REACTION NORMS OF MORPHOLOGICAL TRAITS IN DROSOPHILA: ADAPTIVE SHAPE CHANGES IN A STENOTHERM CIRCUMTROPICAL SPECIES?

Reaction norms of wing length, thorax length, and ovariole number were studied according to growth temperature in the circumtropical Drosophila ananassae, and compared to similar data from the cosmopolitan D. melanogaster. In the two species convex reaction norms were observed, but they were not parallel and sometimes exhibited intersections either at high (wing) or at low (thorax) temperature. On average, D. ananassae may be considered as a species with a bigger thorax but shorter wings than D. melanogaster. The shapes of reaction norms were analyzed and compared after quadratic polynomial adjustments. Significant differences were observed, in several cases between polynomial parameters, and in all cases between characteristic points that is, Maximum Value (MV) and Temperature of Maximum Value (TMV). The wing/thorax ratio may also be considered as a specific trait related to wing loading. Major differences were observed between the two species for the mean value and the shape of the response curves of this trait. The main observation of this work was however a shift of TMVs for wing and thorax length and ovariole number in D. ananassae toward higher temperatures. These variations in the reaction norms corresponded to a shift in the species thermal range, suggesting that temperature adaptation was accompanied by a modification of the shape of the response curves.     

BEHAVIORAL DIFFERENTIATION IN OVIPOSITION ACTIVITY IN DROSOPHILA BUZZATII FROM HIGHLAND AND LOWLAND POPULATIONS IN ARGENTINA: PLASTICITY OR THERMAL ADAPTATION?

Highland populations of several Drosophila species in Argentina were active early in the afternoon in the field as opposed to populations from a much warmer lowland site, where flies were mainly active in the early evening prior to sunset. For one of these species, Drosophila buzzatii, we tested for a genetic component of activity differences by carrying out crosses within and between populations and measuring oviposition activity of the progeny in the laboratory. We found that activity in the highland population exceeded that in the lowland one during the midafternoon, whereas activity in the lowland population exceeded that in the highland one prior to the beginning of the dark period. Oviposition activity for the period corresponding to the field observations was regressed on the proportion of the genome derived from the highland population. This variable significantly predicted oviposition activity between 1400 and 1600 and between 2000 and 2200 h. Activity of both reciprocal crosses was intermediate and not significantly different from each other, suggesting that nuclear genetic, rather than cytoplasmic factors contribute to differences in oviposition activity between the populations. Two morphological, one genetic, and one stress resistance trait were also scored to examine whether temperature differences between environments were associated with other differences between populations. Wing length of wild-caught and laboratory-reared flies from the highland population significantly exceeded that in the lowland. Thorax length of laboratory-reared flies from the highland population also significantly exceeded that from the lowland. Chromosomal inversion frequencies differed significantly between the two populations with a fivefold reduction in the frequency of arrangement 2st in the highland as compared to the lowland population. This arrangement is known for its negative dose effect on size, and thus, the highland population has experienced a genetic change, perhaps as a result of adaptation to the colder environment, where body size and the frequency of arrangement 2st have changed in concert. Finally, a heat knockdown test revealed that the lowland population was significantly more resistant to high temperature than the highland one. In conclusion, we suggest that temperature has been an important selective agent causing adaptive differentiation between these two populations. We also suggest that the activity rhythms of the two populations have diverged as a consequence of behavioral evolution, that is, through avoidance of stressful temperatures as a mean of thermal adaptation.     

AUXIN,AN ENDOGENOUS REGULATOR OF GROWTH IN ALGAE?1,2

The effects of 5 pairs of synthetic auxins and chemically related, but biologically inactive, derivatives (e.g., 2,4- and 3,5-dichlorophenoxyacetic acid, respectively) on blade growth of the brown alga, Alaria esculenta (L.) Grev.(Laminariales) were studied. The significant result was the inability to divide the growth responses into auxin and non-auxin groups. At high concentrations (10^?3 M) 9 test substances inhibited blade growth; lower concentrations (<10^?3 M) were either slightly inhibitory or showed no effect. The data suggest that a higher plant auxin-specific recognition mechanism is lacking in this alga. As this mechanism is central to higher plant concepts of growth control by auxin, the role of auxin as an endogenous regulator of growth in Alaria, and perhaps other algae as well, seems unlikely. This interpretation is consistent with recent negative biochemical data from auxin binding studies using subcellular preparations from algae.     

EVOLUTION OF COURTSHIP SONG AND REPRODUCTIVE ISOLATION IN THE DROSOPHILA WILLISTONI SPECIES COMPLEX: DO SEXUAL SIGNALS DIVERGE THE MOST QUICKLY?

Reproductive isolation increases with genetic distance between species. Although sexual selection may drive divergence of sexual signals and traits, causing rapid evolution of sexual isolation, quantitative data supporting this idea are rare. We examine the rates of divergence of a species-specific courtship signal, sexual isolation, and postmating isolation in the Drosophila willistoni group. Both types of isolation increase with genetic distance and postmating isolation is the most strongly correlated with genetic divergence, suggesting this has the least variable divergence rate. Song divergence is not correlated with genetic divergence. Homoplasy in song pattern results in poorly resolved phylogenies that are different from molecular phylogenies. Song evolves more quickly than sexual isolation, which evolves more quickly than postmating isolation.     

HABITAT AVOIDANCE: OVERLOOKING AN IMPORTANT ASPECT OF HOST‐SPECIFIC MATING AND SYMPATRIC SPECIATION?

Understanding speciation requires discerning how reproductive barriers to gene flow evolve between previously interbreeding populations. Models of sympatric speciation for phytophagous insects posit that reproductive isolation can evolve in the absence of geographic isolation as a consequence of an insect shifting and ecologically adapting to a new host plant. One important adaptation contributing to sympatric differentiation is host-specific mating. When organisms mate in preferred habitats, a system of positive assortative mating is established that facilitates sympatric divergence. Models of host fidelity generally assume that host choice is determined by the aggregate effect of alleles imparting positive preferences for different plant species. But negative effect genes for avoiding nonnatal plants may also influence host use. Previous studies have shown that apple and hawthorn-infesting races of Rhagoletis pomonella flies use volatile compounds emitted from the surface of fruit as key chemosensory cues to recognize and distinguish between their host plants. Here, we report results from field trials indicating that in addition to preferring the odor of their natal fruit, apple and hawthorn flies, and their undescribed sister species infesting flowering dogwood (Cornus florida), also avoid the odors of nonnatal fruit. We discuss the implications of nonnatal fruit avoidance for the evolutionary dynamics and genetics of sympatric speciation. Our findings reveal an underappreciated role for habitat avoidance as a potential postmating, as well as prezygotic, barrier to gene flow.     

TWO NEW GENERA, FOUR NEW SPECIES OF PLUSIINAE AND REVISION OF SOME OF ITS KNOWN SPECIES (LEPIDOPTERA: NOCTUIDAE)

This new genus is related to Arggrogramma Hubner and Acanthoplusia Dufy,but differs from them in the following characters: the stigma below the cell offore--wing stripe-shaped, long or short, white or grey, but never Y- or U-shapedand silvery, the valvae of male genitalia long and dilated at apex, and without     

INVERSION LENGTH AND BREAKPOINT DISTRIBUTION IN THE DROSOPHILA BUZZATII SPECIES COMPLEX: IS INVERSION LENGTH A SELECTED TRAIT?

Length and position of breakpoints are characteristics of inversions that can be precisely determined on the polytene chromosomes of Drosophila species, and they provide crucial information about the processes that govern the origin and evolution of inversions. Eighty-six paracentric inversions described in the Drosophila buzzatii species complex and 18 inversions induced by introgressive hybridization in D. buzzatii were analyzed. In contrast to previous studies, inversion length and breakpoint distribution have been considered simultaneously. We conclude that: (1) inversion length is a selected trait; rare inversions are predominantly small while evolutionarily successful inversions, polymorphic and fixed, are predominantly intermediate in length; a nearly continuous variation in length, from small to medium sized, is found between less and more successful inversions; (2) there exists a significant negative correlation between length and number of polymorphic inversions per species which explains 39% of the inversion length variance; (3) natural selection on inversion length seems the main factor determining the relative position of breakpoints along the chromosomes; (4) the distribution of breakpoints according to their band location is non-random, with chromosomal segments that accumulate up to eight breakpoints.     

CAN INTRASPECIFIC COMPETITION DRIVE DISRUPTIVE SELECTION? AN EXPERIMENTAL TEST IN NATURAL POPULATIONS OF STICKLEBACKS

Theory suggests that frequency-dependent resource competition will disproportionately impact the most common phenotypes in a population. The resulting disruptive selection forms the driving force behind evolutionary models of niche diversification, character release, ecological sexual dimorphism, resource polymorphism, and sympatric speciation. However, there is little empirical support for the idea that intraspecific competition generates disruptive selection. This paper presents a test of this theory, using natural populations of the three-spine stickleback, Gasterosteus aculeatus. Sticklebacks exhibit substantial individual specialization associated with phenotypic variation and so are likely to experience frequency-dependent competition and hence disruptive selection. Using body size and relative gonad mass as indirect measures of potential fecundity and hence fitness, I show that an important aspect of trophic morphology, gill raker length, is subject to disruptive selection in one of two natural lake populations. To test whether this apparent disruptive selection could have been caused by competition, I manipulated population densities in pairs of large enclosures in each of five lakes. In each lake I removed fish from one enclosure and added them to the other to create paired low- and high-population-density treatments with natural phenotype distributions. Again using indirect measures of fitness, disruptive selection was consistently stronger in high-density than low-density enclosures. These results support long-standing theoretical arguments that intraspecific competition drives disruptive selection and thus may be an important causal agent in the evolution of ecological variation.     

DOES SELECTION ON FLORAL ODOR PROMOTE DIFFERENTIATION AMONG POPULATIONS AND SPECIES OF THE SEXUALLY DECEPTIVE ORCHID GENUS OPHRYS?

Sexually deceptive orchids from the genus Ophrys attract their pollinators primarily through the chemical mimicry of female hymenopteran sex pheromones, thereby deceiving males into attempted matings with the orchid labellum. Floral odor traits are crucial for the reproductive success of these pollinator-limited orchids, as well as for maintaining reproductive isolation through the attraction of specific pollinators. We tested for the signature of pollinator-mediated selection on floral odor by comparing intra and interspecific differentiation in odor compounds with that found at microsatellite markers among natural populations. Three regions from southern Italy were sampled. We found strong floral odor differentiation among allopatric populations within species, among allopatric species and among sympatric species. Population differences in odor were also reflected in significant variation in the attractivity of floral extracts to the pollinator, Colletes cunicularius. Odor compounds that are electrophysiologically active in C. cunicularius males, especially alkenes, were more strongly differentiated among conspecific populations than nonactive compounds in the floral odor. In marked contrast to these odor patterns, there was limited population or species level differentiation in microsatellites (FST range 0.005 to 0.127, mean FST 0.075). We propose that the strong odor differentiation and lack of genetic differentiation among sympatric taxa indicates selection imposed by the distinct odor preferences of different pollinating species. Within species, low FST values are suggestive of large effective population sizes and indicate that divergent selection rather than genetic drift accounts for the strong population differentiation in odor. The higher differentiation in active versus non-active odor compounds suggests that divergent selection among orchid populations may be driven by local pollinator preferences for those particular compounds critical for pollinator attraction.     

DOES VARIATION IN SELECTION IMPOSED BY BEARS DRIVE DIVERGENCE AMONG POPULATIONS IN THE SIZE AND SHAPE OF SOCKEYE SALMON?

Few studies have determined whether formal estimates of selection explain patterns of trait divergence among populations, yet this is one approach for evaluating whether the populations are in equilibria. If adaptive divergence is complete, directional selection should be absent and stabilizing selection should prevail. We estimated natural selection, due to bear predation, acting on the body size and shape of male salmon in three breeding populations that experience differing predation regimes. Our approach was to (1) estimate selection acting within each population on each trait based on an empirical estimate of reproductive activity, (2) test for trait divergence among populations, and (3) test whether selection coefficients were correlated with trait divergence among populations. Stabilizing selection was never significant, indicating that these populations have yet to attain equilibria. Directional selection varied among populations in a manner consistent with trait divergence, indicating ongoing population differentiation. Specifically, the rank order of the creeks in terms of patterns of selection paralleled the rank order in terms of size and shape. The shortest and least deep-bodied males had the highest reproductive activity in the creek with the most intense predation and longer and deeper-bodied males were favored in the creeks with lower predation risk.     

SPECTROSCOPIC DETERMINATION OF THE TOXICITY,ABSORPTION, REDUCTION,AND TRANSLOCATION OF Cr(VI) IN TWO MAGNOLIOPSIDA SPECIES

Hexavalent chromium is a contaminant highly mobile in the environment that is toxic for plants at low concentrations. In this work, the physiological response of Convolvulus arvensis and Medicago truncatula plants to Cr(VI) treatments was compared. C. arvensis is a potential Cr hyperaccumulator well adapted to semiarid conditions that biotransform Cr(VI) to the less toxic Cr(III). M. truncatula is a model plant well adapted to semiarid conditions with a well studied genetic response to heavy metal stress. The results demonstrated that C. arvensis is more tolerant to Cr toxicity and has a higher Cr translocation to the leaves. The inductively coupled plasma optical emission spectroscopy results showed that C. arvensis plants treated with 10 mg Cr(VI) L^–1 accumulated 1512, 210, and 131 mg Cr kg^–1 in roots, stems, and leaves, respectively. While M. truncatula plants treated with the same Cr(VI) concentration accumulated 1081, 331, and 44 (mg Cr kg^–1) in roots, stems, and leaves, respectively. Enzymatic assays demonstrated that Cr(VI) decreased ascorbate peroxidase activity and increased catalase activity in M. truncatula, while an opposite response was found in C. arvensis. The x-ray absorption spectroscopy studies showed that both plant species reduced Cr(VI) to the less toxic Cr(III).     

THE DESCRIPTI0NS OF TWO NEW GENERA AND TWO NEW SPECIES OF ACRIDIDAE FROM CHINA(ACRIDOIDEA,ORTHOPTERA)

After Rehn erected new the genus Mongolotettix in 1928,three newspecies of the genus were described from China,viz.M.japonicus vitattus(Uv.),M.anomopterus(Caudell)and M.qinghaiensis Yin.Duringstudying the representives of genus Mongolotettix from China,we found     

ALTITUDINAL CLINAL VARIATION IN WING SIZE AND SHAPE IN AFRICAN DROSOPHILA MELANOGASTER: ONE CLINE OR MANY?

Geographical patterns of morphological variation have been useful in addressing hypotheses about environmental adaptation. In particular, latitudinal clines in phenotypes have been studied in a number of Drosophila species. Some environmental conditions along latitudinal clines—for example, temperature—also vary along altitudinal clines, but these have been studied infrequently and it remains unclear whether these environmental factors are similar enough for convergence or parallel evolution. Most clinal studies in Drosophila have dealt exclusively with univariate phenotypes, allowing for the detection of clinal relationships, but not for estimating the directions of covariation between them. We measured variation in wing shape and size in D. melanogaster derived from populations at varying altitudes and latitudes across sub‐Saharan Africa. Geometric morphometrics allows us to compare shape changes associated with latitude and altitude, and manipulating rearing temperature allows us to quantify the extent to which thermal plasticity recapitulates clinal effects. Comparing effect vectors demonstrates that altitude, latitude, and temperature are only partly associated, and that the altitudinal shape effect may differ between Eastern and Western Africa. Our results suggest that selection responsible for these phenotypic clines may be more complex than just thermal adaptation.     

FLIPPERS AND PINNIPED PHYLOGENY: HAS THE PROBLEM OF CONVERGENCE BEEN OVERRATED?

The phylogenetic relationships of the major groups of pinnipeds are of longstanding controversy. According to prevailing paleontological opinion, pinnipeds comprise two distinct lineages of independent terrestrial carnivoran origin, A logical correlate of this view is that an enormous degree of convergence accounts for the striking resemblances of these groups.
It has been generally supposed that derived similarities common to pinnipeds are independently acquired adaptations to a highly constraining environment. This has not been adequately substantiated. Moreover, considerable evidence favors a contrary conclusion. Acceptance of convergence necessarily rests on demonstration that taxa possessing characters suspected to be convergent are in fact not mutal nearest allies. In the absence of such phylogenetic information, shared derived characters are indicative of common ancestry irrespective of whether they are deemed "functionally important." Given meager support for the proposition that pinnipeds are related to different terrestrial lineages, it is currently more judicious to regard the group's origin as monophyletic. In addition to the presumed prevalence of convergence, biogeography, the high degree of morphological divergence of phocids, and the aberrant nature of phocines have improperly contributed to acceptance of independent pinniped origins.