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PubMed2002

Sympatric speciation in phytophagous insects: moving beyond controversy?

Sympatric speciation is the splitting of one evolutionary lineage into two without the occurrence of geographic isolation. The concept has been intimately tied to entomology since the 1860s, when Benjamin Walsh proposed that many host-specific phytophagous insects originate by shifting and adapting to new host plant species. If true, sympatric speciation would have tremendous implications for our understanding of species and their origins, biodiversity (25-40% of all animals are thought to be phytophagous specialists), insect-plant coevolution, community ecology, phylogenetics, and systematics, as well as practical significance for the management of insect pests. During much of the twentieth century sympatric speciation was viewed as much less plausible than geographic (allopatric) speciation. However, empirical field studies, laboratory experiments, developments in population genetics theory, and phylogenetic and biogeographic data have all recently combined to shed a more favorable light on the process. We review the evidence for sympatric speciation via host shifting for phytophagous insects and propose a set of testable predictions for distinguishing geographic mode (allopatric versus sympatric) of divergence. Our conclusion is that sympatric speciation is a viable hypothesis. We highlight areas where more thorough testing is needed to move sympatric speciation into the realm of accepted scientific theory.

Animals↗
PubMed2004

The species flocks of East African cichlid fishes: recent advances in molecular phylogenetics and population genetics.

With more than 3,000 species, the fish family Cichlidae is one of the most species-rich families of vertebrates. Cichlids occur in southern and central America, Africa, Madagascar, and India. The hotspot of their biodiversity is East Africa, where they form adaptive radiations composed of hundreds of endemic species in several lakes of various sizes and ages. The unparalleled species richness of East African cichlids has been something of a conundrum for evolutionary biologists and ecologists, since it has been in doubt whether these hundreds of species arose by allopatric speciation or whether it is necessary to invoke somewhat less traditional models of speciation, such as micro-allopatric, peripatric, or even sympatric speciation or evolution through sexual selection mediated by female choice. Ernst Mayr's analyses of these evolutionary uniquely diverse species assemblages have contributed to a more direct approach to this problem and have led to a deeper understanding of the patterns and processes that caused the formation of these huge groups of species. We review here recent molecular data on population differentiation and phylogenetics, which have helped to unravel, to some extent, the patterns and processes that led to the formation and ecological maintenance of cichlid species flocks. It is becoming apparent that sexually selected traits do play an important role in speciation in micro-allopatric or even sympatric settings. Species richness seems to be roughly correlated with the surface area, but not the age, of the lakes. We observe that the oldest lineages of a species flock of cichlids are often less species-rich and live in the open water or deepwater habitats. While the species flocks of the Lake Malawai and the Lake Victoria areas were shown to be monophyletic, the cichlid assemblage of Lake Tanganyika seems to consist of several independent species flocks. Cichlids emerge as an evolutionary model system in which many fundamental questions in evolution and ecology can be tested successfully, yet for other fish species flocks the relative importance of alternative mechanisms of speciation is likely to differ from that in cichlid fish.

Africa, Eastern↗
PubMed2005

Speciation: more likely through a genetic or through a learned habitat preference?

A problem in understanding sympatric speciation is establishing how reproductive isolation can arise when there is disruptive selection on an ecological trait. One of the solutions that has been proposed is that a habitat preference evolves, and that mates are chosen within the preferred habitat. We present a model where the habitat preference can evolve either by means of a genetic mechanism or by means of learning. Employing an adaptive-dynamical analysis, we show that evolution proceeds either to a single population of specialists with a genetic preference for their optimal habitat, or to a population of generalists without a habitat preference. The generalist population subsequently experiences disruptive selection. Learning promotes speciation because it increases the intensity of disruptive selection. An individual-based version of the model shows that, when loci are completely unlinked and learning confers little cost, the presence of disruptive selection most probably leads to speciation via the simultaneous evolution of a learned habitat preference. For high costs of learning, speciation is most likely to occur via the evolution of a genetic habitat preference. However, the latter only happens when the effect of mutations is large, or when there is linkage between genes coding for the different traits.

Adaptation, Biological↗
PubMed2005

Counteracting selective regimes and host preference evolution in ecotypes of two species of walking-sticks.

The evolution of ecological specialization has been a central topic in ecology because specialized adaptations to divergent environments can result in reproductive isolation and facilitate speciation. However, the order in which different aspects of habitat adaptation and habitat preference evolve is unclear. Timema walking-stick insects feed and mate on the host plants on which they rest. Previous studies of T. cristinae ecotypes have documented divergent, host-specific selection from visual predators and the evolution of divergent host and mate preferences between populations using different host-plant species (Ceanothus or Adenostoma). Here we present new data that show that T. podura, a nonsister species of T. cristinae, has also formed ecotypes on these host genera and that in both species these ecotypes exhibit adaptive divergence in color-pattern and host preference. Color-pattern morphs exhibit survival trade-offs on different hosts due to differential predation. In contrast, fecundity trade-offs on different hosts do not occur in either species. Thus, host preference in both species has evolved before divergent physiological adaptation but in concert with morphological adaptations. Our results shed light onto which traits are involved in the initial stages of ecological specialization and ecologically based reproductive isolation.

Adaptation, Biological↗
PubMed1997

Stress-resistance genotypes, metabolic efficiency and interpreting evolutionary change.

Assuming stress levels to which free-living populations are normally exposed, an association between rapid development time, a long life, success in mating and size of sexual ornaments can be predicted. Fitness at one stage of the life cycle should therefore correlate with fitness at other stages under this environmental model. Assuming that stress targets energy carriers, high-energy efficiency underlain by stress-resistance genotypes that are likely to be heterozygous is the basis of this prediction. Stress-resistance genotypes therefore have a role in promoting the energy efficiency required for organisms to accommodate a stressed world. Selection for energy efficiency to utilize heterogenous resources implies that the process of speciation should normally occur rapidly and be rarely observed. It follows that the ecological species concept is primary to other species concepts. The intensity of selection for stress resistance goes from an extreme in the highly disturbed and stressful environments of living fossils to relatively stable abiotic habitats, where specialist diversifications and adaptive radiations are likely. Between these extremes, a punctuated pattern of evolutionary change may occur in perturbed environments during a transient phase of increased resources. In abiotically benign tropical habitats where energy constraints are low, specialization of resource utilization by learning appears possible.

Animals↗
PubMed2002

Horizontal gene transfer and bacterial diversity.

Bacterial genomes are extremely dynamic and mosaic in nature. A substantial amount of genetic information is inserted into or deleted from such genomes through the process of horizontal transfer. Through the introduction of novel physiological traits from distantly related organisms, horizontal gene transfer often causes drastic changes in the ecological and pathogenic character of bacterial species and thereby promotes microbial diversification and speciation. This review discusses how the recent influx of complete chromosomal sequences of various microorganisms has allowed for a quantitative assessment of the scope, rate and impact of horizontally transmitted information on microbial evolution.

Animals↗
PubMed2005

Radiation and diversification within the Ligularia-Cremanthodium-Parasenecio complex (Asteraceae) triggered by uplift of the Qinghai-Tibetan Plateau.

The Ligularia-Cremanthodium-Parasenecio (L-C-P) complex of the Tussilagininae (Asteraceae: Senecioneae) contains more than 200 species that are endemic to the Qinghai-Tibetan Plateau in eastern Asia. These species are morphologically distinct; however, their relationships appear complex. A phylogenetic analysis of members of the complex and selected taxa of the tribe Senecioneae was conducted using chloroplast (ndhF and trnL-F) and nuclear (ITS) sequences. Phylogenetic trees were constructed from individual and combined datasets of the three different sequences. All analyses suggested that Doronicum, a genus that has been included in the Tussilagininae, should be excluded from this subtribe and placed at the base of the tribe Senecioneae. In addition, the Tussilagininae should be broadly circumscribed to include the Tephroseridinae. Within the expanded Tussilagininae containing all 13 genera occurring in eastern Asia, Tussilago and Petasites diverged early as a separate lineage, while the remaining 11 genera comprise an expanded L-C-P complex clade. We suggest that the L-C-P clade, which is largely unresolved, most likely originated as a consequence of an explosive radiation. The few monophyletic subclades identified in the L-C-P clade with robust support further suggest that some genera of Tussilagininae from eastern Asia require generic re-circumscriptions given the occurrence of subclades containing species of the same genus in different parts of the phylogentic tree due to homoplasy of important morphological characters used to delimit them. Molecular-clock analyses suggest that the explosive radiation of the L-C-P complex occurred mostly within the last 20 million years, which falls well within the period of recent major uplifts of the Qinghai-Tibetan Plateau between the early Miocene to the Pleistocene. It is proposed that significant increases in geological and ecological diversity that accompanied such uplifting, most likely promoted rapid and continuous allopatric speciation in small and isolated populations, and allowed fixation or acquisition of similar morphological characters within unrelated lineages. This phenomenon, possibly combined with interspecific diploid hybridization because of secondary sympatry during relatively stable stages between different uplifts, could be a major cause of high species diversity in the Qinghai-Tibetan Plateau and adjacent areas of eastern Asia.

Asteraceae↗
PubMed2007

Learning the ecological niche.

A cornerstone of ecological theory is the ecological niche. Yet little is known about how individuals come to adopt it: whether it is innate or learned. Here, we report a cross-fostering experiment in the wild where we transferred eggs of blue tits, Cyanistes caeruleus, to nests of great tits, Parus major, and vice versa, to quantify the consequences of being reared in a different social context, but in an environment otherwise natural to the birds. We show that early learning causes a shift in the feeding niche in the direction of the foster species and that this shift lasts for life (foraging conservatism). Both species changed their feeding niches, but the change was greater in the great tit with its less specialized feeding behaviour. The study shows that cultural transmission through early learning is fundamental to the realization of ecological niches, and suggests a mechanism to explain learned habitat preference and sympatric speciation in animals.

Animals↗
PubMed2005

Genealogical evidence of homoploid hybrid speciation in an adaptive radiation of Scaevola (goodeniaceae) in the Hawaiian Islands.

Although homoploid hybrid speciation is increasingly recognized as an important phenomenon in plant evolution, its role in adaptive radiations is poorly documented. We studied a clade of seven extant species of Scaevola that are endemic to the Hawaiian Islands and show substantial ecological and morphological diversity. We estimated the genealogies for alleles isolated from multiple accessions of each species at four nuclear loci: the ITS region, and the introns of three nuclear genes, LEAFY (LFY), NITRATE REDUCTASE (NIA), and GLYCERALDEHYDE 3-PHOSPHATE DEHYDROGENASE (G3PDH). For five of the seven species, there was complete concordance among the genealogies estimated from the four loci and, when all four regions were combined, the relationships among these five species were fully resolved. Inclusion of alleles from the remaining two species, S. procera and S. kilaueae, resulted in incongruence among loci, which appears to reflect a history of hybridization. Based on the distribution of alleles, we infer that S. procera is the result of a homoploid hybrid speciation event between S. gaudichaudii and S. mollis and that S. kilaueae is probably the result of hybrid speciation between S. coriacea and S. chamissoniana. In each case the inferred hybridization is consistent with morphological, ecological, and geographic information. We conclude that homoploid hybrid speciation may be more common than is perceived and may play a role in generating novel combinations of adaptive traits that arise during island radiations.

Adaptation, Physiological↗
PubMed1978

Some aspects of monogenean existence.

This paper deals with some ecology and evolution problems of monogeneans--gill parasites of fishes, such as congeneric simultaneous doublets, spatial distribution of species on the gills, interspecific restrictions of biotopes etc. The author proves competitive character of site selection in monogeneans. The role of hermaphroditism in the evolution and biology of monogeneans, and morphological adaptations (mainly androgynous) directed to increasing of mating chance are discussed. The author concentrates on analyzing the cases of monoxenous distribution and speciation and also on examining the concept of symxenity and alloxenity. He attaches great importance to ecological and evolutionary investigations of Monogenoidea.

Animals↗
PubMed1994

Ecological genetic studies in the chromosomal form Mopti of Anopheles gambiae s.str. in Mali, west Africa.

Among the sibling species of the Afrotropical Anopheles gambiae complex, the nominal taxon (An. gambiae s.str.) is the major malaria vector. Its bionomics suggest a man-dependent speciation process which involves, in West Africa, various incipient species chromosomally recognized by different combinations of 2R paracentric inversions. One of the most recent evolutionary steps of such a speciation process appears to be the chromosomal form Mopti, which is associated with dry season irrigation in arid zones, and is characterized by a remarkable ecological flexibility related to three 2R alternative arrangements, namely bc, u and +, whose expected karyotypes are found in Hardy-Weinberg equilibrium. The study of this chromosomal polymorphism in samples from a 16-locality transect in Mali shows wide variations and highly significant correlation with both temporal and spatial climatic differences. Mosquitoes homokaryotypic for 2Rbc are the actual dry season and arid areas breeders. The regular rise of 2Rbc frequency, up to fixation, during each dry season, corresponds to the South-North clinal increase of the same arrangement along the transect, from about 30% in the humid savanna to near fixation in the South-Saharan zone. This coherent ecological genetics case provides full support to the hypothesis of the adaptive nature of paracentric inversions. Moreover, the very peculiar system of combinations of contiguous 2R inversions, utilized by Mopti as well as by other chromosomal forms of An. gambiae, suggests a process of polygenic reorganization based on linkage disequilibria and involving the inversions as driving selection units.

Animals↗
PubMed2001

Phylogenetic analysis of partial sequences of elongation factor 1alpha identifies major groups of lice (Insecta: Phthiraptera).

As a first attempt to use molecular data to resolve the relationships between the four suborders of lice and within the suborder Ischnocera, we sequenced a 347-bp fragment of the elongation factor 1alpha gene of 127 lice (Insecta: Phthiraptera) as well as outgroup taxa from the order Psocoptera. A number of well-supported monophyletic groups were found but the relationships among many of these groups could not be resolved. While it is probable that multiple substitutions at high divergences and ancient radiation over a short period of time have contributed to the problem, we attribute most of this lack of resolution to the high ratio of taxa to characters. Nevertheless, the sequence data unequivocally support a number of important relationships that are at variance with the conclusions of morphological taxonomy. These include the sister group relationship of Chelopistes and Oxylipeurus, two lice occupying different ecological niches on the same host, which have previously been assigned to different families. These results provide evidence in support of the hypothesis that lice have speciated in situ on the host in response to niche specialization and that this has given rise to convergent morphologies in the lice of different host groups which share similar ecological niches. We discuss our attempts to overcome the limitations of this large data set, including the use of leaf stability analysis, a new method for analyzing the stability of taxa in a phylogenetic tree, and examine a number of hypotheses of relationships based on both traditional taxonomy and host associations.

Animals↗
PubMed2004

Harmonic-hopping in Wallacea's bats.

Evolutionary divergence between species is facilitated by ecological shifts, and divergence is particularly rapid when such shifts also promote assortative mating. Horseshoe bats are a diverse Old World family (Rhinolophidae) that have undergone a rapid radiation in the past 5 million years. These insectivorous bats use a predominantly pure-tone echolocation call matched to an auditory fovea (an over-representation of the pure-tone frequency in the cochlea and inferior colliculus) to detect the minute changes in echo amplitude and frequency generated when an insect flutters its wings. The emitted signal is the accentuated second harmonic of a series in which the fundamental and remaining harmonics are filtered out. Here we show that three distinct, sympatric size morphs of the large-eared horseshoe bat (Rhinolophus philippinensis) echolocate at different harmonics of the same fundamental frequency. These morphs have undergone recent genetic divergence, and this process has occurred in parallel more than once. We suggest that switching harmonics creates a discontinuity in the bats' perception of available prey that can initiate disruptive selection. Moreover, because call frequency in horseshoe bats has a dual function in resource acquisition and communication, ecological selection on frequency might lead to assortative mating and ultimately reproductive isolation and speciation, regardless of external barriers to gene flow.

Acoustics↗
PubMed1976

Distribution of group D streptococci in rivers and streams.

A study was undertaken to determine sources of bacteriological contamination of rivers as well as the ecology of faecal streptococci in natural and contaminated waters. Media used to characterize and speciate group D streptococci were also evaluated using isolates from the water and sediment. Due to the low concentrations of faecal coliforms (FC) and faecal streptococci (FS) in river water samples, the FC/FS ratio was shown to be of little value in determining sources of contamination. High concentrations of FC and FS from sediment samples gave more credible FC/FS ratios. The actual distribution of group D streptococcal species in rivers and streams was also shown. High concentrations of all division II species (S. faecium, S. faecium var. casseliflavus, and S. faecium var. durans) were found in the water and sediment samples, with S. faecium var. durans comprising 50% of the total number of isolates. Low concentrations of division I group D streptococci (S. faecalis and varieties) were found, while only one isolation of division III group D streptococci (S. bovis and S. equinus) was made.

Enterococcus faecalis↗
PubMed2026

Genetic (Genomic) and Morphological Evidence Suggest That the Korean Endemic Fat Minnow (Rhynchocypris kumgangensis) and the Deogyu Population Represent Distinct Species.

Geographically disconnected populations of freshwater fishes often show ecological and genetic divergence in response to opposing selection differentials in different habitat environments, sometimes leading to the formation of ecotypes and even speciation. Nevertheless, evidence for the speciation through allopatric processes in freshwater fish systems remains scarce. Kumkang fat minnow (Rhynchocypris kumgangensis), a Korean endemic coldwater fish, has recently been suggested to diverge into a separate species (Rhynchocypris deogyuensis). However, the level of their genetic and ecological divergence remains largely unknown. We analyzed population genetic structure of R. kumgangensis together with R. deogyuensis using mitochondrial DNA (mtDNA) and eight newly developed microsatellite markers. Genetic divergence at mitogenome level was further assessed between the presumed two species. Moreover, we examined morphology between two groups by analyzing morphometric traits and also conducted geometric morphometrics on body shape. We found distinct population structure between R. kumgangensis and R. deogyuensis at both mtDNA and microsatellites. One remnant population of R. deogyuensis harbored only a single haplotype and showed a very high level of inbreeding. Comparative analysis of the mitogenomes showed approximately 2.9% divergence between R. kumgangensis and R. deogyuensis, supporting the species-level divergence. The analyses of both morphometric traits and geometric morphometrics indicated significant morphological divergence between the two species. The observed low values of length-weight relationship and condition factor for R. deogyuensis are likely to be attributed to effects of the elevated level of inbreeding and depleted genetic diversity. Overall, our combined genetic/genomic and morphological analyses suggest the considerable divergence between R. kumgangensis and R. deogyuensis, supporting the hypothesis that they are distinct species. The mechanisms underpinning how they speciate still need to be studied further in detail.

Deogyu fat minnow↗