Geographic variation of reproductive diapause in the Drosophila auraria complex (Diptera: Drosophilidae)

ABSTRACT. In the Drosophila auraria complex (D. auraria Peng, D. biauraria Bock & Wheeler, D. triauraria Bock & Wheeler, D. quadraria Bock & Wheeler and D. subauraria Kimura), D. triauraria from the island of Yaku (30.3N in latitude) and D. quadraria from Taiwan (24.1N) had no or weak diapause, while strains of all the four species from the main islands of Japan had a firm reproductive diapause. These strains entered diapause at short daylengths and the critical daylength was longer and the incidence of diapause higher at a low rather than high temperature. In each species, the critical daylength was longer in strains from higher latitudes. Among sympatric populations of different species, D. subauraria always had the longest critical daylength, while D. auraria had the shortest one. The populations of D. biauraria and D. triauraria had longer critical daylengths than the sympatric populations of D. auraria , but this difference became smaller northwards. Since a longer critical daylength induces diapause earlier in autumn, D. subauraria would enter diapause earliest among these species, and D. auraria would do so latest. The late start of diapause in D. auraria may be related to its adaptation to domestic environments. On the other hand, the adaptive significance of the late start of diapause in northern populations of D. biauraria and D. triauraria is not clear.     

Molecular phylogeny of the Drosophila auraria species complex and allied species of Japan based on nuclear and mitochondrial DNA sequences

We studied the phylogenetic relationships among the six species of the Drosophila auraria species complex and three species of the montium species subgroup endemic to Japan. To do this, we examined the DNA sequences of the nuclear ITS1 and the mitochondrial COII of these species. Intraspecific variation in ITS1 was observed for most of the species studied. However, interspecific variation was small and of the same magnitude as intraspecific variation among D. auraria, D. triauraria, and D. quadraria. In addition, the amount of intraspecific variation between COII sequences from D. auraria and D. triauraria was almost the same as that of the interspecific variation between these species. Phylogenetic trees based on ITS1 or COII data reveal that, with the exception of D. pectinifera, these species can be separated into two taxonomic groups. D. rufa formed a taxonomic lineage with two Japanese endemic species, D. asahinai and D. lacteicornis. Physiological and behavioral differences between D. auraria and D. triauraria have been reported, but our results differed from those previously reported. Such differences may be better explained by hybridization between D. auraria and D. triauraria than by similarity due to recent common ancestry. Both the ITS1- and COII-based phylogenetic trees placed D. pectinifera outside the auraria complex. However, D. pectinifera sequences were more similar to those of the auraria complex than those of D. punjabiensis, another species thought to be closely related to members of the auraria complex.     

Different cell size and cell number contribution in two newly established and one ancient body size cline of Drosophila subobscura

Latitudinal genetic clines in body size occur in many ectotherms including Drosophila species. In the wing of D. melanogaster, these clines are generally based on latitudinal variation in cell number. In contrast, differences in wing area that evolve by thermal selection in the laboratory are in general based on cell size. To investigate possible reasons for the different cellular bases of these two types of evolutionary response, we compared the newly established North and South American wing size clines of Drosophila subobscura. The new clines are based on latitudinal variation in cell area in North America and cell number in South America. The ancestral European cline is also based on latitudinal variation in cell number. The difference in the cellular basis of wing size variation in the American clines, which are roughly the same age, together with the similar cellular basis of the new South American cline and the ancient European one, suggest that the antiquity of a cline does not explain its cellular basis. Furthermore, the results indicate that wing size as a whole, rather than its cellular basis, is under selection. The different cellular bases of different size clines are most likely explained either entirely by chance or by different patterns of genetic variance--or its expression--in founding populations.     

Geographic variation and genetic aspects of reproductive diapause in Drosophila triauraria and D. quadraria

ABSTRACT. Geographic variation and genetic aspect of reproductive diapause were studied in Drosophila triauraria Bock & Wheeler and D. quadraria Bock & Wheeler, in relation to their quantitative response to photoperiods. D. quadraria from the subtropical region had no photoperiodic diapause. In D. triauraria strains, diapause was induced under LD 10:14 or 12:12, but not under LD 14:10 or longer photoperiods. Their diapause was induced more effectively and maintained longer by LD 10:14 than by LD 12:12. The duration of diapause was longer in a northern strain, but the diapause inducing process varied little among different geographical strains. Diapause incidence was 50% or lower in F₁ hybrids between D. triauraria and D. quadraria and backcross progenies between F₁ and D. quadraria , and about 70% in backcross progenies between F₁ and D. triauraria under LD 10:14, but very low under LD 12:12. The lower incidence of diapause in these F; and backcross progenies is assumed to be due to the less efficient induction of diapause, since once diapause was induced in them, it was maintained for a long time, especially in the backcross progenies between F₁ and D. triauraria. These experiments suggest that diapause induction and maintenance are different physiological processes controlled by different genetic systems.     

Re-establishment of clinal variation in flowering time among introduced populations of purple loosestrife (Lythrum salicaria, Lythraceae)

Range expansion during biological invasion requires that invaders adapt to geographical variation in climate, which should yield latitudinal clines in reproductive phenology. We investigated geographic variation in life history among 25 introduced populations of Lythrum salicaria, a widespread European invader of North American wetlands. We detected a strong latitudinal cline in initiation of flowering and size at flowering, which paralleled that reported among native populations. Plants from higher latitudes flowered earlier and at a smaller size than those from lower latitudes, even when raised in a uniform glasshouse. Early flowering was associated with greatly reduced reproductive output, but this was not associated with latitudinal variation in abundance, and probably did not result from a genetic correlation between time to and size at flowering. As introduction to North America c. 200 years ago, L. salicaria has re-established latitudinal clines in life history, probably as an evolutionary response to climatic selection.     

A genetic analysis of photoperiodic reproductive diapause in Drosophila triauraria

Abstract. Recombinant inbred lines were produced from hybrids between diapausing and non-diapausing strains of Drosophila triauraria Bock & Wheeler by twenty generations of full-sib mating. The analysis of these inbred lines suggests that the difference in the photoperiodic response between the original diapausing and non-diapausing strains is due to genes at three or four loci and at least one of these loci is located on the X chromosome. The original diapausing strain and two inbred lines exhibited circadian peaks when subjected to the Nanda-Hamner protocol, although they had different critical daylengths. This suggests that critical daylength is modified independently of the circadian oscillation system in this species. On the other hand, diapause duration was correlated with critical daylength among the inbred lines and the original diapausing strain, suggesting that these two traits are under the control of the same genetic system.     

Shifting clinal patterns of stress resistance traits in Drosophila ananassae

Drosophila ananassae, a desiccation and cold sensitive species, is abundant along the latitudinal gradient of the Indian subcontinent. Analysis of seasonally varying wild-caught flies showed two independent patterns of melanisation: (1) narrow to broad melanic stripes on three anterior abdominal segments only; (2) a novel body color pattern (dark vs. light background). We investigated the degree to which these two melanisation systems vary; first with latitude and secondly among seasons. There is a shallow latitudinal cline for percent striped melanisation as well as for frequency of body color alleles during the rainy season. The frequencies of body color alleles vary significantly across seasons in the northern populations i.e. the light allele occur abundantly (>0.94) during the rainy season while the frequency of the dark allele increases (0.22–0.35) during the dry season causing steeper clines during the dry season. By contrast, the low variations in abdominal stripes showed non-significant changes and the cline was similar across seasons. Furthermore, both types of melanisation patterns showed no plasticity with respect to temperature. The present study also investigated clines related to desiccation, heat and cold stress in D. ananassae females across seasons (rainy and dry) from nine latitudinal populations. The clines for stress related traits changes to steeper and non-linear during the dry season. Thus, latitudinal populations of D. ananassae differ in slope values of clines for stress related traits across seasons. This study reports seasonal changes in latitudinal clines of stress resistance traits as seen in a changing frequency of body color alleles of D. ananassae in northern locality, while in southern localities it remains constant. This is presumably the result of only minor seasonal changes in humidity and temperature in the South, whereas in the North seasonal climatic variability is much higher.     

The polytene chromosomes of Drosophila triauraria and D. quadraria, sibling species of D. auraria.

The polytene chromosomes of Drosophila triauraria and D. quadraria, two of the sibling species of D. auraria, were examined. The polytene chromosomes of all three species exhibit very clear homology. Unlike the stock of D. auraria that we studied, D. triauraria and D. quadraria carry heterozygous paracentric inversions. In both species, 2R and 3R are the arms where these inversions are concentrated. In addition, in D. quadraria, the 3L chromosome arm is very complicated because of heterozygous inversions. The mode of inheritance of these rearrangements was studied. A homozygous strain for all chromosome arms of D. triauraria was isolated, while a homozygous strain was obtained only for the arms X, 2L, 3L, and 4 of D. quadraria. Like D. auraria, both species show a large number of inverted tandem duplications in the paired condition, even in the chromosomes of their hybrids. Small deletions were also detected, one of which, in D. triauraria, is homozygous terminal. Hypotheses are discussed concerning the relationships of the species and the existence of inverted tandem duplications.     

Presence of an invasive species reverses latitudinal clines of multiple traits in a native species

Understanding the processes driving formation and maintenance of latitudinal clines has become increasingly important in light of accelerating global change. Many studies have focused on the role of abiotic factors, especially temperature, in generating clines, but biotic factors, including the introduction of non‐native species, may also drive clinal variation. We assessed the impact of invasion by predatory fire ants on latitudinal clines in multiple fitness‐relevant traits—morphology, physiological stress responsiveness, and antipredator behavior—in a native fence lizard. In areas invaded by fire ants, a latitudinal cline in morphology is opposite both the cline found in museum specimens from historical populations across the species’ full latitudinal range and that found in current populations uninvaded by fire ants. Similarly, clines in stress‐relevant hormone response to a stressor and in antipredator behavior differ significantly between the portions of the fence lizard range invaded and uninvaded by fire ants. Changes in these traits within fire ant‐invaded areas are adaptive and together support increased and more effective antipredator behavior that allows escape from attacks by this invasive predator. However, these changes may mismatch lizards to the environments under which they historically evolved. This research shows that novel biotic pressures can alter latitudinal clines in multiple traits within a single species on ecological timescales. As global change intensifies, a greater understanding of novel abiotic and biotic pressures and how affected organisms adapt to them across space and time will be central to predicting and managing our changing environment.     

Starvation resistance and adult body composition in a latitudinal cline of Drosophila melanogaster

Abstract Latitudinal geographic variation in Drosophila melanogaster is pervasive. Parallel clines in traits such as body size, egg size, ovariole number, and development time have been found on several continents throughout the world. However, a cline in starvation resistance and fat content in D. melanogaster has so far been found only in India. Here we investigate starvation resistance and fat content in 10 populations from South America, in which clines in body size, egg size, and development time have previously been found. We find no evidence for a cline in starvation resistance or fat content in South America. We therefore suggest that the cline in starvation resistance in India may have evolved in response to specific climatic variation found only in India.     

Investigating latitudinal clines for life history and stress resistance traits in Drosophila simulans from eastern Australia

Latitudinal clines have been demonstrated for many quantitative traits in Drosophila and are assumed to be due to climatic selection. However, clinal studies are often performed in species of Drosophila that contain common cosmopolitan inversion polymorphisms that also show clinal patterns. These inversion polymorphisms may be responsible for much of the observed clinal variation. Here, we consider latitudinal clines for quantitative traits in Drosophila simulans from eastern Australia. Drosophila simulans does not contain cosmopolitan inversion polymorphisms, so allows the study of clinal selection on quantitative traits that are not confounded by associations with inversions. Body size showed a strong linear cline for both females and males. Starvation resistance exhibited a weak linear cline in females, whereas chill-coma recovery exhibited a significant nonlinear cline in females only. No clinal pattern was evident for development time, male chill-coma recovery, desiccation or heat resistance. We discuss these results with reference to the role inversion polymorphisms play in generating clines in quantitative traits of Drosophila.     

Latitudinal clines in the properties of a circadian pacemaker

The circadian rhythm of eclosion activity and its pacemaker were analyzed in a series of latitudinal races of Drosophila auraria ranging from 34.2 degrees to 42.9 degrees N in Japan. The phase of the rhythm (psi EL) to the daily photoperiod (PP) changes as daylength is increased, and the slope of psi EL (PP) changes with latitude. Is is sufficiently greater in the north to cause a phase reversal of northern and southern races on long versus short photoperiods. This reversal is found in assays of the pacemaker's phase (psi PL) as well as that of the rhythm (psi EL). Assay of the pacemaker shows that its period (tau) is longer in northern than in southern races, and that the amplitude of its phase response curve (PRC) is lower in the north. The period of the rhythm in all latitudinal races is longer than 24 hr in short photoperiods (LD 1:23), but is probably less than 24 hr (as an aftereffect of photoperiod) in longer days such as LD 14:10. The observed north-south differences in the phase relation of both pacemaker and rhythm to the light cycle are explained by the latitudinal clines in pacemaker properties and a postulated aftereffect of photoperiod on tau. It is suggested that the latitudinal cline in PRC amplitude has functional significance in conserving the amplitude of the pacemaker's signal to the rest of the system it times. Computer simulation shows that without such a reduction in the perceived light intensity, pacemaker amplitude will be lowered by the increase in duration of the daily light at higher latitudes.     

用RAPD标记探讨金色果蝇复合种内的遗传分化

以随机扩增多态性DNA（RAPD）技术分析了金以果蝇复合种的5个姊妹种（Drosophile auraria、D．biauraria、D.triauraria、D．quadraria和D．subauraria）共12个地理种群的遗传变异。在40种10碱基随机引物中有30种引物对每个种群都可获得令人满意的扩增结果。在161个RAPD标记中有129个呈多态性。以遗传距离为尺度用UPGMA法构建了该复合种的聚类关系图。聚类分析结果结果表明：D.subauraria处于聚类关系图的基部,为该复合种中最早分化的种类;其后才是D.biauraria的分化,而D.auraria和D.quadraria的分化相对较晚。此结果不支持以往认为D.quadraria为金色果蝇复合种祖先种的观点。RAPD分子标记为金色果蝇复合种的系统演化的研究提供了新的、更有价值的信息。     

Clinal variation in post‐winter male fertility retention; an adaptive overwintering strategy in Drosophila melanogaster

In insects including Drosophila melanogaster, females can overwinter at the adult stage by adopting a shallow reproductive diapause, but almost nothing is known about male reproductive diapause. In this study, we test for the maintenance of fertility in overwintering males from the eastern Australian D. melanogaster cline. Males from southern temperate populations maintained in field cages in temperate Melbourne had a higher fertility in spring compared with males from tropical locations. Temperate males successfully inseminated more females, and there were also more offspring produced per inseminated female. The resulting linear post‐winter fertility clines were unrelated to male body size. In contrast, there was no clinal variation for fertility in nonoverwintering males held in the laboratory. The cline in overwintering male fertility is likely to have evolved as an adaptive response to latitudinal climatic variation over the last 100 years.     

Chromosome inversion polymorphisms in Drosophila melanogaster II. Geographic clines and climatic associations in Australasia,North America and Asia

The four paracentric autosomal chromosome inversions In(2L)t, In(2R)NS, In(3L)P and In(3R)R are commonly polymorphic in natural populations of D. melanogaster in Australasia, North America and Asia, with latitudinal clines in the frequencies of each inversion in each region. In each region inversion frequency decreases with increasing distance from the equator, although the precise relationship between frequency and latitude varies between inversions and, for In(2L)t and In(2R)NS, among regions. Each inversion also shows a longitudinal cline in at least one region but none show such a cline in all three. Although no inversion's frequency is associated with the same climatic variable in all three regions, inversion frequencies are generally positively related to annual maximum temperature and, more particularly, minimum temperature and minimum rainfall. The directions of the latitudinal clines and the climatic associations are consonant with evidence from D. melanogaster that inversion frequencies decline in winter. They are also consonant with evidence from some other Drosophila species that inversion heterozygosities are lower at the geographic margins than at the centre of the species' ranges.     

What determines conformity to Bergmann's rule?

Aim  Bergmann's rule, the tendency of body size within species in bird and mammal populations to be positively correlated with latitude, is among the best known biogeographical generalizations. The factors behind such clines, however, are not well understood. Here we use a large data base of 79 mammalian carnivore species to examine the factors affecting latitudinal size clines.
Location  Worldwide.
Methods  We measured the skulls and teeth of carnivores in natural history museums, and calculated the amount of variation in size explained by latitude, supplementing our measurements with published data. We examined the effects of a number of variables on the tendency to show latitudinal clines.
Results  We found that geographical range and latitudinal extent are strongly related to size clines. Minimum temperatures across the range, net primary productivity and habitat diversity also have some, albeit much less, influence.
Main conclusions  We suggest that species with large geographical ranges are likely to encounter significant heterogeneity in those factors that influence body size, and are thus likely to exhibit size clines. However, the key factors that determine body size may not always operate along a latitudinal (or other geographical) cline, but be spatially linked to patches in the species range. One such important factor is likely to be food availability, which we show is a strong predictor of size in the brown bear ( Ursus arctos ) but is not associated with a latitudinal cline. We argue that the spatial distribution of key resources within the species range constitutes a significant predictor of carnivore body size.     

Latitudinal clines in the timing and temperature-sensitivity of photoperiodic reproductive diapause in Drosophila montana

Reproductive diapause is a primary mechanism used by arthropods to synchronize their life cycle with seasonal changes in temperate regions. Our study species, Drosophila montana, represents the northern insect species where flies enter reproductive diapause under short day conditions and where the precise timing of diapause is crucial for both survival and offspring production. We have studied clinal variation in the critical day length for female diapause induction (CDL) and their overall susceptibility to enter diapause (diapause incidence), as well as the temperature sensitivity of these traits. The study was performed using multiple strains from four latitudinal clines of the species – short clines in Finland and Alaska and long clines in the Rocky Mountains and the western coast of North America – and from one population in Kamchatka, Russia. CDL showed strong latitudinal clines on both continents, decreasing by one hour per five degrees decline in latitude, on average. CDL also decreased in all populations along with an increase in fly rearing temperature postponing the diapause to later calendar time, the effects of temperature being stronger in southern than in northern population. Female diapause incidence was close to 100% under short day/low temperature conditions in all populations, but decreased below 50% even under short days in 19°C in the southern North American western coast populations and in 22°C in most populations. Comparing a diversity of climatic data for the studied populations showed that while CDL is under a tight photoperiodic regulation linked with latitude, its length depends also on climatic factors determining the growing season length. Overall, the study deepens our understanding of how spatial and environmental parameters affect the seasonal timing of an important biological event, reproductive diapause and helps to estimate the evolutionary potential of insect populations to survive in changing climatic conditions.     

Geographic patterning of variation in segment number in geophilomorph centipedes: clines and speciation

SUMMARY Since their origin as a metameric group, arthropods have diversified considerably in their number of segments. Present-day geophilomorph centipedes provide a model system for investigating the evolutionary origins of this diversification, because they exhibit intraspecific variation in segment number. (This variation is, however, derived; it is not a plesiomorphic condition within the Chilopoda.) Previous studies have shown that there are significant differences in segment number between populations within several geophilomorph species. In one (arguably two) species, it has been demonstrated that there is a particular form of geographic patterning of the variation, namely a latitudinal cline, with the segment number decreasing with increasing distance north. Here, we provide additional data on four more species, all of which show evidence of a latitudinal cline in either one or both sexes. It is therefore becoming clear that this is a general phenomenon, applying widely (perhaps universally) across the Geophilomorpha, a group consisting of some 1000 known species. It may be that latitudinal clines are a frequent part of the speciation cycle in this group.     

Clinal variation in Drosophila serrata for stress resistance and body size

Clines for size and stress resistance traits have been described for several Drosophila species and replicable clines across different species may indicate climatic selection. Here we consider clines in stress resistance traits in an Australian endemic species, D. serrata, by comparing levels of variation within and among isofemale lines initiated with flies collected from the eastern coast of Australia. We also consider clinical variation in chill coma recovery, a trait that has recently been shown to exhibit high levels of variation among Drosophila species. Patterns were compared with those in the cosmopolitan species D. melanogaster from the same area. Both desiccation and starvation resistance showed no clinical pattern despite heritable variation among isofemale lines. In contrast chill coma resistance exhibited a linear cline in the anticipated direction, resistance increasing with latitude. Body size was measured as wing length and body weight. Both traits showed geographic variation and strong non-linear clines with a sharp reduction in size in the tropics. These results are discussed in the context of climatic selection and evolutionary processes limiting species borders.     

The influence of eclosion timing on winter survival and triacylglycerol accumulation in four temperate species of Drosophila

Abstract. Diapause incidence, winter survival and triacylglycerol content were studied in temperate species of Drosophila by outdoor rearing in Sapporo (a cool-temperate region), northern Japan. In strains of D.subauraria and D.triauraria (cool-temperate species) from northern Japan, diapause was induced in adults having eclosed after early September, but in those having eclosed after mid October in strains of D.rufa and D.lutescens (warm-temperate species) from southern Japan. A subtropical strain of D.triauraria did not enter diapause. In the strains of cool-temperate species from northern Japan, about 70% survived until spring when eclosed in mid autumn, whereas when eclosed earlier and later flies had a lower ability to overwinter. The warm-temperate species and a subtropical strain of D.triauraria also survived longer when eclosed in mid autumn than when eclosed later, but they were unable to survive until spring. The triacylglycerol content was higher in the cool-temperate species from northern Japan than in the warm-temperate species and a subtropical strain of D.trauraria. In each species the triacylglycerol content of adults was higher when they eclosed in early and mid than in late autumn. It is assumed that triacylglycerol plays an important role in overwintering of these Drosophila species and the low triacylglycerol level is the primary cause of the low overwintering capacity of individuals eclosing in late autumn.