Jaco Greeff

• Professor at University of Pretoria

The nematode genus Bursaphelenchus is a highly divergent group. This genus mainly consists of mycophagous entomophilic species, but some species have specialized as obligate or facultative plant parasites, facultative insect parasites, or exhibit feeding dimorphism (phenotypic plasticity) leading to mycophagous and predatory forms. In the present s...

Local mate competition (LMC) favours female biased clutch sex ratios because it reduces competition between brothers and provides extra mating opportunities for sons. Fig wasps seem to fit LMC model assumptions and lay female-biased sex ratios as predicted. These female biased sex ratios increase fitness greatly. In line with predictions, their sex...

Nematodes of figs and fig wasps have received limited attention in Africa since their discovery in 1973. Sixteen of the 25 species of native South African figs were sampled for nematode associates using molecular barcoding with three loci (SSU, LSU D2-D3 and mtCOI) and fourteen (93%) were positive for at least one nematode species. Thirty-three put...

While male mate choice in insects is a widely accepted concept, there is still limited evidence showing that lek formation is compatible with the evolution of male mate choice. In the woodwasp Sirex noctilio, males form leks that are used by females to select a mate. However, males have been observed to ignore certain females, suggesting the presen...

Ever since Darwin's discovery of natural selection, we expect traits to evolve to increase organisms' fitness. As a result, we can use optimization models to make a priori predictions of phenotypic variation, even when selection is frequency-dependent. A notable example is the prediction of female-biased sex ratios resulting from local mate competi...

Most plants flower and fruit at times of year when probabilities of pollination and seedling establishment are high. Fig trees (Ficus spp.) are often considered as keystone resources for vertebrate frugivores, in part because of year‐round fig production. This unusual fruiting phenology results in the maintenance of fig wasp populations, but in sea...

Genetic considerations are rarely applied in forest conservation management strategies, but forest fragmentation can reduce pollen and seed dispersal both between and within isolated fragments. Gene flow and immigration rates determine the extent to which individual plants are related to each other at different distances from themselves. This grada...

Background: The Afrikaner population of South Africa is the descendants of European colonists who started to colonize the Cape of Good Hope in the 1600s. In the early days of the colony, mixed unions between European males and non-European females gave rise to admixed children who later became incorporated into either the Afrikaner or the Coloured...

Abstract Sirex noctilio is an economically important invasive pest of commercial pine forestry in the Southern Hemisphere. Newly established invasive populations of this woodwasp are characterized by highly male‐biased sex ratios that subsequently revert to those seen in the native range. This trend was not observed in the population of S. noctilio...

The Afrikaner population of South Africa are the descendants of European colonists who started to colonize the Cape of Good Hope in the 1600’s. In the early days of the colony, mixed unions between European males and non-European females gave rise to admixed children who later became incorporated into either the Afrikaner or the “Coloured” populati...

Sex allocation theory has long generated insights into the nature of natural selection. Classical models have elucidated causal phenomena such as local mate competition and inbreeding on the degree of female bias exhibited by various invertebrates. Typically, these models assume mothers facultatively adjust sex allocation using predictive cues of f...

Amylostereum areolatum is a wood‐decaying homobasidiomycete fungal symbiont of Sirex noctilio. Together, they cause serious damage to pine plantations in the Southern Hemisphere. The fungus reproduces asexually and is vertically transmitted by S. noctilio females, which results in extensive spread of clones. Specific A. areolatum clones are often d...

Spirocerca lupi is a parasitic nematode of canids and occurs in most tropical and subtropical regions around the world. While its life cycle is well known, insight is lacking about its mating structure within-hosts, genetic variability and long-distance dispersal ability. These characteristics contribute significantly to the dynamics and spread of...

Deladenus siricidicola is the primary biocontrol agent of the invasive woodwasp, Sirex noctilio. The nematode is mass-reared in culture on the S. noctilio symbiotic fungus, A. areolatum, but can also be induced to convert into its infective form in culture. The aim of this study was to explore the level of variation among a collection of D. siricid...

The Afrikaner population was founded mainly by European immigrants that arrived in South Africa from 1652. However, female slaves from Asia and Africa and local KhoeSan women may have contributed as much as 7% to this population's genes. We quantified variation at two tandem repeats to see if this historical founder effect and/or admixture could be...

When cuckoldry is frequent we can expect fathers to withhold investment in offspring that may not be theirs. Human paternal investment can be substantial and is in line with observations from tens of thousands of conceptions that suggest that cuckoldry is rare in humans. The generality of this claim seems to be in question as the rate of cuckoldry...

Parasitodiplogaster salicifoliae n. sp. was isolated from Ficus salicifolia and F. ingens from South Africa and is described and depicted herein. Molecular sequence (D2-D3 expansion segments of the large subunit (LSU) ribosomal DNA and a fragment of mtCOI) and morphological comparisons with P. australis from F. virens from Australia support a monop...

Facultative bacterial endosymbionts are associated with many arthropods and are primarily transmitted vertically from mother to offspring. However, phylogenetic affiliations suggest that horizontal transmission must also occur. Such horizontal transfer can have important biological and agricultural consequences when endosymbionts increase host fitn...

Previous work showed high agreement in facial attractiveness preferences within and across cultures. The aims of the current study were twofold. First, we tested cross-cultural agreement in the attractiveness judgements of White Scottish and Black South African students for own- and other-ethnicity faces. Results showed significant agreement betwee...

A Parasitodiplogaster sp. was isolated from syconia of Ficus burkei from Pretoria, South Africa, and determined to be conspecific with P. sycophilon, originally described by Poinar in 1979 from Harare, Zimbabwe, and also from F. burkei. Examination of type material of P. sycophilon revealed inaccuracies in the former description necessitating a red...

In 1683 Maria Kickers and Jan Cornelitz got married in Cape Town. Today, 330 years later, the living patrilineal descendants of Maria's four sons, number in excess of 76,000 people. Curiously, none of them carry the surname Cornelitz - in fact, they are all called Botha and include former President P.W. Botha, general Louis Botha and Minister Pik B...

Wolbachia are very common and widespread endosymbionts of arthropods. They can have a considerable effect on their host's fitness. It has been estimated that as many as 40% of arthropod species are infected with Wolbachia , but particular taxonomic groups and ecological niches display significantly higher or lower incidences. In this study, an Afri...

Bemisia tabaci (Hemiptera: Aleyrodidae) is a globally distributed pest composed of at least 34 morphologically indistinguishable cryptic species. At least seven species of endosymbiont have been found infecting some or all members of the complex. The origin(s) of the associations between specific endosymbionts and their whitefly hosts is unknown. I...

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