GERMINATION AND SEEDLING RESPONSE OF ATLANTIC AND GULF COASTS POPULATIONS OF UNIOLA PANICULATA

Germination response following various periods of cold treatment and seedling response to temperature, daylength, and salinity were studied for several Atlantic and Gulf coasts populations of Uniola paniculata L. Results indicated that Atlantic coast Florida populations did not require cold treatment prior to germination at 95–65 F, but that populations from Virginia and North Carolina did. Gulf coast populations exhibited a germination response intermediate between those just mentioned. Seedling studies revealed that alternating diurnal thermoperiods with daytime temperatures of 80 F and above produced good vegetative growth in all populations with little preference for either short- or long-day conditions. Gulf coast populations produced the most biomass under all treatment conditions. Seedlings from a North Carolina and a Florida population indicated no difference in substrate salt tolerance. Salt tolerance was reduced in the higher temperature thermoperiod for both populations. Seedlings from these two populations produced more biomass in a salt spray treatment than in substrate salinity treatments.     

SEED GERMINATION RESPONSE AND EVIDENCE FOR HEIGHT ECOPHENES IN SPARTINA ALTERNIFLORA FROM NORTH CAROLINA

A study was conducted to determine germination response to temperature and salinity and seedling response to salinity by three height forms of the salt marsh grass Spartina alterniflora Loisel. Germination tests showed that seeds cannot withstand drying at moderate temperature, as viability was lost within 40 days in seeds stored dry at 72 F. Cold storage at 43 F is adequate to prevent desiccation up to 40 days, but after 8 months viability is lost. Viability is retained at least 8 months when seeds are stored in sea water at 43 F. Germination response was good in a 65–95 F alternating diurnal thermoperiod but was poor in a 72 F constant thermoperiod. Germination response to salinity was an inverse curvilinear relationship with germination inhibition at high salinities apparently due to osmotic effects. The maximum tolerance limit for germination lies between 6 and 8 % NaCl. Seeds from short, medium, and tall plants responded similarly in storage and temperature studies. However, in salinity studies, seeds of the Ocracoke Island short form and the Oak Island tall form performed best. A logarithmic curve best described seedling growth response to various NaCl levels. Growth response as measured by seedling dry weight was best in 0.5 % NaCl solution. Seedlings grew taller in both 0.5 and 1.0 % NaCl than in 0 % NaCl. No significant difference in seedling growth response due to height form of the parent plant was detected. Thus, on the basis of germination and seedling responses, the height forms of S. alterniflora in North Carolina salt marshes are best described as ecophenes.     

RESPONSE TO PHOTOPERIOD AND TEMPERATURE BY SPARTINA ALTERNIFLORA (POACEAE) FROM NORTH CAROLINA AND SPARTINA FOLIOSA FROM CALIFORNIA

Seedlings of Spartina alterniflora Loisel. from Oregon Inlet, North Carolina were generally taller and produced significantly more culms and total dry weight than those of S. foliosa Trin. from two California populations (Alameda Beach and Marin County) in eight photoperiod-temperature treatments over a 17-wk period. Seedlings of S. alterniflora produced maximal biomass in 30–26 C whereas those of S. foliosa produced maximal biomass in 22–18 C, both under long-day conditions. The average photosynthesis rate for S. alterniflora (3.0 mg C g dry wt^−- hr^−-1) was 1.6 times higher than that for S. foliosa (1.9 mg C g dry wt^−-1 hr^−-1), but the dark respiration rates (0.3 and 0.4 mg C g dry wt^−-1 hr^−-1, respectively) were not significantly different. The proportion of rhizomes was greater under short than long-day conditions for both species in most temperature regimes. The average shoot soluble carbohydrate and starch concentrations were higher for S. foliosa (8.4 and 0.9%, respectively) than those for S. alterniflora (6.0 and 0.4%, respectively). The average rhizome soluble carbohydrate concentration (18%) for S. alterniflora under long-day conditions was significantly lower than that under short-day conditions (28%) and also lower than those for S. foliosa under both long (26%) and short-day (25%) conditions. Rhizome starch concentrations of S. alterniflora were significantly higher in the short than in most long-day temperatures and were generally higher for S. alterniflora than for S. foliosa under short-day conditions. The root starch concentration of S. alterniflora under short-day conditions (1.3%) was higher than that under long-day conditions (0.2%) and also higher than those of S. foliosa under both long (0.2%) and short-day (0.7%) conditions. The two species exhibited similar patterns of carbohydrate storage in belowground organs, similar flower initiation processes not under strict photoperiod control, and similar respiration rates, but significantly different photosynthetic rates and growth responses with S. alterniflora having the potential to be the more productive species.     

Different ecological strategies during the seed germination phase of nine grasses inhabiting the hyper‐arid Arabian desert

The effect of photoperiod, thermoperiod and their interaction on seed germination and its rate was studied for nine grasses growing in the Arabian desert. Germination tests were conducted under two photoperiods and three thermoperiods. Germination of light‐incubated seeds of Hyparrhenia hirta, Pennisetum divisum, Stipacapensis, Centropodia forsskaolii, Stipagrostis plumosa, Cymbopogon parkeri and Panicum turgidum was significantly higher than that detected in the darkness. Photoperiod did not influence the seed germination of Aristida adscensionis and Imperata cylindrica. Seeds of all species, except P. divisum, C. parkeri and I. cylindrica, germinated indepen dently of the tested temperature. Our results indicate that species belonging to the same family and growing in the same hyper‐arid desert habitat may influence and act in different ways during the seed germination phase, causing species‐specific effects, and therefore might affect the ecology of each taxon in this harsh environment.     

Photoperiodic and thermoperiodic interactions in the regulation of the larval diapause of Diatraea grandiosella

The effect of various combinations of photoperiod and temperature on the induction and termination of the mature larval diapause of a Missouri strain of the southwestern corn borer. Diatraea grandiosella, was examined. Larval exposure to regimes in which the low phase of a 30°:23°C thermoperiod coincided with a scotophase of 10 to 14 hr duration led to high incidence of diapause. Larval exposure to 30°:24°C, 33°:21°C, and 36°:18°C thermoperiods with half cycles of 12 hr in continuous darkness yielded a diapause incidence of 16%, 22%, and 59%, respectively, whereas exposure to a 30°:24°C thermoperiod in continuous illumination yielded a completely nondiapause generation. Larval exposure to one of a series of 36°:18°C thermoperiods in which the duration of the high phase was increased in 2 hr increments from 0 to 24 hr in continuous darkness showed that “short-day” thermoperiods yielded a high incidence of diapause. However, no clearly defined critical thermoperiod was observed. An examination of photoperiodic and thermoperiodic effects on diapause development showed that, in general, those combinations of temperature and light cycles which were diapause inductive also retarded diapause development. The relationship between seasonal photoperiods and thermoperiods in southeastern Missouri was examined.     

Interacting effect of thermoperiod and photoperiod on the eclosion rhythm in the onion fly, Delia antiqua supports the two-oscillator model

Daily light and temperature cycles entrain adult eclosion rhythms in many insect species, but little is known about their interaction. We studied this problem in the onion fly, Delia antiqua. Pupae were subjected to various combinations of a photoperiod of 12L:12D and thermoperiods. The thermoperiods consisted of 12 h warm phase (W) and 12 h cool phase (C), giving a mean temperature of 25 °C with different temperature steps of 8, 4 and 1 °C. As the phase relation of the two Zeitgebers was varied, the phase of eclosion rhythm was shifted, depending on the phase angle with the light cycle and the amplitude of the temperature cycle. When the temperature step in the thermoperiod was 8 °C (WC 29:21 °C), the eclosion rhythm was entrained mainly to thermoperiod rather than photoperiod. In the regime with a 4 °C temperature step (WC 27:23 °C), both thermoperiod and photoperiod affected eclosion rhythm, and a phase jump of the eclosion rhythm occurred when the warm phase of thermoperiod was delayed 15-18 h from light-on. In regimes with a 1 °C temperature step (WC 25.5:24.5 °C), the eclosion rhythm was completely entrained to photoperiod. The observed interacting effect of light and temperature cycle on the eclosion rhythm in D. antiqua can be explained by the two-oscillator model proposed by Pittendrigh and Bruce (1959).     

Evolutionary divergence in thermal sensitivity and diapause of field and laboratory populations of manduca sexta

The tobacco hornworm Manduca sexta has been an important model system in insect biology for more than half a century. Here we report the evolutionary divergence in thermal sensitivity and diapause initiation between field and laboratory populations that were separated for more than 35 yr (>240 laboratory generations) and that are descendants from the same field populations in central North Carolina. At intermediate rearing temperatures (20 degrees-25 degrees C), mean body size was significantly larger and development time significantly faster in the laboratory than in the field populations. At higher temperatures (30 degrees -35 degrees C), these mean differences between populations were reduced or eliminated, and larval survival at 35 degrees C was significantly lower in the laboratory population than in the field population. F(1) crosses had survival and development time to wandering similar to the field population times at both 25 degrees and 35 degrees C; body mass at wandering for F(1) crosses was intermediate compared with that of the field and laboratory populations. Comparisons with earlier field and laboratory studies suggest evolutionary reductions in thermal tolerance and performance at high temperatures in the laboratory population. The critical photoperiod initiating diapause in field populations in North Carolina did not change detectably between the 1960s and 2005. In contrast, the laboratory population has evolved a reduced tendency to diapause under short-day conditions, relative to the field population.     

Thermoperiodic response and effect of photoperiod on thermoperiodic induction of diapause in Colaphellus bowringi

The effects of thermoperiods on diapause induction under continuous darkness (DD), continuous light (LL), and an L12:D12 photoperiod were investigated in the cabbage beetle, Colaphellus bowringi Baly (Coleoptera: Chrysomelidae), a short‐day species. Diapause could be induced by thermoperiod under both LL and DD; however, in the range of 24–30 °C, lower incidences of diapause were observed under LL than under DD. The critical cryophase was found to be dependent on the mean temperature of the thermoperiod applied. Although the thermoperiodic response pattern was similar under LL and DD, the incidence of diapause was higher under LL when the duration of the cryophase did not exceed 12 h. In contrast, when the duration of the cryophase was longer than 12 h, the incidence of diapause under LL was lower or equal to that under DD. When a thermoperiod of 24 °C (cryophase) and 28 °C (thermophase) was applied, the incidence of diapause was higher under LL than under DD, regardless of the duration of the cryophase. Thermoperiodic responses under a photoperiod of L12:D12 and under DD further revealed that induction of diapause was strongly influenced by the photophase temperature. Moreover, the incidence of diapause was lower when the thermophase coincided with the photophase than when the cryophase coincided with the photophase.     

Effects of thermoperiods on the reproductive activity of females and on the maternal induction of larval diapause in the blowfly, <Emphasis Type="Italic">Calliphora vicina</Emphasis> R.-D. (Diptera,Calliphoridae)

The interaction of thermoperiod and photoperiod in their influence on the reproductive maturation of females and on the induction of the maternal effect determining larval diapause of the progeny of the blowfly, Calliphora vicina, was first investigated under laboratory conditions. Under the combination of a day length of 12 h with a thermoperiod (the alternation of 12 h long periods with temperatures of 10 and 20°C) the reproductive maturation of females was faster than at the corresponding mean constant temperature of 15°C. Under the “natural” thermoperiod, when the period with a temperature of 10°C coincided with “night-time” (the dark phase of the diurnal light-dark cycle) the maturation of females was slower than that under the “inverted” thermoperiod, when the period with a temperature of 10°C coincided with “day-time” (the light phase of the diurnal light-dark cycle). The proportion of diapausing individuals was maximal in the progeny of females kept at 20°C and decreased with the increase in temperature. Under thermoperiods (the alternations of 12 h long periods with temperatures of 20 and 26°C) the proportion of diapausing progeny was lower than that under the corresponding mean constant temperature of 23°C, but under the inverted thermoperiod with a high night temperature this effect was much stronger. In combination with the results of our previous studies, these data support the hypothesis that the effects of “night” and “day” temperatures are substantially different only when the thermal response interacts with a strong photoperiodic response.     

Enhancement of supercooling capacity and survival by cold acclimation, rapid cold and heat hardening in Spodoptera exigua

Insects can increase their resistance to cold stress by prior exposure to non-lethal cold temperatures. Here, we investigated the supercooling capacity and survival of eggs, 3rd and 5th instar larvae, and pupae of Spodoptera exigua (Lepidoptera: Noctuidae) during CA, and responses to various pre-treatment protocols, including constant temperatures, thermoperiods, and RCH, RHH, RCH + RHH and RHH + RCH combined with thermoperiods. Only acclimated eggs demonstrated a significant decrease in SCP, from −20.7 ± 0.3 to −22.9 ± 0.3 °C, among all experimental groups compared to non-acclimated stages. Survival increased by 17.5% for eggs, 40.0% and 13.3% for 3rd and 5th instar larvae, and by 20.0% for pupae after CA. Compared to controls, survival of eggs under the conditions of thermoperiod (5:15 °C), thermoperiod (5:15 °C) + RHH, and thermoperiod (5:15, 10:20, and 15:25 °C) + RCH significantly increased. In addition, survival of 3rd and 5th instar larvae and pupae increased under the conditions of thermoperiod (5:15 °C) and thermoperiod (5:15 °C) + RCH, possibly due to the induction of heat shock proteins or cryoprotectants. However, the pre-treatments of thermoperiod + RCH + RHH and thermoperiod + RHH + RCH did not significantly enhance survival of any developmental stage. These adaptive responses may allow S. exigua to enhance supercooling capacity and survival in response to seasonal or unexpected diurnal decreases in environmental temperatures.     

RECENT VERSUS RELIC: DISCERNING THE GENETIC SIGNATURE OF FUCUS VESICULOSUS (HETEROKONTOPHYTA; PHAEOPHYCEAE) IN THE NORTHWESTERN ATLANTIC1

Fucus vesiculosus L. is one of the most widespread macrophytes in the northwestern Atlantic, ranging from North Carolina (USA) to Greenland (DK). We investigated genetic diversity, population differentiation, patterns of isolation by distance, and putative glacial refugial populations across seven locations from North Carolina (USA) to Cape Breton Island, Nova Scotia (Canada), with microsatellite analyses. Distinct northern versus southern (Delaware–North Carolina) populations were revealed by microsatellite data. Five of six microsatellite loci were fixed in populations in North Carolina, suggesting a recent founder event or a bottleneck, and the same homozygous genotype was found in herbarium materials collected on the North Carolina coast from more than 60 years ago. An additional set of individuals from the northern limit in Greenland was included in our analysis of mitochondrial intergenic spacer (mt IGS) haplotypes in the northwestern Atlantic. Remarkably, 184 of 188 F. vesiculosus specimens from North Carolina to Greenland shared the same haplotype. Recent colonization of the North American shore from Europe is hypothesized based upon the ubiquity of this common haplotype, which was earlier reported from Europe.     

Seed Germination Biology of the Narrowly Endemic Species Lesquerella stonensis (Brassicaceae)

Abstract Lesquerella stonensis (Brassicaceae) is an obligate winter annual endemic to a small portion of Rutherford County in the Central Basin of Tennessee, where it grows in disturbed habitats. This species forms a persistent seed bank, and seeds remain viable in the soil for at least 6 years. Seeds are dormant at maturity in May and are dispersed as soon as they ripen. Some of the seeds produced in the current year, as well as some of those in the persistent seed bank, afterripen during late spring and summer; others do not afterripen and thus remain dormant. Seeds require actual or simulated spring/summer temperatures to come out of dormancy. Germination occurs in September and October. Fully afterripened seeds germinate over a wide range of thermoperiods (15/6–35/20°C) and to a much higher percentage in light (14 h photoperiod) than in darkness. The optimum daily thermoperiod for germination was 30/15°C. Nondormant seeds that do not germinate in autumn are induced back into dormancy (secondary dormancy) by low temperatures (e.g., 5°C) during winter, and those that are dormant do not afterripen; thus seeds cannot germinate in spring. These seed dormancy/ germination characteristics of L. stonensis do not differ from those reported for some geographically widespread, weedy species of winter annuals and thus do not help account for the narrow endemism of this species.     

Diapause induction in Eotetranychus smithi (Acari: Tetranychidae): effect of average temperature,but not of thermoperiod

Facultative diapause of Eotetranychus smithi appears to occur at the egg stage and is induced by temperatures ≤17.5 °C, independent of photoperiod. However, the effect of thermoperiod on the induction of diapause remains unclear. To answer this question, we exposed female E. smithi to various thermoperiods under constant light conditions. First, we found that the deposition order of eggs affected the incidence of diapause: the first eggs (exclusively males) tended to avert diapause compared with the second and third eggs (most of them are females), possibly because of the sex of the eggs. Next, the incidence of diapause of the second eggs decreased with shortening of the cryophase, which was associated with an increase of the average temperature, and it showed clear long‐day‐type thermoperiodic response curves. However, this species does not sense the ratio of day (thermophase) to night (cryophase) of a given thermoperiod. Short thermoperiods did not increase the incidence of diapause, but rather precluded the entry into diapause. We detected no sign of the involvement of the circadian system in diapause induction in the thermoperiodic Nanda–Hamner protocol. We conclude that diapause induction of E. smithi does not involve the circadian system, and thus does not show thermoperiodism. Diapause induction under the various thermoperiodic conditions tested in the present study appears to be derived from the temperature itself. E. smithi is an exceptional species that relies on temperature alone to induce diapause.     

Effects of Photoperiod, Temperature and Asynchrony between Thermoperiod and Photoperiod on Development to Panicle Initiation in Sorghum

The duration of the vegetative phase (i.e. days from sowingto panicle initiation) in sorghum [Sorghum bicolor (L.) Moench]is affected by photoperiod and temperature. Plants of severalcontrasting genotypes of sorghum were grown in controlled-environmentgrowth cabinets with either synchronous or asynchronous photoperiodsand thermoperiods. Apical development was recorded. Diurnalasynchrony between photoperiod and thermoperiod reduced durationsto panicle initiation when the temperature warmed after lightswent on and cooled after lights went off, but increased thesedurations when the temperature warmed before lights went onand cooled before lights went off. These effects were shownin the maturity lines 60M and SM100 and also in the USA cv.RS610 and the Sudanese landrace IS22365, but their magnitudevaried with genotype, photothermal regime, and the degree ofasynchrony. The greatest effect was detected in IS22365 grownat 30/21 °C (12 h/12 h) with a 12 h d^-1photoperiod whenthe temperature warmed 2.5 h before lights went on and cooled2.5 h before lights went off, when the duration from sowingto panicle initiation was 69 d compared with 37 d in the control(synchronous photoperiod and thermoperiod in each diurnal cycle). Reciprocal transfers of plants of IS22365 between short andlong days revealed that asynchrony principally affected theduration of the photoperiod-insensitive pre-inductive phaseof development; i.e. asynchrony affected the time (age) at whichthe plants were first able to respond to photoperiod. In thatinvestigation in controlled-environment growth chambers, thesubsequent photoperiod-sensitive inductive phase continued untilpanicle initiation. Subsequent reciprocal transfer experimentsin controlled-environment glasshouses in four different alternatingtemperature regimes employed synchronous photoperiods and thermoperiodsin short (11 h) days with temperature warming 1.5 h after thebeginning of the day in long (12.5 h) days. In those investigations,photoperiod sensitivity ended some time before (2.5–8.1d, mean 5.7 d) panicle initiation in IS22365, Naga White andSeredo. Moreover, whereas the duration of the photoperiod-insensitivepre-inductive phase was affected by temperature, the durationsof the photoperiod-sensitive inductive and the photoperiod-insensitivepost-inductive phases were not. Sorghum bicolor (L.) Moench; sorghum; asynchrony; photoperiod; thermoperiod; vegetative phase; panicle initiation     

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.     

Thermoperiodic acclimations enhance cold hardiness of the eggs of the migratory locust

Treatment of thermoperiods that simulate the patterns of natural occurrence is most efficient in enhancing cold hardiness. To examine the effects of different thermoperiods on cold hardiness of eggs in the migratory locust, Locusta migratoria (L.), the survival rates, cryoprotectant levels and three hsps expressions in mid-stage eggs (7-day-old) were measured after the eggs were subjected to three different thermoperiod regimes, : short (2 day), long (10 day), and nature-mimicking thermoperiodic acclimation. The thermoperiodic acclimations resulted in the highest egg survival rates in both the short and the long period acclimation groups in comparison with the groups treated with constant temperatures. The egg survival of nature-mimicking thermoperiod groups was significantly higher than those of constant temperature groups for the same acclimation duration. The survival rate of eggs under single daily thermoperiod was higher than that of multiple daily thermoperiods. The concentration of cryoprotectants (myo-inositol, trehalose, mannitol and sorbitol) and the expression levels of hsp20.5, hsp70, and hsp90 all increased in thermoperiodic acclimation eggs.     

Effects of constant and changing temperature conditions on diapause induction in Helicoverpa armigera (Lepidoptera: Noctuidae)

The effects of photoperiod and temperature on the induction and termination of facultative pupal diapause in Helicoverpa armigera (Lepidoptera: Noctuidae) were investigated under laboratory conditions. Exposing H. armigera larvae to both constant and fluctuating temperature regimes with a mean of 25°C and 20°C resulted in a type-III photoperiodic response curve of a short-long day insect. The long-day critical daylengths for diapause induction were ten hours and 12 hours at the constant temperatures of 25°C and 20°C, respectively. Higher incidences of diapause and higher values both for the longer and the shorter critical photoperiods for diapause induction were observed at fluctuating regimes compared with the corresponding constant ones. At alternating temperatures, the incidence of diapause ranged from 4.2% to 33.3% and was determined by the temperature amplitude of the thermoperiod and by the interaction of cryophase or thermophase with the photoperiod. Helicoverpa armigera larvae seem to respond to photoperiodic stimuli at temperatures >15°C and <30°C; all insects entered diapause at a constant temperature of 15°C, whereas none did so at a constant temperature of 30°C under all the photoperiodic regimes examined. Although chilling was not a prerequisite for diapause termination, exposure of diapausing pupae to chilling conditions significantly accelerated diapause development and the time of adult emergence. Therefore, temperature may be the primary factor controlling the termination of diapause in H. armigera.     

Asymbiotic seed germination,in vitro seedling development,and greenhouse acclimatization of the threatened terrestrial orchid <Emphasis Type="Italic">Bletia purpurea</Emphasis>

Procedures for asymbiotic seed germination and seedling acclimatization were developed for Bletia purpurea, a threatened North America native terrestrial orchid. Six asymbiotic orchid seed germination media (Knudson C, PhytoTechnology Orchid Seed Sowing Medium, Malmgren Modified Terrestrial Orchid Medium, Vacin &; Went Modified Orchid Medium, ½-strengh Murashige &; Skoog, and BM-1 Terrestrial Orchid Medium) were examined for their effectiveness in promoting seed germination and protocorm development of B. purpurea in either a 0/24 h or 16/8 h L/D photoperiod. Germination occurred regardless of medium or photoperiod treatment. However, advanced seedling development (Stage 6) only occurred on Vacin &; Went Modified Orchid Medium in the 16/8 h L/D photoperiod. Further effects of photoperiod on in vitro seedling development were also examined. Shoot length, leaf width, root number and length, and fresh weight and dry weight in the 16/8 h L/D photoperiod were all significantly different when compared to the 8/16 h and 12/12 L/D photoperiods. In vitro seedlings were readily acclimatized to greenhouse conditions. Seedlings showed high survival all potting media. Seedlings acclimatized in Fafard Mix 4 potting medium developed significantly longer roots. Corm formation occurred regardless of potting media used.     

A microsatellite analysis of five Colonial Spanish horse populations of the southeastern United States

The domestic horse (Equus caballus) was re-introduced to the Americas by Spanish explorers. Although horses from other parts of Europe were subsequently introduced, some New World populations maintain characteristics ascribed to their Spanish heritage. The southeastern United States has a history of Spanish invasion and settlement, and this influence on local feral horse populations includes two feral-recaptured breeds: the Florida Cracker and the Marsh Tacky, both of which are classified as Colonial Spanish horses. The feral Banker horses found on islands off the coast of North Carolina, which include, among others, the Shackleford Banks, the Corolla and the Ocracoke, are also Colonial Spanish horses. Herein we analyse 15 microsatellite loci from 532 feral and 2583 domestic horses in order to compare the genetic variation of these five Colonial Spanish Horse populations to 40 modern horse breeds. We find that the Corolla horse has very low heterozygosity and that both the Corolla and Ocracoke populations have a low mean number of alleles. We also find that the Florida Cracker population has a heterozygosity deficit. In addition, we find evidence of similarity of the Shackleford Banks, Marsh Tacky and Florida Cracker populations to New World Iberian horse breeds, while the origins of the other two populations are less clear.     

Effects of thermoperiods on diapause induction in the cabbage beetle, Colaphellus bowringi (Coleoptera: Chrysomelidae)

Abstract. The effects of thermoperiods on diapause induction in continuous darkness or under a 12 : 12 h LD photoperiod were investigated in the cabbage beetle, Colaphellus bowringi Baly, a typical short‐day species. The diapause response curves both at different constant temperatures and at the thermocycle of format CT x: (24 ? x) h (16 : 28 °C) under continuously dark rearing conditions showed that the incidence of diapause depended mainly on whether or not the mean temperature was ≤20 °C or >20 °C. If the mean temperature was ≤20 °C, all individuals entered diapause; if >20 °C, the incidence of diapause declined gradually with increasing mean temperatures. The thermocycle (CT 12 : 12 h) with a series of different cryophases (8–22 °C) and thermophases (24–32 °C) under continuous darkness demonstrated a cryophase response threshold temperature of approximately 19 °C and a thermophase response threshold temperature of approximately 31 °C. Thermoperiodic amplitude (temperature difference between cryophase and thermophase) was shown to have a significant influence on diapause induction at the mean temperatures of 22, 23 and 24 °C, but not at ≥25 °C. Thermoperiodic responses under LD 12 : 12 h clearly showed that the incidence of diapause was influenced strongly by the photophase temperature. The thermoperiod under LD 12 : 12 h induced a much lower incidence of diapause than the thermoperiod with the same temperature in continuous darkness. The ecological significance of thermoperiodic induction of diapause in this species is discussed.