Jaco Greeff
University of Pretoria, Genetics, Faculty Member
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Fig wasps (Hymenoptera, Agaonidae) have been widely utilized in studies of sex ratio evolution, especially local mate competition (LMC), and good fits have been obtained between empirical data and model predictions incorporating LMC and... more
Fig wasps (Hymenoptera, Agaonidae) have been widely utilized in studies of sex ratio evolution, especially local mate competition (LMC), and good fits have been obtained between empirical data and model predictions incorporating LMC and inbreeding effects. These models assume that foundress females within a patch (a fig) oviposit synchronously, producing roughly equal numbers of offspring with the same progeny sex ratios. Working with the fig wasp Eupristina belagaumensis, which pollinates the fig tree Ficus drupacea in India, we investigated whether these assumptions are valid, and then produced an alternative model which incorporates revised biological assumptions. Egg loads at adult emergence were compared with those remaining in females after they had completed their egg-laying and had died. As foundress numbers increased, so did variation in the numbers of eggs which the females managed to lay. In multi-foundress figs certain females (most likely the first ones to enter) often contributed almost complete egg loads while others (which may have entered when most of the oviposition sites had been utilised) contributed relatively few eggs. Assumptions of previous models were therefore violated. Our model assumes totally sequential oviposition by foundresses and differential contributions to broods. The predicted overall sex ratios of the fig wasp progeny are qualitatively similar to models based on LMC and inbreeding effects, despite being based on different biological assumptions, suggesting that previous models may have given the right answers for the wrong reasons. Explicit tests between the models are possible, as the sequential oviposition model predicts that the progeny sex ratios of individual foundresses should vary depending on where in the sequence they enter a fig.
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It is shown that when females can adjust their offspring sex ratios conditionally to the identity of their mates, i.e. sib or non‐sib, split sex ratios are expected. These split sex ratios result from variation in relatedness between... more
It is shown that when females can adjust their offspring sex ratios conditionally to the identity of their mates, i.e. sib or non‐sib, split sex ratios are expected. These split sex ratios result from variation in relatedness between females and their daughters. Haplodiploid females' relatedness to their daughters increases as their relatedness to their mates increases. Therefore, sibmated females' optimal progeny sex ratio is more female biased than that of outbred females. Inbreeding depression that can result from complementary sex determination (CSD) is also considered. The genetic load caused by CSD can be so costly to sibmated females that they switch to the production of males only. The evolutionarily stable sex ratios for a sibmating model is found to be of a weak type. These weak equilibria and split sex ratios can lead to high variation about the mean and are an incentive for further studies on sex ratio variation in conjunction with mating behaviour. The occurrence of split sex ratios in haplodiploid taxa is important because it favours the evolution of eusociality. Partial local mating and alternative mating strategies can thus eventually lead to the evolution of eusociality.
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Research Interests: Botany, Zoology, Morphometrics, Taxonomy, Nematology, and 7 moreBiology, Morphology, Molecular, Phylogeny, Ficus, Monophyly, and Subgenus
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A mere 16 years ago it was suggested that the Cape honeybee (Apis mellifera capensis) should be protected from invasion by the African 'killer bees' (A. m. scutellata). During the last five years, quite the opposite happened when... more
A mere 16 years ago it was suggested that the Cape honeybee (Apis mellifera capensis) should be protected from invasion by the African 'killer bees' (A. m. scutellata). During the last five years, quite the opposite happened when A. m. capensis caused a catastrophe in the A. m. scutellata bee industry. In 1993 an estimated 50 000 A. m. scutellata colonies died) and in 1996 many farmers had to replace 100% or more of their colonies per annum. The disaster is not restricted to the loss of colonies and bee produces. but the pollination service that beekeepers is also seriously impeded.
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Research Interests: Biology and Population
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Sperm Digestion and Reciprocal Sperm Transfer Can Drive Hermaphrodite Sex Allocation to Equality. JM Greeff, NK Michiels American Naturalist 153:44, 421-430, 4/1999. The intensity of sperm competition determines how much reproductive... more
Sperm Digestion and Reciprocal Sperm Transfer Can Drive Hermaphrodite Sex Allocation to Equality. JM Greeff, NK Michiels American Naturalist 153:44, 421-430, 4/1999. The intensity of sperm competition determines how much reproductive effort should be invested in sperm. ...
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The optimal progeny sex ratio produced by a mother depends on the amount of competition between same sexed sibs (Hamilton, 1967; Clark, 1978) and on the mother’s relatedness to each sex (Hamilton, 1972; Herre, 1985). In haplodiploid... more
The optimal progeny sex ratio produced by a mother depends on the amount of competition between same sexed sibs (Hamilton, 1967; Clark, 1978) and on the mother’s relatedness to each sex (Hamilton, 1972; Herre, 1985). In haplodiploid species where the mating population is structured in groups of related individuals, two phenomena of importance occur: (1) brothers compete against each other for mating opportunities, referred to as local mating competition or LMC (Hamilton, 1967) and (2) sib-mating occurs, which results in mothers being more related to daughters than sons (Hamilton, 1972; Herre, 1985). Due to these two factors, optimal sex ratios become more female biased as relatedness in the local mating population increases. Agaonine fig wasps (Hymenoptera: Agaonidae: Agaoninae) have provided a useful empirical system for testing models of sex ratio optimization. Their usefulness is due to various aspects of their natural history, which is characterized by a mutualism with plants of the genus Ficus (Moraceae). Ficus inflorescences are shaped like a hollow ball, lined on the inside with hundreds or thousands of unisexual flowers. When the female flowers are ready to be pollinated, attractive volatiles are released (Ware et af., 1993) and the bracts lining the ostiole (a bract-lined tunnel) loosen to allow the female wasps to squeeze their way through (Galil, 1977). The duration of volatile release and ostiole opening are linked to pollinator entry. Unentered figs can remain attractive for several weeks, whereas after a single pollinator had entered syconia of Ecarica and Eaurea they were found to remain attractive for a maximum of 4 days (Khadari et al., 1995). Once one or more pollen-bearing mated fig wasp females (foundresses) have passed through the ostiole they reach the lumen of the fruit, where they pollinate the fig flowers and lay their eggs inside a proportion of the ovules. Females have a short adult life-span ofjust 1-3 days (Kjellberg etal., 1988; Compton et al.; 1994) and typically die inside the fruit. The length of the period between entry of the first wasp and the fig flowers becoming unsuitable for oviposition is not known. The offspring develop to maturity in the galled ovules, whereupon the male wasps emerge, chew holes in the females’ galls and mate with
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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... more
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 from the summer rainfall regions in South Africa, which remained highly male‐biased for almost a decade. The aim of this study was to determine the cause of this persistent male bias. As an explanation for this pattern, we test hypotheses related to mating success, female investment in male versus female offspring, and genetic diversity affecting diploid male production due to complementary sex determination. We found that 61% of females in a newly established S. noctilio population were mated. Microsatellite data analysis showed that populations of S. noctilio from the summer rainfall regions in South Africa are far less genetically diverse than ...
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Calculation of the probability of sibmating, derivation of the indiscriminate model and supplementary tables.
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Book Title: DispersalBook editors: J. Clobert, E. Danchin,A.A. Dhondt & J.D. Nichols.Oxford University Press, Oxford. 2001. Pp. 452. Price £24.95 (paperback). ISBN 0 19 85065 9
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Additional file 4. Figure 10 data. Single Foundress sex ratios, fraction of single foundress figs and clutch size of 39 species.
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... more
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 ratios become less female-biased as the number of mothers laying in the same fig increases. However, this variation results in comparatively small fitness benefits compared to just biased ratios and data suggest substantial mismatches with LMC theory. The mismatches are due to several factors. (1) Multiple foundresses typically lay too many daughters. (2) Single foundress sex ratios are explained by sequential oviposition and ladies-last models. (3) Mortality that typically exceeds 10% may decouple the link between primary sex ratios, the focus of model predictions, and secondary sex ratios of adult wasps that are counted by researchers. ...
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Additional file 1: Figure S1. Non-European admixture fractions (of K=6) sorted by ancestry fraction. Figure S2. Principal component analysis for PC1-PC10 and the variation explained by PCs. Figure S3. Results from f3-test. Populations are... more
Additional file 1: Figure S1. Non-European admixture fractions (of K=6) sorted by ancestry fraction. Figure S2. Principal component analysis for PC1-PC10 and the variation explained by PCs. Figure S3. Results from f3-test. Populations are colored according to regional affiliation. Figure S4. Results from f3-test. The CEU (A) and Khomani (B) populations are fixed to show the best African and non-African sources to the Afrikaner population. Figure S5. Fraction of shared private alleles between the Afrikaner population and a comparative population. Figure S6. Shared private alleles between the Afrikaner populations and populations with West-African ancestry. Figure S7. A) Afrikaner individuals (black circles) projected on a PCA based on European genetic variation from the POPRES dataset. B) Population variation on PC 1 and 2 summarized as averages and standard deviations. Figure S8. Admixture analyses of the Asian extended dataset. Figure S9. Manhattan plot of Locus specific branch len...
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... more
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 future offspring mating conditions. Here we relax this assumption by developing a sex allocation model for haplodiploid mothers experiencing local mate competition that lay a fixed number of male eggs first. Female egg number is determined by remaining oviposition sites or remaining eggs of the mother, depending on which is exhausted first. Our model includes parameters for variation in foundress number, patch size, fecundity and offspring mortality that allow us to generate secondary sex ratio predictions based on specific parameterizations for natural populations. Simulations show that: 1) in line with classical models, factors that increase sib-mating result in mothers laying relatively more female eggs; 2) high offspring mortality leads to relatively more males as fertilization insurance; 3) unlike classical model predictions, sub-optimal predictions, such as more males than females are possible. In addition, our model provides the first quantitative predictions for the expected number of males and females in a patch where typically only one mother utilizes a given patch. We parameterized the model with data obtained from seven species of southern African fig wasps to predict expected means and variances for numbers of male and female offspring for typical numbers of mothers utilizing a patch. These predictions were compared to secondary sex ratio data from single foundress patches, the most commonly encountered situation for these species. Our predictions matched both the observed number and variance of male and female offspring with a high degree of accuracy suggesting that facultative adjustment is not required to produce evolutionary stable sex ratios
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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... more
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 presence of male mate choice despite the presence of a lek mating system. In this study we demonstrate that males only attempt to mate with certain females. To understand the criteria used by males and females to select a mate, we also tested the effect of age, size, and male to female size ratio on the number of mating attempts made by males and on female receptivity. We demonstrate that size and age play a role in both male and female mate choice. Our results suggest that males must reach sexual maturity after emergence and are neither receptive nor attractive to females during the first few days of their lives. We also show that older females...
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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... more
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 putative species of nematodes were identified and classified according to the loci that were amplified and successfully sequenced. Fourteen putative nematode species were classified as Aphelenchoididae, of which nine were identified as Ficophagus from four species of Ficus from the section Galoglychia (i.e., five ex F. burkei including one shared with F. natalensis, one ex F. glumosa, one ex F. lutea, and one ex F. stuhlmannii) and one species ex F. sur from the section Sycomorus. In addition, there were four nematode species classified as Schistonchus s.s. from section Galoglychia figs (i.e., one ex F. burkei, two ex F. trichopoda, and one e...
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Research Interests: Psychology, Visual perception, Face, Ethnicity, Medicine, and 14 moreMultidisciplinary, Cross-Cultural Comparison, Humans, Judgment, Beauty, Cross Cultural Psychology, Female, Male, Regression Analysis, Young Adult, Facial Attractiveness, PLoS one, Sex Factors, and European Continental Ancestry Group
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The cotton whitefly, Bemisia tabaci (Gennadius), is a cryptic species complex, and members of the complex have become serious pests in Pakistan because of their feeding and their ability to transmit cotton leaf curl virus (CLCuV). Here,... more
The cotton whitefly, Bemisia tabaci (Gennadius), is a cryptic species complex, and members of the complex have become serious pests in Pakistan because of their feeding and their ability to transmit cotton leaf curl virus (CLCuV). Here, an analysis was made of the identity of B. tabaci collected from cotton and a range of non-cotton hosts in the cotton-growing zones in Punjab and Sindh, the main cotton-producing provinces of Pakistan, using a portion of the mitochondrial cytochrome oxidase 1 gene. The geographic distribution of the different members of the complex was then compared with the incidence of CLCuD. Using the Dinsdale nomenclature, the results revealed three putative species, Asia 1, Asia II 1 and Middle East-Asia Minor 1. Asia II 1 (also referred to in the literature as biotypes K, P, PCG-1, PK1, SY and ZHJ2) was only recorded from Punjab cotton plants, whereas Asia 1 (also referred to in the literature as biotypes H, M, NA and PCG-2) was found in both Sindh and Punjab. Middle East-Asia Minor 1 (commonly known as biotype B and B2) was found only in Sindh. Moreover, Asia II 1 was associated with high incidences of CLCuD, whereas regions where Middle East-Asia Minor 1 was present had a lower incidence. Phylogenetic analysis showed that the Middle East-Asia Minor 1 population in Sindh formed a distinct genetic subgroup within the putative species, suggesting that the Sindh province of Pakistan may form part of its home range. So far, no individuals from the putative species Mediterranean (commonly known as biotypes Q, J and L) have been found in Pakistan. The capacity to manage pests and disease effectively relies on knowledge of the identity of the agents causing the damage. In the case of CLCuD in Pakistan, this knowledge has been obscured to some extent because of the inconsistent approach to identifying and distinguishing the different B. tabaci associated with CLCuD. The situation has now been clarified, and a strong association between disease incidence and vector identity and abundance has been shown. Given this advance, future research can now focus on factors that influence the capacity of different vector species to transmit the viruses that cause CLCuD, the reason for differences in vector abundance and the lack of geographic overlap between the cryptic vector species. This knowledge will contribute to the development of improved methods with which to manage the disease in Pakistan.
Research Interests: Zoology, Pest Management, Pakistan, Biology, Ecology, and 14 moreMedicine, Phylogeny, Plant diseases, Animals, Hemiptera, Genotype, Genetic variation, Begomovirus, Pest Management Science, ENVIRONMENTAL SCIENCE AND MANAGEMENT, Insect Vectors, Mitochondrial Proteins, Molecular Sequence Data, and Gossypium
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.... more
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 redescription which is provided herein. Additionally, the original description lacked molecular data, which is also provided. Originally, the stoma of P. sycophilon was described as reduced without teeth. However, we observed a large dorsal stegostomal tooth and an almost equally-sized right subventral tooth which was typologically similar to the stoma of P. laeviagata from Florida. In addition, a pore-like phasmid was observed in both males and females just above the tail tip. Most other characters were as formerly described. Based upon molecular inferences from sequences of the D2/D3 expansion segments of the rDNA of the large subunit (LSU)...
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... Branch and Whiting, 1997). Dotted along the rocky banks of the river are Na-maqua fig trees (Ficus cordata cordata). Apart from the fig trees, the rocky banks are largely devoid of other vegetation. The lizards inhabit crevices ...
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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... more
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. Infection is normally vertical, but horizontal transmission does occur and is one way for new infections to be introduced into individuals. The relationships between the different members of the cryptic species complex and the endosymbionts have not been well explored. In this study, the phylogenies of different cryptic species of the host with those of their endosymbionts were compared. Of particular interest was whether there was evidence for both coevolution and horizontal transmission. Congruence was observed for the primary endosymbiont, Portiera aleyrodidarum, and partial incongruence in the case of two secondary endosymbionts, Arseno...
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The males of many fig wasps fight fatally for mating opportunities. The concentration of females in space has been proposed as one factor selecting for their aggressive behaviour. We studied the temporal distribution of receptive females... more
The males of many fig wasps fight fatally for mating opportunities. The concentration of females in space has been proposed as one factor selecting for their aggressive behaviour. We studied the temporal distribution of receptive females to obtain a clearer impression of the operational sex ratio in figs. Females of nonpollinating species emerged from figs over a protracted period of time and this resulted in an extremely male-biased operational sex ratio, conducive to extreme fighting. Since there were so few receptive females at any one time, a male could defend an eclosing female. Consequently, the largest Otitesella longicauda male in a fig had a much higher mating success than smaller males. This suggests that larger males have a larger fitness advantage than larger females and a Trivers–Willard effect could have important implications for sex allocation. Apterous and seemingly nondispersing males routinely left their figs. Such dispersal can affect both (1) sex allocation by r...
A mere 16 years ago it was suggested that the Cape honeybee (Apis mellifera capensis) should be protected from invasion by the African 'killer bees' (A. m. scutellata). During the last five years, quite the opposite happened when... more
A mere 16 years ago it was suggested that the Cape honeybee (Apis mellifera capensis) should be protected from invasion by the African 'killer bees' (A. m. scutellata). During the last five years, quite the opposite happened when A. m. capensis caused a catastrophe in the A. m. scutellata bee industry. In 1993 an estimated 50 000 A. m. scutellata colonies died) and in 1996 many farmers had to replace 100% or more of their colonies per annum. The disaster is not restricted to the loss of colonies and bee produces. but the pollination service that beekeepers is also seriously impeded.
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Introduced species face numerous biological barriers before they can establish in a new environment. Understanding how they overcome these obstacles is crucial for the development of effective risk assessment and regulation. Reproductive... more
Introduced species face numerous biological barriers before they can establish in a new environment. Understanding how they overcome these obstacles is crucial for the development of effective risk assessment and regulation. Reproductive biology is known to influence establishment capacity in plants and is widely used for risk assessment. This biological field should receive more attention, and particularly in the case of insects, as they display a wide range of reproductive traits and have a great impact on the economy and environment. Among insects, the order Hymenoptera is of interest for its diversity, both in terms of reproductive traits and introduction history, as invasive species and biological control agents. We review the main reproductive strategies of Hymenoptera, spanning parthenogenesis, sex determination, reproductive parasites and mating strategies, and evaluate their effect on invasive potential. For instance, thelytoky could decrease the strength of Allee effects while Arrhenotoky could increase adaptive potential. A species with complementary sex determination could be more affected by inbreeding than other species, while paternal genome elimination could lead to high levels of homozygosity. Finally, some reproductive behaviours could decrease inbreeding, facilitate mate location or adaptation by encouraging admixture. The two invasive species Apis mellifera scutellata and Leptocybe invasa and the biocontrol agent Aphidius ervi serve as case studies to illustrate the effect of reproductive traits on species capacities to become established in a new area.
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Abstract 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... more
Abstract 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 gradation in relatedness is known as a population's fine scale spatial genetic structure (SGS). Specifically, reduced but clumped immigration from distant fragments reduces fine scale SGS, whereas reduced gene flow within fragments increases fine scale SGS. In addition, non-random mortality caused by post-dispersal ecological processes can also affect SGS. We studied the effects of fragmentation on the fine scale SGS of Ficus species with different habitat preferences and distributional ranges in an archipelago of South African forest patches. Significant fine scale SGS present in all three species suggests gene dispersal is restricted, even within forest fragments, probably due to localised seed dispersal. An endemic forest specialist, F. bizanae, has an unusually high fine scale SGS for a monoecious Ficus. This may be explained by several features that reduce pollen dispersal distances and are more typical of dioecious Ficus. A significant negative kinship coefficient in one F. bizanae population suggests that clumped long-distance immigration may have occurred in the past. Significant fine scale SGS in adult but not juvenile F. craterostoma suggests that recent population fragmentation has negatively affected long-distance immigration. Supplementation of F. craterostoma gene flow would maintain its genetic diversity. In contrast, the limited range of F. bizanae may result from its pollinator’s behavior, rather than specific habitat requirements and ensuring its long-term survival may require artificial introductions to other forests.
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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... more
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 future offspring mating conditions. Here we relax this assumption by developing a sex allocation model for haplodiploid mothers experiencing local mate competition that lay a fixed number of male eggs first. Female egg number is determined by remaining oviposition sites or remaining eggs of the mother, depending on which is exhausted first. Our model includes parameters for variation in foundress number, patch size, fecundity and offspring mortality that allow us to generate secondary sex ratio predictions based on specific parameterizations for natural populations. Simulations show that: 1) in line with classical models, factors that increase sib‐mating result in mothers laying relatively more female eggs; 2) high offspring mortality leads to relatively more males as fertilization insurance; 3) unlike classical model predictions, sub‐optimal predictions, such as more males than females are possible. In addition, our model provides the first quantitative predictions for the expected number of males and females in a patch where typically only one mother utilizes a given patch. We parameterized the model with data obtained from seven species of southern African fig wasps to predict expected means and variances for numbers of male and female offspring for typical numbers of mothers utilizing a patch. These predictions were compared to secondary sex ratio data from single foundress patches, the most commonly encountered situation for these species. Our predictions matched both the observed number and variance of male and female offspring with a high degree of accuracy suggesting that facultative adjustment is not required to produce evolutionary stable sex ratios.
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Under local mate competition, sex ratio theory predicts that increasing numbers of ovipositing females (foundresses) on a site should lead to higher proportions of males in their broods. Fig pollinators have confirmed this prediction. It... more
Under local mate competition, sex ratio theory predicts that increasing numbers of ovipositing females (foundresses) on a site should lead to higher proportions of males in their broods. Fig pollinators have confirmed this prediction. It is also predicted that with decreasing clutch size, solitary foundresses should produce increasing proportions of sons. We show this to be true. Further, when several females compete, brood size decreases. As a result, the proportion of males increases, and this could provide a mechanistic explanation of sex ratio response to numbers of colonizing females. Therefore, sex ratio data on fig wasps need to be reassessed to determine whether females 'count' other foundresses, as is generally accepted, or whether they simply 'count' the number of eggs that they lay. To cite this article: F. Kjellberg et al., C. R. Biologies 328 (2005).
Research Interests: Sex ratio and Clutch Size
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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... more
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 competition (LMC) and inbreeding. LMC models incorporate the effects of LMC and inbreeding. Fig wasp sex ratio adjustments fit LMC predictions well. However, the appropriateness of LMC models to fig wasps has been questioned, and the role that a coincidental by-product plays in creating the apparent fit has been clearly illustrated. Here, we show that the sex ratio adjustments of a fig wasp are the result of a dual mechanism. It consists of a standard facultative LMC response favoured by natural selection, as well as a mechanism that may be the result of selection, but that could also be a coincidental by-product. If it is a by-product, t...
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ABSTRACTThe 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... more
ABSTRACTThe 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” populations of South Africa. Ancestry, social class, culture, sex ratio and geographic structure affected admixture patterns and caused different ancestry and admixture patterns in Afrikaner and Coloured populations. The Afrikaner population has a predominant European composition, whereas the Coloured population has more diverse ancestries. Genealogical records estimated the non-European contributions into the Afrikaners to 5.5%-7.2%. To investigate the genetic ancestry of the Afrikaner population today (11-13 generations after initial colonization) we genotyped ~5 million genome-wide markers in 77 Afrikaner individuals and compared their ...
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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... more
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 monophyletic lineage of fig wasp-associated diplogastrids within what is currently accepted as Parasitodiplogaster from figs in the subgenus Urostigma, section Urostigma, subsection Urostigma. This ranking within Parasitodiplogaster is conditional upon examination of more material from figs from the subsection Urostigma from its putative centre of origin (Indo-Australasia) because the morphology (presence of one prodelphic ovary vs two amphidelphic ovaries and several other autapomorphic features) and molecular data are suggestive of a potentially well-defined radiation of nematode species. Parasitodiplogaster salicifoliae n. sp. can be typolog...
Research Interests: Zoology, Morphometrics, Taxonomy, Nematology, Biology, and 3 moreMorphology, Molecular, and Phylogeny
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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... more
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 varies across populations and studies have mostly been on Western populations. Two additional factors complicate our conclusions, (1) current estimates of the rate of cuckoldry in humans may not reflect our past behaviour as adultery can be concealed by the use of contraceptives; and (2) it is difficult to obtain samples that are random with respect to their paternity certainty. Studies that combine genealogies with Y-chromosome haplotyping are able to circumvent some of these problems by probing into humans' historical behaviour. Here we use this approach to investigate 1273 conceptions over a period of 330 years in 23 families of the...
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Understanding genetic diversity and movement patterns in parasitic organisms is paramount to establish control and management strategies. In this study we developed a microsatellite resource as well as a diagnostic multiplex for the... more
Understanding genetic diversity and movement patterns in parasitic organisms is paramount to establish control and management strategies. In this study we developed a microsatellite resource as well as a diagnostic multiplex for the cosmopolitan parasitic nematode Spirocerca lupi, known to cause spirocercosis in canids. A combination of microsatellite enrichment and 454 sequencing was used to identify 149 unique microsatellite loci in S. lupi. Twenty loci were characterized further in two sampling sites in South Africa, with 10 loci identified as polymorphic (allele ranges from 4 to 17). These loci were designed into a single diagnostic multiplex suitable for species identification and population genetics studies. The markers were also successful in cross-species amplification in Cylicospirura felineus, Philonema oncorhynchi and Gongylonema pulchrum. Our resource provides a large set of candidate loci for a number of nematode studies as well as loci suitable for diversity and popula...
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Sperm Digestion and Reciprocal Sperm Transfer Can Drive Hermaphrodite Sex Allocation to Equality. JM Greeff, NK Michiels American Naturalist 153:44, 421-430, 4/1999. The intensity of sperm competition determines how much reproductive... more
Sperm Digestion and Reciprocal Sperm Transfer Can Drive Hermaphrodite Sex Allocation to Equality. JM Greeff, NK Michiels American Naturalist 153:44, 421-430, 4/1999. The intensity of sperm competition determines how much reproductive effort should be invested in sperm. ...
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Research Interests: Reproduction, Sex Allocation, Biological Sciences, Color, Wasps, and 7 morePollen, Sex ratio, Female, Animals, Male, Mating System, and Ficus
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... Apis mellifera capensis JACO M. GREEFF ... SUMMARY Apis mellifera capensis workers are able to produce female eggs by the process of thelytoky, whereas the workers of other races of honeybee and most other eusocial Hymenoptera produce... more
... Apis mellifera capensis JACO M. GREEFF ... SUMMARY Apis mellifera capensis workers are able to produce female eggs by the process of thelytoky, whereas the workers of other races of honeybee and most other eusocial Hymenoptera produce males only (arrhenotoky). ...
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ABSTRACT
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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... more
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 fitness. So far horizontal transmission is considered rare and has been difficult to document. Here, we use fluorescence in situ hybridization (FISH) and multi locus sequence typing (MLST) to reveal a potentially common pathway of horizontal transmission of endosymbionts via parasitoids of insects. We illustrate that the mouthparts and ovipositors of an aphelinid parasitoid become contaminated with Wolbachia when this wasp feeds on or probes Wolbachia-infected Bemisia tabaci AsiaII7, and non-lethal probing of uninfected B. tabaci AsiaII7 nymphs by parasitoids carrying Wolbachia resulted in newly and stably infected B. tabaci matrilines. After ...
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We investigate the evolution of male morphology in the fig wasps belonging to the genus Philotrypesis (Chalcidoidea, Sycorectinae). We first reconstruct the phylogenetic relationships of Philotrypesis associated with African figs using... more
We investigate the evolution of male morphology in the fig wasps belonging to the genus Philotrypesis (Chalcidoidea, Sycorectinae). We first reconstruct the phylogenetic relationships of Philotrypesis associated with African figs using nuclear and mitochondrial DNA. We then determine male morphotypes in the species included in our phylogeny and show that intraspecific polymorphism is common. Most species present two types of
Research Interests: Evolutionary Biology, Genetics, Zoology, Macroevolution, Polymorphism, and 17 moreSexual Selection, DNA, Software, Phylogeny, Mitochondrial DNA, Wasps, Maximum Likelihood, Animals, Male, Polymerase Chain Reaction, Molecular Phylogenetics and Evolution, Phenotype, Sex Factors, Time Factors, Phenotypic variation, Character Evolution, and Likelihood Functions
Mixed mating systems are somewhat of an enigma as most models predict that organisms should either inbreed when inbreeding depression is low, or outbreed when inbreeding depression is high. Many wasps mix routine inbreeding with a little... more
Mixed mating systems are somewhat of an enigma as most models predict that organisms should either inbreed when inbreeding depression is low, or outbreed when inbreeding depression is high. Many wasps mix routine inbreeding with a little random mating. This random mating is most common when all local sibmating opportunities are exhausted and dispersal is the only way males can further increase their fitness. The males of the pollinating fig wasp, Platyscapa awekei, are slightly different in that they disperse before all sibmating opportunities have been exhausted. To see if this is a response to inbreeding depression we quantify inbreeding depression by comparing females' life time reproductive success to their heterozygosity at multiple microsatellite loci. We find that a female wasp's heterozygosity is an accurate predictor of her inbreeding coefficient and that P. awekei females actually seem to suffer from outbreeding depression and possibly from a little inbreeding depression. Male dispersal is thus not a means to effect the optimal mating system, but more likely a mechanism to reduce competition among brothers. The number of mature offspring a female produces depends on her own heterozygosity and not on that of the offspring, and may be determined by egg and gall quality.