DST-NRF Centre of Excellence for Invasion Biology

We modelled the present and future sub-Saharan winter distributions of 64 trans-Saharan migrant passerines to predict the potential impacts of climate change. These predictions used the recent ensemble modelling developments and the latest IPCC climatic simulations to account for possible methodological uncertainties. Results suggest that 37 species would face a range reduction by 2100 (16 of these by more than 50%); however, the median range size variation is -13 per cent (from -97 to +980%) under a full dispersal hypothesis. Range centroids were predicted to shift by 500+/-373 km. Predicted changes in range size and location were spatially structured, with species that winter in southern and eastern Africa facing larger range contractions and shifts. Predicted changes in regional species richness for these long-distance migrants are increases just south of the Sahara and on the Arabian Peninsula and major decreases in southern and eastern Africa.

The Cape bee (Apis mellifera capensis) is unique among honeybees in that workers can lay eggs that instead of developing into males develop into females via thelytokous parthenogenesis. We show that this ability allows workers to compete directly with the queen over the production of new queens. Genetic analyses using microsatellites revealed that 23 out of 39 new queens produced by seven colonies were offspring of workers and not the resident queen. Of these, eight were laid by resident workers, but the majority were offspring of parasitic workers from other colonies. The parasites were derived from several clonal lineages that entered the colonies and successfully targeted queen cells for parasitism. Hence, these parasitic workers had the potential to become genetically reincarnated as queens. Of the daughter queens laid by the resident queen, three were produced asexually, suggesting that queens can 'choose' to produce daughter queens clonally and thus have the potential for genetic immortality.

Although the impacts of climate change and invasive species are typically studied in isolation, they likely interact to reduce the viability of plant and animal populations. Indeed, invasive species, by definition, have succeeded in areas outside of their native range and may therefore have higher adaptive capacity relative to native species. Nevertheless, the genetic architecture of the thermal niche, which sets a limit to the potential for populations to evolve rapidly under climate change, has never been measured in an invasive species in its introduced range. Here, we estimate the genetic architecture of thermal performance in the harlequin beetle (Harmonia axyridis), a Central Asian species that has invaded four continents. We measured thermal performance curves in more than 400 third-generation offspring from a paternal half-sib breeding experiment and analyzed the genetic variance-covariance matrix. We show that while the critical thermal limits in this species have an additive genetic basis, most components of the thermal performance curve have low heritability. Moreover, we found evidence that genetic correlations may constrain the evolution of beetles under climate change. Our results suggest that some invasive species may have limited evolutionary capacity under climate change, despite their initial success in colonizing novel environments.

This study, investigated the salt excretion efficiency and the level of the physiological response to salt-induced stresses between the native and exotic Tamarix species as well as their hybrids (Tamarix chinensis × Tamarix ramosissima and Tamarix chinensis × Tamarix usneoides). Ten potted plants from each of the five taxa were exposed to salt at a concentration of 3% (w/w) (180 mM) for 3 weeks. Measurements of electro-conductivity (EC), physiological parameters such as stomatal conductance, chlorophyll fluorescence, and water pressure and plant growth were taken from salt-treated and control plants. The EC in the exotic T. chinensis significantly increased by >30% compared with all other Tamarix taxa, suggesting that it is the most effective taxon for phytoremediation. Although there was no significant difference in plant growth between T. chinensis and T. usneoides, they both showed a significantly greater plant growth than the other taxa. However, the plant physiological parameters indicated that T. usneoides was less stressed by the salt exposure than the T. chinensis and the others. Thus, considering the T. usneoides greater tolerance to salt-induced and/water stresses and the strict environmental regulations of planting exotic Tamarix, the native Tamarix remains the preferred plant of choice for phytoremediation in South Africa.

Invasive alien plants are considered as a major threat to many ecological and socio-economic systems. Nevertheless, the management of some of these plants is often controversial due to the positive socio-economic and ecosystem roles they play. This necessitates proper mapping and monitoring of the extent and spatial distribution of such plants to prioritize resource allocation and management. However, mapping plant species using remote sensing in a heterogeneous environment such as an urban area is often challenged by high levels of spectral muddle. This study investigated the utility of the high and medium spectral and spatial resolution imageries from the WorldView-2 (WV-2) and SPOT-7 satellites, respectively, to map eucalypts trees in urban areas. Furthermore, the classification performances of Random Forest (RF) and Support Vector Machines (SVM) were compared. Both WV-2 and SPOT-7 imageries attained overall accuracies of 81.67% (0.78 kappa) and 72.78% (0.67 kappa), respectively, when the RF algorithm was used and 80% (0.76 Kappa) and 71.11% (0.65 Kappa), respectively when SVM algorithm was used. The user’s accuracies for the eucalypts class in both WV-2 and SPOT 7 imageries were 73.33% and 60%, respectively, for the RF and 70% and 56.67% for the SVM algorithm, respectively. Thus, WV-2 imagery is more suitable for mapping eucalypts trees in a heterogeneous urban environment. Therefore, the classification of WV-2 imageries using RF produced a relatively more accurate map of the eucalypts trees for the study areas, the southern part of Johannesburg city.

Invasive alien species are routinely moved around the world as horticultural specimens. An additional route through the traditional medicine trade may exist, especially where cultures from different continents coalesce. South African traditional medicine, for example, has a long history of association with its Indian Ayurvedic equivalent via migration of people from the sub-continent as either slaves or indentured labour. This study investigated the occurrence and viability of alien species in South African traditional medicine markets and shops. Forty-two species of alien plants were found, of which 26 species were propagules and 22 were viable. Seven of the viable species are listed as invasive in South Africa. However, all but one of the 22 species that were tested and identified are known to be invasive somewhere in the world. Most of the viable alien species were sold as seeds, seedpods or nuts (64%, n = 14 of 22 species) from Indian-owned shops, while mainly tubers, stems and rhizomes were found in African-run markets. Alien plant species moving within this trade route have circumvented all dispersal barriers and may have exerted propagule pressure over at least a century, and should therefore be considered as candidates for monitoring.

Abstract Freshwater fish are in decline worldwide as a result of introduced non‐native species, impoundment, water quality changes, over‐abstraction, and climate change. The Clanwilliam sandfish Labeo seeberi is an endangered migratory cyprinid endemic to a single river system in South Africa's Cape Fold Ecoregion. It has declined across its range and persists as fragmented populations in the Doring River system. One of the last recruiting populations occurs in the Oorlogskloof River, where three non‐native fish species are present: smallmouth bass Micropterus dolomieu , bluegill sunfish Lepomis macrochirus (both alien and invasive), and banded tilapia Tilapia sparrmanii (extralimital). Impacts of these non‐natives, together with climate change, may pose a serious threat to this important sandfish population and to other cohabiting native fish species. A 6 year data set, collected over 9 years and spanning 25 km of the Oorlogskloof River, was analysed to characterize spatio‐temporal variation in sandfish abundance and size structure and to evaluate the relative impacts of biotic and abiotic factors on population trends. Sandfish experienced a 92.6% decline in relative abundance from 2013 to 2018, driven by a 99.6% decline in young‐of‐the‐year individuals. A combination of extreme rainfall events and drought appear to have played a key role in the decline and subsequently prevented recovery. Small sandfish (≤200 mm) were almost entirely absent from the centrarchid‐invaded section of the Oorlogskloof but were relatively abundant where these centrarchids were absent, suggesting a strong adverse impact of these non‐native species. Banded tilapia co‐occurred with sandfish without any apparent adverse impacts on the relative abundance or size structure of sandfish. Improved water resource management and preventing the further spread of non‐natives must be conservation priorities. Localized eradication of non‐native species must also be considered to reclaim habitat and restore connectivity. Translocations may be required to prevent species extinctions.

Stress in animals has been linked to behavioural and physiological changes in response to environmental, social and anthropogenic stimuli. Hence, stress-related responses in animals, especially in rodents, have been used as biological indicators of ecosystem health. This study aimed to establish an enzyme immunoassay (EIA) for monitoring adrenocortical activity in free-ranging Namaqua rock mice Micaelamys namaquensis (Rodentia: Muridae) using faeces as a prerequisite for assessing the effects of anthropogenic land use and season on faecal glucocorticoid metabolite (fGCM) concentration. Rodents were live-trapped seasonally across four land use types: an agricultural crop farm, an agricultural livestock farm, a human-populated site and a nature reserve; all situated in Limpopo Province, South Africa. Determined fGCM concentrations from capture and recapture events were used for biologically validating an EIA detecting steroids with a 5α-3β-11β-diol structure. Recapturing resulted in a significant overall 40% elevation of individual fGCM concentrations demonstrating the effectiveness of the chosen EIA to reliably detect glucocorticoid output in the study species. Neither land use type nor season affected fGCM concentrations in the species, suggesting that land use and season-related environmental changes do not necessarily act as stressors for M. namaquensis, presumably due to their adaptive and resilient nature. Such species can be used to identify ecosystems affected by human-mediated disturbances and allow insights into the management and restoration of these threatened ecosystems and their associated species.

The South African Working for Water (WfW) programme is a short-term public works programme (PWP) focused on clearing invasive alien plants, while training and empowering the marginalised poor to find employment. Furthermore, it aims to develop independent, entrepreneurial contractors who should ‘exit’ from the programme into the broader labour market. However, evidence indicates that many beneficiaries have become financially dependent on this employment, and find it difficult to search for alternatives. Understanding the reasons for this dependence from the perspective of the beneficiaries of this PWP is crucial to align such projects to the actual needs of the beneficiaries, but these have not yet been considered from a sociological perspective. This article reports on data collected, through face-to-face interviews, on WfW beneficiaries’ aspirations to permanent employment in four projects in the Winelands and Overberg districts of the Western Cape. It presents the novel finding that the social structures within projects themselves seem to create a need to remain in the WfW programme. In addition, a misalignment between these projects’ implementation and beneficiaries’ aspirations to financial stability (associated with permanent employment in WfW) is highlighted. The authors argue that WfW should respond to these aspirations, rather than pursue the ostensibly unrealistic aim of creating independent entrepreneurs. Finally, the implications of these findings for PWPs globally, and their concerns regarding the inadvertent creation of beneficiary dependence, are outlined.

The degree of maxillary molar tooth-row eruption and wear were used to assign samples of the social giant mole-rat, Fukomys mechowii, from Zambia, into nine relative age classes in order to assess ontogenetic (age) variation and craniometric sexual dimorphism, with reference to body mass. Univariate and multivariate statistical analyses showed craniometric differences between age classes 1–3 and age classes 5–9, with age class 4 being intermediate between these two age class groupings. This suggests that age class 4 lies at a point on a hypothetical growth curve where growth begins to stabilize. The intermediate placement of age class 4 in multivariate space broadly coincided with body mass categorizations into juveniles (age classes 1–3; <100 g), subadults (age class 4; c. 100–150 g), and adults (age classes 5–9; >150 g). The analyses also revealed the absence of sexual dimorphism in the relatively younger age classes 1–4 but its presence in the relatively older age classes 5–9, and these results are supported by data on body mass. These results may have implications in our understanding of the population and social structures, and reproductive strategies in this little-studied giant mole-rat.

Abstract The management of bio‐invasions relies upon the development of methods to trace their origin and expansion. Cointroduced parasites, especially monogenean flatworms, are ideal tags for the movement of their hosts due to their short generations, direct life cycles and host specificity. However, they are yet to be applied to trace the intraspecific movement of host lineages in their native ranges. As proof of this concept, we conducted a comparative phylogeographic analysis based upon two mitochondrial markers of a globally invasive frog Xenopus laevis and its monogenean parasite Protopolystoma xenopodis in its native range in southern Africa and invasive range in Europe. Translocation of lineages was largely masked in the frog's phylogeography. However, incongruent links between host and parasite phylogeography indicated host switches from one host lineage to another after these were brought into contact in the native range. Thus, past translocation of host lineages is revealed by the invasion success of its cointroduced parasite lineage. This study demonstrates that parasite data can serve as an independent line of evidence in invasion biology, also on the intraspecific level, shedding light on previously undetected invasion dynamics. Based upon the distribution of these invasive parasite lineages, we infer that there is widespread anthropogenic translocation of this frog, not only via official export routes, but also facilitated by the frog's use as live bait by angling communities. Synthesis and applications . Data from cointroduced, host‐specific parasites, as tags for translocation, can add value to investigations in invasion biology and conservation. A better understanding of the translocation history and resulting genetic mixing of host and parasite lineages in the native range can shed light on the genetic make‐up of parasite assemblages cointroduced to the invasive range. Knowledge of the intraspecific movement of different lineages of animals in their native ranges also has conservation implications, since contact between divergent lineages of hosts and parasites can facilitate host switches and altered parasite dynamics in both native and invasive populations. Therefore, we recommend the inclusion of parasite data as a more holistic approach to the invasion ecology of animals on the intraspecific level.

This laboratory-based study sought to determine the efficacy of using carbofuran in an exclusion experiment aimed at assessing the impacts of biocontrol agents on Lantana camara L. (sensu lato) (Verbenaceae). Two separate experiments were conducted, the first one on insect-free plants, to determine the effects of carbofuran solely on plant growth; and the second one, on Teleonemia scrupulosa Stål (Hemiptera: Tingidae) infested plants, with the objective of determining the impact of carbofuran on this biocontrol agent, as well as its impacts on plant growth. Carbofuran granules (10% a.i.) were applied at 7 g/m2 a.i. to the potting medium. It was found that carbofuran did not have a significant effect on plant growth. Total removal of T. scrupulosa from exclusion plants (carbofuran-treated plants) was not achieved; however the low level of leaf feeding lesions on those plants indicated that carbofuran had considerably reduced the insect’s population density. Results from a bioassay showed 100% and 40% T. scrupulosa mortality on leaves collected from carbofuran-treated and control plants, respectively, within three weeks of exposure. Analysis of chemical residue levels in the leaf material revealed that carbofuran potency only persisted for about three weeks, and was detectable at trace levels (<0.1 mg/kg). It was therefore concluded that carbofuran was effective at reducing the population of T. scrupulosa on its host plant, but only briefly. Carbofuran should be applied at least once every three weeks or at a higher dosage in order to maintain a low insect population for the duration of an experiment or to achieve total exclusion. For better insect removal, one should consider combining carbofuran and foliar insecticides.

This dataset is a an inventory of 475 alien plant taxa (447 identified to species), including a photo-guide to 96 plants, mostly sold as traditional medicines in three South African cities by traders of South African, West African, East African, Indian and Chinese origin (Williams et al., 2021). The dataset also incorporates species documented in a literature survey of alien plants used for traditional medicines in South Africa. The species inventory is a consolidation of the data from two separate investigations of 106 medicinal plant traders: firstly, a study conducted in 2010/2011 of 77 traders in markets and shops in Johannesburg, Pretoria and Durban (Williams et al., 2021); and secondly, a study conducted in 2017/2018 of plants sold by 29 (im)migrant traders of West African, East African, and Indian origin in Johannesburg, and of alien species listed in a TCM (Traditional Chinese Medicine) catalogue (Burness, 2019). Accompanying each plant photograph in the photo-guide is the following information: species name; common name(s) provided by the survey respondents; invasive alien plant category; introduction status; voucher specimen number(s); nationality of the medicine traders; and, notes on source localities (e.g. imported or collected in southern Africa). Overall, most of the taxa were from the Asteraceae (12%), Fabaceae (9%) and Poaceae (5%). The species are mostly unlisted (76%) with respect to their legal status in South Africa in terms of the National Environmental Management: Biodiversity Act (NEM:BA), 2004 Alien & Invasive Species (A&IS) regulations. The most frequently recorded species in the various surveys were Glycyrrhiza glabra, Acorus calamus, Angelica sinensis and Zingiber officinale.

Abstract An evaluation of genetic structuring and morphometric variation within tusked king crickets, Libanasidus vittatus (Kirby, 1899), from South Africa suggests two main population assemblages. Maximum likelihood (ML), Parsimony, Bayesian and phenetic analyses of mitochondrial cytochrome oxidase I (COI) sequence data recovered two well-supported clades corresponding to two biogeographically distinct populations. Canonical variates (discriminant) analysis (CVA) also showed evidence of two phenetic assemblages that correspond to the genetically delineated groups. Libanasidus vittatus is the recognized species occurring within an eastern population in South Africa (Mpumalanga and Eastern Cape Provinces), while a possible novel species occurs within a north–western population in South Africa (Limpopo and Gauteng Provinces). Using a molecular clock estimate of 2.0% divergence per million years, suggests isolation of the two populations at approx. 1.65 million years ago, possibly due to the formation of isolating forest pockets during the dry Pleistocene Epoch. The average genetic divergence of 3.3% between the two populations, and low migration rate estimates corresponding to less than one female migration per generation further support the presence of two cryptic tusked king cricket species in South Africa.

Abstract Freshwater ecosystems are the most threatened on Earth, with many species facing extinction. The Clanwilliam sandfish ( Labeo seeberi ) is South Africa's most threatened migratory freshwater fish and is endemic to the Olifants–Doring River system in the Cape Fold Ecoregion. Non‐native fish predation and river desiccation have caused a recruitment bottleneck, severely compromising juvenile survival and resulting in a declining population of aging sandfish. The Saving Sandfish Project launched an emergency head‐start intervention in 2020 to reduce extinction risk. We (1) rescued juvenile sandfish from drying pools in a key spawning tributary (the Biedouw River); (2) relocated them to 6 off‐stream reservoirs; and (3) released reservoir‐reared sandfish back into their natal river once large enough to evade non‐native fish predation. Here, we estimate survival in the reservoir environment, evaluate return rates relative to wild run size, and assess the probability of return based on conditions at release. Between 2020 and 2022, we stocked 33,391 juvenile sandfish into the 6 reservoirs. After 1 year, the estimated survival rate at one reservoir was 0.679 (range based on 95% CI: 0.385–0.973). Release and return results are presented only for the first (2020) rescue cohort. In 2021, we released 1277 sandfish from 2 reservoirs into the Biedouw River, comprising 16.6% of the 2020 rescue cohort. Mean size at release was 169 mm (SE 0.6) total length. Of those released, 994 were PIT‐tagged. A total of 77 PIT‐tagged sandfish were recorded during the 2022 spawning migration—a return rate of 7.7% of tagged releases in the first year of returns. Size of fish and distance from the Doring River at release were significant predictors of return probability, with larger fish released further from the Doring experiencing a higher probability of return. This program serves as a model for the conservation of freshwater fish where there is an imminent and high risk of extinction.

South Africa is home to a native Tamarix species, while two were introduced in the early 1900s to mitigate the effects of mining on soil. The introduced species have spread to other ecosystems resulting in ecological deteriorations. The problem is compounded by hybridization of the species making identification between the native and exotic species difficult. This study investigated the potential of remote sensing in identifying native, non-native and hybrid Tamarix species recorded in South Africa. Leaf- and canopy-level classifications of the species were conducted using field spectroradiometer data that provided two inputs: original hyperspectral data and bands simulated according to Landsat-8, Sentinel-2, SPOT-6 and WorldView-3. The original hyperspectral data yielded high accuracies for leaf- and plot-level discriminations (>90%), while promising accuracies were also obtained using Landsat-8, Sentinel-2 and Worldview-3 simulations (>75%). These findings encourage for investigating the performance of actual space-borne multispectral data in classifying the species.

ABSTRACT The African Clawed Frog Xenopus laevis , a global invader, exhibits marked phylogeographic divergence among native populations in southern Africa, which enhances its invasive potential. The polystomatid flatworm Protopolystoma xenopodis , as the frog’s most frequently co-introduced metazoan parasite, may be the ideal biological tag for the frog’s movement, if corresponding divergence can be demonstrated. In an integrative approach, we utilised morphometrics and molecular markers to assess divergence in P. xenopodis in its native range. We measured twelve key morphological characters from 23 flatworms and compared these statistically between flatworms collected to the north and south of the Great Escarpment Mountain Range in South Africa. Phylogenetic analyses were based on three concatenated markers, namely 28S and 12S rDNA and COX1 , from six flatworms. The combination of five morphological characters, which involve egg size, gut morphology and size of the attachment hooks, differentiated northern and southern populations of P. xenopodis in South Africa. The multilocus phylogenetic analyses supported these findings, showing a well-supported cluster of northern P. xenopodis . These findings suggest that taxonomic studies of polystomatid flatworms should make use of geographically representative data sets that consider both morphological and molecular evidence. Moreover, the findings demonstrate that the frog host and flatworm parasite exhibit corresponding phylogeographic structuring in the native range. Consequently, the phylogeography of P. xenopodis , both in the native and invasive range of its host, may act as a key piece of evidence to reconstruct past invasion pathways of X. laevis .

The combined impact of biocontrol agents on the seed regenerative capacity, i.e. seed production, seed-rain, soil seedbank, seed germination and seedling density, of Lantana camara L. (sensu lato) (Verbenaceae), was measured in the field in an inland area of South Africa. The study was conducted on 10 plots (20 × 50 m each) along part of the Sabie River catchment. The most prevalent biocontrol agents at the site were Aceria lantanae (Cook) (Acari: Trombidiformes: Eriophyidae), Hypena laceratalis Walker (Lepidoptera: Noctuidae), Octotoma scabripennis Guérin-Méneville (Coleoptera: Chrysomelidae), Ophiomyia camarae Spencer (Diptera: Agromyzidae) and Teleonemia scrupulosa Stål (Hemiptera: Tingidae). Using the insecticidal exclusion method, comparisons of seed regenerative capacity were made between exclusion (insecticide treated) and biocontrol (untreated) plants over a three-year period. Lantana camara seed production per plant was slightly lower in biocontrol (5831 ± 844 seeds) compared to exclusion plants (6718 ± 1571 seeds), seed-rain density was significantly lower in biocontrol (1080 ± 122 seeds m−2) compared to exclusion plants (1419 ± 154 seeds m−2). Seed germination was lower in biocontrol (98 ± 41 seeds m−2) compared to exclusion plants (116 ± 38 seeds m−2). Seedling density was higher in biocontrol (36 ± 14 seedlings m−2) compared to exclusion plants (32 ± 11 seedlings m−2). Adult plants appeared to suppress their own seedlings. This study showed that the impact of the current suite of biocontrol agents on the recruitment potential of L. camara is minimal, emphasising the need for additional agents, better adapted to the cooler high altitude inland environmental conditions.

ABSTRACT Troglobiont species show common traits derived from adaptation to subterranean life. Due to lack of light in cave environments most troglobiont species show eye reduction or even loss, often accompanied by a disruption of diel rhythmicity. Although cave adaptation and eye absence generally imply the loss of capability to perceive light, several cave‐adapted species have retained this function, showing some degree of phototaxy or rhythmicity. Flatworms are ubiquitous in natural habitats and the response to light or diel rhythmicity of surface‐dwelling species has received considerable scientific attention in the past and is increasingly studied. Conversely, responses to light stimuli have been poorly investigated in eyeless troglobiont flatworms. Here we coupled field monitoring and behavioural experiments to investigate phototactic responses and variation in diel activity patterns in the troglobiont eyeless flatworm Dendrocoelum italicum . We tested 27 D. italicum individuals from ‘Bus del Budrio’ cave, measuring their response to light stimuli in a semi‐obscured experimental arena under different light‐exposure treatments: dim light, bright light and darkness. Besides, during a 2‐year period we conducted 18 visual‐count surveys to monitor daytime and nighttime flatworm abundance in the cave. Behavioural tests showed that flatworms selected the darker side of the arena under both bright and dim light exposure, revealing a marked negative phototaxis. Field surveys revealed that flatworm abundance was significantly affected by the diurnal cycle, with a higher number of individuals visible during the night. These outcomes offer interesting insights on adaptation to cave environments, showing that key functions, such as the capability to respond to light or diurnal cycles, can be retained in troglobiont species and call for future investigation assessing the potential adaptive roles of these traits in mediating their exploitation of subterranean environments or their interface with the surface. Besides, this study proposes an effective in‐field method for conducting studies on subterranean fauna responses to light stimuli.

Data used in Wagener, Kruger and Measey (2021, <em>J. Exp. Biol.</em>,<em> </em>doi:<em> </em>10.1242/jeb.233031).