Functional divergence of spatially conserved olfactory glomeruli in two related moth species

In different moth species, the number and spatial arrangement of olfactory glomeruli in the antennal lobe (AL) vary widely, but the spatial map within a species is thought to be invariant, making it possible to identify single glomeruli across individuals. We investigated the relationship between the physiological tuning of pheromone-selective interneurons and their association with specific, identified glomeruli in the macroglomerular complex (MGC) of the noctuid moth, Heliothis subflexa. Three odorants that are required for pheromone-source location in this species were tested individually and in blends. Recordings from 27 pheromone-specific projection neurons (PNs) indicated that the majority (48%) were selectively activated by the major pheromone component of this species, Z-11-hexadecenal (Z11-16:Ald), with 33% primarily tuned to Z-9-hexadecenal and 19% to Z-11-hexadecenol. Intracellular staining revealed that the dendrites of PNs tuned to Z11-16:Ald always branched within the largest glomerulus of the MGC, the cumulus. Similarly, each of the other two classes of PN was associated with a different 'satellite' glomerulus in the MGC. The spatial configuration of the four-glomerulus H. subflexa MGC was indistinguishable from that previously reported in the closely related species, Heliothis virescens. Hence, as these two species diverged, changes in the association of satellite MGC glomeruli with particular odorants have occurred without a measurable change in the anatomical arrangement of the glomerular array.     

Acoustic convergence and divergence in two sympatric burrowing nocturnal seabirds

Shearwaters are nocturnal burrowing seabirds. They return to their colony at dusk and exhibit high vocal activity, underlining the usefulness of acoustic cues to nocturnal communication. The present study aimed to test whether acoustic communication systems of two sympatric shearwater species, the Yelkouan shearwater Puffinus yelkouan and the Mediterranean Cory's shearwater Calonectris diomedea diomedea , converge to similar strategies. Inter-annual mate fidelity and incubation relays led us to focus on sex and individual acoustic signatures. We first characterized those two signatures by analysing the major call emitted by incubating birds. Second, we performed playback experiments to assess ability of birds to vocally discriminate between sexes and mate versus non-mate. The results obtained show that both species use a reliable sex vocal signature supported by frequency and energy features, enabling sex identification of the emitter. By responding only to conspecific same-sex calls, birds may ensure burrow and mate guarding. Conversely, individual vocal signature was mainly supported by temporal parameters, and was more reliable in the Cory's shearwater. Moreover, this species uses vocal exchanges to identify the mate during incubation relays, whereas Yelkouan shearwaters probably need additional cues. In conclusion, we observe an evolutionary convergence in intra-sex communication process but a divergence in mate greeting strategy.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 115–134.     

The influence of gene flow and drift on genetic and phenotypic divergence in two species of Zosterops in Vanuatu

Colonization of an archipelago sets the stage for adaptive radiation. However, some archipelagos are home to spectacular radiations, while others have much lower levels of diversification. The amount of gene flow among allopatric populations is one factor proposed to contribute to this variation. In island colonizing birds, selection for reduced dispersal ability is predicted to produce changing patterns of regional population genetic structure as gene flow-dominated systems give way to drift-mediated divergence. If this transition is important in facilitating phenotypic divergence, levels of genetic and phenotypic divergence should be associated. We consider population genetic structure and phenotypic divergence among two co-distributed, congeneric (Genus: Zosterops) bird species inhabiting the Vanuatu archipelago. The more recent colonist, Z. lateralis, exhibits genetic patterns consistent with a strong influence of distance-mediated gene flow. However, complex patterns of asymmetrical gene flow indicate variation in dispersal ability or inclination among populations. The endemic species, Z. flavifrons, shows only a partial transition towards a drift-mediated system, despite a long evolutionary history on the archipelago. We find no strong evidence that gene flow constrains phenotypic divergence in either species, suggesting that levels of inter-island gene flow do not explain the absence of a radiation across this archipelago.     

Asymmetric reproductive interference between specialist and generalist predatory ladybirds

1.?Closely related species often differ greatly in the quality and breadth of resources exploited, but the actual mechanisms causing these differences are poorly understood. Because in the laboratory specialized species often survive and perform as well or better on host species that are never utilized in nature, negative ecological interactions restricting host range must exist. Here, we focused on reproductive interference, which has been theoretically predicted to drive niche separation between closely related species with overlapping mating signals. 2.?We examined the interspecific sexual interactions in relation to ecological specialization and generalization in two sibling ladybird species, Harmonia yedoensis and Harmonia axyridis. Harmonia yedoensis is a specialist predator that preys only on pine aphids, which are highly elusive prey for ladybird hatchlings, whereas H.?axyridis is a generalist predator with a broad prey and habitat range. 3.?We experimentally showed that conspecific sperm fertilized the vast majority of eggs regardless of mating order (i.e. conspecific sperm precedence) when a female of H.?yedoensis or H.?axyridis mated with both a conspecific and a heterospecific male. Moreover, we demonstrated that mating opportunities of H.?yedoensis females strongly decreased as heterospecific density increased relative to conspecific density. In contrast, in H.?axyridis, female mating success was high regardless of conspecific or heterospecific density. 4.?Our results suggest that the generalist H.?axyridis should be dominant to the specialist H.?yedoensis in terms of reproductive interference. Our results support the hypothesis that asymmetric reproductive interference from the dominant species may force the non-dominant species to become a specialist predator that exclusively utilizes less preferred prey in nature.     

Intraspecific morphological divergence in two Cichlid species from Benin

Selection on morphological traits can vary across the range of species, inducing a mosaic of phenotypes across populations. Intraspecific morphological divergence had been demonstrated for many fish groups inhabiting environments with varying abiotic or biotic selective pressures. Such intraspecific phenotypic variation can have a strong influence on the ecologies of species. In the current study, we examined patterns of intraspecific morphological divergence between two populations of Sarotherodon melanotheron and Coptodon guineensis in Lake Ahémé and Porto-Novo lagoon, Benin. Using multiple morphological traits, we demonstrated intraspecific morphological divergence between Lake Ahémé and Porto-Novo lagoon for these species. However, evidence for parallel divergence was found for these two species, implying a similar response to selective pressures might have been acting on labile traits. In addition, species specific morphological changes observed in the current study might be because of differing responses to similar selective forces or taxon-specific selective forces acting on labile traits. The intraspecific trait divergence demonstrated in the current study suggests several possible selective pressures acting on these populations, yet the cause of this divergence remains unknown and additional studies are required to test these inferences.     

Functional convergence of two lysyl-tRNA synthetases with unrelated topologies

Lysyl-tRNA can be synthesized by both a class I (LysRS-I) and a class II (LysRS-II) lysyl-tRNA synthetase. The crystal structure of LysRS-I from Pyrococcus horikoshii at 2.6 A resolution reveals extensive similarity with glutamyl-tRNA synthetase (GluRS). A comparison of the structures of LysRS-I and LysRS-II in complex with lysine shows that both enzymes use similar strategies for substrate recognition within unrelated active site topologies. A docking model based upon the GluRS-tRNA complex suggests how LysRS-I and LysRS-II can recognize the same molecular determinants in tRNALys, as shown by biochemical results, while approaching the acceptor helix of the tRNA from opposite sides.     

Functional and phenotypic characterization of two HL60 clones resistant to dimethylsulfoxide

Two HL60 clones (C12 and C13) totally insensitive to differentiation induction by dimethylsulfoxide (Me2SO) are described. They have been growing continuously in the presence of the inducer for more than 6 months. The morphological and cytochemical features of the two populations are quite similar to those of the original HL60 cell line, whereas a different karyotype with marked hyperploidy (modal chromosome number of 86 for C12 and 82 for C13) was detected. An antigenic pattern analogous to that of the native HL60 cell line was found in C12 and C13 populations using three monoclonal antibodies differently reactive to myeloid cells. Both clones can be induced to differentiate by retinoic acid (RA) and 12-O-tetradecanoylphorbol 13-acetate (TPA). The pattern of differentiation was assessed by morphological, cytochemical, phenotypical and functional markers. Differentiation of C12 cells by RA and TPA was similar to that observed with native HL60 cells, whereas C13 cells showed lower degrees of sensitivity to RA and TPA. The data presented suggest the existence of different mechanisms for induction of differentiation by Me2SO, RA and TPA. In addition, they are in accordance with previous observations of different degrees of inducibility to differentiation among leukemic cell populations in culture.     

Univariate and multivariate analysis on phenotypic divergence in Phleum

Summary An analysis of phenotypic and genetic variability was performed on Phleum ambiguum populations obtained by vegetative propagation and grown in different environments. The investigation on a single character and the canonical analysis on several plant traits indicate that, while genetic variability (h²) is essentially constant, phenotypic variance and covariance are affected by different environments and successive clonations. The observed changes seem not to be reversible when plants, transferred to a different environment, are returned to the original one. Within-clones variability seems to be affected by environmental conditions without being directly related to them. The results reported seem to be in good agreement with the phenotypic divergence hypothesis.     

Decoupling of genetic and phenotypic divergence in a headwater landscape

In stream organisms, the landscape affecting intraspecific genetic and phenotypic divergence is comprised of two fundamental components: the stream network and terrestrial matrix. These components are known to differentially influence genetic structure in stream species, but to our knowledge, no study has compared their effects on genetic and phenotypic divergence. We examined how the stream network and terrestrial matrix affect genetic and phenotypic divergence in two stream salamanders, Gyrinophilus porphyriticus and Eurycea bislineata, in the Hubbard Brook Watershed, New Hampshire, USA. On the basis of previous findings and differences in adult terrestriality, we predicted that genetic divergence and phenotypic divergence in body morphology would be correlated in both species, but structured primarily by distance along the stream network in G. porphyriticus, and by overland distance in E. bislineata. Surprisingly, spatial patterns of genetic and phenotypic divergence were not strongly correlated. Genetic divergence, based on amplified DNA fragment length polymorphisms, increased with absolute geographic distance between sites. Phenotypic divergence was unrelated to absolute geographic distance, but related to relative stream vs. overland distances. In G. porphyriticus, phenotypic divergence was low when sites were close by stream distance alone and high when sites were close by overland distance alone. The opposite was true for E. bislineata. These results show that small differences in life history can produce large differences in patterns of intraspecific divergence, and the limitations of landscape genetic data for inferring phenotypic divergence. Our results also underscore the importance of explicitly comparing how terrestrial and aquatic conditions affect spatial patterns of divergence in species with biphasic life cycles.     

Inducer-dependent phenotypic divergence in an embryonal-carcinoma cell line

Abstract. In monolayer cultures, embryonal carcinoma (EC) cells from the cell line Nulli-SCCI can be induced to differentiate at high efficiency by exposure to either retinoic acid or hexamethylenebisacetamide. Depending on which inducing agent is used, two distinct differentiated phenotypes result. These phenotypes resemble two of the earliest differentiated derivatives of the cells of the inner cell mass of a mouse blastocyst, i.e., parietal and visceral endoderm. Both differ from EC cells as well as from each other on the basis of their morphology, antigenic expression, secretion of plasminogen activator, and protein-synthetic profiles.     

Habitat specialization and adaptive phenotypic divergence of anuran populations

We tested for adaptive population structure in the frog Rana temporaria by rearing tadpoles from 23 populations in a common garden experiment, with and without larval dragonfly predators. The goal was to compare tadpole phenotypes with the habitats of their source ponds. The choice of traits and habitat variables was guided by prior information about phenotypic function. There were large differences among populations in life history, behaviour, morphological shape, and the predator-induced plasticities in most of these. Body size and behaviour were correlated with predation risk in the source pond, in agreement with adaptive population divergence. Tadpoles from large sunny ponds were morphologically distinct from those inhabiting small woodland ponds, although here an adaptive explanation was unclear. There was no evidence that plasticity evolves in populations exposed to more variable environments. Much among-population variation in phenotype and plasticity was not associated with habitat, perhaps reflecting rapid changes in wetland habitats.     

Concordant divergence in proteins and mitochondrial DNA between two vole species in the genusClethrionomys

The bank vole (Clethrionomys glareolus) and the northern red-backed vole (C. rutilus) are two closely related species where interspecific crosses result in fertile female but sterile male offspring. Mitochondrial DNA (mtDNA) fromC. rutilus has passed the species barrier and is found inC. glareolus from northern Fennoscandia. The present report shows that the genetic distance between the two species, calculated from enzyme data (Nei'sD), is 0.64. Isoelectric focusing of muscle proteins resolved around 55 bands, of which each species had 6 or 7 bands not present in the other species. Sequence divergence of mtDNA from the two species is 13.9%. A comparison between protein and mtDNA distances in other species pairs reveals a high correlation between the two measures, indicating that differences in mtDNA between taxa are not random when compared to divergence in protein-coding nuclear genes. The relationship between genetic divergence in proteins and that in mtDNA betweenClethrionomys glareolus andC. rutilus is similar to that found in other species pairs. It is also shown that despite large differences on the protein level it is still, in some cases, possible for species pairs to produce fertile hybrid females.This study was sponsored by the Swedish Natural Science Research Council, the Erik Philip-Sörensen Foundation, and the Nilsson-Ehle Foundation.     

Influence of mating duration on fecundity and fertility in two aphidophagous ladybirds

Abstract:  The influence of different mating durations on fecundity and fertility has been studied in two aphidophagous ladybirds, Cheilomenes sexmaculata and Coelophora saucia . Pre-oviposition period decreased while fecundity and fertility increased with increase in mating duration in both the ladybird species. The increase in fecundity with longer mating durations is probably due to the female response because of cryptic female choice. Mating of 10-s duration resulted in oviposition but of unviable eggs probably because of lack of sperm transfer. A minimum duration of 1 min of mating was probably essential for fertilization of the eggs. Absence of spermatophore in the reproductive tract of females is indicative of direct sperm transfer in both the ladybird species. Trend of fertility (similar fertility at 1 and 5 min followed by increase at 60 min which was again similar to that at complete mating) indicates probable sperm transfer in spurts in C. sexmaculata while continuous transfer in C. saucia is indicated by continuous increase in fertility with increase in mating duration.     

Weak disruptive selection and incomplete phenotypic divergence in two classic examples of sympatric speciation: cameroon crater lake cichlids

Abstract Recent documentation of a few compelling examples of sympatric speciation led to a proliferation of theoretical models. Unfortunately, plausible examples from nature have rarely been used to test model predictions, such as the initial presence of strong disruptive selection. Here I estimated the form and strength of selection in two classic examples of sympatric speciation: radiations of Cameroon cichlids restricted to Lakes Barombi Mbo and Ejagham. I measured five functional traits and relative growth rates in over 500 individuals within incipient species complexes from each lake. Disruptive selection was prevalent in both groups on single and multivariate trait axes but weak relative to stabilizing selection on other traits and most published estimates of disruptive selection. Furthermore, despite genetic structure, assortative mating, and bimodal species-diagnostic coloration, trait distributions were unimodal in both species complexes, indicating the earliest stages of speciation. Long waiting times or incomplete sympatric speciation may result when disruptive selection is initially weak. Alternatively, I present evidence of additional constraints in both species complexes, including weak linkage between coloration and morphology, reduced morphological variance aligned with nonlinear selection surfaces, and minimal ecological divergence. While other species within these radiations show complete phenotypic separation, morphological and ecological divergence in these species complexes may be slow or incomplete outside optimal parameter ranges, in contrast to rapid divergence of their sexual coloration.     

Compositional divergence and convergence in local communities and spatially structured landscapes

Community structure depends on both deterministic and stochastic processes. However, patterns of community dissimilarity (e.g. difference in species composition) are difficult to interpret in terms of the relative roles of these processes. Local communities can be more dissimilar (divergence) than, less dissimilar (convergence) than, or as dissimilar as a hypothetical control based on either null or neutral models. However, several mechanisms may result in the same pattern, or act concurrently to generate a pattern, and much research has recently been focusing on unravelling these mechanisms and their relative contributions. Using a simulation approach, we addressed the effect of a complex but realistic spatial structure in the distribution of the niche axis and we analysed patterns of species co-occurrence and beta diversity as measured by dissimilarity indices (e.g. Jaccard index) using either expectations under a null model or neutral dynamics (i.e., based on switching off the niche effect). The strength of niche processes, dispersal, and environmental noise strongly interacted so that niche-driven dynamics may result in local communities that either diverge or converge depending on the combination of these factors. Thus, a fundamental result is that, in real systems, interacting processes of community assembly can be disentangled only by measuring traits such as niche breadth and dispersal. The ability to detect the signal of the niche was also dependent on the spatial resolution of the sampling strategy, which must account for the multiple scale spatial patterns in the niche axis. Notably, some of the patterns we observed correspond to patterns of community dissimilarities previously observed in the field and suggest mechanistic explanations for them or the data required to solve them. Our framework offers a synthesis of the patterns of community dissimilarity produced by the interaction of deterministic and stochastic determinants of community assembly in a spatially explicit and complex context.     

On the divergence of species

Speciation may be considered as a kind of non-equilibrium phase transition which is caused by bifurcation at a critical point of instability. It can be shown that multiple branching of an evolutionary tree is highly improbable, since non-degenerate mathematical models describe only binary branchings.     

Behavioural elements reflect phenotypic colour divergence in a poison frog

The coexistence of both aposematic and cryptic morphs as different anti-predator strategies within a species seems to be an unusual phenomenon in nature. The strawberry poison frog, Oophaga pumilio, shows an astonishing colour diversity among populations in western Panama. In this study we selected a red and a green colour morph from two Panamanian islands (Isla Solarte and Isla Colón) for behavioural observations and measurements of conspicuousness. We found that red frogs were more visible to both conspecific frogs and potential predators than green frogs. Interestingly the difference in conspicuousness was most pronounced at the substrate that males used as principal calling places. Red males were more active and spent more time foraging than green males, which spent more time hidden. The association between conspicuousness of colouration and behaviour results in a more aposematic and a more cryptic anti-predator strategy. This is the first study which links differences in conspicuousness between animals on their natural backgrounds to differences in foraging as well as anti-predator behaviour and discusses the results in light of previous findings of toxicity analyses and potential costs and benefits of aposematism. To this end, our study adds a novel perspective for explaining extreme colour diversity between populations within an initially aposematic species.