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ABSTRACT: Biological invasions are ecologically and economically costly. Understanding the major mechanisms that contribute to an alien
species becoming invasive is seen as essential for limiting the effects of invasive alien species. However, there are a number
of fundamental questions that need addressing such as why some communities are more vulnerable to invasion than others and,
indeed, why some alien species become widespread and abundant. The enemy release hypothesis (ERH) is widely evoked to explain
the establishment and proliferation of an alien species. ERH predicts that an alien species introduced to a new region should
experience a decrease in regulation by natural enemies which will lead to an increase in the distribution and abundance of
the alien species. At the centre of this theory is the assumption that natural enemies are important regulators of populations.
Additionally, the theory implies that such natural enemies have a stronger regulatory effect on native species than they do
on alien species in the introduced range, and this disparity in enemy regulation results in increased population growth of
the alien species. However, empirical evidence for the role of the ERH in invasion success is lacking, particularly for invertebrates.
Many studies equate a reduction in the number of natural enemies associated with an alien species to release without studying
population effects. Further insight is required in relation to the effects of specific natural enemies on alien and native
species (particularly their ability to regulate populations). We review the role of ecological models in exploring ERH. We
suggest that recent developments in molecular technologies offer considerable promise for investigating ERH in a community
context.
KeywordsNatural enemy release hypothesis–Arthropod predators–Parasitoids–Modelling–Molecular
BioControl 04/2012; 56(4):451-468. · 1.93 Impact Factor
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ABSTRACT: There is growing realisation that integrating genetics and ecology is critical in the context of biological invasions, since
the two are explicitly linked. So far, the focus of ecological genetics of invasive alien species (IAS) has been on determining
the sources and routes of invasions, and the genetic make-up of founding populations, which is critical for defining and testing
ecological and evolutionary hypotheses. However an ecological genetics approach can be extended to investigate questions about
invasion success and impacts on native, recipient species. Here, we discuss recent progress in the field, provide overviews
of recent methodological advances, and highlight areas that we believe are of particular interest for future research. First,
we discuss the main insights from studies that have inferred source populations and invasion routes using molecular genetic
data, with particular focus on the role of genetic diversity, adaptation and admixture in invasion success. Second, we consider
how genetic tools can lead to a better understanding of patterns of dispersal, which is critical to predicting the spread
of invasive species, and how studying invasions can shed light on the evolution of dispersal. Finally, we explore the potential
for combining molecular genetic data and ecological network modelling to investigate community interactions such as those
between predator and prey, and host and parasite. We conclude that invasions are excellent model systems for understanding
the role of natural selection in shaping phenotypes and that an ecological genetics approach offers great potential for addressing
fundamental questions in invasion biology.
KeywordsInvasive alien species–Ecological genetics–Molecular ecology–Invasion routes–Dispersal–Community interactions
BioControl 04/2012; 56(4):409-428. · 1.93 Impact Factor
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E Lombaert,
T Guillemaud,
C E Thomas, L J Lawson Handley,
J Li,
S Wang,
H Pang,
I Goryacheva,
I A Zakharov,
E Jousselin,
R L Poland,
A Migeon,
J Van Lenteren,
P DE Clercq,
N Berkvens,
W Jones,
A Estoup
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ABSTRACT: Correct identification of the source population of an invasive species is a prerequisite for testing hypotheses concerning the factors responsible for biological invasions. The native area of invasive species may be large, poorly known and/or genetically structured. Because the actual source population may not have been sampled, studies based on molecular markers may generate incorrect conclusions about the origin of introduced populations. In this study, we characterized the genetic structure of the invasive ladybird Harmonia axyridis in its native area using various population genetic statistics and methods. We found that native area of H. axyridis most probably consisted of two geographically distinct genetic clusters located in eastern and western Asia. We then performed approximate Bayesian computation (ABC) analyses on controlled simulated microsatellite data sets to evaluate (i) the risk of selecting incorrect introduction scenarios, including admixture between sources, when the populations of the native area are genetically structured and sampling is incomplete and (ii) the ability of ABC analysis to minimize such risks by explicitly including unsampled populations in the scenarios compared. Finally, we performed additional ABC analyses on real microsatellite data sets to retrace the origin of biocontrol and invasive populations of H. axyridis, taking into account the possibility that the structured native area may have been incompletely sampled. We found that the invasive population in eastern North America, which has served as the bridgehead for worldwide invasion by H. axyridis, was probably formed by an admixture between the eastern and western native clusters. This admixture may have facilitated adaptation of the bridgehead population.
Molecular Ecology 11/2011; 20(22):4654-70. · 5.52 Impact Factor
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ABSTRACT: Male-killing bacteria are thought to persist in host populations by vertical transmission and conferring direct and/or indirect fitness benefits to their hosts. Here, we test the role of indirect fitness benefits accrued from resource reallocation in species that engage in sibling egg cannibalism. We found that a single-egg meal significantly increased larval survival in 12 ladybird species, but the value of an egg (to survival) differed substantially between species. Next, we tested the impact of three male-killing bacteria on larval survival in one ladybird species, Adalia bipunctata. Spiroplasma reduced larval survival, whereas Wolbachia and Rickettsia had no effect. However, Spiroplasma-infected larvae showed the greatest response to a single-egg meal. The indirect fitness benefit obtained from a single egg is thus so large that even male-killing bacteria with direct fitness costs can persist in host populations. This study supports the hypothesis that fitness compensation via resource reallocation can explain male-killing bacteria persistence.
Journal of Evolutionary Biology 07/2011; 24(10):2164-72. · 3.28 Impact Factor
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L J Lawson Handley
Heredity 02/2010; 105(3):245-6. · 4.60 Impact Factor
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ABSTRACT: Large-scale evaluations of genetic diversity in domestic livestock populations are necessary so that region-specific conservation measures can be implemented. We performed the first such survey in European sheep by analysing 820 individuals from 29 geographically and phenotypically diverse breeds and a closely related wild species at 23 microsatellite loci. In contrast to most other domestic species, we found evidence of widespread heterozygote deficit within breeds, even after removing loci with potentially high frequency of null alleles. This is most likely due to subdivision among flocks (Wahlund effect) and use of a small number of rams for breeding. Levels of heterozygosity were slightly higher in southern than in northern breeds, consistent with declining diversity with distance from the Near Eastern centre of domestication. Our results highlight the importance of isolation in terms of both geography and management in augmenting genetic differentiation through genetic drift, with isolated northern European breeds showing the greatest divergence and hence being obvious targets for conservation. Finally, using a Bayesian cluster analysis, we uncovered evidence of admixture between breeds, which has important implications for breed management.
Heredity 01/2008; 99(6):620-31. · 4.60 Impact Factor
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ABSTRACT: Recent population expansion and increased migration linked to urbanization are assumed to be eroding the genetic structure of human populations. We investigated change in population structure over three generations by analysing both demographic and mitochondrial DNA (mtDNA) data from a random sample of 2351 men from 22 Iranian populations. Potential changes in genetic diversity (theta) and genetic distance (F(ST)) over the last three generations were analysed by assigning mtDNA sequences to populations based on the individual's place of birth or that of their mother or grandmother. Despite the fact that several areas included cities of over one million inhabitants, we detected no change in genetic diversity, and only a small decrease in population structure, except in the capital city (Tehran), which was characterized by massive immigration, increased theta and a large decrease in F(ST) over time. Our results suggest that recent erosion of human population structure might not be as important as previously thought, except in some large conurbations, and this clearly has important implications for future sampling strategies.
Heredity 04/2007; 98(3):151-6. · 4.60 Impact Factor
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ABSTRACT: Sex-biased dispersal is an almost ubiquitous feature of mammalian life history, but the evolutionary causes behind these patterns still require much clarification. A quarter of a century since the publication of seminal papers describing general patterns of sex-biased dispersal in both mammals and birds, we review the advances in our theoretical understanding of the evolutionary causes of sex-biased dispersal, and those in statistical genetics that enable us to test hypotheses and measure dispersal in natural populations. We use mammalian examples to illustrate patterns and proximate causes of sex-biased dispersal, because by far the most data are available and because they exhibit an enormous diversity in terms of dispersal strategy, mating and social systems. Recent studies using molecular markers have helped to confirm that sex-biased dispersal is widespread among mammals and varies widely in direction and intensity, but there is a great need to bridge the gap between genetic information, observational data and theory. A review of mammalian data indicates that the relationship between direction of sex-bias and mating system is not a simple one. The role of social systems emerges as a key factor in determining intensity and direction of dispersal bias, but there is still need for a theoretical framework that can account for the complex interactions between inbreeding avoidance, kin competition and cooperation to explain the impressive diversity of patterns.
Molecular Ecology 04/2007; 16(8):1559-78. · 5.52 Impact Factor
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ABSTRACT: It is important to characterise the amount of variation on the mammalian Y chromosome in order to assess its potential for use in evolutionary studies. We report very low levels of polymorphism on the Y chromosome of Saudi-Arabian hamadryas baboons, Papio hamadryas hamadryas. We found no segregating sites on the Y, despite sequence analysis of 3 kb noncontiguous intron sequence in 16 males with divergent autosomal microsatellite genotypes, and a further analysis of 1.1 kb intron sequence in 97 males from four populations by SSCP. In addition, we tested seven human-derived Y-linked microsatellites in baboons. Only four of these loci were male-specific and only one was polymorphic in our 97 male sample set. Polymorphism on the Y chromosome of Arabian hamadryas appears to be low compared to other primate species for which data are available (eg humans, chimpanzees and bonobos). Low effective population size (Ne) of paternal genes due to polygyny and female-biased adult sex ratio is a potential reason for low Y chromosome variation in this species. However, low Ne for the Y should be counterbalanced to some extent by the species' atypical pattern of male philopatry and female-biased dispersal. Allelic richness averaged over seven loci was not significantly different between an African and an Arabian population, suggesting that loss of variation during the colonisation of Arabia does not explain low Y variation. Finally, in the absence of nucleotide polymorphism, it is unclear to what extent selection could be responsible for low Y variation in this species.
Heredity 05/2006; 96(4):298-303. · 4.60 Impact Factor
