Speciation in Darwin's darklings: taxonomy and evolution of Stomion beetles in the Galápagos Islands, Ecuador (Insecta: Coleoptera: Tenebrionidae)

Stomion is one of three speciose and taxonomically difficult genera of flightless Darwin's darkling beetles of the Galápagos Islands. The previously named species and subspecies of Stomion are analysed by morphometric and cladistic methods. Eleven species are here recognized, which probably descended from colonization by a single ancestral species. Cladistic analysis yielded two weakly supported clades that are different from previously published morphological and allozyme genotype groups. Phenotypic and genotypic characters may be evolving independently. There is much within-species variation, but there is no compelling evidence of adaptive radiation in Stomion , in contrast to that in the famous Darwin's finches. The analyses show the need for changes in morpho-species taxonomy: S. punctipennis Van Dyke ( syn. nov. ) is elevated to full species from a subspecies of S. galapagoensis Waterhouse. There is no evidence to support the validity of: S. laevigatum santacruzensi Franz ( syn. nov. ), synonomized here under S. l. laevigatum Waterhouse; S. galapagoensis leleupi Kaszab ( syn. nov. ), synonomized here under S. linelli Blair; S. galapagoensis pinzoni Franz ( syn. nov. ), synonomized here under S. obesum Van Dyke. S. genovesa sp. nov. is described from Genovesa Island. Lectotypes are designated for S. galapagoensis Waterhouse, S. laevigatum Waterhouse and S. helopoides Waterhouse .   © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society , 2004, 141 , 135–152.     

Scalesia gordilloi sp. nov. (Asteraceae) from the Galápagos Islands, Ecuador

Scalesia gordilloi está descrita desde la isla San Cristóbal, Islas Galápagos, Ecuador. Tiene una distribución limitada y local al lado de la costa sur en la zona vegetal árida. Está relacionada a S. divisa Anderss. y S. incisa Hook. f. Se discute la taxonomía de S. gordilloi.     

Hybridization and speciation in the carabid beetles of the subgenusOhomopterus (Coleoptera, Carabidae, genusCarabus)

Natural hybridization among wingless carabid beetles of the subgenusOhomopterus (Carabidae, genusCarabus) is reviewed, and its significance in the evolution of this subgenus discussed. Natural hybridization occurs between parapatric species of similar size. Two case studies of natural hybridization suggest that natural hybridization could have affected the evolution of this subgenus in different ways. When there is a large difference in genital morphology between hybridizing species, interspecific copulation often results in genital injuries that causes mortality of copulating individuals, and hence reduces the fitness of hybridizing individuals greatly. In such a case, hybridization may be effective in maintaining the parapatric distribution of the two species, and in the long term, may promote reinforcement selection for traits which are effective in prezygotic reproductive isolation. When the morphological difference in genitalia is not so large as to cause genital injury, a hybrid population may be established at the intermediate zone between two parental species, provided that the immigration rates of the two species into the intermediate zone are small. Thus, natural hybridization may have contributed to both divergence and reticulate evolution in this subgenus.     

Morphological variation among populations of Lecocarpus (Asteraceae) on the Galápagos Islands

Representative samples were collected from almost all known populations of the endemic Galapagos genus Lecocarpus. Multivariate statistical methods were applied to morphological characters to investigate differentiation among species and populations. In discriminant analysis no misclassifications were made among species. Populations of L. darwinii and L. lecocarpoides were better discriminated than populations of L. pinnatifidus . Principal Component Analysis (PCA) separated species well although intermediate populations occur between L. darwinii and L. lecocarpoides . Clear patterns of within-species differentiation were seen among populations of L. darwinii and L. lecocarpoides , but not among populations of L. pinnatifidus .
Populations of L. lecocarpoides at present grow on separate islands. All populations of L. darwinii are found on San Cristóbal, but this island might have been separated into more islands in the past. Lecocarpus pinnatifidus has probably always been growing on only one island. This suggests that the sea is the major barrier to dispersal of the three species. We find it likely that the degree of reproductive isolation caused by the sea is crucial to the differentiation among populations, and that genetic drift rather than adaptation has been responsible. The analyses cast new light on the identity of classic collections made by Darwin in 1835 and Stewart in 1906. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 154 , 523–544.     

Genetic differentiation and speciation among four Phyllotreta species (Coleoptera: Chrysomelidae)

Among the four closely related Phyllotreta species P. dilatata Thomson, 1866, P. flexuosa (Illiger, 1794), P. ochripes (Curtis, 1837) and P. tetrastigma (Comolli, 1837) several systematic problems occur due to the existence of colour pattern variation and morphological similarity. All four species feed on Brassicaceae, but P. tetrastigma , P. flexuosa and P. dilatata are monophagous in the field, whereas P. ochripes is oligophagous. Genetic differentiation and systematic relationships of the four species are studied by means of allozyme electrophoresis of 10 variable loci, with a total of 30 allelomorphs. Of the six alleles that are present only in a single species, none is diagnostic. Rogers modified genetic distance and Cavalli-Sforza & Edwards arc distance between all populations are calculated and Distance Wagner trees are constructed, revealing three major groups. P. ochripes is separated first, being the most distant species. The three other species are more closely related, and within this group P. dilatata is separated from the other two. The last group contains the populations of P. tetrastigma and P. flexuosa. In the differentiation between the different species host plant shifts and consequent genetic differentiation have been important.     

Multiple-chromosome sex systems in the darkling beetles Blaps gigas and Blaps gibba (Coleoptera, Tenebrionidae)

We have studied mitotic and meiotic chromosomes in the males of two species of Blaps: B. gigas and B. gibba. Karyological characteristics such as the occurrence of a multivalent configuration at diakinesis and two types of metaphase-II spreads support the notion that multiple-chromosome sex systems involving five chromosomes in B. gigas and eight chromosomes in B. gibba have developed in these species. Results obtained by means of silver staining and C-banding techniques suggest that the complex sex systems occurring in B. gigas and B. gibba may have originated from exchanges of terminal ribosomal genes among the Y chromosome and some autosomes.     

The allopatric phase of speciation: the sharp-beaked ground finch (Geospiza difficilis) on the Galápagos islands

Using microsatellite DNA variation, morphological measurements and sonagrams made from tape-recordings in the field, we examine die allopatric differentiation of six populations of the sharp-beaked ground finch, Geospiza difficilis , in the Galapagos archipelago. We ask how and why die populations became differentiated, and consider what die differences imply about speciation. An important factor is time; G. difficilis is one of the phylogenetically oldest species. Populations became differentiated by adapting in beak morphology to different food supplies. Since beak size and shape also function in conspecific mate recognition and choice, die potential for reproductive isolation from sister and parental taxa arose as a correlated effect of natural selection on resource-exploiting traits. This conforms to a standard explanation for the origin of pre-mating isolation as a byproduct of adaptive changes in allopatry without being adaptive itself. However, diis explanation is incomplete. Vocal characteristics also differentiated, partly as a result of natural and sexual selection independent of beak size change in environments with different sound transmitting properties. An additional element of chance is indicated by a comparison of closely-related populations on two islands, Wolf and Darwin, that are geographically close, and topographically and floristically similar. The populations have markedly different vocalizations. Morphological characters, vocalizations and genetic traits do not vary concordandy among die six populations. One population (Genovesa) is genetically more similar to other congeneric species. Phenotypic similarities with G. difficilis are the result of a uniquely long retention of shared ancestral traits. Arguments under the phylogenetic species concept justify recognizing this population as a separate species, Geospiza acutirostris. Under the biological species concept it should remain as currentiy classified, G. difficilis.     

Comparative phylogeography and speciation of dung beetles from the Australian Wet Tropics rainforest

In tropical rainforests, insects show especially high species richness and local endemism of species relative to vertebrates. One possible cause is that insects respond to historical fluctuations of rainforests on a smaller spatial scale than do vertebrates. To evaluate this hypothesis, we combine environmental niche models and mitochondrial DNA phylogeography for two pairs of sister species of the dung beetle genus Temnoplectron (T. aeneopiceum-T. subvolitans and T. politulum-T. reyi) from the rainforests of northeastern Australia, where climate-driven rainforest fluctuations in the Quaternary have strongly influenced genetic and species diversity of vertebrates. Within both species pairs, the bioclimatic niche was conserved, but the T. aeneopiceum-T. subvolitans species pair had the narrower environmental range, and thus more restricted potential distribution. Coalescent analyses indicated Late Pliocene or Early Pleistocene divergences for both species pairs, and earlier speciation in (T. aeneopiceum-T. subvolitans) than in (T. politulum-T. reyi). Phylogeographic structure in (T. aeneopiceum-T. subvolitans) was more pronounced than in (T. politulum-T. reyi), with significant isolation-by-distance in the former species-pair only. Nested clade and coalescence analyses indicated local range expansions for the T. aeneopiceum-subvolitans species pair and range-wide expansion for both T. politulum and T. reyi. We suggest that stronger phylogeographic structure and earlier divergence in (T. aeneopiceum-T. subvolitans) than in (T. politulum-T. reyi) reflects a stronger influence of environmental barriers to gene flow under the present climate and greater sensitivity to warmer and drier periods of the Quaternary. The two species pairs evidently responded to Quaternary rainforest fluctuations at spatial scales similar to those seen within low-vagility species of vertebrate. Despite this similarity of scale, these insect lineages are reproductively isolated at parapatric boundaries, whereas analogous lineages of vertebrates often are not. We suggest that rapid evolution of genitalia may facilitate geographic speciation in rainforest beetles.     

Reproductive ecology of the endemic Lecocarpus pinnatifidus (Asteraceae) in an isolated population in the Galápagos Islands

Lecocarpus pinnatifidus is an endemic member of the Asteraceae occurring on only one island in the Galápagos archipelago. The capitula are large with female ray florets and male disc florets. They are self-compatible but this study suggests fruit set is pollen limited. Visits from Xylocopa darwini and other larger insect pollinators are rare, and small insects seem to be the main pollinators. Small insects carry few pollen grains and most likely mediate self-pollinations. Self-compatibility and seed set after selfing are the most common reproductive strategy in the Galápagos Islands and L. pinnatifidus seemingly fits well into this group.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 171–180.     

Pollination biology of the Galápagos endemic, Tournefortia rufo-sericea (Boraginaceae)

Tournefortia rufo-sericea is an endemic member of the Galápagos angiosperm flora. Although not uncommon within the archipelago, its status is presently listed as vulnerable and, as such, a complete knowledge of its pollination biology may prove useful in preventing its decline. Pollination experiments, flower-visitor observations, nectar and fluorescence studies, as well as pollen : ovule ratio and pollen size studies were included in this investigation. The small, white flowers of this species set fruit via open pollination (81%), autonomous self-pollination (80%), diurnal pollination (80%), and nocturnal pollination (85%). Ants are the most common visitor to the flowers of this species, primarily during the day, whereas beetles and moths make visits at night. A small amount of nectar is presumably produced, as moths are often seen probing the corollas. Experiments with fluorescent dust did not support interflower pollen movement. The pollen : ovule ratio was 4972 : 1, which suggests xenogamy, and the mean pollen size was 21 µm. Despite the pollen : ovule ratio, it appears that this species exhibits a breeding strategy of facultative autogamy, in which the majority of flowers set fruit via autonomous self-pollination, but limited outcrossing may occur when pollinators are available. Conservation efforts for T. rufo-sericea should focus on the control or eradication of exotic species.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 153 , 21–31.     

Recent research on the evolution of land birds on the Galápagos

A decade of research on the evolution of Galápagos land birds is reviewed, and outstanding questions to be answered are highlighted. Evolutionary studies have been restric 1 almost entirely to the four species of mockingbirds and the 13 species of Darwin's finches. Long-term field studies have been initiated on representatives of both groups. Co-operative breeding has been discovered in the mockingbirds (and hawks).
Lack's (1945, 1947) monographic treatment of Darwin's finches has been largely upheld and extended by morphological, ecological, behavioural and biochemical studies. While the phylogenetic origins of Darwin's finches still remain uncertain, the major groupings of the finches have been confirmed by the results of protein polymorphism analysis. Fossils of Darwin's finches have been discovered recently: their potential for illuminating evolutionary change has not yet been realized. Three other major developments are (1) quantitative confirmation of the role of interspecific competition in the adaptive radiation, (2) experimental confirmation of the role of morphological and song cues in species recognition, and experimental evidence of their evolution in the speciation process, and (3) direct study of natural selection on heritable quantitative traits in a population, and identification of its causes. Continuing studies of population variation are likely to reveal the contemporary importance of selection, migration and hybridization, and thereby help us to more fully understand the causes of the adaptive radiation of Darwin's finches.     

Diversification in a fluctuating island setting: rapid radiation of Ohomopterus ground beetles in the Japanese Islands

The Japanese Islands have been largely isolated from the East Asian mainland since the Early Pleistocene, allowing the diversification of endemic lineages. Here, we explore speciation rates and historical biogeography of the ground beetles of the subgenus Ohomopterus (genus Carabus) based on nuclear and mitochondrial gene sequences. Ohomopterus diverged into 15 species during the Pleistocene. The speciation rate was 1.92 Ma(-1) and was particularly fast (2.37 Ma(-1)) in a group with highly divergent genitalia. Speciation occurred almost solely within Honshu, the largest island with complex geography. Species diversity is highest in central Honshu, where closely related species occur parapatrically and different-sized species co-occur. Range expansion of some species in the past has resulted in such species assemblages. Introgressive hybridization, at least for mitochondrial DNA, has occurred repeatedly between species in contact, but has not greatly disturbed species distinctness. Small-island populations of some species were separated from main-island populations only after the last glacial (or the last interglacial) period, indicating that island isolation had little role in speciation. Thus, the speciation and formation of the Ohomopterus assemblage occurred despite frequent opportunities for secondary contact and hybridization and the lack of persistent isolation. This radiation was achieved without substantial ecological differentiation, but with marked differentiation in mechanical agents of reproductive isolation (body size and genital morphology).     

Identity and taxonomic affinity of some members of the Amaranthaceae from the Galápagos Islands

ELIASSON, U. H. 1985. Identity and taxonomic affinity of some members of the Amaranthaceae from the Galápagos Islands. The type species of Pleuropetalum, P. DarwiniI, is endemic to the Galápagos and is morphologically closer to P. pleiogynum than to P. sprucei. Pleuropetalum pleiogynum has a wider distribution than previously assumed, ranging from Costa Rica to Peru. Amaranlhus anderssonii is closely related to A. urceolatus, a species of the Pacific coast of S America, and to A. berlandieri, a species of Texas and NE Mexico. Amaranlhus squamulatus, previously regarded as endemic to the Galápagos, is reported from the Guayas province of Ecuador. The genus Galápagosus, proposed for Amaranlhus sclerantoides, is rejected. Lithophila scirpoides, an overlooked taxon from the Galápagos, is believed to be an aberrant specimen of L. radicala. Lithophila subscaposa from the islands of Santiago and Pinzon differs morphologically from the specimens of Floreana. Iresine edmonstonii, probably erroneously reported from the Galápagos, is conspecific with J. angusti/olia. Blutaparon rigidum is morphologically divergent from other members of the genus, being adapted to arid conditions, and is assumed to be extinct.     

Genetic and morphological differentiation in Tephritis bardanae (Diptera: Tephritidae): evidence for host-race formation

The fruit fly Tephritis bardanae infests flower heads of two burdock hosts, Arctium tomentosum and A. minus. Observations suggest host-associated mating and behavioural differences at oviposition indicating host-race status. Previously, flies from each host plant were found to differ slightly in allozyme allele frequencies, but these differences could as well be explained by geographical separation of host plants. In the present study, we explicitly test whether genetic and morphological variance among T. bardanae are explained best by host-plant association or by geographical location, and if this pattern is stable over a 10-year period. Populations of A. tomentosum flies differed significantly from those of A. minus flies in (i) allozyme allele frequencies at the loci Pep-A and Pgd, (ii) mtDNA haplotype frequencies and (iii) wing size. In contrast, geographical location had no significant influence on the variance estimates. While it remains uncertain whether morphometric differentiation reflects genotypic variability or phenotypic plasticity, allozyme and mtDNA differentiation is genetically determined. This provides strong evidence for host-race formation in T. bardanae. However, the levels of differentiation are relatively low indicating that the system is in an early stage of divergence. This might be due to a lack of time (i.e. the host shift occurred recently) or due to relatively high gene flow preventing much differentiation at loci not experiencing selection.     

Phylogenetics of Darwiniothamnus (Asteraceae: Astereae) – molecular evidence for multiple origins in the endemic flora of the Galápagos Islands

Aim The aims of this study were (1) to investigate whether the two growth forms of Darwiniothamnus Harling (Asteraceae) originated from the colonization of a single ancestor, (2) to identify the closest relative(s) of Darwiniothamnus, and (3) to review molecular phylogenies from other plant groups to infer the origin of Galápagos endemics. Location Darwiniothamnus is endemic to the Galápagos Islands. Methods All putative relatives of Darwiniothamnus plus 38 additional species were included. Nucleotide sequences of the internal transcribed spacers of the nuclear ribosomal DNA were used for Bayesian and parsimony analyses. Results Darwiniothamnus is polyphyletic. Two species (D. lancifolius (Hook. f.) Harling and D. tenuifolius (Hook. f.) Harling) are woody shrubs that usually grow to 1–2 m in height; they belong to a clade composed of species otherwise restricted to the Caribbean. These two species are sister to Erigeron bellidiastroides Griseb., a herbaceous species endemic to Cuba. The third species (D. alternifolius Lawesson & Adsersen) is a perennial herbaceous plant, woody at the base and reaching only up to 50 cm in height. It is sister to two Chilean (Coquimbo–Valparaiso region) species that also have a perennial herbaceous habit: E. fasciculatus Colla and E. luxurians (Skottsb.) Solbrig. They are placed in an assemblage restricted to South America. The review of previous molecular phylogenetic studies revealed that two of the endemic genera and endemic species of three non‐endemic genera have their closest relatives in South America. Endemic species belonging to three non‐endemic genera have sister species in North America or the West Indies. One endemic genus and endemic species in three non‐endemic genera have sister taxa with a widespread continental distribution, or their molecular phylogenies yielded equivocal results. Main conclusions The flora of Galápagos has affinities with both North America (including the Antilles) and South America. Darwiniothamnus exhibits both patterns: two species of this genus are sister to a taxon endemic to Cuba, supporting a connection between the Cocos plate and the West Indies; the third species, D. alternifolius, provides a link with the Coquimbo–Valparaiso region, suggesting a biogeographical connection between the Nazca plate and southern South America.     

Genetic and morphological relationships of the Berlenga wall lizard (Podarcis bocagei berlengensis: Lacertidae)

Six biometric characters and 15 electrophoretic loci of three known subspecies of Podarcis bocagei were studied. Contrary to biometric indications, Podarcis bocagei berlengensis showed a closer genetic relationship with Podarcis bocagei carbonelli than with the nominal subspecies. The biometric results were confounded by the relative large size of P. b. berlengensis . Post-glacial colonization from two different areas might explain the greater genetic differentiation between the P. b. bocagei and P. b. carbonelli populations (Nei's D - 0.158 - near the species threshold). It might also explain the known colonization of these two lizards through the islands off the west coast of the Iberian penninsula and their present distributions to the north of (Galicia; Northern Portugal) and to the south of the valley of river Douro (central Portugal, western and Sistema Central), respectively.     

Molecular and morphological divergence in the butterfly genus Lycaeides (Lepidoptera: Lycaenidae) in North America: evidence of recent speciation

Male genital morphology, allozyme allele frequencies and mtDNA sequence variation were surveyed in the butterfly species Lycaeides idas and L. melissa from across much of their range in North America. Despite clear differences in male genital morphology, wing colour patterns and habitat characteristics, genetic variation was not taxonomically or geographically structured and the species were not identifiable by either genetic data set. Genetic distances (Nei's D=0.002–0.078, calculated from allozyme data) between all populations of both species were within the range commonly observed for conspecific populations of other butterflies. The most frequent mtDNA haplotype was present in individuals of both species in populations from southern California to Wisconsin. We conclude that speciation has probably happened recently and the lack of genetic differentiation between the species is the product of either (1) recent or ongoing gene flow at neutral loci, and/or (2) an insufficiency of time for lineage sorting. The evolution of male genital morphology, wing colour patterns and ecological characteristics has proceeded more rapidly than allozyme or mtDNA evolution.     

Hematology, plasma chemistry, and serology of the flightless cormorant (Phalacrocorax harrisi) in the Galapagos Islands, Ecuador

The flightless cormorant (Phalacrocorax harrisi) is an endemic species of the Galápagos Islands, Ecuador. Health studies of the species have not previously been conducted. In August 2003, baseline samples were collected from flightless cormorant colonies on the islands of Isabela and Fernandina. Seventy-six birds, from nestlings to adults, were evaluated. Genetic sexing of 70 cormorants revealed 37 females and 33 males. Hematology assessment consisted of packed cell volume (n=19), leukograms (n=69), and blood smear evaluation (n=69). Microscopic evaluation of blood smears revealed microfilaria in 33% (23/69) of the cormorants. Plasma chemistries were performed on 46 cormorants. There was no significant difference in chemistry values or complete blood counts between male and female cormorants or between age groups. Based on a serologic survey to assess exposure to avian pathogens, birds (n=69) were seronegative for West Nile virus, avian paramyxovirus type 1 (Newcastle disease virus), avian paramyxovirus types 2 and 3, avian influenza, infectious bursal disease, infectious bronchitis, Marek's disease (herpes), reovirus, avian encephalomyelitis, and avian adenovirus type 2. Antibodies to avian adenovirus type 1 and Chlamydophila psittaci were found in 31% (21/68) and 11% (7/65) of flightless cormorants respectively. Chlamydophila psittaci was detected via polymerase chain reaction in 6% (2/33) of the cormorants. The overall negative serologic findings of this research suggest that the flightless cormorant is an immunologically na?ve species, which may have a reduced capacity to cope with the introduction of novel pathogens.