Palaeoclimatic variation, adaptation and biogeography of inversion polymorphisms in natural populations of Drosophila robusta

Studies of natural and sexual selection in wild populations of Drosophila have historically provided strong inference for the maintenance of inversion polymorphism. Analysis of geographical variation in the Drosophila robusta chromosomal data collected over more than 50 years from 133 natural populations across eastern North America has confirmed several north–south and east–west clines in the frequencies of some gene arrangements and linked arrangement combinations. Patterns of geographical variation, including several north–south clines, revealed by regression and spatial autocorrelation analyses are concordant with palaeoclimatic shifts, Pleistocene glaciations and historical changes in the composition of North American forest communities. Because D. robusta is a sap-breeder, using the microbe-infested sap exudates of a number of deciduous tree species in which they carry out their life cycle, shifts in climate and palaeovegetation types since the formation of the eastern deciduous forests in the Miocene are hypothesized to be major factors influencing patterns of inversion polymorphisms across the range of this drosophilid species. In areas where sharp deviations in frequencies have been observed, particularly in the mid-western and western portions of the range, these divisions parallel historical geographical disjunctions in the species range that have yet to promote divergence and species formation despite the long history of D. robusta in North America.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 81 , 395–411.     

Contemporary geography dominates butterfly diversity gradients within the Aegean archipelago (Lepidoptera: Papilionoidea, Hesperioidea)

Aim We compare the influence of contemporary geography and historical influences on butterfly diversity for islands in the Aegean archipelago. Location The Aegean archipelago (Greece) and two islands (Cyprus and Megisti) in the Levantine Sea. Methods Thirty‐one islands were examined. Data are taken from own surveys (Coutsis and Olivier) and from the literature. Stepwise multiple regression is used to determine relationships between species richness, frequency, rarity and endemicity against potential geographical predictors. Stepwise logit regression is used to determine geographical predictors of species incidence on islands. Inter‐island and inter‐species associations have been examined using multivariate ordination and clustering techniques. Results The Aegean butterfly fauna is characterized by decreasing diversity and rarity, and increasing homogeneity, from the periphery to the present geographical centre of the archipelago (Cyclades). Diversity and rarity are shown to relate closely to species richness, and species richness, in turn, is largely explained by contemporary geography, particularly the degree of isolation from the nearest mainland sources of Greece or Turkey, and island dimensions. Islands towards the centre of the archipelago are characterized by a group of mobile species (n ≥ 20 species) with extensive ranges across Europe; species that would have recolonized Santorini (Thira) following the VI6 eruption there c. 1630 bc . Endemic components, indicative of autochthonous evolutionary events, are few (5% of species are endemic) compared to known sedentary organisms (molluscs and isopods), but exceed those for more mobile animals (i.e. birds); their distribution is mainly confined to large isolated islands along the Aegean arc (i.e. Kriti) and in the Dodecanese group. Main conclusions Contemporary geography, i.e. processes currently operating in ecological time, dominates butterfly diversity gradients (species richness, frequency, rarity and incidence) in the archipelago. Two reasons are suggested to account for the lack of endemism and the pattern of decreasing diversity into the Cyclades. First, relict butterfly elements may have become extinct on all but a few larger islands, particularly from environmental changes since the Neolithic (fire and overgrazing). Second, colonization from the continental landmasses is ongoing with more mobile species transferring even to the most isolated islands.     

Latitudinal and ecological correlates of morphological variation in Galaxias platei (Pisces, Galaxiidae) in Patagonia

We examined the morphological variability (23 morphometric traits) among individual Galaxias platei ( N  = 380) collected from 20 postglacial lakes in the southern Andes. The lakes were chosen to cover the latitudinal range of the species in Patagonia. Diet examined for a subset of these fish ( N  = 261) collected during the summer months (January through March), differed among river basins but there were no clear latitudinal trends in the consumption of any prey type. Diet may, however, have partially shaped morphology, as pelvic measures were negatively correlated with consumption of amphipods. Substantial differentiation among populations was observed, primarily in the shape and dimensions of the head, in caudal morphology and in fin length. Our results indicate that the morphology of G. platei varies with latitude, and may be related to risk of predation and diet.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 69–82.     

Chromosomal polymorphism in the Atlantic dog-whelk, Nucella lapillus (Gastropoda: Muricidae): nomenclature, variation and biogeography

Nucella lapillus appears to be unique within the Muricidae, and indeed the Mollusca, in exhibiting a Robertsonian chromosomal polymorphism. The recorded diploid values range from 2 n  = 26 to 2 n  = 36, putatively brought about by fusion of smaller chromosomes to form five pairs of large metacentrics in the 2 n  = 26 form. In this study, the karyotypes of the numerically extreme forms (2 n  = 26 and 2 n  = 36) have been illustrated and described in detail, and a new scheme of nomenclature is proposed for the chromosomal rearrangements observed in N. lapillus . Chromosome numbers and karyotypes were recorded and analysed from 70 sites throughout its wide geographical range, mainly from around the UK coasts but also from sites in Norway, France, Spain, Portugal and the USA, showing remarkable variation in both diploid number and karyotypic configuration. The results provide new evidence that seven chromosomes in the 2 n  = 26 form can be involved in the Robertsonian rearrangements, but the maximum recorded diploid number remains 2 n  = 36. Inversions were confirmed in three chromosomes and one population was found to exhibit aneuploidy. Possible explanations for the geographical trends in karyotypic variation are discussed, but despite the advances in the karyology of N. lapillus , a simple solution to this enigmatic phenomenon remains elusive.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 195–210.     

Geographic variation in the long-nosed snake, Rhinocheilus lecontei (Colubridae): beyond the subspecies debate

Scalation, colour pattern, linear and geometric morphometrics were used to quantify geographical differentiation in the long-nosed snake, Rhinocheilus lecontei, and to test the hypothesis that all four subspecies are morphologically distinct. Also investigated were potential associations between morphological (scalation, colour pattern, linear measurements) and environmental variables (climate, vegetation, soil). Sexual dimorphism was weakest for geometric and strongest for linear morphometric variables. Morphological variables differed widely in their ability to differentiate subspecies. Linear morphometric variables achieved the most statistically significant pairwise Mahalanobis distances between subspecies, while geometric morphometrics largely failed to differentiate them. Colour pattern showed the strongest and linear morphometrics the weakest correlation with environment. Several characters varied continuously along latitudinal or longitudinal gradients, such that, in some cases, the clines for closely related traits were discordant. No one subspecies was consistently divergent in all analyses, leading to the conclusion that the three mainland subspecies are not sufficiently distinct to warrant separate subspecies status. The island subspecies, though not always statistically distinct, is geographically separate from other populations and differs in characters related to size. Given the small number of specimens available, a decision regarding its taxonomic status (i.e. elevation to species level) is best deferred until additional specimens can be examined and data on molecular variation can be analysed.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 65–85.     

Genetic cohesion of Eresus walckenaeri (Araneae, Eresidae) in the eastern Mediterranean

The eresid spider genus Eresus is morphologically and ecologically conservative. At least three species occur in Europe. However, deep genetic divergence among geographical samples within two species, E. cinnaberinus and E. sandaliatus , may suggest more cryptic species. In the present study we investigate the genetic cohesion of the third species, Eresus walckenaeri , throughout its eastern Mediterranean distribution range, relative to the E. cinnaberinus–E. sandaliatus species complex. Eresus walckenaeri specimens were monophyletic. Genetic discreteness of E. walckenaeri in a region of sympatry with its sister species in Greece provides evidence for species integrity of E. walckenaeri within the European Eresus species complex. Eresus walckenaeri exhibited high concordance between geographical location and mtDNA genealogy. Two major phylogeographical clades were found in the Greek–Turkish and Syrian–Israel parts of the investigated area, respectively (∼6.5% sequence divergence). Concordance between geography and genetic divergence was further observed between Aegean island samples and their corresponding Greek and Turkish mainland samples, suggesting regional subdivision with gradual but potentially high dispersal propensity. Monophyly and limited regional distribution indicate Mediterranean endemic origin.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 86 , 1–9.     

Latitudinal variation in axial patterning of the medaka (Actinopterygii: Adrianichthyidae): Jordan's rule is substantiated by genetic variation in abdominal vertebral number

Because the body axes of fish consist of two anatomically distinct vertebrae, abdominal and caudal, one type may be more variable in number than the other and thus contribute more to morphological diversification. Jordan's rule, a geographical tendency for fish from higher latitudes to have more vertebrae, has not been examined in terms of numbers of abdominal and/or caudal vertebrae, despite its prevalence. Vertebral observations of wild populations of the medaka ( Oryzias latipes ) revealed that the latitudinal increase in vertebral number is caused by an increase in abdominal vertebrae; caudal vertebrae did not vary systematically across latitudes. Laboratory experiments revealed that this latitudinal cline in abdominal vertebral number persists in a range of common environments, demonstrating a genetic basis. Phenotypic plasticity was also evident: lower developmental temperatures resulted in more abdominal vertebrae. This indicates that greater numbers of abdominal vertebrae in higher latitude individuals in the wild may be caused not only by genetic factors but by lower habitat temperatures, although the contribution of the former to Jordan's rule is assessed to be much greater. The genetic basis of the latitudinal variation in abdominal vertebral number suggests that selection on functions associated with abdominal regions is the probable explanation for Jordan's rule in this fish.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 856–866.     

Chromosomal variability in the genus Primula (Primulaceae)

Chromosome numbers and measurements were recorded in 47 individuals of ten taxa of Primula , representing eight species and two subspecies from ten populations. The basic numbers of chromosomes were x  = 8, 9 or 11, and they were mostly metacentric, medium-long to medium-small, ranging in length from c . 3.6 µm to 1.6 µm. Diploid chromosome numbers of 2 n  = 2 x  = 24 and 22 were scored for the first time in P. loeseneri Kitag. and P. prenantha Balf. & Sm., respectively. A new ploidy level of 2 n  = 4 x  = 44 was found in P. burmanica Balf. & King. The recorded diploid numbers of the remaining species confirmed earlier reports. Interspecific variability in chromosome numbers was correlated with heterogeneity in their mean length. Comparison of the data with those in the literature revealed that the observed variability of chromosomal characters was compatible with the other taxonomic criteria and supports the current taxonomic delimitation. Chromosomal variation at the diploid level is the predominant feature in Primula evolution, and allopatric speciation has played a major role in its specific diversity. Subgen. Aleuritia could represent the main clade from which the other subgenera have evolved. The origin of the chromosome numbers, geographical distribution and evolution of the species were assessed, and the parallel polyphyletic mode of evolution in the genus was confirmed.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 211–219.     

New chromosome counts in the genus Cousinia (Asteraceae) from Iran

Chromosome counts are reported of 38 populations representing 24 species of the genus Cousinia from Iran, one of the main centres of speciation of the genus. Sixteen of the counts are new to science. Our results confirm that Cousinia exhibits a complex dysploid series ranging from x  = 13 to x  = 9. One of the basic chromosome numbers, x  = 9, is new for the genus and must be confirmed. Some considerations on the correlation between chromosome numbers and section classification are made.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 151 , 411–419.     

Genetic diversity and structure of the cycad Zamia loddigesii Miq. (Zamiaceae): implications for evolution and conservation

The genetic diversity and structure of four populations of the cycad Zamia loddigesii were studied throughout its range in Mexico. Allozyme electrophoresis of 15 loci was conducted. The mean number of alleles per locus was 1.80 ± 0.09, the percentage of polymorphic loci was 66.6 ± 5.4, and the expected heterozygosity was 0.266 ± 0.02. The results indicated that the genetic diversity was relatively higher, with respect to tropical tree species and other cycads. The genetic variation explained by differences among populations was 18%. On average, gene flow between paired populations was similar ( Nm  = 1.6) to other tropical forest trees and cycad species. Our results indicated that the geographical isolation among populations of Z. loddigesii generated allele loss, as well as a clinal variation in the frequencies of two loci ( MDH and MNR2 ), in relation to the latitudinal distribution of populations. The populations have become fragmented due to increasingly higher pressure of habitat conversion and disturbance. The importance of the establishment of sanctuaries and protected areas and a reduction in deforestation is highlighted in this research as a way of preserving the high genetic diversity of this and other endemic species.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 152 , 533–544.     

The evolutionary history of the Mediterranean centipede Scolopendra cingulata (Latreille, 1829) (Chilopoda: Scolopendridae) across the Aegean archipelago

In this study we investigate the evolutionary relationships of Scolopendra cingulata (Latreille, 1829) within insular Greece. Our main goal is to infer the time frame of the differentiation of the species in the study area. In this regard, sequence data originating from three mitochondrial genes are used to reconstruct the evolutionary history of 47 insular populations of S. cingulata from the Aegean archipelago. Within the phylogenetic framework and by implementing a relaxed molecular clock methodology, we infer the time estimates of separations of the S. cingulata lineages. The results of the phylogenetic analysis support the presence of three distinct S. cingulata groups in the region. The first group accommodates populations from the eastern Aegean islands, and is closely related to the second group that hosts mainly populations of northern and central Cyclades. The third group is composed of insular populations originating from southern Cyclades. Different temporal splitting scenarios have been evaluated. Based on the scenario strongly supported by the data, we propose a biogeographical scenario that could account for the contemporary distribution of the species' lineages. The splitting events of S. cingulata are estimated to have occurred within the late Miocene. The historical events of the last 13.77 Myr have shaped, through a series of mostly vicariant and dispersal incidents, the present‐day biogeographical pattern of the species. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 507–521.     

Morphological and geographic variation of the cycad Dioon edule Lindl. (Zamiaceae): ecological and evolutionary implications

The relationship in geographical distribution and morphological variation of leaflet width and length (diagnostic trait), between and within populations of Dioon edule Lindl., has been investigated throughout its known range in eastern Mexico (from the states of Nuevo León to Veracruz, north to south, respectively). A total of 1832 leaflets were measured for width and length from 154 plants distributed amongst five populations using four leaflet replicas from each of three leaves per plant. For leaflet width and length the variation among populations indicated significant stat-istical differences ( F _4,147 = 125.83; P  < 0.0001; R ² = 92.17% and F _4,147 = 9.04; P  < 0.001; R ² = 26.8%), respectively. With respect to leaflet width, the multiple range test showed three groups with a north to south distributional relationship along the range of the species. The correlation coefficient among paired populations, respect to geographical distance and the absolute value of the mean difference of leaflet width in each population, was positive, and different from zero ( r  = 0.82; P  = 0.013). A great variation of important ecological and evolutionary parameters was shown.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 141 , 465–470.     

Geographic allozyme variation in the Japanese clouded salamander, Hynobius nebulosus (Amphibia: Urodela)

Using starch gel electrophoresis, geographical enzyme variation was surveyed in 46 populations of the Japanese salamander Hynobius nebulosus , which occurs widely in western Japan. This species exhibits substantial local genetic differentiation and is more diverse in inland regions than on small islands. In several different analyses, two groups of populations, one from Kyushu Island to the westernmost part of Chugoku district, Honshu (western group), and another from Shikoku through Kinki to Chubu district, Honshu (eastern group), were consistently recognized. Most of the remaining populations were placed in two less clearly-defined groups: the montane group from the Chugoku Mountains and the Chugoku group from the coastal regions of Chugoku district. The divergence patterns of H. nebulosus are thought to be related to the geological history of its range. The populations near the boundary of the western group were found to share several alleles that were predominant on both sides of the boundary, indicating past secondary contact. Differentiation in the montane group did not follow the isolation by distance model, probably because several populations included were genetically mixed with lowland populations of the Chugoku group.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 311–330.     

Taxonomy, evolutionary history and biogeography of the broad-toothed field mouse (Apodemus mystacinus) in the eastern Mediterranean area based on mitochondrial and nuclear genes

The broad-toothed field mouse ( Apodemus mystacinus ) is distributed throughout the Balkan Peninsula, Asia Minor and the Middle East. It is generally split into two different specific entities: Apodemus epimelas occurs on the Balkan Peninsula and A. mystacinus inhabits Asia Minor and the Middle East. This analysis, based on two mitochondrial regions (cytochrome b and the D-loop) and the interstitial retinol binding protein (IRBP) nuclear gene, confirms an important level of genetic divergence between the animals from these regions and their separation from each other at least 4.2–5.1 Mya, which is in favour of a distinct specific status. Finally, the broad-toothed field mice from south-western Turkey appear to be closely related to the animals from Crete but highly distinct from the populations of the other Oriental regions. This supports a distinct subspecific level ( A. m. rhodius ) for the insular animals and also for those from south-western Turkey. From a biogeographical point of view, it can be assumed that either late Pliocene or early Pleistocene cooling led to the isolation of two main groups of A. mystacinus , one in the Balkan region and the other one in Turkey and the Near East (Syria and Israel). In this region, it is suggested that a more recent event appeared during the Quaternary period, isolating broad-toothed field mice in Crete and leading to the appearance of two well-differentiated genetic groups: one in Crete and south-western Turkey, and the other widespread in northern and eastern Turkey as well as in the Near East.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 53–63.     

Chromosome numbers in Brazilian species of Crotalaria (Leguminosae, Papilionoideae) and their taxonomic significance

Chromosome numbers were counted for 23 species of Crotalaria native to Brazil. Among these data there were new counts for 15 taxa, and some confirmed previous reports or represented numbers that were different from those cited previously. The chromosome numbers most frequently found were 2 n  = 16 and 2 n  = 32. Only C. incana L. had 2 n  = 14 and C. tweediana Benth. had 2 n  = 54. The counts 2 n  = 32 and 54 were found in species of section Calycinae and 2 n  = 16 and 14 in species of section Chrysocalycinae . The data revealed the importance of chromosomal parameters in the characterization of sections Calycinae and Chrysocalycinae in Brazil. We discuss the systematic significance and evolutionary aspects for the genus, comparing the results with the two sections that are native in Brazil.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 151 , 271–277.     

A study of the diversity and geographical variation in numbers of leg‐bearing segments in centipedes (Chilopoda: Geophilomorpha) in north‐western Europe

Five species of geophilomorphs, Strigamia maritima (Leach, 1817), Geophilus flavus (De Geer, 1778), Geophilus truncorum Bergsøe and Meinert, 1866, Geophilus proximus C. L. Koch, 1847, and Pachymerium ferrugineum (C. L. Koch, 1835), from various sample sites in north‐western Europe were examined for numbers of leg‐bearing segments. Where data was adequate, mean segment numbers were correlated with latitudinal gradients for each species. Solely in S. maritima and some populations of P. ferrugineum did the results show a highly significant geographic pattern towards more leg‐bearing segments in southern populations of both sexes. As concerns G. proximus, we presented for the first time a remarkable geographic shift towards an increased number of pairs of legs in northern populations. Contrary to the conventional geographic pattern, we found that G. flavus and G. truncorum did not exhibit a north–south increase or decrease in segment number. Although there was no general/universal evidence supporting the occurrence of a significant regression slope between mean segment number and latitude/temperature, more information shows that the overall region‐to‐region segment variation was highly significant in both sexes. In S. maritima and P. ferrugineum mean segment number was correlated with the north–south temperature cline. The same was not observed in G. proximus. Parthenogenesis in G. proximus, and a series of ecological characteristics such as habitat preferences, spatial distribution, and fragmented populations could explain the presence or absence of a geographic patterning of segment number variation along a latitudinal cline. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 899–909.     

Physiological variation along a geographical gradient: is growth rate correlated with routine metabolic rate in Rana temporaria tadpoles?

Shorter season length and lower temperature towards higher latitudes and altitudes often select for intraspecific clines in development and growth rates. However, the physiological mechanisms enabling these clines are not well understood. We studied the relationship between routine metabolic rate (RMR) and larval life-history traits along a 1500-km latitudinal gradient across Sweden. In a laboratory common garden experiment, we exposed eight common frog Rana temporaria populations to two experimental temperatures (15 and 18 °C) and measured RMR using flow-through respirometry. We found significant differences among populations in RMR, but there was no evidence for a linear relationship between latitude and RMR in either temperature treatment. However, we found a concave relationship between latitude and RMR at the lower experimental temperature. RMR was not correlated with growth rate at population or at individual levels. The results obtained suggest that, unlike in growth and development rates, there is no latitudinal cline in RMR in R. temporaria tadpoles.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 217–224.