Terry R. McGuire

Selection for host-finding in Steinernema feltiae

Abstract A hybridized Foundation population of the entomopathogenic nematode Steinernema feltiae was bidirectionally selected for enhanced and diminished host-finding ability. While there was no response to selection for diminished host-finding, 13 rounds of selection for enhancement produced a 20- to 27-fold increase. Moreover, the proportion of infectives initiating positive chemotaxis was increased from less than one-third to more than 80%. Nematodes failing to migrate out of the inoculation zone declined from 33 to 8% after 6 rounds of selection. Relaxation of selection pressure produced a gradual decrease in host-finding. This regression, coupled with the high realized heritability for enhanced host-finding (0.64), suggests that wild-type populations take a passive approach to host-finding. Because for inundative biological control it is desirable that infective stages quickly initiate host-seeking movements, improved host-finding may result in improved field efficacy.

An Environmental Approach to Positive Emotion: Flowers

For more than 5000 years, people have cultivated flowers although there is no known reward for this costly behavior. In three different studies we show that flowers are a powerful positive emotion “inducer”. In Study 1, flowers, upon presentation to women, always elicited the Duchenne or true smile. Women who received flowers reported more positive moods 3 days later. In Study 2, a flower given to men or women in an elevator elicited more positive social behavior than other stimuli. In Study 3, flowers presented to elderly participants (55+ age) elicited positive mood reports and improved episodic memory. Flowers have immediate and long-term effects on emotional reactions, mood, social behaviors and even memory for both males and females. There is little existing theory in any discipline that explains these findings. We suggest that cultivated flowers are rewarding because they have evolved to rapidly induce positive emotion in humans, just as other plants have evolved to induce varying behavioral responses in a wide variety of species leading to the dispersal or propagation of the plants.

Conditioned suppression of proboscis extension in Drosophila melanogaster.

Food-deprived Drosophila melanogaster extend their proboscises following sucrose stimulation of the front tarsi (the proboscis extension reflex). Médioni and Vaysse (1975) reported that the inhibition of this response can be conditioned over trials if such proboscis extensions are punished by applying an aversive stimulus to the foreleg tarsi. In this study, Médioni and Vaysses basic observations of conditioning were replicated, with a different strain of flies and a modified conditioning apparatus.

Fitness of a genetically improved entomopathogenic nematode

Abstract A strain of Steinernema carpocapsae (G-13) selectively bred for improved host-finding was compared against two wild-type strains, the commercially available All strain and the Foundation strain from which the G-13 strain was derived, for changes in fitness. Selection did not affect pathogenicity, mobility, sex ratio, or morphology. However, the G-13 strain showed a gain of fitness with regard to host penetration and reproductive potential and a loss of fitness for storage stability. Acquiring enhanced host-finding abilities does not appear to be correlated with a serious reduction in overall fitness, and the potential of the selected G-13 strain for inundative biological control appears unlikely to be impaired. The possible significance of the three correlated responses to selection are discussed.

Characterization of genes involved with classical conditioning that produce differences between bidirectionally selected strains of the blow flyPhormia regina

Mean response levels for classically conditioned proboscis extensions in hybrid generations from a cross between bidirectionally selected strains of blow flies were used in a biometrical analysis. The best-fitting genetic model suggests the presence of additive, dominance, and digenic epistatic effects from at least four autosomal and X-linked genes. Neither maternal nor Y-linked effects were detected. Earlier studies have described the genetic and behavioral relations between the central excitatory state (CES) and classical conditioning. That evidence indicated that covariability of the two traits is produced by one autosomal gene. The results herein are consistent with such a hypothesis, and they explain why the CES—conditioning correlation is not perfect. Finally, knowledge that some genes associated with conditioning are located on the X chromosome and, therefore, are independent of the CES gene will facilitate efforts to identify new single genes affecting associative learning inPhormia.

The homeotic genespineless-aristapedia affects geotaxis inDrosophila melanogaster

The homeotic mutationspineless-aristapedia (ssa) transforms the aristae into second tarsi. Flies with aSSa phenotype also show extremely positive geotaxis as measured in a Hirsch-type geotaxis maze. Other antennal mutants and flies with their aristae amputated do not show such extreme positive geotaxis. Deletion analysis has comapped the geotaxis effect withSSa in band 89C on the third chromosome. Finally, a biometrical analysis has detected additional genes on the X chromosome that also affects geotaxis.

Further evidence for a relationship between central excitatory state and classical conditioning in the blow flyPhormia regina

A positive phenotypic correlation between the central excitatory state (CES) and classical conditioning was observed in 11 populations of the blow flyPhormia regina including two replicate, selected high and low learning lines and two replicate, selected high and low CES lines. Tullyet al. [(1982)Behav. Genet.12:181–191] have shown that a CES-conditioning correlation remained in the F2 generation of CES-selected lines. The CES-conditioning correlation also remained in the F2 generation of a hybrid cross between selected learning lines. This result suggests that the observed phenotypic correlation was due to pleiotropy and that CES and conditioning share related neural, biochemical, or physiological systems.

A biometrical genetic approach to chromosome analysis inDrosophila: Detection of epistatic interactions in geotaxis

Chromosome analysis has been widely used as a first step in eclucidating the genetic architecture of several behaviors ofDrosophila melanogaster. These chromosome studies have generally used incomplete designs or fairly simple statistical analyses. Here I reanalyze two data sets on geotaxis from Pyle (1978) and Ksander (1966) using a biometrical genetic design. Results from the biometrical genetic reanalysis suggest that individual differences in geotaxis might be due to genes on all three major chromosomes which show extensive epistatic interactions.

Selection for central excitatory state (CES) in the blow flyPhormia regina

Food-deprived but water-satiated blow flies (Phormia regina) were tested for their central excitatory state (CES) response. Bidrectional selection based on individual differences for CES expression resulted in separate high- and low-CES strains in only one generation in three replicate experiments. This suggests that differences in CES expression are correlated with allelic differences at a single locus. The use of such selected lines in a component analysis of classical conditioning is discussed.

Food-search behavior and its relation to the central excitatory state in the genetic analysis of the blow fly Phormia regina.

Dethier (1957) described an aspect of food-search behavior in Phormia regina as the blow fly dance. A hungry fly walks in relatively straight lines with its proboscis retracted until it encounters food (sucrose). After ingesting even a small amount of sucrose, the fly begins making frequent, tight turns, flexes its front tarsi to bring more chemosensory hairs into contact with the substrate and repeatedly extends and retracts its proboscis. Like the central excitatory state (CES), which causes an increase in proboscis extensions to water when a fly is stimulated with sucrose, the dance lasts longer in hungrier flies or with higher sucrose concentrations. It was considered that dance behavior might be an ethologically relevant manifestation of CES. In order to test this hypothesis, dance duration in lines selected for high- and low-CES levels was measured. As predicted, flies from the high-CES line danced longer than those from the low-CES line, and the CES-dance correlation in individual flies was high. This phenotypic correlation disappeared in the F2 generation of a cross between the high- and low-CES lines, a result indicating that the observed variations in CES and dance duration were not caused by the same set of genes. Further characterization of the underlying genetic system showed that several linked autosomal genes with digenic epistatic interactions and a complex pattern of maternal inheritance were responsible for the difference in dance durations between the high- and low-CES lines.