Chemically Mediated Species Recognition in Closely Related Podarcis Wall Lizards

In many animals, chemical signals play an important role in species recognition and may contribute to reproductive isolation and speciation. The Iberian lizards of the genus Podarcis, with up to nine currently recognized lineages that are often sympatric, are highly chemosensory and provide an excellent model for the study of chemically mediated species recognition in closely related taxa. In this study, we tested the ability of male and female lizards of two sister species with widely overlapping distribution ranges (Podarcis bocagei and P. hispanica type 1) to discriminate between conspecific and heterospecific mates by using only substrate-borne chemical cues. We scored the number of tongue flicks directed at the paper substrate by each individual in a terrarium previously occupied by a conspecific or a heterospecific lizard of the opposite sex. Results show that males of P. bocagei and P. hispanica type 1 are capable of discriminating chemically between conspecifics and heterospecifics of the opposite sex, but females are not. These results suggest that differences in female, but not male, chemical cues may underlie species recognition and contribute to reproductive isolation in these species. The apparent inability of females to discriminate conspecific from heterospecific males, which is not because of reduced baseline exploration rates, is discussed in the context of sexual selection theory and species discrimination.     

Species-specific Expression of Major Urinary Proteins in the House Mice (<Emphasis Type="Italic">Mus musculus musculus</Emphasis> and <Emphasis Type="Italic">Mus musculus domesticus</Emphasis>)

The analysis of expression of pheromone-carrying major urinary proteins (MUPs) from two subspecies of house mice (Mus m. musculus, Mus m. domesticus) was studied. It has been previously shown that commensal populations of the two subspecies can discriminate on the basis of urinary signals. MUPs are predominant urinary proteins that protect pheromones from rapid degradation in a hydrophilic environment, and individuals of M. m. musculus tend to rely on these urinary cues in the process of subspecies discrimination more than M. m. domesticus individuals. Although it is not precisely known what triggers phenotypic and epigenetic changes of MUP expression, our results show that in the subspecies M. m. musculus, sex is a significant factor influencing variations in the regulation of selected MUPs in the liver. Furthermore, male M. m. musculus individuals expressed all the studied MUPs’ mRNA significantly more than females or individuals of either sex in M. m. domesticus. Correspondingly, the pattern of mRNA abundance was corroborated with the level of total MUP concentration in the urine, such that the level of sexual dimorphism was also significant and species-specific. Our finding introduces a hypothesis that quantitative variation of these proteins may be an essential part of a subspecies recognition system that maintains homospecific mixing.     

Role of volatile inforchemicals emitted by feces of larvae in host-searching behavior of parasitoidCotesia rubecula (Hymenoptera: Braconidae): A behavioral and chemical study

The role of volatile infochemicals emitted by feces of larvae in the host-searching behavior of the parasitoidCotesia rubecula was evaluated during single- and dual-choice tests inside a wind tunnel. The following treatments were tested: feces produced by second and fourth instars ofPieris rapae (preferred host), second instars ofP. brassicae (inferior host), second instars ofP. napi (nonhost), and wet feces of second instars ofP. rapae. During a single-choice situation females ofC. rubecula oriented to all types of feces tested. When a preference was to be made,C. rubecula preferred feces of second instars ofP. rapae over that of fourth, feces ofP. rapae over that ofP. brassicae, feces ofP. napi over that ofP. brassicae, and wet over normal host feces. No preference was exhibited between feces of second instars ofP. napi and that of second instars ofP. rapae. The relative importance of infochemicals from host feces versus plant damage caused by host larvae to the searching behavior ofC. rubecula was also evaluated. Plant damage was more important to the searching females than host feces when feces were present in specific concentrations in relation to damage. The volatiles released by normal and wet feces of second instars ofP. rapae, wet feces of fourth instars ofP. rapae, and normal and wet feces ofP. brassicae were collected and identified. Overall, 85 chemical compounds were recorded belonging to the following chemical groups: alcohols, ketones, aldehydes, esters, isothiocyanates, sulfides, nitriles, furanoids, terpenoids and pyridines. The blend of chemicals emitted by feces of different instars ofP. rapae and different species ofPieris exhibited an instar and species specificity in both quantity and quality. Wetting of normal feces increased the amount of volatile chemicals released, and it was also responsible for the appearance of new compounds. The role of feces of larvae in the host-seeking behavior ofC. rubecula is discussed.     

Alarm responses in the crayfishOrconectes virilis andOrconectes propinquus

Individuals of two species of crayfish (Orconectes virilis andO. propinquus) were tested in the laboratory for responses to chemicals released from physically damaged conspecifics. Individuals ofO. propinquus did not show an alarm response to crushed conspecifics. Individuals ofO. virilis responded to a water-borne substance released from crushed conspecifics by assuming an intermediate posture and ceasing movement. Similar alarm responses were shown by individuals ofO. virilis to crushed congeneric individuals (O. propinquus), and these responses were not eliminated by either freeze-thawing the crayfish used to prepare the signal or by treating freshly crushed crayfish with the enzyme trypsin. Individuals ofO. virilis showed strong feeding responses to solutions prepared from frozen fish flesh but showed a mixture of alarm and feeding responses to freshly killed fish. These results indicate that the alarm substance used byO. virilis is widespread.     

Semiochemicals from anal exudate of larvae of tsetse fliesGlossina morsitans morsitans Westwood andG. morsitans centralis Machado attract gravid females

Tsetse flies (Diptera: Glossinidae:Glossina) mature their offspring in utero, giving birth to mature larvae that burrow into soil and pupariate. During the hot dry seasons, puparia of some species of tsetse are aggregated in areas of deep shade in dense thickets. We have confirmed the presence of a semiochemical from the prepupariation excretions of larvae ofGlossina morsitans morsitans Westwood and report a similar semiochemical inGlossina morsitans centralis Machado. These semiochemicals are attractive to gravid females and result in the aggregation of puparia. Behavioral studies withG. m. centralis showed that a higher percentage of females larviposited over moist sand conditioned by the anal exudate of larvae. Electroantennogram analyses of extracts of sand conditioned byG. m. centralis andG. m. morsitans confirmed the presence of olfactory receptors on the antennae for the semiochemicals. Both subspecies responded to extracts of the semiochemicals of the other, withG. m. morsitans more responsive to lower concentrations of extract ofG. m. centralis than the converse.     

Comparative responses of annual pasture legume species to superphosphate applications in medium and high rainfall areas of Western Australia

The comparative phosphorus (P) requirement of different annual pasture legume species was measured in seven field experiments in south-western Australia. Superphosphate was applied once only, at the start of each experiment. The duration of the experiments was from one to three years. The amount of P required to produce 90% of the maximum yield of each legume was used to estimate the comparative P requirements of the legumes at each harvest. Ornithopus spp. (O. compressus, O. perpusillus andO. pinnatus) required less P thanTrifolium subterraneum, the most widely sown pasture legume in Western Australia. The P requirements ofMedicago polymorpha varied with soil type when compared to that ofT. subterraneum. M. polymorpha required less P on a soil with a neutral pH value, but had a similar P requirement on a more acidic soil.M. murex, generally required more P thanT. subterraneum. In some experiments, the comparative P requirement of the different legumes varied for different harvests.At each harvest in each experiment, the relationship between yield and P concentration in tissue (internal efficiency curves) usually differed for different legumes. Presumably different legumes take up P from the soil at different rates within each harvest, and utilize the absorbed P differently to produce herbage and seed. The exceptions were that similar internal efficiency curves were measured forO. compressus andT. subterraneum in one experiment, and three cultivars ofO. compressus in another experiment.     

Sequestration of host-plant-derived flavonoids by lycaenid butterflyPolyommatus icarus

Larvae of the lycaenid butterflyPolyommatus icarus were reared on inflorescences ofCoronilla varia andMedicago sativa, which are rich in flavonoids. Twelve different flavonoids (five compounds from the former and nine from the latter), including aglycones andO-glycosides of kaempferol, quercetin, and myricetin were isolated and identified by spectroscopic means. NMR and MS data for the new acylated glycoside kaempferol 3-O-6-(3-hydroxy-3-methylglutaroyl)--d-glucopyranoside are reported. Comparative HPLC analysis of the respective host plants and of larvae, pupae, and imagines ofP. icarus indicated selective uptake and accumulation of kaempferol vs. quercetin and myricetin derivatives. The latter were excreted largely unchanged through the feces. Irrespective of the larval host plant kaempferol 3-O-glucoside was found as the major flavonoid in larvae, pupae, and imagines ofP. icarus, accounting for approximately 83–92% of all soluble flavonoids in adult butterflies. Within the imagines, approximately 80% of all flavonoids are stored in the wings (especially in the orange submarginal lunules), whereas the remaining 20% reside in the bodies. Feeding experiments with artificial diet demonstrated that the insects are able to form kaempferol 3-O-glucoside by glucosylation of dietary kaempferol. Possible functions of the sequestered flavonoids, especially for mate recognition ofP. icarus, are discussed.     

Plant-natural enemy association in tritrophic system,Cotesia rubecula-Pieris rapae-brassicaceae (Cruciferae). III: Collection and identification of plant and frass volatiles

To elucidate the identity of the volatile compounds that could be involved in the searching behavior of the parasitoidCotesia rubecula Marshall (Hymenoptera: Braconidae), the volatiles released by cabbage and frass of Lepidoptera feeding on cabbage were collected and analyzed using a gas chromatograph-mass spectrometer. The volatiles emitted by intact cabbage were -pinene, -pinene, myrcene, 1,8-cineole,n-hexyl acetate,cis-3-hexen-1-yl acetate, and dimethyl trisulfide. Mechanical damage on an intact plant induced the release of two more compounds,trans-2-hexenal and 1-methoxy-3-methylene-2-pentanone. Current feeding by larvae ofPieris rapae L. (Pieridae) induced the plant to release all the compounds released after mechanical damage and additionally 4-methyl-3-pentenal and allyl isothiocyanate. Current feeding by larvae ofPlutella xylostella L. (Plutellidae) induced the plant to release all the compounds present after mechanical damage and additionally allyl isothiocyanate. The volatiles emitted after feeding by the lepidopterans had ceased were the same as those emitted by cabbage damaged by mechanical means. The blend of volatiles emitted by frass was comprised of plant chemicals, mainly sulfur compounds. Frass ofP. rapae emitted allyl isothiocyanate, methyl isothiocyanate, methyl propyl sulfide, dimethyl trisulfide,S-methyl methane thiosulfinate, 4-methyl-3-pentenal,trans-2-hexenal, and 2,3-dihydro-4-methyl furan. Frass ofP. xylostella emitted only dimethyl trisulfide andS-methyl methane thiosulfinate. The blend of volatiles emitted by frass is herbivore-species specific.     

Cardenolides as oviposition deterrents to twoPieris species: Structure-activity relationships

Oviposition responses ofPieris rapae andP. napi oleracea to 18 cardenolides were compared under the same conditions. Effects of different concentrations of selected cardenolides were also tested. Most of the compounds were deterrent to oviposition by both insects, but to significantly different degrees.P. rapae were strongly deterred by K-strophanthoside, K-strophanthin-, cymarin, convallatoxin, oleandrin, erysimoside, erychroside, and gitoxigenin. The most deterrent compounds forP. napi oleracea were erychroside, cymarin, erysimoside, convallatoxin, and K-strophanthoside. Strophanthidin-based glycosides were more deterrent than digitoxigenin-based ones, and the number and type of sugar substitutions can have profound effects on activity. Both similarities and contrasts were found in responses ofP. rapae andP. napi oleracea to these cardenolides. Cymarin was equally deterrent to bothPieris species at all concentrations tested. However, when compared withP. rapae, P. napi oleracea was less sensitive to most of the cardenolides.P. napi oleracea was insensitive to K-strophanthin- and oleandrin at 0.5 × 10^–4 M, which were highly deterrent toP. rapae.     

Plant-natural enemy association in the tritrophic system,Cotesia rubecula-Pieris rapae-brassiceae (cruciferae): I. Sources of infochemicals

The role of airborne infochemicals in host selection by the parasitoidCotesia rubecula (Marshal) (Hymenoptera: Braconidae) was examined in a wind tunnel. To elucidate the role of volatile chemicals in attractingC. rubecula to cabbage infested by the host [Pieris rapae L. (Lepidoptera: Pieridae)], the potential sources of volatiles related toP. rapae infestation on cabbage were tested individually. The responses of females to nonhost plant species, bean and geranium, as well as to frass of a nonhost lepidopteran were also examined.C. rubecula was attracted to cabbage previously infested byP. rapae and to frass and regurgitate ofP. rapae. No attraction was observed to larvae ofP. rapae alone. Females were also attracted to mechanically damaged cabbage, cabbage previously infested byPlutella xylostella L. (Lepidoptera: Plutellidae) (a nonhost lepidopteran herbivore), and cabbage previously infested by snails (a nonhost, noninsect herbivore). Intact cabbage, bean, and geranium plants elicited no attraction. A low frequency of attraction was observed to mechanically damaged bean and geranium. Attraction was also observed to frass ofP. xylostella. Volatiles from cabbage related to damage, and volatiles from frass and regurgitate of the host seem to play an important role in guidingC. rubecula to plants infested by its host.     

Allelopathic potential of sorghum-sudangrass hybrid (sudex)

Experiments were conducted under controlled conditions to investigate the apparent allelopathic effects of sudex [Sorghum bicolor (L.) Moench ×Sorghum Sudanese (P.) Stapf, cv. FFR 201] on weed and vegetable species. Allelopathic potential, as measured by radicle elongation of herbaceous indicator species, decreased with increasing sudex age. Greatest potential allelopathic activity of sudex shoot tissue was observed when sudex was collected at 7 days of age. Small-seeded broadleaf species were more inhibited in the presence of sudex shoot tissue than were grass species. Two major phytoinhibitors were isolated from aqueous extracts of sudex shoot material by partitioning with diethyl ether, followed by thin-layer and liquid column chromatography. Phytoinhibitors were identified asp-hydroxybenzoic acid andp-hydroxybenzaldehyde, potentially the enzymatic breakdown products of the cyanogenic glycoside dhurrin. The I₅₀ values of these compounds using a cress (Lepidium sativum L.) seed bioassay were 140 and 113 g/ml for the acid and aldehyde, respectively. Sudex tissue collected at 7 days of age possessed a greater percentage of these phytoinhibitors on a per gram basis than did older sudex tissue. As sudex tissue age increased, the percentage ofp-hydroxybenzaldehyde in ether extracts of tissue also increased, while the percentage ofp-hydroxybenzoic acid decreased.Journal article No. 88-10-163 of the Kentucky Agricultural Experiment Station.     

Recognition of aphid parasitoids by honeydew-collecting ants: The role of cuticular lipids in a chemical mimicry system

The aphidiid waspLysiphlebus cardui parasitizes in ant-attendedAphis fabae cirsiiacanthoidis colonies without causing aggressive behavior in the antLasius niger. By contrast,Trioxys angelicae, another aphidiid parasitoid of aphids, is rapidly recognized and vigorously attacked by the ants.L. niger workers also responded differently to dead individuals ofL. cardui andT. angelicae. DeadL. cardui parasitoids were often ignored when encountered byL. niger, whereas deadT. angelicae individuals were immediately grasped by ants that discovered them. However, hexane-washed parasitoids caused a similar reaction pattern in the ants, in that both aphidiid species were tolerated in the aphid colony. Lure experiments demonstrated that chemical stimuli on the cuticle are major cues for the ants to distinguish between the parasitoids. The hexane extract ofL. cardui transferred to washed individuals ofT. angelicae resulted in ant responses characteristic towardsL. cardui, andL. niger workers displayed the typical removal pattern they normally showed towardsT. angelicae whenT. angelicae extract was applied toL. cardui individuals. Both parasitoid species treated with the hexane extract ofA. fabae cirsiiacanthoidis were similarily treated by the ants as were aphid control individuals. The suggestion that the aphidiid waspL. cardui uses chemical mimicry is discussed.     

Phosphorus effectiveness in fertilized soils evaluated by chemical solutions and residual value for wheat growth

Nineteen soils from the south east of the Province of Buenos Aires (Argentina) that had been fertilized with moderate amounts of P (10–40 kgP/ha) during the last 10 years were used to investigate the effect of time on the decline of P availability as measured by three soil tests (Bray 1, Bray 2, Olsen) and the null-point method. Differences in rates of P decline among soils and chemical methods were characterized by an exponential coefficient for time (b ₂) in equations which describe the changes of the added P retained by the soil (Pr =ac ^b1 t ^b2). The rate of decline of P for the nineteen soils calculated for the soil test methods was ordered decreasingly as: null-point > Olsen > Bray 1 > Bray 2. The ability of the chemical methods for assessing the residual value of P for wheat growth (RV) was tested in a pot experiment on seven of the soils that differed in their individual rates of reaction with P. Differences between soils in the rate of reaction with P as measured in the laboratory by the null-point method and by the Olsen test were reflected in different residual values for P fertilizer for wheat plants. Thus the value ofb ₂ for these methods was well correlated with the observed residual values. The soil properties commonly associated with the retention of P were not related to the value ofb ₂ suggesting that more than one soil property may be involved in the measure ofb ₂. The exponent for timeb ₂ may be used as an index of the ability of the soil test to reflect the decline of P availability with time.     

Comparative study of hermit crab responses to shell-related chemical cues

The responses of Australian hermit crabs to two types of shell-related odor cues were compared. Introduction of gastropod snail odor elicited an increase in grasping of shells in all four species tested (Clibanarius infraspinatus, C. taeniatus, C. virescens, andDiogenes avarus). However, the magnitude of response in the case ofC. virescens was significantly lower than the responses of individuals of the other species. Individuals ofC. infraspinatus responded to introduction of conspecific hemolymph with an increase in both locomotion and the frequency of grasping of shells.C. infraspinatus also responded to the hemolymph of the other three species, and there were no differences in the magnitude of the responses depending upon the source of the hemolymph. When individuals ofC. infraspinatus were exposed to snail odor and conspecific hemolymph at the same time, the responses were indistinguishable from those shown to hemolymph alone.     

Chemical secretions of two sympatric harvester ants,Pogonomyrmex salinus andMessor lobognathus

Messor lobognathus, an apparent mimic ofPogonomyrmex salinus, shows little chemical resemblance to its exemplar. The mandibular glands ofM. lobognathus gave no volatile compounds. Those ofP. salinus contain chiefly 4-methyl-3-heptanone. Both species contain a mixture of straight-chain alkanes, alkenes, and methyl-branched alkanes in their Dufour glands. Tridecane (64%) is the major substance inM. lobognathus and dodecane (25%) and pentadecane (24%) are the major compounds ofP. salinus. No secretion induced trail-following in either species. A mixture of 9-, 11-, and 13-methylheptacosane formed the largest peak in the chromatograms obtained from the postpharyngeal glands of both species, but otherwise the hydrocarbon mixtures in this gland too were distinct.     

Host-marking pheromones in lepidoptera,with special reference to twoPieris spp

Adult females of several lepidopteran species avoid oviposition near conspecific eggs. Laboratory and field studies indicate that visual factors as well as chemical host markers may be involved in egg avoidance behavior. The oviposition-deterring pheromones (ODP) of two pierids,P. brassicae andP. rapae have been studied in considerable detail. The ODPs are probably produced in the female accessory glands and contain volatile and nonvolatile components. They are perceived by nonspecialized antennal or tarsal receptors, respectively. The ODP ofP. brassicae affects oviposition ofP. rapae females and vice versa. ODPs show promise for insect control programs, but more information on oviposition behavior in the presence of ODP under field conditions is required.     

Empirical correlations between electroantennograms and bioassays forPeriplaneta americana

Determination of electroantennograms (EAGs) with an electroantennometer having a positive and a negative peak detection option, and with a stimulus delivery device providing local stimulation of the antenna ofP. americana, allowed for the detection of three typical EAG patterns for a wide range of compounds tested. Some of the compounds presented at least one positive EAG peak (0.1–0.3 mV), others showed a single negative EAG peak (–1.0 to –1.1 mV), and a third group had more than one negative EAG peak (–0.2 to –0.8 mV). These EAG results correlate with behavioral assays ofP. americana. Thus compounds having a positive EAG response act as repellents, while those having negative EAG responses act as attractants, depending on concentration. EAG patterns thus can permit prediction of behavioral responses ofP. americana.     

Interspecific activity of semiochemicals among sibling species ofPissodes (Coleoptera: Curculionidae)

Pissodes strobi, P. approximatus, andP. nemorensis are sibling species of pine weevils that can hybridize in the laboratory but are presumed to be reproductively isolated in nature. Males of all three species produce the terpenoids grandisol and grandisal; these compounds serve as an aggregation pheromone forP. approximatus andP. nemorensis when deployed with odors from pine bolts. A series of field experiments examined the possibility of cross-attraction among the three species. Tests in New York and Florida found that parapatrically distributedP. approximatus andP. nemorensis were cross-attractive, but different photoperiodic conditioning was required for pheromone production in males of the two species. Long-day pheromone production (P. approximatus-type.) was inherited in interspecific hybrids. Other tests showed thatP. strobi males, or hybrid males from crosses ofP. strobi withP. approximatus, were not attractive to sympatricP. approximatus. When the response ofP. strobi was assessed to males of eitherP. strobi orP. approximatus confined on white pine leaders (the breeding site ofP. strobi), no evidence of cross-attraction or pheromone activity was found;P. strobi were caught in equal numbers onP. strobi-baited leaders,P. approximatus-baited leaders, and unbaited leaders. Tests of interspecific interactions found that maleP. strobi produce an allelochemical signal that interrupts the response ofP. approximatus to its natural or synthetic aggregation pheromone. This interspecific response is apparently adaptive for members of both species (classified as an allomone-kairomone or synomone) because it may ultimately serve to prevent interspecific matings that would lower the fitness of the parents.     

Behavior and survival ofReticulitermes hesperus banks (Isoptera: Rhinotermitidae) on selected sawdusts and wood extracts

Survival ofReticulitermes hesperus workers was assessed inPseudotsuga menziesii, Lysiloma seemanii, andTabebuia ochracea sawdusts; and on heartwood solvent extracts ofP. menziesii, L. seemanii, T. ochracea, Pinus ponderosa, Tabebuia guayacan, and aCentrolobium species. Survival inP. menziesii sawdust was 100% at 5 days and 81–87% at 15 days. Survival inL. seemanii andT. ochracea sawdusts was significantly less over both 5 and 15 days than in the starvation control, indicating toxicity. Survival on filter papers treated with solvent extracts ofT. ochracea andP. ponderosa was significantly less than that on control papers, but onlyP. ponderosa differed significantly from the starvation control. In behavioral assays with groups and with individualR. hesperus workers, extracts ofP. menziesii andP. ponderosa were preferred. In the individual behavioral assays, extracts ofT. guayacan andT. ochracea were repellent. Results of toxicity assays were not predictable from preference assays.     

Orientation behavior of second-instar larvae of eastern spruce budwormChoristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae) in a y-type olfactometer

A two-choice, wind-tunnel olfactometer was designed and contructed to determine whether second-instar eastern spruce budworm larvae,Christoneura fumiferana (Clem.), could detect and discriminate among host-plant volatiles. Volatiles of current year's growth ofPicea glauca were preferred over those ofP. rubens, P. mariana, or air.Abies balsamea was preferred overP. mariana or air.P. rubens andP. mariana were both preferred over air. Two-year-old growth ofP. glauca, A. balsamea, P. rubens, andP. mariana were all preferred over air. Current year's growth of these host evergreen species was usually preferred over former year's growth of the same species in each case.