Plasticity of ontogenetic trajectories in cyprinids: a source of evolutionary novelties

Research in evolutionary developmental (evo‐devo) biology is making an increasingly important contribution to our understanding of the molecular mechanisms underlying the establishment of complex morphological traits. Deciphering the ontogenetic trajectories leading to the differentiation of sister species (and the existence of hybrids) is a new challenge in our understanding of speciation processes. In the present study, we characterized the ontogenetic trajectory of lower lip morphology in two cyprinid species and their hybrids. Chondrostoma toxostoma has an arched lower lip and a generalist diet. Chondrostoma nasus has a straight lower lip and a specialist diet. An analysis of 99 C. toxostoma, 99 C. nasus and 25 first‐generation (F₁) hybrid individuals demonstrated that the difference between arched and straight lip morphology was found to depend strongly on the height/width ratio of the lower lip. A comparison of the ontogenetic trajectories of these morphometric traits showed that the height of the lower lip was isometric to body length in both species, whereas developmental changes involving an acceleration and a hypermorphosis of the widening of the lower lip led to a straight lip morphology in C. nasus. F₁ hybrids were characterized by an extreme phenotype resulting from a rate of lower lip widening slower than that in the two parent species. Therefore, we rejected a codominance hypothesis and concluded that the first stage of hybridization provides the foundations of evolutionary novelty. These results have important evolutionary implications because lower lip shape is linked to dietary behaviour in many fish species. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 342–355.     

Early Triassic conodont clusters from South China: revision of the architecture of the 15 element apparatuses of the superfamily Gondolelloidea

Abstract: Several fused clusters of conodont elements of the genera Neospathodus and Novispathodus were recovered from limestone beds at the Dienerian–Smithian and Smithian–Spathian boundaries, respectively, from several localities in Guangxi province, South China. Conodont clusters are otherwise extremely rare in the Triassic, and these are first described for the Early Triassic. The exceptional specimens partially preserve the relative three‐dimensional position and orientation of ramiform elements and are therefore extremely important for testing hypotheses on the architecture of apparatuses. These specimens partly confirm the previous reconstruction of the Novispathodus apparatus by Orchard. Within apparatuses of members of superfamily Gondolelloidea, elements previously identified as occupying the S₁ and S₂ positions instead occupy the S₂ and S₁ positions. Similarly, within apparatuses of members of the subfamily Novispathodinae, elements previously referred to S₃ and S₄ positions are reinterpreted to have occupied S₄ and S₃ positions, respectively.     

Synchrony in population counts predicts butterfly movement frequencies

1. Measuring functional connectivity, the ability of species to move between resource patches, is essential for conservation in fragmented landscapes. However, current methods are highly time consuming and expensive. 2. Population synchrony‐ the correlation in time series of counts between two long‐term population monitoring sites, has been suggested as a possible proxy measure of functional connectivity. To date, population synchrony has been shown to correlate with proxies for movement frequency such as the coverage of suitable habitat types in intervening landscapes, and also least cost distances around hostile land cover types. 3. This provides tentative evidence that synchrony is directly driven by movements of the focal species, but an alternative explanation is that these land cover types affect the movement of interacting species (e.g. natural enemies of the focal species) which can also drive synchronous population dynamics. Therefore, what is needed is a test directly relating population synchrony to movement frequencies of a focal species. 4. Here we use data from a 21 year mark‐release‐recapture study and show that population synchrony does indeed predict movements of a focal butterfly species Boloria eunomia (Esper). 5. There is growing evidence that population synchrony can be a useful conservation tool to measure functional connectivity.     

European flyway permeability and abmigration in Teal Anas crecca, an analysis based on ringing recoveries

Abmigration, the switch between flyways, is thought to be frequent in dabbling ducks, and supposedly results from high female philopatry combined with winter pairing: a male pairing in winter with a female from another flyway may follow her to her breeding area and thus abmigrate. On this basis, the frequency of abmigration should be much higher amongst males than amongst females, should increase with time since ringing, and be higher if environmental conditions force birds from different flyways into the same geographical area in winter (in this case the Iberian peninsula in the case of cold spells). Analysing more than 9000 recoveries of Teal ringed in the Camargue, southern France, showed that even with the most conservative flyway definition, 15% of Camargue (Mediterranean flyway) individuals (both males and females) were subsequently recovered in the North-west European flyway. Moving a flyway boundary closer to the Camargue (i.e. to the south-east) increased this percentage to c . 32%. None of the predicted patterns were supported by the data: there was no systematic sex difference in abmigration rate; abmigration showed no consistent increase with time from ringing, and was not significantly more frequent after cold spells. These results suggest that there is permeability between these two flyways for all classes of individuals, which might better be considered as a continuum. This should be taken into account in the development of management and conservation policies for Teal in Europe.     

Inferring recent migration rates from individual genotypes

We present a novel and straightforward method for estimating recent migration rates between discrete populations using multilocus genotype data. The approach builds upon a two-step sampling design, where individual genotypes are sampled before and after dispersal. We develop a model that estimates all pairwise backwards migration rates ( m_ij , the probability that an individual sampled in population i is a migrant from population j ) between a set of populations. The method is validated with simulated data and compared with the methods of BayesAss and Structure. First, we use data for an island model and then we consider more realistic data simulations for a metapopulation of the greater white-toothed shrew ( Crocidura russula ). We show that the precision and bias of estimates primarily depend upon the proportion of individuals sampled in each population. Weak sampling designs may particularly affect the quality of the coverage provided by 95% highest posterior density intervals. We further show that it is relatively insensitive to the number of loci sampled and the overall strength of genetic structure. The method can easily be extended and makes fewer assumptions about the underlying demographic and genetic processes than currently available methods. It allows backwards migration rates to be estimated across a wide range of realistic conditions.     

Tug of war between continental gene flow and rearing site philopatry in a migratory bird: the sex-biased dispersal paradigm reconsidered

Nonrandom dispersal has been recently advanced as a mechanism promoting fine-scale genetic differentiation in resident populations, yet how this applies to species with high rates of dispersal is still unclear. Using a migratory species considered a classical example of male-biased dispersal (the greater snow goose, Chen caerulescens atlantica ), we documented a temporally stable fine-scale genetic clustering between spatially distinct rearing sites (5–30 km apart), where family aggregates shortly after hatching. Such genetic differentiation can only arise if, in both sexes, dispersal is restricted and nonrandom, a surprising result considering that pairing occurs among mixed flocks of birds more than 3000 km away from the breeding grounds. Fine-scale genetic structure may thus occur even in migratory species with high gene flow. We further show that looking for genetic structure based on nesting sites only may be misleading. Genetically distinct individuals that segregated into different rearing sites were in fact spatially mixed during nesting. These findings provide new, scale-dependent links between genetic structure, pairing, and dispersal and show the importance of sampling different stages of the breeding cycle in order to detect a spatial genetic structure.     

Evolution of mosaic hybrid zone between invasive and endemic species of Cyprinidae through space and time

Hybridization phenomena can be considered in different ways. Hybridization studies can be used to elucidate some aspects of speciation and adaptation. However, hybridization may be a threat to endemic species. Here, we studied bidirectional introgression between two sympatric species of Cyprinidae: Chondrostoma toxostoma toxostoma and C. nasus nasus . Analysis of morphology, allozymes and mtDNA sequences revealed that the hybridization between these two cyprinids takes different forms in the same river. The mosaic hybrid zone (so called because of the absence of a simple cline) appeared to be partitioned due to the proportions of the two species along a spatial scale. The proportion of each hybrid group in this zone was unstable over a 5-year period. We propose various protection/conservation states for the C. t. toxostoma populations based on the level of introgressive hybridization and the genetic structure of both species in 'pure' populations.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 135–155.     

Reappraisal of the ill-defined Liassic pteridosperm Dichopteris using an ultrastructural approach

This review of the genus Dichopteris De Zigno is based on the original fossil specimens collected from the Lower Jurassic of the Grey Limestones of Veneto (Northern Italy). The cuticular diagnosis of the genus is emended and only Dichopteris visianica De Zigno is retained within the genus. In addition, transverse and longitudinal sections of cuticles examined using a transmission electron microscope (TEM) indicate close similarities between D. visianica and other pteridosperm cuticles, especially the occurrence of granules arranged in areas of different densities in the epidermal cells and stomatal apparatus. Moreover, the dichotomy and the impressive size of the frond of D. visianica imply a specific architecture with a typical arrangement of the pinnae and pinnules. They preclude an herbaceous habit for the plant. Finally, architectural, microstructural and ultrastructural observations are consistent with palaeoclimatic and palaeoenvironmental data, and most probably support an understorey habit for D. visianica .  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 149 , 313–332.