Interactions among stream fishes: predator-induced habitat shifts and larval survival

Summary Adult largemouth bass alter habitat use by, and abundances of, other fishes in small streams. Experimental manipulations of bass in natural stream pools (Brier Creek, Oklahoma) showed that responses of other fishes to adult bass were highly dependent on prey size, and that both direct and indirect effects of adult bass influence the distribution and abundance of other stream fishes. Experiments measuring the distributional responses of members of natural pool assemblages to adult bass revealed differences among adult sunfishes, small fishes (16–80 mm SL), and larval sunfish and minnows. Adult sunfishes (Lepomis spp.) did not detectably alter their depth distribution in response to adult bass, but changes in abundance of adult Lepomis on the whole-pool scale appeared positively related to changes in the number of bass. Small fishes tended to occupy shallower water when adult bass were present; changes in abundance of small fishes were negatively related to the number of adult bass. Larval minnows and larval Lepomis occupied primarily deep, mid-regions of pools, and were found only in pools which contained, or had contained, adult bass. A second set of experiments was motivated by censuses of small prairie-margin streams which revealed co-occurrence of larval fishes (of both minnow and sunfish species) and adult largemouth bass. Experimental manipulation of bass and Lepomis larvae on the whole-pool scale showed that adult bass enhanced short-term survival of Lepomis larvae. This effect appears to be an indirect result of habitat shifts by small fishes in response to bass; additional experiments indicated that these small fishes are potentially important predators of larvae. The interactions suggested in this study are analogous to those hypothesized for bass and sunfish in lakes by Werner and Hall (1988).     

Host-plant mediated geographic variation in the life history of Platycotis vittata (Homoptera: Membracidae)

Abstract.

• 1 The oak treehopper Platycotis vittata (Fabricius) is bivoltine throughout its range with discrete generations in the early spring and autumn. Females of both generations diapause.
• 2 Latitudinal variation in the timing of life history exists among four populations of P. vittata along the eastern coastal plain of the United States.
• 3 We disrupted synchronization between P.vittata life history and host-plant phenology in the springs of 1984 and 1985 by placing southern populations on northern trees with a different phenology. This caused some females to oviposit abnormally in late spring, without entering diapause. The offspring of these females had reduced reproductive success.
• 4 Winter diapause can be broken by providing females with a newly flushing tree with high levels of amino nitrogen in the sap. Females terminated winter diapause on trees breaking winter dormancy while females on trees still in winter dormancy did not, under identical photoperiod and temperature regimes.
• 5 The role of host-plant mediated life history variation as a process promoting intraspecific geographic differentiation in the arboreal sap-feeding guild is discussed.

     

Seasonal variation in generation time, diapause and cold hardiness in a central Ohio population of the flesh fly, Sarcophaga bullata

Abstract.

• 1 Generation time, diapause phenology and cold tolerance of the flesh fly, Sarcophaga bullata, were examined under confined natural conditions in central Ohio. In this locality, the fly can complete a maximum of four generations annually.
• 2 Very few pupae entered diapause in the first and second generations (May to July in 1988). In the third generation (August) 37% of the pupae entered an overwintering diapause, as did all pupae from the fourth generation (September).
• 3 The adult eclosion date in the spring and annual generation time can be predicted accurately from degree day data.
• 4 Cold tolerance of the field-overwintering portion of the population was high. After 30 days under field conditions, diapausing pupae readily survived a 7-day exposure to — 17°C. Glycerol appears to be the major cryoprotectant in S.bullata, and glycerol concentrations in the field population (95–142 mm ) remained high throughout the winter.
• 5 In contrast, diapausing flies reared under laboratory conditions (20°C, 12:12 LD) were less cold tolerant, and glycerol concentrations were lower (6.9–21.2 mm ). Field conditions thus promote the acquisition of high levels of cold tolerance, presumably as a consequence of the accumulation of higher concentrations of glycerol.
• 6 In spite of differences in the cold tolerance of laboratory and field flies, the supercooling points of the two groups of flies were nearly the same, thus implying that the supercooling point is not a good indicator of cold tolerance.

     

Expression of heat shock proteins in response to high and low temperature extremes in diapausing pharate larvae of the gypsy moth,Lymantria dispar

Diapausing pharate first instars of the gypsy moth, Lymantria dispar, respond to high temperature (37–41°C) by suppressing normal protein synthesis and synthesizing a set of seven heat shock proteins with M_rs of 90,000, 75,000, 73,000, 60,000, 42,000, 29,000, and 22,000 as determined by SDS-PAGE. During recovery at 25°C from heat shock, synthesis of the heat shock proteins gradually decreases over a period of 6 h, while normal protein synthesis is restored. A subset of these same heat shock proteins is also expressed during recovery at 4°C or 25°C from brief exposures to low temperature (-10 to 20°C), and its expression is more intense with increased severity of cold exposure. During recovery at 4°C after 24 h at ?20°C, both 90,000 and 75,000 M_r heat shock proteins are expressed for more than 96 h. While normal protein synthesis is suppressed during heat shock and recovery from heat shock, normal protein synthesis coincides with synthesis of the heat shock proteins during recovery from low temperatures, thus implying that expression of the heat shock proteins is not invariably linked to suppression of normal protein synthesis. Western transfer, using a monoclonal antibody that recognizes the inducible form of the human 70,000 M_r heat shock protein, demonstrates that immunologically related proteins in the gypsy moth are expressed at 4°C and during recovery from cold and heat shock.     

Effect of changes in the thermoperiod on reproductive diapause in Bruchidius atrolineatus Pic (Coleoptera: Bruchidae)

Abstract. Bruchidius atrolineatus (Pic) is a tropical bruchid developing in Vigna unguiculata (Walp) pods. Adults are in reproductive diapause during the dry season. In conditions of 40:25C or 35:25C, diapause is induced when larvae develop in thermophases longer than 14 h, in thermophases shorter than 10 h and in continuous darkness. Thermophases of 12 h cause a reduction of the proportion of diapausing beetles. This proportion also depends on the thermoperiod temperatures. Development at low temperatures (23: 16C, 12: 12 h) induces a high percentage of diapausing beetles. However, at low temperatures, the developmental times of the beetles are long and show important interindividual variability. When larvae develop in decreasing temperatures, small changes in thermoperiod temperatures (35:25C to 3O:2OC) have a strong effect on diapause induction. When larvae develop at low temperatures (25:15C) and then at high temperatures (40:25C), the proportion of diapausing beetles depends on the duration of development at low temperatures. Whatever the developmental conditions, both sexually active and diapausing beetles always emerge from the seeds. This interindividual variability is important in this species which has a wide geographical distribution in Africa.     

A diapause associated protein of the pink bollworm Pectinophora gossypiella Saunders.

A diapause associated protein was electrophoretically isolated from the hemolymph of diapausing last instar larvae of the pink bollworm Pectinophora gossypiella. This protein (M(r) approximately 490,000, glycolipoprotein) was given the name Pectinophora diapause protein (PDP). It is composed of one subunit (M(r) 103,000). The concentration of PDP increased dramatically in the hemolymph of diapausing larvae from 17.4% in prediapause (PD) phase to 29.2% in early diapause (ED) phase reaching a level of 38.6% in larval hemolymph of middiapause (MD) phase. The concentrations of total proteins in the hemolymph of active feeding (A), PD, ED, and MD larvae were 69.8, 106,6, 113.3, and 118 mg/ml, respectively, while those in the fat body of the same larvae were 7.1, 7.4, 8.8, and 4.5 mg/g, respectively. In Pectinophora a drop in the concentration of fat body proteins coincided with a corresponding increase in hemolymph proteins, which suggests an active release of protein from the fat body into the hemolymph during the development of diapause. A partial amino acid sequence of pectinophorin showed the first 15 amino acids starting from the amino terminus of the peptide chain: N-ALA-LYS-THR-ILEU-VAL-GLU-ASN-MET-PRO-PRO-THR-PRO-LEU-ASN-ALA-C.     

Quaternary and subunit structure of Calliphora arylphorin as deduced from electron microscopy,electrophoresis, and sequence similarities with arthropod hemocyanin

Summary Arylphorin was purified from larvae of the blowfly Calliphora vicina and studied in its oligomeric form and after dissociation at pH 9.6 into native subunits. In accordance with earlier literature, it was electrophoretically shown to be a 500 kDa hexamer (1×6) consisting of 78 kDa polypeptides (= subunits). Electron micrographs of negatively stained hexamers show a characteristic curvilinear, equilateral triangle of 12 nm in diameter (top view) and a rectangle measuring 10×12 nm (side view). Alternatively, particles in the top view orientation exhibit a roughly circular shape 12 nm in diameter. Crossed immunoelectrophoresis revealed the presence of a major subunit type; the nature of a very minor and a third immunologically separated component remains unclear. A novel 2×6 arylphorin particle was detected and isolated. It comprises less than 10% of the total arylphorin material and shows a long, narrow interhexamer bridge in the electron microscope. An arylphorin dissociation intermediate identified as a trimer (1/2×6) was isolated; its possible quaternary structure is discussed on the basis of electron micrographs. The epitope of monoclonal antibody Ec-7 directed against tarantula (Eurypelma californicum) hemocyanin subunit d and also reactive to Calliphora arylphorin was traced to a highly conserved peptide of 27 amino acids localized in the center of the protein. The primary structure of Calliphora arylphorin as published in our preceding paper (Naumann and Scheller 1991) is compared in detail to the sequences of spider and spiny lobster hemocyanin. This revealed a basic framework of 103 strictly conserved amino acids. Isofunctional exchanges are proposed for another 76 positions. On the basis of these similarities, and the published three-dimensional model of spiny lobster hemocyanin, a detailed model of the quaternary structure of Calliphora arylphorin is presented. A second larval storage protein previously termed protein II was purified from Calliphora hemolymph. It was demonstrated to be a 500 kDa hexamer of 83 kDa subunits. In the electron microscope it shows a cubic view 9 nm in length with a large central hole and a rectangular view (9×10 nm) with a large central cavity. A morphologically very similar hemolymph protein was detected in Drosophila melanogaster larvae. From its structural appearance it is uncertain whether protein II belongs to the hemocyanin superfamily or not.Abbreviations FPLC fast performance liquid chromatography - HPLC high performance liquid chromatography - LSP Larval serum protein - PAGE Polyacrylamide gel electrophoresis - SDS Sodium dodecyl sulphate - Tris Tris-(hydroxymethyl)-aminomethane     

European field collections and Canadian releases ofCeranthia samarensis (Dipt.: Tachinidae), a parasitoid of the gypsy moth

A programme to collect, import and release into Canada the gypsy moth parasitoid,Ceranthia samarensis (Diptera: Tachinidae) is described. The parasitoid's potential for biological control in Canada is also discussed. The parasitoid was collected in Europe by exposing experimental gypsy moth larvae in areas where local gypsy moth populations were at low densities. Following field exposure, the host larvae were returned to the laboratory and parasitoids reared from them. This technique has shown thatC. samarensis is the suffers 7–16% hyperparasitism. From 83–90% of theC. samarensis typically enter diapause as pharate adults within the puparia. Laboratory tests of post-exposure host rearing conditions indicate that constant temperatures disrupt the normal parasitoid diapause and that this effect can not be offset by use of either static long or short photoperiods or natural daylengths. Shipping and cold-storage procedures for puparia are described. Post-storage time to emergence of adultC. samarensis decreased with longer cold storage periods and with higher post-storage incubation temperatures. Emergence requires 112 degree-days above a threshold of 8°C after a period of at least 8 months cold storage. Releases of adultC. samarensis into field cages at four locations in southern Ontario are documented. While dissection of host larvae from the field cages has failed so far to demonstrate evidence of parasitism, we remain hopeful that some establishment of the parasitoid has occurred.      

Diapause, embryo growth and supercooling capacity of Epirrita autumnata eggs from northern Fennoscandia

The supercooling point (SCP) of individual Epirrita autumnata eggs (approx. 60 eggs batch^-1) was tested each month from September (eggs newly laid) to April under laboratory conditions simulating winter temperatures in the field (from +4 to-30 °C). Parallel to each test, one batch of eggs was transferred from the acclimation treatment to room temperature (22 °C) and the incubation duration to the first 50% hatch was recorded, giving a measure of embryo growth at the time of the SCP test. Data also give information on egg mortality, which generally was low.The SCP was found to be equivalent to the lower lethal temperatures for this species. Already in autumn, the SCP was in a low range of-34.9 to-36.5 °C and either rose (at a storage temperature of -3 °C) to a range between-28.3 and-29.8 °C in February, due to reduced cold hardiness during embryogenesis, or remained unchanged because the eggs were in quiescence (at -10 °C).The time to 50% hatch at 22 °C decreased from 60 days to 10–14 days in January when it either continued to decrease up to hatch (at -3 °C), or remained unchanged, indicating end of diapause in January. In December, 260 degree-days (DD) above a threshold of +5.8 °C was required for 50% hatch; in February the corresponding figures were 362 DD and-2 °C.When the supercooling point moved from the low to the high SCP range, the frequency distribution of the individual SCPs changed from positively to negatively skewed. The transition was rapid, intermediary distributions being flat and covering both ranges.Thus, in the field the eggs run the risk of freezing mainly at two temperature levels: below about-36 °C during diapause and post-diapause quiescence (in midwinter) and below about-29 °C during embryogenesis (in late winter spring).

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Résumé La température de congélation (supercooling point: SCP) de chaque uf de E. (Oporinia) autumnata (Lépido, géométride) (environ 60 ufs par ponte) a été examinée chaque mois, de septembre (ufs venant d'être pondus) à avril, dans des conditions simulant les températures hivernales de la nature (de-30° à +4 °C). Parallèlement à chaque expérience, une ponte était transférée aux fins d'acclimatation à la température du laboratoire (22 °C) pour noter la durée d'incubation des premiers 50% d'ufs éclos, afin d'avoir une donnée sur la durée du développement embryonnaire à l'époque de l'expérience de congélation, et sur la mortalité embryonnaire, d'ailleurs généralement basse.Le point de congélation (SCP) a correspondu pour cette espèce aux températures létales les plus basses. En automne déjà, la SCP avait une gamme basse de-34.9 à-36.5 °C et, soit s'élevait (pour une température de conservation >-3 °C) à une gamme de-28.3 à-29.8 °C en février, par suite de la diminution de la résistance au froid pendant l'embryogenèse, soit demeurait inchangée parce que les ufs étaient quiescents (<10 °C).Le temps d'éclosion 50 à 22 °C s'est abaissée de 60 j à 10–14 j en janvier pour ensuite, soit continuer de diminuer jusqu'à l'éclosion (>-3 °C), soit rester inchangé indiquant la fin de la diapause en janvier. En décembre, 260 degrés-jours (DD) au-dessus du seuil de +5.8 °C ont été nécessaires pour obtenir 50% d'éclosions, en février il a fallu 362 DD et-2 °C.Quand la température de congélation était déplacée de faibles à fortes valeurs de la SCP, la distribution des fréquences des SCP individuelles passait d'un biais positif à un biais négatif. La transition était rapide, les distributions intermédiaires étant plates et recouvrant les deux gammes.Ainsi les risques de congélation des ufs dans la nature se situent à deux niveaux: environ audessous de-36 °C pendant la diapause et la quiescence post-diapause (au milieu de l'hiver), et au-dessous d'environ-29 °C pendant l'embryogenèse (en fin d'hiver et au printemps).

     

Alternative schedules of male reproductive diapause in the grasshopperAnacridium aegyptium (L.): Effects of the corpora allata on sexual behavior (Orthoptera: Acrididae)

We studied the ontogeny of male sexual behavior in laboratory cohorts of the grasshopper Anacridium aegyptium to understand how male and female sexual activity is synchronized in this species. Contrary to previous accounts, certain male A. aegyptium undergo an extended period of reproductive diapause and do not show an onset of sexual behavior until several months postfledging. Considerable variation in diapause length existed, however, and some males showed onsets as early as 21 days postfledging, probably a nondiapause condition. A series of allatectomies and implantations of corpora allata (CA) demonstrated that male sexual behavior was dependent upon the presence of active CA and indicated that the periods of natural refractoriness noted above were related to inactive CA. In some cohorts, male longevity was extended in allatectomized individuals or in those exhibiting lengthy reproductive diapause. We speculate that variable diapause periods may represent a bet-hedging strategy of the parental generation selected for by two opposing pressures: the uncertainty of extended survival, selecting for brief periods, and intermale competition in the form of sperm precedence, favoring lengthy diapause.