Experimental evidence of hybrid breakdown between genetically distinct populations of Echinostoma caproni

Parasitology ◽  
1998 ◽  
Vol 117 (2) ◽  
pp. 133-135 ◽  
Author(s):  
S. TROUVÉ ◽  
F. RENAUD ◽  
P. DURAND ◽  
J. JOURDANE
Keyword(s):  
Reproductive Isolation ◽  
Experimental Evidence ◽  
Assortative Mating ◽  
Geographical Area ◽  
F1 Hybrids ◽  
Hybrid Breakdown ◽  
Echinostoma Caproni ◽  
Successive Generations ◽  
Genetic Entity ◽  
Isolating Mechanism

In this paper we investigate whether the assortative mating between individuals of the same genetic entity (i.e. coming from the same geographical area) of Echinostoma caproni, reported in a previous paper, may be explained by a post-zygotic isolating mechanism. The fecundity of the adults of 2 parental genetic entities and of their hybrids (i.e. F1, F2, F3) was quantified through 3 successive generations. Whereas the number of eggs released by F1 hybrids is similar to that of the mid-parent, that of recombinant hybrids (F2–3 hybrids) is significantly lower than that of F1 and that of the mid-parent. Since these results seem to demonstrate hybrid breakdown, 2 important factors maintaining reproductive isolation, i.e. pre-mating reproductive isolation and low hybrid fecundity, may influence the evolution of E. caproni.

scholarly journals Ecological divergence in sympatry causes gene misregulation in hybrids

2019 ◽  
Author(s):  
Joseph A. McGirr ◽  
Christopher H. Martin
Keyword(s):  
Gene Expression ◽  
Reproductive Isolation ◽  
Differentially Expressed ◽  
F1 Hybrids ◽  
Adaptive Divergence ◽  
Lower Hybrid ◽  
Hybrid Fitness ◽  
Hybrid Gene ◽  
San Salvador ◽  
Ecological Selection

AbstractEcological speciation occurs when reproductive isolation evolves as a byproduct of adaptive divergence between populations. However, it is unknown whether divergent ecological selection on gene regulation can directly cause reproductive isolation. Selection favoring regulatory divergence between species could result in gene misregulation in F1 hybrids and ultimately lower hybrid fitness. We combined 58 resequenced genomes with 124 transcriptomes to test this hypothesis in a young, sympatric radiation of Cyprinodon pupfishes endemic to San Salvador Island, Bahamas, which consists of a dietary generalist and two novel trophic specialists – a molluscivore and a scale-eater. We found more differential gene expression between closely related sympatric specialists than between allopatric generalist populations separated by 1000 km. Intriguingly, 9.6% of genes that were differentially expressed between sympatric species were also misregulated in their F1 hybrids. Consistent with divergent ecological selection causing misregulation, a subset of these genes were in highly differentiated genomic regions and enriched for functions important for trophic specialization, including head, muscle, and brain development. These regions also included genes that showed evidence of hard selective sweeps and were significantly associated with oral jaw length – the most rapidly diversifying skeletal trait in this radiation. Our results indicate that divergent ecological selection in sympatry can cause hybrid gene misregulation which may act as a primary reproductive barrier between nascent species.SignificanceIt is unknown whether the same genes that regulate ecological traits can simultaneously contribute to reproductive barriers between species. We measured gene expression in two trophic specialist species of Cyprinodon pupfishes that rapidly diverged from a generalist ancestor. We found genes differentially expressed between species that also showed extreme expression levels in their hybrid offspring. Many of these genes showed signs of selection and have putative effects on the development of traits that are important for ecological specialization. This suggests that genetic variants contributing to adaptive trait divergence between parental species negatively interact to cause hybrid gene misregulation, potentially producing unfit hybrids. Such loci may be important barriers to gene flow during the early stages of speciation, even in sympatry.

scholarly journals Spatial swarm segregation and reproductive isolation between the molecular forms of Anopheles gambiae

2009 ◽  
Vol 276 (1676) ◽  
pp. 4215-4222 ◽  
Author(s):  
Abdoulaye Diabaté ◽  
Adama Dao ◽  
Alpha S. Yaro ◽  
Abdoulaye Adamou ◽  
Rodrigo Gonzalez ◽  
...  
Keyword(s):  
Reproductive Isolation ◽  
Anopheles Gambiae ◽  
Assortative Mating ◽  
Molecular Form ◽  
Mate Recognition ◽  
Spatial Segregation ◽  
Molecular Forms ◽  
Ecological Niches ◽  
Ecological Criteria ◽  
Underlying Mechanisms

Anopheles gambiae , the major malaria vector in Africa, can be divided into two subgroups based on genetic and ecological criteria. These two subgroups, termed the M and S molecular forms, are believed to be incipient species. Although they display differences in the ecological niches they occupy in the field, they are often sympatric and readily hybridize in the laboratory to produce viable and fertile offspring. Evidence for assortative mating in the field was recently reported, but the underlying mechanisms awaited discovery. We studied swarming behaviour of the molecular forms and investigated the role of swarm segregation in mediating assortative mating. Molecular identification of 1145 males collected from 68 swarms in Donéguébougou, Mali, over 2 years revealed a strict pattern of spatial segregation, resulting in almost exclusively monotypic swarms with respect to molecular form. We found evidence of clustering of swarms composed of individuals of a single molecular form within the village. Tethered M and S females were introduced into natural swarms of the M form to verify the existence of possible mate recognition operating within-swarm. Both M and S females were inseminated regardless of their form under these conditions, suggesting no within-mate recognition. We argue that our results provide evidence that swarm spatial segregation strongly contributes to reproductive isolation between the molecular forms in Mali. However this does not exclude the possibility of additional mate recognition operating across the range distribution of the forms. We discuss the importance of spatial segregation in the context of possible geographic variation in mechanisms of reproductive isolation.

Reproductive Isolation and the Integrity of Two Sympatric Species of Choristoneura (Lepidoptera: Tortricidae)

1953 ◽  
Vol 85 (4) ◽  
pp. 141-151 ◽  
Author(s):  
Stanley G. Smith
Keyword(s):  
Reproductive Isolation ◽  
Hybrid Sterility ◽  
Sympatric Species ◽  
Evolutionary Divergence ◽  
Gene Exchange ◽  
Hybrid Breakdown ◽  
Temporal Isolation ◽  
Isolating Mechanisms ◽  
Spatial Isolation ◽  
Mechanical Isolation

According to Dobzhansky (1951a, p. 262) “Species are … groups of populations the gene exchange between which is limited or prevented by one, or by a combination of several, reproductive isolating mechanisms”. This definition follows from his concept of a species not as a static unit but as a stage in the process of evolutionary divergence. Limitation or prevention of gene exchange is a property of geographic and reproductive isolation (Mayr, 1912), the various types of which Dobzhansky lists as follows:I. Geographic or Spatial IsolationII. Reproductive IsolationA. Ecological IsolationB. Seasonal or Temporal IsolationC. Sexual, Psychological or Ethnological IsolationD. Mechanical IsolationE. Gametic IsolationF. Hybrid InviabilityG. Hybrid SterilityH. Hybrid Breakdown

scholarly journals Testing the Role of Habitat Isolation among Ecologically Divergent Gall Wasp Populations

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Scott P. Egan ◽  
Glen R. Hood ◽  
James R. Ott
Keyword(s):  
Reproductive Isolation ◽  
Assortative Mating ◽  
Host Plants ◽  
Habitat Preferences ◽  
Habitat Isolation ◽  
Native Plant ◽  
Gall Wasp ◽  
Quercus Virginiana ◽  
Respective Host

Habitat isolation occurs when habitat preferences lower the probability of mating between individuals associated with differing habitats. While a potential barrier to gene flow during ecological speciation, the effect of habitat isolation on reproductive isolation has rarely been directly tested. Herein, we first estimated habitat preference for each of six populations of the gall waspBelonocnema treataeinhabiting eitherQuercus virginianaorQ. geminata. We then estimated the importance of habitat isolation in generating reproductive isolation betweenB. treataepopulations that were host specific to eitherQ. virginianaorQ. geminataby measuring mate preference in the presence and absence of the respective host plants. All populations exhibited host preference for their native plant, and assortative mating increased significantly in the presence of the respective host plants. This host-plant-mediated assortative mating demonstrates that habitat isolation likely plays an important role in promoting reproductive isolation among populations of this host-specific gall former.

scholarly journals Assortative flocking in crossbills and implications for ecological speciation

2012 ◽  
Vol 279 (1745) ◽  
pp. 4223-4229 ◽  
Author(s):  
Julie W. Smith ◽  
Stephanie M. Sjoberg ◽  
Matthew C. Mueller ◽  
Craig W. Benkman
Keyword(s):  
Natural Selection ◽  
Reproductive Isolation ◽  
Assortative Mating ◽  
Ecological Speciation ◽  
Central Question ◽  
Loxia Curvirostra ◽  
Call Type ◽  
Divergent Natural Selection ◽  
Contact Calls ◽  
Red Crossbills

How reproductive isolation is related to divergent natural selection is a central question in speciation. Here, we focus on several ecologically specialized taxa or ‘call types’ of red crossbills ( Loxia curvirostra complex), one of the few groups of birds providing much evidence for ecological speciation. Call types differ in bill sizes and feeding capabilities, and also differ in vocalizations, such that contact calls provide information on crossbill phenotype. We found that two call types of red crossbills were more likely to approach playbacks of their own call type than those of heterotypics, and that their propensity to approach heterotypics decreased with increasing divergence in bill size. Although call similarity also decreased with increasing divergence in bill size, comparisons of responses to familiar versus unfamiliar call types indicate that the decrease in the propensity to approach heterotypics with increasing divergence in bill size was a learned response, and not a by-product of calls diverging pleiotropically as bill size diverged. Because crossbills choose mates while in flocks, assortative flocking could lead indirectly to assortative mating as a by-product. These patterns of association therefore provide a mechanism by which increasing divergent selection can lead to increasing reproductive isolation.

scholarly journals Sexual selection on color and behavior within and between cichlid populations: Implications for speciation

2012 ◽  
Vol 58 (3) ◽  
pp. 475-483 ◽  
Author(s):  
Michael J. Pauers ◽  
Jeffrey S. Mckinnon
Keyword(s):  
Sexual Selection ◽  
Mate Choice ◽  
Reproductive Isolation ◽  
Assortative Mating ◽  
Mate Preferences ◽  
Separate Experiment ◽  
Color Patterns ◽  
Male Behavior ◽  
Female Population ◽  
Different Color

Abstract Sexual selection is widely viewed as playing a central role in haplochromine cichlid speciation. Hypothetically, once divergent mate preferences evolve among populations of these fishes, reproductive isolation follows and the populations begin to behave as different species. Various studies have examined patterns of assortative mating among species and sometimes populations, but few have examined variation in directional preferences, especially among populations of the same species. We investigated mate choice behavior in two populations of Labeotropheus fuelleborni, a Lake Malawi endemic. We test whether mating preferences between populations are based on the same traits and in the same direction as preferences within populations. We examine the potential contributions of two classes of trait, color patterns and behaviors, to reproductive isolation. When females chose between either two males of their own population, or two from another, female preferences were generally similar (for the female population) across the two contexts. Mate choice patterns differed between (female) populations for a measure of color, but only modestly for male behavior. In a separate experiment we simultaneously offered females a male of their own population and a male from a different population. In these trials, females consistently preferred males from their own population, which were also the males that displayed more frequently than their opponents, but not necessarily those with color traits suggested to be most attractive in the previous experiment. Thus directional preferences for chroma and related aspects of color may be important when females are presented with males of otherwise similar phenotypes, but may play little role in mediating assortative mating among populations with substantially different color patterns. A preference for male behavior could play some role in speciation if males preferentially court same-population females, as we have observed for the populations studied herein.

scholarly journals Assortative mating in hybrid zones is remarkably ineffective in promoting speciation

2019 ◽  
Author(s):  
Darren E. Irwin
Keyword(s):  
Assortative Mating ◽  
F1 Hybrids ◽  
Secondary Contact ◽  
Hybrid Zones ◽  
Mating Types ◽  
Postzygotic Isolation ◽  
Small Reduction ◽  
Hybrid Fitness ◽  
Prezygotic Isolation ◽  
Two Populations

AbstractAssortative mating and other forms of partial prezygotic isolation are often viewed as being more important than partial postzygotic isolation (low fitness of hybrids) early in the process of speciation. Here I simulate secondary contact between two populations (‘species’) to examine effects of pre- and postzygotic isolation in preventing blending. A small reduction in hybrid fitness (e.g., 10%) produces a narrower hybrid zone than a strong but imperfect mating preference (e.g., 10x stronger preference for conspecific over heterospecific mates). This is because, in the latter case, rare F1 hybrids find each other attractive (due to assortative mating), leading to the gradual buildup of a full continuum of intermediates between the two species. The cline is narrower than would result from purely neutral diffusion over the same number of generations, largely due to the frequency-dependent mating disadvantage of individuals of rare mating types. Hybrids tend to pay this cost of rarity more than pure individuals, meaning there is an induced postzygotic isolation effect of assortative mating. These results prompt a questioning of the concept of partial prezygotic isolation, since it is not very isolating unless there is also postzygotic isolation.

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