Period Of Geographical Isolation Research Articles

Israeli Oncocyclus irises: Phylogenetic relationships and evolutionary history

Abstract Oncocyclus is a large group of bearded irises with poorly known phylogeny and evolutionary history. In Israel, Iris sect. Oncocyclus comprises eight species belonging to three aggregates. We used a combination of approaches to resolve the phylogenetic relationships of these species and indicate the evolutionary forces responsible for their origin. We sequenced the whole chloroplast genomes of species and integrated a phylogenetic tree with results of genetic (AFLP) divergence, degree of reproductive isolation, and species distribution modeling. Our findings suggest that quantitative and even qualitative morphological characters, such as flower color, are unreliable diagnostic traits for Oncocyclus taxonomy; that some recognized species comprise more than one species; and that group evolution did not involve the origin of distinct flower aggregates. A lack of pre-zygotic reproductive isolation agrees with the very low variability of the Oncocyclus plastome, suggesting that Israeli Oncocyclus species are very young. Homoploid hybridization followed or preceded by long periods of geographic isolation, and local selection likely contributed to speciation in Oncocyclus. In the group evolutionary history, importance of homoploid hybridization and local selection differed among species, but limited gene flow played a crucial role for all species.

Diversification of the orchid genus Tridactyle: Origin of endemism on the oceanic islands of São Tomé & Príncipe in the Gulf of Guinea

AbstractAimOceanic islands have played an important role in our understanding of the diversification of organisms, and phylogenetic estimates have been used in this context to investigate the origin of island diversity and its relationship to the continent. Using a typical orchid genus rich in island endemics and with widespread continental relatives, we aim to compare alternative hypotheses of diversification with a focus on island endemism.LocationTropical Africa and the Gulf of Guinea Islands of São Tomé & Príncipe, Central Africa.TaxonTridactyle genus (Orchidaceae).MethodsWe used genome skimming to sequence the whole chloroplast genome and nuclear ribosomal genes from 157 individuals of 34 Tridactyle species and 15 individuals of 12 other orchid genera (outgroups) to infer a time‐calibrated phylogenetic tree of the genus Tridactyle. We also used multiple statistical methods to infer the geographical ranges of the ancestral nodes from the estimated phylogeny. Alternative hypotheses for the origins of endemism on the islands of São Tomé and Príncipe were investigated based on the biogeographical reconstruction of the genus.ResultsThe estimated phylogeny of Tridactyle and reconstruction of geographical ranges for the ancestral nodes suggested a general history of allopatric speciation for the genus, in particular via colonization of the islands of the Gulf of Guinea that induced a long period of geographical isolation. The most parsimonious hypothesis to explain island endemism in Tridactyle involved six independent colonizations of the islands from the continent.Main conclusionsIn contrast to other cases of oceanic island endemism that involved adaptive radiation on an island or within an archipelago, endemism in Tridactyle is better explained by multiple colonization events from the continent to São Tomé and Príncipe, with subsequent divergences due to geographical isolation but only one potential instance of further diversification on the islands.

Cover Picture: Steel Construction 1/2022

AbstractWith the completion of the Pelješac Bridge, the northern and southern Croatian territories ended their long period of geographical isolation since their independence from Yugoslavia in June 1991. Under the severe influence of the global epidemic, the main contractor, China Road and Bridge Corporation (CRBC), has struggled diligently for more than three years to realize the Croatian people's long‐cherished aspiration. The steel structure of this bridge is purchased from raw materials, steel box girders are fabricated in the workshop, long‐distance transportation, and on‐site erection are all performed under EU specifications by Chinese companies. Mr. Bicheng Tang and Mr. Xuefeng Wang, the contractors' steel structure expert and construction chief manager of this project respectively, authored this technical article and described the entire manufacturing procedure of such a huge number of steel structures (s. p. 26).

Population Evolution, Genetic Diversity and Structure of the Medicinal Legume, Glycyrrhiza uralensis and the Effects of Geographical Distribution on Leaves Nutrient Elements and Photosynthesis.

Glycyrrhiza uralensis is a valuable medicinal legume, which occurs widely in arid and semi-arid regions. G. uralensis demand has risen steeply due to its high medical and commercial value. Interpret genome-wide information can stimulate the G. uralensis development as far as its increased bioactive compound levels, and plant yield are concerned. In this study, leaf nutrient concentration and photosynthetic chlorophyll index of G. uralensis were evaluated to determine the G. uralensis growth physiology in three habitats. We observed that G. uralensis nutrient levels and photosynthesis differed significantly in three regions (p < 0.05). Whole-genome re-sequencing of the sixty G. uralensis populations samples from different habitats was performed using an Illumina HiSeq sequencing platform to elucidate the distribution patterns, population evolution, and genetic diversity of G. uralensis. 150.06 Gb high-quality clean data was obtained after strict filtering. The 895237686 reads were mapped against the reference genome, with an average 89.7% mapping rate and 87.02% average sample coverage rate. A total of 6985987 SNPs were identified, and 117970 high-quality SNPs were obtained after filtering, which were subjected to subsequent analysis. Principal component analysis (PCA) based on interindividual SNPs and phylogenetic analysis based on interindividual SNPs showed that the G. uralensis samples could be categorized into central, southern, and eastern populations, which reflected strong genetic differentiation due to long periods of geographic isolation. In this study, a total of 131 candidate regions were screened, and 145 candidate genes (such as Glyur001802s00036258, Glyur003702s00044485, Glyur001802s00036257, Glyur007364s00047495, Glyur000028s00003476, and Glyur000398s00034457) were identified by selective clearance analysis based on Fst and θπ values. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed significant enrichment of 110 GO terms including carbohydrate metabolic process, carbohydrate biosynthetic process, carbohydrate derivative biosynthetic process, and glucose catabolic process (p < 0.05). Alpha-linolenic acid metabolism, biosynthesis of unsaturated fatty acids, and fatty acid degradation pathways were significantly enriched (p < 0.05). This study provides information on the genetic diversity, genetic structure, and population adaptability of the medicinal legumes, G. uralensis. The data obtained in this study provide valuable information for plant development and future optimization of breeding programs for functional genes.

Evolutionary history of a desert perennial Arnebia szechenyi (Boraginaceae): Intraspecific divergence, regional expansion and asymmetric gene flow

The complex interactions of historical, geological and climatic events on plant evolution have been an important research focus for many years. However, the role of desert formation and expansion in shaping the genetic structures and demographic histories of plants occurring in arid areas has not been well explored. In the present study, we investigated the phylogeography of Arnebia szechenyi, a desert herb showing a near-circular distribution surrounding the Tengger Desert in Northwest China. We measured genetic diversity of populations using three maternally inherited chloroplast DNA (cpDNA) fragments and seven bi-paternally inherited nuclear DNA (nDNA) loci that were sequenced from individuals collected from 16 natural populations across its range and modelled current and historical potential habitats of the species. Our data indicated a considerably high level of genetic variation within A. szechenyi and noteworthy asymmetry in historical migration from the east to the west. Moreover, two nuclear genetic groups of populations were revealed, corresponding to the two geographic regions separated by the Tengger Desert. However, analysis of cpDNA data did not show significant geographic structure. The most plausible explanation for the discrepancy between our findings based on cpDNA and nDNA data is that A. szechenyi populations experienced long periods of geographic isolation followed by range expansion, which would have promoted generalized recombination of the nuclear genome. Our findings further highlight the important role that the Tengger Desert, together with the Helan Mountains, has played in the evolution of desert plants and the preservation of biodiversity in arid Northwest China.

A mirage of cryptic species: Genomics uncover striking mitonuclear discordance in the butterfly Thymelicus sylvestris

Mitochondrial DNA (mtDNA) sequencing has led to an unprecedented rise in the identification of cryptic species. However, it is widely acknowledged that nuclear DNA (nuDNA) sequence data are also necessary to properly define species boundaries. Next generation sequencing techniques provide a wealth of nuclear genomic data, which can be used to ascertain both the evolutionary history and taxonomic status of putative cryptic species. Here, we focus on the intriguing case of the butterfly Thymelicus sylvestris (Lepidoptera: Hesperiidae). We identified six deeply diverged mitochondrial lineages; three distributed all across Europe and found in sympatry, suggesting a potential case of cryptic species. We then sequenced these six lineages using double-digest restriction-site associated DNA sequencing (ddRADseq). Nuclear genomic loci contradicted mtDNA patterns and genotypes generally clustered according to geography, i.e., a pattern expected under the assumption of postglacial recolonization from different refugia. Further analyses indicated that this strong mtDNA/nuDNA discrepancy cannot be explained by incomplete lineage sorting, sex-biased asymmetries, NUMTs, natural selection, introgression or Wolbachia-mediated genetic sweeps. We suggest that this mitonuclear discordance was caused by long periods of geographic isolation followed by range expansions, homogenizing the nuclear but not the mitochondrial genome. These results highlight T.sylvestris as a potential case of multiple despeciation and/or lineage fusion events. We finally argue, since mtDNA and nuDNA do not necessarily follow the same mechanisms of evolution, their respective evolutionary history reflects complementary aspects of past demographic and biogeographic events.

Analysis of Genome-Wide Differentiation between Native and Introduced Populations of the Cupped Oysters Crassostrea gigas and Crassostrea angulata.

The Pacific cupped oyster is genetically subdivided into two sister taxa, Crassostrea gigas and Crassostrea angulata, which are in contact in the north-western Pacific. The nature and origin of their genetic and taxonomic differentiation remains controversial due the lack of known reproductive barriers and the high degree of morphologic similarity. In particular, whether the presence of ecological and/or intrinsic isolating mechanisms contributes to species divergence is unknown. The recent co-introduction of both taxa into Europe offers a unique opportunity to test how genetic differentiation is maintained under new environmental and demographic conditions. We generated a pseudochromosome assembly of the Pacific oyster genome using a combination of BAC-end sequencing and scaffold anchoring to a new high-density linkage map. We characterized genome-wide differentiation between C. angulata and C. gigas in both their native and introduced ranges, and showed that gene flow between species has been facilitated by their recent co-introductions in Europe. Nevertheless, patterns of genomic divergence between species remain highly similar in Asia and Europe, suggesting that the environmental transition caused by the co-introduction of the two species did not affect the genomic architecture of their partial reproductive isolation. Increased genetic differentiation was preferentially found in regions of low recombination. Using historical demographic inference, we show that the heterogeneity of differentiation across the genome is well explained by a scenario whereby recent gene flow has eroded past differentiation at different rates across the genome after a period of geographical isolation. Our results thus support the view that low-recombining regions help in maintaining intrinsic genetic differences between the two species.

Genomic variation across the Yellow-rumped Warbler species complex

ABSTRACT Populations that have experienced long periods of geographic isolation will diverge over time. The application of high-throughput sequencing technologies to study the genomes of related taxa now allows us to quantify, at a fine scale, the consequences of this divergence across the genome. Throughout a number of studies, a notable pattern has emerged. In many cases, estimates of differentiation across the genome are strongly heterogeneous; however, the evolutionary processes driving this striking pattern are still unclear. Here we quantified genomic variation across several groups within the Yellow-rumped Warbler species complex (Setophaga spp.), a group of North and Central American wood warblers. We showed that genomic variation is highly heterogeneous between some taxa and that these regions of high differentiation are relatively small compared to those in other study systems. We found that the clusters of highly differentiated markers between taxa occur in gene-rich regions of the genome and e...

European sea bass genome and its variation provide insights into adaptation to euryhalinity and speciation.

The European sea bass (Dicentrarchus labrax) is a temperate-zone euryhaline teleost of prime importance for aquaculture and fisheries. This species is subdivided into two naturally hybridizing lineages, one inhabiting the north-eastern Atlantic Ocean and the other the Mediterranean and Black seas. Here we provide a high-quality chromosome-scale assembly of its genome that shows a high degree of synteny with the more highly derived teleosts. We find expansions of gene families specifically associated with ion and water regulation, highlighting adaptation to variation in salinity. We further generate a genome-wide variation map through RAD-sequencing of Atlantic and Mediterranean populations. We show that variation in local recombination rates strongly influences the genomic landscape of diversity within and differentiation between lineages. Comparing predictions of alternative demographic models to the joint allele-frequency spectrum indicates that genomic islands of differentiation between sea bass lineages were generated by varying rates of introgression across the genome following a period of geographical isolation.

The use of microsatellite loci for accurate hybrid detection in a recent contact zone between an endangered and a recently-arrived hummingbird

Interspecies hybridisation frequently occurs when the distributional ranges of two closely-related species overlap after a period of geographic isolation. From a conservation perspective, such hybridisation events can incur detrimental effects on the viability of each species involved, especially for species which are already threatened by other ecological processes, such as human-induced declines in population size. The early and accurate detection of hybrids within recent contact zones is therefore of crucial importance for conservation strategies. A recent contact zone occurs in the north of Chile between the endangered Chilean Woodstar (Eulidia yarrellii) and the non-native and recently-arrived Peruvian Sheartail (Thaumastura cora), which expanded its range from Peru into Chile during the 1970s. Several factors suggest that these species may be hybridising. We here describe a set of microsatellite loci which prove to be a powerful tool in detecting F1 hybrids and backcrosses between the two species. These loci will be an invaluable tool for future research to ascertain the degree of hybridisation that is occurring between the two species and to devise appropriate conservation strategies.

Divergence with Gene Flow: Models and Data

Since Darwin first proposed that new species could arise without geographic separation, biologists have debated whether or not divergence occurs in the presence of gene exchange. Today we understand that new species can diverge while exchanging genes, depending on the strength of disruptive natural selection and the factors that affect the linkage relationships of genes under disruptive selection. This mode of diversification—divergence with gene flow—includes sympatric speciation, in which gene exchange occurs since onset of divergence, and secondary contact following a period of geographic isolation, as well as all sorts of situations in which gene flow happens intermittently. In recent years, statistical tools have been developed that can reveal the action of gene flow during divergence. Isolation-with-migration (IM) models include parameters for population size, time of population separation, and gene exchange, and they have been used extensively to estimate levels of gene exchange. A survey of studies that have used these models shows that a plurality find little evidence of gene flow; however, many report nonzero gene exchange.

Divergence time of the two regional medaka populations in Japan as a new time scale for comparative genomics of vertebrates

The southern and northern Japanese populations of the medaka fish provide useful tools to gain insights into the comparative genomics and speciation of vertebrates, because they can breed to produce healthy and fertile offspring despite their highly divergent genetic backgrounds compared with those of human-chimpanzee. Comparative genomics analysis has suggested that such large genetic differences between the two populations are caused by higher molecular evolutionary rates among the medakas than those of the hominids. The argument, however, was based on the assumption that the two Japanese populations diverged approximately at the same time (4.0-4.7 Myr ago) as the human-chimpanzee lineage (5.0-6.0 Myr ago). This can be misleading, because the divergence time of the two populations was calculated based on estimated, extremely higher molecular evolutionary rates of other fishes with an implicit assumption of a global molecular clock. Here we show that our estimate, based on a Bayesian relaxed molecular-clock analysis of whole mitogenome sequences from 72 ray-finned fishes (including 14 medakas), is about four times older than that of the previous study (18 Myr). This remarkably older estimate can be reconciled with the vicariant events of the Japanese archipelago, and the resulting rates of molecular evolution are almost identical between the medaka and hominid lineages. Our results further highlight the fact that reproductive isolation may not evolve despite a long period of geographical isolation.

Mitochondrial DNA polymorphisms of the house mouse Mus musculus domesticus from Greece, focusing on the Robertsonian chromosomal system of north-west Peloponnese

This study focused on the sequence variation in a mitochondrial region in house mice Mus musculus domesticus from chromosomally variable populations in the north-west Peloponnese, Greece. The mitochondrial molecular variation revealed was among the highest found so far for M. m. domesticus populations. The haplotype distribution pattern was rather complex. There was no clear differentiation between the populations characterized by Robertsonian chromosomes and standard all-acrocentric populations. There is therefore no indication that the Robertsonian populations were formed during a prolonged period of geographical isolation.

Ancient DNA evidence for Old World origin of New World dogs.

Mitochondrial DNA sequences isolated from ancient dog remains from Latin America and Alaska showed that native American dogs originated from multiple Old World lineages of dogs that accompanied late Pleistocene humans across the Bering Strait. One clade of dog sequences was unique to the New World, which is consistent with a period of geographic isolation. This unique clade was absent from a large sample of modern dogs, which implies that European colonists systematically discouraged the breeding of native American dogs.

Genetic Similarity and Variation in the Cultured and Wild Crucian Carp (Carassius carassius) Estimated with Random Amplified Polymorphic DNA

Random amplified polymorphic DNA (RAPD) analysis based on numerous polymorphic bands have been used to investigate genetic similarity and diversity among and within two cultured and wild populations represented by the species crucian carp (Carassius carassius). From RAPD analysis using five primers, a total of 442 polymorphic bands were obtained in the two populations and 273 were found to be specific to a wild population. 169 polymorphic bands were also produced in wild and cultured population. According to RAPD-based estimates, the average number of polymorphic bands in the wild population was approximately 1.5 times as diverse as that in cultured. The average number of polymorphic bands in each population was found to be different and was higher in the wild than in the cultured population. Comparison of banding patterns in the cultured and wild populations revealed substantial differences supporting a previous assessment that the populations may have been subjected to a long period of geographical isolation from each other. The values in wild population altered from 0.21 to 0.51 as calculated by bandsharing analysis. Also, the average level of bandsharing values was 0.40±0.05 in the wild population, compared to 0.69±0.08 in the cultured. With reference to bandsharing values and banding patterns, the wild population was considerably more diverse than the cultured. Knowledge of the genetic diversity of crucian carp could help in formulating more effective strategies for managing this aquacultural fish species and also in evaluating the potential genetic effects induced by hatchery operations. (Asian-Aust. J. Anim. Sci. 2002. Vol 15, No. 4 : 470-476)

Chloroplast DNA variation in the cultivated and wild olive taxa of the genus Olea L.

Polymorphism in the lengths of restriction fragments of the whole cpDNA molecule were studied in 15 taxa (species or subspecies) of the genus Olea. From restriction analysis using nine endonucleases, 28 site mutations and five length polymorphisms were identified, corresponding to 12 distinct chlorotypes. From a phenetic analysis based on a Nei’s dissimilarity matrix and a Dollo parsimony cladistic analysis using, as an outgroup, a species of the genus Phillyrea close to Olea, the ten taxa of section Olea were distinguished clearly from the five taxa of section Ligustroides which appear to posses more ancestral cpDNA variants. Within the section Ligustroides, the tropical species from central-western Africa, Olea hochtetteri, showed a chlorotype which differed substantially from those of the other four Olea taxa growing in southern Africa, supporting a previous assessment according to which O. hochtetteri may have been subjected to a long period of geographical isolation from the other Olea taxa. Within the Olea section, three phyla were identified corresponding to South and East Africa taxa, Asiatic taxa, and a group including Saharan, Macaronesian and Mediteranean taxa, respectively. On the basis of cpDNA variation, the closest Olea taxa to the single Mediterranean species, Olea europaea, represented by its very predominant chlorotype, observed in both wild and cultivated olive, were found to be Olea laperrinei (from the Sahara), Olea maroccana (from Maroccan High Atlas) and Olea cerasiformis (from Macaronesia). These three taxa, which all share the same chlorotype, may have a common maternal origin.

GENETIC BASE AND EVOLUTIONARY CHANGE OF MIGRATORY DIRECTIONS IN A EUROPEAN PASSERINE MIGRANT SYLVIA ATRICAPILLA

Summary Helbig, A. J. 1994. Genetic basis and evolutionary change of migratory directions in a European Passerine migrant Sylvia atricapilla. Ostrich 65: 157–159. Early displacement experiments and more recent experimental studies with hand-raised Blackcaps Sylvia atricapilla are reviewed in order to describe our current state of understanding of the genetic basis and recent evolutionary changes of migratory directions in birds. Hand-raised Blackcaps from east and west of the Central European migratory divide, when tested under identical conditions, exibited population-specific migratory directions in orientation cages. Cross-breeding of birds from these two populations demonstrated an intermediate mode of inheritance of this behavioural character. New data on the mitochondrial genetic population structure of the Blackcap indicate that population differentiation at the behavioural level is not necessarily related to long periods of geographic isolation (e.g. during ice ages). Migratory adaptations may hav...

The Biogeography of the Maltese Islands, Illustrated by the Clausiliidae

Published data on the geology and biogeography of the Maltese islands are reviewed. The islands consist of Oligo-Miocene limestones of marine origin, and probably rose above sea level during the Late Miocene. During the Messinian crisis, the Straits of Sicily were probably above sea level, and terres- trial organisms could migrate between Europe and Africa. It is likely that the flooding of the Mediterranean basin which took place at the start of the Pliocene separated Malta from both Africa and Sicily. If any land connection with Lampedusa or North Africa persisted, this must have been destroyed by the extensive subsidence in the middle of the strait of Sicily which occurred during the Pliocene. Tectonism on the Malta-Sicily submarine ridge was less extensive and may have occurred during the Pleistocene. Late Pleistocene eustatic sea level lows during glacials were sufficient to connect Malta to Sicily. The Maltese biota closely resembles the biota of Sicily, but there are also several endemics. A few species occur on Malta and North Africa, but are not found in Sicily. The distributions of the various Maltese species of Alopiini (Mollusca: Clausi- hidae) are figured. Most of the species are endemic to the archipelago and exhibit allopatric or parapatric distribution patterns. The genus Lampedusa (Imitatrix) possesses a relict distribution, with three species in as many isolated refugia. These species appear to be descended from a single ancestral species which was displaced by members of the genus Muticaria invading from Sicily during glacials when the intervening continental shelf was exposed. Invasion byMuticaria appears to have occurred twice, the earlier invaders evolving into an endemic species (Muticaria oscitans). Maltese biogeography is interpreted in terms of sea level changes and tectonic events which established or severed land connections with Sicily. The following hypothesis is proposed: Malta received terrestrial biota from Europe and presum- ably also from North Africa during the Messinian crisis. A long period of isolation during the Pliocene was followed by an Early-Middle Pleistocene connection with Sicily, during which some Sicilian forms invaded the islands. A second period of isolation followed, perhaps due to subsidence on the Malta-Sicily submarine ridge during the Middle Pleistocene. The islands' endemics evolved during the two periods of geographic isolation. The latest Pleistocene eustatic fluctuations were extensive enough to connect Malta to Sicily during glacials, and the islands' biota acquired an essentially Sicilian character. The North African elements in the Maltese biota seem interpretable in terms of active dispersal across the sea or

Acclimation and energy metabolism of the dingo, Cards dingo and the coyote, Canis latrans

Twelve dingos were divided into three groups each containing four animals. One group was warm‐acclimated at +30° to +45°C, the second cool‐acclimated at −20° to − 40°C and a third control group was kept in animal quarters maintained at about +23°C. Three coyotes were also kept in animal quarters but they had free access to outside runs which they used during all seasons.The four warm‐acclimated animals tolerated temperatures of +45°C at 25% relative humidity with a mean rectal temperature of 39.3°C and a mean O2 consumption rate of 8.2 ml/kg min.Cool‐acclimated dingos became distressed at ambient temperatures between +37.5 and +42.5°C and at 40% relative humidity the mean rectal temperature of this group was 40.6°C. The O2 consumption rate of one animal at an ambient temperature of +42.5°C was 16.7 ml/kg min.The mean minimum O2 consumption rate for the warm‐acclimated group in its thermal neutral range was 4.4 ml/kg min and the comparable rate for the cool‐acclimated group was 7.8 ml/kg min, a difference of 77% in their standard metabolic rates.At an ambient temperature of −70°C the mean O2 consumption rate of the four warm‐acclimated animals was about six times the mean rate recorded in their thermal neutral range. Despite this high energy usage all had low rectal temperatures and were frostbitten when they were removed from the chamber.The cool‐acclimated animals increased their O2 consumption rates by a factor of only 2.2 at −70°C when compared with the standard rate in their thermal neutral zone. At −70°C the mean O2 consumption rate of the cool‐acclimated group was only 69% of the warm group mean. With this lower energy usage they maintained their rectal temperature at normal values and did not suffer any frostbite.The weight of fur insulation per unit area increased in the cool‐acclimated animals and in some body areas the mean value was three times that of the corresponding mean for the warm‐acclimated group. When calculated from the slope of the O2 consumption vs. ambient temperature relation below the lower critical temperature the cool‐acclimated group had 64% more insulation than the warm‐acclimated group.The three coyotes had a mean O2 consumption rate at −70°C (17.7 ml/kg min) which was about equal to that of the cool‐acclimated dingos at the same ambient temperature. This rate was 2.4 times the standard metabolic rate in their thermal neutral zone and is about the same proportional increase as that shown by the cool‐acclimated dingos. However the lower critical temperature of the coyotes (−10°C) was much lower than that of the cold‐acclimated dingos (+ 10°C).When compared with other canid studies these results suggest that, even when acclimated to heat, dingos have a tolerance of high temperatures which is little or no better than that of the domestic dog. When held at −70°C cool‐acclimated dingos maintained their body temperatures with moderate energy expenditure but even so were not as metabolically economical as the wolf or the husky but were comparable with the coyote.It is concluded that the dingo as a species during its period of geographical isolation in Australia has changed but little in its ability to tolerate extremes of temperature and that seasonal acclimatization in part accouts for its acceptance of a wide range of environmental temperatures.

Disruptive selection on sternopleural chaeta number in Drosophila melanogaster

It is generally accepted that reproductive isolation leading to the irreversible division of a Mendelian population into two species must be initiated during a period of geographical isolation (see Mayr, 1963). Thoday &amp; Gibson (1962, Gibson &amp; Thoday, 1963) obtained partial isolation within a population of Drosophila melanogaster by artificial disruptive selection for the number of sternopleural chaetae. This occurred in two experiments from the same base population after seven and twelve generations respectively. On the strength of these results they concluded that speciation does not require geographical isolation and that sympatric speciation by disruptive selection in a heterogeneous habitat is at least a theoretical possibility.