Population Structure of Guppies in North-Eastern Venezuela, the Area of Putative Incipient Speciation

Background Geographic barriers to gene flow and divergence among populations in sexual traits are two important causes of genetic isolation which may lead to speciation. Genetic isolation may be facilitated if these two mechanisms act synergistically. The guppy from the Cumaná region (within the Cariaco drainage) of eastern Venezuela has been previously described as a case of incipient speciation driven by sexual selection, significantly differentiated in sexual colouration and body shape from the common guppy, Poecilia reticulata. The latter occurs widely in northern Venezuela, including the south-eastern side of Cordillera de la Costa, where it inhabits streams belonging to the San Juan drainage. Here, we present molecular and morphological analyses of differentiation among guppy populations in the Cariaco and San Juan drainages. Our analyses are based on a 953 bp long mtDNA fragment, a set of 15 microsatellites (519 fish from 20 populations), and four phenotypic traits. Results Both microsatellite and mtDNA data showed that guppies inhabiting the two drainages are characterised by a significant genetic differentiation, but a higher proportion of the genetic variance was distributed among populations within regions. Most guppies in the Cariaco drainage had mtDNA from a distinct lineage, but we also found evidence for widespread introgression of mtDNA from the San Juan drainage into the Cariaco drainage. Phenotypically, populations in the two regions differed significantly only in the number of black crescents. Phenotypic clustering did not support existence of two distinct groupings, but indicated a degree of distinctiveness of Central Cumaná (CC) population. However, CC population showed little differentiation at the neutral markers from the proximate populations within the Cariaco drainage. Conclusions Our findings are consistent with only partial genetic isolation between the two geographic regions and indicate that the geographic barrier of Cordillera de la Costa has not played an important role in strengthening the incomplete pre-zygotic reproductive barrier between Cumaná and common guppy. Significant phenotypic differentiation between genetically similar (in terms of neutral variation) populations suggests that mate choice can maintain divergence at sexually selected traits despite gene flow. However, neither genetic nor phenotypic clustering supported delineation of two species within the region

A Conserved Supergene Locus Controls Colour Pattern Diversity in Heliconius Butterflies

We studied whether similar developmental genetic mechanisms are involved in both convergent and divergent evolution. Mimetic insects are known for their diversity of patterns as well as their remarkable evolutionary convergence, and they have played an important role in controversies over the respective roles of selection and constraints in adaptive evolution. Here we contrast three butterfly species, all classic examples of Müllerian mimicry. We used a genetic linkage map to show that a locus, Yb, which controls the presence of a yellow band in geographic races of Heliconius melpomene, maps precisely to the same location as the locus Cr, which has very similar phenotypic effects in its co-mimic H. erato. Furthermore, the same genomic location acts as a “supergene”, determining multiple sympatric morphs in a third species, H. numata. H. numata is a species with a very different phenotypic appearance, whose many forms mimic different unrelated ithomiine butterflies in the genus Melinaea. Other unlinked colour pattern loci map to a homologous linkage group in the co-mimics H. melpomene and H. erato, but they are not involved in mimetic polymorphism in H. numata. Hence, a single region from the multilocus colour pattern architecture of H. melpomene and H. erato appears to have gained control of the entire wing-pattern variability in H. numata, presumably as a result of selection for mimetic “supergene” polymorphism without intermediates. Although we cannot at this stage confirm the homology of the loci segregating in the three species, our results imply that a conserved yet relatively unconstrained mechanism underlying pattern switching can affect mimicry in radically different ways. We also show that adaptive evolution, both convergent and diversifying, can occur by the repeated involvement of the same genomic regions

Especiación híbrida homoploide en animales

Among animals, evidence for homoploid hybrid speciation (HHS, i.e . the creation of a hybrid lineage without a change in chromosome number) was limited until recently to the virgin chub, Gila seminuda , and some controversial data in support of hybrid status for the red wolf, Canis rufus . This scarcity of evidence, together with pessimistic attitudes among zoologists about the evolutionary importance of hybridisation, prompted the view that HHS is extremely rare among animals, especially as compared with plants. However, in recent years, the literature on animal HHS has expanded to include several new putative examples in butterflies, ants, flies and fishes. We argue that this evidence suggests that HHS is far more common than previously thought and use it to provide insights into some of the genetic and ecological aspects associated with this type of speciation among animals

Espeletia saboyana (Millerieae, Asteraceae), a New Critically Endangered Caulirosula from Cordillera Oriental, Colombia

International audienceAbstract— Espeletia saboyana , a new species from Páramo de Saboyá, Boyacá department, Colombia, is described and illustrated. It is a caulescent rosette up to 5 m tall, with whitish-cinereous appearance, sessile leaves with elliptic laminae, cymose capitulescences with aphyllous unbranched portion and 3‐5 capitula, 5‐13 phyllaries, the external ones 17.4‐26.0 mm long, 49‐92 ray florets 13.0‐18.4 mm long, and 162‐347 disc florets 8.2‐12.2 mm long. Espeletia saboyana is similar to E. incana , but with longer laminae, bigger foliar area, and fewer ray floret series. It is also similar to E. murilloi , but with longer ray tubes, ray paleae, disc corollas, disc styles, disc anther appendages, and disc paleae. In addition, E. saboyana is distributed allopatrically in regard to E. incana and E. murilloi . This species is informally proposed to be listed as IUCN Critically Endangered (CR), since it is restricted to a single population with extent of occurrence = 1.83 km 2 and area of occupancy = 0.48 km 2 . Besides, this population is severely fragmented into 40‐50 demes, the largest one covering only 34,000 m 2 . Most demes are found in humid soils and wetlands submitted to continuous habitat deterioration as water is drained for use in agriculture. Espeletia saboyana is rare or absent in these newly drained areas, which are either colonized by other species that thrive on drier soils or transformed into pastures for cattle grazing. Furthermore, analyses of size class distributions show that recruitment rates of E. saboyana are significantly lower in small demes, which, if not reversed, can further reduce population size in the near future

Espeletia ocetana (Millerieae, Asteraceae), a New Tall Caulirosula from Colombia

International audienceAbstract— A new species, Espeletia ocetana (Asteraceae), from about 3500 m a. s. l. in Páramo de Ocetá, Mongua, Boyacá department, Colombia, is described and illustrated. The new species exhibits a caulescent rosette habit (0.7‐1.8 m tall), sessile leaves, elliptic leaf laminae with greyish indumentum, robust bracteate thyrsoid capitulescences spreading laterally from rosette, each holding 16‐37(‐69) capitula, external phyllaries 14.2‐31.1 mm long, and ray florets 13.9‐21.3 mm long arranged in 2.0‐2.9 series. It is markedly different from the majority of other members of the genus, and only slightly similar to E. jaramilloi , from which it can be easily distinguished by its taller stems, wider leaves with a smaller length/width ratio, and longer sheaths. Furthermore, E. ocetana has capitula with ray florets arranged in fewer series, and with longer phyllaries, ray corollas, ray corolla limbs, ray styles, ray style branches, disc florets, and disc styles. In addition, E. ocetana is distributed allopatrically in regard to E. jaramilloi , and differs as well in its ecological preference for humid to very humid shrubby páramos. Espeletia ocetana is rather abundant in its type locality, which is a relatively well-conserved páramo located within the limits of Parque Natural Regional Siscunsí-Ocetá. However, it is absent from road margins, abandoned agriculture fields, and other areas impacted by human activities. Further studies will be necessary to know appropriately the extent of the geographic distribution of E. ocetana , its ecological requirements and its phylogenetic affinities with other species

Speciation with gene flow: Evidence from a complex of alpine butterflies (Coenonympha , Satyridae)

International audienceHybridization between diverging taxa is possible throughout the speciation process until complete reproductive isolation is achieved

Ecology and Biogeography of Arbuscular Mycorrhizal Fungi Belonging to the Family Gigasporaceae in La Gran Sabana Region (Guayana Shield), Venezuela

International audienceArbuscular mycorrhizal fungi (AMF) play a crucial role in ecosystem functioning by improving plant nutrition and resistance to environmental stress. In La Gran Sabana (LGS), a high plateau belonging to the Venezuelan Guayana Shield, with vegetation mainly composed by savannas intermixed with forests, shrublands, meadows and palm swamps, the AMF are determinant for plant survival due to the acidic, sandy and oligotrophic nature of its soils. In this region a high diversity of species of Gigasporaceae has been found and four species discovered there (Scutellospora spinosissima, S. crenulata, S. striata, S. tepuiensis), and some undescribed morphotypes, are considered endemic. In this work, some ecological and historical factors possibly involved with the restricted distribution of these species are evaluated. The elevated plant endemism and the particular edaphic conditions present in shrublands appear like the main drivers of the important diversification processes within Gigasporaceae detected in LGS. The monophyletic origin of some of these endemic Gigasporaceae suggests that their endemism could be the result of a process of in situ diversification combined with limitations for dispersal and/or establishment in other regions. These findings and the presence of a basal lineage for the family allows proposing LGS as an evolutionary hotspot for Gigasporaceae

Data from: Speciation with gene flow: evidence from a complex of alpine butterflies (Coenonympha, Satyridae)

Until complete reproductive isolation is achieved, the extent of differentiation between two diverging lineages is the result of a dynamic equilibrium between genetic isolation and mixing. This is especially true for hybrid taxa, for which the degree of isolation in regard to their parental species is decisive in their capacity to rise as a new and stable entity. In this work, we explored the past and current patterns of hybridization and divergence within a complex of closely related butterflies in the genus Coenonympha in which two alpine species, C. darwiniana and C. macromma, have been shown to result from hybridization between the also alpine C. gardetta and the lowland C. arcania. By testing alternative scenarios of divergence among species, we show that gene flow has been uninterrupted throughout the speciation process, although leading to different degrees of current genetic isolation between species in contact zones depending on the pair considered. Nonetheless, at broader geographic scale, analyses reveal a clear genetic differentiation between hybrid lineages and their parental species, pointing out to an advanced stage of the hybrid speciation process. Finally, the positive correlation observed between ecological divergence and genetic isolation among these butterflies suggests a potential role for ecological drivers during their speciation processes

Current and future distributions of Espeletiinae (Asteraceae) in the Venezuelan Andes based on statistical downscaling of climatic variables and niche modelling

International audienc