Differences In Host Preference Research Articles

Preferential nodulation of Glycine max, Glycine soja and Macroptilium atropurpureum by two Bradyrhizobium species japonicum and elkanii

Soybean bradyrhizobia, Bradyrhizobium japonicum and Bradyrhizobium elkanii differ in various traits such as DNA fingerprint, rhizobitoxine production, indole-3-acetic acid production and uptake of hydrogenase. In this communication, we investigated whether the differences between both species extend to host preference in multistrain environments. Nodule occupancy of B. japonicum and B. elkanii significantly depended on host plants. B. japonicum and B. elkanii preferentially nodulated Glycine max and M. atropurpureum, respectively. Both bacterial species were shown to nodulate G. soja with similar efficiency. There was a significant divergence of DNA sequences in and around nodulation genes between the B. japonicum and B. elkanii field isolates. However, flavonoid and lipo-chitin nodulation signals were not involved in the difference in host preference of B. japonicum and B. elkanii. The ecological implications of host preference are discussed.

Odor-mediated flight behavior ofAnopheles gambiae gilesSensu Stricto andAn. stephensi liston in response to CO2, acetone, and 1-octen-3-ol (Diptera: Culicidae)

The flight behavior of Anopheles gambiae s.s. Giles and An. stephensi Patton exposed to different odor cues was studied in a wind tunnel. Odors consisted of CO2, CO2 + acetone (at two concentrations), and CO2 + 1-octen-3-ol. Mosquitoes were released singly and their behavior was recorded on video. Parameters studied included flight velocity, percentage of time spent flying, percentage of time spent in plume, and number of turns toward the plume. Large differences in behavior toward the odors tested were observed. An. gambiaedid not respond well to CO 2,whereas An. stephansiwas positively affected by this compound. In contrast, An. gambiaeresponded significantly to CO 2 + acetone (at a low concentration), but the behavior of An. stephensiwas completely suppressed by this combination of odor stimuli. CO 2 + a high concentration of acetone or CO 2 + 1-octen-3-ol did not cause significant effects in An. gambiaecompared to no odor, while these treatments elicited strong behavioral responses in An. stephensi.The latter species responded particularly well to CO 2 + 1-octen-3-ol. The results suggest that the observed differences may be inherent to the known differences in host preferences, where An. gambiaeis highly anthropophilic and An. stephensimore zoophilic. This would explain why the latter species responds well to CO 2 and even better to CO 2 + 1-octen-3-ol, a compound readily emitted by bovine ruminants.

Host fidelity is an effective premating barrier between sympatric races of the apple maggot fly.

Models of sympatric speciation for phytophagous insects posit a central role for host plant-associated mating as a premating isolating mechanism in lieu of geographic barriers to gene flow. Here, by means of three mark-and-recapture studies, we confirm that host fidelity (i.e., the tendency of an insect to reproduce on the same host species that it used in earlier life-history stages) restricts gene flow between sympatric apple- and hawthorn-infesting races of Rhagoletis pomonella (Diptera: Tephritidae) to approximately 6% per generation. Genetically based differences in host preference, adult eclosion under the "correct" host species, and allochronic isolation contribute to host fidelity in various degrees in the races. The results verify that host-associated adaptation can produce reproductive isolation as a correlated character (a key premise of sympatric speciation). The study also represents one of the few or perhaps only example in animals where the intra-specific isolating effects of specific phenotypes have been quantified in nature.

Phylogenetic position of Cowdria ruminantium (Rickettsiales) determined by analysis of amplified 16S ribosomal DNA sequences.

The 16S ribosomal DNA sequence of Cowdria ruminantium, the causative agent of heartwater disease in ruminants, was determined. An analysis of this sequence showed that C. ruminantium forms a tight phylogenetic cluster with the canine pathogen Ehrlichia canis and the human pathogen Ehrlichia chaffeensis. Although a close relationship between the genus Cowdria and several members of the tribe Ehrlichieae has been suspected previously, the tight phylogenetic cluster with E. canis and E. chaffeensis is surprising in view of known differences in host preference and target cells.

Feeding and Host Preference of Immature Ixodes dammini, I. scapularis, and I. pacificus (Acari: Ixodidae)

A comparative study of feeding and host preference was made among immatures of Ixodes dammini Spielman, Clifford, Piesman & Corwin, I. scapularis Say, and I. pacificus Cooley & Kohls, using white laboratory mice, Eumeces lizards, and chickens (3-4 d old) as hosts. Larval feeding of each species when placed on hosts was greater (P less than 0.05) on mice than on chickens and lizards and higher on lizards than on chickens (P less than 0.05). When larvae of the three species were given a choice between mouse and lizard and mouse and chicken, they preferred mice (except no statistical difference was found between mice and chickens for I. pacificus larvae). When given a choice between lizard and chicken, no significant difference in host preference was seen. Nymphs of I. dammini, I. scapularis, and I. pacificus displayed no statistical difference in feeding ability between mice and lizards when placed on these hosts, but more ticks fed on mice and lizards than on chickens. Nymphs of all three species also showed no preference between mice and lizards but preferred either of these hosts to chickens (however, no statistical difference was found between mice and chickens for I. dammini nymphs or between lizards and chickens for I. pacificus nymphs).

Mixed blood feeding by the malaria vectors in the Anopheles punctulatus complex (Diptera: Culicidae).

Using a refined indirect enzyme-linked immunosorbent assay to identify serum proteins of different host species, the blood meal sources and the amount of multiple blood feeding among heterologous host species were investigated for members of the Anopheles punctulatus complex in Papua, New Guinea. Differences in host preferences were found among members of the complex; A. punctulatus and A. koliensis were more anthropophilic than A. farauti. Blood from two or more hosts species was detected in 5.2% of the engorged anophelines captured outdoors and in 4.3% of those captured indoors. Based on ABO blood group markers on human red blood cells, 13% of human fed anophelines captured indoors in experiments with selected mother-child pairs contained blood of both individuals. A model is presented that predicts the probability of a mosquito being interrupted while blood feeding. The epidemiological implications of the findings are discussed.

Interpopulation Differences in Host Preference and the Evolution of Learning in the Butterfly, Battus philenor

Interpopulation Differences in Host Preference and the Evolution of Learning in the Butterfly, Battus philenor

TRADEOFFS IN PERFORMANCE ON DIFFERENT HOSTS: EVIDENCE FROM WITHIN‐ AND BETWEEN‐SITE VARIATION IN THE BEETLE DELOYALA GUTTATA

Host races of phytophagous insects are sympatric populations that have different host preferences and between which gene flow is restricted because of the difference in host preference. Sympatric, host-associated sibling species are sympatric populations that use different host plants and that do not interbreed because of the presence of isolating mechanisms not related to host preference (Jaenike, 1981; see Mayr, 1970, and Bush, 1969, for slightly different definitions of these terms). Although the existence of host races and host-associated sibling species of phytophagous insects has been suspected for over 50 years (e.g., Thorpe, 1930), the evolutionary mechanism of host race formation remains controversial. In particular, there is disagreement about the importance of sympatric divergence in generating host races and species. White (1978) has argued that sympatric speciation must be invoked to explain, in part, the great diversity of specialized herbivorous insects, while Bush (1974, 1975) has forcefully advocated the operation of sympatric divergence in the creation of sympatric host races of tephritid flies. By contrast, Futuyma and Mayer (1980; see also Futuyma, 1983a) have argued that there is no reliable experimental evidence to support these claims and that models of sympatric speciation are based on assumptions that are probably not met by most phytophagous insects. Several authors have developed formal models of sympatric divergence and speciation (Maynard Smith, 1966; Dickinson and Antonovics, 1973; Caisse and Antonovics, 1978; Pimm, 1979; Felsenstein, 1981). Although these models do not account for the evolution of differences in host plant preference associated with purported sympatric speciation in phytophagous insects, Bush and Diehl (1983) and Rausher (1984) have suggested how modification of these models could remedy this problem. A common assumption of all these models is that fitness on one host is negatively correlated with fitness on a second. This type of negative correlation is manifested in these models in the assumption that genetic variation exists at loci that exhibit a genotype x host plant interaction, i.e., at loci at which some genotypes have high fitness on one host but low fitness on a second host while other genotypes have low fitness on the first but high fitness on the second host. This negative correlation seems to be necessary for sympatric speciation because it permits linkage disequilibrium to be established between loci influencing, say, viability on different hosts and loci influencing host preference. The resulting coadapted preference-viability gene complexes represent incipient host races or species. Moreover, the breakdown of these coadapted gene complexes by recombination provides the selection pressure that improves reproductive isolation, whether isolation is achieved via mating on the host (e.g., Bush, 1974, 1975) or by a separate assortative mating locus in linkage disequilibrium with loci affecting preference and fitness (e.g., Felsenstein, 1981). Without a crossing interaction, one homozygote genotype would have maximal fitness on both host species. Consequently, unless reproductive isolation were achieved instantaneously by a mutation

Food plant choices of two goldenrod beetles: Relation to plant quality.

The leaf beetles Trirhabda borealis and T. virgata are specialist herbivores of meadow goldenrods, Solidago spp., in central New York. Upon emergence, both larvae and adults must actively search for food plants, and must choose among the five goldenrod species (S. canadensis, S. gigantea, S. graminifolia, S. juncea and S. rugosa) that co-occur in old fields. The relationship between Trihabda foraging decisions and plant quality was examined by comparing food preferences in the field with the performance of beetles caged on each host. Trirhabda adults were highly selective in their use of food plants. Adults of T. borealis preferred a single host, S. canadensis, while T. virgata adults were most common on S. canadensis and S. gigantea. These preferences were not strictly related to variation in plant quality. In the laboratory, T. borealis performed equally well on four goldenrods (but completely failed to reproduce when fed S. graminifolia), and T. virgata performed equally well on all five hosts.Larval feeding preferences in each beetle species were broader, and were more in accord with subtle variation in plant quality. Newly-hatched T. borealis larvae readily colonized four hosts and rejected only S. graminifolia, which conferred the lowest survivorship and the slowest growth. Larvae of T. virgata accepted each host, even though growth rates were somewhat slower on S. graminifolia and S. juncea.Ontogenetic differences in host preference and host tolerance may have evolved because of the different host-finding abilities of each beetle stage. During host search, the sluggish, newly-emerged larvae may be more food-limited and accept even marginally inferior food plants. The relatively mobile adults are more discriminating and use a subset of suitable hosts. The intermingled dispersion of Solidago species in old fields results in frequent larval colonization of hosts seldom used by adults. In diverse plant communities, ultimate patterns of food plant choice can be a complex function of at least three factors: intrinisic plant quality, local plant dispersion, and the host-search abilities of the insect forager.

Effects of Fertilization and Vesicular‐Arbuscular Mycorrhizal Inoculation on Growth of Hardwood Seedlings

AbstractEight hardwood species were grown in fumigated soil without vesicular‐arbuscular mycorrhizae (VAM) or in soil infested with a mixture of Glomus mosseae and Glomus etunicatus. Three fertilizer treatments of 140, 560, and 1,120 kg/ha of 10‐10‐10 fertilizer were established in combination with the two mycorrhizal treatments. Ten equal applications of NH4NO3, totaling 1,680 kg/ha, were added to all the treatment plots during the growing season. For six of the eight species, the VAM seedlings showed greater height and diameter growth and dry weight production than nonmycorrhizal seedlings. Sugar maple (Acer saccharum Marsh.) and walnut (Juglans nigra L.) displayed no height growth differences. Only boxelder (Acer negundo L.), of the inoculated seedlings, consistently responded to increases in fertilizer level. Nonmycorrhizal seedlings generally showed increased growth with increased fertilizer applications. The growth of the nonmycorrhizal seedlings at the higher fertilizer levels was not sufficient to produce plantable seedlings for artificial regeneration. A difference in host preference for the Glomus spp. symbionts is suggested by the large difference in infection between species. Infection values varied from a high of about 80% for sycamore (Platanus occidentalis L.), green ash (Fraxinus pennsylvanica Marsh.), and boxelder to a low of 40% for sugar maple and sweetgum. The growth data suggest that high quality seedling stock of most of these hardwood tree species can be obtained in nurseries as long as cultural practices in the nursery encourage VAM development.

Biosystematic and evolutionary statuses of two sympatric populations ofAphytis mytilaspidis [Hym.: Aphelinidae

Studies on 2 sympatric morphologically identical populations ofAphytis mytilaspidisLe Baron frpm Greece were conducted on their mating behavior, reproductive isolation, hybridization in the laboratory, host preferences and adult survivorships at different temperatures. These studies revealed that the 2 populations were partially reproductively isolated and qualify at least for the rank of strong “semispecies” with respect to one another. Marked differences were also recorded in their host preferences and adult survivorships at different temperatures. Gene flow among these populations in nature is likely to occur only in one direction. Differences in host preference may further reduce gene flow by providing ecological reproductive isolation. Also hybrid sterility is indicated which if complete would prove these 2 forms to be sibling species. Based on the experimental evidence, an hypothesis is presented that these 2 populations represent a case of incipient if not complete sympatric speciation, with the presumed descendant population (R-69-120) possessing a broader host range and better adult longevity, in comparison to the proposed progenitor population (R-63-63-4).

Evidence of an Aggregating Pheromone in Pissodes approximates and P. strobi1, 2

Preliminary field studies in central New York State indicate that an aggregating pheromone is released by males of the northern pine weevil, Pissodes approximatus Hopkins. Males of the white pine weevil, P. strobi (Peck), may also release a pheromone which attracts P. approximates. These closely related species are extremely similar morphologically. Chemotaxonomy (Peckham 1969), cytotaxonomy (Manna and Smith 1959, Smith 1962), analysis of sonic signals (Harman and Kranzler 1969) and breeding experiments (Godwin and O'Dell 1967) have yielded equivocal evidence that P. strobi and P. approximatus are separate species. Nevertheless, discriminant analysis of several characters has been used to identify individuals to species (Godwin et al. 1959) and differences in host preference and breeding site of the 2 entities are widely recognized (Hopkins 1911, Smith and Sugden 1969, Baker 1972).