Sibling Species Group Research Articles

Unusual Braarudosphaera bigelowii and Micrantholithus vesper enrichment in the Early Miocene sediments from the Slovenian Corridor, a seaway linking the Central Paratethys and the Mediterranean

During a stratigraphic survey of an Early Miocene sedimentary sequence outcropping in SE Slovenia an unusual enrichment of the calcareous nannoplankton assemblage with pentaliths – pentagonal nannoliths consisting of five crystal units and showing radial symmetry – was detected. Pentaliths were only abundant in a short interval, which was sampled in detail. The lithological composition of this interval was indistinguishable from that of the underlying and the overlying strata. The composition of nannoplankton assemblages and distribution patterns of different taxa were studied. Mineral composition, total calcite content and δ 13C values of chosen sediment samples were analysed as well. The pentalith-enriched strata were deposited in the lower Early Miocene, corresponding to the Egerian stage of the Central Paratethys and the Aquitanian of the Mediterranean, in the Slovenian Corridor — a seaway linking the Central Paratethys and the Mediterranean. The presence of rare specimens of Discoaster druggii and Helicosphaera carteri allows stratigraphic correlation with the transition of NN1 — Triquetrorhabdulus carinatus Zone and NN2 — Discoaster druggii Zone of Martini [Martini, E., 1971. Standard Tertiary and Quarternary calcareous nannoplankton zonation. In: Farinacci, A. (Ed.), Proceedings of the II Planctonic Conference, Roma, 1970, Ed. Technoscienza, pp. 739–785]. Pentaliths belong to two species: Braarudosphaera bigelowii and Micrantholithus vesper. Both species display a wide range of morphological variation and most likely represent a group of sibling species. The pattern of distribution of both species displays obvious similarities throughout most of the studied interval. In the upper part of the studied interval B. bigelowii reaches maximum abundance, while M. vesper disappears. Since the ability of B. bigelowii to thrive in hyposaline water is well known, it appears that M. vesper tolerates reduced water salinity as well, but to a lesser extent than B. bigelowii. No significant paleoclimatic and paleogeographical changes are known in this particular region during the Early Miocene, however, the onset of far reaching extensional tectonic processes took place during this time. The enrichment of nannoplankton assemblage with pentaliths may represent a reflection of a short-lived episode of hyposaline conditions. Enhanced influx of freshwater and terrigenous material is indicated by a drop in 13C values, a rise in nannoplankton productivity and the presence of sand in some samples from the pentalith-enriched strata. The most likely causes of this episode are regional tectonic changes, associated with the onset of intensive tectonic activity in the western part of the Central Paratethys.

Divergence of genomic DNA in species of the subgenus Camptochironomus (Diptera, Chironomidae) differing in their cytogenetic similarity levels

The variation and divergence of genomic DNA in four species of the subgenus Camptochironomus (C. tentans, C. dilutus, C. pallidivittatus, and C. setivalva) differing in the level of their cytological similarity were analyzed using the RAPD (Randomly Amplified Polymorphic DNA) method. A high level of variation in the RAPD markers was found in the species studied. Genetic distances (GD) were assessed between natural C. tentans populations, between different species of the camptochironomus sibling species group (C. tentans, C. dilutus, and C. pallidivittatus), and between these species and C. setivalva which is outside this sibling species group. The GD values obtained characterize the levels of genomic differentiation among natural populations (GD = 0.248), among sibling species (GD = 0.635), and between incipient species (GD = 0.784) of the subgenus Camptochironomus. The degree of genomic DNA divergence between sibling and incipient species in the subgenus Camptochironomus was found to be lower than that in the genus Chironomus. The rate of genomic DNA divergence appears to be lower than the rate of chromosomal divergence in species of the subgenus Camptochironomus.

THE EVOLUTIONARY ENIGMA OF BONEFISHES (ALBULA SPP.): CRYPTIC SPECIES AND ANCIENT SEPARATIONS IN A GLOBALLY DISTRIBUTED SHOREFISH

Abstract Many examples of cryptic marine species have been demonstrated with biochemical and molecular studies. In most cases, a broadly distributed taxon is actually a group of sibling species that can be distinguished (upon closer examination) by ecological or morphological characters. Fishes of the family Albulidae constitute a notable exception. Bonefish (Albula spp.) morphology and ecology are highly conserved around the globe, and their extended pelagic larval stage could allow population connections on a vast geographic scale. Based on this perceived homogeneity, bonefishes were classified as a single pantropical species, A. vulpes. However, allozyme studies of Hawaiian populations indicated that two sympatric species (A. glossodonta and A. neoguinaica) are included in the synonymy of A. vulpes. To ascertain the number and distribution of evolutionary partitions in Albula, we surveyed 564 bp of mitochondrial DNA (mtDNA) cytochrome b from 174 individuals collected at 26 locations. Sequence comparisons reveal eight deep lineages (d= 5.56–30.6%) and significant population structure within three of the four lineages that could be tested (φST= 0.047–0.678). These findings confirm the genetic distinctiveness of the three species noted above and invoke the possibility of five additional species. Clock estimates for mtDNA indicate that these putative species arose 4–20 million years ago. Distinct evolutionary lineages coexist in several sample locations, yet show little morphological or ecological differentiation in sympatry. Thus, bonefish species seem to defy the evolutionary conventions of morphological differentiation over time and ecological displacement in sympatry. Despite multiple cases of sympatry, sister‐taxa relationships inferred from mtDNA indicate that divergence in allopatry has been the predominant speciation mechanism in Albula. Stabilizing selection in the homogeneous habitat occupied by bonefishes (tropical sand flats) could promote the retention of highly conserved morphology and ecology.

Reproductive relationships and degree of synapsis in the polytene chromosomes of the Drosophila buzzatii species cluster

The process of speciation occurs through the evolution of any of several forms of reproductive isolation between taxa, including inviability of hybrids. In this work, strains derived from allopatric populations of Drosophila buzzatii cluster species were experimentally crossed in order to evaluate their reproductive and cytogenetic relationships, and to contribute toward understanding the reproductive isolation in this group of sibling species. Although intrastrain crosses were highly fertile, we consider it relevant to discuss the differences in intra- and interspecific fertility and fecundity here. Among 30 interspecific crosses, about 63% were partially or completely sterile. Fifty three percent of interspecific F1 crosses (female and male F1 crossed) were also partially or completely sterile, in contrast to only one out of 24 intraspecific F1 crosses that was partially sterile. An analysis of hybrid polytene chromosomes revealed complete synapsis, except in the microchromosomes (VI) and in the proximal region of the X chromosome. The intraspecific divergence observed in this study and the variable degree of chromosome pairing shown here reveal part of the complexity of the speciation process pertinent to Drosophila buzzatii cluster, which is consistent with different traits studied in this cluster.

Variation and Divergence of Multilocus Genome Markers in the Species of the Genus Chironomus (Diptera, Chironomidae)

Variation and divergence patterns of the multilocus genome markers in twelve Chironomus species belonging to the plumosus and piger sibling-species groups were examined by use of polymerase chain reaction with random primers (RAPD method). The chironomid species showed high levels of the RAPD markers polymorphism. The genetic distances (GD) were determined between the species within the group of closely related species, as well as between the species from different groups. The estimates obtained characterized the divergence levels between the sibling species (GD = 0.739) and morphologically distinct species (GD = 0.935). Comparison of the variation and divergence levels of the RAPD markers with those for the other genome markers, namely, the enzyme-coding genes and chromosomes (gene linkage groups) have demonstrated different divergence rates for different genome components during speciation of Chironimids.

Are Polyommatus hispana and Polyommatus slovacus bivoltine Polyommatus coridon (Lepidoptera: Lycaenidae)? The discriminatory value of genetics in taxonomy

Taxonomic confusion exists in several sibling species groups. The Polyommatus coridon species complex (Chalk Hill Blues) serves as a model group of sibling species in which genetic analyses provide suitable means for taxonomic clarification. We studied the allozyme patterns of the two described bivoltine species of this complex, Polyommatus hispana and Polyommatus slovacus, and compared them to the two genetic lineages of the univoltine P. coridon. P. hispana is well distinguished from P. coridon (genetic distance: 0.081), and most probably is a sibling species that has evolved during glacial isolation on the Iberian Peninsula. P. slovacus is genetically indistinguishable from the eastern, Pontic–Mediterranean lineage of P. coridon; therefore we suggest that it represents a local bivoltine population only. Since the spring generation of P. slovacus was much less common than the summer generation and showed less genetic diversity, it is probable that uni-/bivoltinism is a dimorphism affecting only part of the whole population. We suggest that the higher genetic diversity of the second generation may be a consequence of gene flow from adjacent single-brooded populations.

Divergence of the polytene chromosome banding sequences as a reflection of evolutionary rearrangements of the genome linear structure

Banding sequences of five chromosomal arms (A, C, D, E, and F), accounting for about 70% of the total genome size in 63 Chironomus species, were used as phylogenetic markers to analyze divergence patterns of the linear genome structure during the evolution. The number of chromosomal breakpoints between the pairs of banding sequences compared served as a measure of divergence. It was demonstrated that the greater the divergence between the species compared, the higher the number of chromosomal breakpoints and the smaller the size of the conserved chromosomal regions. A banding sequences comparison in sibling species demonstrated a lower number of chromosomal breakpoints; the breakpoint number was maximum in a comparison of the banding sequences in the subgenera Chironomus and Camptochironomus. The use of the number of chromosomal breakpoints as a divergence measure provided establishment of phylogenetic relationships between 63 Chironomus species and discrimination of sibling species groups and cytocomplexes on a phylogenetic tree.

A reanalysis of protein polymorphism in Drosophila melanogaster, D. simulans, D. sechellia and D. mauritiana: effects of population size and selection.

Comparison of synonymous and nonsynonymous variation/substitution within and between species at individual genes has become a widely used general approach to detect the effect of selection versus drift. The sibling species group comprised of two cosmopolitan (Drosophila melanogaster and Drosophila simulans) and two island (Drosophila mauritiana and Drosophila sechellia) species has become a model system for such studies. In the present study we reanalyzed the pattern of protein variation in these species, and the results were compared against the patterns of nucleotide variation obtained from the literature, mostly available for melanogaster and simulans. We have mainly focused on the contrasting patterns of variation between the cosmopolitan pair. The results can be summarized as follows: (1) As expected the island species D. mauritiana and D. sechellia showed much less variation than the cosmopolitan species D. melanogaster and D. simulans. (2) The chromosome 2 showed significantly less variation than chromosome 3 and X in all four species which may indicate effects of past selective sweeps. (3) In contrast to its overall low variation, D. mauritiana showed highest variation for X-linked loci which may indicate introgression from its sibling, D. simulans. (4) An average population of D. simulans was as heterozygous as that of D. melanogaster (14.4% v.s. 13.9%) but the difference was large and significant when considering only polymorphic loci (37.2% v.s. 26.1%). (5) The species-wise pooled populations of these two species showed similar results (all loci = 18.3% v.s. 20.0%, polymorphic loci = 47.2% v.s. 37.6%). (6) An average population of D. simulans had more low-frequency alleles than D. melanogaster, and the D. simulans alleles were found widely distributed in all populations whereas the D. melanogaster alleles were limited to local populations. As a results of this, pooled populations of D. melanogaster showed more polymorphic loci than those of D. simulans (48.0% v.s. 32.0%) but the difference was reduced when the comparison was made on the basis of an average population (29.1% v.s. 21.4%). (7) While the allele frequency distributions within populations were nonsignificant in both D. melanogaster and D. simulans, melanogaster had fewer than simulans, but more than expected from the neutral theory, low frequency alleles. (8) Diallelic loci with the second allele with a frequency less than 20% had similar frequencies in all four species but those with the second allele with a frequency higher than 20% were limited to only melanogaster the latter group of loci have clinal (latitudinal) patterns of variation indicative of balancing selection. (9) The comparison of D. simulans/D. melanogaster protein variation gave a ratio of 1.04 for all loci and 1.42 for polymorphic loci, against a ratio of approximately 2-fold difference for silent nucleotide sites. This suggests that the species ratios of protein and silent nucleotide polymorphism are too close to call for selective difference between silent and allozyme variation in D. simulans. In conclusion, the contrasting levels of allozyme polymorphism, distribution of rare alleles, number of diallelic loci and the patterns of geographic differentiation between the two species suggest the role of natural selection in D. melanogaster, and of possibly ancient population structure and recent worldwide migration in D. simulans. Population size differences alone are insufficient as an explanation for the patterns of variation between these two species.

SPECIES IDENTIFICATION WITHIN THE ANOPHELES FUNESTUS GROUP OF MALARIA VECTORS IN CAMEROON AND EVIDENCE FOR A NEW SPECIES

Anopheles funestus is a major vector of malaria in Africa. It belongs to a group of sibling species that can be identified morphologically only at certain stages of their development. A diagnostic polymerase chain reaction (PCR)-based tool made it possible to differentiate five species of the group. The assay seems to be applicable over all their distribution area for four of these species: An. funestus, An. leesoni, An. parensis, and An. vaneedenip. The fifth species, An. rivulorum, is the second most abundant species of the group and can be mistaken at its adult stage for the major vector of malaria An. funestus. Molecular and morphologic observations of specimens identified as An. rivulorum from Cameroon and South Africa showed that they belong to two different taxa. The species identified in Cameroon, and named here An. rivulorum-like, might extend to western Africa and central Africa. The species-specific PCR assay is supplemented by a primer specific to An. rivulorum-like and thus makes it possible to differentiate the five species of the An. funestus group and the newly defined taxon.

A lacewing with the wanderlust: the European song species ‘Maltese’, Chrysoperla agilis, sp.n., of the carnea group of Chrysoperla (Neuroptera: Chrysopidae)

Abstract. A fifth European member of the Holarctic carnea sibling species group, Chrysoperla agilis, sp.n. is described. This species was initially recognized because of its unique song phenotype. Both sexes produce one type of song, characterized by a single very long volley averaging 4.5 s in duration and repeated every 9.5 s. The unit of exchange during heterosexual duets (the shortest repeated unit) is the single volley. The carrier frequency is upwardly, then downwardly, modulated during each volley. The maximum frequency is higher (around 110 Hz) than in other members of the carnea group. Each volley ends with an audible, percussive ‘rattle’. Song features vary only slightly over a large geographical range that extends from northern Iran westward to the Azores and northward to southern Switzerland. Discriminant function analysis confirms the uniqueness of the C. agilis song in comparison with nine other song species. Morphologically, the adult of C. agilis is very similar to C. carnea and C. pallida and is generally intermediate between them with respect to the size of the pretarsal basal dilation, the shape of the genital lip and chin, the colour and type of setae on the abdomen, and colour markings on the head and mouthparts. No single feature will distinguish C. agilis from either C. carnea or C. pallida, but a suite of physical attributes can be used with reasonable success. Larval morphology fails to distinguish clearly C. agilis from other song species. Ecologically, C. agilis shares an affinity for low vegetation with C. lucasina and C. carnea, and a preference for milder, Mediterranean climates with C. mediterranea. Adults undergo a colour change to pale yellowish brown during winter diapause, and eggs are laid singly rather than in groups. Based on its ecological characteristics, C. agilis may prove to be an effective agent of biological control in the agricultural fields of warmer, drier parts of southern Europe and the Middle East, where other members of the carnea group are less common or absent.

Dispersal, Genetic Differentiation and Speciation in Estuarine Organisms

For some of their occupants, estuaries represent spatially discrete habitats, isolated from each other by barriers to dispersal or physiological tolerance. We present contrasting strategies for the retention or export of larvae from their estuary of origin, and consider the implications these have on population structure and divergence. Reported patterns of genetic differentiation and inferred gene flow in estuarine taxa (principally animals) are reviewed, and difficulties in the interpretation of existing genetic data discussed. Species concepts and models of speciation relevant to estuaries are outlined, and patterns of speciation of estuarine taxa reviewed. It is concluded that estuarine environments tend to restrict gene flow and impose distinct selective regimes, generating physiologically adapted populations divergent from their marine counterparts, and the potential for in situ speciation in complete or partial isolation. The resulting taxa may represent sibling or cryptic species groups of truly estuarine origin, rather than simply estuarine populations of marine eurytopes.

The role of ecologic diversification in sibling speciation of Empidonax flycatchers (Tyrannidae): multigene evidence from mtDNA.

Avian genera characterized by sibling species with distinctive habitat preferences present an evolutionary enigma in view of the more commonplace occurrence of syntopic congeners that differ strikingly in colour and pattern. No existing theory has explained the evolutionary background that led to these differences. Here we propose that great phenotypic similarity among some groups of sibling species limits their coexistence and that clues to their radiation can be seen in patterns of geographical occurrence. To illustrate our thesis we focused on the New World flycatcher genus Empidonax, a group of 15 species notorious for their great phenotypic similarity. Using 3069 base pairs of mitochondrial DNA from four genes, we produced a complete molecular phylogeny that identified four clades, three of which represent close relatives. The fourth clade includes only E. virescens, which apparently has no close living relatives. The majority of species, including many distant relatives, are completely (58.1%) or essentially (6.7%) allopatric in breeding distribution and exhibit striking ecological segregation into distinctive climate-vegetation zones. Even where ranges overlap, occupancy of the same habitat by different species is rare. Phylogenetic and distributional patterns in Empidonax suggest a peripatric model of stepwise colonization and then range expansion of small groups of pioneers during glacial periods into initially enlarging, distinctive habitats destined to be widespread during interglacials. Vicariance is not indicated in the absence of barriers of appropriate age and geographical position. Rapoport's rule that northern species have larger ranges than southern species is strongly supported.

The evolutionary enigma of bonefishes (Albula spp.): cryptic species and ancient separations in a globally distributed shorefish.

Many examples of cryptic marine species have been demonstrated with biochemical and molecular studies. In most cases, a broadly distributed taxon is actually a group of sibling species that can be distinguished (upon closer examination) by ecological or morphological characters. Fishes of the family Albulidae constitute a notable exception. Bonefish (Albula spp.) morphology and ecology are highly conserved around the globe, and their extended pelagic larval stage could allow population connections on a vast geographic scale. Based on this perceived homogeneity, bonefishes were classified as a single pantropical species, A. vulpes. However, allozyme studies of Hawaiian populations indicated that two sympatric species (A. glossodonta and A. neoguinaica) are included in the synonymy of A. vulpes. To ascertain the number and distribution of evolutionary partitions in Albula, we surveyed 564 bp of mitochondrial DNA (mtDNA) cytochrome b from 174 individuals collected at 26 locations. Sequence comparisons reveal eight deep lineages (d = 5.56-30.6%) and significant population structure within three of the four lineages that could be tested (phiST = 0.047-0.678). These findings confirm the genetic distinctiveness of the three species noted above and invoke the possibility of five additional species. Clock estimates for mtDNA indicate that these putative species arose 4-20 million years ago. Distinct evolutionary lineages coexist in several sample locations, yet show little morphological or ecological differentiation in sympatry. Thus, bonefish species seem to defy the evolutionary conventions of morphological differentiation over time and ecological displacement in sympatry. Despite multiple cases of sympatry, sister-taxa relationships inferred from mtDNA indicate that divergence in allopatry has been the predominant speciation mechanism in Albula. Stabilizing selection in the homogeneous habitat occupied by bonefishes (tropical sand flats) could promote the retention of highly conserved morphology and ecology.

Intercontinental karyotypic differentiation of Chironomus entis Shobanov, a Holarctic member of the C. plumosus group (Diptera, Chironomidae).

Analysis of banding sequences of polytene chromosomes in Palearctic (Russian) and Nearctic (North American) Chironomus entis shows strong karyotype divergence between populations on the two continents. Four out of seven chromosomal arms in the North American C. entis karyotype are characterized by sequences found only in the Nearctic. In total, 44 banding sequences are now known for this species across the Holarctic, including 22 exclusively Palearctic, 6 Holarctic, and 16 exclusively Nearctic sequences. The degree of cytogenetic differentiation between Palearctic and Nearctic C. entis populations is an order of magnitude greater than differentiation among populations within either continent, but is only one third as great as the cytogenetic distance between the sibling species C. entis and C. plumosus. C. entis is the only sibling species of C. plumosus uncovered during cytological identification of Chironomus species from more than 50 North American lakes, indicating that the plumosus sibling-species group is much smaller in the Nearctic than in the Palearctic, where a dozen sibling species are known. Cytogenetic distance values calculated between Nearctic and Palearctic representatives of both C. entis and its sibling species C. plumosus are similar, but result from different patterns of karyotype divergence. New World C. entis is distinguished from Old World populations by the 16 uniquely Nearctic sequences, four of which occur in the homozygous state. In contrast, North American C. plumosus has fewer uniquely Nearctic sequences, and only one that occurs as a homozygote. However, four chromosomal arms in C. plumosus that are polymorphic in the Palearctic show fixation, or near fixation, of Holarctic sequences in the Nearctic C. plumosus karyotype. Thus, both the fixation of Holarctic sequences, and the occurrence or fixation of distinctly Nearctic sequences, contribute significantly to karyotype divergence. Patterns of karyotype divergence in Palearctic and Nearctic populations of different Holarctic chironomid species are discussed relative to intercontinental cytogenetic differentiation in other dipterans.

A phylogeographical analysis of the bemisia tabaci species complex based on mitochondrial DNA markers

Mitochondrial 16S ( approximately 550 bp) and cytochrome oxidase I (COI) ( approximately 700 bp) sequences were utilized as markers to reconstruct a phylogeography for representative populations or biotypes of Bemisia tabaci. 16S sequences exhibited less divergence than COI sequences. Of the 429 characters examined for COI sequences, 185 sites were invariant, 244 were variable and 108 were informative. COI sequence identities yielded distances ranging from less than 1% to greater than 17%. Whitefly 16S sequences of 456 characters were analysed which consisted of 298 invariant sites, 158 variable sites and 53 informative sites. Phylogenetic analyses conducted by maximum parsimony, maximum-likelihood and neighbour-joining methods yielded almost identical phylogenetic reconstructions of trees that separated whiteflies based on geographical origin. The 16S and COI sequence data indicate that the B-biotype originated in the Old World (Europe, Asia and Africa) and is most closely related to B-like variants from Israel and Yemen, with the next closest relative being a biotype from Sudan. These data confirm the biochemical, genetic and behavioural polymorphisms described previously for B. tabaci. The consideration of all global variants of B. tabaci as a highly cryptic group of sibling species is argued.

The utility of internally transcribed spacer 2 DNA sequences of the nuclear ribosomal gene for distinguishing sibling species of Trichogramma

The usefulness of the internally transcribed spacer 2 (ITS2) of the nuclear ribosomal gene complex is tested for providing taxonomic characters to identify Trichogramma species. The ITS2 sequences of a group of sibling species of the T. deion/T. pretiosum complexes were determined. A simple and precise identification key to the species of these assemblages was constructed using as taxonomic characters the size of the ITS2 and the difference in restriction length polymorphism of species with similarly sized ITS2. Individual wasps can be identified by amplification of their ITS2 with general primers, determining the size of the PCR product using standard agarose electrophoresis, followed in some species by a DNA-digestion with a restriction enzyme. Because this system works well for a number of closely related species we are hopeful that similar PCR-based identification can be extended to all species of the genus once their ITS2 sequences have been determined. The advantage of this identification system over the morphology-based system is that non-specialists are able to quickly and cheaply identify individual specimens. In addition, species specific primers were tested for the two most common species of these groups (i.e. T. pretiosum and T. deion). These primers can be used either as a direct identification tool or as a method to confirm the identification using the general key. The phylogeny of this group of wasps was also analyzed based on the ITS2 sequence.

Evolution and Systematics ofAnopheles:Insights from a Molecular Phylogeny of Australasian Mosquitoes

Relationships among the genusAnophelesand its many sibling species-groups are obscure despite the importance of anophelines as the vectors of human malaria. For the first time, the interrelationships and the origin of Australasian members of the subgenusCelliaare investigated by a cladistic analysis of sequence variation within the mitochondrial cytochrome oxidase subunit II gene. Estimated divergence times between many Australasian and Oriental taxa predate the mid Miocene collision of Australasia and Southeast Asia. Phylogenetic analysis suggests that two-way exchanges with Oriental mosquitoes rather than only immigration may have been a characteristic of anopheline paleobiogeography in Australasia. The Australasian fauna is mostly included in a large clade. The medically important Punctulatus Group is monophyletic and appears derived from Oriental stock. Populations within this group from as far apart as Australia and Vanuatu were in contact in the recent past (i.e., 0.35–2.44 mya), supporting dispersal rather than vicariance explanations. Some support for the monophyly of the Myzomyia, Neomyzomyia, and Pyretophorus Series was found. However, the subgeneraAnophelesandCelliaand the Neocellia Series are paraphyletic, but branch support at these taxonomic levels was poor. The COII gene shows promise for questions concerning alpha taxonomy but appears to be of limited use for resolving deeper relationships within theAnopheles.

The phylogeny ofOphryotrocha(Dorvilleidae: Eunicida: Polychaeta)

The phylogeny of 20 cultured species of Ophryotrocha, including a group of sibling species that can only be identified by biochemical or reproductive information, is estimated from a combined parsimony analysis of 32 morphological, reproductive and electrophoretic characters, with selected members of Dorvillea, Ougia and Protodorvillea used as outgroups. Sexual production in the group include simultaneous hermaphroditism, protandrous sex reversal, an exceptional male/hermaphrodite system, and gonochorism. According to the presented phylogeny, simultaneous hermaphroditism appears as the primitive state in the group. It is suggested that sequential hermaphroditism and gonochorism are independently acquired, the latter state also giving rise to the male/hermaphrodite system.

Some pathways and factors of monogenean microevolution

This paper discusses probable causes for the origin and evolution of groups of monogenean congeneric sibling species infecting one fish host species, with special reference to freshwater fishes. These causes comprise strict specificity, topological differentiation of parasite micropopulations in microniches (microhabitats), ecological and geographic isolation of various parasite and host populations, paleogeographic or geomorphologic (but not paleogeologic) changes during the late Tertiary and Quaternary periods, with alternating marine transgressions and regressions acting upon continents which, after the Miocene, have been less affected by continental drift, orogenesis, and climatic fluctuations. Co-evolving with their hosts, Monogenea usually diverge faster than their hosts.

Rapid evolution of courtship song pattern in Drosophila willistoni sibling species

AbstractCourtship behaviours may provide a more reliable means of identifying reproductively isolated taxa than traits such as morphology or many genetic markers. Here we describe the courtship songs of the Drosophila willistoni sibling species group, which consists of several species and subspecies. We find that song pattern is species‐specific, despite significant differences among strains within species. D. paulistorum has the most variable song pattern, which reflects this species' traditional subdivision into semispecies. All the other species could be unambiguously identified by song. The major differences among these species was in the interpulse interval, as has been found in other studies of fly song. However, the interpulse intervals of the species studied here were often multimodal. This was partly due to the presence of multiple song types within the courtship repertoire, but it also reflected changes in interpulse interval within a song type by some males. Unusually, some species had distinctively patterned variation in interpulse interval. Song must have evolved rapidly within the species complex, probably due to sexual selection.