Sex? and species?biased gene flow in a spotted eagle hybrid zone

Background  

Recent theoretical and empirical work points toward a significant role for sex-chromosome linked genes in the evolution of traits that induce reproductive isolation and for traits that evolve under influence of sexual selection. Empirical studies including recently diverged (Pleistocene), short-lived avian species pairs with short generation times have found that introgression occurs on the autosomes but not on the Z-chromosome. Here we study genetic differentiation and gene flow in the long-lived greater spotted eagle (Aquila clanga) and lesser spotted eagle (A. pomarina), two species with comparatively long generation times.     

Are hybrid species more fit than ancestral parent species in the current hybrid species habitats?

Hybrid speciation is thought to be facilitated by escape of early generation hybrids into new habitats, subsequent environmental selection and adaptation. Here, we ask whether two homoploid hybrid plant species (Helianthus anomalus, H. deserticola) diverged sufficiently from their ancestral parent species (H. annuus, H. petiolaris) during hybrid speciation so that they are more fit than the parent species in hybrid species habitats. Hybrid and parental species were reciprocally transplanted into hybrid and parental habitats. Helianthus anomalus was more fit than parental species in the H. anomalus actively moving desert dune habitat. The abilities to tolerate burial and excavation and to obtain nutrients appear to be important for success in the H. anomalus habitat. In contrast, H. deserticola failed to outperform the parental species in the H. deserticola stabilized desert dune habitat, and several possible explanations are discussed. The home site advantage of H. anomalus is consistent with environmental selection having been a mechanism for adaptive divergence and hybrid speciation and supports the use of H. anomalus as a valuable system for further assessment of environmental selection and adaptive traits.     

Has Arabidopsis SWEETIE protein a role in sugar flux and utilization?

In plants, sugars affect growth and development and play an important role in the intricate machinery of signal transduction. Understanding the mechanisms behind the flux of sugar in the plant is of central interest. We recently characterized an Arabidopsis mutant: sweetie, which is defective in the control of growth and development, sterile, shows premature senescence and affects sugar metabolism. Our microarray analysis showed that 15 genes annotated as sugar transporter related proteins were found to be upregulated in sweetie while one sugar transporter gene was found to be downregulated. Most of them are unspecified sugar transporters but four genes have been annotated as monosaccharide transporters and one has been annotated as a disaccharide transporter. Moreover, as computer analyses predicted that SWEETIE might be a membrane protein and might have a function of glycosyl transferase, our data suggest that SWEETIE could be involved in the general control of sugar flux and modulates many important processes such as morphogenesis, flowering, stress responses and senescence.Key words: Arabidopsis thaliana, sweetie mutant, microarray, sugar flux, sugar transport     

Parasite infectivity to hybridising host species: a link between hybrid resistance and allopolyploid speciation?

Variation in host-specific infectivity was studied in monogenean polystome parasites (Protopolystoma spp.) of the interfertile, parapatric anurans Xenopus laevis laevis and Xenopus muelleri. Laboratory-raised host F1 hybrids were resistant to parasites respectively specific to each parent taxon in nature. This resistance occurred against parasite isolates from both inside and outside a host hybrid/sympatric zone (and no isolate was compatible with the foreign host species under experimental conditions). Geographical Protopolystoma xenopodis isolates showed variable infectivity to a single full-sib group of their usual host, X. l. laevis, and strains with high or low infectivity to these sibs co-occurred in spatially distant local areas (separated by 1,700 km). The host compatibility of P. xenopodis was also subject to host genotypexparasite genotype interactions. Refractoriness to some parasites or pathogens, as a consequence of hybridisation, may have conferred a selective advantage on the allopolyploid pathway by which most Xenopus spp. are believed to have evolved.     

Do ecological niches differ between sexual and asexual lineages of an aphid species?

According to environmental-based theories on the maintenance of sexual reproduction, sexual and asexual populations may coexist if they occupy different ecological niches. The aphid Rhopalosiphum padi offers a good opportunity to test this hypothesis since sexual and asexual lineages show local coexistence during a large part of their respective life-cycles. Because these two reproductive variants are morphologically identical but genetically distinct, we first characterized them using genetic markers in populations of R. padi in areas where sexual and asexual lineages may occur in sympatry. We then inferred the natal host plant of sexual and asexual genotypes by analysing stable isotopic ratios and showed that sexual ones mostly originated from C₃ Poaceae while asexual ones originated from C₃ and C₄ plants, although the majority came from C₄ Poaceae. These findings indicate that ecological niches of sexual and asexual lineages of R. padi differ, offering a plausible explanation for the local coexistence of the two reproductive modes in this species through habitat specialisation.     

When is a parasite species a species?

Regrettably, 140 years after the publication of Darwin's Origin of Species, we face the grotesque situation that we still do not know what is a species whose origin Darwin wanted to explain. A generally applicable species definition is not available. Is there a basic unit of biodiversity above the level of individuals? Do we try to define something that does not exist in reality? The strong potential for the evolution of genetic variability in parasites together with the importance of species diagnosis for applied fields of parasite research make biodiversity research a key role in parasitology. Frequent occurrence of sympatric speciation, clonal reproduction, selfing, sib mating or parthenogenesis imply exceptional conditions for the evolution of gene pool diversities in parasites.     

How do species barriers decay? Concordance and local introgression in mosaic hybrid zones of mussels

The Mytilus complex of marine mussel species forms a mosaic of hybrid zones, found across temperate regions of the globe. This allows us to study ‘replicated’ instances of secondary contact between closely related species. Previous work on this complex has shown that local introgression is both widespread and highly heterogeneous, and has identified SNPs that are outliers of differentiation between lineages. Here, we developed an ancestry‐informative panel of such SNPs. We then compared their frequencies in newly sampled populations, including samples from within the hybrid zones, and parental populations at different distances from the contact. Results show that close to the hybrid zones, some outlier loci are near to fixation for the heterospecific allele, suggesting enhanced local introgression, or the local sweep of a shared ancestral allele. Conversely, genomic cline analyses, treating local parental populations as the reference, reveal a globally high concordance among loci, albeit with a few signals of asymmetric introgression. Enhanced local introgression at specific loci is consistent with the early transfer of adaptive variants after contact, possibly including asymmetric bi‐stable variants (Dobzhansky‐Muller incompatibilities), or haplotypes loaded with fewer deleterious mutations. Having escaped one barrier, however, these variants can be trapped or delayed at the next barrier, confining the introgression locally. These results shed light on the decay of species barriers during phases of contact.     

What is a species? Essences and generation

Arguments against essentialism in biology rely strongly on a claim that modern biology abandoned Aristotle’s notion of a species as a class of necessary and sufficient properties. However, neither his theory of essentialism, nor his logical definition of species and genus (eidos and genos) play much of a role in biological research and taxonomy, including his own. The objections to natural kinds thinking by early twentieth century biologists wrestling with the new genetics overlooked the fact that species have typical developmental cycles and most have a large shared genetic component. These are the “what-it-is-to-be” members of that species. An intrinsic biological essentialism does not commit us to Aristotelian notions, nor even modern notions, of essence. There is a long-standing definition of “species” and its precursor notions that goes back to the Greeks, and which Darwin and pretty well all biologists since him share, that I call the Generative Conception of Species. It relies on there being a shared generative power that makes progeny resemble parents. The “what-it-is-to-be” a member of that species is that developmental type, mistakes in development notwithstanding. Moreover, such “essences” have always been understood to include deviations from the type. Finally, I shall examine some implications of the collapse of the narrative about essences in biology.     

Native or not? Tracing the origin of wild-caught and captive freshwater turtles in a threatened and widely distributed species (Emys orbicularis)

Pet and food trade are among the major threats for many chelonians species worldwide. We investigate the impact of the present and past trade in European pond turtles (Emys orbicularis, E. trinacris) on their extant distribution pattern. Using a comprehensive mtDNA dataset of cytochrome b haplotypes derived from more than 1,550 individuals, we assigned wild-caught allochthonous and captive turtles from six European countries to their native regions across the entire distribution range. We found allochthonous haplotypes in all countries surveyed, providing evidence of long-distance translocations owing to past and present trade, illegal poaching or collection by tourists. In summary, we identify source regions of allochthonous turtles and past and present trade routes. Moreover, we point out future directions which would contribute to conservation and management of these threatened species.     

Testing isonymy with paternal and maternal lineages in the early Québec population: the impact of polyphyletism and demographic differentials

Isonymy is an ingenious and useful approach to studying kinship in human populations. However, it relies on assumptions that are difficult to verify. In this study, we provided a way to assess, in the early Québec population, the impact of factors such as polyphyletism, unbalanced sex-ratio among founders, and age differentials between spouses. All data were taken from the Population Register of Early Québec, which contains births, marriages, and deaths (>712,000) recorded in parish registers from the beginning of colonization (in 1608) to 1800. More specifically, using the 70,869 marriages recorded during that period, we compared kinship estimates given by genealogies, surnames, and paternal and maternal lineages. We also calculated a fifth coefficient of kinship by combining paternal and maternal lineage, thus providing a new way to test the isonymy method. The results show a good agreement between genealogical and isonymous estimates. However, this good correspondence is due to counterbalancing biases. Some of the implications of our results are discussed in the context of colonial America.     

Vigour-related traits and immunity in hybrids of evolutionary divergent cyprinoid species: advantages of hybrid heterosis?

Hybrid advantage, described as the superiority of hybrids in some traits over their parents and termed the “heterosis effect,” is widely documented in the case of reciprocal crosses of parental species (i.e., hybrids representing the F1 generation). In fish, high survival, fast growth and better health status have been widely documented in F1 hybrids. Nonetheless, the effects of interspecific hybridization on vigour, physiology and immunity-related traits in fish are largely unknown, especially concerning native systems of coexisting parental and hybrid genomes in the same habitat. The present study examined the potential physiological and immune aspects of hybrid heterosis by comparing condition status (measured especially by indexes), haematological profile, glucose concentration and selected parameters of non-specific and specific immunity between the evolutionarily divergent non-congeneric cyprinoid species Abramis brama and Rutilus rutilus and their hybrids representing the F1 generation, all of them caught in nature. Clear differences were documented for vigour-related, physiological and immune parameters between the two divergent species. Hybrids generally tended to express intermediate characters of the measured traits, likely generated by the evolutionary divergence of the hybridizing species; nonetheless, for some traits, hybrids exhibited a character that was more similar to one parental species than to the other. This was interpreted as the heterozygote advantage for F1 hybrids. It is suggested that a maternally inherited genetic background may potentially influence the expression of some branches of non-specific immunity or other aspects related to the fish health status.     

The species concept in parasites and other pathogens: a pragmatic approach?

Although the problem of speciation is a puzzle for evolutionists, species are not mere fantasies. In many cases, it is possible to identify evolutionary entities that deserve to be attributed the name 'species' and that are relevant to medical researchers and decision makers. All approaches to the problem of speciation in pathogens are specific cases of four main concepts (or combinations thereof): biological, phylogenetic, phenetic and phenotypic. Modern genetic concepts and technologies help to juggle these concepts.     

Does origin always matter? Evaluating the influence of nonlocal seed provenances for ecological restoration purposes in a widespread and outcrossing plant species

For restoration purposes, nature conservation generally enforces the use of local seed material based on the “local‐is‐best” (LIB) approach. However, in some cases recommendations to refrain from this approach have been made. Here we test if a common widespread species with no obvious signs of local adaptation may be a candidate species for abandoning LIB during restoration. Using 10 microsatellite markers we compared population genetic patterns of the generalist species Daucus carota in indigenous and formerly restored sites (nonlocal seed provenances). Gene diversity overall ranged between H_e = 0.67 and 0.86 and showed no significant differences between the two groups. Hierarchical AMOVA and principal component analysis revealed very high genetic population admixture and negligible differentiation between indigenous and restored sites (F_CT = 0.002). Moreover, differentiation between groups was caused by only one outlier population, where inbreeding effects are presumed. We therefore conclude that the introduction of nonlocal seed provenances in the course of landscape restoration did not jeopardize regional species persistence by contributing to inbreeding or outbreeding depressions, or any measurable adverse population genetic effect. On the basis of these results, we see no obvious objections to the current practice to use the 10‐fold cheaper, nonlocal seed material of D. carota for restoration projects.     

Viral proteins functioning in organelles: a cryptic origin?

Although mitochondria derive from alpha-proteobacteria, many proteins acting in this organelle did not originate from bacteria. In particular, phylogenetic evidence indicates that RNA polymerase, DNA polymerase and DNA primase--with homologues encoded by T3/T7-like bacteriophages--have replaced the ancestral proteins of bacterial origin. To date, there was no clear explanation for this puzzling observation. Bacterial genomics has now revealed the presence of cryptic prophages that are related to T3/T7 in several genomes of proteobacteria. We propose that such a prophage was present in the ancestral alpha-proteobacterium at the origin of mitochondria and that RNA polymerase, DNA polymerase and DNA primase encoded by this prophage replaced the original bacterial enzymes to function in mitochondria. Another T3/T7 viral-like RNA polymerase is functional in the chloroplast, indicating that a strong selection pressure has favored replacement of some cellular proteins by viral proteins in organelle evolution.     

Maternal steroids and contaminants in common tern eggs: a mechanism of endocrine disruption?

We looked for evidence for the hypothesis that exposure of female birds to polychlorinated biphenyls (PCBs) results in alteration of blood steroid hormone concentrations and alters subsequent hormone transfer of steroids to eggs. Eggs of three-egg clutches were collected from a PCB-exposed common tern (Sterna hirundo) colony (Ram Island, Buzzards Bay, MA, USA) and from a relatively clean colony (Bodkin Island, Chesapeake Bay, MD, USA), and were analyzed for concentrations of organochlorine contaminants and steroid hormones (17beta-estradiol, 5alpha-dihydrotestosterone, testosterone and androstenedione). There was no relationship between total PCBs and steroid concentrations considering all eggs together, considering eggs of different laying order or considering differences between sequentially laid eggs in a clutch. Similarly, concentrations of di- and tri-chlorinated biphenyls and steroids in eggs were not related. The concentrations of PCBs, mercury and selenium were below estimated thresholds for toxicity to embryos. Maternal steroids, except estradiol, were present in yolk of all eggs, with increasing concentrations in the second and third eggs laid. Our data provided no evidence for a maternal toxicological event that might alter the amount of maternal steroid hormone transferred to eggs.     

What makes a species central in a cleaning mutualism network?

Mutualisms often form networks of interacting species, characterized by the existence of a central core of species that potentially drive the ecology and the evolution of the whole community. Centrality measures allow quantification of how central or peripheral a species is within a network, thus informing about the role of each species in network organization, dynamics, and stability. In the present study we addressed the question whether the structural position of species in the network (i.e. their topological importance) relates to their ecological traits. We studied interactions between cleaner and client reef fishes to identify central and peripheral species within a mutualistic network, and investigated five ecological correlates. We used three measures to estimate the level of centrality of a species for distinct structural patterns, such as the number of interactions and the structural proximity to other species. Through the use of a principal component analysis (PCA) we observed that the centrality measures were highly correlated (92.5%) in the studied network, which indicates that the same species plays a similar role for the different structural patterns. Three cleaner and ten client species had positive values of centrality, which suggests that these species are modulating ecological and evolutionary dynamics within the network. Higher centralities were related to higher abundances and feeding habits for client fishes, but not for cleaners. The high correlation between centrality measures in the present study is likely related to the nested structure of the cleaning network. The cleaner species’ set, by having central species that are not necessarily the most abundant ones, bears potentially more vulnerable points for network cohesiveness. Additionally, the present study generalizes previous findings for plant–animal mutualisms, as it shows that the structure of marine mutualisms is also related to a complex interplay between abundance and niche‐related features.     

A hybrid of bovine pancreatic ribonuclease and human angiogenin: an external loop as a module controlling substrate specificity?

A comparison of the sequences of three homologous ribonucleases (RNase A, angiogenin and bovine seminal RNase) identifies three surface loops that are highly variable between the three proteins. Two hypotheses were contrasted: (i) that this variation might be responsible for the different catalytic activities of the three proteins; and (ii) that this variation is simply an example of surface loops undergoing rapid neutral divergence in sequence. Three hybrids of angiogenin and bovine pancreatic ribonuclease (RNase) A were prepared where regions in these loops taken from angiogenin were inserted into RNase A. Two of the three hybrids had unremarkable catalytic properties. However, the RNase A mutant containing residues 63-74 of angiogenin had greatly diminished catalytic activity against uridylyl-(3'----5')-adenosine (UpA), and slightly increased catalytic activity as an inhibitor of translation in vitro. Both catalytic behaviors are characteristic of angiogenin. This is one of the first examples of an engineered external loop in a protein. Further, these results are complementary to those recently obtained from the complementary experiment, where residues 59-70 of RNase were inserted into angiogenin [Harper and Vallee (1989) Biochemistry, 28, 1875-1884]. Thus, the external loop in residues 63-74 of RNase A appears to behave, at least in part, as an interchangeable 'module' that influences substrate specificity in an enzyme in a way that is isolated from the influences of other regions in the protein.