PHOTOPERIODIC ADAPTATION IN DESERT POPULATIONS OF XANTHIUM STRUMARIUM

Reproductive adaptation to photoperiod is diverse among desert populations of Xanthium. Chihuahuan Desert populations require dark periods of 9.5–10.5 hr for reproduction, and Sonoran Desert populations require 9–10.5 hr. Many Chihuahuan populations from western Texas two weeks from sowing need only 10 cycles of 11-hr nights to produce 100% flowering, but Sonoran populations from western Mexico four weeks from sowing need 18 cycles or more. Some Sonoran plants produce buds only at a cooler temperature program, 24–15 C, but Chihuahuan plants produce them more readily under the warmer program, 30–24 C. Chihuahuan plants that were germinated under 11-hr nights and four different temperature programs were induced to flower in each condition. Differences in photoperiod and ripeness-to-flower (maturity) responses were also demonstrated under natural day lengths in central Texas. Although desert populations occurring at approximately the same latitude in either the Chihuahuan or Sonoran Desert are exposed to similar day lengths, each population may be adapted to different photoperiod cues that maximize its utilization of the local growing conditions.     

Seasonal adaptations of populations of the southwestern corn borer, Diatraea grandiosella, from tropical and temperate regions

Seasonal adaptations of populations of the southwestern corn borer, Diatraea grandiosella, obtained from south-central Mexico (19°N latitude) and southeast Missouri (37°N latitude) were compared. Day length and temperature were found to serve as environmental cues to programme the larval diapause of both populations, but different critical values were observed. The critical day length for diapause induction was about 13 hr light/day for Mexican larvae and about 15 hr light/day for Missouri larvae, and was relatively stable at 20 to 30°C. Mexican larvae displayed a less-intense diapause than did Missouri larvae. Some diapausing Mexican larvae maintained at 25 or 30°C pupated in about 15 days, regardless of the day length to which they were exposed. The rate of diapause development of Mexican larvae was high at day lengths between 14 hr and 16 hr, whereas that of Missouri larvae was accelerated at day lengths of 16 hr at 25 and 30°C. Diapause development of Mexican larvae was virtually unaffected by chilling at 10°C, whereas that of Missouri larvae continued at a low rate at 10°C. Selection of Mexican larvae for diapause showed that only four generations were needed to significantly increase the incidence of diapause.     

Differentiation in habitat response in taxodium distichum,taxodium mucronatum,platanus occidentalis,and liquidambar styraciflua from the United States and Mexico

Summary Habitat specialization in populations of three broadly distributed trees includes adaptive differentiation to day length and temperature. Low sensitivity to environmental cues is the adaptive strategy of the southernmost populations (from northeastern Mexico). Early cessation of growth and sensitivity to the environment is adaptive for the northernmost populations (southern Illinois). Intermediate responses characterize trees of Texas. In a comparison under four photoperiod-temperature conditions, the Mexico plants were adapted to the longest growing season. Under out-of-doors conditions in central Texas, these trees from Mexico continue to demonstrate adaptive strategies different from those of Texas or Illinois trees. Stipule production and leaf area inPlatanus showed modifications correlated with latitude. Northernmost trees had the smallest leaves and did not produce stipules under 12-h day lengths and 24–15 °C temperatures. The Mexico trees had stipules under each of the four experimental conditions. The results suggest that populations of deciduous trees in a given climate are selected toward convergence in some responses to that climate. As a result, populations of the three trees resemble each other in behavior in a given ecosystem. Research funds were provided by a grant from the U.S. Forest Service and from National Science Foundation Grant GB-6097. I acknowledge help of David S. May and George J. Williams.     

REPRODUCTIVE PHYSIOLOGY IN THE SEAGRASS,SYRINGODIUM FILIFORME,FROM THE GULF OF MEXICO AND THE CARIBBEAN

Reproductive physiology in Syringodium filiforme Kütz. is controlled primarily by temperature under day lengths ranging from 12 hr to continuous light. Texas plants can be induced to flower at temperatures ranging from 20 to 24 C, but southern Gulf of Mexico and Caribbean plants are most readily induced at 23–24 C. Texas plants proceed to anthesis at temperatures above 22 C, but St. Croix plants require higher temperatures, above 25 C, for emergence of flowers from the bracts. Flowers induced under continuous light proceed to anthesis under day lengths shortened to 11 hr, but further floral induction is inhibited even under inductive temperatures. In natural seagrass beds, flowering occurs primarily under lengthening day lengths and warming temperatures that follow winter minima, but inflorescences may occur at other times of the year if temperatures permit.     

Laboratory-simulated naturally-decreasing day lengths, twilight and aphid photoperiodism

Abstract. Day-length changes, as well as periods of twilight, that occur in the course of each natural day-night cycle, were recreated for two chosen latitudes in a computer-controlled 'natural-day-length simulator'.The photoperiodic responses of two aphid species, Aphis fabae and Megoura viciae , were examined in conditions which mimicked late summer to autumn at two simulated latidudes, 51.5N (e.g.Ascot, Southern Britain) and 60°N (e.g.southern tip of Shetland Islands, Northern Britain), with temperatures between 16°C ('night') and 18°C ('day').The responses under simulated natural photoperiodic conditions were similar to those observed under conventional experimental conditions of squarewave light-dark cycles (with abrupt lights-on and lights-off and constant light intensities during the light phase): both aphid species responded to civil twilight as light, and the critical day lengths (including civil twilight) for the induction of sexual morphs by the two aphid species observed in the simulator were the same as those found in squarewave light-dark cycles.
Autumn field experiments (51.5°N) with the same clones of A. fabae and M.viciae revealed much longer critical day lengths for gynopara and male induction in A. fabae compared with those in the laboratory, but the same critical day length for ovipara induction in M.viciue. Minimal night temperatures in the field were on average 6°C, whereas maximal day temperatures declined from around 30°C in early September to 12°C at the end of October; it seems that the critical day lengths in A.fabae are temperature dependent, whereas the findings for M.viciae confirm that the critical day length is temperature compensated.     

Photoperiodic clock of diapause induction in Pseudopidorus fasciata (Lepidoptera: Zygaenidae)

Pseudopidorus fasciata enters diapause as fourth instar larvae at short day lengths. Using 24-h light-dark cycles, the photoperiodic response curves in this species appeared to be similar with a critical night length of 10.5h at temperatures below 30 degrees C. At an average temperature of 30.5 degrees C, the critical night length had shifted to between 15 and 17h. In experiments using non-24-h light-dark cycles, it was clearly demonstrated that the dark period (scotophase) was the decisive phase for a diapause determination. In night interruption experiments using 24-h light-dark cycles, a 1-h light pulse at LD12:12 completely reversed the long night effect and averted diapause in all treatments. At LD 9:15 light pulses of 1-h, 30- or 15-min also averted diapause effectively when both the pre-interruption (D(1)) or the post-interruption scotophases (D(2)) did not exceed the critical night length. If D(1) or D(2) exceeded the critical night length diapause was induced. The most crucial event for the photoperiodic time measurement in this species is the length of the scotophase. A 10-min light pulse placed in the most photosensitive phase reversed diapause in over 50% of the individuals. Night interruption experiments under non-24-h light-dark cycles indicated that the photoperiodic clock measured only D(1) regardless of the length of D(2), suggesting that the most inductive cycles are often those in which L+D are close to 24h. In resonance experiments, this species showed a circadian periodicity at temperatures of 24.5 or 26 degrees C, but not at 30.5 and 23.3 degrees C. On the other hand, Bünsow and skeleton photoperiod experiments failed to reveal the involvement of a circadian system in this photoperiodic clock. These results suggest the photoperiodic clock in this species is a long-night measuring hourglass and the circadian effect found in the final expression of the photoperiodic response in the resonance experiments may be caused by a disturbing effect of the circadian system in unnatural regimes.     

On critical night lengths and temperature compensation in the photoperiodic response of two geographical clones of the black bean aphid, Aphis fabae

Photoperiodic response curves were determined for two clones of the black bean aphid, Aphis fabae Scopoli, at three temperatures, 12.5, 15 and 17.5°C. Critical night lengths for the induction of winged females in an English clone (52° N) were 10.5, 11 and 11.5 h, respectively, and 10, 10.5 and 11 h in a Scottish clone (57° N). Critical night lengths for male induction were 10.5, 11 and 11 h at 12.5, 15 and 17.5°C in the English clone, and 10, 10.5 and 10.5 h, respectively, in the Scottish clone. High incidences of winged females and males were observed at all scotophases longer than the critical night length in both clones. In addition, in the English clone, the incidences of winged female and male producers in continuous darkness were 0% at 15 and 17.5°C, and 6% at 12.5°C. In the Scottish clone, however, continuous darkness resulted in high incidences of both winged female and male producers at 12.5 and 15°C, but 0% winged female producers and 6% male producers at 17.5°C. In scotophases shorter than the critical night length, including continuous light, no males or winged females were observed in either clone under the non‐crowded rearing conditions used. The results are discussed in terms of the ‘double circadian oscillator model’ for photoperiodic induction.     

Photoperiodic responses ofXanthium strumarium L. (Compositae) introduced and indigenous in eastern asia

Photoperiodic responses among populations ofXanthium strumarium L. in eastern Asia from Vladivostok, USSR, to Hong Kong and Taiwan include a wide range of adaptation. Among indigenous populations of thestrumarium morphological complex, responses range from near day neutrality (Vladivostok) to approximately a night length requirement of 9.5 hr (Hong Kong). Introduced populations in Japan include a night length requirement of 9.75 hr in theitalicum morphological complex and of 10.25–10.5 hr in thechinense morphological complex. The range of photoperiodic adaptation is nearly as wide as among populations of North America.     

Geographical variation in photoperiodic induction of diapause in the spider mite (Tetranychus urticae): a causal relation between critical nightlength and circadian period?

The photoperiodic response of 10 strains of the two-spotted spider mite (Tetranychus urticae), originating between 40.5 degrees and 60 degrees N in Western and Central Europe, was found to be highly variable. The critical nightlength for photoperiodic induction of diapause was strongly correlated with latitude for the lowland populations and varied from 7.75 hr in the north to 13.25 hr in the south. The length of the circadian period, taken as the peak-to-peak interval in response curves of resonance experiments done with T. urticae, varied between 17.75 and 21.5 hr and appeared weakly correlated with latitude. Only a very weak correlation was observed between critical nightlength and circadian period. These results do not provide evidence in favor of a circadian-based photoperiodic clock in T. urticae. On the other hand, they also do not refute this possibility, as there may be other circadian or noncircadian factors affecting the critical nightlength, which could mask the influence of circadian period.     

Inheritance of photoperiodic induction of larval diapause in the Asian corn borer Ostrinia furnacalis

The Asian corn borer Ostrinia furnacalis (Guenée) enters facultative diapause as fully‐developed larvae in response to short‐day conditions. As a consequence of geographical variation in photoperiodic response, moths from Nanchang (28°46′N, 115°50′E) enter diapause in response to short day‐lengths (D strain), even at the high temperatures whereas moths from Ledong (18°47′N, 108°89′E) exhibit almost no diapause under the same conditions (N strain). In the present study, crosses between the two strains are used to evaluate the inheritance of diapause under different photoperiods at temperatures of 22, 25 and 28 °C. The moths, both reciprocal crosses and backcrosses, show a clear long‐day response, similar to that of the D strain, suggesting that the photoperiodic response controlling diapause in this moth is heritable. However, the critical day‐length for induction of diapause is shorter in hybrids than in the D strain. The N strain also shows a short‐day photoperiodic response at the lower temperature of 22 °C, indicating that the N strain still has the capacity to enter a photoperiodically‐induced diapause, depending on the rearing temperature. The incidence of diapause in all crosses is highest with D strain fathers or grandfathers and lowest with N strain fathers or grandfathers, indicating that the male parent has significantly more influence on the incidence of diapause of subsequent progeny than the female. The results obtained from all crosses under LD 12 : 12 h or LD 13 : 11 h photocycles at 25 °C show that inheritance of diapause in O. furnacalis does not fit an additive hypothesis and that the capacity for diapause is transmitted genetically in the manner of incomplete dominance.     

Inheritance of photoperiodic response in the bird cherry aphid, Rhopalosiphum padi

Abstract. The photoperiodic induction of presexual females (gynoparae) and males of the aphid Rhopalosiphum padi (L.) was examined in single clones collected from different latitudes (N clone from Blair Atholl, 56.5N 3.1W; C clone from Leeds, 53.5N 1.4W and S clone from Exeter, 50.4N 3.3W). Critical night lengths (CNLs) for gynopara and male production (CNLs: 50% of maximum production) and inter-clonal differences, defined by the different forms of progeny produced at a single discriminating night length (12 h 30 min), were measured at 16 ± 1C. The aphid clones differed in CNL and in the morphs produced at the discriminating night length. These differences were used to investigate the inheritance of the photoperiodic response. In crosses between clones the photoperiodic response showed considerable overall variation. The variation in CNLs indicated that the photoperiodic response was unlikely to affect the overwintering success after long-distance movement of clones from one latitude to another.     

Photo-thermal regulation of diapause in Trichogramma piceum Djur. (Hymenoptera, Trichogrammatidae)

Interaction of the photoperiodic conditions of development of maternal females (day lengths of 2 to 22 h at 20°C) with the thermal regime of development of their progeny (temperature of 12 to 15°C at day length of 12 h) in determination of prepupal diapause in Trichogramma piceum was studied under laboratory conditions. At 15°C the diapause was practically absent. At lower temperatures, the proportion of diapausing prepupae was maximal (25% of larvae at 14°C, 70% of larvae at 13°, and 80% of larvae at 12°C) if the maternal females developed under short day conditions (10–12 h). When maternal females developed at day lengths of 18–20 h, diapause was rarely recorded at all temperatures, while ultra-short (less than 8–10 h) days also caused a decrease in the proportion of diapausing progeny. The right (ecologically important) threshold of this maternal long-day photoperiodic response was about 14–15 h independently of the temperature during the progeny development. These results make it possible to clarify the mechanism of the “maternal photoperiodic correction of the progeny thermal response.” Although the impact of the maternal photoperiodic response can be revealed only within a very narrow thermal range, the relative strength of the diapause-inducing effect of different day lengths is independent of the temperature regimen of the progeny development.     

PHOTOPERIODIC ADAPTATION TO LATITUDE IN XANTHIUM STRUMARIUM

Photoperiodic responses of collections of Xanthium strumarium L., grown from seed obtained in nature at various localities in North America between latitudes 20° and 45.5° N, were examined. The critical night length was found to vary noticeably with latitude of origin, from about 7.5 hr in the northernmost strains to above 10 hr in the southern strains. These differences are considered to represent genetic adaptation of the reproductive system to environmental variables as a result of natural selection. Several strains showed a quantitative short day response rather than the more usual qualitative response. Strains from Hawaii exhibited a surprisingly tardy and erratic short-day response with a critical night length of about 11 hr, which may be an adaptation to a tropical climate.     

The photoperiodic control of wing development in the black bean aphid,Aphis fabae

Newly born presumptive gynoparae of Aphis fabae were transferred from their prenatal short-day rearing conditions (light-dark 12:12, 15°C) to a variety of postnatal photoperiodic regimes. Long days prevented wing formation and the majority of aphids developed into apterous or alate-apterous intermediate adults. Continued short days resulted, almost exclusively, in winged adults. The photoperiodic-response curve (T = 24) revealed a critical photoperiod of light-dark 13.5:10.5 and further investigations showed that morphogenesis depended more upon night- than day-length. Maximal apterization occurred with 8 or 9 h dark regardless of the length of the photophase but at photophases of 12 h or less the critical night length was reduced to 8.5 h. Night-interruption experiments revealed two peaks of photosensitivity when the scotophase was 12–14 h long but only a single peak was seen with longer dark periods. A series of experiments using early night interruptions followed by extended dark revealed apparent critical night lengths which decreased as the interruption was placed later in the scotophase. Resonance experiments involving 12 or 16 h photophases and extended scotophases at 15°C revealed long-day effects with scotophases shorter than critical and short-day effects with longer dark periods. However, similar regimes at 20°C produced three peaks of apterization 24 and 20 h apart indicating the possibility of a circadian element involved in the photoperiodic response. The results are compared with the photoperiodic responses of other insects.     

THE EFFECT OF SHORT PERIODS OF HIGH TEMPERATURE DURING DAY AND NIGHT PERIODS ON PEA YIELDS

Karr , E. J. (Ohio State U., Columbus), A. J. Linck , and C. A. Swanson . The effect of short periods of high temperature during day and night periods on pea yields. Amer. Jour. Bot. 46(2) : 91-93. Illus. 1959.—The effect of high temperatures during periods of relatively short duration (3-4 days) at various stages following anthesis at the first bloom node was studied in relation to yield of peas at this node. Except for the periods of differential temperature treatments, the plants were maintained in a standard environment room (24°C., light, 12 hr.; 15°C., darkness, 12 hr.). Three different temperature regimes during the treatment periods were studied: high day temperature—standard night temperature (32°—15°C.) ; standard day temperature—high night temperature (24°—30°C.) ; and high day and night temperatures combined (32°—30°C.). The data reveal the existence of a relatively well-defined thermal-sensitive period, with maximal sensitivity to high day temperatures occurring at about 9-11 days from full bloom, and maximal sensitivity to high night temperatures occurring about 6-9 days from full bloom. High night temperatures proved more critical, resulting in a maximal reduction of 25% in yield, as opposed to about 8% for high day temperatures. The effect of high day and night temperatures combined tended to be roughly additive.     

Hourglass and rhythmic components of photoperiodic time measurement in the pitcher plant mosquito, Wyeomyia smithii

The mosquito, Wyeomyia smithii, enters a larval dormancy or diapause that is initiated, maintained, and terminated by photoperiod. The median or critical photoperiod regulating diapause increases from 12 h of light per day along the Gulf of Mexico, USA (30° N), to over 15 h in southern Canada (49° N). Photoperiodic time measurement in W. smithii comprises both rhythmic and hourglass (interval timer) components. Using interrupted-night and resonance experiments, we show that both the rhythmic and hourglass components are prominent in the southern (ancestral) populations and that the influence of the rhythmic component declines with increasing latitude, while the hourglass component remains strong in northern (derived) populations. Previously, it has been shown that the genetic differences in critical photoperiod between northern populations and their southern ancestors involve not only the additive (independent) effects of genes, but also gene-gene interaction (epistasis). We therefore conclude that adaptive evolution of W. smithii has probably involved the progressive epistatic masking of the ancestral rhythmic component resulting in photoperiodic time measurement in northern populations accomplished principally through a day-interval timer. A comparison of W. smithii with previous studies indicates that the decline in critical photoperiod with increasing latitude represents an overall decrease in response to light rather than a shift in the timing of photosensitivity among arthropods in general. We propose that the underlying functional components of photoperiodic time measurement, as well as the overt photoperiodic response, are either homologous or are themselves responding directly to selection over latitudinal gradients in seasonality. Received: 18 May 1998 / Accepted: 14 September 1998     

Seasonal adaptations of different geographical populations of the sunflower moth, Homoeosoma electellum

A photothermogram constructed for a central Missouri population (ca. 39°N latitude) of the sunflower moth, Homoeosoma electellum (Hulst) predicted that this population has a seasonal life cycle of 2 complete and a partial third generation per year, and that daylengths of less than 13 h 30 min light/day and mean temperatures of less than 20°C induce the mature larval diapause. A test of the predicted life cycle revealed that larvae entered diapause when they were exposed from their first instar onwards to natural conditions in central Missouri beginning September 15, 1982. Sunflower moths obtained from northwest Texas (ca. 35°N latitude) and northeast South Dakota (ca. 45°N latitude) displayed shorter critical photoperiods for diapause induction at 20°C (12 h 30 min light/day and 12 h 15 min light/day, respectively) than did those from Missouri. The population of the sunflower moth obtained from South Dakota does not, therefore, appear to be adapted to local conditions, and moths might disperse from lower latitudes to establish transiet populations each year.     

Maternal thermal and photoperiodic effects on the progeny diapause in Trichogramma telengai Sorokina (Hymenoptera: Trichogrammatidae)

Although maternal photoperiodic and maternal thermal effects on the progeny diapause have been demonstrated in a number of insect species, their interaction has been rarely studied. We investigated this interaction in Trichogramma telengai. In a series of experiments, maternal females were reared at day lengths of 12–18 h and at temperatures of 17, 20, 25 and 30°C. Their progeny developed under day length of 12 h and temperatures of 13, 14 and 15°C. The experiments showed that both short day and low temperature experienced by the maternal generation significantly increased the proportion of diapausing progeny. In particular, the threshold of the maternal photoperiodic response decreased with temperature. Under combinations of photoperiod with daily thermoperiod, the role of the “night” temperature in the induction of diapause in the progeny was much more important than that of the “day” temperature. We conclude that the interaction pattern between the photoperiodic and thermal maternal effects in T. telengai is generally the same as that between the photoperiodic and thermal responses directly influencing diapause induction in other long‐day insects. The threshold temperature of the maternal thermal response of T. telengai was about 25–27°C, while diapause can be induced if larvae develop at temperatures not higher than 15–16°C. This suggests that, at least in the studied Trichogramma species, the maternal thermal effect has no ecological value. In the practice of biocontrol, however, rearing of Trichogramma wasps at high temperature can drastically reduce the proportion of diapausing progeny.     

EXPERIMENTS ON THE PHOTOPERIODIC RESPONSE IN PINEAPPLE

Gowing , Donald P. (Pineapple Research Institute of Hawaii, Honolulu.) Experiments on the photoperiodic response in pineapple. Amer. Jour. Bot. 48(1): 16–21. 1961.—The initiation of flowering of ‘Smooth Cayenne’ pineapple plants is neither strictly a response to photoperiod (day lengths of 10 hr. 51 min.–13 hr. 24 min.) nor to a minimum temperature (minima from 50° to 72°F. in different areas) under natural Hawaiian conditions. Depending on the kind of planting material used and the time of planting, natural initiation of flowering may take place any month of the year. Slips planted in the fall generally initiate flowering in December of the following year. However, exposure of an 8-mo.-old slip-planting to a day length of 8 hours for 40 days starting Sept. 8 induced flowering irrespective of night temperatures from about 60 to 80°F. Interruption of the dark period by illumination at 30 ft.-c. from midnight to 1 a.m. suppressed the inductive effect. Lowering the night temperature to 60°F. was, of itself, non-inductive. Field-grown, 11-mo.-old plants treated in place responded similarly, in that 25 periods of 8-hr. day length starting Sept. 5 induced 60% of the plants to flower, and the night illumination suppressed the inductive effect as before. Daily application of 0.12 mg. of the major native pineapple auxin (indole-3-acetic acid) at the beginning of the dark period had no detectable effect on the short-day treatment, and similar application of an antiauxin (4-chlorophenoxyisobutyric acid) did not affect the suppression of flowering by the light-break. Supplemental illumination of field-grown 12-mo. plants to provide a photoperiod of more than 15 hr. daily from Nov. 4 to Jan. 30 did not suppress the natural initiation of flowering which occurred in early December (day length about 10 hr. 50 min.). ‘Smooth Cayenne’ pineapple is therefore a quantitative, but not an obligate, short-day plant.     

Rhythmic components of photoperiodic time measurement in the pitcher-plant mosquito, Wyeomyia smithii

Photoperiodic time measurement regulating larval diapause in the pitcher-plant mosquito, Wyeomyia smithii, varies in a close relationship with latitude. The critical photoperiod mediating the maintenance and termination of diapause is positively correlated with latitude (r ² = 0.977) among six populations from southern (30–31° N), intermediate (40° N), and northern (46–49° N) latitudes in North America. The developmental response to unnaturally short and to unnaturally long photoperiods declines with increasing latitude, so that longer critical photoperiods are associated with a downward rather than a lateral shift in the photoperiodic response curve. Exotic light and dark cycles of varying period (T) with a short (10 h) photophase and a scotophase ranging from 14 (T = 24) to 62 (T = 72) h, reveal two geographic patterns: a decline in perturbability of the photoperiodic clock with increasing latitude, and no change with latitude in the 21-h period of rising and falling development with increasing T. These results show (1) that there is a rhythmic component to photoperiodic time measurement in W. smithii, (2) that the period of this rhythm is about 21 h in all populations, and (3) that more northern populations show decreasing responsiveness to photoperiod and increasing stability against perturbation by exotic period lengths (T > 24). Previous studies on W.␣smithii indicate that this single temperate species of a tropical and subtropical genus has evolved from south to north. We therefore conclude that the evolution of increasing critical photoperiod in W. smithii during its adaptive radiation into North America has more likely involved the amplitude and not the period of the underlying circadian pacemaker. Received: 22 July 1996 / Accepted: 30 September 1996