Novo: The role of genetic variability and phenotypic plasticity in the invasiveness of Acacia longifolia Antigo: A global molecular and ecological study of the invasive species Acacia Iongifolia.

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From canopy to single flowers: a downscale approach to flowering of the invasive species Acacia longifolia

Publication . Vicente, Sara; Giovanetti, Manuela; Trindade, Helena; Máguas, C.

Context: Acacia longifolia is a native legume of south-eastern Australia and Tasmania and is invasive in many parts of the world. A key feature to its success is the production of a high quantity of flowers every season, resulting in a massive seedbank that remains dormant in the soil for decades. Many studies have been performed on this species’ reproductive biology, but none has focused on flowering in detail. Aims: Our main objective was to understand this species’ resource allocation strategy that ensures its successful reproduction in the invasive range. Methods: We developed an integrative approach, assessing flowering at different levels, namely, canopy and branch flowering (macro scale), downscaling to individual flower functional stages and their duration, pollen longevity and stigma receptivity (micro scale). We performed this study in three different locations in sand dunes along the Portuguese coast with different environmental conditions. Key results: Canopy flowering shows no difference among sites. Pollen and stigma assessment showed that this species is protogynous, with the stigma being highly receptive long before pollen is released. Once released, pollen lasts roughly 72 h. Individual flowers are relatively short-lived, with a rapid progression from closed flower buds to fully open flowers. Implications: Our results indicated that A. longifolia has a resource trade-off strategy of investing in flowers and pollen that are relatively short-lived, which are counterbalanced by their massive quantities.

2022-12-01Journal article

Open access

Highly diverse and highly successful: invasive Australian acacias have not experienced genetic bottlenecks globally

Publication . Vicente, Sara; Máguas, C.; Richardson, David M.; Trindade, Helena; Wilson, John R. U.; Le Roux, Johannes J.

Background and Aims Invasive species may undergo rapid evolution despite very limited standing genetic diversity. This so-called genetic paradox of biological invasions assumes that an invasive species has experienced (and survived) a genetic bottleneck and then underwent local adaptation in the new range. In this study, we test how often Australian acacias (genus Acacia), one of the world’s worst invasive tree groups, have experienced genetic bottlenecks and inbreeding. Methods We collated genetic data from 51 different genetic studies on Acacia species to compare genetic diversity between native and invasive populations. These studies analysed 37 different Acacia species, with genetic data from the invasive ranges of 11 species, and data from the native range for 36 species (14 of these 36 species are known to be invasive somewhere in the world, and the other 22 are not known to be invasive). Key Results Levels of genetic diversity are similar in native and invasive populations, and there is little evidence of invasive acacia populations being extensively inbred. Levels of genetic diversity in native range populations also did not differ significantly between species that have and that do not have invasive populations.

2021-04-20Journal article

Open access

The role of genetic variability and phenotypic plasticity in the invasiveness of Acacia longifólia

Publication . Vicente, Sara; Le Roux, Johannes; Donato, Maria Helena Machado Trindade de; Hanson, Cristina Maria Filipe Máguas da Silva

Acacia longifolia is a leguminous species native to Southeast Australia and Tasmania. The species was introduced outside Australia and is particularly invasive in Mediterranean-climate regions. Acacia longifolia has two described subspecies – ssp. longifolia and ssp. sophorae – recognized based on differences in morphology and distribution. The invasiveness of A. longifolia has been linked to its prolific seed production leading to the formation of long-lasting seed banks and its capacity to establish symbioses with nitrogen-fixing rhizobia. The population genetic diversity and structure of native and invasive populations of A. longifolia, the identification of native sources of invasive populations, and the contribution of genetic diversity and phenotypic plasticity to the species’ invasiveness are understudied. Moreover, molecular support for the taxonomic classification of the two subspecies of A. longifolia is needed to assist effective management of invasive populations. Therefore, the major objectives of this thesis were to: 1) provide insights into the introduction histories of Australian acacias around the world and their resulting genetic consequences; 2) understand the worldwide invasive history, genetic diversity, and population genetic structure of A. longifolia; 3) test whether population genetics support the classification of A. longifolia as two subspecies; 4) clarify the roles of genetic diversity and phenotypic plasticity in the invasiveness of A. longifolia; and 5) provide more detail on the species’ flower development and reproductive success, and how these are influenced by environmental conditions. To accomplish these aims, various species of Australian acacias and their introduction histories outside of Australia were included in a meta-analysis. Results revealed that acacias generally have not experienced genetic bottlenecks or increased inbreeding upon introduction. The population genetic analysis of A. longifolia followed this general observation, making the identification of native sources of invasive populations challenging. Moreover, the native range population structure of A. longifolia is determined by geographic features and not subspecies identity. This was further supported by Species Distribution Models based on bioclimatic niche variables and a common garden experiment subjecting seedlings of both subspecies to different levels of water and nutrient availability. Rather, in its native range, the species consists of two genetic clusters, corresponding to mainland Australia and Tasmania, while the invasive range lacks genetic structure, yet has similar levels of diversity to native range population. Carbon and nitrogen isotope fractionation of A. longifolia phyllodes, which are tracers of plant-environment interactions, indicated different strategies of resource acquisition and conservation. The common garden experiment also revealed that invasive A. longifolia seedlings have more limited responses to stress than native seedlings. The study of the species’ flowering showed a resource trade-off of “quantity over quality”, independent of environmental conditions: the large number of flowers and amount of pollen produced are counterbalanced by their short functional periods and extended receptivity of the stigma for reproductive assurance. In conclusion, the extensive human-mediated introduction of A. longifolia has significantly shaped the species population genetic diversity and structure making it difficult to identify the native sources of invasive populations. Such information is crucial for management strategies, as well as risk assessment and impact prediction.

2022-10Doctoral thesis

Open access

The role of genetic variability and phenotypic plasticity in the invasiveness of Acacia longifólia

Publication . Vicente, Sara; Le Roux, Johannes; Donato, Maria Helena Machado Trindade de; Hanson, Cristina Maria Filipe Máguas da Silva

Acacia longifolia is a leguminous species native to Southeast Australia and Tasmania. The species was introduced outside Australia and is particularly invasive in Mediterranean-climate regions. Acacia longifolia has two described subspecies – ssp. longifolia and ssp. sophorae – recognized based on differences in morphology and distribution. The invasiveness of A. longifolia has been linked to its prolific seed production leading to the formation of long-lasting seed banks and its capacity to establish symbioses with nitrogen-fixing rhizobia. The population genetic diversity and structure of native and invasive populations of A. longifolia, the identification of native sources of invasive populations, and the contribution of genetic diversity and phenotypic plasticity to the species’ invasiveness are understudied. Moreover, molecular support for the taxonomic classification of the two subspecies of A. longifolia is needed to assist effective management of invasive populations. Therefore, the major objectives of this thesis were to: 1) provide insights into the introduction histories of Australian acacias around the world and their resulting genetic consequences; 2) understand the worldwide invasive history, genetic diversity, and population genetic structure of A. longifolia; 3) test whether population genetics support the classification of A. longifolia as two subspecies; 4) clarify the roles of genetic diversity and phenotypic plasticity in the invasiveness of A. longifolia; and 5) provide more detail on the species’ flower development and reproductive success, and how these are influenced by environmental conditions. To accomplish these aims, various species of Australian acacias and their introduction histories outside of Australia were included in a meta-analysis. Results revealed that acacias generally have not experienced genetic bottlenecks or increased inbreeding upon introduction. The population genetic analysis of A. longifolia followed this general observation, making the identification of native sources of invasive populations challenging. Moreover, the native range population structure of A. longifolia is determined by geographic features and not subspecies identity. This was further supported by Species Distribution Models based on bioclimatic niche variables and a common garden experiment subjecting seedlings of both subspecies to different levels of water and nutrient availability. Rather, in its native range, the species consists of two genetic clusters, corresponding to mainland Australia and Tasmania, while the invasive range lacks genetic structure, yet has similar levels of diversity to native range population. Carbon and nitrogen isotope fractionation of A. longifolia phyllodes, which are tracers of plant-environment interactions, indicated different strategies of resource acquisition and conservation. The common garden experiment also revealed that invasive A. longifolia seedlings have more limited responses to stress than native seedlings. The study of the species’ flowering showed a resource trade-off of “quantity over quality”, independent of environmental conditions: the large number of flowers and amount of pollen produced are counterbalanced by their short functional periods and extended receptivity of the stigma for reproductive assurance. In conclusion, the extensive human-mediated introduction of A. longifolia has significantly shaped the species population genetic diversity and structure making it difficult to identify the native sources of invasive populations. Such information is crucial for management strategies, as well as risk assessment and impact prediction.

2022-10Doctoral thesis

Open access