Innate control of local search behaviour in the house fly, Musca domestica

Abstract. The genetic basis of variation in local searching behaviour in the house fly, Musca domestica L., was examined by estimating the heritability of locomotory parameters using parent—offspring regressions. Pathways of adult flies were videotaped for 3 min after ingestion of a 1 μl drop of 0.25 M sucrose in a 75 cm diameter circular arena with minimal external cues. Locomotory variables computed from digitized walking pathways, including locomotory rate, turning rates per unit of distance and time, turn bias, number of stops, and stop duration, were significantly heritable, but heritabilities (additive genetic variance ÷ total phenotypic variance) was generally low (<0.25). Phenotypic variance in search parameters increased with time since ingestion of the sucrose drop, but heritabilities were highest when only the first 30 s of the searching bout were examined, and declined as longer periods were considered. Significant genetic correlations among search parameters suggest that many of these characters are influenced pleiotropically by the same genes or closely linked genes. However, some aspects of local search were inherited independently (e.g. stop duration and locomotory rate). The independence of controlling mechanisms was supported by observed differences between genetic and environmental correlations. This genetic independence could enhance the likelihood of appropriate population responses to temporally or spatially changing selective forces.     

Search orientation of Musca domestica in patches of sucrose drops

ABSTRACT. The searching tactics of the housefly, Musca dormestica L. (Diptera: Muscidae), have been delineated from digitized pathways of flies walking in patches of sucrose drops arranged in linear (ROW) and hexagonal (HEX) arrays. The areas covered by flies in ROW and HEX patches are distinctly different, but flies seem not to employ different tactics for the two types of resource arrays. The number of drops located, if at least one drop is found, does not differ between ROW and HEX. Most quantitative measures of local search remain constant after the first interdrop interval, although feeding time decreases as flies sample successive drops. Local search intensifies after each drop is ingested, with locomotory rate decreasing and turning rate increasing, followed by decay of both measures toward ranging levels. Searching can be characterized by two movement tendencies resulting from specific, definable, locomotory functions: a forward-moving tendency is expressed by the fly as it leaves a resource in approximately the same direction as it arrives; and local search is characterized by looping, rather than straight walking, with a variable turning rate that generates a rough ‘zigzag’ superimposed on looping. The two movement tendencies, combined, allow flies to locate resources in a linear arrangement, because of the forward-moving tendency, and to locate resources not arranged in a linear array because of the ‘noisy’ loop. M. domestica does not appear to retain and use information gained from one patch of drops in another, so the search tactic of the fly seems therefore to be a compromise between straight movement and circular movement that may be adaptive for an environment subject to frequent changes in the spatial distribution of resources. Giving-up-time, the period between ingesting the last drop and leaving the patch, is a function of the rate of change in the transition from local search to ranging, which is constant in our experiments. If a fly does not encounter another drop while ranging, during which it walks relatively straight, the fly moves out of and away from the patch.     

Associations of stream geomorphic conditions and prevalence of alternative reproductive tactics among sockeye salmon populations

In many species, males may exhibit alternative life histories to circumvent the costs of intrasexual competition and female courtship. While the evolution and underlying genetic and physiological mechanisms behind alternative reproductive tactics are well studied, there has been less consideration of the ecological factors that regulate their prevalence. Here, we examine six decades of age composition records from thirty‐six populations of sockeye salmon (Oncorhynchus nerka) to quantify associations between spawning habitat characteristics and the prevalence of precocious sneakers known as ‘jacks’. Jack prevalence was independent of neutral genetic structure among stream populations, but varied among habitat types and as a function of continuous geomorphic characteristics. Jacks were more common in streams relative to beaches and rivers, and their prevalence was negatively associated with stream width, depth, elevation, slope and area, but positively related to bank cover. Behavioural observations showed that jacks made greater use of banks, wood and shallows than guard males, indicating that their reproductive success depends on the availability of such refuges. Our results emphasize the role of the physical habitat in shaping reproductive tactic frequencies among populations, likely through local adaptation in response to variable fitness expectations under different geomorphic conditions.     

Antennal and locomotor responses to attractive and aversive odors in the searching cockroach

The behavioral responses to attractive and aversive odors were examined in blinded adult male cockroaches under tethered-walking conditions. A sex pheromone-like stimulant derived from adult virgin females and artificially synthesized limonene were used as attractive and aversive odor sources, respectively. When a searching animal was stimulated with the attractive female-derived odor, the horizontal deflections of both the antennae were increased, and in most cases the vertical antennal positions were shifted downward. The stimulation also significantly decreased the walking speed of the animal. These behavioral changes imply a careful search in the immediate surroundings. The aftereffect of the sex pheromone was more pronounced on locomotion than on antennal movement. On the other hand, stimulation with the aversive odor (limonene) tended to suppress active antennal movement, and also increased the walking speed. Immediately after the withdrawal of the aversive odor, the active movement of the antennae was resumed, and the walking speed rapidly decreased to a level approximately the same as that of the control period. These results indicate that the responses to the qualitatively opposite types of odor are reciprocal to each other with regard to both antennal movement and locomotion.     

The effects of resource availability on alternative mating tactics in guppies (Poecilia reticulata)

Food availability can influence the optimal allocation of timeand energy among alternative behaviors such as foraging, courting,and competing for mates. If populations differ consistentlyin food availability, selection may cause geographic divergencein allocation strategies. At the opposite extreme, a norm ofreaction may evolve such that food intake influences the allocationstrategy of individuals in the same way in all populations.Between these two extremes, food intake reaction norms may divergegenetically among populations. For example, at sites where foodis scarce, selection may strengthen the effect of food intakeon behavior, whereas at sites with abundant food, selectionmay be weak or even oppose plasticity. We tested these ideasby raising male guppies from streams differing in food availabilityin a common laboratory environment on either low or high foodlevels, and then observing them in the presence of male competitors(from the same population and diet group) and receptive females.Males from low-food-availability streams spent more time foragingthan males from high-food-availability streams, independentof food intake. Compared with males raised on the high foodlevel, males raised on the low food level spent more time foragingand were less aggressive towards other males. Courtship displayrate increased with food intake but only in males from low-foodstreams. In contrast, males from high-food streams showed greaterplasticity with respect to male-male aggression. These resultsgenerally support the resource availability/behavioral tradeoffhypothesis while also revealing a surprising degree of ontogeneticcomplexity in a relatively simple system.