1, 2001
The genetic structure of six local collections of Pocillopora verrrucosa from six coral reefs in ... more The genetic structure of six local collections of Pocillopora verrrucosa from six coral reefs in KwaZulu-Natal, South Africa, was examined using allozyme electrophoresis. The six separate reefs lie within two dierent reef complexes. Twenty-two enzymes were screened on ®ve buer systems, but only ®ve polymorphic loci (Gpi-1, Gdh-1, Lgg-2, Lpp-1, Est-1) could be consistently resolved. No signi®cant dierences in allelic frequencies were detected among the six sites. All local collections were genotypically diverse, with evidence of only very limited clonal replication at each site. Indeed, the ratio of observed to expected genotypic diversity (mean Go:Ge=0.640.05 SD), the ratio of observed number of genotypes to the number of individuals (mean Ng:N=0.650.04 SE), and deviations from the Hardy± Weinberg equilibrium indicate that sexual reproduction plays a major role in the maintenance of the populations. No genetic dierentiation was found either within (FSR=0.0260.003 SE) or between (FRT=0.000 0.001 SE) reef complexes. The homogeneity of the gene frequencies across the six reefs strongly supports the assumption that the KwaZulu-Natal reef complexes are highly connected by gene¯ow (Nem=44). The reefs in the southern and central reef complexes along the northern Maputaland coastline can therefore be considered part of a single population.
Marine Ecology Progress Series, 1997
The widespread and morphologically variable coral Pocillopora damjcornis has been reported to exh... more The widespread and morphologically variable coral Pocillopora damjcornis has been reported to exhlbit huge variation in Me-history traits (e.g. inode of reproduction, growth rate, longevity and dispersal) both locally and regionally throughout the Indo-Pacific Ocean. Dispersal may b e achieved by the settlement of sexually or asexually generated brooded planula larvae, by broadcast spawning or more locally through asexual fragmentation of large colonies. In the present study, we conducted a hierarchical survey of allozyme variation within and among reef-crest sites on 3 mid-shelf reefs separated by up to 1200 km on the Great Barrier Reef (GBR), Australia. Our objective was to use allozyme data (1) to quantify local and reglonal patterns of varlatlon in P, damicornis (along the northeastern coast of Australia), (2) to determine the relative contr~bution of sexual versus asexual production of planulae in P damicornis, and (3) to estimate levels of gene flow among adlacent sites (>5 km apart) and among reefs separated by 500 to 1200 km. High levels of genotypic dlvers~ty in our samples of P. darn~cornis imply that dispersive propagules in this species are produced sexually rather than asexually along the length of the GBR. Corals a t all sites displayed the same level of multi-locus genotypic diversity expected for randomly mating, sexually derived populations, and the majority of individual colonies possessed unique 7-locus genotypes. We also detected consistent deficits of heterozygotes within each collection (from 3 local sites on each of the 3 widely spaced reefs). This pattern is consistent with the predicted effects of sexual reproduction associated with some localised dispersal of gametes or larvae (although other explanations cannot be excluded). Furthermore, each reef was genetically subdivided, suggesting that larval recruitment was localised and that these populations are slightly inbred: hierarchical analysis of the standardised genetic variances (FsT) (estimated as Weir & Cockerham's 0) revealed that, although there was only moderate variation among all 9 sites (FST = 0.055 t 0.029), more variation was found among sites within reefs (F,, = 0.035 * 0.04 to 0.088 2 0.033) than among distant reefs = 0.008 * 0.014) This homogeneity of gene frequencies across widely separated reefs lmplles that reefs are connected by high levels of gene flow (.V,~m = 31) and that local popu-lat~ons of P. damlcornls separated by >l000 km can interbreed sufficiently to maintain a consistent sulte of life-history characters.
Research on rare and threatened plants is a major focus of conservation biology. We want to know ... more Research on rare and threatened plants is a major focus of conservation biology. We want to know why species are rare or declining, how best to arrest that decline and what is lost when species become locally extinct. Occasionally, understanding decline is straightforward-eg if the species is restricted to fertile soils that are desirable for cultivation. However, managing declining populations is more complex and requires knowledge of genetic diversity and interspecific interactions.
Australian Journal of Marine and Freshwater Research, 1984
Within each of four Western Australian colonies of A. tenebrosa, adults developed gonads and broo... more Within each of four Western Australian colonies of A. tenebrosa, adults developed gonads and brooded asexually produced juveniles during the summer months. The brooded juveniles were released throughout the year but most settlement occurred in autumn and winter. Dispersal of brooded juveniles was highly localized and they typically settled within 2 m of adults. Adults were sedentary and long- lived and recruitment rates were extremely low (about 1% per annum during the study period). Adult size and asexual fecundity differed markedly between colonies over three breeding seasons, but between-colony comparisons revealed no simple relationship between those characteristics. The mean number of juveniles per adult varied up to ninefold between colonies. Sex ratios deviated significantly from a ratio of 1 : 1 in samples from three colonies, and males predominated in two of these. Density-manipulation experiments revealed that intraspecific competition affected adult size, sexual maturity, asexual fecundity and rates of settlement and recruitment.
International Journal of Plant Sciences, 2021
Premise of research. Worldwide, fire-sensitive shrubs have an important but underresearched life ... more Premise of research. Worldwide, fire-sensitive shrubs have an important but underresearched life history, and in Australia they are threatened by anthropogenic changes to fire regimes and habitat loss. Typically, adults are killed by fire, but they can also senesce and die if interfire intervals are prolonged. Populations can regenerate from seed banks displaying fire-stimulated germination; however, populations are ephemeral, and true population sizes and connectedness are difficult to estimate. Persoonia hirsuta ssp. evoluta is an endangered, inconspicuous, fire-sensitive shrub with a soil-stored seed bank currently known only from a small number of locations within the fire-prone Sydney Basin. Although it appears highly fragmented and populations are typically small, we predicted that its seed bank would buffer populations against loss of genetic diversity and population differentiation. Methodology. We used microsatellite markers to assess genetic variation within three aboveground populations of P. hirsuta separated by up to 25 km. The largest and most isolated population, at Appin, New South Wales, Australia, occurs on a mine site and may be subject to disturbance. We compared levels of genetic diversity and estimated the mating systems and genetic connectedness of plants within the three sites. Pivotal results. As predicted, all populations displayed similar genetic diversity, as judged by expected heterozygosity and allelic richness, and displayed little differentiation. All populations appear predominantly outcrossed. However, STRUCTURE and principal coordinates analyses showed that Appin individuals were distinct from those at the other locations. Conclusions. Our data imply that even for fire-sensitive species with few aboveground populations, genetic diversity can be maintained by the buffering effect of persistent seed banks with diversity reflecting historically greater interpopulation gene flow. While all P. hirsuta sites support comparable genetic diversity, the preservation of known populations is critical. Conservation efforts should include searches for additional populations, fire-stimulated germination of seed banks, and collection of seed for propagation in a nursery or direct sowing.
Oecologia, 2017
the importance of conserving the largest possible stands. However, additional work is needed to d... more the importance of conserving the largest possible stands. However, additional work is needed to determine (1) the proportion of recruits within small stands that originate within large stands, (2) how seedling performance varies with fruit size and genotype, and (3) how seedling size and performance vary with the abundance and diversity of pollen.
Geo: Geography and Environment, 2019
Research on rare and threatened plants is a major focus of conservation biology. We want to know ... more Research on rare and threatened plants is a major focus of conservation biology. We want to know why species are rare or declining, how best to arrest that decline and what is lost when species become locally extinct. Occasionally, understanding decline is straightforward - e.g. if the species is restricted to fertile soils that are desirable for cultivation. However, managing declining populations is more complex and requires knowledge of genetic diversity and interspecific interactions.
Biological Journal of the Linnean Society, 2015
Acacia loderi, the ecosystem engineer of the endangered Acacia loderi Shrublands in arid eastern ... more Acacia loderi, the ecosystem engineer of the endangered Acacia loderi Shrublands in arid eastern Australia, spans a persistent (> 15 000 year) but poorly studied landscape feature, the Darling River. We investigated the genetic structure of 19 stands of eight to > 1000 plants separated by < 300 km to test for variation in life histories between semi-arid and arid stands to the east and west of the Darling River, respectively. Eight of nine stands east of the Darling were exclusively sexual, whereas most of those to the west were clonal. Three western stands were monoclonal, two were polyploid, and one was a diverse mix of diploid and triploid phenotypes. Bayesian analysis revealed a complex genetic structure within the western stands, whereas the eastern stands formed only two genetic clusters. Conservation of small stands may require augmentation of genotypic diversity. However, most genotypic diversity resides within the eastern stands. Although arid zone stands of A. loderi are not always clonal, clonality and polyploidy are more common in the arid west. Clear demarcation of life histories either side of the Darling River may reflect ancient or contemporary effects of physical disturbance associated with the river channel, or cryptic environmental differences, with sexual and asexual reproduction, respectively, at a selective premium in the semi-arid east and arid west. The restricted distribution of clones and variation in clonality and polyploidy suggests that smaller stands may be vulnerable and warrant individual management.
Journal of Plant Ecology, 2016
Aims Worldwide, evidence suggests that exotic pollinators can disrupt plant mating patterns. Howe... more Aims Worldwide, evidence suggests that exotic pollinators can disrupt plant mating patterns. However, few studies have determined if pollination by the honeybee Apis mellifera (the world's most widely introduced pollinator) reduces offspring quality when compared with pollination by native birds. The Australian Proteaceae provides an excellent opportunity to test the impact of honeybees in pollination systems that are adapted to birds and non-flying mammals. Methods We compared the frequency of flower visitation and foraging behaviour of birds and insects within seven populations of Banksia ericifolia. Banksia ericifolia is hermaphroditic and has large nectar-rich, orange inflorescences typical of bird and mammal pollinated species. For a subset of the study populations, we compared the quality of seed produced via an exclusion treatment (that only allowed invertebrates to access flowers) with an open-pollination treatment (potentially visited by mammals, birds and invertebrates), by measuring seed weight, germination rates (T 50), percent germination, seedling height after 14 days since the emergence of the cotyledon and time to emergence of the cotyledon. Important Findings Apis mellifera was the only apparent insect pollinator and the most frequent flower visitor, while the open treatment inflorescences were also frequently visited by avian pollinators, primarily honeyeater species. The foraging behaviour of honeybees and honeyeaters showed striking differences that potentially affect patterns of pollen transfer. Honeybees made significantly greater proportions of within cf. among plant movements and only 30% (n = 48) of honeybees foraged for pollen (nectar foragers carried no pollen) whilst all birds were observed to contact both stigmas and anthers when foraging for nectar. Despite these fundamental differences in behaviour, there was little effect of treatment on seed set or quality. Our data show that while honeybees appear to alter patterns of pollen transfer within B. ericifolia populations, they do not impact reproductive rates or performance of early life-stages.
Australian Journal of Botany
Successful long-term conservation and management of populations of plants requires successful man... more Successful long-term conservation and management of populations of plants requires successful management of the suite of factors that determine their ‘realised’ mating systems. Within the genus Grevillea, mating systems are potentially complex. They may vary among species and among populations within a species, reflecting variation in pollinator behaviour and diversity (‘potential’ mating systems) and in breeding system (the ‘preferred’ mating system). We used a combination of pollinator observations, pollination experiments and electrophoretic analysis of seed from open pollinations, to examine variation in potential and preferred mating systems in two populations of each of two ‘spider-flowered’ Grevillea species: G. mucronulata (visited by honeyeaters and honeybees, although only birds effected pollen removal and transfer) and G. sphacelata (visited only by honeybees, which made frequent contact with pollen and stigmas). Almost all observed bird and insect foraging bouts on eithe...
Australian Journal of Botany
In southern New South Wales, a suite of widespread plant species exhibit short-statured ‘dwarf’ g... more In southern New South Wales, a suite of widespread plant species exhibit short-statured ‘dwarf’ growth forms on coastal headlands. It is unclear whether such populations are genetically distinct or whether dwarfism is a plastic response to the environment. We used four microsatellite markers to assess genetic differentiation among populations from coastal and inland sites for Banksia spinulosa var. spinulosa. We sampled plants from six locations, including from three ‘dwarf’ and three ‘normal’ populations. Mean levels of genetic diversity were slightly higher in the forest (Na = 7.07 ± 0.25; He = 0.80 ± 0.09) than on the coast (Na = 5.92 ± 0.70; He = 0.72 ± 0.10). In general, populations displayed genotypic diversity expected for outcrossed sexual reproduction, with 161 of 172 individuals displaying unique genotypes and mean values of FIS close to zero. However, we found evidence of at least limited clonal replication in each of four populations and, within one coastal population, 1...
Molecular ecology, 2018
Many plant species have pollination and seed dispersal systems and evolutionary histories that ha... more Many plant species have pollination and seed dispersal systems and evolutionary histories that have produced strong genetic structuring. These genetic patterns may be consistent with expectations following recent anthropogenic fragmentation, making it difficult to detect fragmentation effects if no prefragmentation genetic data are available. We used microsatellite markers to investigate whether severe habitat fragmentation may have affected the structure and diversity of populations of the endangered Australian bird-pollinated shrub Grevillea caleyi R.Br., by comparing current patterns of genetic structure and diversity with those of the closely related G. longifolia R.Br. that has a similar life history but has not experienced anthropogenic fragmentation. Grevillea caleyi and G. longifolia showed similar and substantial population subdivision at all spatial levels (global F' = 0.615 and 0.454; S = 0.039 and 0.066), marked isolation by distance and large heterozygous deficien...
Ecology and evolution, Nov 1, 2017
Long-lived, widespread plant species are expected to be genetically diverse, reflecting the inter... more Long-lived, widespread plant species are expected to be genetically diverse, reflecting the interaction between large population sizes, overlapping generations, and gene flow. Such species are thought to be resilient to disturbance, but may carry an extinction debt due to reproductive failure. Genetic studies of Australian arid zone plant species suggest an unusually high frequency of asexuality, polyploidy, or both. A preliminary AFLP genetic study implied that the naturally fragmented arid zone tree, Acacia carneorum, is almost entirely dependent on asexual reproduction through suckering, and stands may have lacked genetic diversity and interconnection even prior to the onset of European pastoralism. Here we surveyed microsatellite genetic variation in 20 stands to test for variation in life histories and further assessed the conservation status of the species by comparing genetic diversity within protected stands in National Parks and disturbed range lands. Using herbarium record...
Molecular Ecology Notes
We developed eight primer pairs for Banksia microsatellite markers (five using DNA from Banksia o... more We developed eight primer pairs for Banksia microsatellite markers (five using DNA from Banksia oblongifolia and three from Banksia robur) in order to study the processes of speciation within hybridizing B. oblongifolia , B. robur and Banksia paludosa complex. We genotyped four populations of B. oblongifolia and B. robur , and three of B. paludosa. Numbers of alleles ranged from 1 to 13 across the three species and observed average heterozygosities ranged from 0.000 to 0.833. At least four loci completely discriminated B. robur from B. oblongifolia and three discriminated B. paludosa from B. oblongifolia. Seven of these primers amplified DNA from at least two of three other local species.
Plant Ecology
Populations of the mangrove Avicennia marina in the Sydney region exist as stands of varying size... more Populations of the mangrove Avicennia marina in the Sydney region exist as stands of varying size, reflecting both natural and anthropogenic fragmentation. We hypothesised that, as observed in many terrestrial forests, small stands (plants) would experience lower pollinator densities and altered pollinator behaviour and visitation and, in consequence, would display reduced pollen deposition as compared with large stands (>10,000 plants). Nevertheless, we recognise that such predictions may be overly simplistic because within this region A. marina attracts a diversity of flower visitors, but its only significant pollinator is the exotic honeybee Apis mellifera. Moreover, it is unclear how readily A. mellifera moves among groups of plants within different mangrove stands of varying sizes separated either by water or urban habitat matrix. Our detailed surveys within pairs of large and small stands in two locations support the predictions that pollinator density and pollen deposition are reduced or altered within small stands. Within small stands honeybee abundance and pollen deposition were on average reduced significantly by 84 and 61 %, respectively. Moreover, within small stands there was a non-significant 12 % increase in the mean time that honeybees spent foraging on individual plants and hence potentially depositing self pollen. Taken together, our data indicate that fragmentation affects the performance of A. mellifera as a pollinator of A. marina and reduce pollinator abundance, leading to pollen limitation in small as compared to large stands, which may negatively affect reproductive output.
Ecology, 2016
The production of morphologically different seeds or fruits by the same individual plant is known... more The production of morphologically different seeds or fruits by the same individual plant is known as seed heteromorphism. Such variation is expected to be selected for in disturbance-prone environments to allow germination into inherently variable regeneration niches. However, there are few demonstrations that heteromorphic seed characteristics should be favored by selection or how they may be maintained. In fire-prone ecosystems, seed heteromorphism is found in the temperatures needed to break physical dormancy, with seeds responding to high or low temperatures, ensuring emergence under variable fire-regime-related soil heating. Because of the relationship between dormancy-breaking temperature thresholds and fire severity, we hypothesize that different post-fire resource conditions have selected for covarying seedling traits, which contribute to maintenance of such heteromorphism. Seeds with low thresholds emerge into competitive conditions, either after low-severity fire or in vegetation gaps, and are therefore likely to experience selection for seedling characteristics that make them good competitors. On the other hand, high-temperature-threshold seeds would emerge into less competitive environments, indicative of stand-clearing high-severity fires, and would not experience the same selective forces. We identified high and low-threshold seed morphs via dormancy-breaking heat treatments and germination trials for two study species and compared seed mass and other morphological characteristics between morphs. We then grew seedlings from the two different morphs, with and without competition, and measured growth and biomass allocation as indicators of seedling performance. Seedlings from low-threshold seeds of both species performed better than their high-threshold counterparts, growing more quickly under competitive conditions, confirming that different performance can result from this seed characteristic. Seed mass or appearance did not differ between morphs, indicating that dormancy-breaking temperature threshold variation is a form of cryptic heteromorphism. The potential shown for the selective influence of different post-fire environmental conditions on seedling performance provides evidence of a mechanism for the maintenance of heteromorphic variation in dormancy-breaking temperature thresholds.
Evolution International Journal of Organic Evolution, Sep 30, 2000
Marine Biology, Jul 1, 2001
The genetic structure of six local collections of Pocillopora verrrucosa from six coral reefs in ... more The genetic structure of six local collections of Pocillopora verrrucosa from six coral reefs in KwaZulu-Natal, South Africa, was examined using allozyme electrophoresis. The six separate reefs lie within two dierent reef complexes. Twenty-two enzymes were screened on ®ve buer systems, but only ®ve polymorphic loci (Gpi-1, Gdh-1, Lgg-2, Lpp-1, Est-1) could be consistently resolved. No signi®cant dierences in allelic frequencies were detected among the six sites. All local collections were genotypically diverse, with evidence of only very limited clonal replication at each site. Indeed, the ratio of observed to expected genotypic diversity (mean Go:Ge=0.640.05 SD), the ratio of observed number of genotypes to the number of individuals (mean Ng:N=0.650.04 SE), and deviations from the Hardy± Weinberg equilibrium indicate that sexual reproduction plays a major role in the maintenance of the populations. No genetic dierentiation was found either within (FSR=0.0260.003 SE) or between (FRT=0.000 0.001 SE) reef complexes. The homogeneity of the gene frequencies across the six reefs strongly supports the assumption that the KwaZulu-Natal reef complexes are highly connected by gene¯ow (Nem=44). The reefs in the southern and central reef complexes along the northern Maputaland coastline can therefore be considered part of a single population.
Marine Ecology Progress Series, 1997
The widespread and morphologically variable coral Pocillopora damjcornis has been reported to exh... more The widespread and morphologically variable coral Pocillopora damjcornis has been reported to exhlbit huge variation in Me-history traits (e.g. inode of reproduction, growth rate, longevity and dispersal) both locally and regionally throughout the Indo-Pacific Ocean. Dispersal may b e achieved by the settlement of sexually or asexually generated brooded planula larvae, by broadcast spawning or more locally through asexual fragmentation of large colonies. In the present study, we conducted a hierarchical survey of allozyme variation within and among reef-crest sites on 3 mid-shelf reefs separated by up to 1200 km on the Great Barrier Reef (GBR), Australia. Our objective was to use allozyme data (1) to quantify local and reglonal patterns of varlatlon in P, damicornis (along the northeastern coast of Australia), (2) to determine the relative contr~bution of sexual versus asexual production of planulae in P damicornis, and (3) to estimate levels of gene flow among adlacent sites (>5 km apart) and among reefs separated by 500 to 1200 km. High levels of genotypic dlvers~ty in our samples of P. darn~cornis imply that dispersive propagules in this species are produced sexually rather than asexually along the length of the GBR. Corals a t all sites displayed the same level of multi-locus genotypic diversity expected for randomly mating, sexually derived populations, and the majority of individual colonies possessed unique 7-locus genotypes. We also detected consistent deficits of heterozygotes within each collection (from 3 local sites on each of the 3 widely spaced reefs). This pattern is consistent with the predicted effects of sexual reproduction associated with some localised dispersal of gametes or larvae (although other explanations cannot be excluded). Furthermore, each reef was genetically subdivided, suggesting that larval recruitment was localised and that these populations are slightly inbred: hierarchical analysis of the standardised genetic variances (FsT) (estimated as Weir & Cockerham's 0) revealed that, although there was only moderate variation among all 9 sites (FST = 0.055 t 0.029), more variation was found among sites within reefs (F,, = 0.035 * 0.04 to 0.088 2 0.033) than among distant reefs = 0.008 * 0.014) This homogeneity of gene frequencies across widely separated reefs lmplles that reefs are connected by high levels of gene flow (.V,~m = 31) and that local popu-lat~ons of P. damlcornls separated by >l000 km can interbreed sufficiently to maintain a consistent sulte of life-history characters.
Research on rare and threatened plants is a major focus of conservation biology. We want to know ... more Research on rare and threatened plants is a major focus of conservation biology. We want to know why species are rare or declining, how best to arrest that decline and what is lost when species become locally extinct. Occasionally, understanding decline is straightforward-eg if the species is restricted to fertile soils that are desirable for cultivation. However, managing declining populations is more complex and requires knowledge of genetic diversity and interspecific interactions.
Australian Journal of Marine and Freshwater Research, 1984
Within each of four Western Australian colonies of A. tenebrosa, adults developed gonads and broo... more Within each of four Western Australian colonies of A. tenebrosa, adults developed gonads and brooded asexually produced juveniles during the summer months. The brooded juveniles were released throughout the year but most settlement occurred in autumn and winter. Dispersal of brooded juveniles was highly localized and they typically settled within 2 m of adults. Adults were sedentary and long- lived and recruitment rates were extremely low (about 1% per annum during the study period). Adult size and asexual fecundity differed markedly between colonies over three breeding seasons, but between-colony comparisons revealed no simple relationship between those characteristics. The mean number of juveniles per adult varied up to ninefold between colonies. Sex ratios deviated significantly from a ratio of 1 : 1 in samples from three colonies, and males predominated in two of these. Density-manipulation experiments revealed that intraspecific competition affected adult size, sexual maturity, asexual fecundity and rates of settlement and recruitment.